.github/workflows: use go1.23.x

And also upgrade staticcheck version to 2024.1.1

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
       fail-fast: false
       matrix:
         os: ["windows-latest", "ubuntu-latest", "macOS-latest"]
-        go: ["1.21.x"]
+        go: ["1.23.x"]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3
@@ -21,6 +21,6 @@ jobs:
       - run: "go test -race ./..."
       - uses: dominikh/staticcheck-action@v1.2.0
         with:
-          version: "2023.1.2"
+          version: "2024.1.1"
           install-go: false
           cache-key: ${{ matrix.go }}

cmd/cli/ad_others.go

@@ -0,0 +1,10 @@
+//go:build !windows
+
+package cli
+
+import (
+	"github.com/Control-D-Inc/ctrld"
+)
+
+// addExtraSplitDnsRule adds split DNS rule if present.
+func addExtraSplitDnsRule(_ *ctrld.Config) {}

cmd/cli/ad_windows.go

@@ -0,0 +1,45 @@
+package cli
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/Control-D-Inc/ctrld"
+)
+
+// addExtraSplitDnsRule adds split DNS rule for domain if it's part of active directory.
+func addExtraSplitDnsRule(cfg *ctrld.Config) {
+	domain, err := getActiveDirectoryDomain()
+	if err != nil {
+		mainLog.Load().Debug().Msgf("unable to get active directory domain: %v", err)
+		return
+	}
+	if domain == "" {
+		mainLog.Load().Debug().Msg("no active directory domain found")
+		return
+	}
+	for n, lc := range cfg.Listener {
+		if lc.Policy == nil {
+			lc.Policy = &ctrld.ListenerPolicyConfig{}
+		}
+		domainRule := "*." + strings.TrimPrefix(domain, ".")
+		for _, rule := range lc.Policy.Rules {
+			if _, ok := rule[domainRule]; ok {
+				mainLog.Load().Debug().Msgf("domain rule already exist for listener.%s", n)
+				return
+			}
+		}
+		mainLog.Load().Debug().Msgf("adding active directory domain for listener.%s", n)
+		lc.Policy.Rules = append(lc.Policy.Rules, ctrld.Rule{domainRule: []string{}})
+	}
+}
+
+// getActiveDirectoryDomain returns AD domain name of this computer.
+func getActiveDirectoryDomain() (string, error) {
+	cmd := "$obj = Get-WmiObject Win32_ComputerSystem; if ($obj.PartOfDomain) { $obj.Domain }"
+	output, err := powershell(cmd)
+	if err != nil {
+		return "", fmt.Errorf("failed to get domain name: %w, output:\n\n%s", err, string(output))
+	}
+	return string(output), nil
+}

cmd/cli/cli.go

@@ -37,7 +37,7 @@ import (
 	"github.com/spf13/pflag"
 	"github.com/spf13/viper"
 	"tailscale.com/logtail/backoff"
-	"tailscale.com/net/interfaces"
+	"tailscale.com/net/netmon"
 
 	"github.com/Control-D-Inc/ctrld"
 	"github.com/Control-D-Inc/ctrld/internal/clientinfo"
@@ -52,6 +52,7 @@ const (
 	windowsForwardersFilename = ".forwarders.txt"
 	oldBinSuffix              = "_previous"
 	oldLogSuffix              = ".1"
+	msgExit                   = "$$EXIT$$"
 )
 
 var (
@@ -146,6 +147,7 @@ func initCLI() {
 	runCmd.Flags().IntVarP(&cacheSize, "cache_size", "", 0, "Enable cache with size items")
 	runCmd.Flags().StringVarP(&cdUID, cdUidFlagName, "", "", "Control D resolver uid")
 	runCmd.Flags().StringVarP(&cdOrg, cdOrgFlagName, "", "", "Control D provision token")
+	runCmd.Flags().StringVarP(&customHostname, customHostnameFlagName, "", "", "Custom hostname passed to ControlD API")
 	runCmd.Flags().BoolVarP(&cdDev, "dev", "", false, "Use Control D dev resolver/domain")
 	_ = runCmd.Flags().MarkHidden("dev")
 	runCmd.Flags().StringVarP(&homedir, "homedir", "", "", "")
@@ -194,91 +196,46 @@ NOTE: running "ctrld start" without any arguments will start already installed c
 			isCtrldRunning := status == service.StatusRunning
 			isCtrldInstalled := !errors.Is(err, service.ErrNotInstalled)
 
+			// Get current running iface, if any.
+			var currentIface string
+
 			// If pin code was set, do not allow running start command.
 			if isCtrldRunning {
 				if err := checkDeactivationPin(s, nil); isCheckDeactivationPinErr(err) {
 					os.Exit(deactivationPinInvalidExitCode)
 				}
+				currentIface = runningIface(s)
 			}
 
-			if !startOnly {
-				startOnly = len(osArgs) == 0
-			}
-			// If user run "ctrld start" and ctrld is already installed, starting existing service.
-			if startOnly && isCtrldInstalled {
-				tryReadingConfigWithNotice(false, true)
-				if err := v.Unmarshal(&cfg); err != nil {
-					mainLog.Load().Fatal().Msgf("failed to unmarshal config: %v", err)
-				}
+			ctx, cancel := context.WithCancel(context.Background())
+			defer cancel()
 
-				initLogging()
-				tasks := []task{
-					resetDnsTask(p, s),
-					{s.Stop, false},
-					{func() error {
-						// Save current DNS so we can restore later.
-						withEachPhysicalInterfaces("", "save DNS settings", func(i *net.Interface) error {
-							return saveCurrentStaticDNS(i)
-						})
-						return nil
-					}, false},
-					{s.Start, true},
-					{noticeWritingControlDConfig, false},
-				}
-				mainLog.Load().Notice().Msg("Starting existing ctrld service")
-				if doTasks(tasks) {
-					mainLog.Load().Notice().Msg("Service started")
-					sockDir, err := socketDir()
-					if err != nil {
-						mainLog.Load().Warn().Err(err).Msg("Failed to get socket directory")
-						os.Exit(1)
-					}
-					if cc := newSocketControlClient(s, sockDir); cc != nil {
-						if resp, _ := cc.post(ifacePath, nil); resp != nil && resp.StatusCode == http.StatusOK {
-							if iface == "auto" {
-								iface = defaultIfaceName()
-							}
-							logger := mainLog.Load().With().Str("iface", iface).Logger()
-							logger.Debug().Msg("setting DNS successfully")
+			reportSetDnsOk := func(sockDir string) {
+				if cc := newSocketControlClient(ctx, s, sockDir); cc != nil {
+					if resp, _ := cc.post(ifacePath, nil); resp != nil && resp.StatusCode == http.StatusOK {
+						if iface == "auto" {
+							iface = defaultIfaceName()
 						}
+						logger := mainLog.Load().With().Str("iface", iface).Logger()
+						logger.Debug().Msg("setting DNS successfully")
 					}
-				} else {
-					mainLog.Load().Error().Err(err).Msg("Failed to start existing ctrld service")
-					os.Exit(1)
 				}
-				return
-			}
-
-			if cdUID != "" {
-				doValidateCdRemoteConfig(cdUID)
-			} else if uid := cdUIDFromProvToken(); uid != "" {
-				cdUID = uid
-				mainLog.Load().Debug().Msg("using uid from provision token")
-				removeProvTokenFromArgs(sc)
-				// Pass --cd flag to "ctrld run" command, so the provision token takes no effect.
-				sc.Arguments = append(sc.Arguments, "--cd="+cdUID)
-			}
-			if cdUID != "" {
-				validateCdUpstreamProtocol()
-			}
-
-			if err := p.router.ConfigureService(sc); err != nil {
-				mainLog.Load().Fatal().Err(err).Msg("failed to configure service on router")
 			}
 
 			// No config path, generating config in HOME directory.
 			noConfigStart := isNoConfigStart(cmd)
 			writeDefaultConfig := !noConfigStart && configBase64 == ""
-			if configPath != "" {
-				v.SetConfigFile(configPath)
-			}
 
+			logServerStarted := make(chan struct{})
 			// A buffer channel to gather log output from runCmd and report
 			// to user in case self-check process failed.
 			runCmdLogCh := make(chan string, 256)
 			ud, err := userHomeDir()
 			sockDir := ud
-			if err == nil {
+			if err != nil {
+				mainLog.Load().Warn().Msg("log server did not start")
+				close(logServerStarted)
+			} else {
 				setWorkingDirectory(sc, ud)
 				if configPath == "" && writeDefaultConfig {
 					defaultConfigFile = filepath.Join(ud, defaultConfigFile)
@@ -294,6 +251,7 @@ NOTE: running "ctrld start" without any arguments will start already installed c
 						close(runCmdLogCh)
 						_ = os.Remove(sockPath)
 					}()
+					close(logServerStarted)
 					if conn := runLogServer(sockPath); conn != nil {
 						// Enough buffer for log message, we don't produce
 						// such long log message, but just in case.
@@ -303,11 +261,80 @@ NOTE: running "ctrld start" without any arguments will start already installed c
 							if err != nil {
 								return
 							}
-							runCmdLogCh <- string(buf[:n])
+							msg := string(buf[:n])
+							if _, _, found := strings.Cut(msg, msgExit); found {
+								cancel()
+							}
+							runCmdLogCh <- msg
 						}
 					}
 				}()
 			}
+			<-logServerStarted
+
+			if !startOnly {
+				startOnly = len(osArgs) == 0
+			}
+			// If user run "ctrld start" and ctrld is already installed, starting existing service.
+			if startOnly && isCtrldInstalled {
+				tryReadingConfigWithNotice(false, true)
+				if err := v.Unmarshal(&cfg); err != nil {
+					mainLog.Load().Fatal().Msgf("failed to unmarshal config: %v", err)
+				}
+
+				initLogging()
+				tasks := []task{
+					{s.Stop, false},
+					resetDnsTask(p, s, isCtrldInstalled, currentIface),
+					{func() error {
+						// Save current DNS so we can restore later.
+						withEachPhysicalInterfaces("", "", func(i *net.Interface) error {
+							if err := saveCurrentStaticDNS(i); !errors.Is(err, errSaveCurrentStaticDNSNotSupported) && err != nil {
+								return err
+							}
+							return nil
+						})
+						return nil
+					}, false},
+					{s.Start, true},
+					{noticeWritingControlDConfig, false},
+				}
+				mainLog.Load().Notice().Msg("Starting existing ctrld service")
+				if doTasks(tasks) {
+					mainLog.Load().Notice().Msg("Service started")
+					sockDir, err := socketDir()
+					if err != nil {
+						mainLog.Load().Warn().Err(err).Msg("Failed to get socket directory")
+						os.Exit(1)
+					}
+					reportSetDnsOk(sockDir)
+				} else {
+					mainLog.Load().Error().Err(err).Msg("Failed to start existing ctrld service")
+					os.Exit(1)
+				}
+				return
+			}
+
+			if cdUID != "" {
+				doValidateCdRemoteConfig(cdUID)
+			} else if uid := cdUIDFromProvToken(); uid != "" {
+				cdUID = uid
+				mainLog.Load().Debug().Msg("using uid from provision token")
+				removeOrgFlagsFromArgs(sc)
+				// Pass --cd flag to "ctrld run" command, so the provision token takes no effect.
+				sc.Arguments = append(sc.Arguments, "--cd="+cdUID)
+			}
+			if cdUID != "" {
+				validateCdUpstreamProtocol()
+			}
+
+			if err := p.router.ConfigureService(sc); err != nil {
+				mainLog.Load().Fatal().Err(err).Msg("failed to configure service on router")
+			}
+
+			if configPath != "" {
+				v.SetConfigFile(configPath)
+			}
 
 			tryReadingConfigWithNotice(writeDefaultConfig, true)
 
@@ -334,14 +361,17 @@ NOTE: running "ctrld start" without any arguments will start already installed c
 			}
 
 			tasks := []task{
-				resetDnsTask(p, s),
 				{s.Stop, false},
 				{func() error { return doGenerateNextDNSConfig(nextdns) }, true},
 				{func() error { return ensureUninstall(s) }, false},
+				resetDnsTask(p, s, isCtrldInstalled, currentIface),
 				{func() error {
 					// Save current DNS so we can restore later.
-					withEachPhysicalInterfaces("", "save DNS settings", func(i *net.Interface) error {
-						return saveCurrentStaticDNS(i)
+					withEachPhysicalInterfaces("", "", func(i *net.Interface) error {
+						if err := saveCurrentStaticDNS(i); !errors.Is(err, errSaveCurrentStaticDNSNotSupported) && err != nil {
+							return err
+						}
+						return nil
 					})
 					return nil
 				}, false},
@@ -358,19 +388,19 @@ NOTE: running "ctrld start" without any arguments will start already installed c
 					return
 				}
 
-				ok, status, err := selfCheckStatus(s, ud, sockDir)
+				ok, status, err := selfCheckStatus(ctx, s, sockDir)
 				switch {
 				case ok && status == service.StatusRunning:
 					mainLog.Load().Notice().Msg("Service started")
 				default:
 					marker := bytes.Repeat([]byte("="), 32)
 					// If ctrld service is not running, emitting log obtained from ctrld process.
-					if status != service.StatusRunning {
+					if status != service.StatusRunning || ctx.Err() != nil {
 						mainLog.Load().Error().Msg("ctrld service may not have started due to an error or misconfiguration, service log:")
 						_, _ = mainLog.Load().Write(marker)
 						haveLog := false
 						for msg := range runCmdLogCh {
-							_, _ = mainLog.Load().Write([]byte(msg))
+							_, _ = mainLog.Load().Write([]byte(strings.ReplaceAll(msg, msgExit, "")))
 							haveLog = true
 						}
 						// If we're unable to get log from "ctrld run", notice users about it.
@@ -396,15 +426,7 @@ NOTE: running "ctrld start" without any arguments will start already installed c
 					uninstall(p, s)
 					os.Exit(1)
 				}
-				if cc := newSocketControlClient(s, sockDir); cc != nil {
-					if resp, _ := cc.post(ifacePath, nil); resp != nil && resp.StatusCode == http.StatusOK {
-						if iface == "auto" {
-							iface = defaultIfaceName()
-						}
-						logger := mainLog.Load().With().Str("iface", iface).Logger()
-						logger.Debug().Msg("setting DNS successfully")
-					}
-				}
+				reportSetDnsOk(sockDir)
 			}
 		},
 	}
@@ -419,6 +441,7 @@ NOTE: running "ctrld start" without any arguments will start already installed c
 	startCmd.Flags().IntVarP(&cacheSize, "cache_size", "", 0, "Enable cache with size items")
 	startCmd.Flags().StringVarP(&cdUID, cdUidFlagName, "", "", "Control D resolver uid")
 	startCmd.Flags().StringVarP(&cdOrg, cdOrgFlagName, "", "", "Control D provision token")
+	startCmd.Flags().StringVarP(&customHostname, customHostnameFlagName, "", "", "Custom hostname passed to ControlD API")
 	startCmd.Flags().BoolVarP(&cdDev, "dev", "", false, "Use Control D dev resolver/domain")
 	_ = startCmd.Flags().MarkHidden("dev")
 	startCmd.Flags().StringVarP(&iface, "iface", "", "", `Update DNS setting for iface, "auto" means the default interface gateway`)
@@ -543,7 +566,7 @@ NOTE: running "ctrld start" without any arguments will start already installed c
 					mainLog.Load().Warn().Err(err).Msg("Service was restarted, but could not ping the control server")
 					return
 				}
-				cc := newSocketControlClient(s, dir)
+				cc := newSocketControlClient(context.TODO(), s, dir)
 				if cc == nil {
 					mainLog.Load().Notice().Msg("Service was not restarted")
 					os.Exit(1)
@@ -730,7 +753,7 @@ NOTE: Uninstalling will set DNS to values provided by DHCP.`,
 		Short: "List network interfaces of the host",
 		Args:  cobra.NoArgs,
 		Run: func(cmd *cobra.Command, args []string) {
-			err := interfaces.ForeachInterface(func(i interfaces.Interface, prefixes []netip.Prefix) {
+			err := netmon.ForeachInterface(func(i netmon.Interface, prefixes []netip.Prefix) {
 				fmt.Printf("Index : %d\n", i.Index)
 				fmt.Printf("Name  : %s\n", i.Name)
 				addrs, _ := i.Addrs()
@@ -1035,7 +1058,7 @@ NOTE: Uninstalling will set DNS to values provided by DHCP.`,
 				}
 				if doTasks(tasks) {
 					if dir, err := socketDir(); err == nil {
-						if cc := newSocketControlClient(s, dir); cc != nil {
+						if cc := newSocketControlClient(context.TODO(), s, dir); cc != nil {
 							_, _ = cc.post(ifacePath, nil)
 							return true
 						}
@@ -1141,6 +1164,7 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 		reloadDoneCh:     make(chan struct{}),
 		dnsWatcherStopCh: make(chan struct{}),
 		apiReloadCh:      make(chan *ctrld.Config),
+		apiForceReloadCh: make(chan struct{}),
 		cfg:              &cfg,
 		appCallback:      appCallback,
 	}
@@ -1161,6 +1185,9 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 			p.logConn = lc
 		}
 	}
+	notifyExitToLogServer := func() {
+		_, _ = p.logConn.Write([]byte(msgExit))
+	}
 
 	if daemon && runtime.GOOS == "windows" {
 		mainLog.Load().Fatal().Msg("Cannot run in daemon mode. Please install a Windows service.")
@@ -1186,8 +1213,12 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 		mainLog.Load().Fatal().Err(err).Msg("failed to read base64 config")
 	}
 	processNoConfigFlags(noConfigStart)
+
+	// After s.Run() was called, if ctrld is going to be terminated for any reason,
+	// write msgExit to p.logConn so others (like "ctrld start") won't have to wait for timeout.
 	p.mu.Lock()
 	if err := v.Unmarshal(&cfg); err != nil {
+		notifyExitToLogServer()
 		mainLog.Load().Fatal().Msgf("failed to unmarshal config: %v", err)
 	}
 	p.mu.Unlock()
@@ -1203,6 +1234,7 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 
 	// Wait for network up.
 	if !ctrldnet.Up() {
+		notifyExitToLogServer()
 		mainLog.Load().Fatal().Msg("network is not up yet")
 	}
 
@@ -1217,6 +1249,7 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 	// time for validating server certificate. Some routers need NTP synchronization
 	// to set the current time, so this check must happen before processCDFlags.
 	if err := p.router.PreRun(); err != nil {
+		notifyExitToLogServer()
 		mainLog.Load().Fatal().Err(err).Msg("failed to perform router pre-run check")
 	}
 
@@ -1238,6 +1271,7 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 			if errors.As(err, &uer) && uer.ErrorField.Code == controld.InvalidConfigCode {
 				_ = uninstallInvalidCdUID(p, cdLogger, false)
 			}
+			notifyExitToLogServer()
 			cdLogger.Fatal().Err(err).Msg("failed to fetch resolver config")
 		}
 	}
@@ -1250,6 +1284,7 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 
 	if updated {
 		if err := writeConfigFile(&cfg); err != nil {
+			notifyExitToLogServer()
 			mainLog.Load().Fatal().Err(err).Msg("failed to write config file")
 		} else {
 			mainLog.Load().Info().Msg("writing config file to: " + defaultConfigFile)
@@ -1271,6 +1306,7 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 	}
 
 	if err := validateConfig(&cfg); err != nil {
+		notifyExitToLogServer()
 		os.Exit(1)
 	}
 	initCache()
@@ -1279,11 +1315,13 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 		exe, err := os.Executable()
 		if err != nil {
 			mainLog.Load().Error().Err(err).Msg("failed to find the binary")
+			notifyExitToLogServer()
 			os.Exit(1)
 		}
 		curDir, err := os.Getwd()
 		if err != nil {
 			mainLog.Load().Error().Err(err).Msg("failed to get current working directory")
+			notifyExitToLogServer()
 			os.Exit(1)
 		}
 		// If running as daemon, re-run the command in background, with daemon off.
@@ -1291,6 +1329,7 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 		cmd.Dir = curDir
 		if err := cmd.Start(); err != nil {
 			mainLog.Load().Error().Err(err).Msg("failed to start process as daemon")
+			notifyExitToLogServer()
 			os.Exit(1)
 		}
 		mainLog.Load().Info().Int("pid", cmd.Process.Pid).Msg("DNS proxy started")
@@ -1339,15 +1378,14 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 	close(waitCh)
 	<-stopCh
 
-	// Wait goroutines which watches/manipulates DNS settings terminated,
-	// ensuring that changes to DNS since here won't be reverted.
-	p.dnsWg.Wait()
+	p.stopDnsWatchers()
 	for _, f := range p.onStopped {
 		f()
 	}
 }
 
 func writeConfigFile(cfg *ctrld.Config) error {
+	addExtraSplitDnsRule(cfg)
 	if cfu := v.ConfigFileUsed(); cfu != "" {
 		defaultConfigFile = cfu
 	} else if configPath != "" {
@@ -1473,25 +1511,31 @@ func processNoConfigFlags(noConfigStart bool) {
 
 	endpointAndTyp := func(endpoint string) (string, string) {
 		typ := ctrld.ResolverTypeFromEndpoint(endpoint)
-		return strings.TrimPrefix(endpoint, "quic://"), typ
+		endpoint = strings.TrimPrefix(endpoint, "quic://")
+		if after, found := strings.CutPrefix(endpoint, "h3://"); found {
+			endpoint = "https://" + after
+		}
+		return endpoint, typ
 	}
 	pEndpoint, pType := endpointAndTyp(primaryUpstream)
-	upstream := map[string]*ctrld.UpstreamConfig{
-		"0": {
-			Name:     pEndpoint,
-			Endpoint: pEndpoint,
-			Type:     pType,
-			Timeout:  5000,
-		},
+	puc := &ctrld.UpstreamConfig{
+		Name:     pEndpoint,
+		Endpoint: pEndpoint,
+		Type:     pType,
+		Timeout:  5000,
 	}
+	puc.Init()
+	upstream := map[string]*ctrld.UpstreamConfig{"0": puc}
 	if secondaryUpstream != "" {
 		sEndpoint, sType := endpointAndTyp(secondaryUpstream)
-		upstream["1"] = &ctrld.UpstreamConfig{
+		suc := &ctrld.UpstreamConfig{
 			Name:     sEndpoint,
 			Endpoint: sEndpoint,
 			Type:     sType,
 			Timeout:  5000,
 		}
+		suc.Init()
+		upstream["1"] = suc
 		rules := make([]ctrld.Rule, 0, len(domains))
 		for _, domain := range domains {
 			rules = append(rules, ctrld.Rule{domain: []string{"upstream.1"}})
@@ -1662,7 +1706,7 @@ func netInterface(ifaceName string) (*net.Interface, error) {
 		ifaceName = defaultIfaceName()
 	}
 	var iface *net.Interface
-	err := interfaces.ForeachInterface(func(i interfaces.Interface, prefixes []netip.Prefix) {
+	err := netmon.ForeachInterface(func(i netmon.Interface, prefixes []netip.Prefix) {
 		if i.Name == ifaceName {
 			iface = i.Interface
 		}
@@ -1680,7 +1724,7 @@ func defaultIfaceName() string {
 	if ifaceName := router.DefaultInterfaceName(); ifaceName != "" {
 		return ifaceName
 	}
-	dri, err := interfaces.DefaultRouteInterface()
+	dri, err := netmon.DefaultRouteInterface()
 	if err != nil {
 		// On WSL 1, the route table does not have any default route. But the fact that
 		// it only uses /etc/resolv.conf for setup DNS, so we can use "lo" here.
@@ -1702,7 +1746,7 @@ func defaultIfaceName() string {
 // - External testing, ensuring query could be sent from ctrld -> upstream.
 //
 // Self-check is considered success only if both tests are ok.
-func selfCheckStatus(s service.Service, homedir, sockDir string) (bool, service.Status, error) {
+func selfCheckStatus(ctx context.Context, s service.Service, sockDir string) (bool, service.Status, error) {
 	status, err := s.Status()
 	if err != nil {
 		mainLog.Load().Warn().Err(err).Msg("could not get service status")
@@ -1718,7 +1762,7 @@ func selfCheckStatus(s service.Service, homedir, sockDir string) (bool, service.
 	}
 
 	mainLog.Load().Debug().Msg("waiting for ctrld listener to be ready")
-	cc := newSocketControlClient(s, sockDir)
+	cc := newSocketControlClient(ctx, s, sockDir)
 	if cc == nil {
 		return false, status, errors.New("could not connect to control server")
 	}
@@ -1772,6 +1816,7 @@ func selfCheckResolveDomain(ctx context.Context, addr, scope string, domain stri
 		lastErr    error
 	)
 
+	oi := osinfo.New()
 	for i := 0; i < maxAttempts; i++ {
 		if domain == "" {
 			return errors.New("empty test domain")
@@ -1788,6 +1833,12 @@ func selfCheckResolveDomain(ctx context.Context, addr, scope string, domain stri
 		if errConnectionRefused(exErr) {
 			return exErr
 		}
+		// Return early if this is MacOS 15.0 and error is timeout error.
+		var e net.Error
+		if oi.Name == "darwin" && oi.Version == "15.0" && errors.As(exErr, &e) && e.Timeout() {
+			mainLog.Load().Warn().Msg("MacOS 15.0 Sequoia has a bug with the firewall which may prevent ctrld from starting. Disable the MacOS firewall and try again")
+			return exErr
+		}
 		lastAnswer = r
 		lastErr = exErr
 		bo.BackOff(ctx, fmt.Errorf("ExchangeContext: %w", exErr))
@@ -2314,17 +2365,30 @@ func cdUIDFromProvToken() string {
 	if cdOrg == "" {
 		return ""
 	}
-
+	// Validate custom hostname if provided.
+	if customHostname != "" && !validHostname(customHostname) {
+		mainLog.Load().Fatal().Msgf("invalid custom hostname: %q", customHostname)
+	}
+	req := &controld.UtilityOrgRequest{ProvToken: cdOrg, Hostname: customHostname}
 	// Process provision token if provided.
-	resolverConfig, err := controld.FetchResolverUID(cdOrg, rootCmd.Version, cdDev)
+	resolverConfig, err := controld.FetchResolverUID(req, rootCmd.Version, cdDev)
 	if err != nil {
 		mainLog.Load().Fatal().Err(err).Msgf("failed to fetch resolver uid with provision token: %s", cdOrg)
 	}
 	return resolverConfig.UID
 }
 
-// removeProvTokenFromArgs removes the --cd-org from command line arguments.
-func removeProvTokenFromArgs(sc *service.Config) {
+// removeOrgFlagsFromArgs removes organization flags from command line arguments.
+// The flags are:
+//
+// - "--cd-org"
+// - "--custom-hostname"
+//
+// This is necessary because "ctrld run" only need a valid UID, which could be fetched
+// using "--cd-org". So if "ctrld start" have already been called with "--cd-org", we
+// already have a valid UID to pass to "ctrld run", so we don't have to force "ctrld run"
+// to re-do the already done job.
+func removeOrgFlagsFromArgs(sc *service.Config) {
 	a := sc.Arguments[:0]
 	skip := false
 	for _, x := range sc.Arguments {
@@ -2332,13 +2396,14 @@ func removeProvTokenFromArgs(sc *service.Config) {
 			skip = false
 			continue
 		}
-		// For "--cd-org XXX", skip it and mark next arg skipped.
-		if x == "--"+cdOrgFlagName {
+		// For "--cd-org XXX"/"--custom-hostname XXX", skip them and mark next arg skipped.
+		if x == "--"+cdOrgFlagName || x == "--"+customHostnameFlagName {
 			skip = true
 			continue
 		}
-		// For "--cd-org=XXX", just skip it.
-		if strings.HasPrefix(x, "--"+cdOrgFlagName+"=") {
+		// For "--cd-org=XXX"/"--custom-hostname=XXX", just skip them.
+		if strings.HasPrefix(x, "--"+cdOrgFlagName+"=") ||
+			strings.HasPrefix(x, "--"+customHostnameFlagName+"=") {
 			continue
 		}
 		a = append(a, x)
@@ -2347,14 +2412,13 @@ func removeProvTokenFromArgs(sc *service.Config) {
 }
 
 // newSocketControlClient returns new control client after control server was started.
-func newSocketControlClient(s service.Service, dir string) *controlClient {
+func newSocketControlClient(ctx context.Context, s service.Service, dir string) *controlClient {
 	// Return early if service is not running.
 	if status, err := s.Status(); err != nil || status != service.StatusRunning {
 		return nil
 	}
 	bo := backoff.NewBackoff("self-check", logf, 10*time.Second)
 	bo.LogLongerThan = 10 * time.Second
-	ctx := context.Background()
 
 	cc := newControlClient(filepath.Join(dir, ctrldControlUnixSock))
 	timeout := time.NewTimer(30 * time.Second)
@@ -2374,6 +2438,8 @@ func newSocketControlClient(s service.Service, dir string) *controlClient {
 		select {
 		case <-timeout.C:
 			return nil
+		case <-ctx.Done():
+			return nil
 		default:
 		}
 	}
@@ -2491,7 +2557,7 @@ func checkDeactivationPin(s service.Service, stopCh chan struct{}) error {
 	if s == nil {
 		cc = newSocketControlClientMobile(dir, stopCh)
 	} else {
-		cc = newSocketControlClient(s, dir)
+		cc = newSocketControlClient(context.TODO(), s, dir)
 	}
 	if cc == nil {
 		return nil // ctrld is not running.
@@ -2575,7 +2641,7 @@ func runInCdMode() bool {
 func curCdUID() string {
 	if s, _ := newService(&prog{}, svcConfig); s != nil {
 		if dir, _ := socketDir(); dir != "" {
-			cc := newSocketControlClient(s, dir)
+			cc := newSocketControlClient(context.TODO(), s, dir)
 			if cc != nil {
 				resp, _ := cc.post(cdPath, nil)
 				if resp != nil {
@@ -2621,7 +2687,7 @@ func upgradeUrl(baseUrl string) string {
 // runningIface returns the value of the iface variable used by ctrld process which is running.
 func runningIface(s service.Service) string {
 	if sockDir, err := socketDir(); err == nil {
-		if cc := newSocketControlClient(s, sockDir); cc != nil {
+		if cc := newSocketControlClient(context.TODO(), s, sockDir); cc != nil {
 			resp, err := cc.post(ifacePath, nil)
 			if err != nil {
 				return ""
@@ -2637,17 +2703,20 @@ func runningIface(s service.Service) string {
 
 // resetDnsNoLog performs resetting DNS with logging disable.
 func resetDnsNoLog(p *prog) {
-	lvl := zerolog.GlobalLevel()
-	zerolog.SetGlobalLevel(zerolog.Disabled)
+	// Normally, disable log to prevent annoying users.
+	if verbose < 3 {
+		lvl := zerolog.GlobalLevel()
+		zerolog.SetGlobalLevel(zerolog.Disabled)
+		p.resetDNS()
+		zerolog.SetGlobalLevel(lvl)
+		return
+	}
+	// For debugging purpose, still emit log.
 	p.resetDNS()
-	zerolog.SetGlobalLevel(lvl)
 }
 
 // resetDnsTask returns a task which perform reset DNS operation.
-func resetDnsTask(p *prog, s service.Service) task {
-	status, err := s.Status()
-	isCtrldInstalled := !errors.Is(err, service.ErrNotInstalled)
-	isCtrldRunning := status == service.StatusRunning
+func resetDnsTask(p *prog, s service.Service, isCtrldInstalled bool, currentRunningIface string) task {
 	return task{func() error {
 		if iface == "" {
 			return nil
@@ -2657,10 +2726,14 @@ func resetDnsTask(p *prog, s service.Service) task {
 		// process to reset what setDNS has done properly.
 		oldIface := iface
 		iface = "auto"
-		if isCtrldRunning {
-			iface = runningIface(s)
+		if currentRunningIface != "" {
+			iface = currentRunningIface
 		}
 		if isCtrldInstalled {
+			mainLog.Load().Debug().Msg("restore system DNS settings")
+			if status, _ := s.Status(); status == service.StatusRunning {
+				mainLog.Load().Fatal().Msg("reset DNS while ctrld still running is not safe")
+			}
 			resetDnsNoLog(p)
 		}
 		iface = oldIface

cmd/cli/dns_proxy.go

@@ -9,6 +9,7 @@ import (
 	"net"
 	"net/netip"
 	"runtime"
+	"slices"
 	"strconv"
 	"strings"
 	"sync"
@@ -16,8 +17,7 @@ import (
 
 	"github.com/miekg/dns"
 	"golang.org/x/sync/errgroup"
-	"tailscale.com/net/interfaces"
-	"tailscale.com/net/netaddr"
+	"tailscale.com/net/netmon"
 	"tailscale.com/net/tsaddr"
 
 	"github.com/Control-D-Inc/ctrld"
@@ -149,6 +149,7 @@ func (p *prog) serveDNS(listenerNum string) error {
 				ufr:            ur,
 			})
 			go p.doSelfUninstall(pr.answer)
+
 			answer = pr.answer
 			rtt := time.Since(t)
 			ctrld.Log(ctx, mainLog.Load().Debug(), "received response of %d bytes in %s", answer.Len(), rtt)
@@ -166,6 +167,7 @@ func (p *prog) serveDNS(listenerNum string) error {
 		go func() {
 			p.WithLabelValuesInc(statsQueriesCount, labelValues...)
 			p.WithLabelValuesInc(statsClientQueriesCount, []string{ci.IP, ci.Mac, ci.Hostname}...)
+			p.forceFetchingAPI(domain)
 		}()
 		if err := w.WriteMsg(answer); err != nil {
 			ctrld.Log(ctx, mainLog.Load().Error().Err(err), "serveDNS: failed to send DNS response to client")
@@ -408,6 +410,19 @@ func (p *prog) proxy(ctx context.Context, req *proxyRequest) *proxyResponse {
 	upstreams := req.ufr.upstreams
 	serveStaleCache := p.cache != nil && p.cfg.Service.CacheServeStale
 	upstreamConfigs := p.upstreamConfigsFromUpstreamNumbers(upstreams)
+
+	leaked := false
+	// If ctrld is going to leak query to OS resolver, check remote upstream in background,
+	// so ctrld could be back to normal operation as long as the network is back online.
+	if len(upstreamConfigs) > 0 && p.leakingQuery.Load() {
+		for n, uc := range upstreamConfigs {
+			go p.checkUpstream(upstreams[n], uc)
+		}
+		upstreamConfigs = nil
+		leaked = true
+		ctrld.Log(ctx, mainLog.Load().Debug(), "%v is down, leaking query to OS resolver", upstreams)
+	}
+
 	if len(upstreamConfigs) == 0 {
 		upstreamConfigs = []*ctrld.UpstreamConfig{osUpstreamConfig}
 		upstreams = []string{upstreamOS}
@@ -423,7 +438,11 @@ func (p *prog) proxy(ctx context.Context, req *proxyRequest) *proxyResponse {
 	// 4. Try remote upstream.
 	isLanOrPtrQuery := false
 	if req.ufr.matched {
-		ctrld.Log(ctx, mainLog.Load().Debug(), "%s, %s, %s -> %v", req.ufr.matchedPolicy, req.ufr.matchedNetwork, req.ufr.matchedRule, upstreams)
+		if leaked {
+			ctrld.Log(ctx, mainLog.Load().Debug(), "%s, %s, %s -> %v (leaked)", req.ufr.matchedPolicy, req.ufr.matchedNetwork, req.ufr.matchedRule, upstreams)
+		} else {
+			ctrld.Log(ctx, mainLog.Load().Debug(), "%s, %s, %s -> %v", req.ufr.matchedPolicy, req.ufr.matchedNetwork, req.ufr.matchedRule, upstreams)
+		}
 	} else {
 		switch {
 		case isPrivatePtrLookup(req.msg):
@@ -493,10 +512,11 @@ func (p *prog) proxy(ctx context.Context, req *proxyRequest) *proxyResponse {
 		answer, err := resolve1(n, upstreamConfig, msg)
 		if err != nil {
 			ctrld.Log(ctx, mainLog.Load().Error().Err(err), "failed to resolve query")
-			if errNetworkError(err) {
+			isNetworkErr := errNetworkError(err)
+			if isNetworkErr {
 				p.um.increaseFailureCount(upstreams[n])
 				if p.um.isDown(upstreams[n]) {
-					go p.um.checkUpstream(upstreams[n], upstreamConfig)
+					go p.checkUpstream(upstreams[n], upstreamConfig)
 				}
 			}
 			// For timeout error (i.e: context deadline exceed), force re-bootstrapping.
@@ -567,6 +587,14 @@ func (p *prog) proxy(ctx context.Context, req *proxyRequest) *proxyResponse {
 		return res
 	}
 	ctrld.Log(ctx, mainLog.Load().Error(), "all %v endpoints failed", upstreams)
+	if cdUID != "" && p.leakOnUpstreamFailure() {
+		p.leakingQueryMu.Lock()
+		if !p.leakingQueryWasRun {
+			p.leakingQueryWasRun = true
+			go p.performLeakingQuery()
+		}
+		p.leakingQueryMu.Unlock()
+	}
 	answer := new(dns.Msg)
 	answer.SetRcode(req.msg, dns.RcodeServerFailure)
 	res.answer = answer
@@ -817,7 +845,7 @@ func (p *prog) getClientInfo(remoteIP string, msg *dns.Msg) *ctrld.ClientInfo {
 	} else {
 		ci.Hostname = p.ciTable.LookupHostname(ci.IP, ci.Mac)
 	}
-	ci.Self = queryFromSelf(ci.IP)
+	ci.Self = p.queryFromSelf(ci.IP)
 	// If this is a query from self, but ci.IP is not loopback IP,
 	// try using hostname mapping for lookback IP if presents.
 	if ci.Self {
@@ -887,29 +915,71 @@ func (p *prog) selfUninstallCoolOfPeriod() {
 	p.selfUninstallMu.Unlock()
 }
 
+// performLeakingQuery performs necessary works to leak queries to OS resolver.
+func (p *prog) performLeakingQuery() {
+	mainLog.Load().Warn().Msg("leaking query to OS resolver")
+	// Signal dns watchers to stop, so changes made below won't be reverted.
+	p.leakingQuery.Store(true)
+	p.resetDNS()
+	ns := ctrld.InitializeOsResolver()
+	mainLog.Load().Debug().Msgf("re-initialized OS resolver with nameservers: %v", ns)
+	p.dnsWg.Wait()
+	p.setDNS()
+}
+
+// forceFetchingAPI sends signal to force syncing API config if run in cd mode,
+// and the domain == "cdUID.verify.controld.com"
+func (p *prog) forceFetchingAPI(domain string) {
+	if cdUID == "" {
+		return
+	}
+	resolverID, parent, _ := strings.Cut(domain, ".")
+	if resolverID != cdUID {
+		return
+	}
+	switch {
+	case cdDev && parent == "verify.controld.dev":
+		// match ControlD dev
+	case parent == "verify.controld.com":
+		// match ControlD
+	default:
+		return
+	}
+	_ = p.apiForceReloadGroup.DoChan("force_sync_api", func() (interface{}, error) {
+		p.apiForceReloadCh <- struct{}{}
+		// Wait here to prevent abusing API if we are flooded.
+		time.Sleep(timeDurationOrDefault(p.cfg.Service.ForceRefetchWaitTime, 30) * time.Second)
+		return nil, nil
+	})
+}
+
+// timeDurationOrDefault returns time duration value from n if not nil.
+// Otherwise, it returns time duration value defaultN.
+func timeDurationOrDefault(n *int, defaultN int) time.Duration {
+	if n != nil && *n > 0 {
+		return time.Duration(*n)
+	}
+	return time.Duration(defaultN)
+}
+
 // queryFromSelf reports whether the input IP is from device running ctrld.
-func queryFromSelf(ip string) bool {
+func (p *prog) queryFromSelf(ip string) bool {
+	if val, ok := p.queryFromSelfMap.Load(ip); ok {
+		return val.(bool)
+	}
 	netIP := netip.MustParseAddr(ip)
-	ifaces, err := interfaces.GetList()
+	regularIPs, loopbackIPs, err := netmon.LocalAddresses()
 	if err != nil {
-		mainLog.Load().Warn().Err(err).Msg("could not get interfaces list")
+		mainLog.Load().Warn().Err(err).Msg("could not get local addresses")
 		return false
 	}
-	for _, iface := range ifaces {
-		addrs, err := iface.Addrs()
-		if err != nil {
-			mainLog.Load().Warn().Err(err).Msgf("could not get interfaces addresses: %s", iface.Name)
-			continue
-		}
-		for _, a := range addrs {
-			switch v := a.(type) {
-			case *net.IPNet:
-				if pfx, ok := netaddr.FromStdIPNet(v); ok && pfx.Addr().Compare(netIP) == 0 {
-					return true
-				}
-			}
+	for _, localIP := range slices.Concat(regularIPs, loopbackIPs) {
+		if localIP.Compare(netIP) == 0 {
+			p.queryFromSelfMap.Store(ip, true)
+			return true
 		}
 	}
+	p.queryFromSelfMap.Store(ip, false)
 	return false
 }
 

cmd/cli/hostname.go

@@ -0,0 +1,14 @@
+package cli
+
+import "regexp"
+
+// validHostname reports whether hostname is a valid hostname.
+// A valid hostname contains 3 -> 64 characters and conform to RFC1123.
+func validHostname(hostname string) bool {
+	hostnameLen := len(hostname)
+	if hostnameLen < 3 || hostnameLen > 64 {
+		return false
+	}
+	validHostnameRfc1123 := regexp.MustCompile(`^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])$`)
+	return validHostnameRfc1123.MatchString(hostname)
+}

cmd/cli/hostname_test.go

@@ -0,0 +1,35 @@
+package cli
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_validHostname(t *testing.T) {
+	tests := []struct {
+		name     string
+		hostname string
+		valid    bool
+	}{
+		{"localhost", "localhost", true},
+		{"localdomain", "localhost.localdomain", true},
+		{"localhost6", "localhost6.localdomain6", true},
+		{"ip6", "ip6-localhost", true},
+		{"non-domain", "controld", true},
+		{"domain", "controld.com", true},
+		{"empty", "", false},
+		{"min length", "fo", false},
+		{"max length", strings.Repeat("a", 65), false},
+		{"special char", "foo!", false},
+		{"non-ascii", "fooΩ", false},
+	}
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.hostname, func(t *testing.T) {
+			t.Parallel()
+			assert.True(t, validHostname(tc.hostname) == tc.valid)
+		})
+	}
+}

cmd/cli/main.go

@@ -29,6 +29,7 @@ var (
 	silent            bool
 	cdUID             string
 	cdOrg             string
+	customHostname    string
 	cdDev             bool
 	iface             string
 	ifaceStartStop    string
@@ -45,9 +46,10 @@ var (
 )
 
 const (
-	cdUidFlagName   = "cd"
-	cdOrgFlagName   = "cd-org"
-	nextdnsFlagName = "nextdns"
+	cdUidFlagName          = "cd"
+	cdOrgFlagName          = "cd-org"
+	customHostnameFlagName = "custom-hostname"
+	nextdnsFlagName        = "nextdns"
 )
 
 func init() {

cmd/cli/net.go

@@ -1,34 +0,0 @@
-package cli
-
-import "strings"
-
-// Copied from https://gist.github.com/Ultraporing/fe52981f678be6831f747c206a4861cb
-
-// Mac Address parts to look for, and identify non-physical devices. There may be more, update me!
-var macAddrPartsToFilter = []string{
-	"00:03:FF",       // Microsoft Hyper-V, Virtual Server, Virtual PC
-	"0A:00:27",       // VirtualBox
-	"00:00:00:00:00", // Teredo Tunneling Pseudo-Interface
-	"00:50:56",       // VMware ESX 3, Server, Workstation, Player
-	"00:1C:14",       // VMware ESX 3, Server, Workstation, Player
-	"00:0C:29",       // VMware ESX 3, Server, Workstation, Player
-	"00:05:69",       // VMware ESX 3, Server, Workstation, Player
-	"00:1C:42",       // Microsoft Hyper-V, Virtual Server, Virtual PC
-	"00:0F:4B",       // Virtual Iron 4
-	"00:16:3E",       // Red Hat Xen, Oracle VM, XenSource, Novell Xen
-	"08:00:27",       // Sun xVM VirtualBox
-	"7A:79",          // Hamachi
-}
-
-// Filters the possible physical interface address by comparing it to known popular VM Software addresses
-// and Teredo Tunneling Pseudo-Interface.
-//
-//lint:ignore U1000 use in net_windows.go
-func isPhysicalInterface(addr string) bool {
-	for _, macPart := range macAddrPartsToFilter {
-		if strings.HasPrefix(strings.ToLower(addr), strings.ToLower(macPart)) {
-			return false
-		}
-	}
-	return true
-}

cmd/cli/net_darwin.go

@@ -49,6 +49,7 @@ func validInterface(iface *net.Interface, validIfacesMap map[string]struct{}) bo
 	return ok
 }
 
+// validInterfacesMap returns a set of all valid hardware ports.
 func validInterfacesMap() map[string]struct{} {
 	b, err := exec.Command("networksetup", "-listallhardwareports").Output()
 	if err != nil {

cmd/cli/net_windows.go

@@ -1,7 +1,10 @@
 package cli
 
 import (
+	"bufio"
+	"bytes"
 	"net"
+	"strings"
 )
 
 func patchNetIfaceName(iface *net.Interface) error {
@@ -11,13 +14,21 @@ func patchNetIfaceName(iface *net.Interface) error {
 // validInterface reports whether the *net.Interface is a valid one.
 // On Windows, only physical interfaces are considered valid.
 func validInterface(iface *net.Interface, validIfacesMap map[string]struct{}) bool {
-	if iface == nil {
-		return false
-	}
-	if isPhysicalInterface(iface.HardwareAddr.String()) {
-		return true
-	}
-	return false
+	_, ok := validIfacesMap[iface.Name]
+	return ok
 }
 
-func validInterfacesMap() map[string]struct{} { return nil }
+// validInterfacesMap returns a set of all physical interfaces.
+func validInterfacesMap() map[string]struct{} {
+	out, err := powershell("Get-NetAdapter -Physical | Select-Object -ExpandProperty Name")
+	if err != nil {
+		return nil
+	}
+	m := make(map[string]struct{})
+	scanner := bufio.NewScanner(bytes.NewReader(out))
+	for scanner.Scan() {
+		ifaceName := strings.TrimSpace(scanner.Text())
+		m[ifaceName] = struct{}{}
+	}
+	return m
+}

cmd/cli/os_freebsd.go

@@ -5,6 +5,8 @@ import (
 	"net/netip"
 	"os/exec"
 
+	"tailscale.com/tsd"
+
 	"github.com/Control-D-Inc/ctrld/internal/dns"
 	"github.com/Control-D-Inc/ctrld/internal/resolvconffile"
 )
@@ -36,7 +38,8 @@ func setDnsIgnoreUnusableInterface(iface *net.Interface, nameservers []string) e
 
 // set the dns server for the provided network interface
 func setDNS(iface *net.Interface, nameservers []string) error {
-	r, err := dns.NewOSConfigurator(logf, iface.Name)
+	sys := new(tsd.System)
+	r, err := dns.NewOSConfigurator(logf, sys.HealthTracker(), sys.ControlKnobs(), iface.Name)
 	if err != nil {
 		mainLog.Load().Error().Err(err).Msg("failed to create DNS OS configurator")
 		return err
@@ -60,7 +63,8 @@ func resetDnsIgnoreUnusableInterface(iface *net.Interface) error {
 }
 
 func resetDNS(iface *net.Interface) error {
-	r, err := dns.NewOSConfigurator(logf, iface.Name)
+	sys := new(tsd.System)
+	r, err := dns.NewOSConfigurator(logf, sys.HealthTracker(), sys.ControlKnobs(), iface.Name)
 	if err != nil {
 		mainLog.Load().Error().Err(err).Msg("failed to create DNS OS configurator")
 		return err

cmd/cli/os_linux.go

@@ -14,6 +14,8 @@ import (
 	"syscall"
 	"time"
 
+	"tailscale.com/tsd"
+
 	"github.com/insomniacslk/dhcp/dhcpv4/nclient4"
 	"github.com/insomniacslk/dhcp/dhcpv6"
 	"github.com/insomniacslk/dhcp/dhcpv6/client6"
@@ -54,7 +56,8 @@ func setDnsIgnoreUnusableInterface(iface *net.Interface, nameservers []string) e
 }
 
 func setDNS(iface *net.Interface, nameservers []string) error {
-	r, err := dns.NewOSConfigurator(logf, iface.Name)
+	sys := new(tsd.System)
+	r, err := dns.NewOSConfigurator(logf, sys.HealthTracker(), sys.ControlKnobs(), iface.Name)
 	if err != nil {
 		mainLog.Load().Error().Err(err).Msg("failed to create DNS OS configurator")
 		return err
@@ -136,7 +139,8 @@ func resetDNS(iface *net.Interface) (err error) {
 		if exe, _ := exec.LookPath("/lib/systemd/systemd-networkd"); exe != "" {
 			_ = exec.Command("systemctl", "start", "systemd-networkd").Run()
 		}
-		if r, oerr := dns.NewOSConfigurator(logf, iface.Name); oerr == nil {
+		sys := new(tsd.System)
+		if r, oerr := dns.NewOSConfigurator(logf, sys.HealthTracker(), sys.ControlKnobs(), iface.Name); oerr == nil {
 			_ = r.SetDNS(dns.OSConfig{})
 			if err := r.Close(); err != nil {
 				mainLog.Load().Error().Err(err).Msg("failed to rollback DNS setting")

cmd/cli/os_windows.go

@@ -5,7 +5,7 @@ import (
 	"fmt"
 	"net"
 	"os"
-	"os/exec"
+	"slices"
 	"strconv"
 	"strings"
 	"sync"
@@ -30,6 +30,14 @@ func setDnsIgnoreUnusableInterface(iface *net.Interface, nameservers []string) e
 	return setDNS(iface, nameservers)
 }
 
+func setDnsPowershellCmd(iface *net.Interface, nameservers []string) string {
+	nss := make([]string, 0, len(nameservers))
+	for _, ns := range nameservers {
+		nss = append(nss, strconv.Quote(ns))
+	}
+	return fmt.Sprintf("Set-DnsClientServerAddress -InterfaceIndex %d -ServerAddresses (%s)", iface.Index, strings.Join(nss, ","))
+}
+
 // setDNS sets the dns server for the provided network interface
 func setDNS(iface *net.Interface, nameservers []string) error {
 	if len(nameservers) == 0 {
@@ -41,22 +49,25 @@ func setDNS(iface *net.Interface, nameservers []string) error {
 		if windowsHasLocalDnsServerRunning() {
 			file := absHomeDir(windowsForwardersFilename)
 			oldForwardersContent, _ := os.ReadFile(file)
-			if err := os.WriteFile(file, []byte(strings.Join(nameservers, ",")), 0600); err != nil {
+			hasLocalIPv6Listener := needLocalIPv6Listener()
+			forwarders := slices.DeleteFunc(slices.Clone(nameservers), func(s string) bool {
+				if !hasLocalIPv6Listener {
+					return false
+				}
+				return s == "::1"
+			})
+			if err := os.WriteFile(file, []byte(strings.Join(forwarders, ",")), 0600); err != nil {
 				mainLog.Load().Warn().Err(err).Msg("could not save forwarders settings")
 			}
 			oldForwarders := strings.Split(string(oldForwardersContent), ",")
-			if err := addDnsServerForwarders(nameservers, oldForwarders); err != nil {
+			if err := addDnsServerForwarders(forwarders, oldForwarders); err != nil {
 				mainLog.Load().Warn().Err(err).Msg("could not set forwarders settings")
 			}
 		}
 	})
-	primaryDNS := nameservers[0]
-	if err := setPrimaryDNS(iface, primaryDNS, true); err != nil {
-		return err
-	}
-	if len(nameservers) > 1 {
-		secondaryDNS := nameservers[1]
-		_ = addSecondaryDNS(iface, secondaryDNS)
+	out, err := powershell(setDnsPowershellCmd(iface, nameservers))
+	if err != nil {
+		return fmt.Errorf("%w: %s", err, string(out))
 	}
 	return nil
 }
@@ -85,17 +96,13 @@ func resetDNS(iface *net.Interface) error {
 		}
 	})
 
-	// Restoring ipv6 first.
-	if ctrldnet.SupportsIPv6ListenLocal() {
-		if output, err := netsh("interface", "ipv6", "set", "dnsserver", strconv.Itoa(iface.Index), "dhcp"); err != nil {
-			mainLog.Load().Warn().Err(err).Msgf("failed to reset ipv6 DNS: %s", string(output))
-		}
-	}
-	// Restoring ipv4 DHCP.
-	output, err := netsh("interface", "ipv4", "set", "dnsserver", strconv.Itoa(iface.Index), "dhcp")
+	// Restoring DHCP settings.
+	cmd := fmt.Sprintf("Set-DnsClientServerAddress -InterfaceIndex %d -ResetServerAddresses", iface.Index)
+	out, err := powershell(cmd)
 	if err != nil {
-		return fmt.Errorf("%s: %w", string(output), err)
+		return fmt.Errorf("%w: %s", err, string(out))
 	}
+
 	// If there's static DNS saved, restoring it.
 	if nss := savedStaticNameservers(iface); len(nss) > 0 {
 		v4ns := make([]string, 0, 2)
@@ -112,54 +119,15 @@ func resetDNS(iface *net.Interface) error {
 			if len(ns) == 0 {
 				continue
 			}
-			primaryDNS := ns[0]
-			if err := setPrimaryDNS(iface, primaryDNS, false); err != nil {
+			mainLog.Load().Debug().Msgf("setting static DNS for interface %q", iface.Name)
+			if err := setDNS(iface, ns); err != nil {
 				return err
 			}
-			if len(ns) > 1 {
-				secondaryDNS := ns[1]
-				_ = addSecondaryDNS(iface, secondaryDNS)
-			}
 		}
 	}
 	return nil
 }
 
-func setPrimaryDNS(iface *net.Interface, dns string, disablev6 bool) error {
-	ipVer := "ipv4"
-	if ctrldnet.IsIPv6(dns) {
-		ipVer = "ipv6"
-	}
-	idx := strconv.Itoa(iface.Index)
-	output, err := netsh("interface", ipVer, "set", "dnsserver", idx, "static", dns)
-	if err != nil {
-		mainLog.Load().Error().Err(err).Msgf("failed to set primary DNS: %s", string(output))
-		return err
-	}
-	if disablev6 && ipVer == "ipv4" && ctrldnet.SupportsIPv6ListenLocal() {
-		// Disable IPv6 DNS, so the query will be fallback to IPv4.
-		_, _ = netsh("interface", "ipv6", "set", "dnsserver", idx, "static", "::1", "primary")
-	}
-
-	return nil
-}
-
-func addSecondaryDNS(iface *net.Interface, dns string) error {
-	ipVer := "ipv4"
-	if ctrldnet.IsIPv6(dns) {
-		ipVer = "ipv6"
-	}
-	output, err := netsh("interface", ipVer, "add", "dns", strconv.Itoa(iface.Index), dns, "index=2")
-	if err != nil {
-		mainLog.Load().Warn().Err(err).Msgf("failed to add secondary DNS: %s", string(output))
-	}
-	return nil
-}
-
-func netsh(args ...string) ([]byte, error) {
-	return exec.Command("netsh", args...).Output()
-}
-
 func currentDNS(iface *net.Interface) []string {
 	luid, err := winipcfg.LUIDFromIndex(uint32(iface.Index))
 	if err != nil {
@@ -200,7 +168,9 @@ func currentStaticDNS(iface *net.Interface) ([]string, error) {
 			out, err := powershell(cmd)
 			if err == nil && len(out) > 0 {
 				found = true
-				ns = append(ns, strings.Split(string(out), ",")...)
+				for _, e := range strings.Split(string(out), ",") {
+					ns = append(ns, strings.TrimRight(e, "\x00"))
+				}
 			}
 		}
 	}

cmd/cli/prog.go

@@ -24,7 +24,8 @@ import (
 	"github.com/kardianos/service"
 	"github.com/rs/zerolog"
 	"github.com/spf13/viper"
-	"tailscale.com/net/interfaces"
+	"golang.org/x/sync/singleflight"
+	"tailscale.com/net/netmon"
 	"tailscale.com/net/tsaddr"
 
 	"github.com/Control-D-Inc/ctrld"
@@ -68,19 +69,21 @@ var svcConfig = &service.Config{
 var useSystemdResolved = false
 
 type prog struct {
-	mu               sync.Mutex
-	waitCh           chan struct{}
-	stopCh           chan struct{}
-	reloadCh         chan struct{} // For Windows.
-	reloadDoneCh     chan struct{}
-	apiReloadCh      chan *ctrld.Config
-	logConn          net.Conn
-	cs               *controlServer
-	csSetDnsDone     chan struct{}
-	csSetDnsOk       bool
-	dnsWatchDogOnce  sync.Once
-	dnsWg            sync.WaitGroup
-	dnsWatcherStopCh chan struct{}
+	mu                   sync.Mutex
+	waitCh               chan struct{}
+	stopCh               chan struct{}
+	reloadCh             chan struct{} // For Windows.
+	reloadDoneCh         chan struct{}
+	apiReloadCh          chan *ctrld.Config
+	apiForceReloadCh     chan struct{}
+	apiForceReloadGroup  singleflight.Group
+	logConn              net.Conn
+	cs                   *controlServer
+	csSetDnsDone         chan struct{}
+	csSetDnsOk           bool
+	dnsWg                sync.WaitGroup
+	dnsWatcherClosedOnce sync.Once
+	dnsWatcherStopCh     chan struct{}
 
 	cfg                  *ctrld.Config
 	localUpstreams       []string
@@ -95,6 +98,7 @@ type prog struct {
 	ptrLoopGuard         *loopGuard
 	lanLoopGuard         *loopGuard
 	metricsQueryStats    atomic.Bool
+	queryFromSelfMap     sync.Map
 
 	selfUninstallMu       sync.Mutex
 	refusedQueryCount     int
@@ -104,6 +108,10 @@ type prog struct {
 	loopMu sync.Mutex
 	loop   map[string]bool
 
+	leakingQueryMu     sync.Mutex
+	leakingQueryWasRun bool
+	leakingQuery       atomic.Bool
+
 	started       chan struct{}
 	onStartedDone chan struct{}
 	onStarted     []func()
@@ -239,6 +247,8 @@ func (p *prog) postRun() {
 		ns := ctrld.InitializeOsResolver()
 		mainLog.Load().Debug().Msgf("initialized OS resolver with nameservers: %v", ns)
 		p.setDNS()
+		p.csSetDnsDone <- struct{}{}
+		close(p.csSetDnsDone)
 	}
 }
 
@@ -248,47 +258,48 @@ func (p *prog) apiConfigReload() {
 		return
 	}
 
-	secs := 3600
-	if p.cfg.Service.RefetchTime != nil && *p.cfg.Service.RefetchTime > 0 {
-		secs = *p.cfg.Service.RefetchTime
-	}
-
-	ticker := time.NewTicker(time.Duration(secs) * time.Second)
+	ticker := time.NewTicker(timeDurationOrDefault(p.cfg.Service.RefetchTime, 3600) * time.Second)
 	defer ticker.Stop()
 
 	logger := mainLog.Load().With().Str("mode", "api-reload").Logger()
 	logger.Debug().Msg("starting custom config reload timer")
 	lastUpdated := time.Now().Unix()
+
+	doReloadApiConfig := func(forced bool, logger zerolog.Logger) {
+		resolverConfig, err := controld.FetchResolverConfig(cdUID, rootCmd.Version, cdDev)
+		selfUninstallCheck(err, p, logger)
+		if err != nil {
+			logger.Warn().Err(err).Msg("could not fetch resolver config")
+			return
+		}
+
+		if resolverConfig.Ctrld.CustomConfig == "" {
+			return
+		}
+
+		if resolverConfig.Ctrld.CustomLastUpdate > lastUpdated || forced {
+			lastUpdated = time.Now().Unix()
+			cfg := &ctrld.Config{}
+			if err := validateCdRemoteConfig(resolverConfig, cfg); err != nil {
+				logger.Warn().Err(err).Msg("skipping invalid custom config")
+				if _, err := controld.UpdateCustomLastFailed(cdUID, rootCmd.Version, cdDev, true); err != nil {
+					logger.Error().Err(err).Msg("could not mark custom last update failed")
+				}
+				return
+			}
+			setListenerDefaultValue(cfg)
+			logger.Debug().Msg("custom config changes detected, reloading...")
+			p.apiReloadCh <- cfg
+		} else {
+			logger.Debug().Msg("custom config does not change")
+		}
+	}
 	for {
 		select {
+		case <-p.apiForceReloadCh:
+			doReloadApiConfig(true, logger.With().Bool("forced", true).Logger())
 		case <-ticker.C:
-			resolverConfig, err := controld.FetchResolverConfig(cdUID, rootCmd.Version, cdDev)
-			selfUninstallCheck(err, p, logger)
-			if err != nil {
-				logger.Warn().Err(err).Msg("could not fetch resolver config")
-				continue
-			}
-
-			if resolverConfig.Ctrld.CustomConfig == "" {
-				continue
-			}
-
-			if resolverConfig.Ctrld.CustomLastUpdate > lastUpdated {
-				lastUpdated = time.Now().Unix()
-				cfg := &ctrld.Config{}
-				if err := validateCdRemoteConfig(resolverConfig, cfg); err != nil {
-					logger.Warn().Err(err).Msg("skipping invalid custom config")
-					if _, err := controld.UpdateCustomLastFailed(cdUID, rootCmd.Version, cdDev, true); err != nil {
-						logger.Error().Err(err).Msg("could not mark custom last update failed")
-					}
-					break
-				}
-				setListenerDefaultValue(cfg)
-				logger.Debug().Msg("custom config changes detected, reloading...")
-				p.apiReloadCh <- cfg
-			} else {
-				logger.Debug().Msg("custom config does not change")
-			}
+			doReloadApiConfig(false, logger)
 		case <-p.stopCh:
 			return
 		}
@@ -301,7 +312,11 @@ func (p *prog) setupUpstream(cfg *ctrld.Config) {
 	isControlDUpstream := false
 	for n := range cfg.Upstream {
 		uc := cfg.Upstream[n]
+		sdns := uc.Type == ctrld.ResolverTypeSDNS
 		uc.Init()
+		if sdns {
+			mainLog.Load().Debug().Msgf("initialized DNS Stamps with endpoint: %s, type: %s", uc.Endpoint, uc.Type)
+		}
 		isControlDUpstream = isControlDUpstream || uc.IsControlD()
 		if uc.BootstrapIP == "" {
 			uc.SetupBootstrapIP()
@@ -497,6 +512,8 @@ func (p *prog) metricsEnabled() bool {
 }
 
 func (p *prog) Stop(s service.Service) error {
+	p.stopDnsWatchers()
+	mainLog.Load().Debug().Msg("dns watchers stopped")
 	mainLog.Load().Info().Msg("Service stopped")
 	close(p.stopCh)
 	if err := p.deAllocateIP(); err != nil {
@@ -506,6 +523,15 @@ func (p *prog) Stop(s service.Service) error {
 	return nil
 }
 
+func (p *prog) stopDnsWatchers() {
+	// Ensure all DNS watchers goroutine are terminated,
+	// so it won't mess up with other DNS changes.
+	p.dnsWatcherClosedOnce.Do(func() {
+		close(p.dnsWatcherStopCh)
+	})
+	p.dnsWg.Wait()
+}
+
 func (p *prog) allocateIP(ip string) error {
 	p.mu.Lock()
 	defer p.mu.Unlock()
@@ -533,8 +559,6 @@ func (p *prog) setDNS() {
 	setDnsOK := false
 	defer func() {
 		p.csSetDnsOk = setDnsOK
-		p.csSetDnsDone <- struct{}{}
-		close(p.csSetDnsDone)
 	}()
 
 	if cfg.Listener == nil {
@@ -588,12 +612,21 @@ func (p *prog) setDNS() {
 	if needRFC1918Listeners(lc) {
 		nameservers = append(nameservers, ctrld.Rfc1918Addresses()...)
 	}
+	if needLocalIPv6Listener() {
+		nameservers = append(nameservers, "::1")
+	}
+	slices.Sort(nameservers)
 	if err := setDNS(netIface, nameservers); err != nil {
 		logger.Error().Err(err).Msgf("could not set DNS for interface")
 		return
 	}
 	setDnsOK = true
 	logger.Debug().Msg("setting DNS successfully")
+	if allIfaces {
+		withEachPhysicalInterfaces(netIface.Name, "set DNS", func(i *net.Interface) error {
+			return setDnsIgnoreUnusableInterface(i, nameservers)
+		})
+	}
 	if shouldWatchResolvconf() {
 		servers := make([]netip.Addr, len(nameservers))
 		for i := range nameservers {
@@ -605,11 +638,6 @@ func (p *prog) setDNS() {
 			p.watchResolvConf(netIface, servers, setResolvConf)
 		}()
 	}
-	if allIfaces {
-		withEachPhysicalInterfaces(netIface.Name, "set DNS", func(i *net.Interface) error {
-			return setDnsIgnoreUnusableInterface(i, nameservers)
-		})
-	}
 	if p.dnsWatchdogEnabled() {
 		p.dnsWg.Add(1)
 		go func() {
@@ -644,41 +672,42 @@ func (p *prog) dnsWatchdog(iface *net.Interface, nameservers []string, allIfaces
 		return
 	}
 
-	p.dnsWatchDogOnce.Do(func() {
-		mainLog.Load().Debug().Msg("start DNS settings watchdog")
-		ns := nameservers
-		slices.Sort(ns)
-		ticker := time.NewTicker(p.dnsWatchdogDuration())
-		logger := mainLog.Load().With().Str("iface", iface.Name).Logger()
-		for {
-			select {
-			case <-p.dnsWatcherStopCh:
+	mainLog.Load().Debug().Msg("start DNS settings watchdog")
+	ns := nameservers
+	slices.Sort(ns)
+	ticker := time.NewTicker(p.dnsWatchdogDuration())
+	logger := mainLog.Load().With().Str("iface", iface.Name).Logger()
+	for {
+		select {
+		case <-p.dnsWatcherStopCh:
+			return
+		case <-p.stopCh:
+			mainLog.Load().Debug().Msg("stop dns watchdog")
+			return
+		case <-ticker.C:
+			if p.leakingQuery.Load() {
 				return
-			case <-p.stopCh:
-				mainLog.Load().Debug().Msg("stop dns watchdog")
-				return
-			case <-ticker.C:
-				if dnsChanged(iface, ns) {
-					logger.Debug().Msg("DNS settings were changed, re-applying settings")
-					if err := setDNS(iface, ns); err != nil {
-						mainLog.Load().Error().Err(err).Str("iface", iface.Name).Msgf("could not re-apply DNS settings")
-					}
-				}
-				if allIfaces {
-					withEachPhysicalInterfaces(iface.Name, "re-applying DNS", func(i *net.Interface) error {
-						if dnsChanged(i, ns) {
-							if err := setDnsIgnoreUnusableInterface(i, nameservers); err != nil {
-								mainLog.Load().Error().Err(err).Str("iface", i.Name).Msgf("could not re-apply DNS settings")
-							} else {
-								mainLog.Load().Debug().Msgf("re-applying DNS for interface %q successfully", i.Name)
-							}
-						}
-						return nil
-					})
+			}
+			if dnsChanged(iface, ns) {
+				logger.Debug().Msg("DNS settings were changed, re-applying settings")
+				if err := setDNS(iface, ns); err != nil {
+					mainLog.Load().Error().Err(err).Str("iface", iface.Name).Msgf("could not re-apply DNS settings")
 				}
 			}
+			if allIfaces {
+				withEachPhysicalInterfaces(iface.Name, "", func(i *net.Interface) error {
+					if dnsChanged(i, ns) {
+						if err := setDnsIgnoreUnusableInterface(i, nameservers); err != nil {
+							mainLog.Load().Error().Err(err).Str("iface", i.Name).Msgf("could not re-apply DNS settings")
+						} else {
+							mainLog.Load().Debug().Msgf("re-applying DNS for interface %q successfully", i.Name)
+						}
+					}
+					return nil
+				})
+			}
 		}
-	})
+	}
 }
 
 func (p *prog) resetDNS() {
@@ -713,6 +742,18 @@ func (p *prog) resetDNS() {
 	}
 }
 
+// leakOnUpstreamFailure reports whether ctrld should leak query to OS resolver when failed to connect all upstreams.
+func (p *prog) leakOnUpstreamFailure() bool {
+	if ptr := p.cfg.Service.LeakOnUpstreamFailure; ptr != nil {
+		return *ptr
+	}
+	// Default is false on routers, since this leaking is only useful for devices that move between networks.
+	if router.Name() != "" {
+		return false
+	}
+	return true
+}
+
 func randomLocalIP() string {
 	n := rand.Intn(254-2) + 2
 	return fmt.Sprintf("127.0.0.%d", n)
@@ -830,7 +871,7 @@ func ifaceFirstPrivateIP(iface *net.Interface) string {
 
 // defaultRouteIP returns private IP string of the default route if present, prefer IPv4 over IPv6.
 func defaultRouteIP() string {
-	dr, err := interfaces.DefaultRoute()
+	dr, err := netmon.DefaultRoute()
 	if err != nil {
 		return ""
 	}
@@ -850,7 +891,7 @@ func defaultRouteIP() string {
 	// There could be multiple LAN interfaces with the same Mac address, so we find all private
 	// IPs then using the smallest one.
 	var addrs []netip.Addr
-	interfaces.ForeachInterface(func(i interfaces.Interface, prefixes []netip.Prefix) {
+	netmon.ForeachInterface(func(i netmon.Interface, prefixes []netip.Prefix) {
 		if i.Name == drNetIface.Name {
 			return
 		}
@@ -890,7 +931,7 @@ func canBeLocalUpstream(addr string) bool {
 // log message when error happens.
 func withEachPhysicalInterfaces(excludeIfaceName, context string, f func(i *net.Interface) error) {
 	validIfacesMap := validInterfacesMap()
-	interfaces.ForeachInterface(func(i interfaces.Interface, prefixes []netip.Prefix) {
+	netmon.ForeachInterface(func(i netmon.Interface, prefixes []netip.Prefix) {
 		// Skip loopback/virtual interface.
 		if i.IsLoopback() || len(i.HardwareAddr) == 0 {
 			return
@@ -948,11 +989,13 @@ func saveCurrentStaticDNS(iface *net.Interface) error {
 	if err := os.Remove(file); err != nil && !errors.Is(err, fs.ErrNotExist) {
 		mainLog.Load().Warn().Err(err).Msg("could not remove old static DNS settings file")
 	}
-	mainLog.Load().Debug().Msgf("DNS settings for %s is static, saving ...", iface.Name)
-	if err := os.WriteFile(file, []byte(strings.Join(ns, ",")), 0600); err != nil {
+	nss := strings.Join(ns, ",")
+	mainLog.Load().Debug().Msgf("DNS settings for %q is static: %v, saving ...", iface.Name, nss)
+	if err := os.WriteFile(file, []byte(nss), 0600); err != nil {
 		mainLog.Load().Err(err).Msgf("could not save DNS settings for iface: %s", iface.Name)
 		return err
 	}
+	mainLog.Load().Debug().Msgf("save DNS settings for interface %q successfully", iface.Name)
 	return nil
 }
 
@@ -977,16 +1020,18 @@ func savedStaticNameservers(iface *net.Interface) []string {
 func dnsChanged(iface *net.Interface, nameservers []string) bool {
 	curNameservers, _ := currentStaticDNS(iface)
 	slices.Sort(curNameservers)
-	return !slices.Equal(curNameservers, nameservers)
+	if !slices.Equal(curNameservers, nameservers) {
+		mainLog.Load().Debug().Msgf("interface %q current DNS settings: %v, expected: %v", iface.Name, curNameservers, nameservers)
+		return true
+	}
+	return false
 }
 
 // selfUninstallCheck checks if the error dues to controld.InvalidConfigCode, perform self-uninstall then.
 func selfUninstallCheck(uninstallErr error, p *prog, logger zerolog.Logger) {
 	var uer *controld.UtilityErrorResponse
 	if errors.As(uninstallErr, &uer) && uer.ErrorField.Code == controld.InvalidConfigCode {
-		// Ensure all DNS watchers goroutine are terminated, so it won't mess up with self-uninstall.
-		close(p.dnsWatcherStopCh)
-		p.dnsWg.Wait()
+		p.stopDnsWatchers()
 
 		// Perform self-uninstall now.
 		selfUninstall(p, logger)

cmd/cli/prog_linux.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"os/exec"
 	"strings"
+	"tailscale.com/tsd"
 
 	"github.com/kardianos/service"
 
@@ -14,7 +15,8 @@ import (
 )
 
 func init() {
-	if r, err := dns.NewOSConfigurator(func(format string, args ...any) {}, "lo"); err == nil {
+	sys := new(tsd.System)
+	if r, err := dns.NewOSConfigurator(func(format string, args ...any) {}, sys.HealthTracker(), sys.ControlKnobs(), "lo"); err == nil {
 		useSystemdResolved = r.Mode() == "systemd-resolved"
 	}
 	// Disable quic-go's ECN support by default, see https://github.com/quic-go/quic-go/issues/3911

cmd/cli/resolvconf.go

@@ -40,6 +40,9 @@ func (p *prog) watchResolvConf(iface *net.Interface, ns []netip.Addr, setDnsFn f
 			mainLog.Load().Debug().Msgf("stopping watcher for %s", resolvConfPath)
 			return
 		case event, ok := <-watcher.Events:
+			if p.leakingQuery.Load() {
+				return
+			}
 			if !ok {
 				return
 			}

cmd/cli/resolvconf_not_darwin_unix.go

@@ -6,6 +6,7 @@ import (
 	"net"
 	"net/netip"
 
+	"tailscale.com/tsd"
 	"tailscale.com/util/dnsname"
 
 	"github.com/Control-D-Inc/ctrld/internal/dns"
@@ -13,7 +14,8 @@ import (
 
 // setResolvConf sets the content of resolv.conf file using the given nameservers list.
 func setResolvConf(iface *net.Interface, ns []netip.Addr) error {
-	r, err := dns.NewOSConfigurator(func(format string, args ...any) {}, "lo") // interface name does not matter.
+	sys := new(tsd.System)
+	r, err := dns.NewOSConfigurator(func(format string, args ...any) {}, sys.HealthTracker(), sys.ControlKnobs(), "lo") // interface name does not matter.
 	if err != nil {
 		return err
 	}
@@ -27,7 +29,8 @@ func setResolvConf(iface *net.Interface, ns []netip.Addr) error {
 
 // shouldWatchResolvconf reports whether ctrld should watch changes to resolv.conf file with given OS configurator.
 func shouldWatchResolvconf() bool {
-	r, err := dns.NewOSConfigurator(func(format string, args ...any) {}, "lo") // interface name does not matter.
+	sys := new(tsd.System)
+	r, err := dns.NewOSConfigurator(func(format string, args ...any) {}, sys.HealthTracker(), sys.ControlKnobs(), "lo") // interface name does not matter.
 	if err != nil {
 		return false
 	}

cmd/cli/upstream_monitor.go

@@ -71,19 +71,19 @@ func (um *upstreamMonitor) reset(upstream string) {
 
 // checkUpstream checks the given upstream status, periodically sending query to upstream
 // until successfully. An upstream status/counter will be reset once it becomes reachable.
-func (um *upstreamMonitor) checkUpstream(upstream string, uc *ctrld.UpstreamConfig) {
-	um.mu.Lock()
-	isChecking := um.checking[upstream]
+func (p *prog) checkUpstream(upstream string, uc *ctrld.UpstreamConfig) {
+	p.um.mu.Lock()
+	isChecking := p.um.checking[upstream]
 	if isChecking {
-		um.mu.Unlock()
+		p.um.mu.Unlock()
 		return
 	}
-	um.checking[upstream] = true
-	um.mu.Unlock()
+	p.um.checking[upstream] = true
+	p.um.mu.Unlock()
 	defer func() {
-		um.mu.Lock()
-		um.checking[upstream] = false
-		um.mu.Unlock()
+		p.um.mu.Lock()
+		p.um.checking[upstream] = false
+		p.um.mu.Unlock()
 	}()
 
 	resolver, err := ctrld.NewResolver(uc)
@@ -104,7 +104,13 @@ func (um *upstreamMonitor) checkUpstream(upstream string, uc *ctrld.UpstreamConf
 	for {
 		if err := check(); err == nil {
 			mainLog.Load().Debug().Msgf("upstream %q is online", uc.Endpoint)
-			um.reset(upstream)
+			p.um.reset(upstream)
+			if p.leakingQuery.CompareAndSwap(true, false) {
+				p.leakingQueryMu.Lock()
+				p.leakingQueryWasRun = false
+				p.leakingQueryMu.Unlock()
+				mainLog.Load().Warn().Msg("stop leaking query")
+			}
 			return
 		}
 		time.Sleep(checkUpstreamBackoffSleep)

config.go

@@ -7,6 +7,7 @@ import (
 	"crypto/x509"
 	"encoding/hex"
 	"errors"
+	"fmt"
 	"io"
 	"math/rand"
 	"net"
@@ -22,6 +23,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/ameshkov/dnsstamps"
 	"github.com/go-playground/validator/v10"
 	"github.com/miekg/dns"
 	"github.com/spf13/viper"
@@ -59,6 +61,11 @@ const (
 	controlDComDomain = "controld.com"
 	controlDNetDomain = "controld.net"
 	controlDDevDomain = "controld.dev"
+
+	endpointPrefixHTTPS = "https://"
+	endpointPrefixQUIC  = "quic://"
+	endpointPrefixH3    = "h3://"
+	endpointPrefixSdns  = "sdns://"
 )
 
 var (
@@ -211,6 +218,8 @@ type ServiceConfig struct {
 	DnsWatchdogEnabled      *bool          `mapstructure:"dns_watchdog_enabled" toml:"dns_watchdog_enabled,omitempty"`
 	DnsWatchdogInvterval    *time.Duration `mapstructure:"dns_watchdog_interval" toml:"dns_watchdog_interval,omitempty"`
 	RefetchTime             *int           `mapstructure:"refetch_time" toml:"refetch_time,omitempty"`
+	ForceRefetchWaitTime    *int           `mapstructure:"force_refetch_wait_time" toml:"force_refetch_wait_time,omitempty"`
+	LeakOnUpstreamFailure   *bool          `mapstructure:"leak_on_upstream_failure" toml:"leak_on_upstream_failure,omitempty"`
 	Daemon                  bool           `mapstructure:"-" toml:"-"`
 	AllocateIP              bool           `mapstructure:"-" toml:"-"`
 }
@@ -225,7 +234,7 @@ type NetworkConfig struct {
 // UpstreamConfig specifies configuration for upstreams that ctrld will forward requests to.
 type UpstreamConfig struct {
 	Name        string `mapstructure:"name" toml:"name,omitempty"`
-	Type        string `mapstructure:"type" toml:"type,omitempty" validate:"oneof=doh doh3 dot doq os legacy"`
+	Type        string `mapstructure:"type" toml:"type,omitempty" validate:"oneof=doh doh3 dot doq os legacy sdns ''"`
 	Endpoint    string `mapstructure:"endpoint" toml:"endpoint,omitempty"`
 	BootstrapIP string `mapstructure:"bootstrap_ip" toml:"bootstrap_ip,omitempty"`
 	Domain      string `mapstructure:"-" toml:"-"`
@@ -299,10 +308,13 @@ type Rule map[string][]string
 
 // Init initialized necessary values for an UpstreamConfig.
 func (uc *UpstreamConfig) Init() {
+	if err := uc.initDnsStamps(); err != nil {
+		ProxyLogger.Load().Fatal().Err(err).Msg("invalid DNS Stamps")
+	}
 	uc.initDoHScheme()
 	uc.uid = upstreamUID()
 	if u, err := url.Parse(uc.Endpoint); err == nil {
-		uc.Domain = u.Host
+		uc.Domain = u.Hostname()
 		switch uc.Type {
 		case ResolverTypeDOH, ResolverTypeDOH3:
 			uc.u = u
@@ -676,16 +688,67 @@ func (uc *UpstreamConfig) netForDNSType(dnsType uint16) (string, string) {
 
 // initDoHScheme initializes the endpoint scheme for DoH/DoH3 upstream if not present.
 func (uc *UpstreamConfig) initDoHScheme() {
+	if strings.HasPrefix(uc.Endpoint, endpointPrefixH3) && uc.Type == "" {
+		uc.Type = ResolverTypeDOH3
+	}
 	switch uc.Type {
-	case ResolverTypeDOH, ResolverTypeDOH3:
+	case ResolverTypeDOH:
+	case ResolverTypeDOH3:
+		if after, found := strings.CutPrefix(uc.Endpoint, endpointPrefixH3); found {
+			uc.Endpoint = endpointPrefixHTTPS + after
+		}
 	default:
 		return
 	}
-	if !strings.HasPrefix(uc.Endpoint, "https://") {
-		uc.Endpoint = "https://" + uc.Endpoint
+	if !strings.HasPrefix(uc.Endpoint, endpointPrefixHTTPS) {
+		uc.Endpoint = endpointPrefixHTTPS + uc.Endpoint
 	}
 }
 
+// initDnsStamps initializes upstream config based on encoded DNS Stamps Endpoint.
+func (uc *UpstreamConfig) initDnsStamps() error {
+	if strings.HasPrefix(uc.Endpoint, endpointPrefixSdns) && uc.Type == "" {
+		uc.Type = ResolverTypeSDNS
+	}
+	if uc.Type != ResolverTypeSDNS {
+		return nil
+	}
+	sdns, err := dnsstamps.NewServerStampFromString(uc.Endpoint)
+	if err != nil {
+		return err
+	}
+	ip, port, _ := net.SplitHostPort(sdns.ServerAddrStr)
+	providerName, port2, _ := net.SplitHostPort(sdns.ProviderName)
+	if port2 != "" {
+		port = port2
+	}
+	if providerName == "" {
+		providerName = sdns.ProviderName
+	}
+	switch sdns.Proto {
+	case dnsstamps.StampProtoTypeDoH:
+		uc.Type = ResolverTypeDOH
+		host := sdns.ProviderName
+		if port != "" && port != defaultPortFor(uc.Type) {
+			host = net.JoinHostPort(providerName, port)
+		}
+		uc.Endpoint = "https://" + host + sdns.Path
+	case dnsstamps.StampProtoTypeTLS:
+		uc.Type = ResolverTypeDOT
+		uc.Endpoint = net.JoinHostPort(providerName, port)
+	case dnsstamps.StampProtoTypeDoQ:
+		uc.Type = ResolverTypeDOQ
+		uc.Endpoint = net.JoinHostPort(providerName, port)
+	case dnsstamps.StampProtoTypePlain:
+		uc.Type = ResolverTypeLegacy
+		uc.Endpoint = sdns.ServerAddrStr
+	default:
+		return fmt.Errorf("unsupported stamp protocol %q", sdns.Proto)
+	}
+	uc.BootstrapIP = ip
+	return nil
+}
+
 // Init initialized necessary values for an ListenerConfig.
 func (lc *ListenerConfig) Init() {
 	if lc.Policy != nil {
@@ -738,6 +801,23 @@ func upstreamConfigStructLevelValidation(sl validator.StructLevel) {
 		return
 	}
 
+	// Empty type is ok only for endpoints starts with "h3://" and "sdns://".
+	if uc.Type == "" && !strings.HasPrefix(uc.Endpoint, endpointPrefixH3) && !strings.HasPrefix(uc.Endpoint, endpointPrefixSdns) {
+		sl.ReportError(uc.Endpoint, "type", "type", "oneof", "doh doh3 dot doq os legacy sdns")
+		return
+	}
+
+	// initDoHScheme/initDnsStamps may change upstreams information,
+	// so restoring changed values after validation to keep original one.
+	defer func(ep, typ string) {
+		uc.Endpoint = ep
+		uc.Type = typ
+	}(uc.Endpoint, uc.Type)
+
+	if err := uc.initDnsStamps(); err != nil {
+		sl.ReportError(uc.Endpoint, "endpoint", "Endpoint", "http_url", "")
+		return
+	}
 	uc.initDoHScheme()
 	// DoH/DoH3 requires endpoint is an HTTP url.
 	if uc.Type == ResolverTypeDOH || uc.Type == ResolverTypeDOH3 {
@@ -767,13 +847,19 @@ func defaultPortFor(typ string) string {
 // - If endpoint is an IP address ->  ResolverTypeLegacy
 // - If endpoint starts with "https://" -> ResolverTypeDOH
 // - If endpoint starts with "quic://" -> ResolverTypeDOQ
+// - If endpoint starts with "h3://" -> ResolverTypeDOH3
+// - If endpoint starts with "sdns://" -> ResolverTypeSDNS
 // - For anything else -> ResolverTypeDOT
 func ResolverTypeFromEndpoint(endpoint string) string {
 	switch {
-	case strings.HasPrefix(endpoint, "https://"):
+	case strings.HasPrefix(endpoint, endpointPrefixHTTPS):
 		return ResolverTypeDOH
-	case strings.HasPrefix(endpoint, "quic://"):
+	case strings.HasPrefix(endpoint, endpointPrefixQUIC):
 		return ResolverTypeDOQ
+	case strings.HasPrefix(endpoint, endpointPrefixH3):
+		return ResolverTypeDOH3
+	case strings.HasPrefix(endpoint, endpointPrefixSdns):
+		return ResolverTypeSDNS
 	}
 	host := endpoint
 	if strings.Contains(endpoint, ":") {

config_internal_test.go

@@ -17,7 +17,7 @@ func TestUpstreamConfig_SetupBootstrapIP(t *testing.T) {
 	uc.Init()
 	uc.setupBootstrapIP(false)
 	if len(uc.bootstrapIPs) == 0 {
-		t.Log(nameservers())
+		t.Log(defaultNameservers())
 		t.Fatal("could not bootstrap ip without bootstrap DNS")
 	}
 	t.Log(uc)
@@ -26,6 +26,7 @@ func TestUpstreamConfig_SetupBootstrapIP(t *testing.T) {
 func TestUpstreamConfig_Init(t *testing.T) {
 	u1, _ := url.Parse("https://example.com")
 	u2, _ := url.Parse("https://example.com?k=v")
+	u3, _ := url.Parse("https://freedns.controld.com/p1")
 	tests := []struct {
 		name     string
 		uc       *UpstreamConfig
@@ -178,6 +179,152 @@ func TestUpstreamConfig_Init(t *testing.T) {
 				u:              u2,
 			},
 		},
+		{
+			"h3",
+			&UpstreamConfig{
+				Name:        "doh3",
+				Type:        "doh3",
+				Endpoint:    "h3://example.com",
+				BootstrapIP: "",
+				Domain:      "",
+				Timeout:     0,
+			},
+			&UpstreamConfig{
+				Name:        "doh3",
+				Type:        "doh3",
+				Endpoint:    "https://example.com",
+				BootstrapIP: "",
+				Domain:      "example.com",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+				u:           u1,
+			},
+		},
+		{
+			"h3 without type",
+			&UpstreamConfig{
+				Name:        "doh3",
+				Endpoint:    "h3://example.com",
+				BootstrapIP: "",
+				Domain:      "",
+				Timeout:     0,
+			},
+			&UpstreamConfig{
+				Name:        "doh3",
+				Type:        "doh3",
+				Endpoint:    "https://example.com",
+				BootstrapIP: "",
+				Domain:      "example.com",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+				u:           u1,
+			},
+		},
+		{
+			"sdns -> doh",
+			&UpstreamConfig{
+				Name:        "sdns",
+				Type:        "sdns",
+				Endpoint:    "sdns://AgMAAAAAAAAACjc2Ljc2LjIuMTEAFGZyZWVkbnMuY29udHJvbGQuY29tAy9wMQ",
+				BootstrapIP: "",
+				Domain:      "",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+			},
+			&UpstreamConfig{
+				Name:        "sdns",
+				Type:        "doh",
+				Endpoint:    "https://freedns.controld.com/p1",
+				BootstrapIP: "76.76.2.11",
+				Domain:      "freedns.controld.com",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+				u:           u3,
+			},
+		},
+		{
+			"sdns -> dot",
+			&UpstreamConfig{
+				Name:        "sdns",
+				Type:        "sdns",
+				Endpoint:    "sdns://AwcAAAAAAAAACjc2Ljc2LjIuMTEAFGZyZWVkbnMuY29udHJvbGQuY29t",
+				BootstrapIP: "",
+				Domain:      "",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+			},
+			&UpstreamConfig{
+				Name:        "sdns",
+				Type:        "dot",
+				Endpoint:    "freedns.controld.com:843",
+				BootstrapIP: "76.76.2.11",
+				Domain:      "freedns.controld.com",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+			},
+		},
+		{
+			"sdns -> doq",
+			&UpstreamConfig{
+				Name:        "sdns",
+				Type:        "sdns",
+				Endpoint:    "sdns://BAcAAAAAAAAACjc2Ljc2LjIuMTEAFGZyZWVkbnMuY29udHJvbGQuY29t",
+				BootstrapIP: "",
+				Domain:      "",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+			},
+			&UpstreamConfig{
+				Name:        "sdns",
+				Type:        "doq",
+				Endpoint:    "freedns.controld.com:784",
+				BootstrapIP: "76.76.2.11",
+				Domain:      "freedns.controld.com",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+			},
+		},
+		{
+			"sdns -> legacy",
+			&UpstreamConfig{
+				Name:        "sdns",
+				Type:        "sdns",
+				Endpoint:    "sdns://AAcAAAAAAAAACjc2Ljc2LjIuMTE",
+				BootstrapIP: "",
+				Domain:      "",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+			},
+			&UpstreamConfig{
+				Name:        "sdns",
+				Type:        "legacy",
+				Endpoint:    "76.76.2.11:53",
+				BootstrapIP: "76.76.2.11",
+				Domain:      "76.76.2.11",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+			},
+		},
+		{
+			"sdns without type",
+			&UpstreamConfig{
+				Name:        "sdns",
+				Endpoint:    "sdns://AAcAAAAAAAAACjc2Ljc2LjIuMTE",
+				BootstrapIP: "",
+				Domain:      "",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+			},
+			&UpstreamConfig{
+				Name:        "sdns",
+				Type:        "legacy",
+				Endpoint:    "76.76.2.11:53",
+				BootstrapIP: "76.76.2.11",
+				Domain:      "76.76.2.11",
+				Timeout:     0,
+				IPStack:     IpStackBoth,
+			},
+		},
 	}
 
 	for _, tc := range tests {

config_test.go

@@ -107,6 +107,9 @@ func TestConfigValidation(t *testing.T) {
 		{"invalid doh/doh3 endpoint", configWithInvalidDoHEndpoint(t), true},
 		{"invalid client id pref", configWithInvalidClientIDPref(t), true},
 		{"doh endpoint without scheme", dohUpstreamEndpointWithoutScheme(t), false},
+		{"doh endpoint without type", dohUpstreamEndpointWithoutType(t), true},
+		{"doh3 endpoint without type", doh3UpstreamEndpointWithoutType(t), false},
+		{"sdns endpoint without type", sdnsUpstreamEndpointWithoutType(t), false},
 		{"maximum number of flush cache domains", configWithInvalidFlushCacheDomain(t), true},
 	}
 
@@ -127,6 +130,21 @@ func TestConfigValidation(t *testing.T) {
 	}
 }
 
+func TestConfigValidationDoNotChangeEndpoint(t *testing.T) {
+	cfg := configWithInvalidDoHEndpoint(t)
+	endpointMap := map[string]struct{}{}
+	for _, uc := range cfg.Upstream {
+		endpointMap[uc.Endpoint] = struct{}{}
+	}
+	validate := validator.New()
+	_ = ctrld.ValidateConfig(validate, cfg)
+	for _, uc := range cfg.Upstream {
+		if _, ok := endpointMap[uc.Endpoint]; !ok {
+			t.Fatalf("expected endpoint '%s' to exist", uc.Endpoint)
+		}
+	}
+}
+
 func TestConfigDiscoverOverride(t *testing.T) {
 	v := viper.NewWithOptions(viper.KeyDelimiter("::"))
 	ctrld.InitConfig(v, "test_config_discover_override")
@@ -179,6 +197,27 @@ func dohUpstreamEndpointWithoutScheme(t *testing.T) *ctrld.Config {
 	return cfg
 }
 
+func dohUpstreamEndpointWithoutType(t *testing.T) *ctrld.Config {
+	cfg := defaultConfig(t)
+	cfg.Upstream["0"].Endpoint = "https://freedns.controld.com/p1"
+	cfg.Upstream["0"].Type = ""
+	return cfg
+}
+
+func doh3UpstreamEndpointWithoutType(t *testing.T) *ctrld.Config {
+	cfg := defaultConfig(t)
+	cfg.Upstream["0"].Endpoint = "h3://freedns.controld.com/p1"
+	cfg.Upstream["0"].Type = ""
+	return cfg
+}
+
+func sdnsUpstreamEndpointWithoutType(t *testing.T) *ctrld.Config {
+	cfg := defaultConfig(t)
+	cfg.Upstream["0"].Endpoint = "sdns://AgMAAAAAAAAACjc2Ljc2LjIuMTEAFGZyZWVkbnMuY29udHJvbGQuY29tAy9wMQ"
+	cfg.Upstream["0"].Type = ""
+	return cfg
+}
+
 func invalidUpstreamTimeout(t *testing.T) *ctrld.Config {
 	cfg := defaultConfig(t)
 	cfg.Upstream["0"].Timeout = -1

docs/config.md

@@ -281,6 +281,13 @@ The value must be a positive number, any invalid value will be ignored and defau
 - Required: no
 - Default: 3600
 
+### leak_on_upstream_failure
+Once ctrld is "offline", mean ctrld could not connect to any upstream, next queries will be leaked to OS resolver.
+
+- Type: boolean
+- Required: no
+- Default: true on Windows, MacOS and non-router Linux.
+
 ## Upstream
 The `[upstream]` section specifies the DNS upstream servers that `ctrld` will forward DNS requests to.
 

go.mod

@@ -1,95 +1,126 @@
 module github.com/Control-D-Inc/ctrld
 
-go 1.21
+go 1.23
+
+toolchain go1.23.1
 
 require (
 	github.com/Masterminds/semver v1.5.0
+	github.com/ameshkov/dnsstamps v1.0.3
 	github.com/coreos/go-systemd/v22 v22.5.0
 	github.com/cuonglm/osinfo v0.0.0-20230921071424-e0e1b1e0bbbf
-	github.com/frankban/quicktest v1.14.5
-	github.com/fsnotify/fsnotify v1.6.0
+	github.com/frankban/quicktest v1.14.6
+	github.com/fsnotify/fsnotify v1.7.0
 	github.com/go-playground/validator/v10 v10.11.1
-	github.com/godbus/dbus/v5 v5.1.0
+	github.com/godbus/dbus/v5 v5.1.1-0.20230522191255-76236955d466
 	github.com/hashicorp/golang-lru/v2 v2.0.1
-	github.com/illarion/gonotify v1.0.1
-	github.com/insomniacslk/dhcp v0.0.0-20230407062729-974c6f05fe16
+	github.com/illarion/gonotify/v2 v2.0.3
+	github.com/insomniacslk/dhcp v0.0.0-20231206064809-8c70d406f6d2
 	github.com/jaytaylor/go-hostsfile v0.0.0-20220426042432-61485ac1fa6c
 	github.com/josharian/native v1.1.1-0.20230202152459-5c7d0dd6ab86
 	github.com/kardianos/service v1.2.1
 	github.com/mdlayher/ndp v1.0.1
-	github.com/miekg/dns v1.1.55
+	github.com/miekg/dns v1.1.58
 	github.com/minio/selfupdate v0.6.0
 	github.com/olekukonko/tablewriter v0.0.5
 	github.com/pelletier/go-toml/v2 v2.0.8
-	github.com/prometheus/client_golang v1.15.1
-	github.com/prometheus/client_model v0.4.0
+	github.com/prometheus/client_golang v1.19.1
+	github.com/prometheus/client_model v0.5.0
 	github.com/prometheus/prom2json v1.3.3
 	github.com/quic-go/quic-go v0.42.0
 	github.com/rs/zerolog v1.28.0
-	github.com/spf13/cobra v1.7.0
+	github.com/spf13/cobra v1.8.1
 	github.com/spf13/pflag v1.0.5
 	github.com/spf13/viper v1.16.0
-	github.com/stretchr/testify v1.8.3
+	github.com/stretchr/testify v1.9.0
 	github.com/vishvananda/netlink v1.2.1-beta.2
-	golang.org/x/net v0.23.0
-	golang.org/x/sync v0.2.0
-	golang.org/x/sys v0.18.0
+	golang.org/x/net v0.27.0
+	golang.org/x/sync v0.7.0
+	golang.org/x/sys v0.22.0
 	golang.zx2c4.com/wireguard/windows v0.5.3
-	tailscale.com v1.44.0
+	tailscale.com v1.74.0
 )
 
 require (
 	aead.dev/minisign v0.2.0 // indirect
-	github.com/alexbrainman/sspi v0.0.0-20210105120005-909beea2cc74 // indirect
+	filippo.io/edwards25519 v1.1.0 // indirect
+	github.com/akutz/memconn v0.1.0 // indirect
+	github.com/alexbrainman/sspi v0.0.0-20231016080023-1a75b4708caa // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/bits-and-blooms/bitset v1.13.0 // indirect
 	github.com/cespare/xxhash/v2 v2.2.0 // indirect
-	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/coder/websocket v1.8.12 // indirect
+	github.com/coreos/go-iptables v0.7.1-0.20240112124308-65c67c9f46e6 // indirect
+	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
+	github.com/dblohm7/wingoes v0.0.0-20240119213807-a09d6be7affa // indirect
+	github.com/fxamacker/cbor/v2 v2.6.0 // indirect
+	github.com/gaissmai/bart v0.11.1 // indirect
+	github.com/go-json-experiment/json v0.0.0-20231102232822-2e55bd4e08b0 // indirect
+	github.com/go-ole/go-ole v1.3.0 // indirect
 	github.com/go-playground/locales v0.14.0 // indirect
 	github.com/go-playground/universal-translator v0.18.0 // indirect
 	github.com/go-task/slim-sprig v0.0.0-20230315185526-52ccab3ef572 // indirect
-	github.com/golang/protobuf v1.5.3 // indirect
-	github.com/google/go-cmp v0.5.9 // indirect
-	github.com/google/pprof v0.0.0-20210407192527-94a9f03dee38 // indirect
+	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
+	github.com/golang/protobuf v1.5.4 // indirect
+	github.com/google/btree v1.1.2 // indirect
+	github.com/google/go-cmp v0.6.0 // indirect
+	github.com/google/nftables v0.2.1-0.20240414091927-5e242ec57806 // indirect
+	github.com/google/pprof v0.0.0-20240409012703-83162a5b38cd // indirect
 	github.com/hashicorp/hcl v1.0.0 // indirect
+	github.com/hdevalence/ed25519consensus v0.2.0 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
-	github.com/jsimonetti/rtnetlink v1.3.2 // indirect
+	github.com/jsimonetti/rtnetlink v1.4.0 // indirect
+	github.com/klauspost/compress v1.17.4 // indirect
 	github.com/kr/pretty v0.3.1 // indirect
 	github.com/kr/text v0.2.0 // indirect
 	github.com/leodido/go-urn v1.2.1 // indirect
 	github.com/magiconair/properties v1.8.7 // indirect
 	github.com/mattn/go-colorable v0.1.13 // indirect
-	github.com/mattn/go-isatty v0.0.18 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/mattn/go-runewidth v0.0.14 // indirect
 	github.com/matttproud/golang_protobuf_extensions v1.0.4 // indirect
-	github.com/mdlayher/ethernet v0.0.0-20190606142754-0394541c37b7 // indirect
+	github.com/mdlayher/genetlink v1.3.2 // indirect
 	github.com/mdlayher/netlink v1.7.2 // indirect
-	github.com/mdlayher/raw v0.0.0-20191009151244-50f2db8cc065 // indirect
-	github.com/mdlayher/socket v0.4.1 // indirect
+	github.com/mdlayher/packet v1.1.2 // indirect
+	github.com/mdlayher/socket v0.5.0 // indirect
+	github.com/mitchellh/go-ps v1.0.0 // indirect
 	github.com/mitchellh/mapstructure v1.5.0 // indirect
 	github.com/onsi/ginkgo/v2 v2.9.5 // indirect
-	github.com/pierrec/lz4/v4 v4.1.17 // indirect
-	github.com/pmezard/go-difflib v1.0.0 // indirect
-	github.com/prometheus/common v0.44.0 // indirect
-	github.com/prometheus/procfs v0.9.0 // indirect
+	github.com/pierrec/lz4/v4 v4.1.21 // indirect
+	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
+	github.com/prometheus/common v0.48.0 // indirect
+	github.com/prometheus/procfs v0.12.0 // indirect
 	github.com/quic-go/qpack v0.4.0 // indirect
 	github.com/rivo/uniseg v0.4.4 // indirect
-	github.com/rogpeppe/go-internal v1.10.0 // indirect
+	github.com/rogpeppe/go-internal v1.11.0 // indirect
 	github.com/spf13/afero v1.9.5 // indirect
-	github.com/spf13/cast v1.5.1 // indirect
+	github.com/spf13/cast v1.6.0 // indirect
 	github.com/spf13/jwalterweatherman v1.1.0 // indirect
 	github.com/subosito/gotenv v1.4.2 // indirect
-	github.com/u-root/uio v0.0.0-20230305220412-3e8cd9d6bf63 // indirect
+	github.com/tailscale/go-winio v0.0.0-20231025203758-c4f33415bf55 // indirect
+	github.com/tailscale/goupnp v1.0.1-0.20210804011211-c64d0f06ea05 // indirect
+	github.com/tailscale/hujson v0.0.0-20221223112325-20486734a56a // indirect
+	github.com/tailscale/netlink v1.1.1-0.20240822203006-4d49adab4de7 // indirect
+	github.com/tailscale/wireguard-go v0.0.0-20240905161824-799c1978fafc // indirect
+	github.com/tcnksm/go-httpstat v0.2.0 // indirect
+	github.com/u-root/uio v0.0.0-20240118234441-a3c409a6018e // indirect
 	github.com/vishvananda/netns v0.0.4 // indirect
+	github.com/x448/float16 v0.8.4 // indirect
 	go.uber.org/mock v0.4.0 // indirect
 	go4.org/mem v0.0.0-20220726221520-4f986261bf13 // indirect
-	golang.org/x/crypto v0.21.0 // indirect
-	golang.org/x/exp v0.0.0-20230425010034-47ecfdc1ba53 // indirect
-	golang.org/x/mod v0.11.0 // indirect
-	golang.org/x/text v0.14.0 // indirect
-	golang.org/x/tools v0.9.1 // indirect
+	go4.org/netipx v0.0.0-20231129151722-fdeea329fbba // indirect
+	golang.org/x/crypto v0.25.0 // indirect
+	golang.org/x/exp v0.0.0-20240119083558-1b970713d09a // indirect
+	golang.org/x/mod v0.19.0 // indirect
+	golang.org/x/term v0.22.0 // indirect
+	golang.org/x/text v0.16.0 // indirect
+	golang.org/x/time v0.5.0 // indirect
+	golang.org/x/tools v0.23.0 // indirect
+	golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2 // indirect
 	google.golang.org/protobuf v1.33.0 // indirect
 	gopkg.in/ini.v1 v1.67.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
+	gvisor.dev/gvisor v0.0.0-20240722211153-64c016c92987 // indirect
 )
 
 replace github.com/mr-karan/doggo => github.com/Windscribe/doggo v0.0.0-20220919152748-2c118fc391f8

go.sum

@@ -38,52 +38,79 @@ cloud.google.com/go/storage v1.8.0/go.mod h1:Wv1Oy7z6Yz3DshWRJFhqM/UCfaWIRTdp0RX
 cloud.google.com/go/storage v1.10.0/go.mod h1:FLPqc6j+Ki4BU591ie1oL6qBQGu2Bl/tZ9ullr3+Kg0=
 cloud.google.com/go/storage v1.14.0/go.mod h1:GrKmX003DSIwi9o29oFT7YDnHYwZoctc3fOKtUw0Xmo=
 dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9/go.mod h1:H6x//7gZCb22OMCxBHrMx7a5I7Hp++hsVxbQ4BYO7hU=
+filippo.io/edwards25519 v1.1.0 h1:FNf4tywRC1HmFuKW5xopWpigGjJKiJSV0Cqo0cJWDaA=
+filippo.io/edwards25519 v1.1.0/go.mod h1:BxyFTGdWcka3PhytdK4V28tE5sGfRvvvRV7EaN4VDT4=
+filippo.io/mkcert v1.4.4 h1:8eVbbwfVlaqUM7OwuftKc2nuYOoTDQWqsoXmzoXZdbc=
+filippo.io/mkcert v1.4.4/go.mod h1:VyvOchVuAye3BoUsPUOOofKygVwLV2KQMVFJNRq+1dA=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
 github.com/Masterminds/semver v1.5.0 h1:H65muMkzWKEuNDnfl9d70GUjFniHKHRbFPGBuZ3QEww=
 github.com/Masterminds/semver v1.5.0/go.mod h1:MB6lktGJrhw8PrUyiEoblNEGEQ+RzHPF078ddwwvV3Y=
 github.com/Windscribe/zerolog v0.0.0-20230503170159-e6aa153233be h1:qBKVRi7Mom5heOkyZ+NCIu9HZBiNCsRqrRe5t9pooik=
 github.com/Windscribe/zerolog v0.0.0-20230503170159-e6aa153233be/go.mod h1:/tk+P47gFdPXq4QYjvCmT5/Gsug2nagsFWBWhAiSi1w=
-github.com/alexbrainman/sspi v0.0.0-20210105120005-909beea2cc74 h1:Kk6a4nehpJ3UuJRqlA3JxYxBZEqCeOmATOvrbT4p9RA=
-github.com/alexbrainman/sspi v0.0.0-20210105120005-909beea2cc74/go.mod h1:cEWa1LVoE5KvSD9ONXsZrj0z6KqySlCCNKHlLzbqAt4=
+github.com/akutz/memconn v0.1.0 h1:NawI0TORU4hcOMsMr11g7vwlCdkYeLKXBcxWu2W/P8A=
+github.com/akutz/memconn v0.1.0/go.mod h1:Jo8rI7m0NieZyLI5e2CDlRdRqRRB4S7Xp77ukDjH+Fw=
+github.com/alexbrainman/sspi v0.0.0-20231016080023-1a75b4708caa h1:LHTHcTQiSGT7VVbI0o4wBRNQIgn917usHWOd6VAffYI=
+github.com/alexbrainman/sspi v0.0.0-20231016080023-1a75b4708caa/go.mod h1:cEWa1LVoE5KvSD9ONXsZrj0z6KqySlCCNKHlLzbqAt4=
+github.com/ameshkov/dnsstamps v1.0.3 h1:Srzik+J9mivH1alRACTbys2xOxs0lRH9qnTA7Y1OYVo=
+github.com/ameshkov/dnsstamps v1.0.3/go.mod h1:Ii3eUu73dx4Vw5O4wjzmT5+lkCwovjzaEZZ4gKyIH5A=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
 github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
+github.com/bits-and-blooms/bitset v1.13.0 h1:bAQ9OPNFYbGHV6Nez0tmNI0RiEu7/hxlYJRUA0wFAVE=
+github.com/bits-and-blooms/bitset v1.13.0/go.mod h1:7hO7Gc7Pp1vODcmWvKMRA9BNmbv6a/7QIWpPxHddWR8=
 github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
 github.com/cespare/xxhash/v2 v2.2.0 h1:DC2CZ1Ep5Y4k3ZQ899DldepgrayRUGE6BBZ/cd9Cj44=
 github.com/cespare/xxhash/v2 v2.2.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/chzyer/logex v1.1.10/go.mod h1:+Ywpsq7O8HXn0nuIou7OrIPyXbp3wmkHB+jjWRnGsAI=
 github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e/go.mod h1:nSuG5e5PlCu98SY8svDHJxuZscDgtXS6KTTbou5AhLI=
 github.com/chzyer/test v0.0.0-20180213035817-a1ea475d72b1/go.mod h1:Q3SI9o4m/ZMnBNeIyt5eFwwo7qiLfzFZmjNmxjkiQlU=
-github.com/cilium/ebpf v0.10.0 h1:nk5HPMeoBXtOzbkZBWym+ZWq1GIiHUsBFXxwewXAHLQ=
-github.com/cilium/ebpf v0.10.0/go.mod h1:DPiVdY/kT534dgc9ERmvP8mWA+9gvwgKfRvk4nNWnoE=
+github.com/cilium/ebpf v0.15.0 h1:7NxJhNiBT3NG8pZJ3c+yfrVdHY8ScgKD27sScgjLMMk=
+github.com/cilium/ebpf v0.15.0/go.mod h1:DHp1WyrLeiBh19Cf/tfiSMhqheEiK8fXFZ4No0P1Hso=
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/cncf/udpa/go v0.0.0-20191209042840-269d4d468f6f/go.mod h1:M8M6+tZqaGXZJjfX53e64911xZQV5JYwmTeXPW+k8Sc=
 github.com/cncf/udpa/go v0.0.0-20200629203442-efcf912fb354/go.mod h1:WmhPx2Nbnhtbo57+VJT5O0JRkEi1Wbu0z5j0R8u5Hbk=
 github.com/cncf/udpa/go v0.0.0-20201120205902-5459f2c99403/go.mod h1:WmhPx2Nbnhtbo57+VJT5O0JRkEi1Wbu0z5j0R8u5Hbk=
+github.com/coder/websocket v1.8.12 h1:5bUXkEPPIbewrnkU8LTCLVaxi4N4J8ahufH2vlo4NAo=
+github.com/coder/websocket v1.8.12/go.mod h1:LNVeNrXQZfe5qhS9ALED3uA+l5pPqvwXg3CKoDBB2gs=
+github.com/coreos/go-iptables v0.7.1-0.20240112124308-65c67c9f46e6 h1:8h5+bWd7R6AYUslN6c6iuZWTKsKxUFDlpnmilO6R2n0=
+github.com/coreos/go-iptables v0.7.1-0.20240112124308-65c67c9f46e6/go.mod h1:Qe8Bv2Xik5FyTXwgIbLAnv2sWSBmvWdFETJConOQ//Q=
 github.com/coreos/go-systemd/v22 v22.5.0 h1:RrqgGjYQKalulkV8NGVIfkXQf6YYmOyiJKk8iXXhfZs=
 github.com/coreos/go-systemd/v22 v22.5.0/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
-github.com/cpuguy83/go-md2man/v2 v2.0.2/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46tRHOmNcaadrF8o=
+github.com/cpuguy83/go-md2man/v2 v2.0.4/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46tRHOmNcaadrF8o=
 github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
 github.com/cuonglm/osinfo v0.0.0-20230921071424-e0e1b1e0bbbf h1:40DHYsri+d1bnroFDU2FQAeq68f3kAlOzlQ93kCf26Q=
 github.com/cuonglm/osinfo v0.0.0-20230921071424-e0e1b1e0bbbf/go.mod h1:G45410zMgmnSjLVKCq4f6GpbYAzoP2plX9rPwgx6C24=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc h1:U9qPSI2PIWSS1VwoXQT9A3Wy9MM3WgvqSxFWenqJduM=
+github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/dblohm7/wingoes v0.0.0-20240119213807-a09d6be7affa h1:h8TfIT1xc8FWbwwpmHn1J5i43Y0uZP97GqasGCzSRJk=
+github.com/dblohm7/wingoes v0.0.0-20240119213807-a09d6be7affa/go.mod h1:Nx87SkVqTKd8UtT+xu7sM/l+LgXs6c0aHrlKusR+2EQ=
+github.com/dsnet/try v0.0.3 h1:ptR59SsrcFUYbT/FhAbKTV6iLkeD6O18qfIWRml2fqI=
+github.com/dsnet/try v0.0.3/go.mod h1:WBM8tRpUmnXXhY1U6/S8dt6UWdHTQ7y8A5YSkRCkq40=
 github.com/envoyproxy/go-control-plane v0.9.0/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
 github.com/envoyproxy/go-control-plane v0.9.1-0.20191026205805-5f8ba28d4473/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
 github.com/envoyproxy/go-control-plane v0.9.4/go.mod h1:6rpuAdCZL397s3pYoYcLgu1mIlRU8Am5FuJP05cCM98=
 github.com/envoyproxy/go-control-plane v0.9.7/go.mod h1:cwu0lG7PUMfa9snN8LXBig5ynNVH9qI8YYLbd1fK2po=
 github.com/envoyproxy/go-control-plane v0.9.9-0.20201210154907-fd9021fe5dad/go.mod h1:cXg6YxExXjJnVBQHBLXeUAgxn2UodCpnH306RInaBQk=
 github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
-github.com/frankban/quicktest v1.14.5 h1:dfYrrRyLtiqT9GyKXgdh+k4inNeTvmGbuSgZ3lx3GhA=
-github.com/frankban/quicktest v1.14.5/go.mod h1:4ptaffx2x8+WTWXmUCuVU6aPUX1/Mz7zb5vbUoiM6w0=
-github.com/fsnotify/fsnotify v1.6.0 h1:n+5WquG0fcWoWp6xPWfHdbskMCQaFnG6PfBrh1Ky4HY=
-github.com/fsnotify/fsnotify v1.6.0/go.mod h1:sl3t1tCWJFWoRz9R8WJCbQihKKwmorjAbSClcnxKAGw=
+github.com/frankban/quicktest v1.14.6 h1:7Xjx+VpznH+oBnejlPUj8oUpdxnVs4f8XU8WnHkI4W8=
+github.com/frankban/quicktest v1.14.6/go.mod h1:4ptaffx2x8+WTWXmUCuVU6aPUX1/Mz7zb5vbUoiM6w0=
+github.com/fsnotify/fsnotify v1.7.0 h1:8JEhPFa5W2WU7YfeZzPNqzMP6Lwt7L2715Ggo0nosvA=
+github.com/fsnotify/fsnotify v1.7.0/go.mod h1:40Bi/Hjc2AVfZrqy+aj+yEI+/bRxZnMJyTJwOpGvigM=
+github.com/fxamacker/cbor/v2 v2.6.0 h1:sU6J2usfADwWlYDAFhZBQ6TnLFBHxgesMrQfQgk1tWA=
+github.com/fxamacker/cbor/v2 v2.6.0/go.mod h1:pxXPTn3joSm21Gbwsv0w9OSA2y1HFR9qXEeXQVeNoDQ=
+github.com/gaissmai/bart v0.11.1 h1:5Uv5XwsaFBRo4E5VBcb9TzY8B7zxFf+U7isDxqOrRfc=
+github.com/gaissmai/bart v0.11.1/go.mod h1:KHeYECXQiBjTzQz/om2tqn3sZF1J7hw9m6z41ftj3fg=
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20191125211704-12ad95a8df72/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20200222043503-6f7a984d4dc4/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
-github.com/go-logr/logr v1.2.4 h1:g01GSCwiDw2xSZfjJ2/T9M+S6pFdcNtFYsp+Y43HYDQ=
-github.com/go-logr/logr v1.2.4/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
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@@ -95,12 +122,14 @@ github.com/go-playground/validator/v10 v10.11.1/go.mod h1:i+3WkQ1FvaUjjxh1kSvIA4
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@@ -122,11 +151,12 @@ github.com/golang/protobuf v1.4.0/go.mod h1:jodUvKwWbYaEsadDk5Fwe5c77LiNKVO9IDvq
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@@ -136,12 +166,14 @@ github.com/google/go-cmp v0.5.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/
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@@ -152,8 +184,8 @@ github.com/google/pprof v0.0.0-20200708004538-1a94d8640e99/go.mod h1:ZgVRPoUq/hf
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@@ -165,28 +197,32 @@ github.com/hashicorp/golang-lru/v2 v2.0.1 h1:5pv5N1lT1fjLg2VQ5KWc7kmucp2x/kvFOnx
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@@ -206,28 +242,29 @@ github.com/mattn/go-colorable v0.1.13 h1:fFA4WZxdEF4tXPZVKMLwD8oUnCTTo08duU7wxec
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@@ -320,6 +374,8 @@ go.uber.org/mock v0.4.0 h1:VcM4ZOtdbR4f6VXfiOpwpVJDL6lCReaZ6mw31wqh7KU=
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+go4.org/netipx v0.0.0-20231129151722-fdeea329fbba/go.mod h1:PLyyIXexvUFg3Owu6p/WfdlivPbZJsZdgWZlrGope/Y=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20190605123033-f99c8df09eb5/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
@@ -330,8 +386,8 @@ golang.org/x/crypto v0.0.0-20210421170649-83a5a9bb288b/go.mod h1:T9bdIzuCu7OtxOm
 golang.org/x/crypto v0.0.0-20211209193657-4570a0811e8b/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
 golang.org/x/crypto v0.0.0-20211215153901-e495a2d5b3d3/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
 golang.org/x/crypto v0.0.0-20220722155217-630584e8d5aa/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
-golang.org/x/crypto v0.21.0 h1:X31++rzVUdKhX5sWmSOFZxx8UW/ldWx55cbf08iNAMA=
-golang.org/x/crypto v0.21.0/go.mod h1:0BP7YvVV9gBbVKyeTG0Gyn+gZm94bibOW5BjDEYAOMs=
+golang.org/x/crypto v0.25.0 h1:ypSNr+bnYL2YhwoMt2zPxHFmbAN1KZs/njMG3hxUp30=
+golang.org/x/crypto v0.25.0/go.mod h1:T+wALwcMOSE0kXgUAnPAHqTLW+XHgcELELW8VaDgm/M=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20190510132918-efd6b22b2522/go.mod h1:ZjyILWgesfNpC6sMxTJOJm9Kp84zZh5NQWvqDGG3Qr8=
@@ -342,8 +398,8 @@ golang.org/x/exp v0.0.0-20191227195350-da58074b4299/go.mod h1:2RIsYlXP63K8oxa1u0
 golang.org/x/exp v0.0.0-20200119233911-0405dc783f0a/go.mod h1:2RIsYlXP63K8oxa1u096TMicItID8zy7Y6sNkU49FU4=
 golang.org/x/exp v0.0.0-20200207192155-f17229e696bd/go.mod h1:J/WKrq2StrnmMY6+EHIKF9dgMWnmCNThgcyBT1FY9mM=
 golang.org/x/exp v0.0.0-20200224162631-6cc2880d07d6/go.mod h1:3jZMyOhIsHpP37uCMkUooju7aAi5cS1Q23tOzKc+0MU=
-golang.org/x/exp v0.0.0-20230425010034-47ecfdc1ba53 h1:5llv2sWeaMSnA3w2kS57ouQQ4pudlXrR0dCgw51QK9o=
-golang.org/x/exp v0.0.0-20230425010034-47ecfdc1ba53/go.mod h1:V1LtkGg67GoY2N1AnLN78QLrzxkLyJw7RJb1gzOOz9w=
+golang.org/x/exp v0.0.0-20240119083558-1b970713d09a h1:Q8/wZp0KX97QFTc2ywcOE0YRjZPVIx+MXInMzdvQqcA=
+golang.org/x/exp v0.0.0-20240119083558-1b970713d09a/go.mod h1:idGWGoKP1toJGkd5/ig9ZLuPcZBC3ewk7SzmH0uou08=
 golang.org/x/image v0.0.0-20190227222117-0694c2d4d067/go.mod h1:kZ7UVZpmo3dzQBMxlp+ypCbDeSB+sBbTgSJuh5dn5js=
 golang.org/x/image v0.0.0-20190802002840-cff245a6509b/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
@@ -367,15 +423,14 @@ golang.org/x/mod v0.2.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.4.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.4.1/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
-golang.org/x/mod v0.11.0 h1:bUO06HqtnRcc/7l71XBe4WcqTZ+3AH1J59zWDDwLKgU=
-golang.org/x/mod v0.11.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
+golang.org/x/mod v0.19.0 h1:fEdghXQSo20giMthA7cd28ZC+jts4amQ3YMXiP5oMQ8=
+golang.org/x/mod v0.19.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
 golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190108225652-1e06a53dbb7e/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190213061140-3a22650c66bd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
-golang.org/x/net v0.0.0-20190419010253-1f3472d942ba/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190501004415-9ce7a6920f09/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190503192946-f4e77d36d62c/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190603091049-60506f45cf65/go.mod h1:HSz+uSET+XFnRR8LxR5pz3Of3rY3CfYBVs4xY44aLks=
@@ -402,8 +457,8 @@ golang.org/x/net v0.0.0-20201209123823-ac852fbbde11/go.mod h1:m0MpNAwzfU5UDzcl9v
 golang.org/x/net v0.0.0-20201224014010-6772e930b67b/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
-golang.org/x/net v0.23.0 h1:7EYJ93RZ9vYSZAIb2x3lnuvqO5zneoD6IvWjuhfxjTs=
-golang.org/x/net v0.23.0/go.mod h1:JKghWKKOSdJwpW2GEx0Ja7fmaKnMsbu+MWVZTokSYmg=
+golang.org/x/net v0.27.0 h1:5K3Njcw06/l2y9vpGCSdcxWOYHOUk3dVNGDXN+FvAys=
+golang.org/x/net v0.27.0/go.mod h1:dDi0PyhWNoiUOrAS8uXv/vnScO4wnHQO4mj9fn/RytE=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/oauth2 v0.0.0-20190226205417-e64efc72b421/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
 golang.org/x/oauth2 v0.0.0-20190604053449-0f29369cfe45/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
@@ -423,16 +478,15 @@ golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20200625203802-6e8e738ad208/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20201207232520-09787c993a3a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.2.0 h1:PUR+T4wwASmuSTYdKjYHI5TD22Wy5ogLU5qZCOLxBrI=
-golang.org/x/sync v0.2.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
+golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190312061237-fead79001313/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
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 golang.org/x/sys v0.0.0-20190502145724-3ef323f4f1fd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190507160741-ecd444e8653b/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
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 golang.org/x/sys v0.0.0-20190606165138-5da285871e9c/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190624142023-c5567b49c5d0/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
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@@ -472,13 +526,16 @@ golang.org/x/sys v0.0.0-20210806184541-e5e7981a1069/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.0.0-20210927094055-39ccf1dd6fa6/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220622161953-175b2fd9d664/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
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+golang.org/x/sys v0.1.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
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-golang.org/x/sys v0.18.0 h1:DBdB3niSjOA/O0blCZBqDefyWNYveAYMNF1Wum0DYQ4=
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 golang.org/x/term v0.0.0-20201117132131-f5c789dd3221/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/term v0.22.0 h1:BbsgPEJULsl2fV/AT3v15Mjva5yXKQDyKf+TbDz7QJk=
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@@ -487,8 +544,8 @@ golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
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@@ -541,12 +598,14 @@ golang.org/x/tools v0.0.0-20201208233053-a543418bbed2/go.mod h1:emZCQorbCU4vsT4f
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-golang.org/x/tools v0.9.1 h1:8WMNJAz3zrtPmnYC7ISf5dEn3MT0gY7jBJfw27yrrLo=
-golang.org/x/tools v0.9.1/go.mod h1:owI94Op576fPu3cIGQeHs3joujW/2Oc6MtlxbF5dfNc=
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 golang.zx2c4.com/wireguard/windows v0.5.3/go.mod h1:9TEe8TJmtwyQebdFwAkEWOPr3prrtqm+REGFifP60hI=
 google.golang.org/api v0.4.0/go.mod h1:8k5glujaEP+g9n7WNsDg8QP6cUVNI86fCNMcbazEtwE=
@@ -637,8 +696,6 @@ google.golang.org/protobuf v1.23.0/go.mod h1:EGpADcykh3NcUnDUJcl1+ZksZNG86OlYog2
 google.golang.org/protobuf v1.23.1-0.20200526195155-81db48ad09cc/go.mod h1:EGpADcykh3NcUnDUJcl1+ZksZNG86OlYog2l/sGQquU=
 google.golang.org/protobuf v1.24.0/go.mod h1:r/3tXBNzIEhYS9I1OUVjXDlt8tc493IdKGjtUeSXeh4=
 google.golang.org/protobuf v1.25.0/go.mod h1:9JNX74DMeImyA3h4bdi1ymwjUzf21/xIlbajtzgsN7c=
-google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
-google.golang.org/protobuf v1.26.0/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
 google.golang.org/protobuf v1.33.0 h1:uNO2rsAINq/JlFpSdYEKIZ0uKD/R9cpdv0T+yoGwGmI=
 google.golang.org/protobuf v1.33.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
@@ -653,6 +710,8 @@ gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C
 gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gvisor.dev/gvisor v0.0.0-20240722211153-64c016c92987 h1:TU8z2Lh3Bbq77w0t1eG8yRlLcNHzZu3x6mhoH2Mk0c8=
+gvisor.dev/gvisor v0.0.0-20240722211153-64c016c92987/go.mod h1:sxc3Uvk/vHcd3tj7/DHVBoR5wvWT/MmRq2pj7HRJnwU=
 honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
 honnef.co/go/tools v0.0.0-20190106161140-3f1c8253044a/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
 honnef.co/go/tools v0.0.0-20190418001031-e561f6794a2a/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
@@ -660,8 +719,12 @@ honnef.co/go/tools v0.0.0-20190523083050-ea95bdfd59fc/go.mod h1:rf3lG4BRIbNafJWh
 honnef.co/go/tools v0.0.1-2019.2.3/go.mod h1:a3bituU0lyd329TUQxRnasdCoJDkEUEAqEt0JzvZhAg=
 honnef.co/go/tools v0.0.1-2020.1.3/go.mod h1:X/FiERA/W4tHapMX5mGpAtMSVEeEUOyHaw9vFzvIQ3k=
 honnef.co/go/tools v0.0.1-2020.1.4/go.mod h1:X/FiERA/W4tHapMX5mGpAtMSVEeEUOyHaw9vFzvIQ3k=
+howett.net/plist v1.0.0 h1:7CrbWYbPPO/PyNy38b2EB/+gYbjCe2DXBxgtOOZbSQM=
+howett.net/plist v1.0.0/go.mod h1:lqaXoTrLY4hg8tnEzNru53gicrbv7rrk+2xJA/7hw9g=
 rsc.io/binaryregexp v0.2.0/go.mod h1:qTv7/COck+e2FymRvadv62gMdZztPaShugOCi3I+8D8=
 rsc.io/quote/v3 v3.1.0/go.mod h1:yEA65RcK8LyAZtP9Kv3t0HmxON59tX3rD+tICJqUlj0=
 rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=
-tailscale.com v1.44.0 h1:MPos9n30kJvdyfL52045gVFyNg93K+bwgDsr8gqKq2o=
-tailscale.com v1.44.0/go.mod h1:+iYwTdeHyVJuNDu42Zafwihq1Uqfh+pW7pRaY1GD328=
+software.sslmate.com/src/go-pkcs12 v0.4.0 h1:H2g08FrTvSFKUj+D309j1DPfk5APnIdAQAB8aEykJ5k=
+software.sslmate.com/src/go-pkcs12 v0.4.0/go.mod h1:Qiz0EyvDRJjjxGyUQa2cCNZn/wMyzrRJ/qcDXOQazLI=
+tailscale.com v1.74.0 h1:J+vRN9o3D4wCqZBiwvDg9kZpQag2mG4Xz5RXNpmV3KE=
+tailscale.com v1.74.0/go.mod h1:3iACpCONQ4lauDXvwfoGlwNCpfbVxjdc2j6G9EuFOW8=

internal/clientinfo/dhcp.go

@@ -13,8 +13,9 @@ import (
 	"strings"
 	"sync"
 
+	"tailscale.com/net/netmon"
+
 	"github.com/fsnotify/fsnotify"
-	"tailscale.com/net/interfaces"
 	"tailscale.com/util/lineread"
 
 	"github.com/Control-D-Inc/ctrld"
@@ -356,7 +357,7 @@ func (d *dhcp) addSelf() {
 	d.ip2name.Store(ipV4Loopback, hostname)
 	d.ip2name.Store(ipv6Loopback, hostname)
 	found := false
-	interfaces.ForeachInterface(func(i interfaces.Interface, prefixes []netip.Prefix) {
+	netmon.ForeachInterface(func(i netmon.Interface, prefixes []netip.Prefix) {
 		mac := i.HardwareAddr.String()
 		// Skip loopback interfaces, info was stored above.
 		if mac == "" {

internal/controld/config.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"crypto/tls"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -64,7 +65,8 @@ type utilityRequest struct {
 	ClientID string `json:"client_id,omitempty"`
 }
 
-type utilityOrgRequest struct {
+// UtilityOrgRequest contains request data for calling Org API.
+type UtilityOrgRequest struct {
 	ProvToken string `json:"prov_token"`
 	Hostname  string `json:"hostname"`
 }
@@ -81,9 +83,15 @@ func FetchResolverConfig(rawUID, version string, cdDev bool) (*ResolverConfig, e
 }
 
 // FetchResolverUID fetch resolver uid from provision token.
-func FetchResolverUID(pt, version string, cdDev bool) (*ResolverConfig, error) {
-	hostname, _ := os.Hostname()
-	body, _ := json.Marshal(utilityOrgRequest{ProvToken: pt, Hostname: hostname})
+func FetchResolverUID(req *UtilityOrgRequest, version string, cdDev bool) (*ResolverConfig, error) {
+	if req == nil {
+		return nil, errors.New("invalid request")
+	}
+	hostname := req.Hostname
+	if hostname == "" {
+		hostname, _ = os.Hostname()
+	}
+	body, _ := json.Marshal(UtilityOrgRequest{ProvToken: req.ProvToken, Hostname: hostname})
 	return postUtilityAPI(version, cdDev, false, bytes.NewReader(body))
 }
 

internal/dns/README.md

@@ -1,2 +1,2 @@
-This is a fork of https://pkg.go.dev/tailscale.com@v1.34.2/net/dns with modification
+This is a fork of https://pkg.go.dev/tailscale.com@v1.74.0/net/dns with modification
 to fit ctrld use case.

internal/dns/debian_resolvconf.go

@@ -1,12 +1,12 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 //go:build linux || freebsd || openbsd
 
 package dns
 
 import (
+	"bufio"
 	"bytes"
 	_ "embed"
 	"fmt"
@@ -33,7 +33,7 @@ var workaroundScript []byte
 // resolvconf implementations encourage adding a suffix roughly
 // indicating where the config came from, and "inet" is the "none of
 // the above" value (rather than, say, "ppp" or "dhcp").
-const resolvconfConfigName = "ctrld.inet"
+const resolvconfConfigName = "tun-ctrld.inet"
 
 // resolvconfLibcHookPath is the directory containing libc update
 // scripts, which are run by Debian resolvconf when /etc/resolv.conf
@@ -53,8 +53,6 @@ type resolvconfManager struct {
 	scriptInstalled bool // libc update script has been installed
 }
 
-var _ OSConfigurator = (*resolvconfManager)(nil)
-
 func newDebianResolvconfManager(logf logger.Logf) (*resolvconfManager, error) {
 	ret := &resolvconfManager{
 		logf:            logf,
@@ -135,6 +133,43 @@ func (m *resolvconfManager) SetDNS(config OSConfig) error {
 	return nil
 }
 
+func (m *resolvconfManager) SupportsSplitDNS() bool {
+	return false
+}
+
+func (m *resolvconfManager) GetBaseConfig() (OSConfig, error) {
+	var bs bytes.Buffer
+
+	cmd := exec.Command(m.listRecordsPath)
+	// list-records assumes it's being run with CWD set to the
+	// interfaces runtime dir, and returns nonsense otherwise.
+	cmd.Dir = m.interfacesDir
+	cmd.Stdout = &bs
+	if err := cmd.Run(); err != nil {
+		return OSConfig{}, err
+	}
+
+	var conf bytes.Buffer
+	sc := bufio.NewScanner(&bs)
+	for sc.Scan() {
+		if sc.Text() == resolvconfConfigName {
+			continue
+		}
+		bs, err := os.ReadFile(filepath.Join(m.interfacesDir, sc.Text()))
+		if err != nil {
+			if os.IsNotExist(err) {
+				// Probably raced with a deletion, that's okay.
+				continue
+			}
+			return OSConfig{}, err
+		}
+		conf.Write(bs)
+		conf.WriteByte('\n')
+	}
+
+	return readResolv(&conf)
+}
+
 func (m *resolvconfManager) Close() error {
 	if err := m.deleteCtrldConfig(); err != nil {
 		return err

internal/dns/direct.go

@@ -1,9 +1,5 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-//lint:file-ignore U1000 Ignore, this file is forked from upstream code.
-//lint:file-ignore ST1005 Ignore, this file is forked from upstream code.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 package dns
 
@@ -20,11 +16,13 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
+	"slices"
 	"strings"
 	"sync"
 	"time"
 
 	"tailscale.com/health"
+	"tailscale.com/net/tsaddr"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/dnsname"
 	"tailscale.com/version/distro"
@@ -32,11 +30,6 @@ import (
 	"github.com/Control-D-Inc/ctrld/internal/dns/resolvconffile"
 )
 
-const (
-	backupConf = "/etc/resolv.pre-ctrld-backup.conf"
-	resolvConf = "/etc/resolv.conf"
-)
-
 // writeResolvConf writes DNS configuration in resolv.conf format to the given writer.
 func writeResolvConf(w io.Writer, servers []netip.Addr, domains []dnsname.FQDN) error {
 	c := &resolvconffile.Config{
@@ -60,6 +53,8 @@ func readResolv(r io.Reader) (OSConfig, error) {
 // resolvOwner returns the apparent owner of the resolv.conf
 // configuration in bs - one of "resolvconf", "systemd-resolved" or
 // "NetworkManager", or "" if no known owner was found.
+//
+//lint:ignore U1000 used in linux and freebsd code
 func resolvOwner(bs []byte) string {
 	likely := ""
 	b := bytes.NewBuffer(bs)
@@ -123,8 +118,9 @@ func restartResolved() error {
 // The caller must call Down before program shutdown
 // or as cleanup if the program terminates unexpectedly.
 type directManager struct {
-	logf logger.Logf
-	fs   wholeFileFS
+	logf   logger.Logf
+	health *health.Tracker
+	fs     wholeFileFS
 	// renameBroken is set if fs.Rename to or from /etc/resolv.conf
 	// fails. This can happen in some container runtimes, where
 	// /etc/resolv.conf is bind-mounted from outside the container,
@@ -140,19 +136,22 @@ type directManager struct {
 	ctx      context.Context    // valid until Close
 	ctxClose context.CancelFunc // closes ctx
 
-	mu               sync.Mutex
-	wantResolvConf   []byte // if non-nil, what we expect /etc/resolv.conf to contain
+	mu             sync.Mutex
+	wantResolvConf []byte // if non-nil, what we expect /etc/resolv.conf to contain
+	//lint:ignore U1000 used in direct_linux.go
 	lastWarnContents []byte // last resolv.conf contents that we warned about
 }
 
-func newDirectManager(logf logger.Logf) *directManager {
-	return newDirectManagerOnFS(logf, directFS{})
+//lint:ignore U1000 used in manager_{freebsd,openbsd}.go
+func newDirectManager(logf logger.Logf, health *health.Tracker) *directManager {
+	return newDirectManagerOnFS(logf, health, directFS{})
 }
 
-func newDirectManagerOnFS(logf logger.Logf, fs wholeFileFS) *directManager {
+func newDirectManagerOnFS(logf logger.Logf, health *health.Tracker, fs wholeFileFS) *directManager {
 	ctx, cancel := context.WithCancel(context.Background())
 	m := &directManager{
 		logf:     logf,
+		health:   health,
 		fs:       fs,
 		ctx:      ctx,
 		ctxClose: cancel,
@@ -193,13 +192,13 @@ func (m *directManager) ownedByCtrld() (bool, error) {
 }
 
 // backupConfig creates or updates a backup of /etc/resolv.conf, if
-// resolv.conf does not currently contain a Tailscale-managed config.
+// resolv.conf does not currently contain a ctrld-managed config.
 func (m *directManager) backupConfig() error {
 	if _, err := m.fs.Stat(resolvConf); err != nil {
 		if os.IsNotExist(err) {
 			// No resolv.conf, nothing to back up. Also get rid of any
 			// existing backup file, to avoid restoring something old.
-			_ = m.fs.Remove(backupConf)
+			m.fs.Remove(backupConf)
 			return nil
 		}
 		return err
@@ -237,7 +236,7 @@ func (m *directManager) restoreBackup() (restored bool, err error) {
 	if resolvConfExists && !owned {
 		// There's already a non-ctrld config in place, get rid of
 		// our backup.
-		_ = m.fs.Remove(backupConf)
+		m.fs.Remove(backupConf)
 		return false, nil
 	}
 
@@ -278,6 +277,14 @@ func (m *directManager) rename(old, new string) error {
 		return fmt.Errorf("writing to %q in rename of %q: %w", new, old, err)
 	}
 
+	// Explicitly set the permissions on the new file. This ensures that
+	// if we have a umask set which prevents creating world-readable files,
+	// the file will still have the correct permissions once it's renamed
+	// into place. See #12609.
+	if err := m.fs.Chmod(new, 0644); err != nil {
+		return fmt.Errorf("chmod %q in rename of %q: %w", new, old, err)
+	}
+
 	if err := m.fs.Remove(old); err != nil {
 		err2 := m.fs.Truncate(old)
 		if err2 != nil {
@@ -298,53 +305,6 @@ func (m *directManager) setWant(want []byte) {
 	m.wantResolvConf = want
 }
 
-var warnTrample = health.NewWarnable()
-
-// checkForFileTrample checks whether /etc/resolv.conf has been trampled
-// by another program on the system. (e.g. a DHCP client)
-func (m *directManager) checkForFileTrample() {
-	m.mu.Lock()
-	want := m.wantResolvConf
-	lastWarn := m.lastWarnContents
-	m.mu.Unlock()
-
-	if want == nil {
-		return
-	}
-
-	cur, err := m.fs.ReadFile(resolvConf)
-	if err != nil {
-		m.logf("trample: read error: %v", err)
-		return
-	}
-	if bytes.Equal(cur, want) {
-		warnTrample.Set(nil)
-		if lastWarn != nil {
-			m.mu.Lock()
-			m.lastWarnContents = nil
-			m.mu.Unlock()
-			m.logf("trample: resolv.conf again matches expected content")
-		}
-		return
-	}
-	if bytes.Equal(cur, lastWarn) {
-		// We already logged about this, so not worth doing it again.
-		return
-	}
-
-	m.mu.Lock()
-	m.lastWarnContents = cur
-	m.mu.Unlock()
-
-	show := cur
-	if len(show) > 1024 {
-		show = show[:1024]
-	}
-	m.logf("trample: resolv.conf changed from what we expected. did some other program interfere? current contents: %q", show)
-	//lint:ignore ST1005 This error is for human.
-	warnTrample.Set(errors.New("Linux DNS config not ideal. /etc/resolv.conf overwritten. See https://tailscale.com/s/dns-fight"))
-}
-
 func (m *directManager) SetDNS(config OSConfig) (err error) {
 	defer func() {
 		if err != nil && errors.Is(err, fs.ErrPermission) && runtime.GOOS == "linux" &&
@@ -370,7 +330,7 @@ func (m *directManager) SetDNS(config OSConfig) (err error) {
 		}
 
 		buf := new(bytes.Buffer)
-		_ = writeResolvConf(buf, config.Nameservers, config.SearchDomains)
+		writeResolvConf(buf, config.Nameservers, config.SearchDomains)
 		if err := m.atomicWriteFile(m.fs, resolvConf, buf.Bytes(), 0644); err != nil {
 			return err
 		}
@@ -411,12 +371,57 @@ func (m *directManager) SetDNS(config OSConfig) (err error) {
 	return nil
 }
 
+func (m *directManager) SupportsSplitDNS() bool {
+	return false
+}
+
+func (m *directManager) GetBaseConfig() (OSConfig, error) {
+	owned, err := m.ownedByCtrld()
+	if err != nil {
+		return OSConfig{}, err
+	}
+	fileToRead := resolvConf
+	if owned {
+		fileToRead = backupConf
+	}
+
+	oscfg, err := m.readResolvFile(fileToRead)
+	if err != nil {
+		return OSConfig{}, err
+	}
+
+	// On some systems, the backup configuration file is actually a
+	// symbolic link to something owned by another DNS service (commonly,
+	// resolved). Thus, it can be updated out from underneath us to contain
+	// the Tailscale service IP, which results in an infinite loop of us
+	// trying to send traffic to resolved, which sends back to us, and so
+	// on. To solve this, drop the Tailscale service IP from the base
+	// configuration; we do this in all situations since there's
+	// essentially no world where we want to forward to ourselves.
+	//
+	// See: https://github.com/tailscale/tailscale/issues/7816
+	var removed bool
+	oscfg.Nameservers = slices.DeleteFunc(oscfg.Nameservers, func(ip netip.Addr) bool {
+		if ip == tsaddr.TailscaleServiceIP() || ip == tsaddr.TailscaleServiceIPv6() {
+			removed = true
+			return true
+		}
+		return false
+	})
+	if removed {
+		m.logf("[v1] dropped Tailscale IP from base config that was a symlink")
+	}
+	return oscfg, nil
+}
+
 func (m *directManager) Close() error {
-	// We used to keep a file for the ctrld config and symlinked
+	m.ctxClose()
+
+	// We used to keep a file for the tailscale config and symlinked
 	// to it, but then we stopped because /etc/resolv.conf being a
 	// symlink to surprising places breaks snaps and other sandboxing
 	// things. Clean it up if it's still there.
-	_ = m.fs.Remove("/etc/resolv.ctrld.conf")
+	m.fs.Remove("/etc/resolv.ctrld.conf")
 
 	if _, err := m.fs.Stat(backupConf); err != nil {
 		if os.IsNotExist(err) {
@@ -436,9 +441,9 @@ func (m *directManager) Close() error {
 	resolvConfExists := !os.IsNotExist(err)
 
 	if resolvConfExists && !owned {
-		// There's already a non-ctrld config in place, get rid of
+		// There's already a non-tailscale config in place, get rid of
 		// our backup.
-		_ = m.fs.Remove(backupConf)
+		m.fs.Remove(backupConf)
 		return nil
 	}
 
@@ -475,6 +480,14 @@ func (m *directManager) atomicWriteFile(fs wholeFileFS, filename string, data []
 	if err := fs.WriteFile(tmpName, data, perm); err != nil {
 		return fmt.Errorf("atomicWriteFile: %w", err)
 	}
+	// Explicitly set the permissions on the temporary file before renaming
+	// it. This ensures that if we have a umask set which prevents creating
+	// world-readable files, the file will still have the correct
+	// permissions once it's renamed into place. See #12609.
+	if err := fs.Chmod(tmpName, perm); err != nil {
+		return fmt.Errorf("atomicWriteFile: Chmod: %w", err)
+	}
+
 	return m.rename(tmpName, filename)
 }
 
@@ -483,10 +496,11 @@ func (m *directManager) atomicWriteFile(fs wholeFileFS, filename string, data []
 //
 // All name parameters are absolute paths.
 type wholeFileFS interface {
-	Stat(name string) (isRegular bool, err error)
-	Rename(oldName, newName string) error
-	Remove(name string) error
+	Chmod(name string, mode os.FileMode) error
 	ReadFile(name string) ([]byte, error)
+	Remove(name string) error
+	Rename(oldName, newName string) error
+	Stat(name string) (isRegular bool, err error)
 	Truncate(name string) error
 	WriteFile(name string, contents []byte, perm os.FileMode) error
 }
@@ -510,6 +524,10 @@ func (fs directFS) Stat(name string) (isRegular bool, err error) {
 	return fi.Mode().IsRegular(), nil
 }
 
+func (fs directFS) Chmod(name string, mode os.FileMode) error {
+	return os.Chmod(fs.path(name), mode)
+}
+
 func (fs directFS) Rename(oldName, newName string) error {
 	return os.Rename(fs.path(oldName), fs.path(newName))
 }

internal/dns/direct_linux.go

@@ -1,26 +1,26 @@
-// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 package dns
 
 import (
+	"bytes"
 	"context"
 
-	"github.com/illarion/gonotify"
+	"github.com/illarion/gonotify/v2"
+	"tailscale.com/health"
 )
 
 func (m *directManager) runFileWatcher() {
-	in, err := gonotify.NewInotify()
+	ctx, cancel := context.WithCancel(m.ctx)
+	defer cancel()
+	in, err := gonotify.NewInotify(ctx)
 	if err != nil {
 		// Oh well, we tried. This is all best effort for now, to
 		// surface warnings to users.
 		m.logf("dns: inotify new: %v", err)
 		return
 	}
-	ctx, cancel := context.WithCancel(m.ctx)
-	defer cancel()
-	go m.closeInotifyOnDone(ctx, in)
 
 	const events = gonotify.IN_ATTRIB |
 		gonotify.IN_CLOSE_WRITE |
@@ -56,7 +56,53 @@ func (m *directManager) runFileWatcher() {
 	}
 }
 
-func (m *directManager) closeInotifyOnDone(ctx context.Context, in *gonotify.Inotify) {
-	<-ctx.Done()
-	_ = in.Close()
+var resolvTrampleWarnable = health.Register(&health.Warnable{
+	Code:     "ctrld-resolv-conf-overwritten",
+	Severity: health.SeverityMedium,
+	Title:    "Linux DNS configuration issue",
+	Text:     health.StaticMessage("Linux DNS config not ideal. /etc/resolv.conf overwritten. See https://tailscale.com/s/dns-fight"),
+})
+
+// checkForFileTrample checks whether /etc/resolv.conf has been trampled
+// by another program on the system. (e.g. a DHCP client)
+func (m *directManager) checkForFileTrample() {
+	m.mu.Lock()
+	want := m.wantResolvConf
+	lastWarn := m.lastWarnContents
+	m.mu.Unlock()
+
+	if want == nil {
+		return
+	}
+
+	cur, err := m.fs.ReadFile(resolvConf)
+	if err != nil {
+		m.logf("trample: read error: %v", err)
+		return
+	}
+	if bytes.Equal(cur, want) {
+		m.health.SetHealthy(resolvTrampleWarnable)
+		if lastWarn != nil {
+			m.mu.Lock()
+			m.lastWarnContents = nil
+			m.mu.Unlock()
+			m.logf("trample: resolv.conf again matches expected content")
+		}
+		return
+	}
+	if bytes.Equal(cur, lastWarn) {
+		// We already logged about this, so not worth doing it again.
+		return
+	}
+
+	m.mu.Lock()
+	m.lastWarnContents = cur
+	m.mu.Unlock()
+
+	show := cur
+	if len(show) > 1024 {
+		show = show[:1024]
+	}
+	m.logf("trample: resolv.conf changed from what we expected. did some other program interfere? current contents: %q", show)
+	m.health.SetUnhealthy(resolvTrampleWarnable, nil)
 }

internal/dns/direct_notlinux.go

@@ -1,6 +1,5 @@
-// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 //go:build !linux
 

internal/dns/direct_test.go

@@ -1,10 +1,10 @@
-// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 package dns
 
 import (
+	"context"
 	"errors"
 	"fmt"
 	"io/fs"
@@ -79,7 +79,10 @@ func testDirect(t *testing.T, fs wholeFileFS) {
 		}
 	}
 
-	m := directManager{logf: t.Logf, fs: fs}
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	m := directManager{logf: t.Logf, fs: fs, ctx: ctx, ctxClose: cancel}
 	if err := m.SetDNS(OSConfig{
 		Nameservers:   []netip.Addr{netip.MustParseAddr("8.8.8.8"), netip.MustParseAddr("8.8.4.4")},
 		SearchDomains: []dnsname.FQDN{"controld.com."},
@@ -121,7 +124,7 @@ type brokenRemoveFS struct {
 	directFS
 }
 
-func (b brokenRemoveFS) Rename(_, _ string) error {
+func (b brokenRemoveFS) Rename(old, new string) error {
 	return errors.New("nyaaah I'm a silly container!")
 }
 
@@ -178,12 +181,12 @@ func TestReadResolve(t *testing.T) {
 				SearchDomains: []dnsname.FQDN{"controld.com."},
 			},
 		},
-		{in: `search controld.com # typo`,
+		{in: `search controld.com # comment`,
 			want: OSConfig{
 				SearchDomains: []dnsname.FQDN{"controld.com."},
 			},
 		},
-		{in: `searchcontrold.com`, wantErr: true},
+		{in: `searchctrld.com`, wantErr: true},
 		{in: `search`, wantErr: true},
 	}
 

internal/dns/manager_freebsd.go

@@ -1,6 +1,5 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 package dns
 
@@ -8,13 +7,18 @@ import (
 	"fmt"
 	"os"
 
+	"tailscale.com/control/controlknobs"
+	"tailscale.com/health"
 	"tailscale.com/types/logger"
 )
 
-func NewOSConfigurator(logf logger.Logf, _ string) (OSConfigurator, error) {
+// NewOSConfigurator creates a new OS configurator.
+//
+// The health tracker may be nil; the knobs may be nil and are ignored on this platform.
+func NewOSConfigurator(logf logger.Logf, health *health.Tracker, _ *controlknobs.Knobs, _ string) (OSConfigurator, error) {
 	bs, err := os.ReadFile("/etc/resolv.conf")
 	if os.IsNotExist(err) {
-		return newDirectManager(logf), nil
+		return newDirectManager(logf, health), nil
 	}
 	if err != nil {
 		return nil, fmt.Errorf("reading /etc/resolv.conf: %w", err)
@@ -24,16 +28,16 @@ func NewOSConfigurator(logf logger.Logf, _ string) (OSConfigurator, error) {
 	case "resolvconf":
 		switch resolvconfStyle() {
 		case "":
-			return newDirectManager(logf), nil
+			return newDirectManager(logf, health), nil
 		case "debian":
 			return newDebianResolvconfManager(logf)
 		case "openresolv":
-			return newOpenresolvManager()
+			return newOpenresolvManager(logf)
 		default:
 			logf("[unexpected] got unknown flavor of resolvconf %q, falling back to direct manager", resolvconfStyle())
-			return newDirectManager(logf), nil
+			return newDirectManager(logf, health), nil
 		}
 	default:
-		return newDirectManager(logf), nil
+		return newDirectManager(logf, health), nil
 	}
 }

internal/dns/manager_linux.go

@@ -1,8 +1,5 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-//lint:file-ignore U1000 Ignore this file, it's a copy.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 package dns
 
@@ -17,6 +14,7 @@ import (
 	"time"
 
 	"github.com/godbus/dbus/v5"
+	"tailscale.com/control/controlknobs"
 	"tailscale.com/health"
 	"tailscale.com/net/netaddr"
 	"tailscale.com/types/logger"
@@ -38,7 +36,10 @@ func (kv kv) String() string {
 
 var publishOnce sync.Once
 
-func NewOSConfigurator(logf logger.Logf, interfaceName string) (ret OSConfigurator, err error) {
+// NewOSConfigurator created a new OS configurator.
+//
+// The health tracker may be nil; the knobs may be nil and are ignored on this platform.
+func NewOSConfigurator(logf logger.Logf, health *health.Tracker, _ *controlknobs.Knobs, interfaceName string) (ret OSConfigurator, err error) {
 	env := newOSConfigEnv{
 		fs:                directFS{},
 		dbusPing:          dbusPing,
@@ -47,7 +48,7 @@ func NewOSConfigurator(logf logger.Logf, interfaceName string) (ret OSConfigurat
 		nmVersionBetween:  nmVersionBetween,
 		resolvconfStyle:   resolvconfStyle,
 	}
-	mode, err := dnsMode(logf, env)
+	mode, err := dnsMode(logf, health, env)
 	if err != nil {
 		return nil, err
 	}
@@ -59,18 +60,18 @@ func NewOSConfigurator(logf logger.Logf, interfaceName string) (ret OSConfigurat
 	logf("dns: using %q mode", mode)
 	switch mode {
 	case "direct":
-		return newDirectManagerOnFS(logf, env.fs), nil
+		return newDirectManagerOnFS(logf, health, env.fs), nil
 	case "systemd-resolved":
-		return newResolvedManager(logf, interfaceName)
+		return newResolvedManager(logf, health, interfaceName)
 	case "network-manager":
 		return newNMManager(interfaceName)
 	case "debian-resolvconf":
 		return newDebianResolvconfManager(logf)
 	case "openresolv":
-		return newOpenresolvManager()
+		return newOpenresolvManager(logf)
 	default:
 		logf("[unexpected] detected unknown DNS mode %q, using direct manager as last resort", mode)
-		return newDirectManagerOnFS(logf, env.fs), nil
+		return newDirectManagerOnFS(logf, health, env.fs), nil
 	}
 }
 
@@ -84,7 +85,7 @@ type newOSConfigEnv struct {
 	resolvconfStyle   func() string
 }
 
-func dnsMode(logf logger.Logf, env newOSConfigEnv) (ret string, err error) {
+func dnsMode(logf logger.Logf, health *health.Tracker, env newOSConfigEnv) (ret string, err error) {
 	var debug []kv
 	dbg := func(k, v string) {
 		debug = append(debug, kv{k, v})
@@ -145,7 +146,7 @@ func dnsMode(logf logger.Logf, env newOSConfigEnv) (ret string, err error) {
 		// header, but doesn't actually point to resolved. We mustn't
 		// try to program resolved in that case.
 		// https://github.com/tailscale/tailscale/issues/2136
-		if err := resolvedIsActuallyResolver(bs); err != nil {
+		if err := resolvedIsActuallyResolver(logf, env, dbg, bs); err != nil {
 			logf("dns: resolvedIsActuallyResolver error: %v", err)
 			dbg("resolved", "not-in-use")
 			return "direct", nil
@@ -231,7 +232,7 @@ func dnsMode(logf logger.Logf, env newOSConfigEnv) (ret string, err error) {
 		dbg("rc", "nm")
 		// Sometimes, NetworkManager owns the configuration but points
 		// it at systemd-resolved.
-		if err := resolvedIsActuallyResolver(bs); err != nil {
+		if err := resolvedIsActuallyResolver(logf, env, dbg, bs); err != nil {
 			logf("dns: resolvedIsActuallyResolver error: %v", err)
 			dbg("resolved", "not-in-use")
 			// You'd think we would use newNMManager here. However, as
@@ -271,6 +272,14 @@ func dnsMode(logf logger.Logf, env newOSConfigEnv) (ret string, err error) {
 			dbg("nm-safe", "yes")
 			return "network-manager", nil
 		}
+		if err := env.nmIsUsingResolved(); err != nil {
+			// If systemd-resolved is not running at all, then we don't have any
+			// other choice: we take direct control of DNS.
+			dbg("nm-resolved", "no")
+			return "direct", nil
+		}
+
+		//lint:ignore SA1019 upstream code still use it.
 		health.SetDNSManagerHealth(errors.New("systemd-resolved and NetworkManager are wired together incorrectly; MagicDNS will probably not work. For more info, see https://tailscale.com/s/resolved-nm"))
 		dbg("nm-safe", "no")
 		return "systemd-resolved", nil
@@ -324,14 +333,23 @@ func nmIsUsingResolved() error {
 	return nil
 }
 
-// resolvedIsActuallyResolver reports whether the given resolv.conf
-// bytes describe a configuration where systemd-resolved (127.0.0.53)
-// is the only configured nameserver.
+// resolvedIsActuallyResolver reports whether the system is using
+// systemd-resolved as the resolver. There are two different ways to
+// use systemd-resolved:
+//   - libnss_resolve, which requires adding `resolve` to the "hosts:"
+//     line in /etc/nsswitch.conf
+//   - setting the only nameserver configured in `resolv.conf` to
+//     systemd-resolved IP (127.0.0.53)
 //
 // Returns an error if the configuration is something other than
 // exclusively systemd-resolved, or nil if the config is only
 // systemd-resolved.
-func resolvedIsActuallyResolver(bs []byte) error {
+func resolvedIsActuallyResolver(logf logger.Logf, env newOSConfigEnv, dbg func(k, v string), bs []byte) error {
+	if err := isLibnssResolveUsed(env); err == nil {
+		dbg("resolved", "nss")
+		return nil
+	}
+
 	cfg, err := readResolv(bytes.NewBuffer(bs))
 	if err != nil {
 		return err
@@ -348,9 +366,34 @@ func resolvedIsActuallyResolver(bs []byte) error {
 			return fmt.Errorf("resolv.conf doesn't point to systemd-resolved; points to %v", cfg.Nameservers)
 		}
 	}
+	dbg("resolved", "file")
 	return nil
 }
 
+// isLibnssResolveUsed reports whether libnss_resolve is used
+// for resolving names. Returns nil if it is, and an error otherwise.
+func isLibnssResolveUsed(env newOSConfigEnv) error {
+	bs, err := env.fs.ReadFile("/etc/nsswitch.conf")
+	if err != nil {
+		return fmt.Errorf("reading /etc/resolv.conf: %w", err)
+	}
+	for _, line := range strings.Split(string(bs), "\n") {
+		fields := strings.Fields(line)
+		if len(fields) < 2 || fields[0] != "hosts:" {
+			continue
+		}
+		for _, module := range fields[1:] {
+			if module == "dns" {
+				return fmt.Errorf("dns with a higher priority than libnss_resolve")
+			}
+			if module == "resolve" {
+				return nil
+			}
+		}
+	}
+	return fmt.Errorf("libnss_resolve not used")
+}
+
 func dbusPing(name, objectPath string) error {
 	conn, err := dbus.SystemBus()
 	if err != nil {

internal/dns/manager_linux_test.go

@@ -1,6 +1,5 @@
-// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 package dns
 
@@ -71,7 +70,7 @@ func TestLinuxDNSMode(t *testing.T) {
 		{
 			name:    "resolved_alone_without_ping",
 			env:     env(resolvDotConf("# Managed by systemd-resolved", "nameserver 127.0.0.53")),
-			wantLog: "dns: ResolvConfMode error: dbus property not found\ndns: [rc=resolved nm=no resolv-conf-mode=error ret=systemd-resolved]",
+			wantLog: "dns: ResolvConfMode error: dbus property not found\ndns: [rc=resolved resolved=file nm=no resolv-conf-mode=error ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
 		{
@@ -79,16 +78,46 @@ func TestLinuxDNSMode(t *testing.T) {
 			env: env(
 				resolvDotConf("# Managed by systemd-resolved", "nameserver 127.0.0.53"),
 				resolvedRunning()),
-			wantLog: "dns: [resolved-ping=yes rc=resolved nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
+			wantLog: "dns: [resolved-ping=yes rc=resolved resolved=file nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
+		{
+			name: "resolved_and_nsswitch_resolve",
+			env: env(
+				resolvDotConf("# Managed by systemd-resolved", "nameserver 1.1.1.1"),
+				resolvedRunning(),
+				nsswitchDotConf("hosts: files resolve [!UNAVAIL=return] dns"),
+			),
+			wantLog: "dns: [resolved-ping=yes rc=resolved resolved=nss nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
+			want:    "systemd-resolved",
+		},
+		{
+			name: "resolved_and_nsswitch_dns",
+			env: env(
+				resolvDotConf("# Managed by systemd-resolved", "nameserver 1.1.1.1"),
+				resolvedRunning(),
+				nsswitchDotConf("hosts: files dns resolve [!UNAVAIL=return]"),
+			),
+			wantLog: "dns: resolvedIsActuallyResolver error: resolv.conf doesn't point to systemd-resolved; points to [1.1.1.1]\ndns: [resolved-ping=yes rc=resolved resolved=not-in-use ret=direct]",
+			want:    "direct",
+		},
+		{
+			name: "resolved_and_nsswitch_none",
+			env: env(
+				resolvDotConf("# Managed by systemd-resolved", "nameserver 1.1.1.1"),
+				resolvedRunning(),
+				nsswitchDotConf("hosts:"),
+			),
+			wantLog: "dns: resolvedIsActuallyResolver error: resolv.conf doesn't point to systemd-resolved; points to [1.1.1.1]\ndns: [resolved-ping=yes rc=resolved resolved=not-in-use ret=direct]",
+			want:    "direct",
+		},
 		{
 			name: "resolved_and_networkmanager_not_using_resolved",
 			env: env(
 				resolvDotConf("# Managed by systemd-resolved", "nameserver 127.0.0.53"),
 				resolvedRunning(),
 				nmRunning("1.2.3", false)),
-			wantLog: "dns: [resolved-ping=yes rc=resolved nm=yes nm-resolved=no resolv-conf-mode=fortests ret=systemd-resolved]",
+			wantLog: "dns: [resolved-ping=yes rc=resolved resolved=file nm=yes nm-resolved=no resolv-conf-mode=fortests ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
 		{
@@ -97,7 +126,7 @@ func TestLinuxDNSMode(t *testing.T) {
 				resolvDotConf("# Managed by systemd-resolved", "nameserver 127.0.0.53"),
 				resolvedRunning(),
 				nmRunning("1.26.2", true)),
-			wantLog: "dns: [resolved-ping=yes rc=resolved nm=yes nm-resolved=yes nm-safe=yes ret=network-manager]",
+			wantLog: "dns: [resolved-ping=yes rc=resolved resolved=file nm=yes nm-resolved=yes nm-safe=yes ret=network-manager]",
 			want:    "network-manager",
 		},
 		{
@@ -106,7 +135,7 @@ func TestLinuxDNSMode(t *testing.T) {
 				resolvDotConf("# Managed by systemd-resolved", "nameserver 127.0.0.53"),
 				resolvedRunning(),
 				nmRunning("1.27.0", true)),
-			wantLog: "dns: [resolved-ping=yes rc=resolved nm=yes nm-resolved=yes nm-safe=no resolv-conf-mode=fortests ret=systemd-resolved]",
+			wantLog: "dns: [resolved-ping=yes rc=resolved resolved=file nm=yes nm-resolved=yes nm-safe=no resolv-conf-mode=fortests ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
 		{
@@ -115,7 +144,7 @@ func TestLinuxDNSMode(t *testing.T) {
 				resolvDotConf("# Managed by systemd-resolved", "nameserver 127.0.0.53"),
 				resolvedRunning(),
 				nmRunning("1.22.0", true)),
-			wantLog: "dns: [resolved-ping=yes rc=resolved nm=yes nm-resolved=yes nm-safe=no resolv-conf-mode=fortests ret=systemd-resolved]",
+			wantLog: "dns: [resolved-ping=yes rc=resolved resolved=file nm=yes nm-resolved=yes nm-safe=no resolv-conf-mode=fortests ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
 		// Regression tests for extreme corner cases below.
@@ -141,7 +170,7 @@ func TestLinuxDNSMode(t *testing.T) {
 					"nameserver 127.0.0.53",
 					"nameserver 127.0.0.53"),
 				resolvedRunning()),
-			wantLog: "dns: [resolved-ping=yes rc=resolved nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
+			wantLog: "dns: [resolved-ping=yes rc=resolved resolved=file nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
 		{
@@ -156,7 +185,7 @@ func TestLinuxDNSMode(t *testing.T) {
 				"# run \"systemd-resolve --status\" to see details about the actual nameservers.",
 				"nameserver 127.0.0.53"),
 				resolvedRunning()),
-			wantLog: "dns: [resolved-ping=yes rc=resolved nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
+			wantLog: "dns: [resolved-ping=yes rc=resolved resolved=file nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
 		{
@@ -171,7 +200,7 @@ func TestLinuxDNSMode(t *testing.T) {
 				"# 127.0.0.53 is the systemd-resolved stub resolver.",
 				"# run \"systemd-resolve --status\" to see details about the actual nameservers.",
 				"nameserver 127.0.0.53")),
-			wantLog: "dns: ResolvConfMode error: dbus property not found\ndns: [rc=resolved nm=no resolv-conf-mode=error ret=systemd-resolved]",
+			wantLog: "dns: ResolvConfMode error: dbus property not found\ndns: [rc=resolved resolved=file nm=no resolv-conf-mode=error ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
 		{
@@ -183,7 +212,7 @@ func TestLinuxDNSMode(t *testing.T) {
 				"options edns0 trust-ad"),
 				resolvedRunning(),
 				nmRunning("1.32.12", true)),
-			wantLog: "dns: [resolved-ping=yes rc=nm nm-resolved=yes nm-safe=no resolv-conf-mode=fortests ret=systemd-resolved]",
+			wantLog: "dns: [resolved-ping=yes rc=nm resolved=file nm-resolved=yes nm-safe=no resolv-conf-mode=fortests ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
 		{
@@ -194,7 +223,7 @@ func TestLinuxDNSMode(t *testing.T) {
 				"nameserver 127.0.0.53",
 				"options edns0 trust-ad"),
 				nmRunning("1.32.12", true)),
-			wantLog: "dns: ResolvConfMode error: dbus property not found\ndns: [rc=nm nm-resolved=yes nm-safe=no resolv-conf-mode=error ret=systemd-resolved]",
+			wantLog: "dns: ResolvConfMode error: dbus property not found\ndns: [rc=nm resolved=file nm-resolved=yes nm-safe=no resolv-conf-mode=error ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
 		{
@@ -206,7 +235,7 @@ func TestLinuxDNSMode(t *testing.T) {
 				"options edns0 trust-ad"),
 				resolvedRunning(),
 				nmRunning("1.26.3", true)),
-			wantLog: "dns: [resolved-ping=yes rc=nm nm-resolved=yes nm-safe=yes ret=network-manager]",
+			wantLog: "dns: [resolved-ping=yes rc=nm resolved=file nm-resolved=yes nm-safe=yes ret=network-manager]",
 			want:    "network-manager",
 		},
 		{
@@ -217,7 +246,7 @@ func TestLinuxDNSMode(t *testing.T) {
 				"nameserver 127.0.0.53",
 				"options edns0 trust-ad"),
 				resolvedRunning()),
-			wantLog: "dns: [resolved-ping=yes rc=nm nm-resolved=yes nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
+			wantLog: "dns: [resolved-ping=yes rc=nm resolved=file nm-resolved=yes nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
 		{
@@ -228,7 +257,7 @@ func TestLinuxDNSMode(t *testing.T) {
 				"search lan",
 				"nameserver 127.0.0.53"),
 				resolvedRunning()),
-			wantLog: "dns: [resolved-ping=yes rc=nm nm-resolved=yes nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
+			wantLog: "dns: [resolved-ping=yes rc=nm resolved=file nm-resolved=yes nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
 		{
@@ -238,14 +267,26 @@ func TestLinuxDNSMode(t *testing.T) {
 				resolvDotConf("# Managed by systemd-resolved", "nameserver 127.0.0.53"),
 				resolvedDbusProperty(),
 			)),
-			wantLog: "dns: [resolved-ping=yes rc=resolved nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
+			wantLog: "dns: [resolved-ping=yes rc=resolved resolved=file nm=no resolv-conf-mode=fortests ret=systemd-resolved]",
 			want:    "systemd-resolved",
 		},
+		{
+			// regression test for https://github.com/tailscale/tailscale/issues/9687
+			name: "networkmanager_endeavouros",
+			env: env(resolvDotConf(
+				"# Generated by NetworkManager",
+				"search example.com localdomain",
+				"nameserver 10.0.0.1"),
+				nmRunning("1.44.2", false)),
+			wantLog: "dns: resolvedIsActuallyResolver error: resolv.conf doesn't point to systemd-resolved; points to [10.0.0.1]\n" +
+				"dns: [rc=nm resolved=not-in-use ret=direct]",
+			want: "direct",
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			var logBuf tstest.MemLogger
-			got, err := dnsMode(logBuf.Logf, tt.env)
+			got, err := dnsMode(logBuf.Logf, nil, tt.env)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -272,8 +313,9 @@ func (m memFS) Stat(name string) (isRegular bool, err error) {
 	return false, nil
 }
 
-func (m memFS) Rename(_, _ string) error { panic("TODO") }
-func (m memFS) Remove(_ string) error    { panic("TODO") }
+func (m memFS) Chmod(name string, mode os.FileMode) error { panic("TODO") }
+func (m memFS) Rename(oldName, newName string) error      { panic("TODO") }
+func (m memFS) Remove(name string) error                  { panic("TODO") }
 func (m memFS) ReadFile(name string) ([]byte, error) {
 	v, ok := m[name]
 	if !ok {
@@ -297,7 +339,7 @@ func (m memFS) Truncate(name string) error {
 	return nil
 }
 
-func (m memFS) WriteFile(name string, contents []byte, _ os.FileMode) error {
+func (m memFS) WriteFile(name string, contents []byte, perm os.FileMode) error {
 	m[name] = string(contents)
 	return nil
 }
@@ -381,6 +423,12 @@ func resolvDotConf(ss ...string) envOption {
 	})
 }
 
+func nsswitchDotConf(ss ...string) envOption {
+	return envOpt(func(b *envBuilder) {
+		b.fs["/etc/nsswitch.conf"] = strings.Join(ss, "\n")
+	})
+}
+
 // resolvedRunning returns an option that makes resolved reply to a dbusPing
 // and the ResolvConfMode property.
 func resolvedRunning() envOption {

internal/dns/nm.go

@@ -1,6 +1,5 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 //go:build linux
 
@@ -11,6 +10,7 @@ import (
 	"fmt"
 	"net"
 	"net/netip"
+	"sort"
 	"time"
 
 	"github.com/godbus/dbus/v5"
@@ -24,6 +24,13 @@ const (
 	lowerPriority   = int32(200) // lower than all builtin auto priorities
 )
 
+// reconfigTimeout is the time interval within which Manager.{Up,Down} should complete.
+//
+// This is particularly useful because certain conditions can cause indefinite hangs
+// (such as improper dbus auth followed by contextless dbus.Object.Call).
+// Such operations should be wrapped in a timeout context.
+const reconfigTimeout = time.Second
+
 // nmManager uses the NetworkManager DBus API.
 type nmManager struct {
 	interfaceName string
@@ -31,8 +38,6 @@ type nmManager struct {
 	dnsManager    dbus.BusObject
 }
 
-var _ OSConfigurator = (*nmManager)(nil)
-
 func newNMManager(interfaceName string) (*nmManager, error) {
 	conn, err := dbus.SystemBus()
 	if err != nil {
@@ -141,18 +146,17 @@ func (m *nmManager) trySet(ctx context.Context, config OSConfig) error {
 	// tell it explicitly to keep it. Read out the current interface
 	// settings and mirror them out to NetworkManager.
 	var addrs6 []map[string]any
-	if netIface, err := net.InterfaceByName(m.interfaceName); err == nil {
-		if addrs, err := netIface.Addrs(); err == nil {
-			for _, a := range addrs {
-				if ipnet, ok := a.(*net.IPNet); ok {
-					nip, ok := netip.AddrFromSlice(ipnet.IP)
-					nip = nip.Unmap()
-					if ok && nip.Is6() {
-						addrs6 = append(addrs6, map[string]any{
-							"address": nip.String(),
-							"prefix":  uint32(128),
-						})
-					}
+	if tsIf, err := net.InterfaceByName(m.interfaceName); err == nil {
+		addrs, _ := tsIf.Addrs()
+		for _, a := range addrs {
+			if ipnet, ok := a.(*net.IPNet); ok {
+				nip, ok := netip.AddrFromSlice(ipnet.IP)
+				nip = nip.Unmap()
+				if ok && nip.Is6() {
+					addrs6 = append(addrs6, map[string]any{
+						"address": nip.String(),
+						"prefix":  uint32(128),
+					})
 				}
 			}
 		}
@@ -260,6 +264,125 @@ func (m *nmManager) trySet(ctx context.Context, config OSConfig) error {
 	return nil
 }
 
+func (m *nmManager) SupportsSplitDNS() bool {
+	var mode string
+	v, err := m.dnsManager.GetProperty("org.freedesktop.NetworkManager.DnsManager.Mode")
+	if err != nil {
+		return false
+	}
+	mode, ok := v.Value().(string)
+	if !ok {
+		return false
+	}
+
+	// Per NM's documentation, it only does split-DNS when it's
+	// programming dnsmasq or systemd-resolved. All other modes are
+	// primary-only.
+	return mode == "dnsmasq" || mode == "systemd-resolved"
+}
+
+func (m *nmManager) GetBaseConfig() (OSConfig, error) {
+	conn, err := dbus.SystemBus()
+	if err != nil {
+		return OSConfig{}, err
+	}
+
+	nm := conn.Object("org.freedesktop.NetworkManager", dbus.ObjectPath("/org/freedesktop/NetworkManager/DnsManager"))
+	v, err := nm.GetProperty("org.freedesktop.NetworkManager.DnsManager.Configuration")
+	if err != nil {
+		return OSConfig{}, err
+	}
+	cfgs, ok := v.Value().([]map[string]dbus.Variant)
+	if !ok {
+		return OSConfig{}, fmt.Errorf("unexpected NM config type %T", v.Value())
+	}
+
+	if len(cfgs) == 0 {
+		return OSConfig{}, nil
+	}
+
+	type dnsPrio struct {
+		resolvers []netip.Addr
+		domains   []string
+		priority  int32
+	}
+	order := make([]dnsPrio, 0, len(cfgs)-1)
+
+	for _, cfg := range cfgs {
+		if name, ok := cfg["interface"]; ok {
+			if s, ok := name.Value().(string); ok && s == m.interfaceName {
+				// Config for the tailscale interface, skip.
+				continue
+			}
+		}
+
+		var p dnsPrio
+
+		if v, ok := cfg["nameservers"]; ok {
+			if ips, ok := v.Value().([]string); ok {
+				for _, s := range ips {
+					ip, err := netip.ParseAddr(s)
+					if err != nil {
+						// hmm, what do? Shouldn't really happen.
+						continue
+					}
+					p.resolvers = append(p.resolvers, ip)
+				}
+			}
+		}
+		if v, ok := cfg["domains"]; ok {
+			if domains, ok := v.Value().([]string); ok {
+				p.domains = domains
+			}
+		}
+		if v, ok := cfg["priority"]; ok {
+			if prio, ok := v.Value().(int32); ok {
+				p.priority = prio
+			}
+		}
+
+		order = append(order, p)
+	}
+
+	sort.Slice(order, func(i, j int) bool {
+		return order[i].priority < order[j].priority
+	})
+
+	var (
+		ret           OSConfig
+		seenResolvers = map[netip.Addr]bool{}
+		seenSearch    = map[string]bool{}
+	)
+
+	for _, cfg := range order {
+		for _, resolver := range cfg.resolvers {
+			if seenResolvers[resolver] {
+				continue
+			}
+			ret.Nameservers = append(ret.Nameservers, resolver)
+			seenResolvers[resolver] = true
+		}
+		for _, dom := range cfg.domains {
+			if seenSearch[dom] {
+				continue
+			}
+			fqdn, err := dnsname.ToFQDN(dom)
+			if err != nil {
+				continue
+			}
+			ret.SearchDomains = append(ret.SearchDomains, fqdn)
+			seenSearch[dom] = true
+		}
+		if cfg.priority < 0 {
+			// exclusive configurations preempt all other
+			// configurations, so we're done.
+			break
+		}
+	}
+
+	return ret, nil
+}
+
 func (m *nmManager) Close() error {
 	// No need to do anything on close, NetworkManager will delete our
 	// settings when the tailscale interface goes away.

internal/dns/openresolv.go

@@ -1,6 +1,5 @@
-// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 //go:build linux || freebsd || openbsd
 
@@ -10,22 +9,41 @@ import (
 	"bytes"
 	"fmt"
 	"os/exec"
+	"strings"
+
+	"tailscale.com/types/logger"
 )
 
 // openresolvManager manages DNS configuration using the openresolv
 // implementation of the `resolvconf` program.
-type openresolvManager struct{}
+type openresolvManager struct {
+	logf logger.Logf
+}
 
-var _ OSConfigurator = (*openresolvManager)(nil)
+func newOpenresolvManager(logf logger.Logf) (openresolvManager, error) {
+	return openresolvManager{logf}, nil
+}
 
-func newOpenresolvManager() (openresolvManager, error) {
-	return openresolvManager{}, nil
+func (m openresolvManager) logCmdErr(cmd *exec.Cmd, err error) {
+	if err == nil {
+		return
+	}
+
+	commandStr := fmt.Sprintf("path=%q args=%q", cmd.Path, cmd.Args)
+	exerr, ok := err.(*exec.ExitError)
+	if !ok {
+		m.logf("error running command %s: %v", commandStr, err)
+		return
+	}
+
+	m.logf("error running command %s stderr=%q exitCode=%d: %v", commandStr, exerr.Stderr, exerr.ExitCode(), err)
 }
 
 func (m openresolvManager) deleteTailscaleConfig() error {
 	cmd := exec.Command("resolvconf", "-f", "-d", "ctrld")
 	out, err := cmd.CombinedOutput()
 	if err != nil {
+		m.logCmdErr(cmd, err)
 		return fmt.Errorf("running %s: %s", cmd, out)
 	}
 	return nil
@@ -43,11 +61,55 @@ func (m openresolvManager) SetDNS(config OSConfig) error {
 	cmd.Stdin = &stdin
 	out, err := cmd.CombinedOutput()
 	if err != nil {
+		m.logCmdErr(cmd, err)
 		return fmt.Errorf("running %s: %s", cmd, out)
 	}
 	return nil
 }
 
+func (m openresolvManager) SupportsSplitDNS() bool {
+	return false
+}
+
+func (m openresolvManager) GetBaseConfig() (OSConfig, error) {
+	// List the names of all config snippets openresolv is aware
+	// of. Snippets get listed in priority order (most to least),
+	// which we'll exploit later.
+	bs, err := exec.Command("resolvconf", "-i").CombinedOutput()
+	if err != nil {
+		return OSConfig{}, err
+	}
+
+	// Remove the "tailscale" snippet from the list.
+	args := []string{"-l"}
+	for _, f := range strings.Split(strings.TrimSpace(string(bs)), " ") {
+		if f == "tailscale" {
+			continue
+		}
+		args = append(args, f)
+	}
+
+	// List all resolvconf snippets except our own, and parse that as
+	// a resolv.conf. This effectively generates a blended config of
+	// "everyone except tailscale", which is what would be in use if
+	// tailscale hadn't set exclusive mode.
+	//
+	// Note that this is not _entirely_ true. To be perfectly correct,
+	// we should be looking for other interfaces marked exclusive that
+	// predated tailscale, and stick to only those. However, in
+	// practice, openresolv uses are generally quite limited, and boil
+	// down to 1-2 DHCP leases, for which the correct outcome is a
+	// blended config like the one we produce here.
+	var buf bytes.Buffer
+	cmd := exec.Command("resolvconf", args...)
+	cmd.Stdout = &buf
+	if err := cmd.Run(); err != nil {
+		m.logCmdErr(cmd, err)
+		return OSConfig{}, err
+	}
+	return readResolv(&buf)
+}
+
 func (m openresolvManager) Close() error {
 	return m.deleteTailscaleConfig()
 }

internal/dns/osconfig.go

@@ -1,20 +1,20 @@
-// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 package dns
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
 	"net/netip"
+	"slices"
+	"strings"
 
 	"tailscale.com/types/logger"
 	"tailscale.com/util/dnsname"
 )
 
-var _ OSConfigurator = (*directManager)(nil)
-
 // An OSConfigurator applies DNS settings to the operating system.
 type OSConfigurator interface {
 	// SetDNS updates the OS's DNS configuration to match cfg.
@@ -23,8 +23,21 @@ type OSConfigurator interface {
 	// SetDNS must not be called after Close.
 	// SetDNS takes ownership of cfg.
 	SetDNS(cfg OSConfig) error
+	// SupportsSplitDNS reports whether the configurator is capable of
+	// installing a resolver only for specific DNS suffixes. If false,
+	// the configurator can only set a global resolver.
+	SupportsSplitDNS() bool
+	// GetBaseConfig returns the OS's "base" configuration, i.e. the
+	// resolver settings the OS would use without Tailscale
+	// contributing any configuration.
+	// GetBaseConfig must return the tailscale-free base config even
+	// after SetDNS has been called to set a Tailscale configuration.
+	// Only works when SupportsSplitDNS=false.
 
-	// Close removes ctrld-related DNS configuration from the OS.
+	// Implementations that don't support getting the base config must
+	// return ErrGetBaseConfigNotSupported.
+	GetBaseConfig() (OSConfig, error)
+	// Close removes Tailscale-related DNS configuration from the OS.
 	Close() error
 
 	Mode() string
@@ -50,14 +63,59 @@ type OSConfig struct {
 	SearchDomains []dnsname.FQDN
 	// MatchDomains are the DNS suffixes for which Nameservers should
 	// be used. If empty, Nameservers is installed as the "primary" resolver.
+	// A non-empty MatchDomains requests a "split DNS" configuration
+	// from the OS, which will only work with OSConfigurators that
+	// report SupportsSplitDNS()=true.
 	MatchDomains []dnsname.FQDN
 }
 
+func (o *OSConfig) WriteToBufioWriter(w *bufio.Writer) {
+	if o == nil {
+		w.WriteString("<nil>")
+		return
+	}
+	w.WriteString("{")
+	if len(o.Hosts) > 0 {
+		fmt.Fprintf(w, "Hosts:%v ", o.Hosts)
+	}
+	if len(o.Nameservers) > 0 {
+		fmt.Fprintf(w, "Nameservers:%v ", o.Nameservers)
+	}
+	if len(o.SearchDomains) > 0 {
+		fmt.Fprintf(w, "SearchDomains:%v ", o.SearchDomains)
+	}
+	if len(o.MatchDomains) > 0 {
+		w.WriteString("MatchDomains:[")
+		sp := ""
+		var numARPA int
+		for _, s := range o.MatchDomains {
+			if strings.HasSuffix(string(s), ".arpa.") {
+				numARPA++
+				continue
+			}
+			w.WriteString(sp)
+			w.WriteString(string(s))
+			sp = " "
+		}
+		w.WriteString("]")
+		if numARPA > 0 {
+			fmt.Fprintf(w, "+%darpa", numARPA)
+		}
+	}
+	w.WriteString("}")
+}
+
 func (o OSConfig) IsZero() bool {
-	return len(o.Nameservers) == 0 && len(o.SearchDomains) == 0 && len(o.MatchDomains) == 0
+	return len(o.Hosts) == 0 &&
+		len(o.Nameservers) == 0 &&
+		len(o.SearchDomains) == 0 &&
+		len(o.MatchDomains) == 0
 }
 
 func (a OSConfig) Equal(b OSConfig) bool {
+	if len(a.Hosts) != len(b.Hosts) {
+		return false
+	}
 	if len(a.Nameservers) != len(b.Nameservers) {
 		return false
 	}
@@ -68,6 +126,15 @@ func (a OSConfig) Equal(b OSConfig) bool {
 		return false
 	}
 
+	for i := range a.Hosts {
+		ha, hb := a.Hosts[i], b.Hosts[i]
+		if ha.Addr != hb.Addr {
+			return false
+		}
+		if !slices.Equal(ha.Hosts, hb.Hosts) {
+			return false
+		}
+	}
 	for i := range a.Nameservers {
 		if a.Nameservers[i] != b.Nameservers[i] {
 			return false
@@ -93,34 +160,39 @@ func (a OSConfig) Equal(b OSConfig) bool {
 // Fixes https://github.com/tailscale/tailscale/issues/5669
 func (a OSConfig) Format(f fmt.State, verb rune) {
 	logger.ArgWriter(func(w *bufio.Writer) {
-		_, _ = w.WriteString(`{Nameservers:[`)
+		w.WriteString(`{Nameservers:[`)
 		for i, ns := range a.Nameservers {
 			if i != 0 {
-				_, _ = w.WriteString(" ")
+				w.WriteString(" ")
 			}
-			_, _ = fmt.Fprintf(w, "%+v", ns)
+			fmt.Fprintf(w, "%+v", ns)
 		}
-		_, _ = w.WriteString(`] SearchDomains:[`)
+		w.WriteString(`] SearchDomains:[`)
 		for i, domain := range a.SearchDomains {
 			if i != 0 {
-				_, _ = w.WriteString(" ")
+				w.WriteString(" ")
 			}
-			_, _ = fmt.Fprintf(w, "%+v", domain)
+			fmt.Fprintf(w, "%+v", domain)
 		}
-		_, _ = w.WriteString(`] MatchDomains:[`)
+		w.WriteString(`] MatchDomains:[`)
 		for i, domain := range a.MatchDomains {
 			if i != 0 {
-				_, _ = w.WriteString(" ")
+				w.WriteString(" ")
 			}
-			_, _ = fmt.Fprintf(w, "%+v", domain)
+			fmt.Fprintf(w, "%+v", domain)
 		}
-		_, _ = w.WriteString(`] Hosts:[`)
+		w.WriteString(`] Hosts:[`)
 		for i, host := range a.Hosts {
 			if i != 0 {
-				_, _ = w.WriteString(" ")
+				w.WriteString(" ")
 			}
-			_, _ = fmt.Fprintf(w, "%+v", host)
+			fmt.Fprintf(w, "%+v", host)
 		}
-		_, _ = w.WriteString(`]}`)
+		w.WriteString(`]}`)
 	}).Format(f, verb)
 }
+
+// ErrGetBaseConfigNotSupported is the error
+// OSConfigurator.GetBaseConfig returns when the OSConfigurator
+// doesn't support reading the underlying configuration out of the OS.
+var ErrGetBaseConfigNotSupported = errors.New("getting OS base config is not supported")

internal/dns/osconfig_test.go

@@ -1,14 +1,15 @@
-// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 package dns
 
 import (
 	"fmt"
 	"net/netip"
+	"reflect"
 	"testing"
 
+	"tailscale.com/tstest"
 	"tailscale.com/util/dnsname"
 )
 
@@ -42,3 +43,13 @@ func TestOSConfigPrintable(t *testing.T) {
 		t.Errorf("format mismatch:\n   got: %s\n  want: %s", s, expected)
 	}
 }
+
+func TestIsZero(t *testing.T) {
+	tstest.CheckIsZero[OSConfig](t, map[reflect.Type]any{
+		reflect.TypeFor[dnsname.FQDN](): dnsname.FQDN("foo.bar."),
+		reflect.TypeFor[*HostEntry](): &HostEntry{
+			Addr:  netip.AddrFrom4([4]byte{100, 1, 2, 3}),
+			Hosts: []string{"foo", "bar"},
+		},
+	})
+}

internal/dns/resolvconf-workaround.sh

@@ -1,7 +1,6 @@
 #!/bin/sh
-# Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
-# Use of this source code is governed by a BSD-style
-# license that can be found in the LICENSE file.
+# Copyright (c) Ctrld Inc & AUTHORS
+# SPDX-License-Identifier: BSD-3-Clause
 #
 # This script is a workaround for a vpn-unfriendly behavior of the
 # original resolvconf by Thomas Hood. Unlike the `openresolv`
@@ -29,7 +28,7 @@ if [ -n "$CTRLD_RESOLVCONF_HOOK_LOOP" ]; then
 	exit 0
 fi
 
-if [ ! -f ctrld.inet ]; then
+if [ ! -f tun-ctrld.inet ]; then
 	# Ctrld isn't trying to manage DNS, do nothing.
 	exit 0
 fi
@@ -60,4 +59,4 @@ if [ -d /etc/resolvconf/update-libc.d ] ; then
 	# Re-notify libc watchers that we've changed resolv.conf again.
 	export CTRLD_RESOLVCONF_HOOK_LOOP=1
 	exec run-parts /etc/resolvconf/update-libc.d
-fi
+fi

internal/dns/resolvconf.go

@@ -1,12 +1,12 @@
-// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 //go:build linux || freebsd || openbsd
 
 package dns
 
 import (
+	"bytes"
 	"os/exec"
 )
 
@@ -14,13 +14,17 @@ func resolvconfStyle() string {
 	if _, err := exec.LookPath("resolvconf"); err != nil {
 		return ""
 	}
-	if _, err := exec.Command("resolvconf", "--version").CombinedOutput(); err != nil {
+	output, err := exec.Command("resolvconf", "--version").CombinedOutput()
+	if err != nil {
 		// Debian resolvconf doesn't understand --version, and
 		// exits with a specific error code.
 		if exitErr, ok := err.(*exec.ExitError); ok && exitErr.ExitCode() == 99 {
 			return "debian"
 		}
 	}
+	if bytes.HasPrefix(output, []byte("Debian resolvconf")) {
+		return "debian"
+	}
 	// Treat everything else as openresolv, by far the more popular implementation.
 	return "openresolv"
 }

internal/dns/resolvconfpath_default.go

@@ -0,0 +1,11 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !gokrazy
+
+package dns
+
+const (
+	resolvConf = "/etc/resolv.conf"
+	backupConf = "/etc/resolv.pre-ctrld-backup.conf"
+)

internal/dns/resolvconfpath_gokrazy.go

@@ -0,0 +1,11 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build gokrazy
+
+package dns
+
+const (
+	resolvConf = "/tmp/resolv.conf"
+	backupConf = "/tmp/resolv.pre-ctrld-backup.conf"
+)

internal/dns/resolved.go

@@ -1,6 +1,5 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
 
 //go:build linux
 
@@ -21,8 +20,6 @@ import (
 	"tailscale.com/util/dnsname"
 )
 
-const reconfigTimeout = time.Second
-
 // DBus entities we talk to.
 //
 // DBus is an RPC bus. In particular, the bus we're talking to is the
@@ -97,16 +94,14 @@ type resolvedManager struct {
 	ctx    context.Context
 	cancel func() // terminate the context, for close
 
-	logf  logger.Logf
-	ifidx int
+	logf   logger.Logf
+	health *health.Tracker
+	ifidx  int
 
 	configCR chan changeRequest // tracks OSConfigs changes and error responses
-	revertCh chan struct{}
 }
 
-var _ OSConfigurator = (*resolvedManager)(nil)
-
-func newResolvedManager(logf logger.Logf, interfaceName string) (*resolvedManager, error) {
+func newResolvedManager(logf logger.Logf, health *health.Tracker, interfaceName string) (*resolvedManager, error) {
 	iface, err := net.InterfaceByName(interfaceName)
 	if err != nil {
 		return nil, err
@@ -119,11 +114,11 @@ func newResolvedManager(logf logger.Logf, interfaceName string) (*resolvedManage
 		ctx:    ctx,
 		cancel: cancel,
 
-		logf:  logf,
-		ifidx: iface.Index,
+		logf:   logf,
+		health: health,
+		ifidx:  iface.Index,
 
 		configCR: make(chan changeRequest),
-		revertCh: make(chan struct{}),
 	}
 
 	go mgr.run(ctx)
@@ -132,8 +127,10 @@ func newResolvedManager(logf logger.Logf, interfaceName string) (*resolvedManage
 }
 
 func (m *resolvedManager) SetDNS(config OSConfig) error {
+	// NOTE: don't close this channel, since it's possible that the SetDNS
+	// call will time out and return before the run loop answers, at which
+	// point it will send on the now-closed channel.
 	errc := make(chan error, 1)
-	defer close(errc)
 
 	select {
 	case <-m.ctx.Done():
@@ -221,14 +218,12 @@ func (m *resolvedManager) run(ctx context.Context) {
 		if err = conn.AddMatchSignal(dbus.WithMatchObjectPath(dbusPath), dbus.WithMatchInterface(dbusInterface), dbus.WithMatchMember(dbusOwnerSignal), dbus.WithMatchArg(0, dbusResolvedObject)); err != nil {
 			m.logf("[v1] Setting DBus signal filter failed: %v", err)
 		}
-		if err = conn.AddMatchSignal(dbus.WithMatchObjectPath(dbusPath), dbus.WithMatchInterface(dbusInterface), dbus.WithMatchMember(dbusOwnerSignal), dbus.WithMatchArg(0, dbusNetworkdObject)); err != nil {
-			m.logf("[v1] Setting DBus signal filter failed: %v", err)
-		}
 		conn.Signal(signals)
 
 		// Reset backoff and SetNSOSHealth after successful on reconnect.
 		bo.BackOff(ctx, nil)
-		health.SetDNSOSHealth(nil)
+		//lint:ignore SA1019 upstream code still use it.
+		m.health.SetDNSOSHealth(nil)
 		return nil
 	}
 
@@ -243,15 +238,13 @@ func (m *resolvedManager) run(ctx context.Context) {
 			if rManager == nil {
 				return
 			}
-			ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 			// RevertLink resets all per-interface settings on systemd-resolved to defaults.
 			// When ctx goes away systemd-resolved auto reverts.
 			// Keeping for potential use in future refactor.
 			if call := rManager.CallWithContext(ctx, dbusRevertLink, 0, m.ifidx); call.Err != nil {
 				m.logf("[v1] RevertLink: %v", call.Err)
+				return
 			}
-			cancel()
-			close(m.revertCh)
 			return
 		case configCR := <-m.configCR:
 			// Track and update sync with latest config change.
@@ -308,7 +301,8 @@ func (m *resolvedManager) run(ctx context.Context) {
 			// Set health while holding the lock, because this will
 			// graciously serialize the resync's health outcome with a
 			// concurrent SetDNS call.
-			health.SetDNSOSHealth(err)
+			//lint:ignore SA1019 upstream code still use it.
+			m.health.SetDNSOSHealth(err)
 			if err != nil {
 				m.logf("failed to configure systemd-resolved: %v", err)
 			}
@@ -426,18 +420,22 @@ func (m *resolvedManager) setConfigOverDBus(ctx context.Context, rManager dbus.B
 		m.logf("[v1] failed to disable DoT: %v", call.Err)
 	}
 
-	if rManager.Path() == dbusResolvedPath {
-		if call := rManager.CallWithContext(ctx, dbusFlushCaches, 0); call.Err != nil {
-			m.logf("failed to flush resolved DNS cache: %v", call.Err)
-		}
+	if call := rManager.CallWithContext(ctx, dbusFlushCaches, 0); call.Err != nil {
+		m.logf("failed to flush resolved DNS cache: %v", call.Err)
 	}
-
 	return nil
 }
 
+func (m *resolvedManager) SupportsSplitDNS() bool {
+	return true
+}
+
+func (m *resolvedManager) GetBaseConfig() (OSConfig, error) {
+	return OSConfig{}, ErrGetBaseConfigNotSupported
+}
+
 func (m *resolvedManager) Close() error {
 	m.cancel() // stops the 'run' method goroutine
-	<-m.revertCh
 	return nil
 }
 

nameservers.go

@@ -1,9 +1,8 @@
 package ctrld
 
-import "net"
-
 type dnsFn func() []string
 
+// nameservers returns DNS nameservers from system settings.
 func nameservers() []string {
 	var dns []string
 	seen := make(map[string]bool)
@@ -21,7 +20,7 @@ func nameservers() []string {
 				continue
 			}
 			seen[ns] = true
-			dns = append(dns, net.JoinHostPort(ns, "53"))
+			dns = append(dns, ns)
 		}
 	}
 

nameservers_linux.go

@@ -6,6 +6,7 @@ import (
 	"encoding/hex"
 	"net"
 	"os"
+	"strings"
 
 	"github.com/Control-D-Inc/ctrld/internal/dns/resolvconffile"
 )
@@ -28,6 +29,7 @@ func dns4() []string {
 
 	var dns []string
 	seen := make(map[string]bool)
+	vis := virtualInterfaces()
 	s := bufio.NewScanner(f)
 	first := true
 	for s.Scan() {
@@ -39,7 +41,10 @@ func dns4() []string {
 		if len(fields) < 2 {
 			continue
 		}
-
+		// Skip virtual interfaces.
+		if vis.contains(string(bytes.TrimSpace(fields[0]))) {
+			continue
+		}
 		gw := make([]byte, net.IPv4len)
 		// Third fields is gateway.
 		if _, err := hex.Decode(gw, fields[2]); err != nil {
@@ -63,12 +68,17 @@ func dns6() []string {
 	defer f.Close()
 
 	var dns []string
+	vis := virtualInterfaces()
 	s := bufio.NewScanner(f)
 	for s.Scan() {
 		fields := bytes.Fields(s.Bytes())
 		if len(fields) < 4 {
 			continue
 		}
+		// Skip virtual interfaces.
+		if vis.contains(string(bytes.TrimSpace(fields[len(fields)-1]))) {
+			continue
+		}
 
 		gw := make([]byte, net.IPv6len)
 		// Fifth fields is gateway.
@@ -95,3 +105,26 @@ func dnsFromSystemdResolver() []string {
 	}
 	return ns
 }
+
+type set map[string]struct{}
+
+func (s *set) add(e string) {
+	(*s)[e] = struct{}{}
+}
+
+func (s *set) contains(e string) bool {
+	_, ok := (*s)[e]
+	return ok
+}
+
+// virtualInterfaces returns a set of virtual interfaces on current machine.
+func virtualInterfaces() set {
+	s := make(set)
+	entries, _ := os.ReadDir("/sys/devices/virtual/net")
+	for _, entry := range entries {
+		if entry.IsDir() {
+			s.add(strings.TrimSpace(entry.Name()))
+		}
+	}
+	return s
+}

nameservers_linux_test.go

@@ -0,0 +1,10 @@
+package ctrld
+
+import (
+	"testing"
+)
+
+func Test_virtualInterfaces(t *testing.T) {
+	vis := virtualInterfaces()
+	t.Log(vis)
+}

resolver.go

@@ -7,11 +7,14 @@ import (
 	"net"
 	"net/netip"
 	"slices"
+	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/miekg/dns"
-	"tailscale.com/net/interfaces"
+	"tailscale.com/net/netmon"
+	"tailscale.com/net/tsaddr"
 )
 
 const (
@@ -29,6 +32,9 @@ const (
 	ResolverTypeLegacy = "legacy"
 	// ResolverTypePrivate is like ResolverTypeOS, but use for local resolver only.
 	ResolverTypePrivate = "private"
+	// ResolverTypeSDNS specifies resolver with information encoded using DNS Stamps.
+	// See: https://dnscrypt.info/stamps-specifications/
+	ResolverTypeSDNS = "sdns"
 )
 
 const (
@@ -39,12 +45,36 @@ const (
 var controldPublicDnsWithPort = net.JoinHostPort(controldPublicDns, "53")
 
 // or is the Resolver used for ResolverTypeOS.
-var or = &osResolver{nameservers: defaultNameservers()}
+var or = newResolverWithNameserver(defaultNameservers())
 
-// defaultNameservers returns OS nameservers plus ControlD public DNS.
+// defaultNameservers is like nameservers with each element formed "ip:53".
 func defaultNameservers() []string {
 	ns := nameservers()
-	return ns
+	nss := make([]string, len(ns))
+	for i := range ns {
+		nss[i] = net.JoinHostPort(ns[i], "53")
+	}
+	return nss
+}
+
+// availableNameservers returns list of current available DNS servers of the system.
+func availableNameservers() []string {
+	var nss []string
+	// Ignore local addresses to prevent loop.
+	regularIPs, loopbackIPs, _ := netmon.LocalAddresses()
+	machineIPsMap := make(map[string]struct{}, len(regularIPs))
+	for _, v := range slices.Concat(regularIPs, loopbackIPs) {
+		machineIPsMap[v.String()] = struct{}{}
+	}
+	for _, ns := range nameservers() {
+		if _, ok := machineIPsMap[ns]; ok {
+			continue
+		}
+		if testNameserver(ns) {
+			nss = append(nss, ns)
+		}
+	}
+	return nss
 }
 
 // InitializeOsResolver initializes OS resolver using the current system DNS settings.
@@ -53,24 +83,75 @@ func defaultNameservers() []string {
 // It's the caller's responsibility to ensure the system DNS is in a clean state before
 // calling this function.
 func InitializeOsResolver() []string {
-	or.nameservers = or.nameservers[:0]
-	for _, ns := range defaultNameservers() {
-		if testNameserver(ns) {
-			or.nameservers = append(or.nameservers, ns)
+	return initializeOsResolver(availableNameservers())
+}
+func initializeOsResolver(servers []string) []string {
+	var (
+		nss       []string
+		publicNss []string
+	)
+	var (
+		lastLanServer         netip.Addr
+		curLanServer          netip.Addr
+		curLanServerAvailable bool
+	)
+	if p := or.currentLanServer.Load(); p != nil {
+		curLanServer = *p
+		or.currentLanServer.Store(nil)
+	}
+	if p := or.lastLanServer.Load(); p != nil {
+		lastLanServer = *p
+		or.lastLanServer.Store(nil)
+	}
+	for _, ns := range servers {
+		addr, err := netip.ParseAddr(ns)
+		if err != nil {
+			continue
+		}
+		server := net.JoinHostPort(ns, "53")
+		// Always use new public nameserver.
+		if !isLanAddr(addr) {
+			publicNss = append(publicNss, server)
+			nss = append(nss, server)
+			continue
+		}
+		// For LAN server, storing only current and last LAN server if any.
+		if addr.Compare(curLanServer) == 0 {
+			curLanServerAvailable = true
+		} else {
+			if addr.Compare(lastLanServer) == 0 {
+				or.lastLanServer.Store(&addr)
+			} else {
+				if or.currentLanServer.CompareAndSwap(nil, &addr) {
+					nss = append(nss, server)
+				}
+			}
 		}
 	}
-	or.nameservers = append(or.nameservers, controldPublicDnsWithPort)
-	return or.nameservers
+	// Store current LAN server as last one only if it's still available.
+	if curLanServerAvailable && curLanServer.IsValid() {
+		or.lastLanServer.Store(&curLanServer)
+		nss = append(nss, net.JoinHostPort(curLanServer.String(), "53"))
+	}
+	if len(publicNss) == 0 {
+		publicNss = append(publicNss, controldPublicDnsWithPort)
+		nss = append(nss, controldPublicDnsWithPort)
+	}
+	or.publicServer.Store(&publicNss)
+	return nss
 }
 
 // testPlainDnsNameserver sends a test query to DNS nameserver to check if the server is available.
 func testNameserver(addr string) bool {
 	msg := new(dns.Msg)
-	msg.SetQuestion(".", dns.TypeNS)
+	msg.SetQuestion("controld.com.", dns.TypeNS)
 	client := new(dns.Client)
 	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
 	defer cancel()
-	_, _, err := client.ExchangeContext(ctx, msg, addr)
+	_, _, err := client.ExchangeContext(ctx, msg, net.JoinHostPort(addr, "53"))
+	if err != nil {
+		ProxyLogger.Load().Debug().Err(err).Msgf("failed to connect to OS nameserver: %s", addr)
+	}
 	return err == nil
 }
 
@@ -104,20 +185,31 @@ func NewResolver(uc *UpstreamConfig) (Resolver, error) {
 }
 
 type osResolver struct {
-	nameservers []string
+	currentLanServer atomic.Pointer[netip.Addr]
+	lastLanServer    atomic.Pointer[netip.Addr]
+	publicServer     atomic.Pointer[[]string]
 }
 
 type osResolverResult struct {
-	answer              *dns.Msg
-	err                 error
-	isControlDPublicDNS bool
+	answer *dns.Msg
+	err    error
+	server string
+	lan    bool
 }
 
 // Resolve resolves DNS queries using pre-configured nameservers.
 // Query is sent to all nameservers concurrently, and the first
 // success response will be returned.
 func (o *osResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, error) {
-	numServers := len(o.nameservers)
+	publicServers := *o.publicServer.Load()
+	nss := make([]string, 0, 2)
+	if p := o.currentLanServer.Load(); p != nil {
+		nss = append(nss, net.JoinHostPort(p.String(), "53"))
+	}
+	if p := o.lastLanServer.Load(); p != nil {
+		nss = append(nss, net.JoinHostPort(p.String(), "53"))
+	}
+	numServers := len(nss) + len(publicServers)
 	if numServers == 0 {
 		return nil, errors.New("no nameservers available")
 	}
@@ -126,43 +218,70 @@ func (o *osResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, error
 
 	dnsClient := &dns.Client{Net: "udp"}
 	ch := make(chan *osResolverResult, numServers)
-	var wg sync.WaitGroup
-	wg.Add(len(o.nameservers))
+	wg := &sync.WaitGroup{}
+	wg.Add(numServers)
 	go func() {
 		wg.Wait()
 		close(ch)
 	}()
-	for _, server := range o.nameservers {
-		go func(server string) {
-			defer wg.Done()
-			answer, _, err := dnsClient.ExchangeContext(ctx, msg.Copy(), server)
-			ch <- &osResolverResult{answer: answer, err: err, isControlDPublicDNS: server == controldPublicDnsWithPort}
-		}(server)
-	}
 
+	do := func(servers []string, isLan bool) {
+		for _, server := range servers {
+			go func(server string) {
+				defer wg.Done()
+				answer, _, err := dnsClient.ExchangeContext(ctx, msg.Copy(), server)
+				ch <- &osResolverResult{answer: answer, err: err, server: server, lan: isLan}
+			}(server)
+		}
+	}
+	do(nss, true)
+	do(publicServers, false)
+
+	logAnswer := func(server string) {
+		if before, _, found := strings.Cut(server, ":"); found {
+			server = before
+		}
+		Log(ctx, ProxyLogger.Load().Debug(), "got answer from nameserver: %s", server)
+	}
 	var (
 		nonSuccessAnswer      *dns.Msg
+		nonSuccessServer      string
 		controldSuccessAnswer *dns.Msg
+		publicServerAnswer    *dns.Msg
+		publicServer          string
 	)
 	errs := make([]error, 0, numServers)
 	for res := range ch {
 		switch {
 		case res.answer != nil && res.answer.Rcode == dns.RcodeSuccess:
-			if res.isControlDPublicDNS {
+			switch {
+			case res.server == controldPublicDnsWithPort:
 				controldSuccessAnswer = res.answer // only use ControlD answer as last one.
-			} else {
+			case !res.lan && publicServerAnswer == nil:
+				publicServerAnswer = res.answer // use public DNS answer after LAN server..
+				publicServer = res.server
+			default:
 				cancel()
+				logAnswer(res.server)
 				return res.answer, nil
 			}
 		case res.answer != nil:
 			nonSuccessAnswer = res.answer
+			nonSuccessServer = res.server
 		}
 		errs = append(errs, res.err)
 	}
-	for _, answer := range []*dns.Msg{controldSuccessAnswer, nonSuccessAnswer} {
-		if answer != nil {
-			return answer, nil
-		}
+	if publicServerAnswer != nil {
+		logAnswer(publicServer)
+		return publicServerAnswer, nil
+	}
+	if controldSuccessAnswer != nil {
+		logAnswer(controldPublicDnsWithPort)
+		return controldSuccessAnswer, nil
+	}
+	if nonSuccessAnswer != nil {
+		logAnswer(nonSuccessServer)
+		return nonSuccessAnswer, nil
 	}
 	return nil, errors.Join(errs...)
 }
@@ -209,11 +328,12 @@ func LookupIP(domain string) []string {
 }
 
 func lookupIP(domain string, timeout int, withBootstrapDNS bool) (ips []string) {
-	resolver := &osResolver{nameservers: nameservers()}
+	nss := defaultNameservers()
 	if withBootstrapDNS {
-		resolver.nameservers = append([]string{net.JoinHostPort(controldBootstrapDns, "53")}, resolver.nameservers...)
+		nss = append([]string{net.JoinHostPort(controldBootstrapDns, "53")}, nss...)
 	}
-	ProxyLogger.Load().Debug().Msgf("resolving %q using bootstrap DNS %q", domain, resolver.nameservers)
+	resolver := newResolverWithNameserver(nss)
+	ProxyLogger.Load().Debug().Msgf("resolving %q using bootstrap DNS %q", domain, nss)
 	timeoutMs := 2000
 	if timeout > 0 && timeout < timeoutMs {
 		timeoutMs = timeout
@@ -286,12 +406,12 @@ func lookupIP(domain string, timeout int, withBootstrapDNS bool) (ips []string)
 //   - Gateway IP address (depends on OS).
 //   - Input servers.
 func NewBootstrapResolver(servers ...string) Resolver {
-	resolver := &osResolver{nameservers: nameservers()}
-	resolver.nameservers = append([]string{controldPublicDnsWithPort}, resolver.nameservers...)
+	nss := defaultNameservers()
+	nss = append([]string{controldPublicDnsWithPort}, nss...)
 	for _, ns := range servers {
-		resolver.nameservers = append([]string{net.JoinHostPort(ns, "53")}, resolver.nameservers...)
+		nss = append([]string{net.JoinHostPort(ns, "53")}, nss...)
 	}
-	return resolver
+	return NewResolverWithNameserver(nss)
 }
 
 // NewPrivateResolver returns an OS resolver, which includes only private DNS servers,
@@ -302,7 +422,7 @@ func NewBootstrapResolver(servers ...string) Resolver {
 //
 // This is useful for doing PTR lookup in LAN network.
 func NewPrivateResolver() Resolver {
-	nss := nameservers()
+	nss := defaultNameservers()
 	resolveConfNss := nameserversFromResolvconf()
 	localRfc1918Addrs := Rfc1918Addresses()
 	n := 0
@@ -328,10 +448,10 @@ func NewPrivateResolver() Resolver {
 		}
 	}
 	nss = nss[:n]
-	return NewResolverWithNameserver(nss)
+	return newResolverWithNameserver(nss)
 }
 
-// NewResolverWithNameserver returns an OS resolver which uses the given nameservers
+// NewResolverWithNameserver returns a Resolver which uses the given nameservers
 // for resolving DNS queries. If nameservers is empty, a dummy resolver will be returned.
 //
 // Each nameserver must be form "host:port". It's the caller responsibility to ensure all
@@ -340,13 +460,31 @@ func NewResolverWithNameserver(nameservers []string) Resolver {
 	if len(nameservers) == 0 {
 		return &dummyResolver{}
 	}
-	return &osResolver{nameservers: nameservers}
+	return newResolverWithNameserver(nameservers)
+}
+
+// newResolverWithNameserver returns an OS resolver from given nameservers list.
+// The caller must ensure each server in list is formed "ip:53".
+func newResolverWithNameserver(nameservers []string) *osResolver {
+	r := &osResolver{}
+	nss := slices.Sorted(slices.Values(nameservers))
+	for i, ns := range nss {
+		ip, _, _ := net.SplitHostPort(ns)
+		addr, _ := netip.ParseAddr(ip)
+		if isLanAddr(addr) {
+			r.currentLanServer.Store(&addr)
+			nss = slices.Delete(nss, i, i+1)
+			break
+		}
+	}
+	r.publicServer.Store(&nss)
+	return r
 }
 
 // Rfc1918Addresses returns the list of local interfaces private IP addresses
 func Rfc1918Addresses() []string {
 	var res []string
-	interfaces.ForeachInterface(func(i interfaces.Interface, prefixes []netip.Prefix) {
+	netmon.ForeachInterface(func(i netmon.Interface, prefixes []netip.Prefix) {
 		addrs, _ := i.Addrs()
 		for _, addr := range addrs {
 			ipNet, ok := addr.(*net.IPNet)
@@ -370,3 +508,11 @@ func newDialer(dnsAddress string) *net.Dialer {
 		},
 	}
 }
+
+// isLanAddr reports whether addr is considered a LAN ip address.
+func isLanAddr(addr netip.Addr) bool {
+	return addr.IsPrivate() ||
+		addr.IsLoopback() ||
+		addr.IsLinkLocalUnicast() ||
+		tsaddr.CGNATRange().Contains(addr)
+}

resolver_test.go

@@ -3,10 +3,13 @@ package ctrld
 import (
 	"context"
 	"net"
+	"slices"
 	"sync"
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/assert"
+
 	"github.com/miekg/dns"
 )
 
@@ -16,7 +19,8 @@ func Test_osResolver_Resolve(t *testing.T) {
 
 	go func() {
 		defer cancel()
-		resolver := &osResolver{nameservers: []string{"127.0.0.127:5353"}}
+		resolver := &osResolver{}
+		resolver.publicServer.Store(&[]string{"127.0.0.127:5353"})
 		m := new(dns.Msg)
 		m.SetQuestion("controld.com.", dns.TypeA)
 		m.RecursionDesired = true
@@ -69,7 +73,8 @@ func Test_osResolver_ResolveWithNonSuccessAnswer(t *testing.T) {
 			server.Shutdown()
 		}
 	}()
-	resolver := &osResolver{nameservers: ns}
+	resolver := &osResolver{}
+	resolver.publicServer.Store(&ns)
 	msg := new(dns.Msg)
 	msg.SetQuestion(".", dns.TypeNS)
 	answer, err := resolver.Resolve(context.Background(), msg)
@@ -81,6 +86,19 @@ func Test_osResolver_ResolveWithNonSuccessAnswer(t *testing.T) {
 	}
 }
 
+func Test_osResolver_InitializationRace(t *testing.T) {
+	var wg sync.WaitGroup
+	n := 10
+	wg.Add(n)
+	for range n {
+		go func() {
+			defer wg.Done()
+			InitializeOsResolver()
+		}()
+	}
+	wg.Wait()
+}
+
 func Test_upstreamTypeFromEndpoint(t *testing.T) {
 	tests := []struct {
 		name         string
@@ -134,3 +152,42 @@ func runLocalPacketConnTestServer(t *testing.T, pc net.PacketConn, handler dns.H
 	waitLock.Lock()
 	return server, addr, nil
 }
+
+func Test_initializeOsResolver(t *testing.T) {
+	lanServer1 := "192.168.1.1"
+	lanServer2 := "10.0.10.69"
+	wanServer := "1.1.1.1"
+	publicServers := []string{net.JoinHostPort(wanServer, "53")}
+
+	// First initialization.
+	initializeOsResolver([]string{lanServer1, wanServer})
+	p := or.currentLanServer.Load()
+	assert.NotNil(t, p)
+	assert.Equal(t, lanServer1, p.String())
+	assert.True(t, slices.Equal(*or.publicServer.Load(), publicServers))
+
+	// No new LAN server, current LAN server -> last LAN server.
+	initializeOsResolver([]string{lanServer1, wanServer})
+	p = or.currentLanServer.Load()
+	assert.Nil(t, p)
+	p = or.lastLanServer.Load()
+	assert.NotNil(t, p)
+	assert.Equal(t, lanServer1, p.String())
+	assert.True(t, slices.Equal(*or.publicServer.Load(), publicServers))
+
+	// New LAN server detected.
+	initializeOsResolver([]string{lanServer2, lanServer1, wanServer})
+	p = or.currentLanServer.Load()
+	assert.NotNil(t, p)
+	assert.Equal(t, lanServer2, p.String())
+	p = or.lastLanServer.Load()
+	assert.NotNil(t, p)
+	assert.Equal(t, lanServer1, p.String())
+	assert.True(t, slices.Equal(*or.publicServer.Load(), publicServers))
+
+	// No LAN server available.
+	initializeOsResolver([]string{wanServer})
+	assert.Nil(t, or.currentLanServer.Load())
+	assert.Nil(t, or.lastLanServer.Load())
+	assert.True(t, slices.Equal(*or.publicServer.Load(), publicServers))
+}