cmd/ctrld: ensure cleaning up done when self-uninstall

While at it, also making DNS reset always use DHCP.

cmd/ctrld/cli.go

@@ -111,11 +111,7 @@ func initCLI() {
 			initCache()
 
 			if iface == "auto" {
-				dri, err := interfaces.DefaultRouteInterface()
-				if err != nil {
-					mainLog.Error().Err(err).Msg("failed to get default route interface")
-				}
-				iface = dri
+				iface = defaultIfaceName()
 			}
 
 			if daemon {
@@ -450,6 +446,7 @@ func readConfigFile(writeDefaultConfig bool) bool {
 	err := v.ReadInConfig()
 	if err == nil {
 		fmt.Println("loading config file from:", v.ConfigFileUsed())
+		defaultConfigFile = v.ConfigFileUsed()
 		return true
 	}
 
@@ -529,6 +526,12 @@ func processCDFlags() {
 			stderrMsg(err.Error())
 			return
 		}
+		if iface == "auto" {
+			iface = defaultIfaceName()
+		}
+		if netIface, _ := netIfaceFromName(iface); netIface != nil {
+			_ = resetDNS(netIface)
+		}
 		tasks := []task{{s.Uninstall, true}}
 		if doTasks(tasks) {
 			log.Println("uninstalled service")
@@ -623,3 +626,11 @@ func netIfaceFromName(ifaceName string) (*net.Interface, error) {
 	}
 	return iface, err
 }
+
+func defaultIfaceName() string {
+	dri, err := interfaces.DefaultRouteInterface()
+	if err != nil {
+		mainLog.Error().Err(err).Msg("failed to get default route interface")
+	}
+	return dri
+}

cmd/ctrld/os_linux.go

@@ -8,6 +8,10 @@ import (
 	"os/exec"
 	"strings"
 
+	"github.com/insomniacslk/dhcp/dhcpv4"
+	"github.com/insomniacslk/dhcp/dhcpv4/client4"
+	"github.com/insomniacslk/dhcp/dhcpv6"
+	"github.com/insomniacslk/dhcp/dhcpv6/client6"
 	"tailscale.com/net/dns"
 	"tailscale.com/util/dnsname"
 
@@ -45,7 +49,7 @@ func setDNS(iface *net.Interface, nameservers []string) error {
 		mainLog.Error().Err(err).Msg("failed to create DNS OS configurator")
 		return err
 	}
-
+	defer r.Close()
 	ns := make([]netip.Addr, 0, len(nameservers))
 	for _, nameserver := range nameservers {
 		ns = append(ns, netip.MustParseAddr(nameserver))
@@ -56,11 +60,44 @@ func setDNS(iface *net.Interface, nameservers []string) error {
 	})
 }
 
-func resetDNS(iface *net.Interface, nameservers []string) error {
-	if err := setDNS(iface, nameservers); err != nil {
-		mainLog.Error().Err(err).Msg("resetDNS failed.")
+func resetDNS(iface *net.Interface) error {
+	c := client4.NewClient()
+	conversation, err := c.Exchange(iface.Name)
+	if err != nil {
 		return err
 	}
+	for _, packet := range conversation {
+		if packet.MessageType() == dhcpv4.MessageTypeAck {
+			nameservers := packet.DNS()
+			ns := make([]string, 0, len(nameservers))
+			for _, nameserver := range nameservers {
+				ns = append(ns, nameserver.String())
+			}
+			_ = setDNS(iface, ns)
+		}
+	}
+
+	if supportsIPv6() {
+		c := client6.NewClient()
+		conversation, err := c.Exchange(iface.Name)
+		if err != nil {
+			return err
+		}
+		for _, packet := range conversation {
+			if packet.Type() == dhcpv6.MessageTypeReply {
+				msg, err := packet.GetInnerMessage()
+				if err != nil {
+					return err
+				}
+				nameservers := msg.Options.DNS()
+				ns := make([]string, 0, len(nameservers))
+				for _, nameserver := range nameservers {
+					ns = append(ns, nameserver.String())
+				}
+				_ = setDNS(iface, ns)
+			}
+		}
+	}
 	return nil
 }
 

cmd/ctrld/os_mac.go

@@ -6,6 +6,8 @@ package main
 import (
 	"net"
 	"os/exec"
+
+	"github.com/Control-D-Inc/ctrld/internal/resolvconffile"
 )
 
 // allocate loopback ip
@@ -44,7 +46,7 @@ func setDNS(iface *net.Interface, nameservers []string) error {
 }
 
 // TODO(cuonglm): use system API
-func resetDNS(iface *net.Interface, _ []string) error {
+func resetDNS(iface *net.Interface) error {
 	cmd := "networksetup"
 	args := []string{"-setdnsservers", iface.Name, "empty"}
 
@@ -56,5 +58,5 @@ func resetDNS(iface *net.Interface, _ []string) error {
 }
 
 func currentDNS(_ *net.Interface) []string {
-	return nil
+	return resolvconffile.NameServers("")
 }

cmd/ctrld/os_windows.go

@@ -4,7 +4,6 @@
 package main
 
 import (
-	"bytes"
 	"errors"
 	"net"
 	"os/exec"
@@ -39,14 +38,18 @@ func setDNS(iface *net.Interface, nameservers []string) error {
 }
 
 // TODO(cuonglm): should we use system API?
-func resetDNS(iface *net.Interface, nameservers []string) error {
-	if err := resetDNSUseDHCP(iface); err != nil {
-		mainLog.Debug().Err(err).Msg("could not reset DNS using DHCP")
+func resetDNS(iface *net.Interface) error {
+	if supportsIPv6ListenLocal() {
+		if output, err := netsh("interface", "ipv6", "set", "dnsserver", strconv.Itoa(iface.Index), "dhcp"); err != nil {
+			mainLog.Warn().Err(err).Msgf("failed to reset ipv6 DNS: %s", string(output))
+		}
 	}
-	if len(nameservers) == 0 {
-		return nil
+	output, err := netsh("interface", "ipv4", "set", "dnsserver", strconv.Itoa(iface.Index), "dhcp")
+	if err != nil {
+		mainLog.Error().Err(err).Msgf("failed to reset ipv4 DNS: %s", string(output))
+		return err
 	}
-	return setDNS(iface, nameservers)
+	return nil
 }
 
 func setPrimaryDNS(iface *net.Interface, dns string) error {
@@ -80,28 +83,11 @@ func addSecondaryDNS(iface *net.Interface, dns string) error {
 	return nil
 }
 
-func resetDNSUseDHCP(iface *net.Interface) error {
-	if supportsIPv6ListenLocal() {
-		if output, err := netsh("interface", "ipv6", "set", "dnsserver", strconv.Itoa(iface.Index), "dhcp"); err != nil {
-			mainLog.Warn().Err(err).Msgf("failed to reset ipv6 DNS: %s", string(output))
-		}
-	}
-	output, err := netsh("interface", "ipv4", "set", "dnsserver", strconv.Itoa(iface.Index), "dhcp")
-	if err != nil {
-		mainLog.Error().Err(err).Msgf("failed to reset ipv4 DNS: %s", string(output))
-		return err
-	}
-	return nil
-}
-
 func netsh(args ...string) ([]byte, error) {
 	return exec.Command("netsh", args...).Output()
 }
 
 func currentDNS(iface *net.Interface) []string {
-	if hasDNSFromDHCP(iface, "ipv4") || hasDNSFromDHCP(iface, "ipv6") {
-		return nil
-	}
 	luid, err := winipcfg.LUIDFromIndex(uint32(iface.Index))
 	if err != nil {
 		mainLog.Error().Err(err).Msg("failed to get interface LUID")
@@ -118,9 +104,3 @@ func currentDNS(iface *net.Interface) []string {
 	}
 	return ns
 }
-
-func hasDNSFromDHCP(iface *net.Interface, ipVer string) bool {
-	idx := strconv.Itoa(iface.Index)
-	output, _ := netsh("interface", ipVer, "show", "dnsservers", idx)
-	return bytes.Contains(output, []byte(" through DHCP:"))
-}

cmd/ctrld/prog.go

@@ -23,9 +23,8 @@ var svcConfig = &service.Config{
 }
 
 type prog struct {
-	cfg     *ctrld.Config
-	cache   dnscache.Cacher
-	origDNS []string
+	cfg   *ctrld.Config
+	cache dnscache.Cacher
 }
 
 func (p *prog) Start(s service.Service) error {
@@ -40,7 +39,6 @@ func (p *prog) run() {
 		if err != nil {
 			mainLog.Error().Err(err).Msg("could not get interface")
 		} else {
-			p.origDNS = currentDNS(netIface)
 			if err := setDNS(netIface, []string{cfg.Listener["0"].IP}); err != nil {
 				mainLog.Error().Err(err).Str("iface", iface).Msgf("could not set DNS for interface")
 			}
@@ -179,7 +177,7 @@ func (p *prog) Stop(s service.Service) error {
 	}
 	if iface != "" {
 		if netIface, err := netIfaceFromName(iface); err == nil {
-			if err := resetDNS(netIface, p.origDNS); err != nil {
+			if err := resetDNS(netIface); err != nil {
 				mainLog.Error().Err(err).Str("iface", iface).Msgf("could not reset DNS")
 			}
 		} else {