Refresh macOS VPN DNS after pf stabilization

cmd/cli/dns_intercept_darwin.go

@@ -1207,7 +1207,6 @@ func stringSlicesEqual(a, b []string) bool {
 	return true
 }
 
-
 // pfStartStabilization enters stabilization mode, suppressing all pf restores
 // until the VPN's ruleset stops changing. This prevents a death spiral where
 // ctrld and the VPN repeatedly overwrite each other's pf rules.
@@ -1284,6 +1283,10 @@ func (p *prog) pfStabilizationLoop(ctx context.Context, stableRequired time.Dura
 			p.pfStabilizing.Store(false)
 			mainLog.Load().Info().Msgf("DNS intercept: pf stable for %s — restoring anchor rules", stableRequired)
 			p.ensurePFAnchorActive()
+			routes, domainlessServers, exemptions := p.refreshDNSAfterVPNSettle("pf_stabilized")
+			if routes == 0 && domainlessServers == 0 && exemptions == 0 {
+				p.scheduleDNSAfterVPNSettleRefresh("pf_stabilized_followup", pfAnchorRecheckDelayLong)
+			}
 			p.pfLastRestoreTime.Store(time.Now().UnixMilli())
 			return
 		}
@@ -1446,6 +1449,15 @@ func (p *prog) ensurePFAnchorActive() bool {
 	return true
 }
 
+func (p *prog) scheduleDNSAfterVPNSettleRefresh(reason string, delay time.Duration) {
+	time.AfterFunc(delay, func() {
+		if p.dnsInterceptState == nil {
+			return
+		}
+		p.refreshDNSAfterVPNSettle(reason)
+	})
+}
+
 // pfWatchdog periodically checks that our pf anchor is still active.
 // Other programs (e.g., Windscribe desktop app, macOS configd) can replace
 // scheduleDelayedRechecks schedules delayed re-checks after a network change event.

cmd/cli/dns_intercept_settle.go

@@ -0,0 +1,50 @@
+package cli
+
+import "github.com/Control-D-Inc/ctrld"
+
+var initializeOsResolver = ctrld.InitializeOsResolver
+
+func (p *prog) refreshDNSAfterVPNSettle(reason string) (routes, domainlessServers, exemptions int) {
+	mainLog.Load().Info().Msgf("DNS intercept: refreshing OS/VPN DNS route state after VPN settle (%s)", reason)
+	ns := initializeOsResolver(true)
+	mainLog.Load().Debug().Msgf("DNS intercept: post-settle OS resolver nameservers: %v", ns)
+
+	if p.vpnDNS == nil {
+		mainLog.Load().Debug().Msg("DNS intercept: post-settle VPN DNS route refresh skipped — manager unavailable")
+		return 0, 0, 0
+	}
+
+	beforeExemptions := p.vpnDNS.CurrentExemptions()
+	routes, domainlessServers, exemptions = p.vpnDNS.RefreshRoutesOnly()
+	afterExemptions := p.vpnDNS.CurrentExemptions()
+
+	if vpnDNSExemptionsEqual(beforeExemptions, afterExemptions) {
+		mainLog.Load().Info().Msgf("DNS intercept: post-settle VPN DNS route refresh completed — %d routes, %d domainless servers, %d exemptions (pf unchanged)",
+			routes, domainlessServers, exemptions)
+		return routes, domainlessServers, exemptions
+	}
+
+	if err := p.exemptVPNDNSServers(afterExemptions); err != nil {
+		mainLog.Load().Warn().Err(err).Msg("DNS intercept: post-settle VPN DNS exemption update failed")
+	} else {
+		mainLog.Load().Info().Msgf("DNS intercept: post-settle VPN DNS exemptions changed — updated pf/WFP with %d exemptions", len(afterExemptions))
+	}
+	return routes, domainlessServers, exemptions
+}
+
+func vpnDNSExemptionsEqual(a, b []vpnDNSExemption) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	seen := make(map[vpnDNSExemption]int, len(a))
+	for _, ex := range a {
+		seen[ex]++
+	}
+	for _, ex := range b {
+		if seen[ex] == 0 {
+			return false
+		}
+		seen[ex]--
+	}
+	return true
+}

cmd/cli/dns_intercept_settle_test.go

@@ -0,0 +1,49 @@
+package cli
+
+import (
+	"context"
+	"testing"
+
+	"github.com/Control-D-Inc/ctrld"
+)
+
+func TestRefreshDNSAfterVPNSettleRefreshesOSResolverAndVPNRoutes(t *testing.T) {
+	oldInitialize := initializeOsResolver
+	defer func() { initializeOsResolver = oldInitialize }()
+
+	var initialized []bool
+	initializeOsResolver = func(force bool) []string {
+		initialized = append(initialized, force)
+		return []string{"10.102.26.10:53"}
+	}
+
+	var exemptionUpdates [][]vpnDNSExemption
+	p := &prog{}
+	p.vpnDNS = newVPNDNSManager(func(exemptions []vpnDNSExemption) error {
+		exemptionUpdates = append(exemptionUpdates, append([]vpnDNSExemption{}, exemptions...))
+		return nil
+	})
+	p.vpnDNS.discoverVPNDNS = func(context.Context) []ctrld.VPNDNSConfig {
+		return []ctrld.VPNDNSConfig{{
+			InterfaceName: "utun4",
+			Servers:       []string{"10.102.26.10"},
+			Domains:       []string{"bmwgroup.net"},
+		}}
+	}
+
+	routes, domainlessServers, exemptions := p.refreshDNSAfterVPNSettle("test")
+
+	if routes != 1 || domainlessServers != 0 || exemptions != 1 {
+		t.Fatalf("expected 1 route, 0 domainless servers, 1 exemption, got routes=%d domainless=%d exemptions=%d",
+			routes, domainlessServers, exemptions)
+	}
+	if len(initialized) != 1 || !initialized[0] {
+		t.Fatalf("expected forced OS resolver refresh once, got %v", initialized)
+	}
+	if got := p.vpnDNS.UpstreamForDomain("jira.cc.bmwgroup.net."); len(got) != 1 || got[0] != "10.102.26.10" {
+		t.Fatalf("expected refreshed VPN DNS route, got %v", got)
+	}
+	if len(exemptionUpdates) != 0 {
+		t.Fatalf("expected route-only refresh to avoid pf exemption updates, got %+v", exemptionUpdates)
+	}
+}

cmd/cli/vpn_dns.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 	"sync"
 
+	"github.com/rs/zerolog"
 	"tailscale.com/net/netmon"
 
 	"github.com/Control-D-Inc/ctrld"
@@ -94,6 +95,8 @@ func (m *vpnDNSManager) Refresh(guardAgainstNoNameservers bool) {
 	m.mu.Lock()
 	defer m.mu.Unlock()
 
+	previousExemptions := m.currentExemptionsLocked()
+
 	if vpnDNSSettlingEnabled && len(configs) == 0 && guardAgainstNoNameservers && m.hasVPNDNSStateLocked() {
 		if !m.retainedAfterEmptyDiscovery {
 			exemptions := m.currentExemptionsLocked()
@@ -180,14 +183,85 @@ func (m *vpnDNSManager) Refresh(guardAgainstNoNameservers bool) {
 	logger.Debug().Msgf("VPN DNS refresh completed: %d configs, %d routes, %d domainless servers, %d unique exemptions",
 		len(m.configs), len(m.routes), len(m.domainlessServers), len(exemptions))
 
-	// Update intercept rules to permit VPN DNS traffic.
-	// Always call onServersChanged — including when exemptions is empty — so that
-	// stale exemptions from a previous VPN session get cleared on disconnect.
-	if m.onServersChanged != nil {
-		if err := m.onServersChanged(exemptions); err != nil {
-			logger.Error().Err(err).Msg("Failed to update intercept exemptions for VPN DNS servers")
+	// Update intercept rules to permit VPN DNS traffic only when the exemption set
+	// actually changes. Network-change events can fire repeatedly while macOS/VPN
+	// state is otherwise identical; rewriting pf for identical exemptions can feed
+	// a self-triggering network-change loop. Empty exemptions are still applied
+	// when they differ from the previous set, so stale VPN exemptions are cleared
+	// on disconnect.
+	m.updateInterceptExemptionsIfChanged(logger, previousExemptions, exemptions, "VPN DNS")
+}
+
+func (m *vpnDNSManager) updateInterceptExemptionsIfChanged(logger *zerolog.Logger, before, after []vpnDNSExemption, reason string) {
+	if m.onServersChanged == nil {
+		return
+	}
+	if vpnDNSExemptionsEqual(before, after) {
+		logger.Debug().Msgf("VPN DNS exemptions unchanged after %s refresh; skipping intercept rule update", reason)
+		return
+	}
+	if err := m.onServersChanged(after); err != nil {
+		logger.Error().Err(err).Msg("Failed to update intercept exemptions for VPN DNS servers")
+	}
+}
+
+// RefreshRoutesOnly re-discovers VPN DNS configs and updates only ctrld's
+// in-memory split-DNS routes. It intentionally does not call onServersChanged,
+// so it does not rewrite/reload pf/WFP rules. Use this for post-settle discovery
+// checks where we only need to learn late-published VPN search domains.
+func (m *vpnDNSManager) RefreshRoutesOnly() (routes, domainlessServers, exemptions int) {
+	logger := mainLog.Load()
+
+	logger.Debug().Msg("Refreshing VPN DNS route state only")
+	discoverVPNDNS := m.discoverVPNDNS
+	if discoverVPNDNS == nil {
+		discoverVPNDNS = ctrld.DiscoverVPNDNS
+	}
+	configs := discoverVPNDNS(context.Background())
+
+	if dri, err := netmon.DefaultRouteInterface(); err == nil && dri != "" {
+		for i := range configs {
+			if configs[i].InterfaceName == dri {
+				configs[i].IsExitMode = true
+			}
 		}
 	}
+
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	m.retainedAfterEmptyDiscovery = false
+	m.configs = configs
+	m.routes = make(map[string][]string)
+
+	for _, config := range configs {
+		for _, domain := range config.Domains {
+			domain = strings.TrimPrefix(domain, "~")
+			domain = strings.TrimPrefix(domain, ".")
+			domain = strings.ToLower(domain)
+			if domain != "" {
+				m.routes[domain] = append([]string{}, config.Servers...)
+			}
+		}
+	}
+
+	var domainless []string
+	seenDomainless := make(map[string]bool)
+	for _, config := range configs {
+		if len(config.Domains) == 0 && len(config.Servers) > 0 {
+			for _, server := range config.Servers {
+				if !seenDomainless[server] {
+					seenDomainless[server] = true
+					domainless = append(domainless, server)
+				}
+			}
+		}
+	}
+	m.domainlessServers = domainless
+
+	logger.Debug().Msgf("VPN DNS route-only refresh completed: %d configs, %d routes, %d domainless servers, %d exemptions",
+		len(m.configs), len(m.routes), len(m.domainlessServers), len(m.currentExemptionsLocked()))
+	return len(m.routes), len(m.domainlessServers), len(m.currentExemptionsLocked())
 }
 
 func (m *vpnDNSManager) hasVPNDNSStateLocked() bool {

cmd/cli/vpn_dns_test.go

@@ -69,6 +69,31 @@ func TestVPNDNSRefreshClearsOnSecondGuardedEmptyDiscovery(t *testing.T) {
 	}
 }
 
+func TestVPNDNSRefreshSkipsUnchangedInterceptExemptions(t *testing.T) {
+	var updates [][]vpnDNSExemption
+	m := newVPNDNSManager(func(exemptions []vpnDNSExemption) error {
+		updates = append(updates, append([]vpnDNSExemption{}, exemptions...))
+		return nil
+	})
+	m.discoverVPNDNS = func(context.Context) []ctrld.VPNDNSConfig {
+		return []ctrld.VPNDNSConfig{{
+			InterfaceName: "utun-test",
+			Servers:       []string{"10.102.26.10"},
+			Domains:       []string{"example.internal"},
+		}}
+	}
+
+	m.Refresh(true)
+	m.Refresh(true)
+
+	if len(updates) != 1 {
+		t.Fatalf("expected exactly one intercept exemption update for unchanged VPN DNS state, got %d", len(updates))
+	}
+	if len(updates[0]) != 1 || updates[0][0].Server != "10.102.26.10" || updates[0][0].Interface != "utun-test" {
+		t.Fatalf("unexpected exemption update: %+v", updates[0])
+	}
+}
+
 func TestVPNDNSTransportFailureSuppressesFallbackOnlyWhileRetainingState(t *testing.T) {
 	withVPNDNSSettlingEnabled(t)
 	m := newVPNDNSManager(nil)