cmd/lopower: force AAAA records in DNS server

Change-Id: I79582e4ffd468c217df3e8c02bbf65d911a4f0fe
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/lopower/lopower.go

@@ -623,14 +623,19 @@ func (lp *lpServer) startTSNet(ctx context.Context) {
 		log.Fatal(err)
 	}
 
-	lp.tsnet = &tsnet.Server{
+	ts := &tsnet.Server{
 		Dir:       filepath.Join(lp.dir, "tsnet"),
 		Hostname:  hostname,
 		UserLogf:  log.Printf,
 		Ephemeral: false,
 	}
+	lp.tsnet = ts
+	ts.PreStart = func() error {
+		ts.Sys().DNSManager.Get().SetForceAAAA(true)
+		return nil
+	}
 
-	if _, err := lp.tsnet.Up(ctx); err != nil {
+	if _, err := ts.Up(ctx); err != nil {
 		log.Fatal(err)
 	}
 }

ipn/ipnlocal/local.go

@@ -4194,7 +4194,11 @@ func (b *LocalBackend) authReconfig() {
 	disableSubnetsIfPAC := nm.HasCap(tailcfg.NodeAttrDisableSubnetsIfPAC)
 	userDialUseRoutes := nm.HasCap(tailcfg.NodeAttrUserDialUseRoutes)
 	dohURL, dohURLOK := exitNodeCanProxyDNS(nm, b.peers, prefs.ExitNodeID())
-	dcfg := dnsConfigForNetmap(nm, b.peers, prefs, b.keyExpired, b.logf, version.OS())
+	var forceAAAA bool
+	if dm, ok := b.sys.DNSManager.GetOK(); ok {
+		forceAAAA = dm.GetForceAAAA()
+	}
+	dcfg := dnsConfigForNetmap(nm, b.peers, prefs, b.keyExpired, forceAAAA, b.logf, version.OS())
 	// If the current node is an app connector, ensure the app connector machine is started
 	b.reconfigAppConnectorLocked(nm, prefs)
 	b.mu.Unlock()
@@ -4294,7 +4298,7 @@ func shouldUseOneCGNATRoute(logf logger.Logf, controlKnobs *controlknobs.Knobs,
 //
 // The versionOS is a Tailscale-style version ("iOS", "macOS") and not
 // a runtime.GOOS.
-func dnsConfigForNetmap(nm *netmap.NetworkMap, peers map[tailcfg.NodeID]tailcfg.NodeView, prefs ipn.PrefsView, selfExpired bool, logf logger.Logf, versionOS string) *dns.Config {
+func dnsConfigForNetmap(nm *netmap.NetworkMap, peers map[tailcfg.NodeID]tailcfg.NodeView, prefs ipn.PrefsView, selfExpired, forceAAAA bool, logf logger.Logf, versionOS string) *dns.Config {
 	if nm == nil {
 		return nil
 	}
@@ -4357,7 +4361,7 @@ func dnsConfigForNetmap(nm *netmap.NetworkMap, peers map[tailcfg.NodeID]tailcfg.
 			// https://github.com/tailscale/tailscale/issues/1152
 			// tracks adding the right capability reporting to
 			// enable AAAA in MagicDNS.
-			if addr.Addr().Is6() && have4 {
+			if addr.Addr().Is6() && have4 && !forceAAAA {
 				continue
 			}
 			ips = append(ips, addr.Addr())

ipn/ipnlocal/local_test.go

@@ -1298,7 +1298,7 @@ func TestDNSConfigForNetmapForExitNodeConfigs(t *testing.T) {
 			}
 
 			prefs := &ipn.Prefs{ExitNodeID: tc.exitNode, CorpDNS: true}
-			got := dnsConfigForNetmap(nm, peersMap(tc.peers), prefs.View(), false, t.Logf, "")
+			got := dnsConfigForNetmap(nm, peersMap(tc.peers), prefs.View(), false, false, t.Logf, "")
 			if !resolversEqual(t, got.DefaultResolvers, tc.wantDefaultResolvers) {
 				t.Errorf("DefaultResolvers: got %#v, want %#v", got.DefaultResolvers, tc.wantDefaultResolvers)
 			}

net/dns/manager.go

@@ -63,7 +63,8 @@ type Manager struct {
 	mu sync.Mutex // guards following
 	// config is the last configuration we successfully compiled or nil if there
 	// was any failure applying the last configuration.
-	config *Config
+	config    *Config
+	forceAAAA bool // whether client wants MagicDNS AAAA even if unsure of host's IPv6 status
 }
 
 // NewManagers created a new manager from the given config.
@@ -128,6 +129,18 @@ func (m *Manager) GetBaseConfig() (OSConfig, error) {
 	return m.os.GetBaseConfig()
 }
 
+func (m *Manager) GetForceAAAA() bool {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	return m.forceAAAA
+}
+
+func (m *Manager) SetForceAAAA(v bool) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.forceAAAA = v
+}
+
 // setLocked sets the DNS configuration.
 //
 // m.mu must be held.

tsnet/tsnet.go

@@ -121,6 +121,11 @@ type Server struct {
 	// field at zero unless you know what you are doing.
 	Port uint16
 
+	// PreStart is an optional hook to run just before LocalBackend.Start,
+	// to reconfigure internals. If it returns an error, Server.Start
+	// will return that error, wrapper.
+	PreStart func() error
+
 	getCertForTesting func(*tls.ClientHelloInfo) (*tls.Certificate, error)
 
 	initOnce         sync.Once
@@ -616,6 +621,13 @@ func (s *Server) start() (reterr error) {
 	prefs.ControlURL = s.ControlURL
 	prefs.RunWebClient = s.RunWebClient
 	authKey := s.getAuthKey()
+
+	if f := s.PreStart; f != nil {
+		if err := f(); err != nil {
+			return fmt.Errorf("PreStart: %w", err)
+		}
+	}
+
 	err = lb.Start(ipn.Options{
 		UpdatePrefs: prefs,
 		AuthKey:     authKey,