cmd/tailscale/cli: do not allow turning Funnel on while shields-up (#7770)

ipn/ipnlocal/local.go

@@ -2549,6 +2549,9 @@ func (b *LocalBackend) checkPrefsLocked(p *ipn.Prefs) error {
 	if err := b.checkExitNodePrefsLocked(p); err != nil {
 		errs = append(errs, err)
 	}
+	if err := b.checkFunnelEnabledLocked(p); err != nil {
+		errs = append(errs, err)
+	}
 	return multierr.New(errs...)
 }
 
@@ -2633,6 +2636,13 @@ func (b *LocalBackend) checkExitNodePrefsLocked(p *ipn.Prefs) error {
 	return nil
 }
 
+func (b *LocalBackend) checkFunnelEnabledLocked(p *ipn.Prefs) error {
+	if p.ShieldsUp && b.serveConfig.IsFunnelOn() {
+		return errors.New("Cannot enable shields-up when Funnel is enabled.")
+	}
+	return nil
+}
+
 func (b *LocalBackend) EditPrefs(mp *ipn.MaskedPrefs) (ipn.PrefsView, error) {
 	b.mu.Lock()
 	if mp.EggSet {

ipn/ipnlocal/serve.go

@@ -218,6 +218,11 @@ func (b *LocalBackend) SetServeConfig(config *ipn.ServeConfig) error {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
+	prefs := b.pm.CurrentPrefs()
+	if config.IsFunnelOn() && prefs.ShieldsUp() {
+		return errors.New("Unable to turn on Funnel while shields-up is enabled")
+	}
+
 	nm := b.netMap
 	if nm == nil {
 		return errors.New("netMap is nil")

ipn/serve.go

@@ -163,6 +163,12 @@ func (sc *ServeConfig) IsServingWeb(port uint16) bool {
 	return sc.TCP[port].HTTPS
 }
 
+// IsFunnelOn checks if ServeConfig is currently allowing
+// funnel traffic for any host:port.
+//
+// View version of ServeConfig.IsFunnelOn.
+func (v ServeConfigView) IsFunnelOn() bool { return v.ж.IsFunnelOn() }
+
 // IsFunnelOn checks if ServeConfig is currently allowing
 // funnel traffic for any host:port.
 func (sc *ServeConfig) IsFunnelOn() bool {