wgengine/router: [bsd/darwin] remove and readd routes on profile change

Noticed when testing FUS on tailscale-on-macOS, that routing would break
completely when switching between profiles. However, it would start working
again when going back to the original profile tailscaled started with.

Turns out that if we change the addrs on the interface we need to remove and readd
all the routes.

Updates #713

Signed-off-by: Maisem Ali <maisem@tailscale.com>

wgengine/router/router_userspace_bsd.go

@@ -26,7 +26,7 @@ type userspaceBSDRouter struct {
 	linkMon *monitor.Mon
 	tunname string
 	local   []netip.Prefix
-	routes  map[netip.Prefix]struct{}
+	routes  map[netip.Prefix]bool
 }
 
 func newUserspaceBSDRouter(logf logger.Logf, tundev tun.Device, linkMon *monitor.Mon) (Router, error) {
@@ -102,15 +102,19 @@ func (r *userspaceBSDRouter) Set(cfg *Config) (reterr error) {
 		cfg = &shutdownConfig
 	}
 
-	var errq error
 	setErr := func(err error) {
-		if errq == nil {
-			errq = err
+		if reterr == nil {
+			reterr = err
 		}
 	}
+	addrsToRemove := r.addrsToRemove(cfg.LocalAddrs)
+
+	// If we're removing all addresses, we need to remove and re-add all
+	// routes.
+	resetRoutes := len(r.local) > 0 && len(addrsToRemove) == len(r.local)
 
 	// Update the addresses.
-	for _, addr := range r.addrsToRemove(cfg.LocalAddrs) {
+	for _, addr := range addrsToRemove {
 		arg := []string{"ifconfig", r.tunname, inet(addr), addr.String(), "-alias"}
 		out, err := cmd(arg...).CombinedOutput()
 		if err != nil {
@@ -137,7 +141,7 @@ func (r *userspaceBSDRouter) Set(cfg *Config) (reterr error) {
 		}
 	}
 
-	newRoutes := make(map[netip.Prefix]struct{})
+	newRoutes := make(map[netip.Prefix]bool)
 	for _, route := range cfg.Routes {
 		if runtime.GOOS != "darwin" && route == tsaddr.TailscaleULARange() {
 			// Because we added the interface address as a /48 above,
@@ -145,11 +149,11 @@ func (r *userspaceBSDRouter) Set(cfg *Config) (reterr error) {
 			// implicitly. We mustn't try to add/delete it ourselves.
 			continue
 		}
-		newRoutes[route] = struct{}{}
+		newRoutes[route] = true
 	}
 	// Delete any preexisting routes.
 	for route := range r.routes {
-		if _, keep := newRoutes[route]; !keep {
+		if resetRoutes || !newRoutes[route] {
 			net := netipx.PrefixIPNet(route)
 			nip := net.IP.Mask(net.Mask)
 			nstr := fmt.Sprintf("%v/%d", nip, route.Bits())
@@ -169,7 +173,7 @@ func (r *userspaceBSDRouter) Set(cfg *Config) (reterr error) {
 	}
 	// Add the routes.
 	for route := range newRoutes {
-		if _, exists := r.routes[route]; !exists {
+		if resetRoutes || !r.routes[route] {
 			net := netipx.PrefixIPNet(route)
 			nip := net.IP.Mask(net.Mask)
 			nstr := fmt.Sprintf("%v/%d", nip, route.Bits())
@@ -185,12 +189,12 @@ func (r *userspaceBSDRouter) Set(cfg *Config) (reterr error) {
 	}
 
 	// Store the interface and routes so we know what to change on an update.
-	if errq == nil {
+	if reterr == nil {
 		r.local = append([]netip.Prefix{}, cfg.LocalAddrs...)
 	}
 	r.routes = newRoutes
 
-	return errq
+	return reterr
 }
 
 func (r *userspaceBSDRouter) Close() error {