net/interfaces: return all Tailscale addresses from Tailscale().

Signed-off-by: David Anderson <danderson@tailscale.com>

cmd/tsshd/tsshd.go

@@ -59,11 +59,11 @@ func main() {
 
 	warned := false
 	for {
-		addr, iface, err := interfaces.Tailscale()
+		addrs, iface, err := interfaces.Tailscale()
 		if err != nil {
 			log.Fatalf("listing interfaces: %v", err)
 		}
-		if addr == nil {
+		if len(addrs) == 0 {
 			if !warned {
 				log.Printf("no tailscale interface found; polling until one is available")
 				warned = true
@@ -75,6 +75,13 @@ func main() {
 			continue
 		}
 		warned = false
+		var addr netaddr.IP
+		for _, a := range addrs {
+			if a.Is4() {
+				addr = a
+				break
+			}
+		}
 		listen := net.JoinHostPort(addr.String(), fmt.Sprint(*port))
 		log.Printf("tailscale ssh server listening on %v, %v", iface.Name, listen)
 		s := &ssh.Server{

net/interfaces/interfaces.go

@@ -26,7 +26,7 @@ var LoginEndpointForProxyDetermination = "https://login.tailscale.com/"
 // Tailscale returns the current machine's Tailscale interface, if any.
 // If none is found, all zero values are returned.
 // A non-nil error is only returned on a problem listing the system interfaces.
-func Tailscale() (net.IP, *net.Interface, error) {
+func Tailscale() ([]netaddr.IP, *net.Interface, error) {
 	ifs, err := net.Interfaces()
 	if err != nil {
 		return nil, nil, err
@@ -39,14 +39,18 @@ func Tailscale() (net.IP, *net.Interface, error) {
 		if err != nil {
 			continue
 		}
+		var tsIPs []netaddr.IP
 		for _, a := range addrs {
 			if ipnet, ok := a.(*net.IPNet); ok {
 				nip, ok := netaddr.FromStdIP(ipnet.IP)
 				if ok && tsaddr.IsTailscaleIP(nip) {
-					return ipnet.IP, &iface, nil
+					tsIPs = append(tsIPs, nip)
 				}
 			}
 		}
+		if len(tsIPs) > 0 {
+			return tsIPs, &iface, nil
+		}
 	}
 	return nil, nil, nil
 }