Fix Tailscale endpoint using wrong source IP with advertise_routes

protocol/tailscale/endpoint.go

@@ -341,26 +341,42 @@ func (t *Endpoint) DialContext(ctx context.Context, network string, destination
 		}
 		return N.DialSerial(ctx, t, network, destination, destinationAddresses)
 	}
-	addr := tcpip.FullAddress{
+	addr4, addr6 := t.server.TailscaleIPs()
+	remoteAddr := tcpip.FullAddress{
 		NIC:  1,
 		Port: destination.Port,
 		Addr: addressFromAddr(destination.Addr),
 	}
+	var localAddr tcpip.FullAddress
 	var networkProtocol tcpip.NetworkProtocolNumber
 	if destination.IsIPv4() {
+		if !addr4.IsValid() {
+			return nil, E.New("missing Tailscale IPv4 address")
+		}
 		networkProtocol = header.IPv4ProtocolNumber
+		localAddr = tcpip.FullAddress{
+			NIC:  1,
+			Addr: addressFromAddr(addr4),
+		}
 	} else {
+		if !addr6.IsValid() {
+			return nil, E.New("missing Tailscale IPv6 address")
+		}
 		networkProtocol = header.IPv6ProtocolNumber
+		localAddr = tcpip.FullAddress{
+			NIC:  1,
+			Addr: addressFromAddr(addr6),
+		}
 	}
 	switch N.NetworkName(network) {
 	case N.NetworkTCP:
-		tcpConn, err := gonet.DialContextTCP(ctx, t.stack, addr, networkProtocol)
+		tcpConn, err := gonet.DialTCPWithBind(ctx, t.stack, localAddr, remoteAddr, networkProtocol)
 		if err != nil {
 			return nil, err
 		}
 		return tcpConn, nil
 	case N.NetworkUDP:
-		udpConn, err := gonet.DialUDP(t.stack, nil, &addr, networkProtocol)
+		udpConn, err := gonet.DialUDP(t.stack, &localAddr, &remoteAddr, networkProtocol)
 		if err != nil {
 			return nil, err
 		}