intra: do not reroute dns meant for ipn.Exit

when firestack sees its own traffic routed back in, the proxy-id is set
to ipn.Exit. In such cases, simply dial out to the address rather than
override DNS to be sent to user-set upstream.

intra/tcp.go

@@ -155,26 +155,6 @@ func (h *tcpHandler) forward(local net.Conn, remote net.Conn, summary *SocketSum
 	go h.sendNotif(summary)
 }
 
-func filteredPort(addr net.Addr) int16 {
-	_, port, err := net.SplitHostPort(addr.String())
-	if err != nil {
-		return -1
-	}
-	if port == "80" {
-		return 80
-	}
-	if port == "443" {
-		return 443
-	}
-	if port == "0" {
-		return 0
-	}
-	if port == "53" {
-		return 53
-	}
-	return -1
-}
-
 // must always be called from a goroutine
 func (h *tcpHandler) sendNotif(summary *SocketSummary) {
 	// sleep a bit to avoid scenario where kotlin-land
@@ -320,7 +300,7 @@ func (h *tcpHandler) Handle(conn net.Conn, target *net.TCPAddr, summary *SocketS
 
 	pid := summary.PID
 
-	if h.dnsOverride(conn, target) {
+	if pid != ipn.Exit && h.dnsOverride(conn, target) {
 		return nil
 	}
 
@@ -420,6 +400,7 @@ func undoAlg(r dnsx.Resolver, algip net.IP) (realips, domains, blocklists string
 	return
 }
 
+// returns proxy-id, conn-id, user-id
 func splitPidCidUid(decision *Mark) (pid, cid, uid string) {
 	if decision == nil {
 		return

intra/udp.go

@@ -391,7 +391,7 @@ func (h *udpHandler) Connect(conn core.UDPConn, target *net.UDPAddr) (res *Mark,
 		return res, errUdpFirewalled // disconnect
 	}
 
-	if h.isDns(target) {
+	if pid != ipn.Exit && h.isDns(target) {
 		return res, nil // connect
 	}
 
@@ -462,15 +462,15 @@ func (h *udpHandler) ReceiveTo(conn core.UDPConn, data []byte, addr *net.UDPAddr
 	nsraddr := conn.RemoteAddr()
 	raddr := addr
 
-	if h.dnsOverride(conn, addr, data) {
-		log.D("udp: egress: dns-override for dstaddr(%v) <- src(l:%v r:%v)", raddr, nsladdr, nsraddr)
-		return nil
-	}
-
 	h.RLock()
 	nat, ok1 := h.udpConns[conn]
 	h.RUnlock()
 
+	if nat.pid != ipn.Exit && h.dnsOverride(conn, addr, data) {
+		log.D("udp: egress: dns-override for dstaddr(%v) <- src(l:%v r:%v)", raddr, nsladdr, nsraddr)
+		return nil
+	}
+
 	if !ok1 {
 		log.W("udp: egress: no nat(%v -> %v [%v])", nsladdr, raddr, nsraddr)
 		return fmt.Errorf("conn %v -> %v [%v] does not exist", nsladdr, raddr, nsraddr)