Fix critical bugs in session opening for TCP and UDP in case of Singleplex mode. (#145)

* Fix critical bugs in session opening for TCP and UDP in case of Singleplex mode.

- In case of TCP, don't open the session in the listener accept thread. This
  causes resource exhaustion of the tcp listener backlog queue in case of internet
  connection disruption or timeout.

- In case of UDP, don't create a new session for every UDP packet.

* Fix race in integration test.

* Fix race condition in session maker

* Code style improvements

* Explicit session.Close() call is indeed needed

Co-authored-by: Andy Wang <cbeuw.andy@gmail.com>

cmd/ck-client/ck-client.go

@@ -169,6 +169,7 @@ func main() {
 		}
 		log.Infof("Listening on %v %v for %v client", network, localConfig.LocalAddr, authInfo.ProxyMethod)
 		seshMaker = func() *mux.Session {
+			authInfo := authInfo // copy the struct because we are overwriting SessionId
 			// sessionID is usergenerated. There shouldn't be a security concern because the scope of
 			// sessionID is limited to its UID.
 			quad := make([]byte, 4)
@@ -184,12 +185,12 @@ func main() {
 			return net.ListenUDP("udp", udpAddr)
 		}
 
-		client.RouteUDP(acceptor, localConfig.Timeout, seshMaker)
+		client.RouteUDP(acceptor, localConfig.Timeout, remoteConfig.Singleplex, seshMaker)
 	} else {
 		listener, err := net.Listen("tcp", localConfig.LocalAddr)
 		if err != nil {
 			log.Fatal(err)
 		}
-		client.RouteTCP(listener, localConfig.Timeout, seshMaker)
+		client.RouteTCP(listener, localConfig.Timeout, remoteConfig.Singleplex, seshMaker)
 	}
 }

internal/client/piper.go

@@ -10,7 +10,7 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-func RouteUDP(bindFunc func() (*net.UDPConn, error), streamTimeout time.Duration, newSeshFunc func() *mux.Session) {
+func RouteUDP(bindFunc func() (*net.UDPConn, error), streamTimeout time.Duration, singleplex bool, newSeshFunc func() *mux.Session) {
 	var sesh *mux.Session
 	localConn, err := bindFunc()
 	if err != nil {
@@ -27,18 +27,22 @@ func RouteUDP(bindFunc func() (*net.UDPConn, error), streamTimeout time.Duration
 			continue
 		}
 
-		if sesh == nil || sesh.IsClosed() || sesh.Singleplex {
+		if !singleplex && (sesh == nil || sesh.IsClosed()) {
 			sesh = newSeshFunc()
 		}
 
 		stream, ok := streams[addr.String()]
 		if !ok {
+			if singleplex {
+				sesh = newSeshFunc()
+			}
+
 			stream, err = sesh.OpenStream()
 			if err != nil {
-				log.Errorf("Failed to open stream: %v", err)
+				if singleplex {
-				if sesh.Singleplex {
 					sesh.Close()
 				}
+				log.Errorf("Failed to open stream: %v", err)
 				continue
 			}
 
@@ -74,7 +78,7 @@ func RouteUDP(bindFunc func() (*net.UDPConn, error), streamTimeout time.Duration
 	}
 }
 
-func RouteTCP(listener net.Listener, streamTimeout time.Duration, newSeshFunc func() *mux.Session) {
+func RouteTCP(listener net.Listener, streamTimeout time.Duration, singleplex bool, newSeshFunc func() *mux.Session) {
 	var sesh *mux.Session
 	for {
 		localConn, err := listener.Accept()
@@ -82,10 +86,14 @@ func RouteTCP(listener net.Listener, streamTimeout time.Duration, newSeshFunc fu
 			log.Fatal(err)
 			continue
 		}
-		if sesh == nil || sesh.IsClosed() || sesh.Singleplex {
+		if !singleplex && (sesh == nil || sesh.IsClosed()) {
 			sesh = newSeshFunc()
 		}
 		go func(sesh *mux.Session, localConn net.Conn, timeout time.Duration) {
+			if singleplex {
+				sesh = newSeshFunc()
+			}
+
 			data := make([]byte, 10240)
 			_ = localConn.SetReadDeadline(time.Now().Add(streamTimeout))
 			i, err := io.ReadAtLeast(localConn, data, 1)
@@ -101,7 +109,7 @@ func RouteTCP(listener net.Listener, streamTimeout time.Duration, newSeshFunc fu
 			if err != nil {
 				log.Errorf("Failed to open stream: %v", err)
 				localConn.Close()
-				if sesh.Singleplex {
+				if singleplex {
 					sesh.Close()
 				}
 				return
@@ -125,5 +133,4 @@ func RouteTCP(listener net.Listener, streamTimeout time.Duration, newSeshFunc fu
 			}
 		}(sesh, localConn, streamTimeout)
 	}
-
 }

internal/test/integration_test.go

@@ -185,7 +185,9 @@ func establishSession(lcc client.LocalConnConfig, rcc client.RemoteConnConfig, a
 	//									whatever connection initiator (including a proper ck-client)
 
 	netToCkServerD, ckServerListener := connutil.DialerListener(10 * 1024)
+
 	clientSeshMaker := func() *mux.Session {
+		ai := ai
 		quad := make([]byte, 4)
 		common.RandRead(ai.WorldState.Rand, quad)
 		ai.SessionId = binary.BigEndian.Uint32(quad)
@@ -206,12 +208,12 @@ func establishSession(lcc client.LocalConnConfig, rcc client.RemoteConnConfig, a
 			addrCh <- conn.LocalAddr().(*net.UDPAddr)
 			return conn, err
 		}
-		go client.RouteUDP(acceptor, lcc.Timeout, clientSeshMaker)
+		go client.RouteUDP(acceptor, lcc.Timeout, rcc.Singleplex, clientSeshMaker)
 		proxyToCkClientD = mDialer
 	} else {
 		var proxyToCkClientL *connutil.PipeListener
 		proxyToCkClientD, proxyToCkClientL = connutil.DialerListener(10 * 1024)
-		go client.RouteTCP(proxyToCkClientL, lcc.Timeout, clientSeshMaker)
+		go client.RouteTCP(proxyToCkClientL, lcc.Timeout, rcc.Singleplex, clientSeshMaker)
 	}
 
 	// set up server