From fed5af68e69da70e4a63b5519dea71a1d2ea1934 Mon Sep 17 00:00:00 2001
From: Milos Gajdos <milosgajdos83@gmail.com>
Date: Tue, 15 Oct 2019 15:03:47 +0100
Subject: [PATCH] Handle Accept errors gracefully.

Originally when Accept fails we log the error and let the program flow
continue. This can lead to us spawning handling connection go routines
on nil connections which in turn leads to Go panics.
---
 network/default.go | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/network/default.go b/network/default.go
index 6952aaa2..a6c759c7 100644
--- a/network/default.go
+++ b/network/default.go
@@ -269,14 +269,21 @@ func (n *network) acceptNetConn(l tunnel.Listener, recv chan *transport.Message)
 	for {
 		// accept a connection
 		conn, err := l.Accept()
-		if err != nil {
-			log.Debugf("Network tunnel [%s] accept error: %v", NetworkChannel, err)
-		}
 
 		select {
 		case <-n.closed:
+			// only try to close the connection if it has been successfully opened
+			if err != nil {
+				if closeErr := conn.Close(); closeErr != nil {
+					log.Debugf("Network tunnel [%s] failed to close connection: %v", NetworkChannel, closeErr)
+				}
+			}
 			return
 		default:
+			if err != nil {
+				log.Debugf("Network tunnel [%s] accept error: %v", NetworkChannel, err)
+				continue
+			}
 			// go handle NetworkChannel connection
 			go n.handleNetConn(conn, recv)
 		}
@@ -558,14 +565,21 @@ func (n *network) acceptCtrlConn(l tunnel.Listener, recv chan *transport.Message
 	for {
 		// accept a connection
 		conn, err := l.Accept()
-		if err != nil {
-			log.Debugf("Network tunnel [%s] accept error: %v", ControlChannel, err)
-		}
 
 		select {
 		case <-n.closed:
+			// only try to close the connection if it has been successfully opened
+			if err != nil {
+				if closeErr := conn.Close(); closeErr != nil {
+					log.Debugf("Network tunnel [%s] failed to close connection: %v", ControlChannel, closeErr)
+				}
+			}
 			return
 		default:
+			if err != nil {
+				log.Debugf("Network tunnel [%s] accept error: %v", ControlChannel, err)
+				continue
+			}
 			// go handle ControlChannel connection
 			go n.handleCtrlConn(conn, recv)
 		}