[SSHD-151] Direct TCP/IP Port Forward sends EOF to client after closing channel

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.6.0
• Fix Version/s: 0.7.0
• Assignee: Guillaume Nodet
• Reporter: Kevin Winchester
• Created: 30/Nov/11 18:26
• Updated: 30/Jan/13 20:20
• Resolved: 21/May/12 15:42

Description

While testing port forwarding from an OpenSSH_5.8p2 client to a MINA SSHD server, I noticed that after the first disconnection of a client from the forwarded port, the entire SSH session would be disconnected. The client command I ran was:

ssh -N -L 60443:<target>:443 -p 50022 tester@<minasshd>

Looking at the traces, I saw the following from SSHD:

13:54:12.823 [NioProcessor-1] DEBUG o.a.s.server.session.ServerSession - Received packet SSH_MSG_CHANNEL_OPEN
13:54:12.823 [NioProcessor-1] INFO o.a.s.server.session.ServerSession - Received SSH_MSG_CHANNEL_OPEN direct-tcpip
13:54:12.826 [NioProcessor-1] INFO o.a.s.s.channel.ChannelDirectTcpip - Receiving request for direct tcpip: hostToConnect=<target>, portToConnect=443, originatorIpAddress=127.0.0.1, originatorPort=54145
13:54:15.588 [NioProcessor-1] DEBUG o.a.s.server.session.ServerSession - Received packet SSH_MSG_CHANNEL_EOF
13:54:15.589 [NioProcessor-1] INFO o.a.s.s.channel.ChannelDirectTcpip - Received SSH_MSG_CHANNEL_EOF on channel 0
13:54:15.589 [NioProcessor-1] INFO o.a.s.s.channel.ChannelDirectTcpip - Send SSH_MSG_CHANNEL_CLOSE on channel 0
13:54:15.590 [NioProcessor-1] DEBUG o.a.s.server.session.ServerSession - Received packet SSH_MSG_CHANNEL_CLOSE
13:54:15.590 [NioProcessor-1] INFO o.a.s.s.channel.ChannelDirectTcpip - Received SSH_MSG_CHANNEL_CLOSE on channel 0
13:54:15.590 [NioProcessor-1] INFO o.a.s.s.channel.ChannelDirectTcpip - Closing channel 0 immediately
13:54:15.591 [NioProcessor-1] INFO o.a.s.s.channel.ChannelDirectTcpip - Closing channel 0 immediately
13:54:15.593 [NioProcessor-26] INFO o.a.s.s.channel.ChannelDirectTcpip - Send SSH_MSG_CHANNEL_EOF on channel 0
13:54:15.595 [NioProcessor-1] DEBUG o.a.s.server.session.ServerSession - Received packet SSH_MSG_DISCONNECT
13:54:15.595 [NioProcessor-1] INFO o.a.s.server.session.ServerSession - Received SSH_MSG_DISCONNECT (reason=2, msg=Received ieof for nonexistent channel 2.)
13:54:15.595 [NioProcessor-1] INFO o.a.s.server.session.ServerSession - Closing session
13:54:15.595 [NioProcessor-1] DEBUG o.a.s.server.session.ServerSession - Closing IoSession
13:54:15.596 [NioProcessor-1] DEBUG o.a.s.server.session.ServerSession - IoSession closed

So if I read this right, the client sends an EOF, then the server sends a CLOSE, then the client sends a CLOSE. After all of this, the server sends back an EOF, but the channel no longer exists at the client, which causes a disconnection.

I looked into the source code, and figured the following change might correct the issue:

Index: sshd-core/src/main/java/org/apache/sshd/server/channel/ChannelDirectTcpip.java
===================================================================
— sshd-core/src/main/java/org/apache/sshd/server/channel/ChannelDirectTcpip.java (revision 1207930)
+++ sshd-core/src/main/java/org/apache/sshd/server/channel/ChannelDirectTcpip.java (working copy)
@@ -109,7 +109,9 @@

@Override
public void sessionClosed(IoSession session) throws Exception {
+ if (!closing)

{ sendEof(); + }

}
};
connector.setHandler(handler);

It appears to work, but I do not know if it is correct, or if it will break other situations. Can anyone comment on it?

Issue Links

• is cloned by: SSHD-207 ChannelForward TCP/IP sends EOF to server after closing channel
• relates to: SSHD-206 Race between SSH_MSG_CHANNEL_DATA and SSH_MSG_CHANNEL_CLOSE in ChannelForwardedTcpip?