https://bugzilla.mindrot.org/show_bug.cgi?id=3220
Bug ID: 3220
Summary: Possible bug if ControlMaster + ControlPersist and
`-t`
Product: Portable OpenSSH
Version: 8.4p1
Hardware: Other
OS: Linux
Status: NEW
Severity: enhancement
Priority: P5
Component: ssh
Assignee: [email protected]
Reporter: [email protected]
Steps to reproduce:
$ cat ~/.ssh/config
ControlMaster auto
ControlPath ~/.ssh/connections/%r@%h:%p
ControlPersist 1
Host workstation
HostName remote.example.com
HostKeyAlias workstation
ForwardX11 yes
ForwardX11Timeout 10h
AddKeysToAgent yes
ForwardAgent yes
With two local terminal sessions A and B.
A: ssh workstation
B: ssh workstation
A: logout
The ssh connection to workstation is immediately completed but stderr
gets an extra message
Shared connection to remote.example.com closed.
This is problematic for two reasons:
(1) The message is incorrect. The shared connection is in fact still
running because connection in terminal B is still using it. The message
should say "Disconnected from shared connection to %s".
(2) The whole message is only suitable for debugging and should not be
emitted in normal cases. I understand that it would be nice with `-v`.
The problematic code is at
https://github.com/openssh/openssh-portable/blob/396d32f3a1a16e54df2a76b2a9b237868580dcbe/mux.c#L2081
Note that all the other mux related messages are emitted with debug1:
ssh -v workstation
...
debug1: Authentication succeeded (publickey).
Authenticated to remote.example.com ([1.2.3.4]:22).
debug1: setting up multiplex master socket
debug1: channel 0: new
[/home/USER/.ssh/connections/[email protected]:22]
debug1: control_persist_detach: backgrounding master process
debug1: forking to background
debug1: Entering interactive session.
debug1: pledge: id
debug1: multiplexing control connection
debug1: channel 1: new [mux-control]
debug1: channel 2: new [client-session]
debug1: client_input_global_request: rtype [email protected]
want_reply 0
debug1: Requesting X11 forwarding with authentication spoofing.
debug1: Requesting authentication agent forwarding.
debug1: Sending environment.
...
debug1: mux_client_request_session: master session id: 2
As a result, I would suggest that the above code should be fixed to
emit
the message at level debug1 only AND the actual message content should
be fixed, too.
Note that the actual verbose output already says during disconnect
...
debug1: client_input_channel_req: channel 2 rtype exit-status reply 0
debug1: client_input_channel_req: channel 2 rtype [email protected] reply
0
debug1: channel 2: free: client-session, nchannels 3
debug1: channel 1: free: mux-control, nchannels 2
Shared connection to remote.example.com closed.
USER@LOCALDOMAIN:~ $ debug1: ControlPersist timeout expired
debug1: channel 0: free:
/home/USER/.ssh/connections/[email protected]:22, nchannels 1
Transferred: sent 3684, received 3904 bytes, in 158.6 seconds
Bytes per second: sent 23.2, received 24.6
debug1: Exit status -1
Note how the message in question is emitted and ssh process ends (local
prompt is displayed) before ControlPersist timout actually happens.
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