openssh bugs - Oct 2007 - [Bug 1384] New: OpenSSH clients causing deadlocks

https://bugzilla.mindrot.org/show_bug.cgi?id=1384

           Summary: OpenSSH clients causing deadlocks
    Classification: Unclassified
           Product: Portable OpenSSH
           Version: 4.7p1
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ssh
        AssignedTo: bitbucket at mindrot.org
        ReportedBy: jca at newtonesque.kicks-ass.net


OpenSSH clients (in all releases I have been able to test with,
including 4.7p1) when talking protocol version 2 seem to be sending
SSH_MSG_CHANNEL_REQUEST messages with the want_reply field set to 0.
This leads to a problem when the server they interact with does not
support the service being requested.

    If the channel request is for, say, command execution, and the
server does not support such a capability, a standards-compliant
server won't send anything back at that point - because the OpenSSH
client has set the want_reply field to 0. However, the OpenSSH client
seems to be assuming that this request will always be successful. That
is, that servers will always support this capability. Because of this
assumption, a deadlock ensues.

    This is a bug in the OpenSSH client. It is true that for some
channel requests (e.g. things like, say, X11 and XON/XOFF requests)
the client can proceed (and does proceed) without the server replying
anything, but for others (most notably SHELL and EXEC) it can't. The
OpenSSH client should always set want_reply to 1 when sending such
requests, in order to prevent deadlocks like the one described above.

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https://bugzilla.mindrot.org/show_bug.cgi?id=1384


Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|OpenSSH clients causing     |client hangs against server
                   |deadlocks                   |lacking common channel
                   |                            |requests
           Severity|normal                      |minor
                 CC|                            |djm at mindrot.org




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https://bugzilla.mindrot.org/show_bug.cgi?id=1384





--- Comment #1 from Damien Miller <djm at mindrot.org>  2008-05-08
23:12:18 ---
A fix for this bug has been committed and will be in OpenSSH 5.1:

> CVSROOT:        /cvs
> Module name:    src
> Changes by:     djm at cvs.openbsd.org     2008/05/08 07:06:11
> 
> Modified files:
>         usr.bin/ssh    : clientloop.c clientloop.h ssh.c
> 
> Log message:
> Use new channel status confirmation callback system to properly deal
> with "important" channel requests that fail, in particular
command exec,
> shell and subsystem requests. Previously we would optimistically assume
> that the requests would always succeed, which could cause hangs if they
> did not (e.g. when the server runs out of fds) or were unimplemented by
> the server (bz #1384)
> 
> Also, properly report failing multiplex channel requests via the mux
> client stderr (subject to LogLevel in the mux master) - better than
> silently failing.
> 
> most bits ok markus@ (as part of a larger diff)
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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED




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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |1452




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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED




--- Comment #2 from Damien Miller <djm at mindrot.org>  2008-07-22
12:20:12 ---
Mass update RESOLVED->CLOSED after release of openssh-5.1

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