openssh bugs - Sep 2005 - [Bug 1086] X forwarding won't start when a command is executed in background

http://bugzilla.mindrot.org/show_bug.cgi?id=1086

           Summary: X forwarding won't start when a command is executed in
                    background
           Product: Portable OpenSSH
           Version: 4.2p1
          Platform: All
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: sshd
        AssignedTo: bitbucket at mindrot.org
        ReportedBy: t8m at centrum.cz


This is actually a regression against openssh-4.1p1.

Try: ssh -Y user at host "(sleep 5; xterm) &"

After 5 seconds it will print: xterm Xt error: Can't open display:
localhost:10.0

It will work fine on openssh-4.1p1 server.



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dtucker at zip.com.au changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED




------- Additional Comments From dtucker at zip.com.au  2005-09-20 11:45 -------
It appears to be fallout from this change (channels.c rev 1.200 and session.c
rev 1.302):

   - djm at cvs.openbsd.org 2005/07/17 06:49:04
     [channels.c channels.h session.c session.h]
     Fix a number of X11 forwarding channel leaks:
     1. Refuse multiple X11 forwarding requests on the same session
     2. Clean up all listeners after a single_connection X11 forward, not just
        the one that made the single connection
     3. Destroy X11 listeners when the session owning them goes away
     testing and ok dtucker@

It's probably (3) since the "()&" causes the child of sshd to
exit immediately.
 Maybe it needs to wait until the session close completes before destroying the
X11 listeners? 



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------- Additional Comments From djm at mindrot.org  2005-09-23 18:57 -------
hm, this is tricky: the /session/ is closed immediately upon child exit, but the
/channel/ persists after this time (until read EOF or error). 

The X11 listeners need to be shut down when the /channel/ goes away, but we
don't have any way to mark the listeners as dependant on the channel. The
choices are:

1. Move x11_chanids from "struct Session" into "struct
Channel", so we can
deallocate them with a cleanup function. (ugly layering violation, but we
already have several of these)

2. Don't session_close() a session until its undelying channel goes away
entirely. This may be a good way to do it - just don't deallocate the
channel in
session_exit_message(), instead let the channel close callback take care of it
(include X11 closure)

3. Make all sessions share a single X11 listener. This could be simple, but it
would move us further away from supporting multiple X11 forwarding in the future
(if we ever chose to do it)





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------- Additional Comments From djm at mindrot.org  2005-09-23 19:36 -------
4. Continue tracking the x11_chanids in session.c in a separate structure to the
session and detach them using a channel callback registered after the normal one
is detached in session_exit_message()

(the obvious approach [2] turns out not to work for reasons that aren't
entirely
clear to me).




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djm at mindrot.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|bitbucket at mindrot.org       |djm at mindrot.org




------- Additional Comments From djm at mindrot.org  2005-09-24 11:47 -------
Created an attachment (id=964)
 --> (http://bugzilla.mindrot.org/attachment.cgi?id=964&action=view)
Probable fix

This is approach #4, creating a new list of X11 channels and the session
channels that they depend upon in session.c.

Please test - we need tests of this particular bug, but also regress and
general usage.



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