openssh bugs - Feb 2010 - [Bug 1719] New: Debug server prints debug messages on client

https://bugzilla.mindrot.org/show_bug.cgi?id=1719

           Summary: Debug server prints debug messages on client
           Product: Portable OpenSSH
           Version: 5.4p1
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: sshd
        AssignedTo: unassigned-bugs at mindrot.org
        ReportedBy: petesea at bigfoot.com


A server started with debugging options (eg "sshd -e -ddd -p4242")
will
print debug and "Environment" messages on the client:

   $ ssh -p4242 127.0.0.1 'date'
   Environment:
     USER=...
     LOGNAME=...
     HOME=...
     PATH=...
     MAIL=...
     SHELL=...
     SSH_CLIENT=...
     SSH_CONNECTION=...
   debug3: channel 0: close_fds r -1 w -1 e -1 c -1
   Sat Feb 27 11:52:32 PST 2010

It's often useful to start a debug server to help track down problems
without interfering with the client... and those extra client-side
debug and "Environment" messages can cause issues for things that
indirectly run ssh (like cvs and svn) if they aren't expecting the
output.

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Darren Tucker <dtucker at zip.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dtucker at zip.com.au

--- Comment #1 from Darren Tucker <dtucker at zip.com.au> 2010-04-09
14:19:47 EST ---
You can prevent (most of this) by specifying -e to sshd, eg:

/usr/local/sbin/sshd -De -o loglevel=debug3 -p 2022

however it looks like there's an extra debug that didn't used to be
there.

$ ssh -p 2022 localhost
Last login: Fri Apr  9 13:23:49 2010 from ...
debug3: channel 0: close_fds r -1 w -1 e -1
$

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--- Comment #2 from petesea at bigfoot.com 2010-04-10 03:13:42 EST ---
(In reply to comment #1)
> You can prevent (most of this) by specifying -e to sshd, eg:
> 
> /usr/local/sbin/sshd -De -o loglevel=debug3 -p 2022
This is true, BUT -D is not the same thing as -d.   The reason I'm
using -d is so the server only runs one time and then exits.  This
doesn't happen with -D.   And as you point out, even with -D
-ologlevel=debug3, there is still a debug3 message generated on the
client.

Running -d or -dd will generate the "Environment" message on the
client, which is actually more troublesome then the "debug" message
generated with -ddd, because it's not an obvious debug message.

I'd be happy to supply a patch for this, but I'm at a loss as to why
the "Environment" and errant "debug3" messages are generated
on the
client.  How does setting debug on the server trigger debug on the
client, but only for some messages?   Does it have to do with when the
message is printed with regards to the creation of the tunnel?

The "Environment" message appears to be coming from session.c line
1299
(as of CVS 2010-04-09).  That code is wrapped with "if (debug_flag)". 
The "debug3" message appears to come from channels.c line 375.  How is
checking the debug_flag and/or calling the debug3() function different
at those points then another other point in the code?

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--- Comment #3 from Damien Miller <djm at mindrot.org> 2010-11-24 11:54:42
EST ---
Created attachment 1965
  --> https://bugzilla.mindrot.org/attachment.cgi?id=1965
/home/djm/ssh-undebug-post-fork.diff

quell debug that appears post-session fork

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #1965|                            |ok?(dtucker at zip.com.au)
              Flags|                            |

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |djm at mindrot.org
             Blocks|                            |1803

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Darren Tucker <dtucker at zip.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #1965|ok?(dtucker at zip.com.au)     |ok+
              Flags|                            |

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Damien Miller <djm at mindrot.org> changed:

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

--- Comment #4 from Damien Miller <djm at mindrot.org> 2010-11-24 12:28:11
EST ---
Printing the environment is intentional, since it is useful in
debugging the server and getting it out of the server's own debug
output would require quite a bit of rearrangement.

The just-attached patch to quell the spurious close_fds debug message
has been committed and will be in 5.7. I'd recommend using "sshd
-DeoLoglevel=debug3" when you want to run a debug server that doesn't
alter client behaviour in any way.

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Damien Miller <djm at mindrot.org> changed:

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

--- Comment #5 from Damien Miller <djm at mindrot.org> 2011-01-24 12:33:51
EST ---
Move resolved bugs to CLOSED after 5.7 release

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