openssh bugs - Jul 2011 - [Bug 1917] New: Escape sequence (~) doesn't work right with ControlMaster/ControlPersist connections

https://bugzilla.mindrot.org/show_bug.cgi?id=1917

             Bug #: 1917
           Summary: Escape sequence (~) doesn't work right with
                    ControlMaster/ControlPersist connections
    Classification: Unclassified
           Product: Portable OpenSSH
           Version: 5.8p1
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ssh
        AssignedTo: unassigned-bugs at mindrot.org
        ReportedBy: mindrot-bugs at trk.nickurak.ca


When in a non-master ssh session connected to a Master session, ~. is
not captured, and therefore the connection cannot be terminated, and
the process cannot be easily closed. When a normal Master ssh process
is present, escapes can be used on it. This is doubly frustrating with
ControlPersist, where the Master connection is always in the background
and never directly accessible.

Open question: Should ~. terminate the master connection? Or should it
simply terminate the ssh client

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Damien Miller <djm at mindrot.org> changed:

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

--- Comment #1 from Damien Miller <djm at mindrot.org> 2011-07-06 05:41:18
EST ---
I can't replicate this - ~? and ~. work fine for slave connections of a
master running in ControlPersist mode. Are you sure you are running
5.8p1 on the client?

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--- Comment #2 from Jeremy Nickurak <mindrot-bugs at trk.nickurak.ca>
2011-07-06 05:55:25 EST ---
nickuj at nickuj:~$ ssh -V
OpenSSH_5.8p1 Debian-1ubuntu3, OpenSSL 0.9.8o 01 Jun 2010

It's the weirdest thing, I can't duplicate it any more either. I'll
keep an eye out to see if I can figure out what changed.

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--- Comment #3 from Jeremy Nickurak <mindrot-bugs at trk.nickurak.ca>
2011-07-06 05:59:29 EST ---
Just hit again. Seems like if the network goes out, the master
connection stalls, and the slave connection can't do escapes anymore.

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--- Comment #4 from Damien Miller <djm at mindrot.org> 2011-07-06 06:26:43
EST ---
Is there any chance you could catch the master where it is stalling
with strace/ktrace/truss/gdb?

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |powerman-asdf at ya.ru

--- Comment #5 from Damien Miller <djm at mindrot.org> 2011-09-22 21:57:53
EST ---
*** Bug 1938 has been marked as a duplicate of this bug. ***

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--- Comment #6 from Alex Efros <powerman-asdf at ya.ru> 2011-09-22
22:07:00 EST ---
I'm not a C developer, but if you provide me (link to) instructions how
to run strace/ktrace/truss/gdb to get info for you - I'll do it when
faced with this problem next time.

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David Woodhouse <dwmw2 at infradead.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dwmw2 at infradead.org

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--- Comment #7 from Damien Miller <djm at mindrot.org> 2011-09-24 14:00:18
EST ---
gdb:

1. find the pid of the unresponsive ssh process using "ps auxww | grep
ssh"

2. attach to it using gdb "gdb /path/to/ssh" then "attach
PID" (using
the pid you found in step (1).

3. Capture a backtrace "where". 

The others depend on which platform you are on. Generally it is a
matter of running "strace -p PID" (or similar for the others). ktrace
is a little different, because you need to start the trace (using
ktrace) then dump the output using kdump later. Check the manpage for
the tool for your system.

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--- Comment #8 from Damien Miller <djm at mindrot.org> 2011-10-21 11:16:47
EST ---
I got a chance to catch a ssh client in this state the other day and
connect to it with a debugger for a couple of minutes before
ServerAliveInterval killed it.

It turns out that the first ~. is actually killing the session, but for
some reason the session isn't being released.

Notes for next time:

1) clear server_alive_count_max to get a longer debugging session
2) try attaching before issuing ~.
3) reset log channel to syslog and loglevel to debug3

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--- Comment #9 from Jeremy Nickurak <mindrot-bugs at trk.nickurak.ca>
2011-11-11 09:15:51 EST ---
I've been hitting this pretty frequently lately, sshing into a machine
with ControlPersist turned on (so the master connection is in a
forked-off background process), and then rebooting it. As soon as the
connection's gone, the session is frozen and ~. won't help, you have to
kill the master process manually.

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