openssh bugs - Dec 2007 - [Bug 1424] New: Cannot signal a process over a channel (rfc 4254, section 6 .9)

https://bugzilla.mindrot.org/show_bug.cgi?id=1424

           Summary: Cannot signal a process over a channel (rfc 4254,
                    section 6.9)
    Classification: Unclassified
           Product: Portable OpenSSH
           Version: 4.7p1
          Platform: ix86
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: sshd
        AssignedTo: bitbucket at mindrot.org
        ReportedBy: dazuma at gmail.com


It does not appear that sshd in OpenSSH implements section 6.9 of rfc
4254. That is, sending SSH_MSG_CHANNEL_REQUEST with type "signal" for
a
channel, has no effect.

This is being reproduced with a custom client, connecting to OpenSSH
4.7p1 sshd running on Linux (Fedora 8 package openssh-4.7p1-4.fc8). I
opened a channel, started a simple long-running remote process (e.g.
sleep) with an "exec", and then attempted to send the "TERM"
signal as
described in the rfc, with want_reply set to TRUE. The server sent back
SSH_MSG_CHANNEL_FAILURE, and the process was unaffected.

However, I do not believe this is platform-specific or usage-specific.
Looking at the code for session.c in cvs, it appears that the function
session_input_channel_req does not recognize an rtype of "signal".
http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/session.c?rev=1.224

This appears to have been reported before on the mailing list, but
there were no replies, and I could not find a bug open for it.
http://marc.info/?l=openssh-unix-dev&m=115992994907390&w=2

Also see this thread from some years ago, which includes a patch
against an older version of OpenSSH:
http://marc.info/?l=openssh-unix-dev&m=104300802407848&w=2

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--- Comment #1 from Darren Tucker <dtucker at zip.com.au>  2008-01-01
10:31:47 ---
Created an attachment (id=1432)
 --> (http://bugzilla.mindrot.org/attachment.cgi?id=1432)
Implement "signal" channel request type, server and client.

Please try this patch, which is based on the one posted by Markus.

The client interace is not documented, but it's an escape sequence
command line:

[CR]~C (should give you the "ssh> " prompt, then
-SHUP

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--- Comment #2 from Daniel Azuma <dazuma at gmail.com>  2008-01-08
08:40:43 ---
(In reply to comment #1)
> Created an attachment (id=1432)
 --> (http://bugzilla.mindrot.org/attachment.cgi?id=1432)
[details]
> Implement "signal" channel request type, server and client.
> 
> Please try this patch, which is based on the one posted by Markus.
> 
> The client interace is not documented, but it's an escape sequence
> command line:
> 
> [CR]~C (should give you the "ssh> " prompt, then
> -SHUP
I haven't tested the client, but the server side of your patch appears
to work. I applied it to the CVS head (as of about noon -0800 on 07 Jan
2008), and compiled and ran sshd on a Fedora 8 i386 box. Sending the
TERM signal from my custom client (based on ruby Net::SSH) now appears
to work as expected.

To get it to compile, I did have to modify your patch to add the
following line to misc.c:

#include <signal.h>

Thanks! Looking forward to seeing this in the release version.

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--- Comment #3 from Daniel Azuma <dazuma at gmail.com>  2008-01-08
09:19:35 ---
(In reply to comment #2)
> I haven't tested the client, but the server side of your patch appears
> to work. I applied it to the CVS head (as of about noon -0800 on 07 Jan
> 2008), and compiled and ran sshd on a Fedora 8 i386 box. Sending the
> TERM signal from my custom client (based on ruby Net::SSH) now appears
> to work as expected.
Sorry, a little (probably unnecessary) clarification... my "applied to
cvs head" != "checked in". I'm not a maintainer. Just
mentioning that
the patch seems to work against my test case. I'd still like to see it
get into cvs and an official release, though, since I'd rather wait for
it to trickle into the package management of our linux distribution
before installing onto our production servers.

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
Attachment #1432 is|0                           |1
           obsolete|                            |




--- Comment #4 from Darren Tucker <dtucker at zip.com.au>  2008-01-08
13:16:30 ---
Created an attachment (id=1438)
 --> (http://bugzilla.mindrot.org/attachment.cgi?id=1438)
Move signo2name functions to channels.c

Minor tweak to the patch: move the signal no -> name functions to
channels.c.  This saves ~120 bytes in some of the other programs the
link in misc.o via libssh.a but don't actually need those channel name
functions.

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--- Comment #5 from Damien Miller <djm at mindrot.org>  2008-01-20
06:42:12 ---
(From update of attachment 1438)
>+} no2name[] = {
>+	{ SIGABRT,	"ABRT" },
>+	{ SIGALRM,	"ALRM" },
>+	{ SIGFPE,	"FPE" },
>+	{ SIGHUP,	"HUP" },
>+	{ SIGILL,	"ILL" },
>+	{ SIGINT,	"INT" },
>+	{ SIGKILL,	"KILL" },
>+	{ SIGPIPE,	"PIPE" },
>+	{ SIGQUIT,	"QUIT" },
>+	{ SIGSEGV,	"SEGV" },
>+	{ SIGTERM,	"TERM" },
>+	{ SIGUSR1,	"USR1" },
>+	{ SIGUSR2,	"USR2" },
I don't think it makes sense to automatically pass some of these from
the client to the server. E.g. SIGSEGV, SIGFPE, SIGILL, SIGBUS,
SIGPIPE, SIGALRM and SIGABRT should be considered "internal" and never
passed (or acted upon by the server).

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

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




--- Comment #6 from Darren Tucker <dtucker at zip.com.au>  2008-01-20
09:50:33 ---
(In reply to comment #5)
> I don't think it makes sense to automatically pass some of these from
> the client to the server. E.g. SIGSEGV, SIGFPE, SIGILL, SIGBUS,
> SIGPIPE, SIGALRM and SIGABRT should be considered "internal" and
never
> passed (or acted upon by the server).
The list of signals is specified in the RFC, but while we can generate
(and process) all of these, only the ones for which the client has a
signal handler will be automatically passed on.

I'm not entirely happy with the client interface, but it worked for
testing.  (Should also interop test with at least one other
implementation, I think PuTTY has it these days.)

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Martin Oberhuber <martin.oberhuber at windriver.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |martin.oberhuber at windriver.
                   |                            |com




--- Comment #7 from Martin Oberhuber <martin.oberhuber at windriver.com> 
2008-09-30 21:38:09 ---
This may be interesting for us. Is there any plan to get this patch
released?

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Andrew Hayden <andrew.hayden at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrew.hayden at gmail.com




--- Comment #8 from Andrew Hayden <andrew.hayden at gmail.com>  2008-11-21
03:11:18 ---
I'm voting for this one.  I sent an email to openssh-unix-dev and
Darren Tucker was kind enough to point me here.

I'm building an app based on JSch, a Java implementation of SSH2, and I
strongly desire the ability to send SIGINT and SIGKILL to the remote
processes that will be spawned via my program.  Currently I have no
clean way to do this, but this patch should allow it.

I concur with Damien Miller (though I am not a contributor) that some
of these signals make little or no sense to send through to clients.  I
would imagine that HUP, INT and KILL are probably the most frequent use
cases for remote clients trying to talk to something they've spawned on
the other side of the channel.  USR1 and USR2 probably make sense as
well for custom magic.

Would people be more comfortable committing this if the signals that
Damien lists as inappropriate (SIGSEGV, SIGFPE, SIGILL, SIGBUS,
SIGPIPE, SIGALRM and SIGABRT) are suppressed?

As a gentle nudge, the patch mentioned by the original poster, Daniel
Azuma, was proposed over 5 years ago.  I'm *not* complaining about the
timeline, as I'm not a committer and don't have any OpenSSH domain
knowledge whatsoever, but it would be *fantastic* if this could
actually make it into a release soon, especially since there's another
independent path here along with confirmation that it, too, works.

I'll be eternally grateful :)

Thanks, regardless.

-Andrew Hayden

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |1626




--- Comment #9 from Darren Tucker <dtucker at zip.com.au>  2009-07-31
11:44:14 ---
look at this for 5.4

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Adrian <adrian at planetcoding.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |adrian at planetcoding.net

--- Comment #10 from Adrian <adrian at planetcoding.net> 2009-10-05
08:34:27 EST ---
Getting signal support would be awesome.
I'm curious if there are any reasons why it wasn't added yet (almost 2
years after the patch was submitted).

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #1438|0                           |1
        is obsolete|                            |

--- Comment #11 from Darren Tucker <dtucker at zip.com.au> 2009-10-18
10:56:25 EST ---
Created an attachment (id=1699)
 --> (https://bugzilla.mindrot.org/attachment.cgi?id=1699)
update, improve the client UI a bit, remove client pass-through of
signal

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--- Comment #12 from Salvador Fandi?o <sfandino at yahoo.com> 2009-10-20
06:16:51 EST ---
Created an attachment (id=1700)
 --> (https://bugzilla.mindrot.org/attachment.cgi?id=1700)
extend the signals patch to accept them over the mux socket

Note, Darren Tucker patch 1699 has to be applied first!

This patch adds support for two new -O commands: ps and kill

- ps will list the PIDs of slave ssh processes
- kill allows to send signals

It also adds support to sshd to accept signals by number.

Sample session:
============== $ ./ssh -S /tmp/mux -M localhost -f perl ~/g/my-ssh/tellsignal.pl
 $ ./ssh -S /tmp/mux localhost -O ps      
 24140
 $ ./ssh -S /tmp/mux localhost -O kill HUP 24140
 Signal request sent.
 signal HUP received
 $ ./ssh -S /tmp/mux localhost -O kill 15 24140
 Signal request sent.
 signal TERM received
 $ ./ssh -S /tmp/mux localhost -O kill KILL 24140
 Signal request sent.
 $ 

Some notes:
==========* A new field "tag" is added to Channel, it is used as the
session
logical name. The current client implementation (muxclient) uses the
process PID as the tag.

* muxclient() now gets the arguments remaining in argv after getopt
processing so it can use them for the -O commands (currently, just
"kill"). I am not completely sure about this because it can be a bit
counterintuitive when the "-O cmd" part is used before the hostname:

  $ ssh -S /tmp/mux -O kill localhost TERM 24140


Bye,

 - Salva

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Salvador Fandi?o <sfandino at yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sfandino at yahoo.com

--- Comment #13 from Salvador Fandi?o <sfandino at yahoo.com> 2009-10-20
06:19:15 EST ---
The silly perl script that tells about the received signals...

$ cat tellsignal.pl 
#!/usr/bin/perl

for my $name (grep /^[A-Z]+$/, keys %SIG) {
    $SIG{$name} = sub { warn "signal $name received\n" };
}

while (1) {
    sleep 1;
}

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Damien Miller <djm at mindrot.org> changed:

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

--- Comment #14 from Damien Miller <djm at mindrot.org> 2009-10-21
21:45:14 EST ---
(In reply to comment #12)
> Created an attachment (id=1700)
 --> (https://bugzilla.mindrot.org/attachment.cgi?id=1700)
[details]
> extend the signals patch to accept them over the mux socket
Nice idea, and I think I like the concept of "friendly names" for
subsessions but this is really a separate enhancement. Could you please
file it under a new bug of its own?

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--- Comment #15 from Salvador Fandi?o <sfandino at yahoo.com> 2009-10-25
22:07:53 EST ---
> Nice idea, and I think I like the concept of "friendly names" for
> subsessions but this is really a separate enhancement. Could you please
> file it under a new bug of its own?
done, see ticket 1664

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Salvador Fandi?o <sfandino at yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #1700|0                           |1
        is obsolete|                            |

--- Comment #16 from Salvador Fandi?o <sfandino at yahoo.com> 2009-10-26
17:47:34 EST ---
Created an attachment (id=1709)
 --> (https://bugzilla.mindrot.org/attachment.cgi?id=1709)
control command for sending signals

This patch contains the implementation of the kill command that allows
to send signals to remote processes.

The patches attached to 1664 must be applied first.

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|1626                        |

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |1708

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--- Comment #17 from Damien Miller <djm at mindrot.org>  ---
We are freezing for the OpenSSH 5.6 release. Retargetting these bugs to
the next release.

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |1803

--- Comment #18 from Damien Miller <djm at mindrot.org>  ---
Targetting OpenSSH 5.7

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|1708                        |

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|1803                        |1845

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Christian Kandeler <christian.kandeler at nokia.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |christian.kandeler at nokia.co
                   |                            |m

--- Comment #19 from Christian Kandeler <christian.kandeler at nokia.com>
2011-07-27 18:39:05 EST ---
In 5.8, there is still no support for the "signal" request. What's
holding it back?

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |1930

--- Comment #20 from Damien Miller <djm at mindrot.org> 2011-09-06
10:34:12 EST ---
Retarget unresolved bugs/features to 6.0 release

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--- Comment #21 from Damien Miller <djm at mindrot.org> 2011-09-06
10:36:25 EST ---
Retarget unresolved bugs/features to 6.0 release

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|1845                        |

--- Comment #22 from Damien Miller <djm at mindrot.org> 2011-09-06
10:39:00 EST ---
Retarget unresolved bugs/features to 6.0 release

(try again - bugzilla's "change several" isn't)

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |1986

--- Comment #23 from Damien Miller <djm at mindrot.org> 2012-02-24
10:34:20 EST ---
Retarget from 6.0 to 6.1

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|1930                        |

--- Comment #24 from Damien Miller <djm at mindrot.org> 2012-02-24
10:37:58 EST ---
Retarget 6.0 => 6.1

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