trying to resurrect discussion about "Cannot signal a process over a channel (rfc 4254, section 6.9)"

[Iain Morgan]

That's great news! Do you have any input regarding the implementation
details? Any suggestions that would ease inclusion of this feature would
be welcome.

-- 
Iain

On Wed, Aug 01, 2018 at 10:55:52 +1000, Damien Miller wrote:
> FWIW, now that privsep is mandatory I have no objection to including
> signal support in sshd.
> 
> On Wed, 25 Jul 2018, Yonathan Bleyfuesz wrote:
> 
> > Hi all,
> > 
> > I would like to propose some ideas to revivify this subject.
> > 
> > -First, we could add support on the client to send signal thanks to the escape characters.
> > (code : https://github.com/JawaGL/openssh-portable/commit/5bc9e6bc959b1b0f89d7ca7b4b04d7c37079fef0 ).
> > 
> > With this, in order to send a message requesting the server to send a SIGTERM to the remote process, you need to type  “~ST” which is not really invasive client-side.
> > 
> > But this means that the client has to enable TTY.
> > 
> > 
> > -Secondly , server-side, there is a problem with the currently suggested patch : it only works when we do an ‘exec’ request to the server (eg : ssh some-host “some; commands;”).
> > 
> > This is because in the other possible configuration, a shell is launched by the server. Then when we launch a process, it is forked by this shell and thus it has its own group-id.
> > 
> > When the user launches a signal-request hoping to reach a blocking process, the pid that is used by the ‘killpg’ function is the one of the shell. So it is this shell that catches the signal resulting in it:
> > 	- dying and leaving zombies 
> > 	- dying and taking its child with him (SIGHUP and SIGKILL)
> > 	- ignoring the signal (SIGINT, SIGTERM, SIGQUIT).
> > 
> > Example of ID’s when I connect to a server and launch the script test_signal.sh :  
> >  PID   PPID  PGID  SID
> >  4060  1598  4060  1556 sshd            sshd: root at pts/2
> >  4062  4060  4062  4062 bash            -bash
> >  4075  4062  4075  4062 sh              sh test_signal.sh
> >  4076  4075  4075  4062 sh              sh test_signal.sh
> > 
> > So in order to take this use case into account we could use the 'tcgetpgrp()’  function from ‘unistd.h’. 
> > (code : https://github.com/JawaGL/openssh-portable/commit/3667c0d90688c43ac0729083f73afa65102226b4 )
> > 
> > Of course this would still work if there are no TTY present since we can still access the PGID of the forked child in the session attributes.
> > 
> > -Finally, in order to test these functionalities, we could integrate a test case in the regress folder. (code : https://github.com/JawaGL/openssh-portable/commit/02c39b15363c54d0e622e5724c721a474e1cacd6).
> > 
> > 
> > I tested all these features on MacOSX and Ubuntu 18.
> > 
> > I hope this helps,
> > Thanks in advance for your returns,
> > 
> > Yonathan
> > 
> > 
> > _______________________________________________
> > openssh-unix-dev mailing list
> > openssh-unix-dev at mindrot.org
> > https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
> > 
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-- 
Iain Morgan