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https://bugzilla.mindrot.org/show_bug.cgi?id=3181

--- Comment #2 from Serge B <zergpro+openssh@yandex.ru> ---
1. OpenCYGWIN_NT-10.0 3.0.7(0.338/5/3) 2019-04-30 18:08 x86_64
CygwinSSH_8.1p1, OpenSSL 1.1.1d 10 Sep 2019

Cygwin version remains live forever.


2. OpenSSH_8.0p1, OpenSSL 1.1.1c FIPS 28 May 2019
Linux 4.18.0-147.3.1.el8_1.x86_64 #1 SMP Fri Jan 3 23:55:26 UTC 2020
x86_64 x86_64 x86_64 GNU/Linux
CentOS Linux 8 (Core)

Linux version do exit after some time.

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--- Comment #3 from Darren Tucker <dtucker@dtucker.net> ---
> CygwinSSH_8.1p1

NO_SA_RESTART was added in 8.3p1
(https://github.com/openssh/openssh-portable/commit/6c6072ba8), in
versions prior to that it's a no-op.

> OpenSSH_8.0p1, OpenSSL 1.1.1c FIPS 28 May 2019
> Linux 4.18.0-147.3.1.el8_1.x86_64

The SA_RESTART change first appeared in 8.2p1
(https://www.openssh.com/txt/release-8.2)

Perhaps it's not SA_RESTART.

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Darren Tucker <dtucker@dtucker.net> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |vinschen@redhat.com

--- Comment #4 from Darren Tucker <dtucker@dtucker.net> ---
(In reply to Serge B from comment #2)
> 1. OpenCYGWIN_NT-10.0 3.0.7(0.338/5/3) 2019-04-30 18:08 x86_64
> CygwinSSH_8.1p1, OpenSSL 1.1.1d 10 Sep 2019
>
> Cygwin version remains live forever.

OK, the reason for that is in check_parent_exists():
{
/*
* If our parent has exited then getppid() will return
(pid_t)1,
* so testing for that should be safe.
*/
if (parent_pid != -1 && getppid() != parent_pid) {
/* printf("Parent has died - Authentication agent
exiting.\n"); */
cleanup_socket();
_exit(2);
}

In this mode, when the ssh-agent forks the agent itself continues as
the child while the parent execs the requested command which is
unusual. I'm not entirely sure why this is, but I suspect it's so job
control works as expected on the executed command.

Based on local testing, on Cygwin getppid() continues to return the
original process id even if that process has exited, instead of being
"reparented" to init as it would be on a Unixlike system. The best
solution we could come up with was to fall back to "kill(getppid(), 0)"
on Cygwin to test for parent process existence, however that'll be
wrong in the case of pid reuse. Corinna, do you have any better ideas?

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--- Comment #5 from Darren Tucker <dtucker@dtucker.net> ---
Created attachment 3412
--> https://bugzilla.mindrot.org/attachment.cgi?id=3412&action=edit
Fallback to using a signal to see if parent process is still alive on
Cygwin.

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Darren Tucker <dtucker@dtucker.net> changed:

What |Removed |Added
----------------------------------------------------------------------------
OS|All |Cygwin on NT/2k/W7/W8/W10
Blocks| |3162


Referenced Bugs:

https://bugzilla.mindrot.org/show_bug.cgi?id=3162
[Bug 3162] Tracking bug for 8.4 release
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--- Comment #6 from Corinna Vinschen <vinschen@redhat.com> ---
Oh, wait!

Before applying a potentially dangerous patch to OpenSSH, did anybody
actually test this on the latest Cygwin 3.1.5?

I tried the setup from the original report with the latest from the
Cygwin
distro:

- Cygwin 3.1.5
- OpenSSH 8.3p1
- OpenSSL 1.1.1f

and I can't reproduce this behaviour. In my case ssh-agent exits after
not more than 10 secs.

If one of you still can reproduce this problem in the above setup,
with the latest of everything from the Cygwin repo, then before
patching OpenSSH, let me check if this isn't a regression in Cygwin's
process handling. There's some history here in terms of ssh-agent.
An 8 years old patch in Cygwin is handling exactly this problem.
However,
there were some recent changes in Cygwin which might have broken this
behaviour.

So, if you still ca reporoduce under Cygwin 3.1.5 and OpenSSH 8.3p1, do
you
have a simple testcase in plain C, by any chance, to reproduce the
getppid
problem and to simplify debugging?


Thanks,
Corinna

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--- Comment #7 from Serge B <zergpro+openssh@yandex.ru> ---
I can confirm. The issue doesn't reproduce with fresh version of
cygwin.

- Cygwin 3.1.6
- OpenSSH 8.3p1
- OpenSSL 1.1.1f

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Darren Tucker <dtucker@dtucker.net> changed:

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

--- Comment #8 from Darren Tucker <dtucker@dtucker.net> ---
(In reply to Corinna Vinschen from comment #6)
> Oh, wait!
>
> Before applying a potentially dangerous patch to OpenSSH, did anybody
> actually test this on the latest Cygwin 3.1.5?

Well I didn't apply this potentially dangerous patch because I wasn't
sure about it, which is why I asked for your opinion in comment #4 :-)
I did, however, add a regression test for this particular behaviour:
https://github.com/openssh/openssh-portable/commit/5dba1fcabacaab46693338ec829b42a1293d1f52.

And while I do occasionally update Cygwin on my test VM, I didn't think
to do it in this case since I'd done it somewhat recently and it's not
the kind of behaviour that usually changes. I updated it and indeed,
the test now passes:

$ make t-exec LTESTS=agent-subprocess
[...]
run test agent-subprocess.sh ...
ok agent subprocess
make[1]: Leaving directory '/home/builder/openssh.anongit/regress'
all t-exec passed

Thanks for the help and sorry for the noise.

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Darren Tucker <dtucker@dtucker.net> changed:

What |Removed |Added
----------------------------------------------------------------------------
Blocks|3162 |


Referenced Bugs:

https://bugzilla.mindrot.org/show_bug.cgi?id=3162
[Bug 3162] Tracking bug for 8.4 release
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