Re: ssh-agent doesn't die

[Ken Brown <kbrown at cornell dot edu>]

On 9/27/2019 10:12 AM, Ken Brown wrote:
> On 9/27/2019 9:37 AM, Norton Allen wrote:
>> On 9/26/2019 10:50 PM, Ken Brown wrote:
>>>
>>>> As a simple test example, consider:
>>>>
>>>> /bin/ssh-agent /bin/sleep 10
>>>>
>>>> While the sleep is still running, ps shows:
>>>>
>>>>          PID    PPID    PGID     WINPID   TTY         UID    STIME COMMAND
>>>>         1694    1693    1694       1576  ?          22534 00:01:10
>>>> /usr/bin/ssh-agent
>>>>         1653       1    1653      11740  cons1      22534 00:00:37 /usr/bin/bash
>>>>         1693    1653    1693       1552  cons1      22534 00:01:10 /usr/bin/sleep
>>>>
>>>> One oddity is that ssh-agent is listed as a subprocess of sleep
>>> ...but this isn't a bug.  ssh-agent forks, and then the parent execs the command.
>>
>> With the salient difference presumably being that the exec is done in the parent
>> instead of the child as usual?
> 
> Yes.  The idea is that 'ssh-agent command' should be more-or-less equivalent to
> running 'command', with ssh-agent running as a subprocess.
> 
> The ssh-agent subprocess periodically checks to see if its parent is still
> alive, and it exits when the parent has died.  Someone should figure out why
> this is not working on Cygwin.

As an aid to someone who might want to debug this (probably Corinna when she 
returns), I've created a test program agent.c (attached) that simulates the 
relevant part of ssh-agent:

1. It forks a subprocess that periodically checks to see if its parent has died, 
and then exits.

2. The parent execs "/usr/bin/sleep 1".

As with ssh-agent, the subprocess never detects that the parent has died, and so 
it never exits.

Running this program under strace shows the following error in the pinfo 
constructor:

pinfo::pinfo: couldn't duplicate parent rd_proc_pipe handle 0x1BC for forked 
child 1666 after exec, Win32 error 5

[Win32 error 5 is ERROR_ACCESS_DENIED.]

I assume this is the source of the problem, but I don't understand the code well 
enough to know why.  I also don't know why the call to DuplicateHandle fails.

Ken

Attachment: agent.c
Description: agent.c

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple