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Fri, 4 Oct 2019 14:27:00 +0000 Received: from DM6PR04MB5738.namprd04.prod.outlook.com ([fe80::6998:197f:bcff:7172]) by DM6PR04MB5738.namprd04.prod.outlook.com ([fe80::6998:197f:bcff:7172%4]) with mapi id 15.20.2305.023; Fri, 4 Oct 2019 14:27:00 +0000 From: Ken Brown To: "cygwin@cygwin.com" Subject: Re: ssh-agent doesn't die Date: Fri, 04 Oct 2019 14:27:00 -0000 Message-ID: <801bca17-2c61-bb6a-f02c-c4912232d9c5@cornell.edu> References: <319e26c0-32f0-40b7-2137-c7de170a3486@rl.ac.uk> <5b225738-c2d7-fbfe-48a7-8c2a38c3398c@cornell.edu> <0ccd17b6-c22a-1a18-9409-1ebcfae60868@huarp.harvard.edu> <9f7a14bb-f81b-c566-bb84-8da7fc6d0fad@cornell.edu> <185c5774-dd8b-5488-b818-4cec5a24bf2d@cornell.edu> In-Reply-To: <185c5774-dd8b-5488-b818-4cec5a24bf2d@cornell.edu> user-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 authentication-results: spf=none (sender IP is ) smtp.mailfrom=kbrown@cornell.edu; x-ms-oob-tlc-oobclassifiers: OLM:9508; received-spf: None (protection.outlook.com: cornell.edu does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-ms-exchange-transport-forked: True Content-Type: text/plain; charset="Windows-1252" Content-ID: <4D5325DEC068814EB2092A95EF29CD0A@namprd04.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: GnMXkj+qtsWWLJpi6T8f2Ha+FVeS4fb97/j06Sb3CZREdpbKvhelBmFP1nnkdTV7/KDZISyGnMIrgCAyCwQdJQ== X-IsSubscribed: yes X-SW-Source: 2019-10/txt/msg00020.txt.bz2 On 9/29/2019 4:05 PM, Ken Brown wrote: > 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: >>>>> >>>>> =A0 =A0=A0=A0=A0=A0 PID=A0=A0=A0 PPID=A0=A0=A0 PGID=A0=A0=A0=A0 WIN= PID=A0=A0 TTY=A0=A0=A0=A0=A0=A0=A0=A0 UID=A0=A0=A0 STIME COMMAND >>>>> =A0 =A0=A0=A0=A0 1694=A0=A0=A0 1693=A0=A0=A0 1694=A0=A0=A0=A0=A0=A0= 1576=A0 ?=A0=A0=A0=A0=A0=A0=A0=A0=A0 22534 00:01:10 >>>>> /usr/bin/ssh-agent >>>>> =A0 =A0=A0=A0=A0 1653=A0=A0=A0=A0=A0=A0 1=A0=A0=A0 1653=A0=A0=A0=A0= =A0 11740=A0 cons1=A0=A0=A0=A0=A0 22534 00:00:37 /usr/bin/bash >>>>> =A0 =A0=A0=A0=A0 1693=A0=A0=A0 1653=A0=A0=A0 1693=A0=A0=A0=A0=A0=A0= 1552=A0 cons1=A0=A0=A0=A0=A0 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.=A0 ssh-agent forks, and then the parent execs= the command. >>> >>> With the salient difference presumably being that the exec is done in t= he parent >>> instead of the child as usual? >> >> Yes. The idea is that 'ssh-agent command' should be more-or-less equiva= lent to >> running 'command', with ssh-agent running as a subprocess. >> >> The ssh-agent subprocess periodically checks to see if its parent is sti= ll >> alive, and it exits when the parent has died. Someone should figure out= why >> this is not working on Cygwin. >=20 > 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 t= he > relevant part of ssh-agent: >=20 > 1. It forks a subprocess that periodically checks to see if its parent ha= s died, > and then exits. >=20 > 2. The parent execs "/usr/bin/sleep 1". >=20 > As with ssh-agent, the subprocess never detects that the parent has died,= and so > it never exits. >=20 > Running this program under strace shows the following error in the pinfo > constructor: >=20 > pinfo::pinfo: couldn't duplicate parent rd_proc_pipe handle 0x1BC for for= ked > child 1666 after exec, Win32 error 5 >=20 > [Win32 error 5 is ERROR_ACCESS_DENIED.] It seems that the pinfo constructor failure happens in=20 cygheap_exec_info::reattach_children(). The latter is preceded by the foll= owing=20 comment: /* Reattach non-reaped subprocesses passed in from the cygwin process which previously operated under this pid. FIXME: Is there a race here if the process exits during cygwin's exec handoff? */ I tried running my test program under gdb with a breakpoint at=20 reattach_children, and the breakpoint was never hit. That gives an affirma= tive=20 answer to the question in the FIXME. As a result, the exec'd program never becomes aware that it has a subproces= s, so=20 it exits without resetting the subprocess's ppid to 1. Is there someone out there familiar enough with Cygwin's exec to suggest a = fix?=20 It would be a nice gift to Corinna to get this fixed before her return. Ken -- 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