Bug#153547: marked as done (start-stop-daemon: pid_is_exec may fails to achieve its goal)
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and subject line Bug#153547: start-stop-daemon: pid_is_exec may fails to achieve its goal
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>From thomas.morin@enst-bretagne.fr Fri Jul 19 05:11:13 2002
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Date: Fri, 19 Jul 2002 12:10:41 +0200
From: Thomas Morin <thomas.morin@enst-bretagne.fr>
To: submit@bugs.debian.org
Subject: start-stop-daemon: pid_is_exec may fails to achieve its goal
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While looking at start-stop-daemon source to help solving #151996 and
#151992, I noticed this piece of code :
static int
pid_is_exec(pid_t pid, const struct stat *esb)
{
struct stat sb;
char buf[32];
sprintf(buf, "/proc/%d/exe", pid);
if (stat(buf, &sb) != 0)
return 0;
return (sb.st_dev == esb->st_dev && sb.st_ino == esb->st_ino);
}
I guess this is meant to check that the process whose PID is found in
/var/run/foo.pid is actually a process executing the daemon started with
the foo command (using '--exec /usr/bin/foo').
There is a case where the test will fail, see for example:
- start-stop-daemon --start --exec /usr/bin/foo --pid-file /var/run/foo.pid
- then for some reason the (inode,dev) of /usr/bin/foo changes.
- then start-stop-daemon --stop --exec /usr/bin/foo --pid-file
/var/run/foo.pid won't stop foo, because it will conclude that the process
which PID is in /var/run/foo.pid is not running foo
This inode change happens when the package reinstalled or upgraded.
This maybe not be a problem since '/etc/init.d/foo stop' is called in .prerm
scrit of packages which have init scripts (dh_installinit does that
automatically). Still some packages don't use dh_installinit and don't restart
daemons during .prerm but after (ssh does this, hopefully, it doesn't use
--exec).
Really, the inode change can happen sometimes (recovering from a backup,
manual operation on file system, etc.), and I feel start-stop-daemon could be
more robust against such cases, perhaps comparing path instead of inodes would
be the solution (maybe symlinks would be problematic ?).
Regards,
-Thomas
( this report is more or less the same as a message I recently posted on
dpkg-dev, but I corrected some points I had wrong ).
--
== Thomas Morin -- GSM: 06 83 20 64 87 -- Tel: 02 98 05 98 54
== thomas.morin@enst-bretagne.fr -- thomas.morin@tuxfamily.org
== PGP Id:8CEA233D Key FP:503BF6CFD3AE8719377B832A02FB94E08CEA233D
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Received: (at 153547-done) by bugs.debian.org; 19 Jul 2002 10:32:57 +0000
>From wichert@wiggy.net Fri Jul 19 05:32:57 2002
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Date: Fri, 19 Jul 2002 12:32:53 +0200
From: Wichert Akkerman <wichert@wiggy.net>
To: Thomas Morin <thomas.morin@enst-bretagne.fr>,
153547-done@bugs.debian.org
Subject: Re: Bug#153547: start-stop-daemon: pid_is_exec may fails to achieve its goal
Message-ID: <20020719103253.GY22887@wiggy.net>
References: <[🔎] 1027073441.3d37e5a1cc190@t0m.dyndns.org>
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Previously Thomas Morin wrote:
> I guess this is meant to check that the process whose PID is found in
> /var/run/foo.pid is actually a process executing the daemon started with
> the foo command (using '--exec /usr/bin/foo').
Indeed, and that is what is documented.
> There is a case where the test will fail, see for example:
>
> - start-stop-daemon --start --exec /usr/bin/foo --pid-file /var/run/foo.pid
> - then for some reason the (inode,dev) of /usr/bin/foo changes.
> - then start-stop-daemon --stop --exec /usr/bin/foo --pid-file
> /var/run/foo.pid won't stop foo, because it will conclude that the process
> which PID is in /var/run/foo.pid is not running foo
Obviously, yes.
> This inode change happens when the package reinstalled or upgraded.
> This maybe not be a problem since '/etc/init.d/foo stop' is called in .prerm
> scrit of packages which have init scripts (dh_installinit does that
> automatically). Still some packages don't use dh_installinit and don't restart
> daemons during .prerm but after (ssh does this, hopefully, it doesn't use
> --exec).
Those packages are broken.
Wichert.
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