linux-kernel - Re: [PATCH 2/2] exec: Make do_coredump more robust and safer when using pipes in core

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Date:	Mon, 29 Jun 2009 06:21:52 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, earl_chew@...lent.com,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 2/2] exec: Make do_coredump more robust and safer when
	using pipes in core_pattern (v3)

On Mon, Jun 29, 2009 at 01:32:00AM +0200, Oleg Nesterov wrote:
> On 06/28, Neil Horman wrote:
> >
> > On Mon, Jun 29, 2009 at 12:24:55AM +0200, Oleg Nesterov wrote:
> > >
> > > Perhaps this sysctl should be added in a separate patch? This patch mixes
> > > differents things imho.
> > >
> > No, I disagree. If we're going to have a sysctl, It should be added in this
> > patch.  I agree that since these processes run as root, we can have all sort of
> > bad things happen.  But I think theres an advantage to being able to limit the
> > damage that a core_pattern process can do if it never exits.
> 
> Yes, but why it should be added in this patch?
> 
I agree with what you said earlier, in that the sysctl is orthogonal to the
wait_for_complete functionality, from an implementation standpoint.  But I don't
feel as though they are independent from a behavioral standpoint.  Given that
the sysctl defines a default value of zero in which unlimited parallel core
dumps are allowed, but none are waited for, separating the patches creates a
behavioral split in which the the core_pattern behavior changes for the span of
one commit, and in such a way that the system can deadlock if the core_pattern
process does bad things.  To illustrate, say we applied the wait_for_core patch
separately from sysctl patch.  If someone built with both patches, their
core_pattern behavior would appear unchanged, but if they built with only the
first patch, and their core_pattern app had a bug in which the process never
exited properly, they would get an unbounded backlog of unreaped processes.  I
could certainly modify the first patch to never wait, and then modify the sysctl
to decide when it was ok to wait, but to add a patch that allows for a wait
state that never happens seems a bit odd to me.

Regards
Neil

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