linux-kernel - Re: [PATCH v2] proc: fix a race in do_io

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Date:	Tue, 5 Jul 2011 14:13:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Vasiliy Kulikov <segoon@...nwall.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
	rientjes@...gle.com, wilsons@...rt.ca, security@...nel.org,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2] proc: fix a race in do_io_accounting()

<wakes up>

On Tue, 5 Jul 2011 00:13:39 +0400
Vasiliy Kulikov <segoon@...nwall.com> wrote:

> There is a ptrace_may_access() check in do_io_accounting() to prevent
> gathering information of setuid'ed and similar binaries.  However, there
> is a race against execve().  Holding task->signal->cred_guard_mutex
> while gathering the information should protect against the race.
> 
> The order of locking is similar to the one inside of
> ptrace_attach(): first goes cred_guard_mutex, then lock_task_sighand().
> 
> v2 - use mutex_lock_killable() instead of mutex_lock().
> 
> Signed-off-by: Vasiliy Kulikov <segoon@...nwall.com>
> Cc: stable@...nel.org

If a patch is to be backported into -stable then its changelog had
better explain why such a thing is needed.  This one doesn't.

Please provide a full description of the conseuqences of the bug.  One
which will permit the -stable maintainers to understand why they're
merging the patch, and one which will help distribution maintainers
decide whether they want to merge it as well.

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