linux-kernel - Re: [PATCH] Enable writing to /proc/PID/mem.

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Date:	Thu, 3 Mar 2011 16:58:49 -0500
From:	Stephen Wilson <wilsons@...rt.ca>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Nick Piggin <npiggin@...nel.dk>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Enable writing to /proc/PID/mem.

On Thu, Mar 03, 2011 at 07:46:26PM +0000, Al Viro wrote:
> Think what happens if the target execs suid-root binary in the middle of your
> call.  After you've done your check.  E.g. during copy_from_user().
> 
> On the read side we actually recheck permissions after having copied into
> buffer and if the check fails we don't copy that buffer into userland.
> Not feasible on the write side...

You are right.  Looks like we would need to hold task_lock over both the
permission check and write -- but I do not see a clean/simple way of doing
that today.  Might be worth looking into...

Thanks!

-- 
steve

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