linux-kernel - Re: [PATCH] futex: futex_find_get_task make credentials check conditional

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Message-ID: <20100630070115.GB3890@tiehlicka.suse.cz>
Date:	Wed, 30 Jun 2010 09:01:15 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Darren Hart <dvhltc@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] futex: futex_find_get_task make credentials check
 conditional

On Tue 29-06-10 09:41:02, Linus Torvalds wrote:
> On Tue, Jun 29, 2010 at 1:42 AM, Michal Hocko <mhocko@...e.cz> wrote:
> >
> > futex_find_get_task is currently used (through lookup_pi_state) from two
> > contexts, futex_requeue and futex_lock_pi_atomic. While credentials check
> > makes sense in the first code path, the second one is more problematic
> > because this check requires that the PI lock holder (pid parameter) has
> > the same uid and euid as the process's euid which is trying to lock the
> > same futex (current).
> 
> So exactly why does it make sense to check the credentials in the
> first code path then? 

I though that requeue needs this for security reasons (don't let requeue
process for other user), but when I thought about that again you are
right and the only what matters should be accessibility of the shared
memory.


-- 
Michal Hocko
L3 team 
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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