linux-kernel - Re: [PATCH 5/6] mempolicy: fix a memory corruption by refcount imbalance in alloc_pages

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Message-ID: <m2r4u1jths.fsf@firstfloor.org>
Date:	Wed, 30 May 2012 13:37:03 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	kosaki.motohiro@...il.com
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...gle.com>, Dave Jones <davej@...hat.com>,
	Mel Gorman <mgorman@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>, stable@...r.kernel.org,
	hughd@...gle.com, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Miao Xie <miaox@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 5/6] mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma()

kosaki.motohiro@...il.com writes:

> From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>
> commit cc9a6c8776 (cpuset: mm: reduce large amounts of memory barrier related
> damage v3) introduced a memory corruption.
>
> shmem_alloc_page() passes pseudo vma and it has one significant unique
> combination, vma->vm_ops=NULL and (vma->policy->flags & MPOL_F_SHARED).
>
> Now, get_vma_policy() does NOT increase a policy ref when vma->vm_ops=NULL
> and mpol_cond_put() DOES decrease a policy ref when a policy has MPOL_F_SHARED.
> Therefore, when cpuset race is happen and alloc_pages_vma() fall in
> 'goto retry_cpuset' path, a policy refcount will be decreased too much and
> therefore it will make memory corruption.
>
> This patch fixes it.

Looks good.

Acked-by: Andi Kleen <ak@...ux.intel.com>

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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