From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx194.postini.com [74.125.245.194]) by kanga.kvack.org (Postfix) with SMTP id 74FDA6B006C for ; Mon, 20 Aug 2012 12:42:32 -0400 (EDT) From: Mel Gorman Subject: [PATCH 5/5] mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma() Date: Mon, 20 Aug 2012 17:36:34 +0100 Message-Id: <1345480594-27032-6-git-send-email-mgorman@suse.de> In-Reply-To: <1345480594-27032-1-git-send-email-mgorman@suse.de> References: <1345480594-27032-1-git-send-email-mgorman@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , KOSAKI Motohiro Cc: Dave Jones , Christoph Lameter , Ben Hutchings , Andi Kleen , Hugh Dickins , LKML , Linux-MM , Mel Gorman [cc9a6c87: cpuset: mm: reduce large amounts of memory barrier related damage v3] introduced a potential memory corruption. shmem_alloc_page() uses a pseudo vma and it has one significant unique combination, vma->vm_ops=NULL and vma->policy->flags & MPOL_F_SHARED. 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 a cpuset update race occurs, alloc_pages_vma() falls in 'goto retry_cpuset' path, decrements the reference count and frees the policy prematurely. Signed-off-by: KOSAKI Motohiro Signed-off-by: Mel Gorman --- mm/mempolicy.c | 17 +++++++++++++++-- 1 files changed, 15 insertions(+), 2 deletions(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 45f9825..82e872f 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1545,15 +1545,28 @@ struct mempolicy *get_vma_policy(struct task_struct *task, struct vm_area_struct *vma, unsigned long addr) { struct mempolicy *pol = task->mempolicy; + int got_ref; if (vma) { if (vma->vm_ops && vma->vm_ops->get_policy) { struct mempolicy *vpol = vma->vm_ops->get_policy(vma, addr); - if (vpol) + if (vpol) { pol = vpol; - } else if (vma->vm_policy) + got_ref = 1; + } + } else if (vma->vm_policy) { pol = vma->vm_policy; + + /* + * shmem_alloc_page() passes MPOL_F_SHARED policy with + * a pseudo vma whose vma->vm_ops=NULL. Take a reference + * count on these policies which will be dropped by + * mpol_cond_put() later + */ + if (mpol_needs_cond_ref(pol)) + mpol_get(pol); + } } if (!pol) pol = &default_policy; -- 1.7.7 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org