Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754429Ab2JNOmS (ORCPT ); Sun, 14 Oct 2012 10:42:18 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:46190 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754344Ab2JNOmJ (ORCPT ); Sun, 14 Oct 2012 10:42:09 -0400 Message-Id: <20121014143551.483150486@decadent.org.uk> User-Agent: quilt/0.60-1 Date: Sun, 14 Oct 2012 15:37:44 +0100 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Mel Gorman , KOSAKI Motohiro , Christoph Lameter , Josh Boyer , Linus Torvalds Subject: [ 131/147] mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma() In-Reply-To: <20121014143533.742627615@decadent.org.uk> X-SA-Exim-Connect-IP: 77.75.106.1 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2182 Lines: 62 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mel Gorman commit 00442ad04a5eac08a98255697c510e708f6082e2 upstream. Commit cc9a6c877661 ("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 Reviewed-by: Christoph Lameter Cc: Josh Boyer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Ben Hutchings --- mm/mempolicy.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 1763418..3d64b36 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1552,8 +1552,18 @@ struct mempolicy *get_vma_policy(struct task_struct *task, addr); if (vpol) pol = vpol; - } else if (vma->vm_policy) + } 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/