Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932490Ab2E3JD2 (ORCPT ); Wed, 30 May 2012 05:03:28 -0400 Received: from mail-vb0-f46.google.com ([209.85.212.46]:46484 "EHLO mail-vb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932380Ab2E3JDX (ORCPT ); Wed, 30 May 2012 05:03:23 -0400 From: kosaki.motohiro@gmail.com To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Dave Jones , Mel Gorman , Linus Torvalds , Christoph Lameter , stable@vger.kernel.org, hughd@google.com, KOSAKI Motohiro , Andrew Morton , Miao Xie , Peter Zijlstra Subject: [PATCH 5/6] mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma() Date: Wed, 30 May 2012 05:02:08 -0400 Message-Id: <1338368529-21784-6-git-send-email-kosaki.motohiro@gmail.com> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1338368529-21784-1-git-send-email-kosaki.motohiro@gmail.com> References: <1338368529-21784-1-git-send-email-kosaki.motohiro@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3071 Lines: 100 From: KOSAKI Motohiro 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. Cc: Dave Jones , Cc: Mel Gorman Cc: Linus Torvalds Cc: Christoph Lameter , Cc: Andrew Morton Cc: Cc: Miao Xie Cc: Peter Zijlstra Signed-off-by: KOSAKI Motohiro --- mm/mempolicy.c | 13 ++++++++++++- mm/shmem.c | 9 +++++---- 2 files changed, 17 insertions(+), 5 deletions(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 7fb7d51..0da0969 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1544,18 +1544,29 @@ 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; + got_ref = 1; + } } else if (vma->vm_policy) pol = vma->vm_policy; } if (!pol) pol = &default_policy; + + /* + * shmem_alloc_page() passes MPOL_F_SHARED policy with vma->vm_ops=NULL. + * Thus, we need to take additional ref for avoiding refcount imbalance. + */ + if (!got_ref && mpol_needs_cond_ref(pol)) + mpol_get(pol); + return pol; } diff --git a/mm/shmem.c b/mm/shmem.c index d576b84..eb5f1eb 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -919,6 +919,7 @@ static struct page *shmem_alloc_page(gfp_t gfp, struct shmem_inode_info *info, pgoff_t index) { struct vm_area_struct pvma; + struct page *page; /* Create a pseudo vma that just contains the policy */ pvma.vm_start = 0; @@ -926,10 +927,10 @@ static struct page *shmem_alloc_page(gfp_t gfp, pvma.vm_ops = NULL; pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, index); - /* - * alloc_page_vma() will drop the shared policy reference - */ - return alloc_page_vma(gfp, &pvma, 0); + page = alloc_page_vma(gfp, &pvma, 0); + + mpol_put(pvma.vm_policy); + return page; } #else /* !CONFIG_NUMA */ #ifdef CONFIG_TMPFS -- 1.7.1 -- 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/