From: KOSAKI Motohiro <kosaki.motoh...@jp.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 alloc_pages_vma() goes 'goto retry_cpuset' path, a policy refcount will be decreased too much and therefore it will make a memory corruption. This patch fixes it. Cc: Dave Jones <da...@redhat.com>, Cc: Mel Gorman <mgor...@suse.de> Cc: Christoph Lameter <c...@linux.com>, Cc: Andrew Morton <a...@linux-foundation.org> Cc: <stable@vger.kernel.org> Cc: Miao Xie <mi...@cn.fujitsu.com> Cc: Peter Zijlstra <a.p.zijls...@chello.nl> Signed-off-by: KOSAKI Motohiro <kosaki.motoh...@jp.fujitsu.com> Acked-by: Andi Kleen <a...@linux.intel.com> --- 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 stable" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html