path: root/mm/mempolicy.c
diff options
authorMel Gorman <mgorman@suse.de>2012-10-08 16:29:20 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-10-09 16:22:22 +0900
commit00442ad04a5eac08a98255697c510e708f6082e2 (patch)
treeab786c94befbda536fbcf76b196358309044d2a0 /mm/mempolicy.c
parent63f74ca21f1fad36d075e063f06dcc6d39fe86b2 (diff)
mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma()
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 <kosaki.motohiro@jp.fujitsu.com> Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Christoph Lameter <cl@linux.com> Cc: Josh Boyer <jwboyer@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mempolicy.c')
1 files changed, 11 insertions, 1 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 1763418f1ad..3d64b369180 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1552,8 +1552,18 @@ struct mempolicy *get_vma_policy(struct task_struct *task,
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;