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authorMel Gorman <mgorman@suse.de>2012-10-09 17:58:41 +0100
committerBen Hutchings <ben@decadent.org.uk>2012-10-17 03:49:59 +0100
commitb99a7496c734f388f65aab959e0c8d32cc8938c6 (patch)
tree38eb040fe5275453c5e242d06d889441a09a3b93
parent54e670386ee302cd17d17ac398d1e718307633f2 (diff)
mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma()
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 <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> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
-rw-r--r--mm/mempolicy.c12
1 files changed, 11 insertions, 1 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 0c13a1b74ab9..4c82c2135bf0 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1522,8 +1522,18 @@ 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;