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.motoh...@jp.fujitsu.com>
Signed-off-by: Mel Gorman <mgor...@suse.de>
Reviewed-by: Christoph Lameter <c...@linux.com>
Cc: Josh Boyer <jwbo...@gmail.com>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Mel Gorman <mgor...@suse.de>
---
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;
--
1.7.9.2
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