diff options
| author | Mel Gorman | 2012-10-08 16:29:20 -0700 |
|---|---|---|
| committer | Linus Torvalds | 2012-10-09 16:22:22 +0900 |
| commit | 00442ad04a5eac08a98255697c510e708f6082e2 (patch) | |
| tree | ab786c94befbda536fbcf76b196358309044d2a0 | |
| parent | 63f74ca21f1fad36d075e063f06dcc6d39fe86b2 (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>
| -rw-r--r-- | mm/mempolicy.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 1763418f1ada..3d64b369180d 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; |