Commit 00442ad0 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds

mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma()

Commit cc9a6c87 ("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: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
Reviewed-by: default avatarChristoph Lameter <cl@linux.com>
Cc: Josh Boyer <jwboyer@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 63f74ca2
...@@ -1552,8 +1552,18 @@ struct mempolicy *get_vma_policy(struct task_struct *task, ...@@ -1552,8 +1552,18 @@ struct mempolicy *get_vma_policy(struct task_struct *task,
addr); addr);
if (vpol) if (vpol)
pol = vpol; pol = vpol;
} else if (vma->vm_policy) } else if (vma->vm_policy) {
pol = 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) if (!pol)
pol = &default_policy; pol = &default_policy;
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment