提交 00442ad0 编写于 作者: M Mel Gorman 提交者: 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: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: NMel Gorman <mgorman@suse.de>
Reviewed-by: NChristoph Lameter <cl@linux.com>
Cc: Josh Boyer <jwboyer@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
上级 63f74ca2
......@@ -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;
......
Markdown is supported
0% .
You are about to add 0 people to the discussion. Proceed with caution.
先完成此消息的编辑!
想要评论请 注册