Patch "mm/mempolicy.c: do not put mempolicy before using its nodemask" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

mm/mempolicy.c: do not put mempolicy before using its nodemask

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-mempolicy.c-do-not-put-mempolicy-before-using-its-nodemask.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Vlastimil Babka <[email protected]>
Date: Tue, 24 Jan 2017 15:18:18 -0800
Subject: mm/mempolicy.c: do not put mempolicy before using its nodemask

From: Vlastimil Babka <[email protected]>

commit d51e9894d27492783fc6d1b489070b4ba66ce969 upstream.

Since commit be97a41b291e ("mm/mempolicy.c: merge alloc_hugepage_vma to alloc_pages_vma") alloc_pages_vma() can potentially free a mempolicy by mpol_cond_put() before accessing the embedded nodemask by __alloc_pages_nodemask(). The commit log says it's so "we can use a single exit path within the function" but that's clearly wrong. We can still do that when doing mpol_cond_put() after the allocation attempt.

Make sure the mempolicy is not freed prematurely, otherwise __alloc_pages_nodemask() can end up using a bogus nodemask, which could lead e.g. to premature OOM.

---
 mm/mempolicy.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -2006,8 +2006,8 @@ retry_cpuset:
 
 	nmask = policy_nodemask(gfp, pol);
 	zl = policy_zonelist(gfp, pol, node);
-	mpol_cond_put(pol);
 	page = __alloc_pages_nodemask(gfp, order, zl, nmask);
+	mpol_cond_put(pol);
 out:
 	if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
 		goto retry_cpuset;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/mm-mempolicy.c-do-not-put-mempolicy-before-using-its-nodemask.patch