From: Vlastimil Babka <vbabka@suse.cz>
Date: Tue, 24 Jan 2017 23:18:18 +0000 (-0800)
Subject: mm/mempolicy.c: do not put mempolicy before using its nodemask
X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=d51e9894d27492783fc6d1b489070b4ba66ce969;p=openwrt%2Fstaging%2Fblogic.git

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

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.

Fixes: be97a41b291e ("mm/mempolicy.c: merge alloc_hugepage_vma to alloc_pages_vma")
Link: http://lkml.kernel.org/r/20170118141124.8345-1-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>	[4.0+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 2e346645eb80..1e7873e40c9a 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2017,8 +2017,8 @@ 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;