linux-kernel - [PATCH 4.9 13/66] mm/mempolicy.c: do not put mempolicy before using its nodemask

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Message-Id: <20170131053603.687721181@linuxfoundation.org>
Date:   Tue, 31 Jan 2017 06:36:17 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.9 13/66] mm/mempolicy.c: do not put mempolicy before using its nodemask

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vlastimil Babka <vbabka@...e.cz>

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.

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@...e.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Acked-by: David Rientjes <rientjes@...gle.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2023,8 +2023,8 @@ 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;