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

From: Greg Kroah-Hartman
Date: Tue Jan 31 2017 - 00:58:28 EST

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


From: Vlastimil Babka <vbabka@xxxxxxx>

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@xxxxxxx
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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);
if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
goto retry_cpuset;