[Devel] [PATCH] mm: Fix int overflow in callers of do_shrink_slab()

[Kirill Tkhai]

do_shrink_slab() returns unsigned long value, and
the placing into int variable cuts high bytes off.
Then we compare ret and 0xfffffffe (since SHRINK_EMPTY
is converted to ret type).

Thus, big number of objects returned by do_shrink_slab()
may be interpreted as SHRINK_EMPTY, if low bytes of
their value are equal to 0xfffffffe. Fix that
by declaration ret as unsigned long in these functions.

Reported-by: Cyrill Gorcunov <gorcunov at openvz.org>
Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 mm/vmscan.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b7a463b5e508..6be538ce81b6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -435,8 +435,8 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			struct mem_cgroup *memcg, int priority)
 {
 	struct memcg_shrinker_map *map;
-	unsigned long freed = 0;
-	int ret, i;
+	unsigned long ret, freed = 0;
+	int i;
 
 	if (!memcg_kmem_enabled())
 		return 0;
@@ -535,9 +535,8 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 				 int priority,
 				 bool for_drop_caches)
 {
+	unsigned long ret, freed = 0;
 	struct shrinker *shrinker;
-	unsigned long freed = 0;
-	int ret;
 
 	if (unlikely(test_tsk_thread_flag(current, TIF_MEMDIE)))
 		return 0;