linux-kernel - [PATCH] mm: Fix int overflow in callers of do_shrink

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Date:   Fri, 28 Sep 2018 14:28:32 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     akpm@...ux-foundation.org, gorcunov@...nvz.org,
        ktkhai@...tuozzo.com, mhocko@...e.com, aryabinin@...tuozzo.com,
        hannes@...xchg.org, penguin-kernel@...ove.SAKURA.ne.jp,
        shakeelb@...gle.com, jbacik@...com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] mm: Fix int overflow in callers of do_shrink_slab()

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@...nvz.org>
Signed-off-by: Kirill Tkhai <ktkhai@...tuozzo.com>
---
 mm/vmscan.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0b63d9a2dc17..8ea87586925e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -581,8 +581,8 @@ 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() || !mem_cgroup_online(memcg))
 		return 0;
@@ -678,9 +678,8 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 				 struct mem_cgroup *memcg,
 				 int priority)
 {
+	unsigned long ret, freed = 0;
 	struct shrinker *shrinker;
-	unsigned long freed = 0;
-	int ret;
 
 	if (!mem_cgroup_is_root(memcg))
 		return shrink_slab_memcg(gfp_mask, nid, memcg, priority);