mm: memcontrol: use flex_array_size() helper in memcpy()

Make use of the flex_array_size() helper to calculate the size of a
flexible array member within an enclosing structure.

This helper offers defense-in-depth against potential integer overflows,
while at the same time makes it explicitly clear that we are dealing with
a flexible array member.

Also, remove unnecessary braces.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Link: https://lkml.kernel.org/r/ddd60dae2d9aea1ccdd2be66634815c93696125e.1596214831.git.gustavoars@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d8bdbe1..e3565ec 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4255,10 +4255,9 @@ static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg,
        new->size = size;
 
        /* Copy thresholds (if any) to new array */
-       if (thresholds->primary) {
-               memcpy(new->entries, thresholds->primary->entries, (size - 1) *
-                               sizeof(struct mem_cgroup_threshold));
-       }
+       if (thresholds->primary)
+               memcpy(new->entries, thresholds->primary->entries,
+                      flex_array_size(new, entries, size - 1));
 
        /* Add new threshold */
        new->entries[size - 1].eventfd = eventfd;