linux-kernel - [PATCH 1/2][next] mm: memcontrol: Use flex_array

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Date:   Fri, 31 Jul 2020 12:12:53 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: [PATCH 1/2][next] 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@...nel.org>
---
 mm/memcontrol.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e84c2b5596f2..bd7f972ceea4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4246,10 +4246,9 @@ 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;
-- 
2.27.0