[patch 078/181] mm: memcontrol: use flex_array_size() helper in memcpy()

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From: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
Subject: 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.

Link: https://lkml.kernel.org/r/ddd60dae2d9aea1ccdd2be66634815c93696125e.1596214831.git.gustavoars@xxxxxxxxxx
Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/memcontrol.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/mm/memcontrol.c~mm-memcontrol-use-flex_array_size-helper-in-memcpy
+++ a/mm/memcontrol.c
@@ -4255,10 +4255,9 @@ static int __mem_cgroup_usage_register_e
 	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;
_



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