[PATCH] mm: memcontrol: use struct_size() in kmalloc()

From: Gustavo A. R. Silva
Date: Fri Jan 04 2019 - 13:37:32 EST


One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct foo {
int stuff;
void *entry[];
};

instance = kmalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
---
mm/memcontrol.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index af7f18b32389..ad256cf7da47 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3626,8 +3626,7 @@ static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg,
size = thresholds->primary ? thresholds->primary->size + 1 : 1;

/* Allocate memory for new array of thresholds */
- new = kmalloc(sizeof(*new) + size * sizeof(struct mem_cgroup_threshold),
- GFP_KERNEL);
+ new = kmalloc(struct_size(new, entries, size), GFP_KERNEL);
if (!new) {
ret = -ENOMEM;
goto unlock;
--
2.20.1