mm/memcontrol.c: use struct_size() in kmalloc()

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.

Link: http://lkml.kernel.org/r/20190104183726.GA6374@embeddedor
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 72414bb..f93f7f2 100644 (file)
--- 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;