[PATCH] mm/memcg: Annotate struct mem_cgroup_threshold_ary with __counted_by

[Kees Cook <keescook@chromium.org>]

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct mem_cgroup_threshold_ary.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/linux/memcontrol.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 45d0c10e86cc..e0cfab58ab71 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -143,7 +143,7 @@ struct mem_cgroup_threshold_ary {
 	/* Size of entries[] */
 	unsigned int size;
 	/* Array of thresholds */
-	struct mem_cgroup_threshold entries[];
+	struct mem_cgroup_threshold entries[] __counted_by(size);
 };
 
 struct mem_cgroup_thresholds {
-- 
2.34.1