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 <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: "Matthew Wilcox (Oracle)" <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
---
 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


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