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

[Shakeel Butt]

On Fri, Sep 22, 2023 at 10:53 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxxxxxxxxxx>
> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  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);

Does 'size' here have to be a member of the same struct as entries? We
have nodeinfo[] in struct mem_cgroup whose size is nr_node_ids which
is global. Will __counted_by() work for that?