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From:   Shakeel Butt <shakeelb@google.com>
Date:   Fri, 22 Sep 2023 11:25:56 -0700
Message-ID: <CALvZod5xVhR_Feq7Wp_P9BLjYHJCxqvA6BmHmzwGzw34niDQ2g@mail.gmail.com>
Subject: Re: [PATCH] mm/memcg: Annotate struct mem_cgroup_threshold_ary with __counted_by
To:     Kees Cook <keescook@chromium.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@suse.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, Yosry Ahmed <yosryahmed@google.com>,
        Yu Zhao <yuzhao@google.com>, Miaohe Lin <linmiaohe@huawei.com>,
        Yafang Shao <laoar.shao@gmail.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Qi Zheng <zhengqi.arch@bytedance.com>,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
        linux-hardening@vger.kernel.org
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On Fri, Sep 22, 2023 at 10:53=E2=80=AFAM Kees Cook <keescook@chromium.org> =
wrote:
>
> Prepare for the coming implementation by GCC and Clang of the __counted_b=
y
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUND=
S
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> As found with Coccinelle[1], add __counted_by for struct mem_cgroup_thres=
hold_ary.
>
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/c=
ounted_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);

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?