linux-kernel - Re: [PATCH bpf-next v2 5/7] mm: introduce BPF kfunc to access memory events

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Message-Id: <8f23848b8ac657b4b4a2da04da242039c59e9ad9826a8d5fa0f5aee55acfecc9@mail.kernel.org>
Date: Sat, 20 Dec 2025 04:29:44 +0000 (UTC)
From: bot+bpf-ci@...nel.org
To: roman.gushchin@...ux.dev,bpf@...r.kernel.org,linux-mm@...ck.org,linux-kernel@...r.kernel.org
Cc: inwardvessel@...il.com,ast@...nel.org,daniel@...earbox.net,shakeel.butt@...ux.dev,mhocko@...nel.org,hannes@...xchg.org,roman.gushchin@...ux.dev,ast@...nel.org,andrii@...nel.org,daniel@...earbox.net,martin.lau@...nel.org,eddyz87@...il.com,yonghong.song@...ux.dev,clm@...a.com,ihor.solodrai@...ux.dev
Subject: Re: [PATCH bpf-next v2 5/7] mm: introduce BPF kfunc to access memory events

> diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c
> index d84fe6f3ed43..858eb43766ce 100644
> --- a/mm/bpf_memcontrol.c
> +++ b/mm/bpf_memcontrol.c
> @@ -103,6 +103,22 @@ __bpf_kfunc unsigned long bpf_mem_cgroup_usage(struct mem_cgroup *memcg)
>  	return mem_cgroup_usage(memcg, false) * PAGE_SIZE;
>  }
>
> +/**
> + * bpf_mem_cgroup_memory_events - Read memory cgroup's memory event value
> + * @memcg: memory cgroup
> + * @event: memory event id
> + *
> + * Returns current memory event count.
> + */
> +__bpf_kfunc unsigned long bpf_mem_cgroup_memory_events(struct mem_cgroup *memcg,
> +						enum memcg_memory_event event)
> +{
> +	if (event >= MEMCG_NR_MEMORY_EVENTS)
> +		return (unsigned long)-1;

Should this also check for negative values?  The enum type is typically
signed, so a BPF program passing a negative event value would pass this
check but cause an out-of-bounds read from memcg->memory_events[].

The similar bpf_mem_cgroup_page_state() in this same file uses:

    if (idx < 0 || idx >= MEMCG_NR_STAT)

which checks both bounds.  Could the check here be changed to:

    if (event < 0 || event >= MEMCG_NR_MEMORY_EVENTS)

to match that pattern?

> +
> +	return atomic_long_read(&memcg->memory_events[event]);
> +}

[ ... ]


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/20389033088