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

[bot+bpf-ci]

> 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]);
> +}

[ ... ]


---
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