Re: [PATCH bpf v2] bpf: Fix off-by-one boundary validation in arena direct-value access

[Emil Tsalapatis]

On Sun Apr 26, 2026 at 1:25 PM EDT, Junyoung Jang wrote:
> BPF_MAP_TYPE_ARENA accepts BPF_PSEUDO_MAP_VALUE offsets at exactly
> the end of the arena mapping (off == arena_size). The boundary check
> in arena_map_direct_value_addr() uses `>` instead of `>=`, which
> incorrectly allows a one-past-end pointer to be accepted.
>
> Change the condition to `>=` to correctly reject offsets that fall
> outside the valid arena user_vm range.
>
> Fixes: 317460317a02 ("bpf: Introduce bpf_arena.")
> Signed-off-by: Junyoung Jang <graypanda.inzag@xxxxxxxxx>
> ---

Reviewed-by: Emil Tsalapatis <emil@xxxxxxxxxxxxxxx>

>  kernel/bpf/arena.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
> index 802656c6fd3c..49a8f7b1beef 100644
> --- a/kernel/bpf/arena.c
> +++ b/kernel/bpf/arena.c
> @@ -511,7 +511,7 @@ static int arena_map_direct_value_addr(const struct bpf_map *map, u64 *imm, u32
>  {
>  	struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
>  
> -	if ((u64)off > arena->user_vm_end - arena->user_vm_start)
> +	if ((u64)off >= arena->user_vm_end - arena->user_vm_start)
>  		return -ERANGE;
>  	*imm = (unsigned long)arena->user_vm_start;
>  	return 0;