Re: [PATCH] bpf: Add nelems overflow check in btf_find_field_one() btf_find_field_one() multiplies a u32 nelems accumulator by each nested array level's element count without checking for overflow. The sibling function __btf_resolve_size() already guards against the same overflow pattern (btf.c line 2110). Currently the BTF array verifier (btf_array_resolve) rejects BTF blobs whose total array size would overflow u32, so this code path is not reachable with crafted BTF input on kernels that include that check. Add check_mul_overflow() anyway to keep btf_find_field_one() self-consistent with __btf_resolve_size() and to guard against future changes in the validation ordering. Fixes: 994796c0256c ("bpf: create repeated fields for arrays.")

[Yonghong Song <yonghong.song@linux.dev>]

On 5/22/26 5:41 AM, Himanshu Anand wrote:
> Signed-off-by: Himanshu Anand <anand.himanshu17@gmail.com>

Looks like patch subject and commit message are messed up. Please
fix it in the next revision.

Please use [PATCH bpf v2] as the tag.

> ---
>   kernel/bpf/btf.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index a62d78581207..b767a9fcf095 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -3765,7 +3765,8 @@ static int btf_find_field_one(const struct btf *btf,
>   	 */
>   	for (i = 0; i < MAX_RESOLVE_DEPTH && btf_type_is_array(var_type); i++) {
>   		array = btf_array(var_type);
> -		nelems *= array->nelems;
> +		if (check_mul_overflow(nelems, array->nelems, &nelems))
> +			return -E2BIG;

Looks correct to me.

>   		var_type = btf_type_by_id(btf, array->type);
>   	}
>   	if (i == MAX_RESOLVE_DEPTH)