Re: [PATCH v2 bpf-next 7/8] selftests/bpf: Fix up __u16 vlen assumptions

[sashiko-bot@kernel.org]

Sashiko AI review found 1 potential issue(s):
- [Medium] The patch fails to fix the 16-bit assumption for `vlen` in `tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c`.
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commit 033bc70f770dbba15f69901f422f7378dd7cd70e
Author: Alan Maguire <alan.maguire@oracle.com>

selftests/bpf: Fix up __u16 vlen assumptions

Fix up a few cases where we assume vlen is 16 bits.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>

> diff --git a/tools/testing/selftests/bpf/prog_tests/btf.c b/tools/testing/selftests/bpf/prog_tests/btf.c
> index 0cc347e32db37..a9de328a86976 100644
> --- a/tools/testing/selftests/bpf/prog_tests/btf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/btf.c
> @@ -8092,7 +8092,7 @@ static struct btf_dedup_test dedup_tests[] = {
>  static int btf_type_size(const struct btf_type *t)
>  {
>  	int base_size = sizeof(struct btf_type);
> -	__u16 vlen = BTF_INFO_VLEN(t->info);
> +	__u32 vlen = BTF_INFO_VLEN(t->info);
>  	__u16 kind = BTF_INFO_KIND(t->info);

Does tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c also need to be
updated to handle 24-bit vlen values?

Looking at find_field_offset_aux(), mnum is still declared as __u16 and
assigned the result of btf_vlen():

tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c:find_field_offset_aux() {
	const struct btf_type *type = btf__type_by_id(btf, btf_id);
	const struct btf_member *m;
	__u16 mnum;
	int i;
	...
	m = btf_members(type);
	mnum = btf_vlen(type);

	for (i = 0; i < mnum; ++i, ++m) {
	...
}

If a structure or union has more than 65,535 members, could mnum be
truncated here, causing the loop to terminate prematurely and failing to
resolve field offsets?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260416143904.1220662-1-alan.maguire@oracle.com?part=7