Re: [PATCH bpf 2/2] selftests/bpf: Test BTF walk into a flexible array of zero-sized elements

[Eduard Zingerman]

On Thu, 2026-09-10 at 20:22 +0800, Jiayuan Chen wrote:
> The program stashes a bpf_obj_new() object whose type ends with a flexible
> array of empty structs, then reads it back as an untrusted kptr. Without
> the previous patch this divides by zero in btf_struct_walk() instead of
> being rejected.
> 
>   # ./test_progs -t verifier_btf_flex_array
>   ...
>   #602     verifier_btf_flex_array:OK
>   Summary: 1/1 PASSED, 0 SKIPPED, 0/0 FAILED
> 
> Signed-off-by: Jiayuan Chen <jiayuan.c...@linux.dev>
> ---

Please simplify test case as follows:

SEC("syscall")
__failure __msg("access beyond struct test_flex_batch at off 4 size 1")
int stash_and_peek(void *ctx)
{
        struct map_value *v;
        int key = 0;

        v = bpf_map_lookup_elem(&batches, &key);
        if (!v || !v->batch)
                return 0;

        return *(char *)&v->batch->events[0];
}

Also, aren't there already test cases for flex arrays somewhere?
Probably no need to add a new file.

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