Re: [PATCH bpf-next] bpf: Reject struct_ops registration that uses module ptr and the module btf_id is missing

[Martin KaFai Lau <martin.lau@linux.dev>]

On 1/2/25 10:14 PM, Eduard Zingerman wrote:
> It was a bit hard for me to figure out what went wrong from the description,
> could you please double-check my understanding below?
> - when struct_ops program is attached,
>    bpf_struct_ops_map_update_elem() scans every member of specific
>    struct_ops type (e.g. struct tcp_congestion_ops) looking for fields
>    with type 'struct module *';
> - to find these fields BTF id of 'struct module' is used, this id does
>    not exist when CONFIG_MODULES=n, bpf_struct_ops_map_update_elem()
>    does not check if 'struct module' BTF id is non-zero;
> - bpf_struct_ops_map_update_elem() initializes 'struct module *'
>    fields using a magic value BPF_MODULE_OWNER, this initialization
>    would not happen if fields are not found;

Thanks for reviewing and testing it!

Yes, the understanding is correct. These are pretty much the only two places 
where st_ops_ids[IDX_MODULE_ID] and BPF_MODULE_OWNER are used.