Re: [PATCH bpf-next v14 7/8] libbpf: Add syscall common attributes support for map_create

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Missing OPTS_VALID() check for the nested `log_opts` structure in `bpf_map_create` breaks ABI forward compatibility guarantees.
--

commit a5ab21cbf48e1fc2cdb0af0f1ff743e2633f6ae8
Author: Leon Hwang <leon.hwang@linux.dev>

libbpf: Add syscall common attributes support for map_create

The commit introduces struct bpf_log_opts and adds a log_opts field to
bpf_map_create_opts to allow users to retrieve detailed error messages when
map creation fails.

> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 9d8740761b7a8..483c02cf21d1f 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c

[ ... ]

> @@ -242,7 +245,18 @@ int bpf_map_create(enum bpf_map_type map_type,
>  	attr.excl_prog_hash = ptr_to_u64(OPTS_GET(opts, excl_prog_hash, NULL));
>  	attr.excl_prog_hash_size = OPTS_GET(opts, excl_prog_hash_size, 0);
>  
> -	fd = sys_bpf_fd(BPF_MAP_CREATE, &attr, attr_sz);
> +	log_opts = OPTS_GET(opts, log_opts, NULL);

Does this code need to validate log_opts with OPTS_VALID(log_opts, bpf_log_opts)?

Libbpf relies on the OPTS_VALID() macro to enforce ABI forward compatibility
by verifying that any unrecognized trailing fields in extended option structs
are explicitly zeroed. While bpf_map_create() correctly validates the outer
bpf_map_create_opts structure, it seems the nested log_opts structure is
accessed without similar validation.

If a newer application populates unsupported fields in struct bpf_log_opts
with non-zero values, could an older libbpf silently ignore them instead of
safely rejecting the request with -EINVAL?

> +	if (log_opts && feat_supported(NULL, FEAT_BPF_SYSCALL_COMMON_ATTRS)) {
> +		memset(&attr_common, 0, attr_common_sz);
> +		attr_common.log_buf = ptr_to_u64(OPTS_GET(log_opts, buf, NULL));
> +		attr_common.log_size = OPTS_GET(log_opts, size, 0);
> +		attr_common.log_level = OPTS_GET(log_opts, level, 0);
> +		fd = sys_bpf_ext_fd(BPF_MAP_CREATE, &attr, attr_sz, &attr_common, attr_common_sz);
> +		OPTS_SET(log_opts, true_size, attr_common.log_true_size);
> +	} else {
> +		fd = sys_bpf_fd(BPF_MAP_CREATE, &attr, attr_sz);
> +		OPTS_SET(log_opts, true_size, 0);
> +	}
>  	return libbpf_err_errno(fd);
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260512153157.28382-1-leon.hwang@linux.dev?part=7