bpf: Allow empty module BTFs

Some modules don't declare any new types and end up with an empty BTF,
containing only valid BTF header and no types or strings sections. This
currently causes BTF validation error. There is nothing wrong with such BTF,
so fix the issue by allowing module BTFs with no types or strings.

Fixes: 36e68442d1af ("bpf: Load and verify kernel module BTFs")
Reported-by: Christopher William Snowhill <chris@kode54.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210110070341.1380086-1-andrii@kernel.org

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 8d6bdb4..84a36ee 100644 (file)
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -4172,7 +4172,7 @@ static int btf_parse_hdr(struct btf_verifier_env *env)
                return -ENOTSUPP;
        }
 
-       if (btf_data_size == hdr->hdr_len) {
+       if (!btf->base_btf && btf_data_size == hdr->hdr_len) {
                btf_verifier_log(env, "No data");
                return -EINVAL;
        }