bpf: btf: Ensure t->type == 0 for BTF_KIND_FWD

The t->type in BTF_KIND_FWD is not used.  It must be 0.
This patch ensures that and also adds a test case in test_btf.c

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 20 insertions, 1 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 84ad532f2854..8653ab004c73 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -1286,8 +1286,27 @@ static struct btf_kind_operations ptr_ops = {
 	.seq_show = btf_ptr_seq_show,
 };
 
+static s32 btf_fwd_check_meta(struct btf_verifier_env *env,
+			      const struct btf_type *t,
+			      u32 meta_left)
+{
+	if (btf_type_vlen(t)) {
+		btf_verifier_log_type(env, t, "vlen != 0");
+		return -EINVAL;
+	}
+
+	if (t->type) {
+		btf_verifier_log_type(env, t, "type != 0");
+		return -EINVAL;
+	}
+
+	btf_verifier_log_type(env, t, NULL);
+
+	return 0;
+}
+
 static struct btf_kind_operations fwd_ops = {
-	.check_meta = btf_ref_type_check_meta,
+	.check_meta = btf_fwd_check_meta,
 	.resolve = btf_df_resolve,
 	.check_member = btf_df_check_member,
 	.log_details = btf_ref_type_log,