bpf: verifier: bail out if the argument is not a map

When a kfunc is declared with a KF_ARG_PTR_TO_MAP, we should have
reg->map_ptr set to a non NULL value, otherwise, that means that the
underlying type is not a map.
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/20240420-bpf_wq-v2-7-6c986a5a741f@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/verifier.c

@@ -11720,6 +11720,11 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 		case KF_ARG_PTR_TO_NULL:
 			continue;
 		case KF_ARG_PTR_TO_MAP:
+			if (!reg->map_ptr) {
+				verbose(env, "pointer in R%d isn't map pointer\n", regno);
+				return -EINVAL;
+			}
+			fallthrough;
 		case KF_ARG_PTR_TO_ALLOC_BTF_ID:
 		case KF_ARG_PTR_TO_BTF_ID:
 			if (!is_kfunc_trusted_args(meta) && !is_kfunc_rcu(meta))