bpf: btf: Check array t->size

This patch ensures array's t->size is 0.

The array size is decided by its individual elem's size and the
number of elements.  Hence, t->size is not used and
it must be 0.

A test case is added to test_btf.c

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

kernel/bpf/btf.c

@@ -1342,6 +1342,11 @@ static s32 btf_array_check_meta(struct btf_verifier_env *env,
 		return -EINVAL;
 	}
 
+	if (t->size) {
+		btf_verifier_log_type(env, t, "size != 0");
+		return -EINVAL;
+	}
+
 	/* Array elem type and index type cannot be in type void,
 	 * so !array->type and !array->index_type are not allowed.
 	 */