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.
 	 */

tools/testing/selftests/bpf/test_btf.c

@@ -1178,6 +1178,29 @@ static struct btf_raw_test raw_tests[] = {
 	.err_str = "Invalid index",
 },
 
+{
+	.descr = "array test. t->size != 0\"",
+	.raw_types = {
+		/* int */				/* [1] */
+		BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),
+		/* int[16] */				/* [2] */
+		BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_ARRAY, 0, 0), 1),
+		BTF_ARRAY_ENC(1, 1, 16),
+		BTF_END_RAW,
+	},
+	.str_sec = "",
+	.str_sec_size = sizeof(""),
+	.map_type = BPF_MAP_TYPE_ARRAY,
+	.map_name = "array_test_map",
+	.key_size = sizeof(int),
+	.value_size = sizeof(int),
+	.key_type_id = 1,
+	.value_type_id = 1,
+	.max_entries = 4,
+	.btf_load_err = true,
+	.err_str = "size != 0",
+},
+
 {
 	.descr = "int test. invalid int_data",
 	.raw_types = {