selftests: bpf: add test for skb_load_bytes

Use bpf_prog_test_run_opts to test the skb_load_bytes function.
Tests behavior when offset is greater than INT_MAX or a normal value.

Signed-off-by: Liu Jian <liujian56@huawei.com>

tools/testing/selftests/bpf/prog_tests/skb_load_bytes.c

@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include <network_helpers.h>
+
+void test_skb_load_bytes(void)
+{
+	struct bpf_map *test_result;
+
+	__u32 map_key = 0;
+	__u32 map_value = 0;
+
+	struct bpf_object *obj;
+	int err, map_fd, prog_fd;
+
+	struct __sk_buff skb = { 0 };
+
+	LIBBPF_OPTS(bpf_test_run_opts, tattr,
+			.data_in = &pkt_v4,
+			.data_size_in = sizeof(pkt_v4),
+			.ctx_in = &skb,
+			.ctx_size_in = sizeof(skb),
+		   );
+
+	err = bpf_prog_test_load("./skb_load_bytes.o", BPF_PROG_TYPE_SCHED_CLS, &obj,
+			&prog_fd);
+	if (CHECK_ATTR(err, "load", "err %d errno %d\n", err, errno))
+		return;
+
+	test_result = bpf_object__find_map_by_name(obj, "test_result");
+	if (CHECK_FAIL(!test_result))
+		goto close_bpf_object;
+
+	map_fd = bpf_map__fd(test_result);
+	if (map_fd < 0)
+		goto close_bpf_object;
+
+	map_key = 0;
+	map_value = -1;
+	err = bpf_map_update_elem(map_fd, &map_key, &map_value, BPF_ANY);
+	if (CHECK_FAIL(err))
+		goto close_bpf_object;
+	tattr.data_out = NULL;
+	tattr.data_size_out = 0;
+	err = bpf_prog_test_run_opts(prog_fd, &tattr);
+	CHECK_ATTR(err != 0, "offset -1", "err %d errno %d\n", err, errno);
+	map_key = 1;
+	bpf_map_lookup_elem(map_fd, &map_key, &map_value);
+	CHECK_ATTR(map_value != -14, "offset -1", "get result error\n");
+
+	map_key = 0;
+	map_value = 10;
+	err = bpf_map_update_elem(map_fd, &map_key, &map_value, BPF_ANY);
+	if (CHECK_FAIL(err))
+		goto close_bpf_object;
+	tattr.data_out = NULL;
+	tattr.data_size_out = 0;
+	err = bpf_prog_test_run_opts(prog_fd, &tattr);
+	CHECK_ATTR(err != 0, "offset 10", "err %d errno %d\n", err, errno);
+	map_key = 1;
+	bpf_map_lookup_elem(map_fd, &map_key, &map_value);
+	CHECK_ATTR(map_value != 0, "offset 10", "get result error\n");
+
+close_bpf_object:
+	bpf_object__close(obj);
+}

tools/testing/selftests/bpf/progs/skb_load_bytes.c

@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 2);
+	__type(key, __u32);
+	__type(value, __u32);
+} test_result SEC(".maps");
+
+SEC("tc")
+int skb_process(struct __sk_buff *skb)
+{
+	char buf[16];
+	int ret = 0;
+	__u32 map_key = 0;
+	__u32 *offset = NULL;
+
+	offset = bpf_map_lookup_elem(&test_result, &map_key);
+	if (offset == NULL) {
+		bpf_printk("get offset failed\n");
+		map_key = 1;
+		ret = -1;
+		bpf_map_update_elem(&test_result, &map_key, &ret, BPF_ANY);
+		return ret;
+	}
+
+	ret = bpf_skb_load_bytes(skb, *offset, buf, 10);
+	map_key = 1;
+	bpf_map_update_elem(&test_result, &map_key, &ret, BPF_ANY);
+
+	return 0;
+}