bpf: adding tests for bpf_xdp_adjust_tail

adding selftests for bpf_xdp_adjust_tail helper. in this synthetic test
we are testing that 1) if data_end < data helper will return EINVAL
2) for normal use case packet's length would be reduced.

Signed-off-by: Nikita V. Shirokov <tehnerd@tehnerd.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/test_progs.c

@@ -166,6 +166,37 @@ out:
 	bpf_object__close(obj);
 }
 
+static void test_xdp_adjust_tail(void)
+{
+	const char *file = "./test_adjust_tail.o";
+	struct bpf_object *obj;
+	char buf[128];
+	__u32 duration, retval, size;
+	int err, prog_fd;
+
+	err = bpf_prog_load(file, BPF_PROG_TYPE_XDP, &obj, &prog_fd);
+	if (err) {
+		error_cnt++;
+		return;
+	}
+
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				buf, &size, &retval, &duration);
+
+	CHECK(err || errno || retval != XDP_DROP,
+	      "ipv4", "err %d errno %d retval %d size %d\n",
+	      err, errno, retval, size);
+
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v6, sizeof(pkt_v6),
+				buf, &size, &retval, &duration);
+	CHECK(err || errno || retval != XDP_TX || size != 54,
+	      "ipv6", "err %d errno %d retval %d size %d\n",
+	      err, errno, retval, size);
+	bpf_object__close(obj);
+}
+
+
+
 #define MAGIC_VAL 0x1234
 #define NUM_ITER 100000
 #define VIP_NUM 5
@@ -1177,6 +1208,7 @@ int main(void)
 {
 	test_pkt_access();
 	test_xdp();
+	test_xdp_adjust_tail();
 	test_l4lb_all();
 	test_xdp_noinline();
 	test_tcp_estats();