selftests/bpf: Add test for XDP metadata support in tun driver

Add a selftest that creates a tap device, attaches XDP and TC programs,
writes a packet with a test payload into the tap device and checks the
test result. This test ensures that the XDP metadata support in the tun
driver is enabled and that the metadata size is correctly passed to the
skb.

See the previous commit ("selftests/bpf: refactor xdp_context_functional
test and bpf program") for details about the test design.

The test runs in its own network namespace. This provides some extra
safety against conflicting interface names.

Signed-off-by: Marcus Wichelmann <marcus.wichelmann@hetzner-cloud.de>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20250305213438.3863922-6-marcus.wichelmann@hetzner-cloud.de

1 files changed, 66 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
index 78ca01edb050..b9d9f0a502ce 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
@@ -8,6 +8,8 @@
 #define TX_NAME "veth1"
 #define TX_NETNS "xdp_context_tx"
 #define RX_NETNS "xdp_context_rx"
+#define TAP_NAME "tap0"
+#define TAP_NETNS "xdp_context_tuntap"
 
 #define TEST_PAYLOAD_LEN 32
 static const __u8 test_payload[TEST_PAYLOAD_LEN] = {
@@ -255,3 +257,67 @@ close:
 	netns_free(tx_ns);
 }
 
+void test_xdp_context_tuntap(void)
+{
+	LIBBPF_OPTS(bpf_tc_hook, tc_hook, .attach_point = BPF_TC_INGRESS);
+	LIBBPF_OPTS(bpf_tc_opts, tc_opts, .handle = 1, .priority = 1);
+	struct netns_obj *ns = NULL;
+	struct test_xdp_meta *skel = NULL;
+	__u8 packet[sizeof(struct ethhdr) + TEST_PAYLOAD_LEN];
+	int tap_fd = -1;
+	int tap_ifindex;
+	int ret;
+
+	ns = netns_new(TAP_NETNS, true);
+	if (!ASSERT_OK_PTR(ns, "create and open ns"))
+		return;
+
+	tap_fd = open_tuntap(TAP_NAME, true);
+	if (!ASSERT_GE(tap_fd, 0, "open_tuntap"))
+		goto close;
+
+	SYS(close, "ip link set dev " TAP_NAME " up");
+
+	skel = test_xdp_meta__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open and load skeleton"))
+		goto close;
+
+	tap_ifindex = if_nametoindex(TAP_NAME);
+	if (!ASSERT_GE(tap_ifindex, 0, "if_nametoindex"))
+		goto close;
+
+	tc_hook.ifindex = tap_ifindex;
+	ret = bpf_tc_hook_create(&tc_hook);
+	if (!ASSERT_OK(ret, "bpf_tc_hook_create"))
+		goto close;
+
+	tc_opts.prog_fd = bpf_program__fd(skel->progs.ing_cls);
+	ret = bpf_tc_attach(&tc_hook, &tc_opts);
+	if (!ASSERT_OK(ret, "bpf_tc_attach"))
+		goto close;
+
+	ret = bpf_xdp_attach(tap_ifindex, bpf_program__fd(skel->progs.ing_xdp),
+			     0, NULL);
+	if (!ASSERT_GE(ret, 0, "bpf_xdp_attach"))
+		goto close;
+
+	/* The ethernet header is not relevant for this test and doesn't need to
+	 * be meaningful.
+	 */
+	struct ethhdr eth = { 0 };
+
+	memcpy(packet, &eth, sizeof(eth));
+	memcpy(packet + sizeof(eth), test_payload, TEST_PAYLOAD_LEN);
+
+	ret = write(tap_fd, packet, sizeof(packet));
+	if (!ASSERT_EQ(ret, sizeof(packet), "write packet"))
+		goto close;
+
+	assert_test_result(skel);
+
+close:
+	if (tap_fd >= 0)
+		close(tap_fd);
+	test_xdp_meta__destroy(skel);
+	netns_free(ns);
+}