new file mode 100644
@@ -0,0 +1,256 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
+
+/*
+ * Test suite of lwt BPF programs that reroutes packets
+ * The file tests focus not only if these programs work as expected normally,
+ * but also if they can handle abnormal situations gracefully. This test
+ * suite currently only covers lwt_xmit hook. lwt_in tests have not been
+ * implemented.
+ *
+ * WARNING
+ * -------
+ * This test suite can crash the kernel, thus should be run in a VM.
+ *
+ * Setup:
+ * ---------
+ * all tests are performed in a single netns. A lwt encap route is setup for
+ * each subtest:
+ *
+ * ip route add 10.0.0.0/24 encap bpf xmit <obj> sec "<section_N>" dev link_err
+ *
+ * Here <obj> is statically defined to test_lwt_reroute.bpf.o, and it contains
+ * a single test program entry. This program sets packet mark by last byte of
+ * the IPv4 daddr. For example, a packet going to 1.2.3.4 will receive a skb
+ * mark 4. A packet will only be marked once, and IP x.x.x.0 will be skipped
+ * to avoid route loop. We didn't use generated BPF skeleton since the
+ * attachment for lwt programs are not supported by libbpf yet.
+ *
+ * The test program will bring up a tun device, and sets up the following
+ * routes:
+ *
+ * ip rule add pref 100 from all fwmark <tun_index> lookup 100
+ * ip route add table 100 default dev tun0
+ *
+ * For normal testing, a ping command is running in the test netns:
+ *
+ * ping 10.0.0.<tun_index> -c 1 -w 1 -s 100
+ *
+ * For abnormal testing, fq is used as the qdisc of the tun device. Then a UDP
+ * socket will try to overflow the fq queue and trigger qdisc drop error.
+ *
+ * Scenarios:
+ * --------------------------------
+ * 1. Reroute to a running tun device
+ * 2. Reroute to a device where qdisc drop
+ *
+ * For case 1, ping packets should be received by the tun device.
+ *
+ * For case 2, force UDP packets to overflow fq limit. As long as kernel
+ * is not crashed, it is considered successful.
+ */
+#include "lwt_helpers.h"
+#include "network_helpers.h"
+#include <linux/net_tstamp.h>
+
+#define BPF_OBJECT "test_lwt_reroute.bpf.o"
+#define LOCAL_SRC "10.0.0.1"
+#define TEST_CIDR "10.0.0.0/24"
+#define XMIT_HOOK "xmit"
+#define XMIT_SECTION "lwt_xmit"
+#define NSEC_PER_SEC 1000000000ULL
+
+/* send a ping to be rerouted to the target device */
+static void ping_once(const char *ip)
+{
+ /* We won't get a reply. Don't fail here */
+ SYS_NOFAIL("ping %s -c1 -w1 -s %d >/dev/null 2>&1",
+ ip, ICMP_PAYLOAD_SIZE);
+}
+
+/* Send snd_target UDP packets to overflow the fq queue and trigger qdisc drop
+ * error. This is done via TX tstamp to force buffering delayed packets.
+ */
+static int overflow_fq(int snd_target, const char *target_ip)
+{
+ struct sockaddr_in addr = {
+ .sin_family = AF_INET,
+ .sin_port = htons(1234),
+ };
+
+ char data_buf[8]; /* only #pkts matter, so use a random small buffer */
+ char control_buf[CMSG_SPACE(sizeof(uint64_t))];
+ struct iovec iov = {
+ .iov_base = data_buf,
+ .iov_len = sizeof(data_buf),
+ };
+ int err = -1;
+ int s = -1;
+ struct sock_txtime txtime_on = {
+ .clockid = CLOCK_MONOTONIC,
+ .flags = 0,
+ };
+ struct msghdr msg = {
+ .msg_name = &addr,
+ .msg_namelen = sizeof(addr),
+ .msg_control = control_buf,
+ .msg_controllen = sizeof(control_buf),
+ .msg_iovlen = 1,
+ .msg_iov = &iov,
+ };
+ struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+
+ memset(data_buf, 0, sizeof(data_buf));
+
+ s = socket(AF_INET, SOCK_DGRAM, 0);
+ if (!ASSERT_GE(s, 0, "socket"))
+ goto out;
+
+ err = setsockopt(s, SOL_SOCKET, SO_TXTIME, &txtime_on, sizeof(txtime_on));
+ if (!ASSERT_OK(err, "setsockopt(SO_TXTIME)"))
+ goto out;
+
+ err = inet_pton(AF_INET, target_ip, &addr.sin_addr);
+ if (!ASSERT_EQ(err, 1, "inet_pton"))
+ goto out;
+
+ while (snd_target > 0) {
+ struct timespec now;
+
+ memset(control_buf, 0, sizeof(control_buf));
+ cmsg->cmsg_type = SCM_TXTIME;
+ cmsg->cmsg_level = SOL_SOCKET;
+ cmsg->cmsg_len = CMSG_LEN(sizeof(uint64_t));
+
+ err = clock_gettime(CLOCK_MONOTONIC, &now);
+ if (!ASSERT_OK(err, "clock_gettime(CLOCK_MONOTONIC)")) {
+ err = -1;
+ goto out;
+ }
+
+ *(uint64_t *)CMSG_DATA(cmsg) = (now.tv_nsec + 1) * NSEC_PER_SEC +
+ now.tv_nsec;
+
+ /* we will intentionally send more than fq limit, so ignore
+ * the error here.
+ */
+ sendmsg(s, &msg, MSG_NOSIGNAL);
+ snd_target--;
+ }
+
+ /* no kernel crash so far is considered success */
+ err = 0;
+
+out:
+ if (s >= 0)
+ close(s);
+
+ return err;
+}
+
+static int setup(const char *tun_dev)
+{
+ int target_index = -1;
+ int tap_fd = -1;
+
+ tap_fd = open_tuntap(tun_dev, false);
+ if (!ASSERT_GE(tap_fd, 0, "open_tun"))
+ return -1;
+
+ target_index = if_nametoindex(tun_dev);
+ if (!ASSERT_GE(target_index, 0, "if_nametoindex"))
+ return -1;
+
+ SYS(fail, "ip link add link_err type dummy");
+ SYS(fail, "ip link set lo up");
+ SYS(fail, "ip addr add dev lo " LOCAL_SRC "/32");
+ SYS(fail, "ip link set link_err up");
+ SYS(fail, "ip link set %s up", tun_dev);
+
+ SYS(fail, "ip route add %s dev link_err encap bpf xmit obj %s sec lwt_xmit",
+ TEST_CIDR, BPF_OBJECT);
+
+ SYS(fail, "ip rule add pref 100 from all fwmark %d lookup 100",
+ target_index);
+ SYS(fail, "ip route add t 100 default dev %s", tun_dev);
+
+ return tap_fd;
+
+fail:
+ if (tap_fd >= 0)
+ close(tap_fd);
+ return -1;
+}
+
+static void test_lwt_reroute_normal_xmit(void)
+{
+ const char *tun_dev = "tun0";
+ int tun_fd = -1;
+ int ifindex = -1;
+ char ip[256];
+ struct timeval timeo = {
+ .tv_sec = 0,
+ .tv_usec = 250000,
+ };
+
+ tun_fd = setup(tun_dev);
+ if (!ASSERT_GE(tun_fd, 0, "setup_reroute"))
+ return;
+
+ ifindex = if_nametoindex(tun_dev);
+ snprintf(ip, 256, "10.0.0.%d", ifindex);
+
+ /* ping packets should be received by the tun device */
+ ping_once(ip);
+
+ if (!ASSERT_EQ(wait_for_packet(tun_fd, __expect_icmp_ipv4, &timeo), 1,
+ "wait_for_packet"))
+ log_err("%s xmit", __func__);
+}
+
+/*
+ * Test the failure case when the skb is dropped at the qdisc. This is a
+ * regression prevention at the xmit hook only.
+ */
+static void test_lwt_reroute_qdisc_dropped(void)
+{
+ const char *tun_dev = "tun0";
+ int tun_fd = -1;
+ int ifindex = -1;
+ char ip[256];
+
+ tun_fd = setup(tun_dev);
+ if (!ASSERT_GE(tun_fd, 0, "setup_reroute"))
+ goto fail;
+
+ SYS(fail, "tc qdisc replace dev %s root fq limit 5 flow_limit 5", tun_dev);
+
+ ifindex = if_nametoindex(tun_dev);
+ snprintf(ip, 256, "10.0.0.%d", ifindex);
+ ASSERT_EQ(overflow_fq(10, ip), 0, "overflow_fq");
+
+fail:
+ if (tun_fd >= 0)
+ close(tun_fd);
+}
+
+static void *test_lwt_reroute_run(void *arg)
+{
+ netns_delete();
+ RUN_TEST(lwt_reroute_normal_xmit);
+ RUN_TEST(lwt_reroute_qdisc_dropped);
+ return NULL;
+}
+
+void test_lwt_reroute(void)
+{
+ pthread_t test_thread;
+ int err;
+
+ /* Run the tests in their own thread to isolate the namespace changes
+ * so they do not affect the environment of other tests.
+ * (specifically needed because of unshare(CLONE_NEWNS) in open_netns())
+ */
+ err = pthread_create(&test_thread, NULL, &test_lwt_reroute_run, NULL);
+ if (ASSERT_OK(err, "pthread_create"))
+ ASSERT_OK(pthread_join(test_thread, NULL), "pthread_join");
+}
new file mode 100644
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <inttypes.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_endian.h>
+#include <bpf/bpf_helpers.h>
+#include <linux/if_ether.h>
+#include <linux/ip.h>
+
+/* This function extracts the last byte of the daddr, and uses it
+ * as output dev index.
+ */
+SEC("lwt_xmit")
+int test_lwt_reroute(struct __sk_buff *skb)
+{
+ struct iphdr *iph = NULL;
+ void *start = (void *)(long)skb->data;
+ void *end = (void *)(long)skb->data_end;
+
+ /* set mark at most once */
+ if (skb->mark != 0)
+ return BPF_OK;
+
+ if (start + sizeof(*iph) > end)
+ return BPF_DROP;
+
+ iph = (struct iphdr *)start;
+ skb->mark = bpf_ntohl(iph->daddr) & 0xff;
+
+ /* do not reroute x.x.x.0 packets */
+ if (skb->mark == 0)
+ return BPF_OK;
+
+ return BPF_LWT_REROUTE;
+}
+
+char _license[] SEC("license") = "GPL";
There is no lwt selftest for BPF_REROUTE yet. Add test cases for both normal and abnormal situations. The abnormal situation is set up with an fq qdisc on the reroute target device. Without proper fixes, BPF_REROUTE to this device and overflow this qdisc queue limit (to trigger a drop) would panic the kernel, so please run the test in a VM for safety. Signed-off-by: Yan Zhai <yan@cloudflare.com> --- .../selftests/bpf/prog_tests/lwt_reroute.c | 256 ++++++++++++++++++ .../selftests/bpf/progs/test_lwt_reroute.c | 36 +++ 2 files changed, 292 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/lwt_reroute.c create mode 100644 tools/testing/selftests/bpf/progs/test_lwt_reroute.c