selftests/bpf: Add lwt_xmit tests for BPF_REDIRECT

There is no lwt_xmit test case for BPF_REDIRECT yet. Add test cases for
both normal and abnormal situations. For abnormal test cases, devices
are set down or have its carrier set down. Without proper fixes,
BPF_REDIRECT to either ingress or egress of such device would panic the
kernel.

Signed-off-by: Yan Zhai <yan@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/96bf435243641939d9c9da329fab29cb45f7df22.1692326837.git.yan@cloudflare.com

Author: yanzhai-cf

tools/testing/selftests/bpf/config

@@ -16,6 +16,7 @@ CONFIG_CRYPTO_USER_API_HASH=y
 CONFIG_DEBUG_INFO=y
 CONFIG_DEBUG_INFO_BTF=y
 CONFIG_DEBUG_INFO_DWARF4=y
+CONFIG_DUMMY=y
 CONFIG_DYNAMIC_FTRACE=y
 CONFIG_FPROBE=y
 CONFIG_FTRACE_SYSCALLS=y

tools/testing/selftests/bpf/prog_tests/lwt_helpers.h

@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __LWT_HELPERS_H
+#define __LWT_HELPERS_H
+
+#include <time.h>
+#include <net/if.h>
+#include <linux/if_tun.h>
+#include <linux/icmp.h>
+
+#include "test_progs.h"
+
+#define log_err(MSG, ...) \
+	fprintf(stderr, "(%s:%d: errno: %s) " MSG "\n", \
+		__FILE__, __LINE__, strerror(errno), ##__VA_ARGS__)
+
+#define RUN_TEST(name)                                                        \
+	({                                                                    \
+		if (test__start_subtest(#name))                               \
+			if (ASSERT_OK(netns_create(), "netns_create")) {      \
+				struct nstoken *token = open_netns(NETNS);    \
+				if (ASSERT_OK_PTR(token, "setns")) {          \
+					test_ ## name();                      \
+					close_netns(token);                   \
+				}                                             \
+				netns_delete();                               \
+			}                                                     \
+	})
+
+#define NETNS "ns_lwt"
+
+static inline int netns_create(void)
+{
+	return system("ip netns add " NETNS);
+}
+
+static inline int netns_delete(void)
+{
+	return system("ip netns del " NETNS ">/dev/null 2>&1");
+}
+
+static int open_tuntap(const char *dev_name, bool need_mac)
+{
+	int err = 0;
+	struct ifreq ifr;
+	int fd = open("/dev/net/tun", O_RDWR);
+
+	if (!ASSERT_GT(fd, 0, "open(/dev/net/tun)"))
+		return -1;
+
+	ifr.ifr_flags = IFF_NO_PI | (need_mac ? IFF_TAP : IFF_TUN);
+	memcpy(ifr.ifr_name, dev_name, IFNAMSIZ);
+
+	err = ioctl(fd, TUNSETIFF, &ifr);
+	if (!ASSERT_OK(err, "ioctl(TUNSETIFF)")) {
+		close(fd);
+		return -1;
+	}
+
+	err = fcntl(fd, F_SETFL, O_NONBLOCK);
+	if (!ASSERT_OK(err, "fcntl(O_NONBLOCK)")) {
+		close(fd);
+		return -1;
+	}
+
+	return fd;
+}
+
+#define ICMP_PAYLOAD_SIZE     100
+
+/* Match an ICMP packet with payload len ICMP_PAYLOAD_SIZE */
+static int __expect_icmp_ipv4(char *buf, ssize_t len)
+{
+	struct iphdr *ip = (struct iphdr *)buf;
+	struct icmphdr *icmp = (struct icmphdr *)(ip + 1);
+	ssize_t min_header_len = sizeof(*ip) + sizeof(*icmp);
+
+	if (len < min_header_len)
+		return -1;
+
+	if (ip->protocol != IPPROTO_ICMP)
+		return -1;
+
+	if (icmp->type != ICMP_ECHO)
+		return -1;
+
+	return len == ICMP_PAYLOAD_SIZE + min_header_len;
+}
+
+typedef int (*filter_t) (char *, ssize_t);
+
+/* wait_for_packet - wait for a packet that matches the filter
+ *
+ * @fd: tun fd/packet socket to read packet
+ * @filter: filter function, returning 1 if matches
+ * @timeout: timeout to wait for the packet
+ *
+ * Returns 1 if a matching packet is read, 0 if timeout expired, -1 on error.
+ */
+static int wait_for_packet(int fd, filter_t filter, struct timeval *timeout)
+{
+	char buf[4096];
+	int max_retry = 5; /* in case we read some spurious packets */
+	fd_set fds;
+
+	FD_ZERO(&fds);
+	while (max_retry--) {
+		/* Linux modifies timeout arg... So make a copy */
+		struct timeval copied_timeout = *timeout;
+		ssize_t ret = -1;
+
+		FD_SET(fd, &fds);
+
+		ret = select(1 + fd, &fds, NULL, NULL, &copied_timeout);
+		if (ret <= 0) {
+			if (errno == EINTR)
+				continue;
+			else if (errno == EAGAIN || ret == 0)
+				return 0;
+
+			log_err("select failed");
+			return -1;
+		}
+
+		ret = read(fd, buf, sizeof(buf));
+
+		if (ret <= 0) {
+			log_err("read(dev): %ld", ret);
+			return -1;
+		}
+
+		if (filter && filter(buf, ret) > 0)
+			return 1;
+	}
+
+	return 0;
+}
+
+#endif /* __LWT_HELPERS_H */