[PATCH bpf-next v6 1/6] selftests/bpf: Add traffic monitor functions.

Kui-Feng Lee
2024-08-07T18:31:55Z

Add functions that capture packets and print log in the background. They
are supposed to be used for debugging flaky network test cases. A monitored
test case should call traffic_monitor_start() to start a thread to capture
packets in the background for a given namespace and call
traffic_monitor_stop() to stop capturing. (Or, option '-m' implemented by
the later patches.)

IPv4 TCP packet: 127.0.0.1:48423 -> 127.0.0.1:40991, len 68, ifname lo (In), SYN
IPv4 TCP packet: 127.0.0.1:40991 -> 127.0.0.1:48423, len 60, ifname lo (In), SYN, ACK
IPv4 TCP packet: 127.0.0.1:48423 -> 127.0.0.1:40991, len 60, ifname lo (In), ACK
IPv4 TCP packet: 127.0.0.1:40991 -> 127.0.0.1:48423, len 52, ifname lo (In), ACK
IPv4 TCP packet: 127.0.0.1:48423 -> 127.0.0.1:40991, len 52, ifname lo (In), FIN, ACK
IPv4 TCP packet: 127.0.0.1:40991 -> 127.0.0.1:48423, len 52, ifname lo (In), RST, ACK
Packet file: packets-2173-86-select_reuseport:sockhash_IPv4_TCP_LOOPBACK_test_detach_bpf-test.log
#280/87 select_reuseport/sockhash IPv4/TCP LOOPBACK test_detach_bpf:OK

The above is the output of an example. It shows the packets of a connection
and the name of the file that contains captured packets in the directory
/tmp/tmon_pcap. The file can be loaded by tcpdump or wireshark.

This feature only works if libpcap is available. (Could be found by pkg-config)

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
---
tools/testing/selftests/bpf/Makefile | 4 +
tools/testing/selftests/bpf/network_helpers.c | 454 ++++++++++++++++++
tools/testing/selftests/bpf/network_helpers.h | 18 +
3 files changed, 476 insertions(+)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index f54185e96a95..098e1092f1f5 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -41,6 +41,10 @@ CFLAGS += -g $(OPT_FLAGS) -rdynamic \
LDFLAGS += $(SAN_LDFLAGS)
LDLIBS += $(LIBELF_LIBS) -lz -lrt -lpthread

+LDLIBS += $(shell $(PKG_CONFIG) --libs libpcap 2>/dev/null)
+CFLAGS += $(shell $(PKG_CONFIG) --cflags libpcap 2>/dev/null)
+CFLAGS += $(shell $(PKG_CONFIG) --exists libpcap 2>/dev/null && echo "-DTRAFFIC_MONITOR=1")
+
# The following tests perform type punning and they may break strict
# aliasing rules, which are exploited by both GCC and clang by default
# while optimizing. This can lead to broken programs.
diff --git a/tools/testing/selftests/bpf/network_helpers.c b/tools/testing/selftests/bpf/network_helpers.c
index a3f0a49fb26f..462aeadd767e 100644
--- a/tools/testing/selftests/bpf/network_helpers.c
+++ b/tools/testing/selftests/bpf/network_helpers.c
@@ -11,6 +11,7 @@
#include <arpa/inet.h>
#include <sys/mount.h>
#include <sys/stat.h>
+#include <sys/types.h>
#include <sys/un.h>

#include <linux/err.h>
@@ -18,10 +19,22 @@
#include <linux/in6.h>
#include <linux/limits.h>

+#include <linux/ip.h>
+#include <linux/udp.h>
+#include <netinet/tcp.h>
+#include <net/if.h>
+
#include "bpf_util.h"
#include "network_helpers.h"
#include "test_progs.h"

+#ifdef TRAFFIC_MONITOR
+/* Prevent pcap.h from including pcap/bpf.h and causing conflicts */
+#define PCAP_DONT_INCLUDE_PCAP_BPF_H 1
+#include <pcap/pcap.h>
+#include <pcap/dlt.h>
+#endif
+
#ifndef IPPROTO_MPTCP
#define IPPROTO_MPTCP 262
#endif
@@ -660,3 +673,444 @@ int send_recv_data(int lfd, int fd, uint32_t total_bytes)

return err;
}
+
+#ifdef TRAFFIC_MONITOR
+struct tmonitor_ctx {
+ pcap_t *pcap;
+ pcap_dumper_t *dumper;
+ pthread_t thread;
+ int wake_fd_r;
+ int wake_fd_w;
+
+ bool done;
+ char pkt_fname[PATH_MAX];
+ int pcap_fd;
+};
+
+/* Is this packet captured with a Ethernet protocol type? */
+static bool is_ethernet(const u_char *packet)
+{
+ u16 arphdr_type;
+
+ memcpy(&arphdr_type, packet + 8, 2);
+ arphdr_type = ntohs(arphdr_type);
+
+ /* Except the following cases, the protocol type contains the
+ * Ethernet protocol type for the packet.
+ *
+ * https://www.tcpdump.org/linktypes/LINKTYPE_LINUX_SLL2.html
+ */
+ switch (arphdr_type) {
+ case 770: /* ARPHRD_FRAD */
+ case 778: /* ARPHDR_IPGRE */
+ case 803: /* ARPHRD_IEEE80211_RADIOTAP */
+ return false;
+ }
+ return true;
+}
+
+static const char * const pkt_types[] = {
+ "In",
+ "B", /* Broadcast */
+ "M", /* Multicast */
+ "C", /* Captured with the promiscuous mode */
+ "Out",
+};
+
+static const char *pkt_type_str(u16 pkt_type)
+{
+ if (pkt_type < ARRAY_SIZE(pkt_types))
+ return pkt_types[pkt_type];
+ return "Unknown";
+}
+
+/* Show the information of the transport layer in the packet */
+static void show_transport(const u_char *packet, u16 len, u32 ifindex,
+ const char *src_addr, const char *dst_addr,
+ u16 proto, bool ipv6, u8 pkt_type)
+{
+ char *ifname, _ifname[IF_NAMESIZE];
+ const char *transport_str;
+ u16 src_port, dst_port;
+ struct udphdr *udp;
+ struct tcphdr *tcp;
+
+ ifname = if_indextoname(ifindex, _ifname);
+ if (!ifname) {
+ snprintf(_ifname, sizeof(_ifname), "unknown(%d)", ifindex);
+ ifname = _ifname;
+ }
+
+ if (proto == IPPROTO_UDP) {
+ udp = (struct udphdr *)packet;
+ src_port = ntohs(udp->source);
+ dst_port = ntohs(udp->dest);
+ transport_str = "UDP";
+ } else if (proto == IPPROTO_TCP) {
+ tcp = (struct tcphdr *)packet;
+ src_port = ntohs(tcp->source);
+ dst_port = ntohs(tcp->dest);
+ transport_str = "TCP"
+;
+ } else if (proto == IPPROTO_ICMP) {
+ printf("IPv4 ICMP packet: %s -> %s, len %d, type %d, code %d, ifname %s (%s)\n",
+ src_addr, dst_addr, len, packet[0], packet[1], ifname,
+ pkt_type_str(pkt_type));
+ return;
+ } else if (proto == IPPROTO_ICMPV6) {
+ printf("IPv6 ICMPv6 packet: %s -> %s, len %d, type %d, code %d, ifname %s (%s)\n",
+ src_addr, dst_addr, len, packet[0], packet[1], ifname,
+ pkt_type_str(pkt_type));
+ return;
+ } else {
+ printf("%s (proto %d): %s -> %s, ifname %s (%s)\n",
+ ipv6 ? "IPv6" : "IPv4", proto, src_addr, dst_addr,
+ ifname, pkt_type_str(pkt_type));
+ return;
+ }
+
+ /* TCP */
+
+ flockfile(stdout);
+ if (ipv6)
+ printf("IPv6 %s packet: [%s]:%d -> [%s]:%d, len %d, ifname %s (%s)",
+ transport_str, src_addr, src_port,
+ dst_addr, dst_port, len, ifname, pkt_type_str(pkt_type));
+ else
+ printf("IPv4 %s packet: %s:%d -> %s:%d, len %d, ifname %s (%s)",
+ transport_str, src_addr, src_port,
+ dst_addr, dst_port, len, ifname, pkt_type_str(pkt_type));
+
+ if (proto == IPPROTO_TCP) {
+ if (tcp->fin)
+ printf(", FIN");
+ if (tcp->syn)
+ printf(", SYN");
+ if (tcp->rst)
+ printf(", RST");
+ if (tcp->ack)
+ printf(", ACK");
+ }
+
+ printf("\n");
+ funlockfile(stdout);
+}
+
+static void show_ipv6_packet(const u_char *packet, u32 ifindex, u8 pkt_type)
+{
+ char src_str[INET6_ADDRSTRLEN], dst_str[INET6_ADDRSTRLEN];
+ struct ipv6hdr *pkt = (struct ipv6hdr *)packet;
+ struct in6_addr src;
+ struct in6_addr dst;
+ u_char proto;
+
+ memcpy(&src, &pkt->saddr, sizeof(src));
+ memcpy(&dst, &pkt->daddr, sizeof(dst));
+ inet_ntop(AF_INET6, &src, src_str, sizeof(src_str));
+ inet_ntop(AF_INET6, &dst, dst_str, sizeof(dst_str));
+ proto = pkt->nexthdr;
+ show_transport(packet + sizeof(struct ipv6hdr),
+ ntohs(pkt->payload_len),
+ ifindex, src_str, dst_str, proto, true, pkt_type);
+}
+
+static void show_ipv4_packet(const u_char *packet, u32 ifindex, u8 pkt_type)
+{
+ char src_str[INET_ADDRSTRLEN], dst_str[INET_ADDRSTRLEN];
+ struct iphdr *pkt = (struct iphdr *)packet;
+ struct in_addr src;
+ struct in_addr dst;
+ u_char proto;
+
+ memcpy(&src, &pkt->saddr, sizeof(src));
+ memcpy(&dst, &pkt->daddr, sizeof(dst));
+ inet_ntop(AF_INET, &src, src_str, sizeof(src_str));
+ inet_ntop(AF_INET, &dst, dst_str, sizeof(dst_str));
+ proto = pkt->protocol;
+ show_transport(packet + sizeof(struct iphdr),
+ ntohs(pkt->tot_len),
+ ifindex, src_str, dst_str, proto, false, pkt_type);
+}
+
+static void *traffic_monitor_thread(void *arg)
+{
+ char *ifname, _ifname[IF_NAMESIZE];
+ const u_char *packet, *payload;
+ struct tmonitor_ctx *ctx = arg;
+ pcap_dumper_t *dumper = ctx->dumper;
+ int fd = ctx->pcap_fd, nfds, r;
+ int wake_fd = ctx->wake_fd_r;
+ struct pcap_pkthdr header;
+ pcap_t *pcap = ctx->pcap;
+ u32 ifindex;
+ fd_set fds;
+ u16 proto;
+ u8 ptype;
+
+ nfds = (fd > wake_fd ? fd : wake_fd) + 1;
+ FD_ZERO(&fds);
+
+ while (!ctx->done) {
+ FD_SET(fd, &fds);
+ FD_SET(wake_fd, &fds);
+ r = select(nfds, &fds, NULL, NULL, NULL);
+ if (!r)
+ continue;
+ if (r < 0) {
+ if (errno == EINTR)
+ continue;
+ log_err("Fail to select on pcap fd and wake fd: %s", strerror(errno));
+ break;
+ }
+
+ packet = pcap_next(pcap, &header);
+ if (!packet)
+ continue;
+
+ /* According to the man page of pcap_dump(), first argument
+ * is the pcap_dumper_t pointer even it's argument type is
+ * u_char *.
+ */
+ pcap_dump((u_char *)dumper, &header, packet);
+
+ /* Not sure what other types of packets look like. Here, we
+ * parse only Ethernet and compatible packets.
+ */
+ if (!is_ethernet(packet)) {
+ printf("Packet captured\n");
+ continue;
+ }
+
+ /* Skip SLL2 header
+ * https://www.tcpdump.org/linktypes/LINKTYPE_LINUX_SLL2.html
+ *
+ * Although the document doesn't mention that, the payload
+ * doesn't include the Ethernet header. The payload starts
+ * from the first byte of the network layer header.
+ */
+ payload = packet + 20;
+
+ memcpy(&proto, packet, 2);
+ proto = ntohs(proto);
+ memcpy(&ifindex, packet + 4, 4);
+ ifindex = ntohl(ifindex);
+ ptype = packet[10];
+
+ if (proto == ETH_P_IPV6) {
+ show_ipv6_packet(payload, ifindex, ptype);
+ } else if (proto == ETH_P_IP) {
+ show_ipv4_packet(payload, ifindex, ptype);
+ } else {
+ ifname = if_indextoname(ifindex, _ifname);
+ if (!ifname) {
+ snprintf(_ifname, sizeof(_ifname), "unknown(%d)", ifindex);
+ ifname = _ifname;
+ }
+
+ printf("Unknown network protocol type %x, ifname %s (%s)\n",
+ proto, ifname, pkt_type_str(ptype));
+ }
+ }
+
+ return NULL;
+}
+
+/* Prepare the pcap handle to capture packets.
+ *
+ * This pcap is non-blocking and immediate mode is enabled to receive
+ * captured packets as soon as possible. The snaplen is set to 1024 bytes
+ * to limit the size of captured content. The format of the link-layer
+ * header is set to DLT_LINUX_SLL2 to enable handling various link-layer
+ * technologies.
+ */
+static pcap_t *traffic_monitor_prepare_pcap(void)
+{
+ char errbuf[PCAP_ERRBUF_SIZE];
+ pcap_t *pcap;
+ int r;
+
+ /* Listen on all NICs in the namespace */
+ pcap = pcap_create("any", errbuf);
+ if (!pcap) {
+ log_err("Failed to open pcap: %s", errbuf);
+ return NULL;
+ }
+ /* Limit the size of the packet (first N bytes) */
+ r = pcap_set_snaplen(pcap, 1024);
+ if (r) {
+ log_err("Failed to set snaplen: %s", pcap_geterr(pcap));
+ goto error;
+ }
+ /* To receive packets as fast as possible */
+ r = pcap_set_immediate_mode(pcap, 1);
+ if (r) {
+ log_err("Failed to set immediate mode: %s", pcap_geterr(pcap));
+ goto error;
+ }
+ r = pcap_setnonblock(pcap, 1, errbuf);
+ if (r) {
+ log_err("Failed to set nonblock: %s", errbuf);
+ goto error;
+ }
+ r = pcap_activate(pcap);
+ if (r) {
+ log_err("Failed to activate pcap: %s", pcap_geterr(pcap));
+ goto error;
+ }
+ /* Determine the format of the link-layer header */
+ r = pcap_set_datalink(pcap, DLT_LINUX_SLL2);
+ if (r) {
+ log_err("Failed to set datalink: %s", pcap_geterr(pcap));
+ goto error;
+ }
+
+ return pcap;
+error:
+ pcap_close(pcap);
+ return NULL;
+}
+
+static void encode_test_name(char *buf, size_t len, const char *test_name, const char *subtest_name)
+{
+ char *p;
+
+ if (subtest_name)
+ snprintf(buf, len, "%s:%s", test_name, subtest_name);
+ else
+ snprintf(buf, len, "%s", test_name);
+ while ((p = strchr(buf, '/')))
+ *p = '_';
+ while ((p = strchr(buf, ' ')))
+ *p = '_';
+}
+
+#define PCAP_DIR "/tmp/tmon_pcap"
+
+/* Start to monitor the network traffic in the given network namespace.
+ *
+ * netns: the name of the network namespace to monitor. If NULL, the
+ * current network namespace is monitored.
+ * test_name: the name of the running test.
+ * subtest_name: the name of the running subtest if there is. It should be
+ * NULL if it is not a subtest.
+ *
+ * This function will start a thread to capture packets going through NICs
+ * in the give network namespace.
+ */
+struct tmonitor_ctx *traffic_monitor_start(const char *netns, const char *test_name,
+ const char *subtest_name)
+{
+ struct tmonitor_ctx *ctx = NULL;
+ struct nstoken *nstoken = NULL;
+ int pipefd[2] = {-1, -1};
+ char test_name_buf[64];
+ static int tmon_seq;
+ int r;
+
+ if (netns) {
+ nstoken = open_netns(netns);
+ if (!nstoken)
+ return NULL;
+ }
+ ctx = malloc(sizeof(*ctx));
+ if (!ctx) {
+ log_err("Failed to malloc ctx");
+ goto fail_ctx;
+ }
+ memset(ctx, 0, sizeof(*ctx));
+
+ encode_test_name(test_name_buf, sizeof(test_name_buf), test_name, subtest_name);
+ snprintf(ctx->pkt_fname, sizeof(ctx->pkt_fname),
+ PCAP_DIR "/packets-%d-%d-%s-%s.log", getpid(), tmon_seq++,
+ test_name_buf, netns ? netns : "unknown");
+
+ r = mkdir(PCAP_DIR, 0755);
+ if (r && errno != EEXIST) {
+ log_err("Failed to create " PCAP_DIR);
+ goto fail_pcap;
+ }
+
+ ctx->pcap = traffic_monitor_prepare_pcap();
+ if (!ctx->pcap)
+ goto fail_pcap;
+ ctx->pcap_fd = pcap_get_selectable_fd(ctx->pcap);
+ if (ctx->pcap_fd < 0) {
+ log_err("Failed to get pcap fd");
+ goto fail_dumper;
+ }
+
+ /* Create a packet file */
+ ctx->dumper = pcap_dump_open(ctx->pcap, ctx->pkt_fname);
+ if (!ctx->dumper) {
+ log_err("Failed to open pcap dump: %s", ctx->pkt_fname);
+ goto fail_dumper;
+ }
+
+ /* Create a pipe to wake up the monitor thread */
+ r = pipe(pipefd);
+ if (r) {
+ log_err("Failed to create pipe: %s", strerror(errno));
+ goto fail;
+ }
+ ctx->wake_fd_r = pipefd[0];
+ ctx->wake_fd_w = pipefd[1];
+
+ r = pthread_create(&ctx->thread, NULL, traffic_monitor_thread, ctx);
+ if (r) {
+ log_err("Failed to create thread: %s", strerror(r));
+ goto fail;
+ }
+
+ close_netns(nstoken);
+
+ return ctx;
+
+fail:
+ close(pipefd[0]);
+ close(pipefd[1]);
+
+ pcap_dump_close(ctx->dumper);
+ unlink(ctx->pkt_fname);
+
+fail_dumper:
+ pcap_close(ctx->pcap);
+
+fail_pcap:
+ free(ctx);
+
+fail_ctx:
+ close_netns(nstoken);
+
+ return NULL;
+}
+
+static void traffic_monitor_release(struct tmonitor_ctx *ctx)
+{
+ pcap_close(ctx->pcap);
+ pcap_dump_close(ctx->dumper);
+
+ close(ctx->wake_fd_r);
+ close(ctx->wake_fd_w);
+
+ free(ctx);
+}
+
+/* Stop the network traffic monitor.
+ *
+ * ctx: the context returned by traffic_monitor_start()
+ */
+void traffic_monitor_stop(struct tmonitor_ctx *ctx)
+{
+ if (!ctx)
+ return;
+
+ /* Stop the monitor thread */
+ ctx->done = true;
+ write(ctx->wake_fd_w, "x", 1);
+ pthread_join(ctx->thread, NULL);
+
+ printf("Packet file: %s\n", strrchr(ctx->pkt_fname, '/') + 1);
+
+ traffic_monitor_release(ctx);
+}
+#endif /* TRAFFIC_MONITOR */
diff --git a/tools/testing/selftests/bpf/network_helpers.h b/tools/testing/selftests/bpf/network_helpers.h
index cce56955371f..0d032ae706c6 100644
--- a/tools/testing/selftests/bpf/network_helpers.h
+++ b/tools/testing/selftests/bpf/network_helpers.h
@@ -136,4 +136,22 @@ static inline __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
return csum_fold((__u32)s);
}

+struct tmonitor_ctx;
+
+#ifdef TRAFFIC_MONITOR
+struct tmonitor_ctx *traffic_monitor_start(const char *netns, const char *test_name,
+ const char *subtest_name);
+void traffic_monitor_stop(struct tmonitor_ctx *ctx);
+#else
+static inline struct tmonitor_ctx *traffic_monitor_start(const char *netns, const char *test_name,
+ const char *subtest_name)
+{
+ return NULL;
+}
+
+static inline void traffic_monitor_stop(struct tmonitor_ctx *ctx)
+{
+}
+#endif
+
#endif
--
2.34.1