selftests/bpf: add a test case for sock_ops perf-event notification

This patch provides a tcp_bpf based eBPF sample. The test

- ncat(1) as the TCP client program to connect() to a port
  with the intention of triggerring SYN retransmissions: we
  first install an iptables DROP rule to make sure ncat SYNs are
  resent (instead of aborting instantly after a TCP RST)

- has a bpf kernel module that sends a perf-event notification for
  each TCP retransmit, and also tracks the number of such notifications
  sent in the global_map

The test passes when the number of event notifications intercepted
in user-space matches the value in the global_map.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 95 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/test_tcpnotify_kern.c b/tools/testing/selftests/bpf/test_tcpnotify_kern.c
new file mode 100644
index 000000000000..edbca203ce2d
--- /dev/null
+++ b/tools/testing/selftests/bpf/test_tcpnotify_kern.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stddef.h>
+#include <string.h>
+#include <linux/bpf.h>
+#include <linux/if_ether.h>
+#include <linux/if_packet.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/types.h>
+#include <linux/socket.h>
+#include <linux/tcp.h>
+#include <netinet/in.h>
+#include "bpf_helpers.h"
+#include "bpf_endian.h"
+#include "test_tcpnotify.h"
+
+struct bpf_map_def SEC("maps") global_map = {
+	.type = BPF_MAP_TYPE_ARRAY,
+	.key_size = sizeof(__u32),
+	.value_size = sizeof(struct tcpnotify_globals),
+	.max_entries = 4,
+};
+
+struct bpf_map_def SEC("maps") perf_event_map = {
+	.type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
+	.key_size = sizeof(int),
+	.value_size = sizeof(__u32),
+	.max_entries = 2,
+};
+
+int _version SEC("version") = 1;
+
+SEC("sockops")
+int bpf_testcb(struct bpf_sock_ops *skops)
+{
+	int rv = -1;
+	int op;
+
+	op = (int) skops->op;
+
+	if (bpf_ntohl(skops->remote_port) != TESTPORT) {
+		skops->reply = -1;
+		return 0;
+	}
+
+	switch (op) {
+	case BPF_SOCK_OPS_TIMEOUT_INIT:
+	case BPF_SOCK_OPS_RWND_INIT:
+	case BPF_SOCK_OPS_NEEDS_ECN:
+	case BPF_SOCK_OPS_BASE_RTT:
+	case BPF_SOCK_OPS_RTO_CB:
+		rv = 1;
+		break;
+
+	case BPF_SOCK_OPS_TCP_CONNECT_CB:
+	case BPF_SOCK_OPS_TCP_LISTEN_CB:
+	case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
+	case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
+		bpf_sock_ops_cb_flags_set(skops, (BPF_SOCK_OPS_RETRANS_CB_FLAG|
+					  BPF_SOCK_OPS_RTO_CB_FLAG));
+		rv = 1;
+		break;
+	case BPF_SOCK_OPS_RETRANS_CB: {
+			__u32 key = 0;
+			struct tcpnotify_globals g, *gp;
+			struct tcp_notifier msg = {
+				.type = 0xde,
+				.subtype = 0xad,
+				.source = 0xbe,
+				.hash = 0xef,
+			};
+
+			rv = 1;
+
+			/* Update results */
+			gp = bpf_map_lookup_elem(&global_map, &key);
+			if (!gp)
+				break;
+			g = *gp;
+			g.total_retrans = skops->total_retrans;
+			g.ncalls++;
+			bpf_map_update_elem(&global_map, &key, &g,
+					    BPF_ANY);
+			bpf_perf_event_output(skops, &perf_event_map,
+					      BPF_F_CURRENT_CPU,
+					      &msg, sizeof(msg));
+		}
+		break;
+	default:
+		rv = -1;
+	}
+	skops->reply = rv;
+	return 1;
+}
+char _license[] SEC("license") = "GPL";