Add eBPF connection tracking

Introduces connection tracking via eBPF. This allows scope to get
notified of every connection event, without relying on the parsing of
/proc/$pid/net/tcp{,6} and /proc/$pid/fd/*, and therefore improve
performance.

The eBPF program is in a python script using bcc: docker/tcpv4tracer.py.
It is contributed upstream via iovisor/bcc#762
It is using kprobes on the following kernel functions:
- tcp_v4_connect
- inet_csk_accept
- tcp_close

It generates "connect", "accept" and "close" events containing the
connection tuple but also the pid and the netns.

The python script is piped into the Scope Probe and
probe/endpoint/ebpf.go maintains the list of connections. Similarly to
conntrack, we keep the dead connections for one iteration in order to
report the short-lived connections.

The code for parsing /proc/$pid/net/tcp{,6} and /proc/$pid/fd/*is still
there and still used at start-up because eBPF only brings us the events
and not the initial state. However, the /proc parsing for the initial
state is now done in foreground instead of background, via
newForegroundReader().

Scope Probe also falls back on the the old /proc parsing if eBPF is not
working (e.g. too old kernel, or missing kernel headers). There is also
a flag "probe.ebpf.connections" that could disable eBPF if set to false.

NAT resolutions on connections from eBPF works in the same way as it did
on connections from /proc: by using conntrack.

The Scope Docker image is bigger because we need a few more packages
for bcc:
- weaveworks/scope in current master:  22 MB
- weaveworks/scope with this patch:   147 MB

Limitations:
- [ ] Does not support IPv6
- [ ] Sets `procspied: true` on connections coming from eBPF

docker/Dockerfile

@@ -1,14 +1,12 @@
-FROM alpine:3.3
+FROM zlim/bcc
 MAINTAINER Weaveworks Inc <help@weave.works>
 LABEL works.weave.role=system
 WORKDIR /home/weave
-RUN echo "http://dl-cdn.alpinelinux.org/alpine/edge/community" >>/etc/apk/repositories && \
-	apk add --update bash runit conntrack-tools iproute2 util-linux curl && \
-	rm -rf /var/cache/apk/*
+RUN apt-get update -y && apt-get install -y bash runit conntrack iproute2 util-linux curl python bcc-tools python-bcc libbcc
 ADD ./docker.tgz /
 ADD ./demo.json /
 ADD ./weave /usr/bin/
-COPY ./scope ./runsvinit ./entrypoint.sh /home/weave/
+COPY ./scope ./runsvinit ./entrypoint.sh ./tcpv4tracer.py /home/weave/
 COPY ./run-app /etc/service/app/run
 COPY ./run-probe /etc/service/probe/run
 EXPOSE 4040

docker/tcpv4tracer.py

@@ -0,0 +1,291 @@
+#!/usr/bin/python
+#
+# tcpv4tracer   Trace TCP IPv4 connections.
+#               For Linux, uses BCC, eBPF. Embedded C.
+#
+# USAGE: tcpv4tracer [-h] [-p PID]
+#
+from __future__ import print_function
+from bcc import BPF
+
+import argparse
+import ctypes
+
+parser = argparse.ArgumentParser(
+    description="Trace TCP IPv4 connections",
+    formatter_class=argparse.RawDescriptionHelpFormatter)
+parser.add_argument("-p", "--pid",
+    help="trace this PID only")
+args = parser.parse_args()
+
+# define BPF program
+bpf_text = """
+#include <uapi/linux/ptrace.h>
+#include <net/sock.h>
+#include <net/inet_sock.h>
+#include <net/net_namespace.h>
+#include <bcc/proto.h>
+
+#define TCP_EVENT_TYPE_CONNECT 1
+#define TCP_EVENT_TYPE_ACCEPT  2
+#define TCP_EVENT_TYPE_CLOSE   3
+
+struct tcp_event_t {
+        u32 type;
+        u32 netns;
+        u32 pid;
+        u32 saddr;
+        u32 daddr;
+        u16 sport;
+        u16 dport;
+};
+
+BPF_PERF_OUTPUT(tcp_event);
+BPF_HASH(connectsock, u64, struct sock *);
+BPF_HASH(closesock, u64, struct sock *);
+
+int kprobe__tcp_v4_connect(struct pt_regs *ctx, struct sock *sk)
+{
+        u64 pid = bpf_get_current_pid_tgid();
+
+        ##FILTER_PID##
+
+        // stash the sock ptr for lookup on return
+        connectsock.update(&pid, &sk);
+
+        return 0;
+};
+
+int kretprobe__tcp_v4_connect(struct pt_regs *ctx)
+{
+        int ret = PT_REGS_RC(ctx);
+        u64 pid = bpf_get_current_pid_tgid();
+
+        struct sock **skpp;
+        skpp = connectsock.lookup(&pid);
+        if (skpp == 0) {
+                return 0;       // missed entry
+        }
+
+        if (ret != 0) {
+                // failed to send SYNC packet, may not have populated
+                // socket __sk_common.{skc_rcv_saddr, ...}
+                connectsock.delete(&pid);
+                return 0;
+        }
+
+
+        // pull in details
+        struct sock *skp = *skpp;
+        struct ns_common *ns;
+        u32 saddr = 0, daddr = 0;
+        u16 sport = 0, dport = 0;
+        u32 net_ns_inum = 0;
+        bpf_probe_read(&sport, sizeof(sport), &((struct inet_sock *)skp)->inet_sport);
+        bpf_probe_read(&saddr, sizeof(saddr), &skp->__sk_common.skc_rcv_saddr);
+        bpf_probe_read(&daddr, sizeof(daddr), &skp->__sk_common.skc_daddr);
+        bpf_probe_read(&dport, sizeof(dport), &skp->__sk_common.skc_dport);
+
+// Get network namespace id, if kernel supports it
+#ifdef CONFIG_NET_NS
+        possible_net_t skc_net = {0,};
+        bpf_probe_read(&skc_net, sizeof(skc_net), &skp->__sk_common.skc_net);
+        bpf_probe_read(&net_ns_inum, sizeof(net_ns_inum), &skc_net.net->ns.inum);
+#else
+        net_ns_inum = 0;
+#endif
+
+        // output
+        struct tcp_event_t evt = {
+                .type = TCP_EVENT_TYPE_CONNECT,
+                .pid = pid >> 32,
+                .saddr = saddr,
+                .daddr = daddr,
+                .sport = ntohs(sport),
+                .dport = ntohs(dport),
+                .netns = net_ns_inum,
+        };
+
+        u16 family = 0;
+        bpf_probe_read(&family, sizeof(family), &skp->__sk_common.skc_family);
+
+        tcp_event.perf_submit(ctx, &evt, sizeof(evt));
+
+        connectsock.delete(&pid);
+
+        return 0;
+}
+
+int kprobe__tcp_close(struct pt_regs *ctx, struct sock *sk)
+{
+        u64 pid = bpf_get_current_pid_tgid();
+
+        ##FILTER_PID##
+
+        // stash the sock ptr for lookup on return
+        closesock.update(&pid, &sk);
+
+        return 0;
+};
+
+int kretprobe__tcp_close(struct pt_regs *ctx)
+{
+        u64 pid = bpf_get_current_pid_tgid();
+
+        struct sock **skpp;
+        skpp = closesock.lookup(&pid);
+        if (skpp == 0) {
+                return 0;       // missed entry
+        }
+
+        // pull in details
+        struct sock *skp = *skpp;
+        u32 saddr = 0, daddr = 0;
+        u16 sport = 0, dport = 0;
+        u32 net_ns_inum = 0;
+        bpf_probe_read(&saddr, sizeof(saddr), &skp->__sk_common.skc_rcv_saddr);
+        bpf_probe_read(&daddr, sizeof(daddr), &skp->__sk_common.skc_daddr);
+        bpf_probe_read(&sport, sizeof(sport), &((struct inet_sock *)skp)->inet_sport);
+        bpf_probe_read(&dport, sizeof(dport), &skp->__sk_common.skc_dport);
+
+// Get network namespace id, if kernel supports it
+#ifdef CONFIG_NET_NS
+        possible_net_t skc_net = {0,};
+        bpf_probe_read(&skc_net, sizeof(skc_net), &skp->__sk_common.skc_net);
+        bpf_probe_read(&net_ns_inum, sizeof(net_ns_inum), &skc_net.net->ns.inum);
+#else
+        net_ns_inum = 0;
+#endif
+
+        // output
+        struct tcp_event_t evt = {
+                .type = TCP_EVENT_TYPE_CLOSE,
+                .pid = pid >> 32,
+                .saddr = saddr,
+                .daddr = daddr,
+                .sport = ntohs(sport),
+                .dport = ntohs(dport),
+                .netns = net_ns_inum,
+        };
+
+        u16 family = 0;
+        bpf_probe_read(&family, sizeof(family), &skp->__sk_common.skc_family);
+
+        // do not send event if IP address is 0.0.0.0 or port is 0
+        if (evt.saddr != 0 && evt.daddr != 0 && evt.sport != 0 && evt.dport != 0) {
+            tcp_event.perf_submit(ctx, &evt, sizeof(evt));
+        }
+
+        closesock.delete(&pid);
+
+        return 0;
+}
+
+int kretprobe__inet_csk_accept(struct pt_regs *ctx)
+{
+        struct sock *newsk = (struct sock *)PT_REGS_RC(ctx);
+        u64 pid = bpf_get_current_pid_tgid();
+
+        ##FILTER_PID##
+
+        if (newsk == NULL)
+                return 0;
+
+        // check this is TCP
+        u8 protocol = 0;
+        // workaround for reading the sk_protocol bitfield:
+        bpf_probe_read(&protocol, 1, (void *)((long)&newsk->sk_wmem_queued) - 3);
+        if (protocol != IPPROTO_TCP)
+                return 0;
+
+        // pull in details
+        u16 family = 0, lport = 0, dport = 0;
+        u32 net_ns_inum = 0;
+        bpf_probe_read(&family, sizeof(family), &newsk->__sk_common.skc_family);
+        bpf_probe_read(&lport, sizeof(lport), &newsk->__sk_common.skc_num);
+        bpf_probe_read(&dport, sizeof(dport), &newsk->__sk_common.skc_dport);
+
+// Get network namespace id, if kernel supports it
+#ifdef CONFIG_NET_NS
+        possible_net_t skc_net = {0,};
+        bpf_probe_read(&skc_net, sizeof(skc_net), &newsk->__sk_common.skc_net);
+        bpf_probe_read(&net_ns_inum, sizeof(net_ns_inum), &skc_net.net->ns.inum);
+#else
+        net_ns_inum = 0;
+#endif
+
+        if (family == AF_INET) {
+                struct tcp_event_t evt = {
+                        .type = TCP_EVENT_TYPE_ACCEPT,
+                        .pid = pid >> 32,
+                        .netns = net_ns_inum,
+                };
+
+                bpf_probe_read(&evt.saddr, sizeof(u32),
+                        &newsk->__sk_common.skc_rcv_saddr);
+                bpf_probe_read(&evt.daddr, sizeof(u32),
+                        &newsk->__sk_common.skc_daddr);
+                        evt.sport = lport;
+                evt.dport = ntohs(dport);
+                tcp_event.perf_submit(ctx, &evt, sizeof(evt));
+        }
+        // else drop
+
+        return 0;
+}
+"""
+
+class TCPEvt(ctypes.Structure):
+        _fields_ = [
+                ("type", ctypes.c_uint),
+                ("netns", ctypes.c_uint),
+                ("pid", ctypes.c_uint),
+                ("saddr", ctypes.c_uint),
+                ("daddr", ctypes.c_uint),
+                ("sport", ctypes.c_ushort),
+                ("dport", ctypes.c_ushort),
+        ]
+
+def print_event(cpu, data, size):
+        event = ctypes.cast(data, ctypes.POINTER(TCPEvt)).contents
+        if event.type == 1:
+            type_str = "connect"
+        elif event.type == 2:
+            type_str = "accept"
+        elif event.type == 3:
+            type_str = "close"
+        else:
+            type_str = "unknown-" + str(event.type)
+
+        print("%s %s %s %s %s %s %s" % (type_str, event.pid,
+            inet_ntoa(event.saddr),
+            inet_ntoa(event.daddr),
+            event.sport,
+            event.dport,
+            event.netns,
+            ))
+
+if args.pid:
+    bpf_text = bpf_text.replace('##FILTER_PID##',
+        'if (pid != %s) { return 0; }' % args.pid)
+else:
+    bpf_text = bpf_text.replace('##FILTER_PID##', '')
+
+# initialize BPF
+b = BPF(text=bpf_text)
+
+# header
+print("TYPE PID SADDR DADDR SPORT DPORT NETNS")
+
+def inet_ntoa(addr):
+        dq = ''
+        for i in range(0, 4):
+                dq = dq + str(addr & 0xff)
+                if (i != 3):
+                        dq = dq + '.'
+                addr = addr >> 8
+        return dq
+
+b["tcp_event"].open_perf_buffer(print_event)
+while True:
+        b.kprobe_poll()