Move all of tun into overlay (#577)

overlay/tun_disabled.go

@@ -0,0 +1,175 @@
+package overlay
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+	"net"
+	"strings"
+
+	"github.com/rcrowley/go-metrics"
+	"github.com/sirupsen/logrus"
+)
+
+type disabledTun struct {
+	read chan []byte
+	cidr *net.IPNet
+
+	// Track these metrics since we don't have the tun device to do it for us
+	tx metrics.Counter
+	rx metrics.Counter
+	l  *logrus.Logger
+}
+
+func newDisabledTun(cidr *net.IPNet, queueLen int, metricsEnabled bool, l *logrus.Logger) *disabledTun {
+	tun := &disabledTun{
+		cidr: cidr,
+		read: make(chan []byte, queueLen),
+		l:    l,
+	}
+
+	if metricsEnabled {
+		tun.tx = metrics.GetOrRegisterCounter("messages.tx.message", nil)
+		tun.rx = metrics.GetOrRegisterCounter("messages.rx.message", nil)
+	} else {
+		tun.tx = &metrics.NilCounter{}
+		tun.rx = &metrics.NilCounter{}
+	}
+
+	return tun
+}
+
+func (*disabledTun) Activate() error {
+	return nil
+}
+
+func (t *disabledTun) CidrNet() *net.IPNet {
+	return t.cidr
+}
+
+func (*disabledTun) DeviceName() string {
+	return "disabled"
+}
+
+func (t *disabledTun) Read(b []byte) (int, error) {
+	r, ok := <-t.read
+	if !ok {
+		return 0, io.EOF
+	}
+
+	if len(r) > len(b) {
+		return 0, fmt.Errorf("packet larger than mtu: %d > %d bytes", len(r), len(b))
+	}
+
+	t.tx.Inc(1)
+	if t.l.Level >= logrus.DebugLevel {
+		t.l.WithField("raw", prettyPacket(r)).Debugf("Write payload")
+	}
+
+	return copy(b, r), nil
+}
+
+func (t *disabledTun) handleICMPEchoRequest(b []byte) bool {
+	// Return early if this is not a simple ICMP Echo Request
+	//TODO: make constants out of these
+	if !(len(b) >= 28 && len(b) <= 9001 && b[0] == 0x45 && b[9] == 0x01 && b[20] == 0x08) {
+		return false
+	}
+
+	// We don't support fragmented packets
+	if b[7] != 0 || (b[6]&0x2F != 0) {
+		return false
+	}
+
+	buf := make([]byte, len(b))
+	copy(buf, b)
+
+	// Swap dest / src IPs and recalculate checksum
+	ipv4 := buf[0:20]
+	copy(ipv4[12:16], b[16:20])
+	copy(ipv4[16:20], b[12:16])
+	ipv4[10] = 0
+	ipv4[11] = 0
+	binary.BigEndian.PutUint16(ipv4[10:], ipChecksum(ipv4))
+
+	// Change type to ICMP Echo Reply and recalculate checksum
+	icmp := buf[20:]
+	icmp[0] = 0
+	icmp[2] = 0
+	icmp[3] = 0
+	binary.BigEndian.PutUint16(icmp[2:], ipChecksum(icmp))
+
+	// attempt to write it, but don't block
+	select {
+	case t.read <- buf:
+	default:
+		t.l.Debugf("tun_disabled: dropped ICMP Echo Reply response")
+	}
+
+	return true
+}
+
+func (t *disabledTun) Write(b []byte) (int, error) {
+	t.rx.Inc(1)
+
+	// Check for ICMP Echo Request before spending time doing the full parsing
+	if t.handleICMPEchoRequest(b) {
+		if t.l.Level >= logrus.DebugLevel {
+			t.l.WithField("raw", prettyPacket(b)).Debugf("Disabled tun responded to ICMP Echo Request")
+		}
+	} else if t.l.Level >= logrus.DebugLevel {
+		t.l.WithField("raw", prettyPacket(b)).Debugf("Disabled tun received unexpected payload")
+	}
+	return len(b), nil
+}
+
+func (t *disabledTun) WriteRaw(b []byte) error {
+	_, err := t.Write(b)
+	return err
+}
+
+func (t *disabledTun) NewMultiQueueReader() (io.ReadWriteCloser, error) {
+	return t, nil
+}
+
+func (t *disabledTun) Close() error {
+	if t.read != nil {
+		close(t.read)
+		t.read = nil
+	}
+	return nil
+}
+
+type prettyPacket []byte
+
+func (p prettyPacket) String() string {
+	var s strings.Builder
+
+	for i, b := range p {
+		if i > 0 && i%8 == 0 {
+			s.WriteString(" ")
+		}
+		s.WriteString(fmt.Sprintf("%02x ", b))
+	}
+
+	return s.String()
+}
+
+func ipChecksum(b []byte) uint16 {
+	var c uint32
+	sz := len(b) - 1
+
+	for i := 0; i < sz; i += 2 {
+		c += uint32(b[i]) << 8
+		c += uint32(b[i+1])
+	}
+	if sz%2 == 0 {
+		c += uint32(b[sz]) << 8
+	}
+
+	for (c >> 16) > 0 {
+		c = (c & 0xffff) + (c >> 16)
+	}
+
+	return ^uint16(c)
+}