// writeARP writes an ARP request for each address on our local network to the
// pcap handle.
func writeARP(handle *pcap.Handle, iface *net.Interface, addr *net.IPNet) error {
// Set up all the layers' fields we can.
eth := layers.Ethernet{
SrcMAC: iface.HardwareAddr,
DstMAC: net.HardwareAddr{0xff, 0xff, 0xff, 0xff, 0xff, 0xff},
EthernetType: layers.EthernetTypeARP,
}
arp := layers.ARP{
AddrType: layers.LinkTypeEthernet,
Protocol: layers.EthernetTypeIPv4,
HwAddressSize: 6,
ProtAddressSize: 4,
Operation: layers.ARPRequest,
SourceHwAddress: []byte(iface.HardwareAddr),
SourceProtAddress: []byte(addr.IP),
DstHwAddress: []byte{0, 0, 0, 0, 0, 0},
}
// Set up buffer and options for serialization.
buf := gopacket.NewSerializeBuffer()
opts := gopacket.SerializeOptions{
FixLengths: true,
ComputeChecksums: true,
}
// Send one packet for every address.
for _, ip := range ips(addr) {
arp.DstProtAddress = []byte(ip)
gopacket.SerializeLayers(buf, opts, ð, &arp)
if err := handle.WritePacketData(buf.Bytes()); err != nil {
return err
}
}
return nil
}
// newScanner creates a new scanner for a given destination IP address, using
// router to determine how to route packets to that IP.
func newScanner(ip net.IP, router routing.Router) (*scanner, error) {
s := &scanner{
dst: ip,
opts: gopacket.SerializeOptions{
FixLengths: true,
ComputeChecksums: true,
},
buf: gopacket.NewSerializeBuffer(),
}
// Figure out the route to the IP.
iface, gw, src, err := router.Route(ip)
if err != nil {
return nil, err
}
log.Printf("scanning ip %v with interface %v, gateway %v, src %v", ip, iface.Name, gw, src)
s.gw, s.src, s.iface = gw, src, iface
// Open the handle for reading/writing.
// Note we could very easily add some BPF filtering here to greatly
// decrease the number of packets we have to look at when getting back
// scan results.
handle, err := pcap.OpenLive(iface.Name, 65536, true, pcap.BlockForever)
if err != nil {
return nil, err
}
s.handle = handle
return s, nil
}
func TestInformationElement(t *testing.T) {
bin := []byte{
0, 0,
0, 2, 1, 3,
221, 5, 1, 2, 3, 4, 5,
}
pkt := gopacket.NewPacket(bin, LayerTypeDot11InformationElement, gopacket.NoCopy)
buf := gopacket.NewSerializeBuffer()
var sLayers []gopacket.SerializableLayer
for _, l := range pkt.Layers() {
sLayers = append(sLayers, l.(*Dot11InformationElement))
}
if err := gopacket.SerializeLayers(buf, gopacket.SerializeOptions{}, sLayers...); err != nil {
t.Error(err.Error())
}
if !bytes.Equal(bin, buf.Bytes()) {
t.Error("build failed")
}
}
func (s *Server) ListenAndServeUDPv4() {
ipAddr := &net.IPAddr{IP: net.IPv4zero}
conn, err := net.ListenIP("ip4:udp", ipAddr)
if err != nil {
l.Info(err.Error())
return
}
defer conn.Close()
if err = bindToDevice(conn, "tap"+s.name); err != nil {
l.Info(err.Error())
return
}
s.Lock()
s.ipv4conn, err = ipv4.NewRawConn(conn)
s.Unlock()
if err != nil {
l.Info(err.Error())
return
}
if err = s.ipv4conn.SetControlMessage(ipv4.FlagDst, true); err != nil {
l.Warning(err.Error())
return
}
buffer := make([]byte, 1500)
var gw net.IP
for _, addr := range s.metadata.Network.IP {
if addr.Family == "ipv4" && addr.Host == "true" && addr.Gateway == "true" {
gw = net.ParseIP(addr.Address)
}
}
iface, err := net.InterfaceByName("tap" + s.name)
if err != nil {
l.Info(fmt.Sprintf("failed to get iface: %s", err.Error()))
return
}
for {
select {
case <-s.done:
return
default:
s.ipv4conn.SetReadDeadline(time.Now().Add(time.Second))
hdr, _, _, err := s.ipv4conn.ReadFrom(buffer)
if err != nil {
switch v := err.(type) {
case *net.OpError:
if v.Timeout() {
continue
}
case *net.AddrError:
if v.Timeout() {
continue
}
case *net.UnknownNetworkError:
if v.Timeout() {
continue
}
default:
l.Warning(err.Error())
return
}
}
var ip4 layers.IPv4
var udp layers.UDP
var dhcp4req layers.DHCPv4
parser := gopacket.NewDecodingLayerParser(layers.LayerTypeIPv4, &ip4, &udp, &dhcp4req)
decoded := []gopacket.LayerType{}
err = parser.DecodeLayers(buffer, &decoded)
for _, layerType := range decoded {
switch layerType {
case layers.LayerTypeDHCPv4:
if dhcp4req.Operation == layers.DHCP_MSG_REQ {
dhcp4res, err := s.ServeUDPv4(&dhcp4req)
if err != nil {
l.Warning(err.Error())
continue
}
if dhcp4res == nil {
// ignore empty dhcp packets
continue
}
buf := gopacket.NewSerializeBuffer()
opts := gopacket.SerializeOptions{true, true}
gopacket.SerializeLayers(buf, opts,
&layers.UDP{SrcPort: 67, DstPort: 68},
dhcp4res)
wcm := ipv4.ControlMessage{TTL: 255}
wcm.Dst = net.IPv4bcast.To4()
wcm.Src = gw.To4()
wcm.IfIndex = iface.Index
err = s.ipv4conn.WriteTo(&ipv4.Header{Len: 20, TOS: hdr.TOS, TotalLen: 20 + int(len(buf.Bytes())), FragOff: 0, TTL: 255, Protocol: int(layers.IPProtocolUDP), Src: gw.To4(), Dst: net.IPv4bcast.To4()}, buf.Bytes(), &wcm)
if err != nil {
l.Warning(err.Error())
continue
}
} else {
continue
}
}
}
}
}
}
