func fragment(eth layers.Ethernet, ip layers.IPv4, pmtu int, frame *ForwardedFrame, forward func(*ForwardedFrame)) error {
// We are not doing any sort of NAT, so we don't need to worry
// about checksums of IP payload (eg UDP checksum).
headerSize := int(ip.IHL) * 4
// &^ is bit clear (AND NOT). So here we're clearing the lowest 3
// bits.
maxSegmentSize := (pmtu - headerSize) &^ 7
opts := gopacket.SerializeOptions{
FixLengths: false,
ComputeChecksums: true}
payloadSize := int(ip.Length) - headerSize
payload := ip.BaseLayer.Payload[:payloadSize]
offsetBase := int(ip.FragOffset) << 3
origFlags := ip.Flags
ip.Flags = ip.Flags | layers.IPv4MoreFragments
ip.Length = uint16(headerSize + maxSegmentSize)
if eth.EthernetType == layers.EthernetTypeLLC {
// using LLC, so must set eth length correctly. eth length
// is just the length of the payload
eth.Length = ip.Length
} else {
eth.Length = 0
}
for offset := 0; offset < payloadSize; offset += maxSegmentSize {
var segmentPayload []byte
if len(payload) <= maxSegmentSize {
// last one
segmentPayload = payload
ip.Length = uint16(len(payload) + headerSize)
ip.Flags = origFlags
if eth.EthernetType == layers.EthernetTypeLLC {
eth.Length = ip.Length
} else {
eth.Length = 0
}
} else {
segmentPayload = payload[:maxSegmentSize]
payload = payload[maxSegmentSize:]
}
ip.FragOffset = uint16((offset + offsetBase) >> 3)
buf := gopacket.NewSerializeBuffer()
segPayload := gopacket.Payload(segmentPayload)
err := gopacket.SerializeLayers(buf, opts, ð, &ip, &segPayload)
if err != nil {
return err
}
// make copies of the frame we received
segFrame := *frame
segFrame.frame = buf.Bytes()
forward(&segFrame)
}
return nil
}
func (dec *EthernetDecoder) sendICMPFragNeeded(mtu int, sendFrame func([]byte) error) error {
buf := gopacket.NewSerializeBuffer()
opts := gopacket.SerializeOptions{
FixLengths: true,
ComputeChecksums: true}
ipHeaderSize := int(dec.ip.IHL) * 4 // IHL is the number of 32-byte words in the header
payload := gopacket.Payload(dec.ip.BaseLayer.Contents[:ipHeaderSize+8])
err := gopacket.SerializeLayers(buf, opts,
&layers.Ethernet{
SrcMAC: dec.eth.DstMAC,
DstMAC: dec.eth.SrcMAC,
EthernetType: dec.eth.EthernetType},
&layers.IPv4{
Version: 4,
TOS: dec.ip.TOS,
Id: 0,
Flags: 0,
FragOffset: 0,
TTL: 64,
Protocol: layers.IPProtocolICMPv4,
DstIP: dec.ip.SrcIP,
SrcIP: dec.ip.DstIP},
&layers.ICMPv4{
TypeCode: 0x304,
Id: 0,
Seq: uint16(mtu)},
&payload)
if err != nil {
return err
}
log.Printf("Sending ICMP 3,4 (%v -> %v): PMTU= %v\n", dec.ip.DstIP, dec.ip.SrcIP, mtu)
return sendFrame(buf.Bytes())
}
func (sender *RawUDPSender) Send(msg []byte) error {
payload := gopacket.Payload(msg)
sender.udpHeader.DstPort = layers.UDPPort(sender.conn.RemoteUDPAddr().Port)
err := gopacket.SerializeLayers(sender.ipBuf, sender.opts, sender.udpHeader, &payload)
if err != nil {
return err
}
packet := sender.ipBuf.Bytes()
_, err = sender.socket.Write(packet)
if err == nil || PosixError(err) != syscall.EMSGSIZE {
return err
}
f, err := sender.socket.File()
if err != nil {
return err
}
defer f.Close()
fd := int(f.Fd())
log.Println("EMSGSIZE on send, expecting PMTU update (IP packet was",
len(packet), "bytes, payload was", len(msg), "bytes)")
pmtu, err := syscall.GetsockoptInt(fd, syscall.IPPROTO_IP, syscall.IP_MTU)
if err != nil {
return err
}
return MsgTooBigError{PMTU: pmtu}
}
func (dec *EthernetDecoder) formICMPMTUPacket(mtu int) ([]byte, error) {
buf := gopacket.NewSerializeBuffer()
opts := gopacket.SerializeOptions{
FixLengths: true,
ComputeChecksums: true}
ipHeaderSize := int(dec.ip.IHL) * 4 // IHL is the number of 32-byte words in the header
payload := gopacket.Payload(dec.ip.BaseLayer.Contents[:ipHeaderSize+8])
err := gopacket.SerializeLayers(buf, opts,
&layers.Ethernet{
SrcMAC: dec.eth.DstMAC,
DstMAC: dec.eth.SrcMAC,
EthernetType: dec.eth.EthernetType},
&layers.IPv4{
Version: 4,
TOS: dec.ip.TOS,
Id: 0,
Flags: 0,
FragOffset: 0,
TTL: 64,
Protocol: layers.IPProtocolICMPv4,
DstIP: dec.ip.SrcIP,
SrcIP: dec.ip.DstIP},
&layers.ICMPv4{
TypeCode: 0x304,
Id: 0,
Seq: uint16(mtu)},
&payload)
if err != nil {
return []byte{}, err
}
return buf.Bytes(), nil
}
//sendPacket generates & sends a packet of arbitrary size to a specific destination.
//The size specified should be larger then 40bytes.
func sendPacket(sourceIP string, destinationIP string, size int, message string, appID int, chanID int, icmpType layers.ICMPv4TypeCode) []byte {
var payloadSize int
if size < 28 {
//Unable to create smaller packets.
payloadSize = 0
} else {
payloadSize = size - 28
}
//Convert IP to 4bit representation
srcIP := net.ParseIP(sourceIP).To4()
dstIP := net.ParseIP(destinationIP).To4()
//IP Layer
ip := layers.IPv4{
SrcIP: srcIP,
DstIP: dstIP,
Version: 4,
TTL: 64,
Protocol: layers.IPProtocolICMPv4,
}
icmp := layers.ICMPv4{
TypeCode: icmpType,
}
opts := gopacket.SerializeOptions{
FixLengths: true,
ComputeChecksums: true,
}
ipHeaderBuf := gopacket.NewSerializeBuffer()
err := ip.SerializeTo(ipHeaderBuf, opts)
if err != nil {
panic(err)
}
//Set "Don't Fragment"-Flag in Header
ipHeader, err := ipv4.ParseHeader(ipHeaderBuf.Bytes())
ipHeader.Flags |= ipv4.DontFragment
if err != nil {
panic(err)
}
payloadBuf := gopacket.NewSerializeBuffer()
//Influence the payload size
payload := gopacket.Payload(generatePayload(payloadSize, ","+strconv.Itoa(appID)+","+strconv.Itoa(chanID)+","+message+","))
err = gopacket.SerializeLayers(payloadBuf, opts, &icmp, payload)
if err != nil {
panic(err)
}
//Send packet
var packetConn net.PacketConn
var rawConn *ipv4.RawConn
packetConn, err = net.ListenPacket("ip4:icmp", srcIP.String())
if err != nil {
panic(err)
}
rawConn, err = ipv4.NewRawConn(packetConn)
if err != nil {
panic(err)
}
err = rawConn.WriteTo(ipHeader, payloadBuf.Bytes(), nil)
return append(ipHeaderBuf.Bytes(), payloadBuf.Bytes()...)
}
//Detectinitcwnd attempts to detect the initial congession window of an http endpoint.
//First does a 3 way tcp handshake, sends GET request and then does not ack any response while measuring the packets received. This allows us to see how much data the server can send without acknowledgement.
func Detectinitcwnd(host, url string, dstip net.IP) (pkt_count, payload_size int, fullpayload []byte, err error) {
pldata := []byte(fmt.Sprintf("GET %s HTTP/1.1\r\nHost: %s\r\n\r\n", url, host))
var dstport layers.TCPPort
dstport = layers.TCPPort(80)
srcip, sport := localIPPort(dstip)
srcport := layers.TCPPort(sport)
log.Printf("using srcip: %v", srcip.String())
log.Printf("using dstip: %v", dstip.String())
// Our IP header... not used, but necessary for TCP checksumming.
ip := &layers.IPv4{
SrcIP: srcip,
DstIP: dstip,
Protocol: layers.IPProtocolTCP,
}
//layers.TCPOption{3, 3, []byte{7}} maybe for window scaling... dunno
tcpopts := []layers.TCPOption{layers.TCPOption{2, 4, []byte{5, 172}}} //Set MSS 1452
// Our TCP header
tcp := &layers.TCP{
SrcPort: srcport,
DstPort: dstport,
Seq: 1105024978,
SYN: true,
Window: 65535,
Options: tcpopts,
}
tcp.SetNetworkLayerForChecksum(ip)
// Serialize. Note: we only serialize the TCP layer, because the
// socket we get with net.ListenPacket wraps our data in IPv4 packets
// already. We do still need the IP layer to compute checksums
// correctly, though.
buf := gopacket.NewSerializeBuffer()
opts := gopacket.SerializeOptions{
ComputeChecksums: true,
FixLengths: true,
}
err = gopacket.SerializeLayers(buf, opts, tcp)
if err != nil {
return
}
var out1 bytes.Buffer
iptset := exec.Command("iptables", "-A", "OUTPUT", "-p", "tcp", "--tcp-flags", "RST", "RST", "-s", srcip.String(), "--sport", porttoint(srcport), "--dport", porttoint(dstport), "-j", "DROP")
iptset.Stderr = &out1
log.Println(iptset)
err = iptset.Run()
if err != nil {
return
}
log.Println(out1.String())
iptrem := exec.Command("iptables", "-D", "OUTPUT", "-p", "tcp", "--tcp-flags", "RST", "RST", "-s", srcip.String(), "--sport", porttoint(srcport), "--dport", porttoint(dstport), "-j", "DROP")
conn, err := net.ListenPacket("ip4:tcp", "0.0.0.0")
if err != nil {
return
}
defer func() {
fmt.Println(iptrem)
var out bytes.Buffer
iptrem.Stderr = &out
err = iptrem.Run()
if err != nil {
log.Println(err)
}
fmt.Printf(out.String())
log.Println("Removed iptable rule")
//Now RST should be allowed... send it
rst_pkt := &layers.TCP{
SrcPort: srcport,
DstPort: dstport,
Seq: 1105024980,
Window: 65535,
RST: true,
}
rst_pkt.SetNetworkLayerForChecksum(ip)
if err := gopacket.SerializeLayers(buf, opts, rst_pkt); err != nil {
//Shadowing err since we dont care
log.Println(err)
}
if _, err := conn.WriteTo(buf.Bytes(), &net.IPAddr{IP: dstip}); err != nil {
//Shadowing err since we dont care
log.Println(err)
}
}()
log.Println("writing request")
_, err = conn.WriteTo(buf.Bytes(), &net.IPAddr{IP: dstip})
if err != nil {
return
}
// Set deadline so we don't wait forever.
err = conn.SetDeadline(time.Now().Add(15 * time.Second))
if err != nil {
return
}
//Capture synack from our syn, return the ack value
ack, err := getack(conn, srcport, dstip.String())
if err != nil {
log.Println(err)
return
} else {
//Prepare http request, ack the synack
payload := &layers.TCP{
SrcPort: srcport,
DstPort: dstport,
Seq: 1105024979,
ACK: true,
Window: 65535,
Ack: ack + 1,
}
payload.SetNetworkLayerForChecksum(ip)
if err := gopacket.SerializeLayers(buf, opts, payload, gopacket.Payload(pldata)); err != nil {
log.Fatal(err)
}
if _, err := conn.WriteTo(buf.Bytes(), &net.IPAddr{IP: dstip}); err != nil {
log.Fatal(err)
}
pkt_count, payload_size, fullpayload = listenandcount(conn, dstip.String(), srcport)
log.Println("Initcwnd: ", pkt_count)
log.Println("Data: ", payload_size)
return
}
return
}