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main.go
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main.go
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package main
import (
"flag"
"github.com/google/gopacket"
"github.com/google/gopacket/layers"
"github.com/google/gopacket/pcap"
"log"
"time"
)
var (
fInterface = flag.String("i", "eth0", "interface to listen")
fSnapLen = flag.Int("s", 1600, "maximum size in byte of a packet")
fPromiscuous = flag.Bool("p", false, "promiscuous mode")
fExpression = flag.String("e", "", "expression, example: tcp and port 80")
fBufferPkt = flag.Int("b", 10000, "count of packets in buffer")
fDoubleMode = flag.String("m", "", "mode: ttl / eb (evil bit)")
fTtl = flag.Uint("ttl", 164, "ttl value, ttl mode only")
mTtl = false
mEB = false
sendCh chan gopacket.Packet
handle *pcap.Handle
)
func main() {
flag.Parse()
if *fDoubleMode == "ttl" {
mTtl = true
} else if *fDoubleMode == "eb" {
mEB = true
} else {
log.Fatal("mode is not specified")
}
var err error
handle, err = pcap.OpenLive(*fInterface, int32(*fSnapLen), *fPromiscuous, 30*time.Second)
if err != nil {
log.Fatal("open interface error:", err)
}
defer handle.Close()
sendCh = make(chan gopacket.Packet, *fBufferPkt)
go sender()
err = handle.SetBPFFilter(*fExpression)
if err != nil {
log.Fatal("set filter error:", err)
}
log.Println("running...")
packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
for packet := range packetSource.Packets() {
handlePacket(packet)
}
}
func handlePacket(packet gopacket.Packet) {
ip4Layer := packet.Layer(layers.LayerTypeIPv4)
if ip4Layer == nil {
return
}
ip4, _ := ip4Layer.(*layers.IPv4)
if mTtl {
if ip4.TTL == uint8(*fTtl) {
return
}
ip4.TTL = uint8(*fTtl)
} else if mEB {
if ip4.Flags&layers.IPv4EvilBit > 0 {
return
}
ip4.Flags |= layers.IPv4EvilBit
} else {
return
}
if tcpLayer := packet.Layer(layers.LayerTypeTCP); tcpLayer != nil {
tcp := tcpLayer.(*layers.TCP)
tcp.SetNetworkLayerForChecksum(ip4)
}
ip4.Checksum = 0
sendCh <- packet
}
func sender() {
opts := gopacket.SerializeOptions{
ComputeChecksums: true,
}
for pkt := range sendCh {
buf := gopacket.NewSerializeBuffer()
err := gopacket.SerializePacket(buf, opts, pkt)
if err != nil {
log.Println("serialize error:", err)
continue
}
b := buf.Bytes()
err = handle.WritePacketData(b)
// log.Println("send", len(b))
if err != nil {
log.Println("send error:", err)
}
}
}