/
main.go
176 lines (149 loc) · 3.41 KB
/
main.go
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// Package main is the example of DNSSEC using go-packet.
package main
import (
"fmt"
"log"
"os"
"os/signal"
"time"
"github.com/google/gopacket"
"github.com/google/gopacket/layers"
"github.com/google/gopacket/pcap"
"github.com/miekg/dns"
)
var (
appLog = log.New(os.Stderr, "", 0)
)
func main() {
if err := run(); err != nil {
panic(err)
}
}
func run() error {
const (
device = "eth0"
filter = "udp and port 53"
snapshotLen = int32(1600)
promiscuous = false
timeout = 1 * time.Second
)
defer func() { appLog.Println("DONE") }()
// --------------------------------------
// Open capture handle
// --------------------------------------
var (
handle *pcap.Handle
err error
)
handle, err = pcap.OpenLive(device, snapshotLen, promiscuous, timeout)
if err != nil {
return fmt.Errorf("error open handle: %w", err)
}
defer handle.Close()
// --------------------------------------
// Apply capture filter (optional)
// --------------------------------------
if filter != "" {
err = handle.SetBPFFilter(filter)
if err != nil {
return fmt.Errorf("error apply filter: %w", err)
}
}
// --------------------------------------
// Set signal handler
// --------------------------------------
var (
doneCh = make(chan struct{})
sigCh = make(chan os.Signal, 1)
)
signal.Notify(sigCh, os.Interrupt)
// --------------------------------------
// Make packet source and display.
// --------------------------------------
var (
dataSource gopacket.PacketDataSource = handle
decoder gopacket.Decoder = handle.LinkType()
packetSource *gopacket.PacketSource = gopacket.NewPacketSource(dataSource, decoder)
packetCh <-chan gopacket.Packet = packetSource.Packets()
)
appLog.Println("START")
LOOP:
for {
select {
case <-sigCh:
close(doneCh)
break LOOP
case p, ok := <-packetCh:
if !ok {
break LOOP
}
if err = see(p); err != nil {
return err
}
}
}
return nil
}
func see(p gopacket.Packet) error {
//
// レイヤーを確認
//
udpLayer := p.Layer(layers.LayerTypeUDP)
if udpLayer == nil {
return nil
}
//
// ペイロードを取得
//
var (
udp = udpLayer.(*layers.UDP)
payload = udp.LayerPayload()
)
appLog.Printf("[Src Port ] %v", udp.SrcPort)
appLog.Printf("[Dst Port ] %v", udp.DstPort)
appLog.Printf("[Length ] %v", udp.Length)
appLog.Printf("[Checksum ] %v", udp.Checksum)
if len(payload) == 0 {
return nil
}
defer func() { appLog.Println("------------------------------------") }()
//
// DNSペイロードとして解釈する
//
var (
msg = new(dns.Msg)
err error
)
err = msg.Unpack(payload)
if err != nil {
return err
}
var (
hasQuestion = len(msg.Question) > 0
hasAnswer = len(msg.Answer) > 0
)
// DNS Question
if hasQuestion {
appLog.Println("[DNS Questions]")
for _, q := range msg.Question {
appLog.Printf("\t%v\n", q.String())
}
}
// DNS Answer
if hasAnswer {
appLog.Println("[DNS Answers]")
for _, a := range msg.Answer {
// 単純なDNS要求の場合は *dns.A のみとなるが
// DNSSECの場合は, *dns.DNSKEY または *dns.RRSIG もあり得る
switch t := a.(type) {
case *dns.A:
appLog.Printf("\t[A ] %v\n", t.String())
case *dns.DNSKEY:
appLog.Printf("\t[DNSKEY] %v\n", t.String())
case *dns.RRSIG:
appLog.Printf("\t[RRSIG ] %v\n", t.String())
}
}
}
return nil
}