forked from timest/goscan
/
mdns.go
163 lines (150 loc) · 4.73 KB
/
mdns.go
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package main
import (
"encoding/binary"
"strings"
"github.com/google/gopacket/layers"
"github.com/google/gopacket"
"github.com/google/gopacket/pcap"
"time"
"net"
"bytes"
"context"
)
func listenMDNS(ctx context.Context) {
handle, err := pcap.OpenLive(iface, 1024, false, 10 * time.Second)
if err != nil {
log.Fatal("pcap打开失败:", err)
}
defer handle.Close()
handle.SetBPFFilter("udp and port 5353")
ps := gopacket.NewPacketSource(handle, handle.LinkType())
for {
select {
case <- ctx.Done():
return
case p := <-ps.Packets():
if len(p.Layers()) == 4 {
c := p.Layers()[3].LayerContents()
if c[2] == 0x84 && c[3] == 0x00 && c[6] == 0x00 && c[7] == 0x01{
// 从网络层(ipv4)拿IP, 不考虑IPv6
i := p.Layer(layers.LayerTypeIPv4)
if i == nil {
continue
}
ipv4 := i.(*layers.IPv4)
ip := ipv4.SrcIP.String()
// 把 hostname 存入到数据库
h := ParseMdns(c)
if len(h) > 0 {
pushData(ip, nil, h, "")
}
}
}
}
}
}
// 根据ip生成含mdns请求包,包存储在 buffer里
func mdns(buffer *Buffer, ip string) {
b := buffer.PrependBytes(12)
binary.BigEndian.PutUint16(b, uint16(0)) // 0x0000 标识
binary.BigEndian.PutUint16(b[2:], uint16(0x0100)) // 标识
binary.BigEndian.PutUint16(b[4:], uint16(1)) // 问题数
binary.BigEndian.PutUint16(b[6:], uint16(0)) // 资源数
binary.BigEndian.PutUint16(b[8:], uint16(0)) // 授权资源记录数
binary.BigEndian.PutUint16(b[10:], uint16(0)) // 额外资源记录数
// 查询问题
ipList := strings.Split(ip, ".")
for j := len(ipList) - 1; j >= 0; j-- {
ip := ipList[j]
b = buffer.PrependBytes(len(ip) + 1)
b[0] = uint8(len(ip))
for i := 0; i < len(ip); i++ {
b[i + 1] = uint8(ip[i])
}
}
b = buffer.PrependBytes(8)
b[0] = 7 // 后续总字节
copy(b[1:], []byte{'i', 'n', '-', 'a', 'd', 'd', 'r'})
b = buffer.PrependBytes(5)
b[0] = 4 // 后续总字节
copy(b[1:], []byte{'a', 'r', 'p', 'a'})
b = buffer.PrependBytes(1)
// terminator
b[0] = 0
// type 和 classIn
b = buffer.PrependBytes(4)
binary.BigEndian.PutUint16(b, uint16(12))
binary.BigEndian.PutUint16(b[2:], 1)
}
func sendMdns(ip IP, mhaddr net.HardwareAddr) {
srcIp := net.ParseIP(ipNet.IP.String()).To4()
dstIp := net.ParseIP(ip.String()).To4()
ether := &layers.Ethernet{
SrcMAC: localHaddr,
DstMAC: mhaddr,
EthernetType: layers.EthernetTypeIPv4,
}
ip4 := &layers.IPv4{
Version: uint8(4),
IHL: uint8(5),
TTL: uint8(255),
Protocol: layers.IPProtocolUDP,
SrcIP: srcIp,
DstIP: dstIp,
}
bf := NewBuffer()
mdns(bf, ip.String())
udpPayload := bf.data
udp := &layers.UDP{
SrcPort: layers.UDPPort(60666),
DstPort: layers.UDPPort(5353),
}
udp.SetNetworkLayerForChecksum(ip4)
udp.Payload = udpPayload // todo
buffer := gopacket.NewSerializeBuffer()
opt := gopacket.SerializeOptions{
FixLengths: true, // 自动计算长度
ComputeChecksums: true, // 自动计算checksum
}
err := gopacket.SerializeLayers(buffer, opt, ether, ip4, udp, gopacket.Payload(udpPayload))
if err != nil {
log.Fatal("Serialize layers出现问题:", err)
}
outgoingPacket := buffer.Bytes()
handle, err := pcap.OpenLive(iface, 1024, false, 10 * time.Second)
if err != nil {
log.Fatal("pcap打开失败:", err)
}
defer handle.Close()
err = handle.WritePacketData(outgoingPacket)
if err != nil {
log.Fatal("发送udp数据包失败..")
}
}
// 参数data 开头是 dns的协议头 0x0000 0x8400 0x0000 0x0001(ans) 0x0000 0x0000
// 从 mdns响应报文中获取主机名
func ParseMdns(data []byte) string {
var buf bytes.Buffer
i := bytes.Index(data, []byte{0x05, 0x6c, 0x6f, 0x63, 0x61, 0x6c, 0x00})
if i < 0 {
return ""
}
for s := i - 1; s > 1; s-- {
num := i - s
if s - 2 < 0 {
break
}
// 包括 .local_ 7 个字符
if bto16([]byte{data[s - 2], data[s - 1]}) == uint16(num + 7) {
return Reverse(buf.String())
}
buf.WriteByte(data[s])
}
return ""
}
func bto16(b []byte) uint16 {
if len(b) != 2 {
log.Fatal("b只能是2个字节")
}
return uint16(b[0]) << 8 + uint16(b[1])
}