如何将修改的GO数据包序列化为真实的IP数据包

Question

为什么

我想编写代理服务器，代理服务器更改数据包的IP/端口并进行了修改。

尝试

package main
import (
  "encoding/hex"
  "github.com/google/gopacket"
  "github.com/google/gopacket/layers"
  "fmt"
  "net"
)
func main() {
  packetData := []byte{
    69, 0, 0, 63, 64, 237, 64, 0, 64, 6, 74, 221, 192,
    168, 1, 90, 52, 85, 184, 151, 141, 230, 0, 80,
    174, 147, 86, 192, 18, 107, 243, 149, 128, 24,
    0, 229, 92, 65, 0, 0, 1, 1, 8, 10, 22, 138, 85, 109,
    48, 16, 32, 253, 49, 50, 51, 52, 53, 54, 55, 56,
    57, 48, 10,
  }
  fmt.Println("Hex dump of real IP packet taken as input:n")
  fmt.Println(hex.Dump(packetData))
  packet := gopacket.NewPacket(packetData, layers.LayerTypeIPv4, gopacket.Default)
  if ipLayer := packet.Layer(layers.LayerTypeIPv4); ipLayer != nil {
    ip := ipLayer.(*layers.IPv4)
    dst := ip.DstIP.String()
    src := ip.SrcIP.String()
    if tcpLayer := packet.Layer(layers.LayerTypeTCP); tcpLayer != nil {
      tcp := tcpLayer.(*layers.TCP)
      dst = fmt.Sprintf("%s:%d", dst, tcp.DstPort)
      src = fmt.Sprintf("%s:%d", src, tcp.SrcPort)
      fmt.Printf("From %s to %snn", src, dst)
      ip.DstIP = net.ParseIP("8.8.8.8")
      options := gopacket.SerializeOptions{
        ComputeChecksums: true,
        FixLengths: true,
      }
      newBuffer := gopacket.NewSerializeBuffer()
      gopacket.SerializeLayers(newBuffer, options,
          ip,
          tcp,
      )
      outgoingPacket := newBuffer.Bytes()
      fmt.Println("Hex dump of go packet serialization output:n")
      fmt.Println(hex.Dump(outgoingPacket))
    }
  }
}

输出

Hex dump of real IP packet taken as input:
00000000  45 00 00 3f 40 ed 40 00  40 06 4a dd c0 a8 01 5a  |E..?@.@.@.J....Z|
00000010  34 55 b8 97 8d e6 00 50  ae 93 56 c0 12 6b f3 95  |4U.....P..V..k..|
00000020  80 18 00 e5 5c 41 00 00  01 01 08 0a 16 8a 55 6d  |....A........Um|
00000030  30 10 20 fd 31 32 33 34  35 36 37 38 39 30 0a     |0. .1234567890.|
From 192.168.1.90:36326 to 52.85.184.151:80
Hex dump of go packet serialization output:
00000000  8d e6 00 50 ae 93 56 c0  12 6b f3 95 80 18 00 e5  |...P..V..k......|
00000010  00 00 00 00 01 01 08 0a  16 8a 55 6d 30 10 20 fd  |..........Um0. .|

什么问题

第二HEX转储必须以45开始（大多数IPv4数据包以45开始，其中4是该协议的版本）。第二个Hexdump必须与第一个相同的详细信息相同，只是一个更改的IP地址，TCP校验和尺寸值。第二个十六进制转储必须包含有效载荷1234567890n。

类似的问题

1. 如何使用golang撰写RAW TCP数据包（使用Gopacket）并通过RAW套接字发送
2. 用gopacket发送UDP数据包
3. 更改gopacket的IP地址并使用原始插座重新传输

Answer 1

首先，请务必检查返回的错误 - 这是您的反馈：

err := gopacket.SerializePacket(newBuffer, options, packet)
// OR
err := gopacket.SerializeLayers(newBuffer, options,
  ip,
  tcp,
)
// THEN
if err != nil {
  panic(err)
}

从上面的代码中，您将获得：TCP/IP layer 4 checksum cannot be computed without network layer... call SetNetworkLayerForChecksum to set which layer to use

然后，解决方案是使用tcp.SetNetworkLayerForChecksum(ip)和最终工作代码：

package main
import (
  "encoding/hex"
  "github.com/google/gopacket"
  "github.com/google/gopacket/layers"
  "fmt"
  "net"
)
func main() {
  packetData := []byte{
    69, 0, 0, 63, 64, 237, 64, 0, 64, 6, 74, 221, 192,
    168, 1, 90, 52, 85, 184, 151, 141, 230, 0, 80,
    174, 147, 86, 192, 18, 107, 243, 149, 128, 24,
    0, 229, 92, 65, 0, 0, 1, 1, 8, 10, 22, 138, 85, 109,
    48, 16, 32, 253, 49, 50, 51, 52, 53, 54, 55, 56,
    57, 48, 10,
  }
  fmt.Println("Hex dump of real IP packet taken as input:n")
  fmt.Println(hex.Dump(packetData))
  packet := gopacket.NewPacket(packetData, layers.LayerTypeIPv4, gopacket.Default)
  if ipLayer := packet.Layer(layers.LayerTypeIPv4); ipLayer != nil {
    ip := ipLayer.(*layers.IPv4)
    dst := ip.DstIP.String()
    src := ip.SrcIP.String()
    if tcpLayer := packet.Layer(layers.LayerTypeTCP); tcpLayer != nil {
      tcp := tcpLayer.(*layers.TCP)
      dst = fmt.Sprintf("%s:%d", dst, tcp.DstPort)
      src = fmt.Sprintf("%s:%d", src, tcp.SrcPort)
      fmt.Printf("From %s to %snn", src, dst)
      ip.DstIP = net.ParseIP("8.8.8.8")
      options := gopacket.SerializeOptions{
        ComputeChecksums: true,
        FixLengths: true,
      }
      tcp.SetNetworkLayerForChecksum(ip)
      newBuffer := gopacket.NewSerializeBuffer()
      err := gopacket.SerializePacket(newBuffer, options, packet)
      if err != nil {
        panic(err)
      }
      outgoingPacket := newBuffer.Bytes()
      fmt.Println("Hex dump of go packet serialization output:n")
      fmt.Println(hex.Dump(outgoingPacket))
    }
  }
}

输出

Hex dump of real IP packet taken as input:
00000000  45 00 00 3f 40 ed 40 00  40 06 4a dd c0 a8 01 5a  |E..?@.@.@.J....Z|
00000010  34 55 b8 97 8d e6 00 50  ae 93 56 c0 12 6b f3 95  |4U.....P..V..k..|
00000020  80 18 00 e5 5c 41 00 00  01 01 08 0a 16 8a 55 6d  |....A........Um|
00000030  30 10 20 fd 31 32 33 34  35 36 37 38 39 30 0a     |0. .1234567890.|
From 192.168.1.90:36326 to 52.85.184.151:80
Hex dump of go packet serialization output:
00000000  45 00 00 3f 40 ed 40 00  40 06 27 ba c0 a8 01 5a  |E..?@.@.@.'....Z|
00000010  08 08 08 08 8d e6 00 50  ae 93 56 c0 12 6b f3 95  |.......P..V..k..|
00000020  80 18 00 e5 39 1e 00 00  01 01 08 0a 16 8a 55 6d  |....9.........Um|
00000030  30 10 20 fd 31 32 33 34  35 36 37 38 39 30 0a     |0. .1234567890.|

正如您所看到的08 08 08 08是一个新的IP，有效载荷1234567890n也保留了，IP数据包以45开始。