Golang调用gopacket库编写网络数据包捕获、注入、分析工具

Golang调用gopacket库编写网络数据包捕获、注入、分析工具,使用Google推出的 github.com/google/gopacket 包来实现对网络数据包的操作,gopacket基于libpcap。

1. libpcap 介绍

gopacket是基于libpcap(数据包捕获函数库)的,该库提供的C函数接口用于捕捉经过指定网络接口的数据包,该接口应该是被设为混杂模式。
著名的软件TCPDUMP就是在Libpcap的基础上开发而成的。Libpcap提供的接口函数实现和封装了与数据包截获有关的过程。Libpcap可以在绝大多数Linux平台上运行。

主要有以下功能:

  • 数据包捕获:捕获流经网卡的原始数据包
  • 自定义数据包发送:构造任何格式的原始数据包
  • 流量采集与统计:采集网络中的流量信息
  • 规则过滤:提供自带规则过滤功能,按需要选择过滤规则

2. 准备工作

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# Get the gopacket package from GitHub
go get github.com/google/gopacket
# Pcap dev headers might be necessary
sudo apt-get install libpcap-dev

从Github上获取 Gopacket

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go get -u -v github.com/google/gopacket

在你的系统上安装 libpcap-dev

  • MacOS (默认已经安装)

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    brew install libpcap
  • Ubuntu

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    apt-get install libpcap-dev
  • CentOS

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    yum install libpcap-dev

3. 代码部分

获取所有网络设备

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package main

import (
"fmt"
"log"
"github.com/google/gopacket/pcap"
)

func main() {
// Find all devices
devices, err := pcap.FindAllDevs()
if err != nil {
log.Fatal(err)
}

// Print device information
fmt.Println("Devices found:")
for _, device := range devices {
fmt.Println("\nName: ", device.Name)
fmt.Println("Description: ", device.Description)
fmt.Println("Devices addresses: ", device.Description)
for _, address := range device.Addresses {
fmt.Println("- IP address: ", address.IP)
fmt.Println("- Subnet mask: ", address.Netmask)
}
}
}

打开设备实时捕捉

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package main

import (
"fmt"
"github.com/google/gopacket"
"github.com/google/gopacket/pcap"
"log"
"time"
)

var (
device string = "eth0"
snapshot_len int32 = 1024
promiscuous bool = false
err error
timeout time.Duration = 30 * time.Second
handle *pcap.Handle
)

func main() {
// Open device
handle, err = pcap.OpenLive(device, snapshot_len, promiscuous, timeout)
if err != nil {log.Fatal(err) }
defer handle.Close()

// Use the handle as a packet source to process all packets
packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
for packet := range packetSource.Packets() {
// Process packet here
fmt.Println(packet)
}
}

抓取结果保存为pcap格式文件

要写一个pcap格式的文件,我们必须使用gapacket / pcapgo包。这是一个Writer接口和两个有用的函数:WriteFileHeader()和WritePacket()

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package main

import (
"fmt"
"os"
"time"

"github.com/google/gopacket"
"github.com/google/gopacket/layers"
"github.com/google/gopacket/pcap"
"github.com/google/gopacket/pcapgo"
)

var (
deviceName string = "eth0"
snapshotLen int32 = 1024
promiscuous bool = false
err error
timeout time.Duration = -1 * time.Second
handle *pcap.Handle
packetCount int = 0
)

func main() {
// Open output pcap file and write header
f, _ := os.Create("test.pcap")
w := pcapgo.NewWriter(f)
w.WriteFileHeader(snapshotLen, layers.LinkTypeEthernet)
defer f.Close()

// Open the device for capturing
handle, err = pcap.OpenLive(deviceName, snapshotLen, promiscuous, timeout)
if err != nil {
fmt.Printf("Error opening device %s: %v", deviceName, err)
os.Exit(1)
}
defer handle.Close()

// Start processing packets
packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
for packet := range packetSource.Packets() {
// Process packet here
fmt.Println(packet)
w.WritePacket(packet.Metadata().CaptureInfo, packet.Data())
packetCount++

// Only capture 100 and then stop
if packetCount > 100 {
break
}
}
}

读取pcap格式文件来查看分析网络数据包

我们不用打开一个设备进行实时捕获,也可以打开pcap文件进行离线检查。您可以使用tcpdump创建要使用的测试文件。

抓包:

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# Capture packets to test.pcap file
sudo tcpdump -w test.pcap

代码:

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package main

// Use tcpdump to create a test file
// tcpdump -w test.pcap
// or use the example above for writing pcap files

import (
"fmt"
"github.com/google/gopacket"
"github.com/google/gopacket/pcap"
"log"
)

var (
pcapFile string = "test.pcap"
handle *pcap.Handle
err error
)

func main() {
// Open file instead of device
handle, err = pcap.OpenOffline(pcapFile)
if err != nil { log.Fatal(err) }
defer handle.Close()

// Loop through packets in file
packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
for packet := range packetSource.Packets() {
fmt.Println(packet)
}
}

设置过滤器

只抓取tcp协议80端口的数据

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package main

import (
"fmt"
"github.com/google/gopacket"
"github.com/google/gopacket/pcap"
"log"
"time"
)

var (
device string = "eth0"
snapshot_len int32 = 1024
promiscuous bool = false
err error
timeout time.Duration = 30 * time.Second
handle *pcap.Handle
)

func main() {
// Open device
handle, err = pcap.OpenLive(device, snapshot_len, promiscuous, timeout)
if err != nil {
log.Fatal(err)
}
defer handle.Close()

// Set filter
var filter string = "tcp and port 80"
err = handle.SetBPFFilter(filter)
if err != nil {
log.Fatal(err)
}
fmt.Println("Only capturing TCP port 80 packets.")

packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
for packet := range packetSource.Packets() {
// Do something with a packet here.
fmt.Println(packet)
}

}

解码抓取的数据

我们可以使用原始数据包,并且可将其转换为已知格式。它与不同的层兼容,所以我们可以轻松访问以太网,IP和TCP层。layers包是Go库中新增的,在底层pcap库中不可用。这是一个令人难以置信的有用的包,它是gopacket库的一部分。它允许我们容易地识别包是否包含特定类型的层。该代码示例将显示如何使用layers包来查看数据包是以太网,IP和TCP,并轻松访问这些头文件中的元素。 查找有效载荷取决于所涉及的所有层。每个协议是不同的,必须相应地计算。这就是layer包的魅力所在。 gopacket的作者花了时间为诸如以太网,IP,UDP和TCP等众多已知层创建了相应类型。有效载荷是应用层的一部分。

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package main

import (
"fmt"
"github.com/google/gopacket"
"github.com/google/gopacket/layers"
"github.com/google/gopacket/pcap"
"log"
"strings"
"time"
)

var (
device string = "eth0"
snapshotLen int32 = 1024
promiscuous bool = false
err error
timeout time.Duration = 30 * time.Second
handle *pcap.Handle
)

func main() {
// Open device
handle, err = pcap.OpenLive(device, snapshotLen, promiscuous, timeout)
if err != nil {log.Fatal(err) }
defer handle.Close()

packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
for packet := range packetSource.Packets() {
printPacketInfo(packet)
}
}

func printPacketInfo(packet gopacket.Packet) {
// Let's see if the packet is an ethernet packet
ethernetLayer := packet.Layer(layers.LayerTypeEthernet)
if ethernetLayer != nil {
fmt.Println("Ethernet layer detected.")
ethernetPacket, _ := ethernetLayer.(*layers.Ethernet)
fmt.Println("Source MAC: ", ethernetPacket.SrcMAC)
fmt.Println("Destination MAC: ", ethernetPacket.DstMAC)
// Ethernet type is typically IPv4 but could be ARP or other
fmt.Println("Ethernet type: ", ethernetPacket.EthernetType)
fmt.Println()
}

// Let's see if the packet is IP (even though the ether type told us)
ipLayer := packet.Layer(layers.LayerTypeIPv4)
if ipLayer != nil {
fmt.Println("IPv4 layer detected.")
ip, _ := ipLayer.(*layers.IPv4)

// IP layer variables:
// Version (Either 4 or 6)
// IHL (IP Header Length in 32-bit words)
// TOS, Length, Id, Flags, FragOffset, TTL, Protocol (TCP?),
// Checksum, SrcIP, DstIP
fmt.Printf("From %s to %s\n", ip.SrcIP, ip.DstIP)
fmt.Println("Protocol: ", ip.Protocol)
fmt.Println()
}

// Let's see if the packet is TCP
tcpLayer := packet.Layer(layers.LayerTypeTCP)
if tcpLayer != nil {
fmt.Println("TCP layer detected.")
tcp, _ := tcpLayer.(*layers.TCP)

// TCP layer variables:
// SrcPort, DstPort, Seq, Ack, DataOffset, Window, Checksum, Urgent
// Bool flags: FIN, SYN, RST, PSH, ACK, URG, ECE, CWR, NS
fmt.Printf("From port %d to %d\n", tcp.SrcPort, tcp.DstPort)
fmt.Println("Sequence number: ", tcp.Seq)
fmt.Println()
}

// Iterate over all layers, printing out each layer type
fmt.Println("All packet layers:")
for _, layer := range packet.Layers() {
fmt.Println("- ", layer.LayerType())
}

// When iterating through packet.Layers() above,
// if it lists Payload layer then that is the same as
// this applicationLayer. applicationLayer contains the payload
applicationLayer := packet.ApplicationLayer()
if applicationLayer != nil {
fmt.Println("Application layer/Payload found.")
fmt.Printf("%s\n", applicationLayer.Payload())

// Search for a string inside the payload
if strings.Contains(string(applicationLayer.Payload()), "HTTP") {
fmt.Println("HTTP found!")
}
}

// Check for errors
if err := packet.ErrorLayer(); err != nil {
fmt.Println("Error decoding some part of the packet:", err)
}
}

构造发送数据包

这个例子做了几件事情。首先将显示如何使用网络设备发送原始字节。这样就可以像串行连接一样使用它来发送数据。这对于真正的低层数据传输非常有用,但如果您想与应用程序进行交互,您应该构建可以识别该数据包的其他硬件和软件。接下来,它将显示如何使用以太网,IP和TCP层创建一个数据包。一切都是默认空的。要完成它,我们创建另一个数据包,但实际上填写了以太网层的一些MAC地址,IPv4的一些IP地址和TCP层的端口号。你应该看到如何伪装数据包和仿冒网络设备。TCP层结构体具有可读取和可设置的SYN,FIN,ACK标志。这有助于操纵和模糊TCP三次握手,会话和端口扫描。pcap库提供了一种发送字节的简单方法,但gopacket中的图层可帮助我们为多层创建字节结构。

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package main

import (
"github.com/google/gopacket"
"github.com/google/gopacket/layers"
"github.com/google/gopacket/pcap"
"log"
"net"
"time"
)

var (
device string = "eth0"
snapshot_len int32 = 1024
promiscuous bool = false
err error
timeout time.Duration = 30 * time.Second
handle *pcap.Handle
buffer gopacket.SerializeBuffer
options gopacket.SerializeOptions
)

func main() {
// Open device
handle, err = pcap.OpenLive(device, snapshot_len, promiscuous, timeout)
if err != nil {log.Fatal(err) }
defer handle.Close()

// Send raw bytes over wire
rawBytes := []byte{10, 20, 30}
err = handle.WritePacketData(rawBytes)
if err != nil {
log.Fatal(err)
}

// Create a properly formed packet, just with
// empty details. Should fill out MAC addresses,
// IP addresses, etc.
buffer = gopacket.NewSerializeBuffer()
gopacket.SerializeLayers(buffer, options,
&layers.Ethernet{},
&layers.IPv4{},
&layers.TCP{},
gopacket.Payload(rawBytes),
)
outgoingPacket := buffer.Bytes()
// Send our packet
err = handle.WritePacketData(outgoingPacket)
if err != nil {
log.Fatal(err)
}

// This time lets fill out some information
ipLayer := &layers.IPv4{
SrcIP: net.IP{127, 0, 0, 1},
DstIP: net.IP{8, 8, 8, 8},
}
ethernetLayer := &layers.Ethernet{
SrcMAC: net.HardwareAddr{0xFF, 0xAA, 0xFA, 0xAA, 0xFF, 0xAA},
DstMAC: net.HardwareAddr{0xBD, 0xBD, 0xBD, 0xBD, 0xBD, 0xBD},
}
tcpLayer := &layers.TCP{
SrcPort: layers.TCPPort(4321),
DstPort: layers.TCPPort(80),
}
// And create the packet with the layers
buffer = gopacket.NewSerializeBuffer()
gopacket.SerializeLayers(buffer, options,
ethernetLayer,
ipLayer,
tcpLayer,
gopacket.Payload(rawBytes),
)
outgoingPacket = buffer.Bytes()
}

更多的解码/构造数据包的例子

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package main

import (
"fmt"
"github.com/google/gopacket"
"github.com/google/gopacket/layers"
)

func main() {
// If we don't have a handle to a device or a file, but we have a bunch
// of raw bytes, we can try to decode them in to packet information

// NewPacket() takes the raw bytes that make up the packet as the first parameter
// The second parameter is the lowest level layer you want to decode. It will
// decode that layer and all layers on top of it. The third layer
// is the type of decoding: default(all at once), lazy(on demand), and NoCopy
// which will not create a copy of the buffer

// Create an packet with ethernet, IP, TCP, and payload layers
// We are creating one we know will be decoded properly but
// your byte source could be anything. If any of the packets
// come back as nil, that means it could not decode it in to
// the proper layer (malformed or incorrect packet type)
payload := []byte{2, 4, 6}
options := gopacket.SerializeOptions{}
buffer := gopacket.NewSerializeBuffer()
gopacket.SerializeLayers(buffer, options,
&layers.Ethernet{},
&layers.IPv4{},
&layers.TCP{},
gopacket.Payload(payload),
)
rawBytes := buffer.Bytes()

// Decode an ethernet packet
ethPacket :=
gopacket.NewPacket(
rawBytes,
layers.LayerTypeEthernet,
gopacket.Default,
)

// with Lazy decoding it will only decode what it needs when it needs it
// This is not concurrency safe. If using concurrency, use default
ipPacket :=
gopacket.NewPacket(
rawBytes,
layers.LayerTypeIPv4,
gopacket.Lazy,
)

// With the NoCopy option, the underlying slices are referenced
// directly and not copied. If the underlying bytes change so will
// the packet
tcpPacket :=
gopacket.NewPacket(
rawBytes,
layers.LayerTypeTCP,
gopacket.NoCopy,
)

fmt.Println(ethPacket)
fmt.Println(ipPacket)
fmt.Println(tcpPacket)
}

自定义layer

下一个程序将显示如何创建自己的layer。构建gopacket layer包不包含的协议。如果您要创建自己的l33t协议,甚至不使用TCP / IP或以太网,这是很有用的。

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package main

import (
"fmt"
"github.com/google/gopacket"
)

// Create custom layer structure
type CustomLayer struct {
// This layer just has two bytes at the front
SomeByte byte
AnotherByte byte
restOfData []byte
}

// Register the layer type so we can use it
// The first argument is an ID. Use negative
// or 2000+ for custom layers. It must be unique
var CustomLayerType = gopacket.RegisterLayerType(
2001,
gopacket.LayerTypeMetadata{
"CustomLayerType",
gopacket.DecodeFunc(decodeCustomLayer),
},
)

// When we inquire about the type, what type of layer should
// we say it is? We want it to return our custom layer type
func (l CustomLayer) LayerType() gopacket.LayerType {
return CustomLayerType
}

// LayerContents returns the information that our layer
// provides. In this case it is a header layer so
// we return the header information
func (l CustomLayer) LayerContents() []byte {
return []byte{l.SomeByte, l.AnotherByte}
}

// LayerPayload returns the subsequent layer built
// on top of our layer or raw payload
func (l CustomLayer) LayerPayload() []byte {
return l.restOfData
}

// Custom decode function. We can name it whatever we want
// but it should have the same arguments and return value
// When the layer is registered we tell it to use this decode function
func decodeCustomLayer(data []byte, p gopacket.PacketBuilder) error {
// AddLayer appends to the list of layers that the packet has
p.AddLayer(&CustomLayer{data[0], data[1], data[2:]})

// The return value tells the packet what layer to expect
// with the rest of the data. It could be another header layer,
// nothing, or a payload layer.

// nil means this is the last layer. No more decoding
// return nil

// Returning another layer type tells it to decode
// the next layer with that layer's decoder function
// return p.NextDecoder(layers.LayerTypeEthernet)

// Returning payload type means the rest of the data
// is raw payload. It will set the application layer
// contents with the payload
return p.NextDecoder(gopacket.LayerTypePayload)
}

func main() {
// If you create your own encoding and decoding you can essentially
// create your own protocol or implement a protocol that is not
// already defined in the layers package. In our example we are just
// wrapping a normal ethernet packet with our own layer.
// Creating your own protocol is good if you want to create
// some obfuscated binary data type that was difficult for others
// to decode

// Finally, decode your packets:
rawBytes := []byte{0xF0, 0x0F, 65, 65, 66, 67, 68}
packet := gopacket.NewPacket(
rawBytes,
CustomLayerType,
gopacket.Default,
)
fmt.Println("Created packet out of raw bytes.")
fmt.Println(packet)

// Decode the packet as our custom layer
customLayer := packet.Layer(CustomLayerType)
if customLayer != nil {
fmt.Println("Packet was successfully decoded with custom layer decoder.")
customLayerContent, _ := customLayer.(*CustomLayer)
// Now we can access the elements of the custom struct
fmt.Println("Payload: ", customLayerContent.LayerPayload())
fmt.Println("SomeByte element:", customLayerContent.SomeByte)
fmt.Println("AnotherByte element:", customLayerContent.AnotherByte)
}
}

更快地解码数据包

如果我们知道我们要预期的得到的层,我们可以使用现有的结构来存储分组信息,而不是为每个需要时间和内存的分组创建新的结构。使用DecodingLayerParser更快。就像编组和解组数据一样。

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package main

import (
"fmt"
"github.com/google/gopacket"
"github.com/google/gopacket/layers"
"github.com/google/gopacket/pcap"
"log"
"time"
)

var (
device string = "eth0"
snapshot_len int32 = 1024
promiscuous bool = false
err error
timeout time.Duration = 30 * time.Second
handle *pcap.Handle
// Will reuse these for each packet
ethLayer layers.Ethernet
ipLayer layers.IPv4
tcpLayer layers.TCP
)

func main() {
// Open device
handle, err = pcap.OpenLive(device, snapshot_len, promiscuous, timeout)
if err != nil {
log.Fatal(err)
}
defer handle.Close()

packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
for packet := range packetSource.Packets() {
parser := gopacket.NewDecodingLayerParser(
layers.LayerTypeEthernet,
&ethLayer,
&ipLayer,
&tcpLayer,
)
foundLayerTypes := []gopacket.LayerType{}

err := parser.DecodeLayers(packet.Data(), &foundLayerTypes)
if err != nil {
fmt.Println("Trouble decoding layers: ", err)
}

for _, layerType := range foundLayerTypes {
if layerType == layers.LayerTypeIPv4 {
fmt.Println("IPv4: ", ipLayer.SrcIP, "->", ipLayer.DstIP)
}
if layerType == layers.LayerTypeTCP {
fmt.Println("TCP Port: ", tcpLayer.SrcPort, "->", tcpLayer.DstPort)
fmt.Println("TCP SYN:", tcpLayer.SYN, " | ACK:", tcpLayer.ACK)
}
}
}
}

TCP流重组

gopacket包提供了一些名为Flow和Endpoint的类型。我没有机会深入探索这些文档,但文档中有一个使用它来将特定TCP流发送到数据包通道的示例。https://godoc.org/github.com/google/gopacket

4. 简述

写这篇博文是因为gopacket这个包资料案例不是很多,百度上唯一一篇质量还可以的文章是来自虾米的博客 发布在CSDN上的一篇关于gopacket的golang语言代码实现的文章,但是CSS出现问题,导致阅读障碍,为了防止文章资源丢失,这里特此将文章内容通过更简洁的方式重写,并在后期针对于对Google推出的 GoPacket包 的理解续写这篇文章,感谢作者 @ptmozhu 提供的精彩文章内容。