326 lines
8.3 KiB
Go
326 lines
8.3 KiB
Go
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// Copyright 2012 Google, Inc. All rights reserved.
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// Copyright 2009-2011 Andreas Krennmair. All rights reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the LICENSE file in the root of the source
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// tree.
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package layers
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import (
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"encoding/binary"
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"errors"
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"fmt"
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"net"
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"strings"
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"github.com/google/gopacket"
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)
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type IPv4Flag uint8
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const (
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IPv4EvilBit IPv4Flag = 1 << 2 // http://tools.ietf.org/html/rfc3514 ;)
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IPv4DontFragment IPv4Flag = 1 << 1
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IPv4MoreFragments IPv4Flag = 1 << 0
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)
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func (f IPv4Flag) String() string {
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var s []string
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if f&IPv4EvilBit != 0 {
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s = append(s, "Evil")
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}
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if f&IPv4DontFragment != 0 {
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s = append(s, "DF")
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}
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if f&IPv4MoreFragments != 0 {
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s = append(s, "MF")
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}
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return strings.Join(s, "|")
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}
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// IPv4 is the header of an IP packet.
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type IPv4 struct {
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BaseLayer
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Version uint8
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IHL uint8
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TOS uint8
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Length uint16
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Id uint16
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Flags IPv4Flag
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FragOffset uint16
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TTL uint8
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Protocol IPProtocol
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Checksum uint16
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SrcIP net.IP
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DstIP net.IP
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Options []IPv4Option
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Padding []byte
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}
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// LayerType returns LayerTypeIPv4
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func (i *IPv4) LayerType() gopacket.LayerType { return LayerTypeIPv4 }
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func (i *IPv4) NetworkFlow() gopacket.Flow {
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return gopacket.NewFlow(EndpointIPv4, i.SrcIP, i.DstIP)
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}
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type IPv4Option struct {
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OptionType uint8
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OptionLength uint8
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OptionData []byte
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}
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func (i IPv4Option) String() string {
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return fmt.Sprintf("IPv4Option(%v:%v)", i.OptionType, i.OptionData)
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}
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// for the current ipv4 options, return the number of bytes (including
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// padding that the options used)
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func (ip *IPv4) getIPv4OptionSize() uint8 {
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optionSize := uint8(0)
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for _, opt := range ip.Options {
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switch opt.OptionType {
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case 0:
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// this is the end of option lists
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optionSize++
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case 1:
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// this is the padding
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optionSize++
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default:
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optionSize += opt.OptionLength
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}
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}
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// make sure the options are aligned to 32 bit boundary
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if (optionSize % 4) != 0 {
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optionSize += 4 - (optionSize % 4)
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}
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return optionSize
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}
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// SerializeTo writes the serialized form of this layer into the
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// SerializationBuffer, implementing gopacket.SerializableLayer.
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func (ip *IPv4) SerializeTo(b gopacket.SerializeBuffer, opts gopacket.SerializeOptions) error {
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optionLength := ip.getIPv4OptionSize()
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bytes, err := b.PrependBytes(20 + int(optionLength))
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if err != nil {
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return err
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}
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if opts.FixLengths {
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ip.IHL = 5 + (optionLength / 4)
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ip.Length = uint16(len(b.Bytes()))
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}
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bytes[0] = (ip.Version << 4) | ip.IHL
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bytes[1] = ip.TOS
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binary.BigEndian.PutUint16(bytes[2:], ip.Length)
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binary.BigEndian.PutUint16(bytes[4:], ip.Id)
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binary.BigEndian.PutUint16(bytes[6:], ip.flagsfrags())
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bytes[8] = ip.TTL
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bytes[9] = byte(ip.Protocol)
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if err := ip.AddressTo4(); err != nil {
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return err
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}
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copy(bytes[12:16], ip.SrcIP)
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copy(bytes[16:20], ip.DstIP)
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curLocation := 20
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// Now, we will encode the options
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for _, opt := range ip.Options {
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switch opt.OptionType {
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case 0:
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// this is the end of option lists
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bytes[curLocation] = 0
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curLocation++
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case 1:
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// this is the padding
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bytes[curLocation] = 1
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curLocation++
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default:
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bytes[curLocation] = opt.OptionType
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bytes[curLocation+1] = opt.OptionLength
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// sanity checking to protect us from buffer overrun
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if len(opt.OptionData) > int(opt.OptionLength-2) {
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return errors.New("option length is smaller than length of option data")
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}
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copy(bytes[curLocation+2:curLocation+int(opt.OptionLength)], opt.OptionData)
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curLocation += int(opt.OptionLength)
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}
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}
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if opts.ComputeChecksums {
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ip.Checksum = checksum(bytes)
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}
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binary.BigEndian.PutUint16(bytes[10:], ip.Checksum)
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return nil
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}
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func checksum(bytes []byte) uint16 {
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// Clear checksum bytes
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bytes[10] = 0
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bytes[11] = 0
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// Compute checksum
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var csum uint32
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for i := 0; i < len(bytes); i += 2 {
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csum += uint32(bytes[i]) << 8
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csum += uint32(bytes[i+1])
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}
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for {
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// Break when sum is less or equals to 0xFFFF
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if csum <= 65535 {
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break
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}
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// Add carry to the sum
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csum = (csum >> 16) + uint32(uint16(csum))
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}
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// Flip all the bits
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return ^uint16(csum)
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}
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func (ip *IPv4) flagsfrags() (ff uint16) {
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ff |= uint16(ip.Flags) << 13
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ff |= ip.FragOffset
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return
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}
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// DecodeFromBytes decodes the given bytes into this layer.
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func (ip *IPv4) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
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if len(data) < 20 {
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df.SetTruncated()
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return fmt.Errorf("Invalid ip4 header. Length %d less than 20", len(data))
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}
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flagsfrags := binary.BigEndian.Uint16(data[6:8])
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ip.Version = uint8(data[0]) >> 4
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ip.IHL = uint8(data[0]) & 0x0F
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ip.TOS = data[1]
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ip.Length = binary.BigEndian.Uint16(data[2:4])
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ip.Id = binary.BigEndian.Uint16(data[4:6])
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ip.Flags = IPv4Flag(flagsfrags >> 13)
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ip.FragOffset = flagsfrags & 0x1FFF
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ip.TTL = data[8]
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ip.Protocol = IPProtocol(data[9])
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ip.Checksum = binary.BigEndian.Uint16(data[10:12])
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ip.SrcIP = data[12:16]
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ip.DstIP = data[16:20]
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ip.Options = ip.Options[:0]
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ip.Padding = nil
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// Set up an initial guess for contents/payload... we'll reset these soon.
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ip.BaseLayer = BaseLayer{Contents: data}
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// This code is added for the following enviroment:
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// * Windows 10 with TSO option activated. ( tested on Hyper-V, RealTek ethernet driver )
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if ip.Length == 0 {
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// If using TSO(TCP Segmentation Offload), length is zero.
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// The actual packet length is the length of data.
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ip.Length = uint16(len(data))
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}
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if ip.Length < 20 {
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return fmt.Errorf("Invalid (too small) IP length (%d < 20)", ip.Length)
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} else if ip.IHL < 5 {
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return fmt.Errorf("Invalid (too small) IP header length (%d < 5)", ip.IHL)
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} else if int(ip.IHL*4) > int(ip.Length) {
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return fmt.Errorf("Invalid IP header length > IP length (%d > %d)", ip.IHL, ip.Length)
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}
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if cmp := len(data) - int(ip.Length); cmp > 0 {
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data = data[:ip.Length]
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} else if cmp < 0 {
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df.SetTruncated()
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if int(ip.IHL)*4 > len(data) {
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return errors.New("Not all IP header bytes available")
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}
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}
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ip.Contents = data[:ip.IHL*4]
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ip.Payload = data[ip.IHL*4:]
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// From here on, data contains the header options.
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data = data[20 : ip.IHL*4]
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// Pull out IP options
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for len(data) > 0 {
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if ip.Options == nil {
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// Pre-allocate to avoid growing the slice too much.
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ip.Options = make([]IPv4Option, 0, 4)
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}
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opt := IPv4Option{OptionType: data[0]}
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switch opt.OptionType {
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case 0: // End of options
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opt.OptionLength = 1
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ip.Options = append(ip.Options, opt)
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ip.Padding = data[1:]
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return nil
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case 1: // 1 byte padding
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opt.OptionLength = 1
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data = data[1:]
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ip.Options = append(ip.Options, opt)
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default:
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if len(data) < 2 {
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df.SetTruncated()
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return fmt.Errorf("Invalid ip4 option length. Length %d less than 2", len(data))
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}
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opt.OptionLength = data[1]
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if len(data) < int(opt.OptionLength) {
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df.SetTruncated()
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return fmt.Errorf("IP option length exceeds remaining IP header size, option type %v length %v", opt.OptionType, opt.OptionLength)
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}
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if opt.OptionLength <= 2 {
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return fmt.Errorf("Invalid IP option type %v length %d. Must be greater than 2", opt.OptionType, opt.OptionLength)
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}
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opt.OptionData = data[2:opt.OptionLength]
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data = data[opt.OptionLength:]
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ip.Options = append(ip.Options, opt)
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}
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}
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return nil
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}
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func (i *IPv4) CanDecode() gopacket.LayerClass {
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return LayerTypeIPv4
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}
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func (i *IPv4) NextLayerType() gopacket.LayerType {
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if i.Flags&IPv4MoreFragments != 0 || i.FragOffset != 0 {
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return gopacket.LayerTypeFragment
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}
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return i.Protocol.LayerType()
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}
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func decodeIPv4(data []byte, p gopacket.PacketBuilder) error {
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ip := &IPv4{}
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err := ip.DecodeFromBytes(data, p)
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p.AddLayer(ip)
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p.SetNetworkLayer(ip)
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if err != nil {
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return err
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}
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return p.NextDecoder(ip.NextLayerType())
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}
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func checkIPv4Address(addr net.IP) (net.IP, error) {
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if c := addr.To4(); c != nil {
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return c, nil
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}
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if len(addr) == net.IPv6len {
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return nil, errors.New("address is IPv6")
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}
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return nil, fmt.Errorf("wrong length of %d bytes instead of %d", len(addr), net.IPv4len)
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}
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func (ip *IPv4) AddressTo4() error {
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var src, dst net.IP
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if addr, err := checkIPv4Address(ip.SrcIP); err != nil {
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return fmt.Errorf("Invalid source IPv4 address (%s)", err)
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} else {
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src = addr
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}
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if addr, err := checkIPv4Address(ip.DstIP); err != nil {
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return fmt.Errorf("Invalid destination IPv4 address (%s)", err)
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} else {
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dst = addr
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}
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ip.SrcIP = src
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ip.DstIP = dst
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return nil
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}
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