Dirty version, only for remote access
Ursprung
af165f5573
Commit
ee257888d7
GPG-Schlüssel-ID:
96B3365A234B500C
@ -0,0 +1,246 @@
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// based on https://github.com/aler9/landiscover/blob/main/layer-nbns.go (MIT License)
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package layer_nbns
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import (
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"encoding/binary"
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"fmt"
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"strings"
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"github.com/google/gopacket"
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"github.com/google/gopacket/layers"
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)
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type layerNbns struct {
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layers.BaseLayer
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TransactionID uint16
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IsResponse bool
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Opcode uint8
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Truncated bool
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Recursion bool
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Broadcast bool
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Questions []nbnsQuestion
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Answers []nbnsAnswer
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AuthorityCount uint16
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AdditionalCount uint16
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}
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func NewLayerNbns() *layerNbns {
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return &layerNbns{}
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}
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type nbnsQuestion struct {
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Query string
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Type uint16
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Class uint16
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}
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type nbnsAnswer struct {
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Query string
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Type uint16
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Class uint16
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TTL uint32
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Names []nbnsAnswerName
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}
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type nbnsAnswerName struct {
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Name string
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Type uint8
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Flags uint16
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}
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func (l *layerNbns) DecodeFromBytes(data []byte) error {
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l.BaseLayer = layers.BaseLayer{Contents: data}
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if len(data) < 12 {
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return fmt.Errorf("invalid packet")
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}
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l.TransactionID = binary.BigEndian.Uint16(data[0:2])
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l.IsResponse = (data[3] >> 7) == 0x01
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l.Opcode = (data[3] >> 3) & 0x0F
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l.Truncated = (data[3] >> 1) == 0x01
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l.Recursion = data[3] == 0x01
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l.Broadcast = (data[4] >> 4) == 0x01
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questionCount := binary.BigEndian.Uint16(data[4:6])
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answerCount := binary.BigEndian.Uint16(data[6:8])
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l.AuthorityCount = binary.BigEndian.Uint16(data[8:10])
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l.AdditionalCount = binary.BigEndian.Uint16(data[10:12])
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pos := 12
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if questionCount > 0 {
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return fmt.Errorf("is question, unsupported")
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}
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l.Questions = nil
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for i := uint16(0); i < questionCount; i++ {
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q := nbnsQuestion{}
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var read int
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q.Query, read = dnsQueryDecode(data, pos)
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if read <= 0 {
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return fmt.Errorf("invalid string")
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}
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pos += read
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q.Type = binary.BigEndian.Uint16(data[pos+0 : pos+2])
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q.Class = binary.BigEndian.Uint16(data[pos+2 : pos+4])
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pos += 4
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l.Questions = append(l.Questions, q)
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}
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l.Answers = nil
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for i := uint16(0); i < answerCount; i++ {
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a := nbnsAnswer{}
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var read int
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a.Query, read = dnsQueryDecode(data, pos)
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if read <= 0 {
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return fmt.Errorf("invalid string")
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}
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pos += read
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a.Type = binary.BigEndian.Uint16(data[pos+0 : pos+2])
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a.Class = binary.BigEndian.Uint16(data[pos+2 : pos+4])
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a.TTL = binary.BigEndian.Uint32(data[pos+4 : pos+8])
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dataLen := binary.BigEndian.Uint16(data[pos+8 : pos+10])
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pos += 10
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if a.Type == 0x21 { // NB_STAT
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pos2 := pos
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nameCount := data[pos2]
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pos2++
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for j := uint8(0); j < nameCount; j++ {
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a.Names = append(a.Names, nbnsAnswerName{
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Name: strings.TrimSuffix(string(data[pos2:pos2+15]), " "),
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Type: data[pos2+15],
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Flags: binary.BigEndian.Uint16(data[pos2+16 : pos2+18]),
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})
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pos2 += 18
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}
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}
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pos += int(dataLen)
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l.Answers = append(l.Answers, a)
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}
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// TODO: Decode Authorities and Additional Information
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return nil
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}
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func (l *layerNbns) SerializeTo(b gopacket.SerializeBuffer) error {
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data, err := b.AppendBytes(12)
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if err != nil {
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panic(err)
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}
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binary.BigEndian.PutUint16(data[0:2], l.TransactionID)
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if l.IsResponse {
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data[3] |= 0x01 << 7
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}
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data[3] |= l.Opcode << 3
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if l.Truncated {
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data[3] |= 0x01 << 1
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}
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if l.Recursion {
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data[3] |= 0x01
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}
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if l.Broadcast {
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data[4] |= 0x01 << 4
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}
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binary.BigEndian.PutUint16(data[4:6], uint16(len(l.Questions)))
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binary.BigEndian.PutUint16(data[6:8], uint16(len(l.Answers)))
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binary.BigEndian.PutUint16(data[8:10], l.AuthorityCount)
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binary.BigEndian.PutUint16(data[10:12], l.AdditionalCount)
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for _, q := range l.Questions {
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enc := dnsQueryEncode(q.Query)
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data, err := b.AppendBytes(len(enc) + 4)
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if err != nil {
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panic(err)
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}
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copy(data[:len(enc)], enc)
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data = data[len(enc):]
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binary.BigEndian.PutUint16(data[0:2], q.Type)
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binary.BigEndian.PutUint16(data[2:4], q.Class)
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}
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// TODO: encode answers, authorities and additional informations
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return nil
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}
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// Source: https://github.com/aler9/landiscover/blob/main/utils.go
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// <size>part<size>part
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func dnsQueryDecode(data []byte, start int) (string, int) {
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var read []byte
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toread := uint8(0)
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pos := start
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for ; true; pos++ {
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if pos >= len(data) { // decoding terminated before null character
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return "", -1
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}
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if data[pos] == 0x00 {
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if toread > 0 { // decoding terminated before part parsing
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return "", -1
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}
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break // query correctly decoded
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}
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if toread == 0 { // we need a size or pointer
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if len(read) > 0 { // add separator
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read = append(read, '.')
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}
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if (data[pos] & 0xC0) == 0xC0 { // pointer
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ptr := int(binary.BigEndian.Uint16(data[pos:pos+2]) & 0x3FFF)
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pos++ // skip next byte
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substr, subread := dnsQueryDecode(data, ptr)
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if subread <= 0 {
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return "", -1
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}
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read = append(read, []byte(substr)...)
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break // query correctly decoded
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} else { // size
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toread = data[pos]
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}
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} else { // byte inside part
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read = append(read, data[pos])
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toread--
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}
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}
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return string(read), pos + 1 - start
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}
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func dnsQueryEncode(in string) []byte {
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tmp := strings.Split(in, ".")
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l := 0
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for _, part := range tmp {
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bpart := []byte(part)
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l++
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l += len(bpart)
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}
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l++
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ret := make([]byte, l)
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i := 0
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for _, part := range tmp {
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bpart := []byte(part)
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ret[i] = uint8(len(bpart))
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i++
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copy(ret[i:], bpart)
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i += len(bpart)
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}
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ret[i] = uint8(0)
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return ret
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}
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