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// DNS packet assembly, see RFC 1035. Converting from - Unpack() -
// and to - Pack() - wire format.
// All the packers and unpackers take a (msg []byte, off int)
// and return (off1 int, ok bool). If they return ok==false, they
// also return off1==len(msg), so that the next unpacker will
// also fail. This lets us avoid checks of ok until the end of a
// packing sequence.
package dns
//go:generate go run msg_generate.go
import (
crand "crypto/rand"
"encoding/binary"
"fmt"
"math/big"
"math/rand"
"strconv"
"strings"
"sync"
)
const (
maxCompressionOffset = 2 << 13 // We have 14 bits for the compression pointer
maxDomainNameWireOctets = 255 // See RFC 1035 section 2.3.4
// This is the maximum number of compression pointers that should occur in a
// semantically valid message. Each label in a domain name must be at least one
// octet and is separated by a period. The root label won't be represented by a
// compression pointer to a compression pointer, hence the -2 to exclude the
// smallest valid root label.
//
// It is possible to construct a valid message that has more compression pointers
// than this, and still doesn't loop, by pointing to a previous pointer. This is
// not something a well written implementation should ever do, so we leave them
// to trip the maximum compression pointer check.
maxCompressionPointers = (maxDomainNameWireOctets+1)/2 - 2
// This is the maximum length of a domain name in presentation format. The
// maximum wire length of a domain name is 255 octets (see above), with the
// maximum label length being 63. The wire format requires one extra byte over
// the presentation format, reducing the number of octets by 1. Each label in
// the name will be separated by a single period, with each octet in the label
// expanding to at most 4 bytes (\DDD). If all other labels are of the maximum
// length, then the final label can only be 61 octets long to not exceed the
// maximum allowed wire length.
maxDomainNamePresentationLength = 61*4 + 1 + 63*4 + 1 + 63*4 + 1 + 63*4 + 1
)
// Errors defined in this package.
var (
ErrAlg error = &Error{err: "bad algorithm"} // ErrAlg indicates an error with the (DNSSEC) algorithm.
ErrAuth error = &Error{err: "bad authentication"} // ErrAuth indicates an error in the TSIG authentication.
ErrBuf error = &Error{err: "buffer size too small"} // ErrBuf indicates that the buffer used is too small for the message.
ErrConnEmpty error = &Error{err: "conn has no connection"} // ErrConnEmpty indicates a connection is being used before it is initialized.
ErrExtendedRcode error = &Error{err: "bad extended rcode"} // ErrExtendedRcode ...
ErrFqdn error = &Error{err: "domain must be fully qualified"} // ErrFqdn indicates that a domain name does not have a closing dot.
ErrId error = &Error{err: "id mismatch"} // ErrId indicates there is a mismatch with the message's ID.
ErrKeyAlg error = &Error{err: "bad key algorithm"} // ErrKeyAlg indicates that the algorithm in the key is not valid.
ErrKey error = &Error{err: "bad key"}
ErrKeySize error = &Error{err: "bad key size"}
ErrLongDomain error = &Error{err: fmt.Sprintf("domain name exceeded %d wire-format octets", maxDomainNameWireOctets)}
ErrNoSig error = &Error{err: "no signature found"}
ErrPrivKey error = &Error{err: "bad private key"}
ErrRcode error = &Error{err: "bad rcode"}
ErrRdata error = &Error{err: "bad rdata"}
ErrRRset error = &Error{err: "bad rrset"}
ErrSecret error = &Error{err: "no secrets defined"}
ErrShortRead error = &Error{err: "short read"}
ErrSig error = &Error{err: "bad signature"} // ErrSig indicates that a signature can not be cryptographically validated.
ErrSoa error = &Error{err: "no SOA"} // ErrSOA indicates that no SOA RR was seen when doing zone transfers.
ErrTime error = &Error{err: "bad time"} // ErrTime indicates a timing error in TSIG authentication.
)
// Id by default, returns a 16 bits random number to be used as a
// message id. The random provided should be good enough. This being a
// variable the function can be reassigned to a custom function.
// For instance, to make it return a static value:
//
// dns.Id = func() uint16 { return 3 }
var Id = id
var (
idLock sync.Mutex
idRand *rand.Rand
)
// id returns a 16 bits random number to be used as a
// message id. The random provided should be good enough.
func id() uint16 {
idLock.Lock()
if idRand == nil {
// This (partially) works around
// https://github.com/golang/go/issues/11833 by only
// seeding idRand upon the first call to id.
var seed int64
var buf [8]byte
if _, err := crand.Read(buf[:]); err == nil {
seed = int64(binary.LittleEndian.Uint64(buf[:]))
} else {
seed = rand.Int63()
}
idRand = rand.New(rand.NewSource(seed))
}
// The call to idRand.Uint32 must be within the
// mutex lock because *rand.Rand is not safe for
// concurrent use.
//
// There is no added performance overhead to calling
// idRand.Uint32 inside a mutex lock over just
// calling rand.Uint32 as the global math/rand rng
// is internally protected by a sync.Mutex.
id := uint16(idRand.Uint32())
idLock.Unlock()
return id
}
// MsgHdr is a a manually-unpacked version of (id, bits).
type MsgHdr struct {
Id uint16
Response bool
Opcode int
Authoritative bool
Truncated bool
RecursionDesired bool
RecursionAvailable bool
Zero bool
AuthenticatedData bool
CheckingDisabled bool
Rcode int
}
// Msg contains the layout of a DNS message.
type Msg struct {
MsgHdr
Compress bool `json:"-"` // If true, the message will be compressed when converted to wire format.
Question []Question // Holds the RR(s) of the question section.
Answer []RR // Holds the RR(s) of the answer section.
Ns []RR // Holds the RR(s) of the authority section.
Extra []RR // Holds the RR(s) of the additional section.
}
// ClassToString is a maps Classes to strings for each CLASS wire type.
var ClassToString = map[uint16]string{
ClassINET: "IN",
ClassCSNET: "CS",
ClassCHAOS: "CH",
ClassHESIOD: "HS",
ClassNONE: "NONE",
ClassANY: "ANY",
}
// OpcodeToString maps Opcodes to strings.
var OpcodeToString = map[int]string{
OpcodeQuery: "QUERY",
OpcodeIQuery: "IQUERY",
OpcodeStatus: "STATUS",
OpcodeNotify: "NOTIFY",
OpcodeUpdate: "UPDATE",
}
// RcodeToString maps Rcodes to strings.
var RcodeToString = map[int]string{
RcodeSuccess: "NOERROR",
RcodeFormatError: "FORMERR",
RcodeServerFailure: "SERVFAIL",
RcodeNameError: "NXDOMAIN",
RcodeNotImplemented: "NOTIMP",
RcodeRefused: "REFUSED",
RcodeYXDomain: "YXDOMAIN", // See RFC 2136
RcodeYXRrset: "YXRRSET",
RcodeNXRrset: "NXRRSET",
RcodeNotAuth: "NOTAUTH",
RcodeNotZone: "NOTZONE",
RcodeBadSig: "BADSIG", // Also known as RcodeBadVers, see RFC 6891
// RcodeBadVers: "BADVERS",
RcodeBadKey: "BADKEY",
RcodeBadTime: "BADTIME",
RcodeBadMode: "BADMODE",
RcodeBadName: "BADNAME",
RcodeBadAlg: "BADALG",
RcodeBadTrunc: "BADTRUNC",
RcodeBadCookie: "BADCOOKIE",
}
// compressionMap is used to allow a more efficient compression map
// to be used for internal packDomainName calls without changing the
// signature or functionality of public API.
//
// In particular, map[string]uint16 uses 25% less per-entry memory
// than does map[string]int.
type compressionMap struct {
ext map[string]int // external callers
int map[string]uint16 // internal callers
}
func (m compressionMap) valid() bool {
return m.int != nil || m.ext != nil
}
func (m compressionMap) insert(s string, pos int) {
if m.ext != nil {
m.ext[s] = pos
} else {
m.int[s] = uint16(pos)
}
}
func (m compressionMap) find(s string) (int, bool) {
if m.ext != nil {
pos, ok := m.ext[s]
return pos, ok
}
pos, ok := m.int[s]
return int(pos), ok
}
// Domain names are a sequence of counted strings
// split at the dots. They end with a zero-length string.
// PackDomainName packs a domain name s into msg[off:].
// If compression is wanted compress must be true and the compression
// map needs to hold a mapping between domain names and offsets
// pointing into msg.
func PackDomainName(s string, msg []byte, off int, compression map[string]int, compress bool) (off1 int, err error) {
return packDomainName(s, msg, off, compressionMap{ext: compression}, compress)
}
func packDomainName(s string, msg []byte, off int, compression compressionMap, compress bool) (off1 int, err error) {
// XXX: A logical copy of this function exists in IsDomainName and
// should be kept in sync with this function.
ls := len(s)
if ls == 0 { // Ok, for instance when dealing with update RR without any rdata.
return off, nil
}
// If not fully qualified, error out.
if !IsFqdn(s) {
return len(msg), ErrFqdn
}
// Each dot ends a segment of the name.
// We trade each dot byte for a length byte.
// Except for escaped dots (\.), which are normal dots.
// There is also a trailing zero.
// Compression
pointer := -1
// Emit sequence of counted strings, chopping at dots.
var (
begin int
compBegin int
compOff int
bs []byte
wasDot bool
)
loop:
for i := 0; i < ls; i++ {
var c byte
if bs == nil {
c = s[i]
} else {
c = bs[i]
}
switch c {
case '\\':
if off+1 > len(msg) {
return len(msg), ErrBuf
}
if bs == nil {
bs = []byte(s)
}
// check for \DDD
if i+3 < ls && isDigit(bs[i+1]) && isDigit(bs[i+2]) && isDigit(bs[i+3]) {
bs[i] = dddToByte(bs[i+1:])
copy(bs[i+1:ls-3], bs[i+4:])
ls -= 3
compOff += 3
} else {
copy(bs[i:ls-1], bs[i+1:])
ls--
compOff++
}
wasDot = false
case '.':
if wasDot {
// two dots back to back is not legal
return len(msg), ErrRdata
}
wasDot = true
labelLen := i - begin
if labelLen >= 1<<6 { // top two bits of length must be clear
return len(msg), ErrRdata
}
// off can already (we're in a loop) be bigger than len(msg)
// this happens when a name isn't fully qualified
if off+1+labelLen > len(msg) {
return len(msg), ErrBuf
}
// Don't try to compress '.'
// We should only compress when compress is true, but we should also still pick
// up names that can be used for *future* compression(s).
if compression.valid() && !isRootLabel(s, bs, begin, ls) {
if p, ok := compression.find(s[compBegin:]); ok {
// The first hit is the longest matching dname
// keep the pointer offset we get back and store
// the offset of the current name, because that's
// where we need to insert the pointer later
// If compress is true, we're allowed to compress this dname
if compress {
pointer = p // Where to point to
break loop
}
} else if off < maxCompressionOffset {
// Only offsets smaller than maxCompressionOffset can be used.
compression.insert(s[compBegin:], off)
}
}
// The following is covered by the length check above.
msg[off] = byte(labelLen)
if bs == nil {
copy(msg[off+1:], s[begin:i])
} else {
copy(msg[off+1:], bs[begin:i])
}
off += 1 + labelLen
begin = i + 1
compBegin = begin + compOff
default:
wasDot = false
}
}
// Root label is special
if isRootLabel(s, bs, 0, ls) {
return off, nil
}
// If we did compression and we find something add the pointer here
if pointer != -1 {
// We have two bytes (14 bits) to put the pointer in
binary.BigEndian.PutUint16(msg[off:], uint16(pointer^0xC000))
return off + 2, nil
}
if off < len(msg) {
msg[off] = 0
}
return off + 1, nil
}
// isRootLabel returns whether s or bs, from off to end, is the root
// label ".".
//
// If bs is nil, s will be checked, otherwise bs will be checked.
func isRootLabel(s string, bs []byte, off, end int) bool {
if bs == nil {
return s[off:end] == "."
}
return end-off == 1 && bs[off] == '.'
}
// Unpack a domain name.
// In addition to the simple sequences of counted strings above,
// domain names are allowed to refer to strings elsewhere in the
// packet, to avoid repeating common suffixes when returning
// many entries in a single domain. The pointers are marked
// by a length byte with the top two bits set. Ignoring those
// two bits, that byte and the next give a 14 bit offset from msg[0]
// where we should pick up the trail.
// Note that if we jump elsewhere in the packet,
// we return off1 == the offset after the first pointer we found,
// which is where the next record will start.
// In theory, the pointers are only allowed to jump backward.
// We let them jump anywhere and stop jumping after a while.
// UnpackDomainName unpacks a domain name into a string. It returns
// the name, the new offset into msg and any error that occurred.
//
// When an error is encountered, the unpacked name will be discarded
// and len(msg) will be returned as the offset.
func UnpackDomainName(msg []byte, off int) (string, int, error) {
s := make([]byte, 0, maxDomainNamePresentationLength)
off1 := 0
lenmsg := len(msg)
budget := maxDomainNameWireOctets
ptr := 0 // number of pointers followed
Loop:
for {
if off >= lenmsg {
return "", lenmsg, ErrBuf
}
c := int(msg[off])
off++
switch c & 0xC0 {
case 0x00:
if c == 0x00 {
// end of name
break Loop
}
// literal string
if off+c > lenmsg {
return "", lenmsg, ErrBuf
}
budget -= c + 1 // +1 for the label separator
if budget <= 0 {
return "", lenmsg, ErrLongDomain
}
for _, b := range msg[off : off+c] {
switch b {
case '.', '(', ')', ';', ' ', '@':
fallthrough
case '"', '\\':
s = append(s, '\\', b)
default:
if b < ' ' || b > '~' { // unprintable, use \DDD
s = append(s, escapeByte(b)...)
} else {
s = append(s, b)
}
}
}
s = append(s, '.')
off += c
case 0xC0:
// pointer to somewhere else in msg.
// remember location after first ptr,
// since that's how many bytes we consumed.
// also, don't follow too many pointers --
// maybe there's a loop.
if off >= lenmsg {
return "", lenmsg, ErrBuf
}
c1 := msg[off]
off++
if ptr == 0 {
off1 = off
}
if ptr++; ptr > maxCompressionPointers {
return "", lenmsg, &Error{err: "too many compression pointers"}
}
// pointer should guarantee that it advances and points forwards at least
// but the condition on previous three lines guarantees that it's
// at least loop-free
off = (c^0xC0)<<8 | int(c1)
default:
// 0x80 and 0x40 are reserved
return "", lenmsg, ErrRdata
}
}
if ptr == 0 {
off1 = off
}
if len(s) == 0 {
return ".", off1, nil
}
return string(s), off1, nil
}
func packTxt(txt []string, msg []byte, offset int, tmp []byte) (int, error) {
if len(txt) == 0 {
if offset >= len(msg) {
return offset, ErrBuf
}
msg[offset] = 0
return offset, nil
}
var err error
for _, s := range txt {
if len(s) > len(tmp) {
return offset, ErrBuf
}
offset, err = packTxtString(s, msg, offset, tmp)
if err != nil {
return offset, err
}
}
return offset, nil
}
func packTxtString(s string, msg []byte, offset int, tmp []byte) (int, error) {
lenByteOffset := offset
if offset >= len(msg) || len(s) > len(tmp) {
return offset, ErrBuf
}
offset++
bs := tmp[:len(s)]
copy(bs, s)
for i := 0; i < len(bs); i++ {
if len(msg) <= offset {
return offset, ErrBuf
}
if bs[i] == '\\' {
i++
if i == len(bs) {
break
}
// check for \DDD
if i+2 < len(bs) && isDigit(bs[i]) && isDigit(bs[i+1]) && isDigit(bs[i+2]) {
msg[offset] = dddToByte(bs[i:])
i += 2
} else {
msg[offset] = bs[i]
}
} else {
msg[offset] = bs[i]
}
offset++
}
l := offset - lenByteOffset - 1
if l > 255 {
return offset, &Error{err: "string exceeded 255 bytes in txt"}
}
msg[lenByteOffset] = byte(l)
return offset, nil
}
func packOctetString(s string, msg []byte, offset int, tmp []byte) (int, error) {
if offset >= len(msg) || len(s) > len(tmp) {
return offset, ErrBuf
}
bs := tmp[:len(s)]
copy(bs, s)
for i := 0; i < len(bs); i++ {
if len(msg) <= offset {
return offset, ErrBuf
}
if bs[i] == '\\' {
i++
if i == len(bs) {
break
}
// check for \DDD
if i+2 < len(bs) && isDigit(bs[i]) && isDigit(bs[i+1]) && isDigit(bs[i+2]) {
msg[offset] = dddToByte(bs[i:])
i += 2
} else {
msg[offset] = bs[i]
}
} else {
msg[offset] = bs[i]
}
offset++
}
return offset, nil
}
func unpackTxt(msg []byte, off0 int) (ss []string, off int, err error) {
off = off0
var s string
for off < len(msg) && err == nil {
s, off, err = unpackString(msg, off)
if err == nil {
ss = append(ss, s)
}
}
return
}
// Helpers for dealing with escaped bytes
func isDigit(b byte) bool { return b >= '0' && b <= '9' }
func dddToByte(s []byte) byte {
_ = s[2] // bounds check hint to compiler; see golang.org/issue/14808
return byte((s[0]-'0')*100 + (s[1]-'0')*10 + (s[2] - '0'))
}
func dddStringToByte(s string) byte {
_ = s[2] // bounds check hint to compiler; see golang.org/issue/14808
return byte((s[0]-'0')*100 + (s[1]-'0')*10 + (s[2] - '0'))
}
// Helper function for packing and unpacking
func intToBytes(i *big.Int, length int) []byte {
buf := i.Bytes()
if len(buf) < length {
b := make([]byte, length)
copy(b[length-len(buf):], buf)
return b
}
return buf
}
// PackRR packs a resource record rr into msg[off:].
// See PackDomainName for documentation about the compression.
func PackRR(rr RR, msg []byte, off int, compression map[string]int, compress bool) (off1 int, err error) {
headerEnd, off1, err := packRR(rr, msg, off, compressionMap{ext: compression}, compress)
if err == nil {
// packRR no longer sets the Rdlength field on the rr, but
// callers might be expecting it so we set it here.
rr.Header().Rdlength = uint16(off1 - headerEnd)
}
return off1, err
}
func packRR(rr RR, msg []byte, off int, compression compressionMap, compress bool) (headerEnd int, off1 int, err error) {
if rr == nil {
return len(msg), len(msg), &Error{err: "nil rr"}
}
headerEnd, err = rr.Header().packHeader(msg, off, compression, compress)
if err != nil {
return headerEnd, len(msg), err
}
off1, err = rr.pack(msg, headerEnd, compression, compress)
if err != nil {
return headerEnd, len(msg), err
}
rdlength := off1 - headerEnd
if int(uint16(rdlength)) != rdlength { // overflow
return headerEnd, len(msg), ErrRdata
}
// The RDLENGTH field is the last field in the header and we set it here.
binary.BigEndian.PutUint16(msg[headerEnd-2:], uint16(rdlength))
return headerEnd, off1, nil
}
// UnpackRR unpacks msg[off:] into an RR.
func UnpackRR(msg []byte, off int) (rr RR, off1 int, err error) {
h, off, msg, err := unpackHeader(msg, off)
if err != nil {
return nil, len(msg), err
}
return UnpackRRWithHeader(h, msg, off)
}
// UnpackRRWithHeader unpacks the record type specific payload given an existing
// RR_Header.
func UnpackRRWithHeader(h RR_Header, msg []byte, off int) (rr RR, off1 int, err error) {
if newFn, ok := TypeToRR[h.Rrtype]; ok {
rr = newFn()
*rr.Header() = h
} else {
rr = &RFC3597{Hdr: h}
}
if noRdata(h) {
return rr, off, nil
}
end := off + int(h.Rdlength)
off, err = rr.unpack(msg, off)
if err != nil {
return nil, end, err
}
if off != end {
return &h, end, &Error{err: "bad rdlength"}
}
return rr, off, nil
}
// unpackRRslice unpacks msg[off:] into an []RR.
// If we cannot unpack the whole array, then it will return nil
func unpackRRslice(l int, msg []byte, off int) (dst1 []RR, off1 int, err error) {
var r RR
// Don't pre-allocate, l may be under attacker control
var dst []RR
for i := 0; i < l; i++ {
off1 := off
r, off, err = UnpackRR(msg, off)
if err != nil {
off = len(msg)
break
}
// If offset does not increase anymore, l is a lie
if off1 == off {
l = i
break
}
dst = append(dst, r)
}
if err != nil && off == len(msg) {
dst = nil
}
return dst, off, err
}
// Convert a MsgHdr to a string, with dig-like headers:
//
//;; opcode: QUERY, status: NOERROR, id: 48404
//
//;; flags: qr aa rd ra;
func (h *MsgHdr) String() string {
if h == nil {
return "<nil> MsgHdr"
}
s := ";; opcode: " + OpcodeToString[h.Opcode]
s += ", status: " + RcodeToString[h.Rcode]
s += ", id: " + strconv.Itoa(int(h.Id)) + "\n"
s += ";; flags:"
if h.Response {
s += " qr"
}
if h.Authoritative {
s += " aa"
}
if h.Truncated {
s += " tc"
}
if h.RecursionDesired {
s += " rd"
}
if h.RecursionAvailable {
s += " ra"
}
if h.Zero { // Hmm
s += " z"
}
if h.AuthenticatedData {
s += " ad"
}
if h.CheckingDisabled {
s += " cd"
}
s += ";"
return s
}
// Pack packs a Msg: it is converted to to wire format.
// If the dns.Compress is true the message will be in compressed wire format.
func (dns *Msg) Pack() (msg []byte, err error) {
return dns.PackBuffer(nil)
}
// PackBuffer packs a Msg, using the given buffer buf. If buf is too small a new buffer is allocated.
func (dns *Msg) PackBuffer(buf []byte) (msg []byte, err error) {
// If this message can't be compressed, avoid filling the
// compression map and creating garbage.
if dns.Compress && dns.isCompressible() {
compression := make(map[string]uint16) // Compression pointer mappings.
return dns.packBufferWithCompressionMap(buf, compressionMap{int: compression}, true)
}
return dns.packBufferWithCompressionMap(buf, compressionMap{}, false)
}
// packBufferWithCompressionMap packs a Msg, using the given buffer buf.
func (dns *Msg) packBufferWithCompressionMap(buf []byte, compression compressionMap, compress bool) (msg []byte, err error) {
if dns.Rcode < 0 || dns.Rcode > 0xFFF {
return nil, ErrRcode
}
// Set extended rcode unconditionally if we have an opt, this will allow
// reseting the extended rcode bits if they need to.
if opt := dns.IsEdns0(); opt != nil {
opt.SetExtendedRcode(uint16(dns.Rcode))
} else if dns.Rcode > 0xF {
// If Rcode is an extended one and opt is nil, error out.
return nil, ErrExtendedRcode
}
// Convert convenient Msg into wire-like Header.
var dh Header
dh.Id = dns.Id
dh.Bits = uint16(dns.Opcode)<<11 | uint16(dns.Rcode&0xF)
if dns.Response {
dh.Bits |= _QR
}
if dns.Authoritative {
dh.Bits |= _AA
}
if dns.Truncated {
dh.Bits |= _TC
}
if dns.RecursionDesired {
dh.Bits |= _RD
}
if dns.RecursionAvailable {
dh.Bits |= _RA
}
if dns.Zero {
dh.Bits |= _Z
}
if dns.AuthenticatedData {
dh.Bits |= _AD
}
if dns.CheckingDisabled {
dh.Bits |= _CD
}
dh.Qdcount = uint16(len(dns.Question))
dh.Ancount = uint16(len(dns.Answer))
dh.Nscount = uint16(len(dns.Ns))
dh.Arcount = uint16(len(dns.Extra))
// We need the uncompressed length here, because we first pack it and then compress it.
msg = buf
uncompressedLen := msgLenWithCompressionMap(dns, nil)
if packLen := uncompressedLen + 1; len(msg) < packLen {
msg = make([]byte, packLen)
}
// Pack it in: header and then the pieces.
off := 0
off, err = dh.pack(msg, off, compression, compress)
if err != nil {
return nil, err
}
for _, r := range dns.Question {
off, err = r.pack(msg, off, compression, compress)
if err != nil {
return nil, err
}
}
for _, r := range dns.Answer {
_, off, err = packRR(r, msg, off, compression, compress)
if err != nil {
return nil, err
}
}
for _, r := range dns.Ns {
_, off, err = packRR(r, msg, off, compression, compress)
if err != nil {
return nil, err
}
}
for _, r := range dns.Extra {
_, off, err = packRR(r, msg, off, compression, compress)
if err != nil {
return nil, err
}
}
return msg[:off], nil
}
func (dns *Msg) unpack(dh Header, msg []byte, off int) (err error) {
// If we are at the end of the message we should return *just* the
// header. This can still be useful to the caller. 9.9.9.9 sends these
// when responding with REFUSED for instance.
if off == len(msg) {
// reset sections before returning
dns.Question, dns.Answer, dns.Ns, dns.Extra = nil, nil, nil, nil
return nil
}
// Qdcount, Ancount, Nscount, Arcount can't be trusted, as they are
// attacker controlled. This means we can't use them to pre-allocate
// slices.
dns.Question = nil
for i := 0; i < int(dh.Qdcount); i++ {
off1 := off
var q Question
q, off, err = unpackQuestion(msg, off)
if err != nil {
return err
}
if off1 == off { // Offset does not increase anymore, dh.Qdcount is a lie!
dh.Qdcount = uint16(i)
break
}
dns.Question = append(dns.Question, q)
}
dns.Answer, off, err = unpackRRslice(int(dh.Ancount), msg, off)
// The header counts might have been wrong so we need to update it
dh.Ancount = uint16(len(dns.Answer))
if err == nil {
dns.Ns, off, err = unpackRRslice(int(dh.Nscount), msg, off)
}
// The header counts might have been wrong so we need to update it
dh.Nscount = uint16(len(dns.Ns))
if err == nil {
dns.Extra, off, err = unpackRRslice(int(dh.Arcount), msg, off)
}
// The header counts might have been wrong so we need to update it
dh.Arcount = uint16(len(dns.Extra))
// Set extended Rcode
if opt := dns.IsEdns0(); opt != nil {
dns.Rcode |= opt.ExtendedRcode()
}
if off != len(msg) {
// TODO(miek) make this an error?
// use PackOpt to let people tell how detailed the error reporting should be?
// println("dns: extra bytes in dns packet", off, "<", len(msg))
}
return err
}
// Unpack unpacks a binary message to a Msg structure.
func (dns *Msg) Unpack(msg []byte) (err error) {
dh, off, err := unpackMsgHdr(msg, 0)
if err != nil {
return err
}
dns.setHdr(dh)
return dns.unpack(dh, msg, off)
}
// Convert a complete message to a string with dig-like output.
func (dns *Msg) String() string {
if dns == nil {
return "<nil> MsgHdr"
}
s := dns.MsgHdr.String() + " "
s += "QUERY: " + strconv.Itoa(len(dns.Question)) + ", "
s += "ANSWER: " + strconv.Itoa(len(dns.Answer)) + ", "
s += "AUTHORITY: " + strconv.Itoa(len(dns.Ns)) + ", "
s += "ADDITIONAL: " + strconv.Itoa(len(dns.Extra)) + "\n"
if len(dns.Question) > 0 {
s += "\n;; QUESTION SECTION:\n"
for _, r := range dns.Question {
s += r.String() + "\n"
}
}
if len(dns.Answer) > 0 {
s += "\n;; ANSWER SECTION:\n"
for _, r := range dns.Answer {
if r != nil {
s += r.String() + "\n"
}
}
}
if len(dns.Ns) > 0 {
s += "\n;; AUTHORITY SECTION:\n"
for _, r := range dns.Ns {
if r != nil {
s += r.String() + "\n"
}
}
}
if len(dns.Extra) > 0 {
s += "\n;; ADDITIONAL SECTION:\n"
for _, r := range dns.Extra {
if r != nil {
s += r.String() + "\n"
}
}
}
return s
}
// isCompressible returns whether the msg may be compressible.
func (dns *Msg) isCompressible() bool {
// If we only have one question, there is nothing we can ever compress.
return len(dns.Question) > 1 || len(dns.Answer) > 0 ||
len(dns.Ns) > 0 || len(dns.Extra) > 0
}
// Len returns the message length when in (un)compressed wire format.
// If dns.Compress is true compression it is taken into account. Len()
// is provided to be a faster way to get the size of the resulting packet,
// than packing it, measuring the size and discarding the buffer.
func (dns *Msg) Len() int {
// If this message can't be compressed, avoid filling the
// compression map and creating garbage.
if dns.Compress && dns.isCompressible() {
compression := make(map[string]struct{})
return msgLenWithCompressionMap(dns, compression)
}
return msgLenWithCompressionMap(dns, nil)
}
func msgLenWithCompressionMap(dns *Msg, compression map[string]struct{}) int {
l := headerSize
for _, r := range dns.Question {
l += r.len(l, compression)
}
for _, r := range dns.Answer {
if r != nil {
l += r.len(l, compression)
}
}
for _, r := range dns.Ns {
if r != nil {
l += r.len(l, compression)
}
}
for _, r := range dns.Extra {
if r != nil {
l += r.len(l, compression)
}
}
return l
}
func domainNameLen(s string, off int, compression map[string]struct{}, compress bool) int {
if s == "" || s == "." {
return 1
}
escaped := strings.Contains(s, "\\")
if compression != nil && (compress || off < maxCompressionOffset) {
// compressionLenSearch will insert the entry into the compression
// map if it doesn't contain it.
if l, ok := compressionLenSearch(compression, s, off); ok && compress {
if escaped {
return escapedNameLen(s[:l]) + 2
}
return l + 2
}
}
if escaped {
return escapedNameLen(s) + 1
}
return len(s) + 1
}
func escapedNameLen(s string) int {
nameLen := len(s)
for i := 0; i < len(s); i++ {
if s[i] != '\\' {
continue
}
if i+3 < len(s) && isDigit(s[i+1]) && isDigit(s[i+2]) && isDigit(s[i+3]) {
nameLen -= 3
i += 3
} else {
nameLen--
i++
}
}
return nameLen
}
func compressionLenSearch(c map[string]struct{}, s string, msgOff int) (int, bool) {
for off, end := 0, false; !end; off, end = NextLabel(s, off) {
if _, ok := c[s[off:]]; ok {
return off, true
}
if msgOff+off < maxCompressionOffset {
c[s[off:]] = struct{}{}
}
}
return 0, false
}
// Copy returns a new RR which is a deep-copy of r.
func Copy(r RR) RR { return r.copy() }
// Len returns the length (in octets) of the uncompressed RR in wire format.
func Len(r RR) int { return r.len(0, nil) }
// Copy returns a new *Msg which is a deep-copy of dns.
func (dns *Msg) Copy() *Msg { return dns.CopyTo(new(Msg)) }
// CopyTo copies the contents to the provided message using a deep-copy and returns the copy.
func (dns *Msg) CopyTo(r1 *Msg) *Msg {
r1.MsgHdr = dns.MsgHdr
r1.Compress = dns.Compress
if len(dns.Question) > 0 {
r1.Question = make([]Question, len(dns.Question))
copy(r1.Question, dns.Question) // TODO(miek): Question is an immutable value, ok to do a shallow-copy
}
rrArr := make([]RR, len(dns.Answer)+len(dns.Ns)+len(dns.Extra))
r1.Answer, rrArr = rrArr[:0:len(dns.Answer)], rrArr[len(dns.Answer):]
r1.Ns, rrArr = rrArr[:0:len(dns.Ns)], rrArr[len(dns.Ns):]
r1.Extra = rrArr[:0:len(dns.Extra)]
for _, r := range dns.Answer {
r1.Answer = append(r1.Answer, r.copy())
}
for _, r := range dns.Ns {
r1.Ns = append(r1.Ns, r.copy())
}
for _, r := range dns.Extra {
r1.Extra = append(r1.Extra, r.copy())
}
return r1
}
func (q *Question) pack(msg []byte, off int, compression compressionMap, compress bool) (int, error) {
off, err := packDomainName(q.Name, msg, off, compression, compress)
if err != nil {
return off, err
}
off, err = packUint16(q.Qtype, msg, off)
if err != nil {
return off, err
}
off, err = packUint16(q.Qclass, msg, off)
if err != nil {
return off, err
}
return off, nil
}
func unpackQuestion(msg []byte, off int) (Question, int, error) {
var (
q Question
err error
)
q.Name, off, err = UnpackDomainName(msg, off)
if err != nil {
return q, off, err
}
if off == len(msg) {
return q, off, nil
}
q.Qtype, off, err = unpackUint16(msg, off)
if err != nil {
return q, off, err
}
if off == len(msg) {
return q, off, nil
}
q.Qclass, off, err = unpackUint16(msg, off)
if off == len(msg) {
return q, off, nil
}
return q, off, err
}
func (dh *Header) pack(msg []byte, off int, compression compressionMap, compress bool) (int, error) {
off, err := packUint16(dh.Id, msg, off)
if err != nil {
return off, err
}
off, err = packUint16(dh.Bits, msg, off)
if err != nil {
return off, err
}
off, err = packUint16(dh.Qdcount, msg, off)
if err != nil {
return off, err
}
off, err = packUint16(dh.Ancount, msg, off)
if err != nil {
return off, err
}
off, err = packUint16(dh.Nscount, msg, off)
if err != nil {
return off, err
}
off, err = packUint16(dh.Arcount, msg, off)
if err != nil {
return off, err
}
return off, nil
}
func unpackMsgHdr(msg []byte, off int) (Header, int, error) {
var (
dh Header
err error
)
dh.Id, off, err = unpackUint16(msg, off)
if err != nil {
return dh, off, err
}
dh.Bits, off, err = unpackUint16(msg, off)
if err != nil {
return dh, off, err
}
dh.Qdcount, off, err = unpackUint16(msg, off)
if err != nil {
return dh, off, err
}
dh.Ancount, off, err = unpackUint16(msg, off)
if err != nil {
return dh, off, err
}
dh.Nscount, off, err = unpackUint16(msg, off)
if err != nil {
return dh, off, err
}
dh.Arcount, off, err = unpackUint16(msg, off)
if err != nil {
return dh, off, err
}
return dh, off, nil
}
// setHdr set the header in the dns using the binary data in dh.
func (dns *Msg) setHdr(dh Header) {
dns.Id = dh.Id
dns.Response = dh.Bits&_QR != 0
dns.Opcode = int(dh.Bits>>11) & 0xF
dns.Authoritative = dh.Bits&_AA != 0
dns.Truncated = dh.Bits&_TC != 0
dns.RecursionDesired = dh.Bits&_RD != 0
dns.RecursionAvailable = dh.Bits&_RA != 0
dns.Zero = dh.Bits&_Z != 0 // _Z covers the zero bit, which should be zero; not sure why we set it to the opposite.
dns.AuthenticatedData = dh.Bits&_AD != 0
dns.CheckingDisabled = dh.Bits&_CD != 0
dns.Rcode = int(dh.Bits & 0xF)
}
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