| // 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 |
| //go:generate go run compress_generate.go |
| |
| import ( |
| crand "crypto/rand" |
| "encoding/binary" |
| "fmt" |
| "math/big" |
| "math/rand" |
| "strconv" |
| "sync" |
| ) |
| |
| const ( |
| maxCompressionOffset = 2 << 13 // We have 14 bits for the compression pointer |
| maxDomainNameWireOctets = 255 // See RFC 1035 section 2.3.4 |
| ) |
| |
| // 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. |
| ErrTruncated error = &Error{err: "failed to unpack truncated message"} // ErrTruncated indicates that we failed to unpack a truncated message. We unpacked as much as we had so Msg can still be used, if desired. |
| ) |
| |
| // 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: "NOTIMPL", |
| 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", |
| } |
| |
| // 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) { |
| off1, _, err = packDomainName(s, msg, off, compression, compress) |
| return |
| } |
| |
| func packDomainName(s string, msg []byte, off int, compression map[string]int, compress bool) (off1 int, labels int, err error) { |
| // special case if msg == nil |
| lenmsg := 256 |
| if msg != nil { |
| lenmsg = len(msg) |
| } |
| ls := len(s) |
| if ls == 0 { // Ok, for instance when dealing with update RR without any rdata. |
| return off, 0, nil |
| } |
| // If not fully qualified, error out, but only if msg == nil #ugly |
| switch { |
| case msg == nil: |
| if s[ls-1] != '.' { |
| s += "." |
| ls++ |
| } |
| case msg != nil: |
| if s[ls-1] != '.' { |
| return lenmsg, 0, 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 |
| nameoffset := -1 |
| pointer := -1 |
| // Emit sequence of counted strings, chopping at dots. |
| begin := 0 |
| bs := []byte(s) |
| roBs, bsFresh, escapedDot := s, true, false |
| for i := 0; i < ls; i++ { |
| if bs[i] == '\\' { |
| for j := i; j < ls-1; j++ { |
| bs[j] = bs[j+1] |
| } |
| ls-- |
| if off+1 > lenmsg { |
| return lenmsg, labels, ErrBuf |
| } |
| // check for \DDD |
| if i+2 < ls && isDigit(bs[i]) && isDigit(bs[i+1]) && isDigit(bs[i+2]) { |
| bs[i] = dddToByte(bs[i:]) |
| for j := i + 1; j < ls-2; j++ { |
| bs[j] = bs[j+2] |
| } |
| ls -= 2 |
| } |
| escapedDot = bs[i] == '.' |
| bsFresh = false |
| continue |
| } |
| |
| if bs[i] == '.' { |
| if i > 0 && bs[i-1] == '.' && !escapedDot { |
| // two dots back to back is not legal |
| return lenmsg, labels, ErrRdata |
| } |
| if i-begin >= 1<<6 { // top two bits of length must be clear |
| return lenmsg, labels, 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 > lenmsg { |
| return lenmsg, labels, ErrBuf |
| } |
| if msg != nil { |
| msg[off] = byte(i - begin) |
| } |
| offset := off |
| off++ |
| for j := begin; j < i; j++ { |
| if off+1 > lenmsg { |
| return lenmsg, labels, ErrBuf |
| } |
| if msg != nil { |
| msg[off] = bs[j] |
| } |
| off++ |
| } |
| if compress && !bsFresh { |
| roBs = string(bs) |
| bsFresh = true |
| } |
| // Don't try to compress '.' |
| // We should only compress when compress it true, but we should also still pick |
| // up names that can be used for *future* compression(s). |
| if compression != nil && roBs[begin:] != "." { |
| if p, ok := compression[roBs[begin:]]; !ok { |
| // Only offsets smaller than this can be used. |
| if offset < maxCompressionOffset { |
| compression[roBs[begin:]] = offset |
| } |
| } else { |
| // 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 pointer == -1 && compress { |
| pointer = p // Where to point to |
| nameoffset = offset // Where to point from |
| break |
| } |
| } |
| } |
| labels++ |
| begin = i + 1 |
| } |
| escapedDot = false |
| } |
| // Root label is special |
| if len(bs) == 1 && bs[0] == '.' { |
| return off, labels, 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 |
| // if msg == nil, we will never do compression |
| binary.BigEndian.PutUint16(msg[nameoffset:], uint16(pointer^0xC000)) |
| off = nameoffset + 1 |
| goto End |
| } |
| if msg != nil && off < len(msg) { |
| msg[off] = 0 |
| } |
| End: |
| off++ |
| return off, labels, nil |
| } |
| |
| // 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. |
| func UnpackDomainName(msg []byte, off int) (string, int, error) { |
| s := make([]byte, 0, 64) |
| off1 := 0 |
| lenmsg := len(msg) |
| maxLen := 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 |
| } |
| for j := off; j < off+c; j++ { |
| switch b := msg[j]; b { |
| case '.', '(', ')', ';', ' ', '@': |
| fallthrough |
| case '"', '\\': |
| s = append(s, '\\', b) |
| // presentation-format \X escapes add an extra byte |
| maxLen++ |
| default: |
| if b < 32 || b >= 127 { // unprintable, use \DDD |
| var buf [3]byte |
| bufs := strconv.AppendInt(buf[:0], int64(b), 10) |
| s = append(s, '\\') |
| for i := 0; i < 3-len(bufs); i++ { |
| s = append(s, '0') |
| } |
| for _, r := range bufs { |
| s = append(s, r) |
| } |
| // presentation-format \DDD escapes add 3 extra bytes |
| maxLen += 3 |
| } 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 > 10 { |
| 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 { |
| s = []byte(".") |
| } else if len(s) >= maxLen { |
| // error if the name is too long, but don't throw it away |
| return string(s), lenmsg, ErrLongDomain |
| } |
| 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 i := range txt { |
| if len(txt[i]) > len(tmp) { |
| return offset, ErrBuf |
| } |
| offset, err = packTxtString(txt[i], 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 = unpackTxtString(msg, off) |
| if err == nil { |
| ss = append(ss, s) |
| } |
| } |
| return |
| } |
| |
| func unpackTxtString(msg []byte, offset int) (string, int, error) { |
| if offset+1 > len(msg) { |
| return "", offset, &Error{err: "overflow unpacking txt"} |
| } |
| l := int(msg[offset]) |
| if offset+l+1 > len(msg) { |
| return "", offset, &Error{err: "overflow unpacking txt"} |
| } |
| s := make([]byte, 0, l) |
| for _, b := range msg[offset+1 : offset+1+l] { |
| switch b { |
| case '"', '\\': |
| s = append(s, '\\', b) |
| default: |
| if b < 32 || b > 127 { // unprintable |
| var buf [3]byte |
| bufs := strconv.AppendInt(buf[:0], int64(b), 10) |
| s = append(s, '\\') |
| for i := 0; i < 3-len(bufs); i++ { |
| s = append(s, '0') |
| } |
| for _, r := range bufs { |
| s = append(s, r) |
| } |
| } else { |
| s = append(s, b) |
| } |
| } |
| } |
| offset += 1 + l |
| return string(s), offset, nil |
| } |
| |
| // Helpers for dealing with escaped bytes |
| func isDigit(b byte) bool { return b >= '0' && b <= '9' } |
| |
| func dddToByte(s []byte) byte { |
| 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) { |
| if rr == nil { |
| return len(msg), &Error{err: "nil rr"} |
| } |
| |
| off1, err = rr.pack(msg, off, compression, compress) |
| if err != nil { |
| return len(msg), err |
| } |
| // TODO(miek): Not sure if this is needed? If removed we can remove rawmsg.go as well. |
| if rawSetRdlength(msg, off, off1) { |
| return off1, nil |
| } |
| return off, ErrRdata |
| } |
| |
| // 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) { |
| end := off + int(h.Rdlength) |
| |
| if fn, known := typeToUnpack[h.Rrtype]; !known { |
| rr, off, err = unpackRFC3597(h, msg, off) |
| } else { |
| rr, off, err = fn(h, msg, off) |
| } |
| if off != end { |
| return &h, end, &Error{err: "bad rdlength"} |
| } |
| return rr, off, err |
| } |
| |
| // 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) { |
| var compression map[string]int |
| if dns.Compress { |
| compression = make(map[string]int) // Compression pointer mappings. |
| } |
| return dns.packBufferWithCompressionMap(buf, compression) |
| } |
| |
| // packBufferWithCompressionMap packs a Msg, using the given buffer buf. |
| func (dns *Msg) packBufferWithCompressionMap(buf []byte, compression map[string]int) (msg []byte, err error) { |
| // We use a similar function in tsig.go's stripTsig. |
| |
| var dh Header |
| |
| if dns.Rcode < 0 || dns.Rcode > 0xFFF { |
| return nil, ErrRcode |
| } |
| if dns.Rcode > 0xF { |
| // Regular RCODE field is 4 bits |
| opt := dns.IsEdns0() |
| if opt == nil { |
| return nil, ErrExtendedRcode |
| } |
| opt.SetExtendedRcode(uint8(dns.Rcode >> 4)) |
| } |
| |
| // Convert convenient Msg into wire-like 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 |
| } |
| |
| // Prepare variable sized arrays. |
| question := dns.Question |
| answer := dns.Answer |
| ns := dns.Ns |
| extra := dns.Extra |
| |
| dh.Qdcount = uint16(len(question)) |
| dh.Ancount = uint16(len(answer)) |
| dh.Nscount = uint16(len(ns)) |
| dh.Arcount = uint16(len(extra)) |
| |
| // We need the uncompressed length here, because we first pack it and then compress it. |
| msg = buf |
| uncompressedLen := compressedLen(dns, false) |
| 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, dns.Compress) |
| if err != nil { |
| return nil, err |
| } |
| for i := 0; i < len(question); i++ { |
| off, err = question[i].pack(msg, off, compression, dns.Compress) |
| if err != nil { |
| return nil, err |
| } |
| } |
| for i := 0; i < len(answer); i++ { |
| off, err = PackRR(answer[i], msg, off, compression, dns.Compress) |
| if err != nil { |
| return nil, err |
| } |
| } |
| for i := 0; i < len(ns); i++ { |
| off, err = PackRR(ns[i], msg, off, compression, dns.Compress) |
| if err != nil { |
| return nil, err |
| } |
| } |
| for i := 0; i < len(extra); i++ { |
| off, err = PackRR(extra[i], msg, off, compression, dns.Compress) |
| if err != nil { |
| return nil, err |
| } |
| } |
| return msg[:off], nil |
| } |
| |
| // Unpack unpacks a binary message to a Msg structure. |
| func (dns *Msg) Unpack(msg []byte) (err error) { |
| var ( |
| dh Header |
| off int |
| ) |
| if dh, off, err = unpackMsgHdr(msg, off); err != nil { |
| return err |
| } |
| |
| 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 |
| dns.AuthenticatedData = (dh.Bits & _AD) != 0 |
| dns.CheckingDisabled = (dh.Bits & _CD) != 0 |
| dns.Rcode = int(dh.Bits & 0xF) |
| |
| // 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 { |
| // Even if Truncated is set, we only will set ErrTruncated if we |
| // actually got the questions |
| 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)) |
| |
| 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)) |
| } else if dns.Truncated { |
| // Whether we ran into a an error or not, we want to return that it |
| // was truncated |
| err = ErrTruncated |
| } |
| return err |
| } |
| |
| // 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 i := 0; i < len(dns.Question); i++ { |
| s += dns.Question[i].String() + "\n" |
| } |
| } |
| if len(dns.Answer) > 0 { |
| s += "\n;; ANSWER SECTION:\n" |
| for i := 0; i < len(dns.Answer); i++ { |
| if dns.Answer[i] != nil { |
| s += dns.Answer[i].String() + "\n" |
| } |
| } |
| } |
| if len(dns.Ns) > 0 { |
| s += "\n;; AUTHORITY SECTION:\n" |
| for i := 0; i < len(dns.Ns); i++ { |
| if dns.Ns[i] != nil { |
| s += dns.Ns[i].String() + "\n" |
| } |
| } |
| } |
| if len(dns.Extra) > 0 { |
| s += "\n;; ADDITIONAL SECTION:\n" |
| for i := 0; i < len(dns.Extra); i++ { |
| if dns.Extra[i] != nil { |
| s += dns.Extra[i].String() + "\n" |
| } |
| } |
| } |
| return s |
| } |
| |
| // 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 { return compressedLen(dns, dns.Compress) } |
| |
| func compressedLenWithCompressionMap(dns *Msg, compression map[string]int) int { |
| l := 12 // Message header is always 12 bytes |
| for _, r := range dns.Question { |
| compressionLenHelper(compression, r.Name, l) |
| l += r.len() |
| } |
| l += compressionLenSlice(l, compression, dns.Answer) |
| l += compressionLenSlice(l, compression, dns.Ns) |
| l += compressionLenSlice(l, compression, dns.Extra) |
| return l |
| } |
| |
| // compressedLen returns the message length when in compressed wire format |
| // when compress is true, otherwise the uncompressed length is returned. |
| func compressedLen(dns *Msg, compress bool) int { |
| // We always return one more than needed. |
| if compress { |
| compression := map[string]int{} |
| return compressedLenWithCompressionMap(dns, compression) |
| } |
| l := 12 // Message header is always 12 bytes |
| |
| for _, r := range dns.Question { |
| l += r.len() |
| } |
| for _, r := range dns.Answer { |
| if r != nil { |
| l += r.len() |
| } |
| } |
| for _, r := range dns.Ns { |
| if r != nil { |
| l += r.len() |
| } |
| } |
| for _, r := range dns.Extra { |
| if r != nil { |
| l += r.len() |
| } |
| } |
| |
| return l |
| } |
| |
| func compressionLenSlice(lenp int, c map[string]int, rs []RR) int { |
| initLen := lenp |
| for _, r := range rs { |
| if r == nil { |
| continue |
| } |
| // TmpLen is to track len of record at 14bits boudaries |
| tmpLen := lenp |
| |
| x := r.len() |
| // track this length, and the global length in len, while taking compression into account for both. |
| k, ok, _ := compressionLenSearch(c, r.Header().Name) |
| if ok { |
| // Size of x is reduced by k, but we add 1 since k includes the '.' and label descriptor take 2 bytes |
| // so, basically x:= x - k - 1 + 2 |
| x += 1 - k |
| } |
| |
| tmpLen += compressionLenHelper(c, r.Header().Name, tmpLen) |
| k, ok, _ = compressionLenSearchType(c, r) |
| if ok { |
| x += 1 - k |
| } |
| lenp += x |
| tmpLen = lenp |
| tmpLen += compressionLenHelperType(c, r, tmpLen) |
| |
| } |
| return lenp - initLen |
| } |
| |
| // Put the parts of the name in the compression map, return the size in bytes added in payload |
| func compressionLenHelper(c map[string]int, s string, currentLen int) int { |
| if currentLen > maxCompressionOffset { |
| // We won't be able to add any label that could be re-used later anyway |
| return 0 |
| } |
| if _, ok := c[s]; ok { |
| return 0 |
| } |
| initLen := currentLen |
| pref := "" |
| prev := s |
| lbs := Split(s) |
| for j := 0; j < len(lbs); j++ { |
| pref = s[lbs[j]:] |
| currentLen += len(prev) - len(pref) |
| prev = pref |
| if _, ok := c[pref]; !ok { |
| // If first byte label is within the first 14bits, it might be re-used later |
| if currentLen < maxCompressionOffset { |
| c[pref] = currentLen |
| } |
| } else { |
| added := currentLen - initLen |
| if j > 0 { |
| // We added a new PTR |
| added += 2 |
| } |
| return added |
| } |
| } |
| return currentLen - initLen |
| } |
| |
| // Look for each part in the compression map and returns its length, |
| // keep on searching so we get the longest match. |
| // Will return the size of compression found, whether a match has been |
| // found and the size of record if added in payload |
| func compressionLenSearch(c map[string]int, s string) (int, bool, int) { |
| off := 0 |
| end := false |
| if s == "" { // don't bork on bogus data |
| return 0, false, 0 |
| } |
| fullSize := 0 |
| for { |
| if _, ok := c[s[off:]]; ok { |
| return len(s[off:]), true, fullSize + off |
| } |
| if end { |
| break |
| } |
| // Each label descriptor takes 2 bytes, add it |
| fullSize += 2 |
| off, end = NextLabel(s, off) |
| } |
| return 0, false, fullSize + len(s) |
| } |
| |
| // Copy returns a new RR which is a deep-copy of r. |
| func Copy(r RR) RR { r1 := r.copy(); return r1 } |
| |
| // Len returns the length (in octets) of the uncompressed RR in wire format. |
| func Len(r RR) int { return r.len() } |
| |
| // 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)) |
| var rri int |
| |
| if len(dns.Answer) > 0 { |
| rrbegin := rri |
| for i := 0; i < len(dns.Answer); i++ { |
| rrArr[rri] = dns.Answer[i].copy() |
| rri++ |
| } |
| r1.Answer = rrArr[rrbegin:rri:rri] |
| } |
| |
| if len(dns.Ns) > 0 { |
| rrbegin := rri |
| for i := 0; i < len(dns.Ns); i++ { |
| rrArr[rri] = dns.Ns[i].copy() |
| rri++ |
| } |
| r1.Ns = rrArr[rrbegin:rri:rri] |
| } |
| |
| if len(dns.Extra) > 0 { |
| rrbegin := rri |
| for i := 0; i < len(dns.Extra); i++ { |
| rrArr[rri] = dns.Extra[i].copy() |
| rri++ |
| } |
| r1.Extra = rrArr[rrbegin:rri:rri] |
| } |
| |
| return r1 |
| } |
| |
| func (q *Question) pack(msg []byte, off int, compression map[string]int, 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 map[string]int, 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) |
| return off, err |
| } |
| |
| 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) |
| return dh, off, err |
| } |