/
dnsutils.go
510 lines (482 loc) · 12.2 KB
/
dnsutils.go
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package main
import (
"encoding/binary"
"errors"
"net"
"strings"
"time"
"unicode/utf8"
"github.com/jedisct1/dlog"
"github.com/miekg/dns"
)
func EmptyResponseFromMessage(srcMsg *dns.Msg) *dns.Msg {
dstMsg := dns.Msg{MsgHdr: srcMsg.MsgHdr, Compress: true}
dstMsg.Question = srcMsg.Question
dstMsg.Response = true
if srcMsg.RecursionDesired {
dstMsg.RecursionAvailable = true
}
dstMsg.RecursionDesired = false
dstMsg.CheckingDisabled = false
dstMsg.AuthenticatedData = false
if edns0 := srcMsg.IsEdns0(); edns0 != nil {
dstMsg.SetEdns0(edns0.UDPSize(), edns0.Do())
}
return &dstMsg
}
func TruncatedResponse(packet []byte) ([]byte, error) {
srcMsg := dns.Msg{}
if err := srcMsg.Unpack(packet); err != nil {
return nil, err
}
dstMsg := EmptyResponseFromMessage(&srcMsg)
dstMsg.Truncated = true
return dstMsg.Pack()
}
func RefusedResponseFromMessage(srcMsg *dns.Msg, refusedCode bool, ipv4 net.IP, ipv6 net.IP, ttl uint32) *dns.Msg {
dstMsg := EmptyResponseFromMessage(srcMsg)
ede := new(dns.EDNS0_EDE)
if edns0 := dstMsg.IsEdns0(); edns0 != nil {
edns0.Option = append(edns0.Option, ede)
}
ede.InfoCode = dns.ExtendedErrorCodeFiltered
if refusedCode {
dstMsg.Rcode = dns.RcodeRefused
} else {
dstMsg.Rcode = dns.RcodeSuccess
questions := srcMsg.Question
if len(questions) == 0 {
return dstMsg
}
question := questions[0]
sendHInfoResponse := true
if ipv4 != nil && question.Qtype == dns.TypeA {
rr := new(dns.A)
rr.Hdr = dns.RR_Header{Name: question.Name, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: ttl}
rr.A = ipv4.To4()
if rr.A != nil {
dstMsg.Answer = []dns.RR{rr}
sendHInfoResponse = false
ede.InfoCode = dns.ExtendedErrorCodeForgedAnswer
}
} else if ipv6 != nil && question.Qtype == dns.TypeAAAA {
rr := new(dns.AAAA)
rr.Hdr = dns.RR_Header{Name: question.Name, Rrtype: dns.TypeAAAA, Class: dns.ClassINET, Ttl: ttl}
rr.AAAA = ipv6.To16()
if rr.AAAA != nil {
dstMsg.Answer = []dns.RR{rr}
sendHInfoResponse = false
ede.InfoCode = dns.ExtendedErrorCodeForgedAnswer
}
}
if sendHInfoResponse {
hinfo := new(dns.HINFO)
hinfo.Hdr = dns.RR_Header{
Name: question.Name, Rrtype: dns.TypeHINFO,
Class: dns.ClassINET, Ttl: ttl,
}
hinfo.Cpu = "This query has been locally blocked"
hinfo.Os = "by dnscrypt-proxy"
dstMsg.Answer = []dns.RR{hinfo}
} else {
ede.ExtraText = "This query has been locally blocked by dnscrypt-proxy"
}
}
return dstMsg
}
func HasTCFlag(packet []byte) bool {
return packet[2]&2 == 2
}
func TransactionID(packet []byte) uint16 {
return binary.BigEndian.Uint16(packet[0:2])
}
func SetTransactionID(packet []byte, tid uint16) {
binary.BigEndian.PutUint16(packet[0:2], tid)
}
func Rcode(packet []byte) uint8 {
return packet[3] & 0xf
}
func NormalizeRawQName(name *[]byte) {
for i, c := range *name {
if c >= 65 && c <= 90 {
(*name)[i] = c + 32
}
}
}
func NormalizeQName(str string) (string, error) {
if len(str) == 0 || str == "." {
return ".", nil
}
hasUpper := false
str = strings.TrimSuffix(str, ".")
strLen := len(str)
for i := 0; i < strLen; i++ {
c := str[i]
if c >= utf8.RuneSelf {
return str, errors.New("Query name is not an ASCII string")
}
hasUpper = hasUpper || ('A' <= c && c <= 'Z')
}
if !hasUpper {
return str, nil
}
var b strings.Builder
b.Grow(len(str))
for i := 0; i < strLen; i++ {
c := str[i]
if 'A' <= c && c <= 'Z' {
c += 'a' - 'A'
}
b.WriteByte(c)
}
return b.String(), nil
}
func getMinTTL(msg *dns.Msg, minTTL uint32, maxTTL uint32, cacheNegMinTTL uint32, cacheNegMaxTTL uint32) time.Duration {
if (msg.Rcode != dns.RcodeSuccess && msg.Rcode != dns.RcodeNameError) ||
(len(msg.Answer) <= 0 && len(msg.Ns) <= 0) {
return time.Duration(cacheNegMinTTL) * time.Second
}
var ttl uint32
if msg.Rcode == dns.RcodeSuccess {
ttl = uint32(maxTTL)
} else {
ttl = uint32(cacheNegMaxTTL)
}
if len(msg.Answer) > 0 {
for _, rr := range msg.Answer {
if rr.Header().Ttl < ttl {
ttl = rr.Header().Ttl
}
}
} else {
for _, rr := range msg.Ns {
if rr.Header().Ttl < ttl {
ttl = rr.Header().Ttl
}
}
}
if msg.Rcode == dns.RcodeSuccess {
if ttl < minTTL {
ttl = minTTL
}
} else {
if ttl < cacheNegMinTTL {
ttl = cacheNegMinTTL
}
}
return time.Duration(ttl) * time.Second
}
func setMaxTTL(msg *dns.Msg, ttl uint32) {
for _, rr := range msg.Answer {
if ttl < rr.Header().Ttl {
rr.Header().Ttl = ttl
}
}
for _, rr := range msg.Ns {
if ttl < rr.Header().Ttl {
rr.Header().Ttl = ttl
}
}
for _, rr := range msg.Extra {
header := rr.Header()
if header.Rrtype == dns.TypeOPT {
continue
}
if ttl < rr.Header().Ttl {
rr.Header().Ttl = ttl
}
}
}
func updateTTL(msg *dns.Msg, expiration time.Time) {
until := time.Until(expiration)
ttl := uint32(0)
if until > 0 {
ttl = uint32(until / time.Second)
if until-time.Duration(ttl)*time.Second >= time.Second/2 {
ttl += 1
}
}
for _, rr := range msg.Answer {
rr.Header().Ttl = ttl
}
for _, rr := range msg.Ns {
rr.Header().Ttl = ttl
}
for _, rr := range msg.Extra {
if rr.Header().Rrtype != dns.TypeOPT {
rr.Header().Ttl = ttl
}
}
}
func hasEDNS0Padding(packet []byte) (bool, error) {
msg := dns.Msg{}
if err := msg.Unpack(packet); err != nil {
return false, err
}
if edns0 := msg.IsEdns0(); edns0 != nil {
for _, option := range edns0.Option {
if option.Option() == dns.EDNS0PADDING {
return true, nil
}
}
}
return false, nil
}
func addEDNS0PaddingIfNoneFound(msg *dns.Msg, unpaddedPacket []byte, paddingLen int) ([]byte, error) {
edns0 := msg.IsEdns0()
if edns0 == nil {
msg.SetEdns0(uint16(MaxDNSPacketSize), false)
edns0 = msg.IsEdns0()
if edns0 == nil {
return unpaddedPacket, nil
}
}
for _, option := range edns0.Option {
if option.Option() == dns.EDNS0PADDING {
return unpaddedPacket, nil
}
}
ext := new(dns.EDNS0_PADDING)
padding := make([]byte, paddingLen)
for i := range padding {
padding[i] = 'X'
}
ext.Padding = padding[:paddingLen]
edns0.Option = append(edns0.Option, ext)
return msg.Pack()
}
func removeEDNS0Options(msg *dns.Msg) bool {
edns0 := msg.IsEdns0()
if edns0 == nil {
return false
}
edns0.Option = []dns.EDNS0{}
return true
}
func dddToByte(s []byte) byte {
return byte((s[0]-'0')*100 + (s[1]-'0')*10 + (s[2] - '0'))
}
func PackTXTRR(s string) []byte {
bs := make([]byte, len(s))
msg := make([]byte, 0)
copy(bs, s)
for i := 0; i < len(bs); i++ {
if bs[i] == '\\' {
i++
if i == len(bs) {
break
}
if i+2 < len(bs) && isDigit(bs[i]) && isDigit(bs[i+1]) && isDigit(bs[i+2]) {
msg = append(msg, dddToByte(bs[i:]))
i += 2
} else if bs[i] == 't' {
msg = append(msg, '\t')
} else if bs[i] == 'r' {
msg = append(msg, '\r')
} else if bs[i] == 'n' {
msg = append(msg, '\n')
} else {
msg = append(msg, bs[i])
}
} else {
msg = append(msg, bs[i])
}
}
return msg
}
type DNSExchangeResponse struct {
response *dns.Msg
rtt time.Duration
priority int
fragmentsBlocked bool
err error
}
func DNSExchange(
proxy *Proxy,
proto string,
query *dns.Msg,
serverAddress string,
relay *DNSCryptRelay,
serverName *string,
tryFragmentsSupport bool,
) (*dns.Msg, time.Duration, bool, error) {
for {
cancelChannel := make(chan struct{})
maxTries := 3
channel := make(chan DNSExchangeResponse, 2*maxTries)
var err error
options := 0
for tries := 0; tries < maxTries; tries++ {
if tryFragmentsSupport {
queryCopy := query.Copy()
queryCopy.Id += uint16(options)
go func(query *dns.Msg, delay time.Duration) {
time.Sleep(delay)
option := DNSExchangeResponse{err: errors.New("Canceled")}
select {
case <-cancelChannel:
default:
option = _dnsExchange(proxy, proto, query, serverAddress, relay, 1500)
}
option.fragmentsBlocked = false
option.priority = 0
channel <- option
}(queryCopy, time.Duration(200*tries)*time.Millisecond)
options++
}
queryCopy := query.Copy()
queryCopy.Id += uint16(options)
go func(query *dns.Msg, delay time.Duration) {
time.Sleep(delay)
option := DNSExchangeResponse{err: errors.New("Canceled")}
select {
case <-cancelChannel:
default:
option = _dnsExchange(proxy, proto, query, serverAddress, relay, 480)
}
option.fragmentsBlocked = true
option.priority = 1
channel <- option
}(queryCopy, time.Duration(250*tries)*time.Millisecond)
options++
}
var bestOption *DNSExchangeResponse
for i := 0; i < options; i++ {
if dnsExchangeResponse := <-channel; dnsExchangeResponse.err == nil {
if bestOption == nil || dnsExchangeResponse.priority < bestOption.priority ||
(dnsExchangeResponse.priority == bestOption.priority && dnsExchangeResponse.rtt < bestOption.rtt) {
bestOption = &dnsExchangeResponse
if bestOption.priority == 0 {
close(cancelChannel)
break
}
}
} else {
err = dnsExchangeResponse.err
}
}
if bestOption != nil {
if bestOption.fragmentsBlocked {
dlog.Debugf("[%v] public key retrieval succeeded but server is blocking fragments", *serverName)
} else {
dlog.Debugf("[%v] public key retrieval succeeded", *serverName)
}
return bestOption.response, bestOption.rtt, bestOption.fragmentsBlocked, nil
}
if relay == nil || !proxy.anonDirectCertFallback {
if err == nil {
err = errors.New("Unable to reach the server")
}
return nil, 0, false, err
}
dlog.Infof(
"Unable to get the public key for [%v] via relay [%v], retrying over a direct connection",
*serverName,
relay.RelayUDPAddr.IP,
)
relay = nil
}
}
func _dnsExchange(
proxy *Proxy,
proto string,
query *dns.Msg,
serverAddress string,
relay *DNSCryptRelay,
paddedLen int,
) DNSExchangeResponse {
var packet []byte
var rtt time.Duration
if proto == "udp" {
qNameLen, padding := len(query.Question[0].Name), 0
if qNameLen < paddedLen {
padding = paddedLen - qNameLen
}
if padding > 0 {
opt := new(dns.OPT)
opt.Hdr.Name = "."
ext := new(dns.EDNS0_PADDING)
ext.Padding = make([]byte, padding)
opt.Option = append(opt.Option, ext)
query.Extra = []dns.RR{opt}
}
binQuery, err := query.Pack()
if err != nil {
return DNSExchangeResponse{err: err}
}
udpAddr, err := net.ResolveUDPAddr("udp", serverAddress)
if err != nil {
return DNSExchangeResponse{err: err}
}
upstreamAddr := udpAddr
if relay != nil {
proxy.prepareForRelay(udpAddr.IP, udpAddr.Port, &binQuery)
upstreamAddr = relay.RelayUDPAddr
}
now := time.Now()
pc, err := net.DialUDP("udp", nil, upstreamAddr)
if err != nil {
return DNSExchangeResponse{err: err}
}
defer pc.Close()
if err := pc.SetDeadline(time.Now().Add(proxy.timeout)); err != nil {
return DNSExchangeResponse{err: err}
}
if _, err := pc.Write(binQuery); err != nil {
return DNSExchangeResponse{err: err}
}
packet = make([]byte, MaxDNSPacketSize)
length, err := pc.Read(packet)
if err != nil {
return DNSExchangeResponse{err: err}
}
rtt = time.Since(now)
packet = packet[:length]
} else {
binQuery, err := query.Pack()
if err != nil {
return DNSExchangeResponse{err: err}
}
tcpAddr, err := net.ResolveTCPAddr("tcp", serverAddress)
if err != nil {
return DNSExchangeResponse{err: err}
}
upstreamAddr := tcpAddr
if relay != nil {
proxy.prepareForRelay(tcpAddr.IP, tcpAddr.Port, &binQuery)
upstreamAddr = relay.RelayTCPAddr
}
now := time.Now()
var pc net.Conn
proxyDialer := proxy.xTransport.proxyDialer
if proxyDialer == nil {
pc, err = net.DialTCP("tcp", nil, upstreamAddr)
} else {
pc, err = (*proxyDialer).Dial("tcp", tcpAddr.String())
}
if err != nil {
return DNSExchangeResponse{err: err}
}
defer pc.Close()
if err := pc.SetDeadline(time.Now().Add(proxy.timeout)); err != nil {
return DNSExchangeResponse{err: err}
}
binQuery, err = PrefixWithSize(binQuery)
if err != nil {
return DNSExchangeResponse{err: err}
}
if _, err := pc.Write(binQuery); err != nil {
return DNSExchangeResponse{err: err}
}
packet, err = ReadPrefixed(&pc)
if err != nil {
return DNSExchangeResponse{err: err}
}
rtt = time.Since(now)
}
msg := dns.Msg{}
if err := msg.Unpack(packet); err != nil {
return DNSExchangeResponse{err: err}
}
return DNSExchangeResponse{response: &msg, rtt: rtt, err: nil}
}