govpn.go

   1 /*
   2 govpn -- high-performance secure virtual private network daemon
   3 Copyright (C) 2014 Sergey Matveev <stargrave@stargrave.org>
   4
   5 This program is free software: you can redistribute it and/or modify
   6 it under the terms of the GNU General Public License as published by
   7 the Free Software Foundation, either version 3 of the License, or
   8 (at your option) any later version.
   9
  10 This program is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 GNU General Public License for more details.
  14
  15 You should have received a copy of the GNU General Public License
  16 along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17 */
  18 package main
  19
  20 import (
  21         "encoding/binary"
  22         "encoding/hex"
  23         "flag"
  24         "fmt"
  25         "io"
  26         "io/ioutil"
  27         "log"
  28         "net"
  29         "time"
  30
  31         "code.google.com/p/go.crypto/poly1305"
  32         "code.google.com/p/go.crypto/salsa20"
  33 )
  34
  35 var (
  36         remoteAddr = flag.String("remote", "", "Remote server address")
  37         bindAddr   = flag.String("bind", "", "Bind to address")
  38         ifaceName  = flag.String("iface", "tap0", "TAP network interface")
  39         keyPath    = flag.String("key", "", "Path to authentication key file")
  40         mtu        = flag.Int("mtu", 1500, "MTU")
  41         timeoutP   = flag.Int("timeout", 60, "Timeout seconds")
  42         verboseP   = flag.Bool("v", false, "Increase verbosity")
  43 )
  44
  45 const (
  46         NonceSize = 8
  47         KeySize   = 32
  48         // S20BS is Salsa20's internal blocksize in bytes
  49         S20BS = 64
  50 )
  51
  52 type TAP interface {
  53         io.Reader
  54         io.Writer
  55 }
  56
  57 type Peer struct {
  58         addr      *net.UDPAddr
  59         key       *[KeySize]byte // encryption key
  60         nonceOur  uint64         // nonce for our messages
  61         nonceRecv uint64         // latest received nonce from remote peer
  62 }
  63
  64 type UDPPkt struct {
  65         addr *net.UDPAddr
  66         size int
  67 }
  68
  69 func main() {
  70         flag.Parse()
  71         timeout := *timeoutP
  72         verbose := *verboseP
  73         log.SetFlags(log.Ldate | log.Lmicroseconds | log.Lshortfile)
  74
  75         // Key decoding
  76         keyData, err := ioutil.ReadFile(*keyPath)
  77         if err != nil {
  78                 panic("Unable to read keyfile: " + err.Error())
  79         }
  80         if len(keyData) < 64 {
  81                 panic("Key must be 64 hex characters long")
  82         }
  83         keyDecoded, err := hex.DecodeString(string(keyData[0:64]))
  84         if err != nil {
  85                 panic("Unable to decode the key: " + err.Error())
  86         }
  87         key := new([KeySize]byte)
  88         copy(key[:], keyDecoded)
  89         keyDecoded = nil
  90         keyData = nil
  91
  92         // Interface listening
  93         maxIfacePktSize := *mtu - poly1305.TagSize - NonceSize
  94         log.Println("Max MTU", maxIfacePktSize, "on interface", *ifaceName)
  95         iface := NewTAP(*ifaceName)
  96         ethBuf := make([]byte, maxIfacePktSize)
  97         ethSink := make(chan int)
  98         ethSinkReady := make(chan bool)
  99         go func() {
 100                 for {
 101                         <-ethSinkReady
 102                         n, err := iface.Read(ethBuf)
 103                         if err != nil {
 104                                 panic(err)
 105                         }
 106                         ethSink <- n
 107                 }
 108         }()
 109         ethSinkReady <- true
 110
 111         // Network address parsing
 112         if (len(*bindAddr) > 1 && len(*remoteAddr) > 1) ||
 113                 (len(*bindAddr) == 0 && len(*remoteAddr) == 0) {
 114                 panic("Either -bind or -remote must be specified only")
 115         }
 116         var conn *net.UDPConn
 117         var remote *net.UDPAddr
 118         serverMode := false
 119         bindTo := "0.0.0.0:0"
 120
 121         if len(*bindAddr) > 1 {
 122                 bindTo = *bindAddr
 123                 serverMode = true
 124         }
 125
 126         bind, err := net.ResolveUDPAddr("udp", bindTo)
 127         if err != nil {
 128                 panic(err)
 129         }
 130         conn, err = net.ListenUDP("udp", bind)
 131         if err != nil {
 132                 panic(err)
 133         }
 134
 135         if len(*remoteAddr) > 1 {
 136                 remote, err = net.ResolveUDPAddr("udp", *remoteAddr)
 137                 if err != nil {
 138                         panic(err)
 139                 }
 140         }
 141
 142         udpBuf := make([]byte, *mtu)
 143         udpSink := make(chan *UDPPkt)
 144         udpSinkReady := make(chan bool)
 145         go func(conn *net.UDPConn) {
 146                 for {
 147                         <-udpSinkReady
 148                         conn.SetReadDeadline(time.Now().Add(time.Second))
 149                         n, addr, err := conn.ReadFromUDP(udpBuf)
 150                         if err != nil {
 151                                 if verbose {
 152                                         fmt.Print("B")
 153                                 }
 154                                 udpSink <- nil
 155                         } else {
 156                                 udpSink <- &UDPPkt{addr, n}
 157                         }
 158                 }
 159         }(conn)
 160         udpSinkReady <- true
 161
 162         // Process packets
 163         var udpPkt *UDPPkt
 164         var udpPktData []byte
 165         var ethPktSize int
 166         var addr string
 167         var peer *Peer
 168         var p *Peer
 169
 170         timeouts := 0
 171         states := make(map[string]*Handshake)
 172         nonce := make([]byte, NonceSize)
 173         keyAuth := new([KeySize]byte)
 174         tag := new([poly1305.TagSize]byte)
 175         buf := make([]byte, *mtu+S20BS)
 176         emptyKey := make([]byte, KeySize)
 177         ethPkt := make([]byte, maxIfacePktSize)
 178         udpPktDataBuf := make([]byte, *mtu)
 179
 180         if !serverMode {
 181                 states[remote.String()] = HandshakeStart(conn, remote, key)
 182         }
 183
 184         finished := false
 185         for {
 186                 if finished {
 187                         break
 188                 }
 189                 select {
 190                 case udpPkt = <-udpSink:
 191                         timeouts++
 192                         if !serverMode && timeouts >= timeout {
 193                                 finished = true
 194                         }
 195                         if udpPkt == nil {
 196                                 udpSinkReady <- true
 197                                 continue
 198                         }
 199                         copy(udpPktDataBuf, udpBuf[:udpPkt.size])
 200                         udpSinkReady <- true
 201                         udpPktData = udpPktDataBuf[:udpPkt.size]
 202                         if isValidHandshakePkt(udpPktData) {
 203                                 addr = udpPkt.addr.String()
 204                                 state, exists := states[addr]
 205                                 if serverMode {
 206                                         if !exists {
 207                                                 state = &Handshake{addr: udpPkt.addr}
 208                                                 states[addr] = state
 209                                         }
 210                                         p = state.Server(conn, key, udpPktData)
 211                                 } else {
 212                                         if !exists {
 213                                                 fmt.Print("[HS?]")
 214                                                 continue
 215                                         }
 216                                         p = state.Client(conn, key, udpPktData)
 217                                 }
 218                                 if p != nil {
 219                                         fmt.Print("[HS-OK]")
 220                                         peer = p
 221                                         delete(states, addr)
 222                                 }
 223                                 continue
 224                         }
 225                         if peer == nil {
 226                                 continue
 227                         }
 228                         nonceRecv, _ := binary.Uvarint(udpPktData[:8])
 229                         if peer.nonceRecv >= nonceRecv {
 230                                 fmt.Print("R")
 231                                 continue
 232                         }
 233                         copy(buf[:KeySize], emptyKey)
 234                         copy(tag[:], udpPktData[udpPkt.size-poly1305.TagSize:])
 235                         copy(buf[S20BS:], udpPktData[NonceSize:udpPkt.size-poly1305.TagSize])
 236                         salsa20.XORKeyStream(
 237                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 238                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 239                                 udpPktData[:NonceSize],
 240                                 peer.key,
 241                         )
 242                         copy(keyAuth[:], buf[:KeySize])
 243                         if !poly1305.Verify(tag, udpPktData[:udpPkt.size-poly1305.TagSize], keyAuth) {
 244                                 fmt.Print("T")
 245                                 continue
 246                         }
 247                         peer.nonceRecv = nonceRecv
 248                         timeouts = 0
 249                         if _, err := iface.Write(buf[S20BS : S20BS+udpPkt.size-NonceSize-poly1305.TagSize]); err != nil {
 250                                 log.Println("Error writing to iface: ", err)
 251                         }
 252                         if verbose {
 253                                 fmt.Print("r")
 254                         }
 255                 case ethPktSize = <-ethSink:
 256                         if ethPktSize > maxIfacePktSize {
 257                                 panic("Too large packet on interface")
 258                         }
 259                         if peer == nil {
 260                                 ethSinkReady <- true
 261                                 continue
 262                         }
 263                         copy(ethPkt, ethBuf[:ethPktSize])
 264                         ethSinkReady <- true
 265                         peer.nonceOur = peer.nonceOur + 2
 266                         binary.PutUvarint(nonce, peer.nonceOur)
 267                         copy(buf[:KeySize], emptyKey)
 268                         copy(buf[S20BS:], ethPkt[:ethPktSize])
 269                         salsa20.XORKeyStream(buf, buf, nonce, peer.key)
 270                         copy(buf[S20BS-NonceSize:S20BS], nonce)
 271                         copy(keyAuth[:], buf[:KeySize])
 272                         dataToSend := buf[S20BS-NonceSize : S20BS+ethPktSize]
 273                         poly1305.Sum(tag, dataToSend, keyAuth)
 274                         if _, err := conn.WriteTo(append(dataToSend, tag[:]...), peer.addr); err != nil {
 275                                 log.Println("Error sending UDP", err)
 276                         }
 277                         if verbose {
 278                                 fmt.Print("w")
 279                         }
 280                 }
 281         }
 282 }