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         HeartBeatSize = 12
  51         HeartBeatMark = "\x00\x00\x00HEARTBEAT"
  52 )
  53
  54 type TAP interface {
  55         io.Reader
  56         io.Writer
  57 }
  58
  59 type Peer struct {
  60         addr      *net.UDPAddr
  61         key       *[KeySize]byte // encryption key
  62         nonceOur  uint64         // nonce for our messages
  63         nonceRecv uint64         // latest received nonce from remote peer
  64 }
  65
  66 type UDPPkt struct {
  67         addr *net.UDPAddr
  68         size int
  69 }
  70
  71 func main() {
  72         flag.Parse()
  73         timeout := *timeoutP
  74         verbose := *verboseP
  75         log.SetFlags(log.Ldate | log.Lmicroseconds | log.Lshortfile)
  76
  77         // Key decoding
  78         keyData, err := ioutil.ReadFile(*keyPath)
  79         if err != nil {
  80                 panic("Unable to read keyfile: " + err.Error())
  81         }
  82         if len(keyData) < 64 {
  83                 panic("Key must be 64 hex characters long")
  84         }
  85         keyDecoded, err := hex.DecodeString(string(keyData[0:64]))
  86         if err != nil {
  87                 panic("Unable to decode the key: " + err.Error())
  88         }
  89         key := new([KeySize]byte)
  90         copy(key[:], keyDecoded)
  91         keyDecoded = nil
  92         keyData = nil
  93
  94         // Interface listening
  95         maxIfacePktSize := *mtu - poly1305.TagSize - NonceSize
  96         log.Println("Max MTU", maxIfacePktSize, "on interface", *ifaceName)
  97         iface := NewTAP(*ifaceName)
  98         ethBuf := make([]byte, maxIfacePktSize)
  99         ethSink := make(chan int)
 100         ethSinkReady := make(chan bool)
 101         go func() {
 102                 for {
 103                         <-ethSinkReady
 104                         n, err := iface.Read(ethBuf)
 105                         if err != nil {
 106                                 panic(err)
 107                         }
 108                         ethSink <- n
 109                 }
 110         }()
 111         ethSinkReady <- true
 112
 113         // Network address parsing
 114         if (len(*bindAddr) > 1 && len(*remoteAddr) > 1) ||
 115                 (len(*bindAddr) == 0 && len(*remoteAddr) == 0) {
 116                 panic("Either -bind or -remote must be specified only")
 117         }
 118         var conn *net.UDPConn
 119         var remote *net.UDPAddr
 120         serverMode := false
 121         bindTo := "0.0.0.0:0"
 122
 123         if len(*bindAddr) > 1 {
 124                 bindTo = *bindAddr
 125                 serverMode = true
 126         }
 127
 128         bind, err := net.ResolveUDPAddr("udp", bindTo)
 129         if err != nil {
 130                 panic(err)
 131         }
 132         conn, err = net.ListenUDP("udp", bind)
 133         if err != nil {
 134                 panic(err)
 135         }
 136
 137         if len(*remoteAddr) > 1 {
 138                 remote, err = net.ResolveUDPAddr("udp", *remoteAddr)
 139                 if err != nil {
 140                         panic(err)
 141                 }
 142         }
 143
 144         udpBuf := make([]byte, *mtu)
 145         udpSink := make(chan *UDPPkt)
 146         udpSinkReady := make(chan bool)
 147         go func(conn *net.UDPConn) {
 148                 for {
 149                         <-udpSinkReady
 150                         conn.SetReadDeadline(time.Now().Add(time.Second))
 151                         n, addr, err := conn.ReadFromUDP(udpBuf)
 152                         if err != nil {
 153                                 if verbose {
 154                                         fmt.Print("B")
 155                                 }
 156                                 udpSink <- nil
 157                         } else {
 158                                 udpSink <- &UDPPkt{addr, n}
 159                         }
 160                 }
 161         }(conn)
 162         udpSinkReady <- true
 163
 164         // Process packets
 165         var udpPkt *UDPPkt
 166         var udpPktData []byte
 167         var ethPktSize int
 168         var frame []byte
 169         var addr string
 170         var peer *Peer
 171         var p *Peer
 172
 173         timeouts := 0
 174         states := make(map[string]*Handshake)
 175         nonce := make([]byte, NonceSize)
 176         keyAuth := new([KeySize]byte)
 177         tag := new([poly1305.TagSize]byte)
 178         buf := make([]byte, *mtu+S20BS)
 179         emptyKey := make([]byte, KeySize)
 180         ethPkt := make([]byte, maxIfacePktSize)
 181         udpPktDataBuf := make([]byte, *mtu)
 182
 183         if !serverMode {
 184                 states[remote.String()] = HandshakeStart(conn, remote, key)
 185         }
 186
 187         heartbeat := time.Tick(time.Second * time.Duration(timeout/3))
 188         heartbeatMark := []byte(HeartBeatMark)
 189
 190         finished := false
 191         for {
 192                 if finished {
 193                         break
 194                 }
 195                 select {
 196                 case <-heartbeat:
 197                         go func() { ethSink <- -1 }()
 198                 case udpPkt = <-udpSink:
 199                         timeouts++
 200                         if !serverMode && timeouts >= timeout {
 201                                 finished = true
 202                         }
 203                         if udpPkt == nil {
 204                                 udpSinkReady <- true
 205                                 continue
 206                         }
 207                         copy(udpPktDataBuf, udpBuf[:udpPkt.size])
 208                         udpSinkReady <- true
 209                         udpPktData = udpPktDataBuf[:udpPkt.size]
 210                         if isValidHandshakePkt(udpPktData) {
 211                                 addr = udpPkt.addr.String()
 212                                 state, exists := states[addr]
 213                                 if serverMode {
 214                                         if !exists {
 215                                                 state = &Handshake{addr: udpPkt.addr}
 216                                                 states[addr] = state
 217                                         }
 218                                         p = state.Server(conn, key, udpPktData)
 219                                 } else {
 220                                         if !exists {
 221                                                 fmt.Print("[HS?]")
 222                                                 continue
 223                                         }
 224                                         p = state.Client(conn, key, udpPktData)
 225                                 }
 226                                 if p != nil {
 227                                         fmt.Print("[HS-OK]")
 228                                         peer = p
 229                                         delete(states, addr)
 230                                 }
 231                                 continue
 232                         }
 233                         if peer == nil {
 234                                 continue
 235                         }
 236                         nonceRecv, _ := binary.Uvarint(udpPktData[:8])
 237                         if peer.nonceRecv >= nonceRecv {
 238                                 fmt.Print("R")
 239                                 continue
 240                         }
 241                         copy(buf[:KeySize], emptyKey)
 242                         copy(tag[:], udpPktData[udpPkt.size-poly1305.TagSize:])
 243                         copy(buf[S20BS:], udpPktData[NonceSize:udpPkt.size-poly1305.TagSize])
 244                         salsa20.XORKeyStream(
 245                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 246                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 247                                 udpPktData[:NonceSize],
 248                                 peer.key,
 249                         )
 250                         copy(keyAuth[:], buf[:KeySize])
 251                         if !poly1305.Verify(tag, udpPktData[:udpPkt.size-poly1305.TagSize], keyAuth) {
 252                                 fmt.Print("T")
 253                                 continue
 254                         }
 255                         peer.nonceRecv = nonceRecv
 256                         timeouts = 0
 257                         frame = buf[S20BS : S20BS+udpPkt.size-NonceSize-poly1305.TagSize]
 258                         if string(frame[0:HeartBeatSize]) == HeartBeatMark {
 259                                 continue
 260                         }
 261                         if _, err := iface.Write(frame); err != nil {
 262                                 log.Println("Error writing to iface: ", err)
 263                         }
 264                         if verbose {
 265                                 fmt.Print("r")
 266                         }
 267                 case ethPktSize = <-ethSink:
 268                         if ethPktSize > maxIfacePktSize {
 269                                 panic("Too large packet on interface")
 270                         }
 271                         if peer == nil {
 272                                 ethSinkReady <- true
 273                                 continue
 274                         }
 275                         if ethPktSize > -1 {
 276                                 copy(ethPkt, ethBuf[:ethPktSize])
 277                                 ethSinkReady <- true
 278                         } else {
 279                                 copy(ethPkt, heartbeatMark)
 280                                 ethPktSize = HeartBeatSize
 281                         }
 282                         peer.nonceOur = peer.nonceOur + 2
 283                         binary.PutUvarint(nonce, peer.nonceOur)
 284                         copy(buf[:KeySize], emptyKey)
 285                         copy(buf[S20BS:], ethPkt[:ethPktSize])
 286                         salsa20.XORKeyStream(buf, buf, nonce, peer.key)
 287                         copy(buf[S20BS-NonceSize:S20BS], nonce)
 288                         copy(keyAuth[:], buf[:KeySize])
 289                         dataToSend := buf[S20BS-NonceSize : S20BS+ethPktSize]
 290                         poly1305.Sum(tag, dataToSend, keyAuth)
 291                         if _, err := conn.WriteTo(append(dataToSend, tag[:]...), peer.addr); err != nil {
 292                                 log.Println("Error sending UDP", err)
 293                         }
 294                         if verbose {
 295                                 fmt.Print("w")
 296                         }
 297                 }
 298         }
 299 }