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         "log"
  26         "net"
  27         "time"
  28
  29         "code.google.com/p/go.crypto/poly1305"
  30         "code.google.com/p/go.crypto/salsa20"
  31         "github.com/chon219/water"
  32 )
  33
  34 var (
  35         remoteAddr = flag.String("remote", "", "Remote server address")
  36         bindAddr   = flag.String("bind", "", "Bind to address")
  37         ifaceName  = flag.String("iface", "tap0", "TAP network interface")
  38         keyHex     = flag.String("key", "", "Authentication key")
  39         mtu        = flag.Int("mtu", 1500, "MTU")
  40         timeout    = flag.Int("timeout", 60, "Timeout seconds")
  41         verbose    = flag.Bool("v", false, "Increase verbosity")
  42 )
  43
  44 const (
  45         NonceSize = 8
  46         KeySize   = 32
  47         // S20BS is Salsa20's internal blocksize in bytes
  48         S20BS = 64
  49 )
  50
  51 type Peer struct {
  52         addr      *net.UDPAddr
  53         key       *[KeySize]byte // encryption key
  54         nonceOur  uint64         // nonce for our messages
  55         nonceRecv uint64         // latest received nonce from remote peer
  56 }
  57
  58 type UDPPkt struct {
  59         addr *net.UDPAddr
  60         size int
  61 }
  62
  63 func main() {
  64         flag.Parse()
  65         log.SetFlags(log.Ldate | log.Lmicroseconds | log.Lshortfile)
  66
  67         // Key decoding
  68         if len(*keyHex) != 64 {
  69                 panic("Key is required argument (64 hex characters)")
  70         }
  71         keyDecoded, err := hex.DecodeString(*keyHex)
  72         if err != nil {
  73                 panic(err)
  74         }
  75         key := new([KeySize]byte)
  76         copy(key[:], keyDecoded)
  77
  78         // Interface listening
  79         maxIfacePktSize := *mtu - poly1305.TagSize - NonceSize
  80         log.Println("Max MTU", maxIfacePktSize, "on interface", *ifaceName)
  81         iface, err := water.NewTAP(*ifaceName)
  82         if err != nil {
  83                 panic(err)
  84         }
  85         ethBuf := make([]byte, maxIfacePktSize)
  86         ethSink := make(chan int)
  87         ethSinkReady := make(chan bool)
  88         go func() {
  89                 for {
  90                         <-ethSinkReady
  91                         n, err := iface.Read(ethBuf)
  92                         if err != nil {
  93                                 panic(err)
  94                         }
  95                         ethSink <- n
  96                 }
  97         }()
  98         ethSinkReady <- true
  99
 100         // Network address parsing
 101         if (len(*bindAddr) > 1 && len(*remoteAddr) > 1) ||
 102                 (len(*bindAddr) == 0 && len(*remoteAddr) == 0) {
 103                 panic("Either -bind or -remote must be specified only")
 104         }
 105         var conn *net.UDPConn
 106         var remote *net.UDPAddr
 107         serverMode := false
 108         bindTo := "0.0.0.0:0"
 109
 110         if len(*bindAddr) > 1 {
 111                 bindTo = *bindAddr
 112                 serverMode = true
 113         }
 114
 115         bind, err := net.ResolveUDPAddr("udp", bindTo)
 116         if err != nil {
 117                 panic(err)
 118         }
 119         conn, err = net.ListenUDP("udp", bind)
 120         if err != nil {
 121                 panic(err)
 122         }
 123
 124         if len(*remoteAddr) > 1 {
 125                 remote, err = net.ResolveUDPAddr("udp", *remoteAddr)
 126                 if err != nil {
 127                         panic(err)
 128                 }
 129         }
 130
 131         udpBuf := make([]byte, *mtu)
 132         udpSink := make(chan *UDPPkt)
 133         udpSinkReady := make(chan bool)
 134         go func(conn *net.UDPConn) {
 135                 for {
 136                         <-udpSinkReady
 137                         conn.SetReadDeadline(time.Now().Add(time.Second))
 138                         n, addr, err := conn.ReadFromUDP(udpBuf)
 139                         if err != nil {
 140                                 if *verbose {
 141                                         fmt.Print("B")
 142                                 }
 143                                 udpSink <- nil
 144                         } else {
 145                                 udpSink <- &UDPPkt{addr, n}
 146                         }
 147                 }
 148         }(conn)
 149         udpSinkReady <- true
 150
 151         // Process packets
 152         var udpPkt *UDPPkt
 153         var udpPktData []byte
 154         var ethPktSize int
 155         var addr string
 156         var peer *Peer
 157         var p *Peer
 158
 159         timeouts := 0
 160         states := make(map[string]*Handshake)
 161         nonce := make([]byte, NonceSize)
 162         keyAuth := new([KeySize]byte)
 163         tag := new([poly1305.TagSize]byte)
 164         buf := make([]byte, *mtu+S20BS)
 165         emptyKey := make([]byte, KeySize)
 166         ethPkt := make([]byte, maxIfacePktSize)
 167         udpPktDataBuf := make([]byte, *mtu)
 168
 169         if !serverMode {
 170                 states[remote.String()] = HandshakeStart(conn, remote, key)
 171         }
 172
 173         finished := false
 174         for {
 175                 if finished {
 176                         break
 177                 }
 178                 select {
 179                 case udpPkt = <-udpSink:
 180                         timeouts++
 181                         if !serverMode && timeouts >= *timeout {
 182                                 finished = true
 183                         }
 184                         if udpPkt == nil {
 185                                 udpSinkReady <- true
 186                                 continue
 187                         }
 188                         copy(udpPktDataBuf, udpBuf[:udpPkt.size])
 189                         udpSinkReady <- true
 190                         udpPktData = udpPktDataBuf[:udpPkt.size]
 191                         if isValidHandshakePkt(udpPktData) {
 192                                 addr = udpPkt.addr.String()
 193                                 state, exists := states[addr]
 194                                 if serverMode {
 195                                         if !exists {
 196                                                 state = &Handshake{addr: udpPkt.addr}
 197                                                 states[addr] = state
 198                                         }
 199                                         p = state.Server(conn, key, udpPktData)
 200                                 } else {
 201                                         if !exists {
 202                                                 fmt.Print("[HS?]")
 203                                                 continue
 204                                         }
 205                                         p = state.Client(conn, key, udpPktData)
 206                                 }
 207                                 if p != nil {
 208                                         fmt.Print("[HS-OK]")
 209                                         peer = p
 210                                         delete(states, addr)
 211                                 }
 212                                 continue
 213                         }
 214                         if peer == nil {
 215                                 continue
 216                         }
 217                         nonceRecv, _ := binary.Uvarint(udpPktData[:8])
 218                         if peer.nonceRecv >= nonceRecv {
 219                                 fmt.Print("R")
 220                                 continue
 221                         }
 222                         copy(buf[:KeySize], emptyKey)
 223                         copy(tag[:], udpPktData[udpPkt.size-poly1305.TagSize:])
 224                         copy(buf[S20BS:], udpPktData[NonceSize:udpPkt.size-poly1305.TagSize])
 225                         salsa20.XORKeyStream(
 226                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 227                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 228                                 udpPktData[:NonceSize],
 229                                 peer.key,
 230                         )
 231                         copy(keyAuth[:], buf[:KeySize])
 232                         if !poly1305.Verify(tag, udpPktData[:udpPkt.size-poly1305.TagSize], keyAuth) {
 233                                 fmt.Print("T")
 234                                 continue
 235                         }
 236                         peer.nonceRecv = nonceRecv
 237                         timeouts = 0
 238                         if _, err := iface.Write(buf[S20BS : S20BS+udpPkt.size-NonceSize-poly1305.TagSize]); err != nil {
 239                                 log.Println("Error writing to iface")
 240                         }
 241                         if *verbose {
 242                                 fmt.Print("r")
 243                         }
 244                 case ethPktSize = <-ethSink:
 245                         if ethPktSize > maxIfacePktSize {
 246                                 panic("Too large packet on interface")
 247                         }
 248                         if peer == nil {
 249                                 ethSinkReady <- true
 250                                 continue
 251                         }
 252                         copy(ethPkt, ethBuf[:ethPktSize])
 253                         ethSinkReady <- true
 254                         peer.nonceOur = peer.nonceOur + 2
 255                         binary.PutUvarint(nonce, peer.nonceOur)
 256                         copy(buf[:KeySize], emptyKey)
 257                         copy(buf[S20BS:], ethPkt[:ethPktSize])
 258                         salsa20.XORKeyStream(buf, buf, nonce, peer.key)
 259                         copy(buf[S20BS-NonceSize:S20BS], nonce)
 260                         copy(keyAuth[:], buf[:KeySize])
 261                         dataToSend := buf[S20BS-NonceSize : S20BS+ethPktSize]
 262                         poly1305.Sum(tag, dataToSend, keyAuth)
 263                         if _, err := conn.WriteTo(append(dataToSend, tag[:]...), peer.addr); err != nil {
 264                                 log.Println("Error sending UDP", err)
 265                         }
 266                         if *verbose {
 267                                 fmt.Print("w")
 268                         }
 269                 }
 270         }
 271 }