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