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
  19 // High-performance secure virtual private network daemon
  20 package main
  21
  22 import (
  23         "bytes"
  24         "encoding/binary"
  25         "encoding/hex"
  26         "flag"
  27         "fmt"
  28         "io"
  29         "io/ioutil"
  30         "log"
  31         "net"
  32         "os"
  33         "os/exec"
  34         "os/signal"
  35         "time"
  36
  37         "golang.org/x/crypto/poly1305"
  38         "golang.org/x/crypto/salsa20"
  39 )
  40
  41 var (
  42         remoteAddr = flag.String("remote", "", "Remote server address")
  43         bindAddr   = flag.String("bind", "", "Bind to address")
  44         ifaceName  = flag.String("iface", "tap0", "TAP network interface")
  45         keyPath    = flag.String("key", "", "Path to authentication key file")
  46         upPath     = flag.String("up", "", "Path to up-script")
  47         downPath   = flag.String("down", "", "Path to down-script")
  48         mtu        = flag.Int("mtu", 1500, "MTU")
  49         timeoutP   = flag.Int("timeout", 60, "Timeout seconds")
  50         verboseP   = flag.Bool("v", false, "Increase verbosity")
  51 )
  52
  53 const (
  54         NonceSize = 8
  55         KeySize   = 32
  56         // S20BS is Salsa20's internal blocksize in bytes
  57         S20BS         = 64
  58         HeartBeatSize = 12
  59         HeartBeatMark = "\x00\x00\x00HEARTBEAT"
  60         // Maximal amount of bytes transfered with single key (4 GiB)
  61         MaxBytesPerKey = 4294967296
  62 )
  63
  64 type TAP interface {
  65         io.Reader
  66         io.Writer
  67 }
  68
  69 type Peer struct {
  70         addr      *net.UDPAddr
  71         key       *[KeySize]byte // encryption key
  72         nonceOur  uint64         // nonce for our messages
  73         nonceRecv uint64         // latest received nonce from remote peer
  74 }
  75
  76 type UDPPkt struct {
  77         addr *net.UDPAddr
  78         size int
  79 }
  80
  81 func ScriptCall(path *string) {
  82         if *path == "" {
  83                 return
  84         }
  85         cmd := exec.Command(*path, *ifaceName)
  86         var out bytes.Buffer
  87         cmd.Stdout = &out
  88         if err := cmd.Run(); err != nil {
  89                 fmt.Println(time.Now(), "script error: ", err.Error(), string(out.Bytes()))
  90         }
  91 }
  92
  93 func main() {
  94         flag.Parse()
  95         timeout := *timeoutP
  96         verbose := *verboseP
  97         log.SetFlags(log.Ldate | log.Lmicroseconds | log.Lshortfile)
  98
  99         // Key decoding
 100         keyData, err := ioutil.ReadFile(*keyPath)
 101         if err != nil {
 102                 panic("Unable to read keyfile: " + err.Error())
 103         }
 104         if len(keyData) < 64 {
 105                 panic("Key must be 64 hex characters long")
 106         }
 107         keyDecoded, err := hex.DecodeString(string(keyData[0:64]))
 108         if err != nil {
 109                 panic("Unable to decode the key: " + err.Error())
 110         }
 111         key := new([KeySize]byte)
 112         copy(key[:], keyDecoded)
 113         keyDecoded = nil
 114         keyData = nil
 115
 116         // Interface listening
 117         maxIfacePktSize := *mtu - poly1305.TagSize - NonceSize
 118         log.Println("Max MTU", maxIfacePktSize, "on interface", *ifaceName)
 119         iface := NewTAP(*ifaceName)
 120         ethBuf := make([]byte, maxIfacePktSize)
 121         ethSink := make(chan int)
 122         ethSinkReady := make(chan bool)
 123         go func() {
 124                 for {
 125                         <-ethSinkReady
 126                         n, err := iface.Read(ethBuf)
 127                         if err != nil {
 128                                 panic(err)
 129                         }
 130                         ethSink <- n
 131                 }
 132         }()
 133         ethSinkReady <- true
 134
 135         // Network address parsing
 136         if (len(*bindAddr) > 1 && len(*remoteAddr) > 1) ||
 137                 (len(*bindAddr) == 0 && len(*remoteAddr) == 0) {
 138                 panic("Either -bind or -remote must be specified only")
 139         }
 140         var conn *net.UDPConn
 141         var remote *net.UDPAddr
 142         serverMode := false
 143         bindTo := "0.0.0.0:0"
 144
 145         if len(*bindAddr) > 1 {
 146                 bindTo = *bindAddr
 147                 serverMode = true
 148         }
 149
 150         bind, err := net.ResolveUDPAddr("udp", bindTo)
 151         if err != nil {
 152                 panic(err)
 153         }
 154         conn, err = net.ListenUDP("udp", bind)
 155         if err != nil {
 156                 panic(err)
 157         }
 158
 159         if len(*remoteAddr) > 1 {
 160                 remote, err = net.ResolveUDPAddr("udp", *remoteAddr)
 161                 if err != nil {
 162                         panic(err)
 163                 }
 164         }
 165
 166         udpBuf := make([]byte, *mtu)
 167         udpSink := make(chan *UDPPkt)
 168         udpSinkReady := make(chan bool)
 169         go func(conn *net.UDPConn) {
 170                 for {
 171                         <-udpSinkReady
 172                         conn.SetReadDeadline(time.Now().Add(time.Second))
 173                         n, addr, err := conn.ReadFromUDP(udpBuf)
 174                         if err != nil {
 175                                 if verbose {
 176                                         fmt.Print("B")
 177                                 }
 178                                 udpSink <- nil
 179                         } else {
 180                                 udpSink <- &UDPPkt{addr, n}
 181                         }
 182                 }
 183         }(conn)
 184         udpSinkReady <- true
 185
 186         // Process packets
 187         var udpPkt *UDPPkt
 188         var udpPktData []byte
 189         var ethPktSize int
 190         var frame []byte
 191         var addr string
 192         var peer *Peer
 193         var p *Peer
 194
 195         timeouts := 0
 196         bytes := 0
 197         states := make(map[string]*Handshake)
 198         nonce := make([]byte, NonceSize)
 199         keyAuth := new([KeySize]byte)
 200         tag := new([poly1305.TagSize]byte)
 201         buf := make([]byte, *mtu+S20BS)
 202         emptyKey := make([]byte, KeySize)
 203
 204         if !serverMode {
 205                 states[remote.String()] = HandshakeStart(conn, remote, key)
 206         }
 207
 208         heartbeat := time.Tick(time.Second * time.Duration(timeout/3))
 209         go func() { <-heartbeat }()
 210         heartbeatMark := []byte(HeartBeatMark)
 211
 212         termSignal := make(chan os.Signal, 1)
 213         signal.Notify(termSignal, os.Interrupt, os.Kill)
 214
 215         finished := false
 216         for {
 217                 if finished {
 218                         break
 219                 }
 220                 if !serverMode && bytes > MaxBytesPerKey {
 221                         states[remote.String()] = HandshakeStart(conn, remote, key)
 222                         bytes = 0
 223                 }
 224                 select {
 225                 case <-termSignal:
 226                         finished = true
 227                 case <-heartbeat:
 228                         go func() { ethSink <- -1 }()
 229                 case udpPkt = <-udpSink:
 230                         timeouts++
 231                         if !serverMode && timeouts >= timeout {
 232                                 finished = true
 233                         }
 234                         if udpPkt == nil {
 235                                 udpSinkReady <- true
 236                                 continue
 237                         }
 238                         udpPktData = udpBuf[:udpPkt.size]
 239                         if isValidHandshakePkt(udpPktData) {
 240                                 addr = udpPkt.addr.String()
 241                                 state, exists := states[addr]
 242                                 if serverMode {
 243                                         if !exists {
 244                                                 state = &Handshake{addr: udpPkt.addr}
 245                                                 states[addr] = state
 246                                         }
 247                                         p = state.Server(conn, key, udpPktData)
 248                                 } else {
 249                                         if !exists {
 250                                                 fmt.Print("[HS?]")
 251                                                 udpSinkReady <- true
 252                                                 continue
 253                                         }
 254                                         p = state.Client(conn, key, udpPktData)
 255                                 }
 256                                 if p != nil {
 257                                         fmt.Print("[HS-OK]")
 258                                         if peer == nil {
 259                                                 go ScriptCall(upPath)
 260                                         }
 261                                         peer = p
 262                                         delete(states, addr)
 263                                 }
 264                                 udpSinkReady <- true
 265                                 continue
 266                         }
 267                         if peer == nil {
 268                                 udpSinkReady <- true
 269                                 continue
 270                         }
 271                         nonceRecv, _ := binary.Uvarint(udpPktData[:8])
 272                         if peer.nonceRecv >= nonceRecv {
 273                                 fmt.Print("R")
 274                                 udpSinkReady <- true
 275                                 continue
 276                         }
 277                         copy(buf[:KeySize], emptyKey)
 278                         copy(tag[:], udpPktData[udpPkt.size-poly1305.TagSize:])
 279                         copy(buf[S20BS:], udpPktData[NonceSize:udpPkt.size-poly1305.TagSize])
 280                         salsa20.XORKeyStream(
 281                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 282                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 283                                 udpPktData[:NonceSize],
 284                                 peer.key,
 285                         )
 286                         copy(keyAuth[:], buf[:KeySize])
 287                         if !poly1305.Verify(tag, udpPktData[:udpPkt.size-poly1305.TagSize], keyAuth) {
 288                                 udpSinkReady <- true
 289                                 fmt.Print("T")
 290                                 continue
 291                         }
 292                         udpSinkReady <- true
 293                         peer.nonceRecv = nonceRecv
 294                         timeouts = 0
 295                         frame = buf[S20BS : S20BS+udpPkt.size-NonceSize-poly1305.TagSize]
 296                         bytes += len(frame)
 297                         if string(frame[0:HeartBeatSize]) == HeartBeatMark {
 298                                 continue
 299                         }
 300                         if _, err := iface.Write(frame); err != nil {
 301                                 log.Println("Error writing to iface: ", err)
 302                         }
 303                         if verbose {
 304                                 fmt.Print("r")
 305                         }
 306                 case ethPktSize = <-ethSink:
 307                         if ethPktSize > maxIfacePktSize {
 308                                 panic("Too large packet on interface")
 309                         }
 310                         if peer == nil {
 311                                 ethSinkReady <- true
 312                                 continue
 313                         }
 314                         peer.nonceOur = peer.nonceOur + 2
 315                         binary.PutUvarint(nonce, peer.nonceOur)
 316                         copy(buf[:KeySize], emptyKey)
 317                         if ethPktSize > -1 {
 318                                 copy(buf[S20BS:], ethBuf[:ethPktSize])
 319                                 ethSinkReady <- true
 320                         } else {
 321                                 copy(buf[S20BS:], heartbeatMark)
 322                                 ethPktSize = HeartBeatSize
 323                         }
 324                         salsa20.XORKeyStream(buf, buf, nonce, peer.key)
 325                         copy(buf[S20BS-NonceSize:S20BS], nonce)
 326                         copy(keyAuth[:], buf[:KeySize])
 327                         dataToSend := buf[S20BS-NonceSize : S20BS+ethPktSize]
 328                         poly1305.Sum(tag, dataToSend, keyAuth)
 329                         bytes += len(dataToSend)
 330                         if _, err := conn.WriteTo(append(dataToSend, tag[:]...), peer.addr); err != nil {
 331                                 log.Println("Error sending UDP", err)
 332                         }
 333                         if verbose {
 334                                 fmt.Print("w")
 335                         }
 336                 }
 337         }
 338         ScriptCall(downPath)
 339 }