govpn.go

   1 /*
   2 govpn -- simple secure virtual private network daemon
   3 Copyright (C) 2014-2015 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 // Simple 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         nonceDiff  = flag.Int("noncediff", 1, "Allow nonce difference")
  50         timeoutP   = flag.Int("timeout", 60, "Timeout seconds")
  51         verboseP   = flag.Bool("v", false, "Increase verbosity")
  52 )
  53
  54 const (
  55         NonceSize = 8
  56         KeySize   = 32
  57         // S20BS is Salsa20's internal blocksize in bytes
  58         S20BS         = 64
  59         HeartBeatSize = 12
  60         HeartBeatMark = "\x00\x00\x00HEARTBEAT"
  61         // Maximal amount of bytes transfered with single key (4 GiB)
  62         MaxBytesPerKey = 4294967296
  63 )
  64
  65 type TAP interface {
  66         io.Reader
  67         io.Writer
  68 }
  69
  70 type Peer struct {
  71         addr      *net.UDPAddr
  72         key       *[KeySize]byte // encryption key
  73         nonceOur  uint64         // nonce for our messages
  74         nonceRecv uint64         // latest received nonce from remote peer
  75 }
  76
  77 type UDPPkt struct {
  78         addr *net.UDPAddr
  79         size int
  80 }
  81
  82 func ScriptCall(path *string) {
  83         if *path == "" {
  84                 return
  85         }
  86         cmd := exec.Command(*path, *ifaceName)
  87         var out bytes.Buffer
  88         cmd.Stdout = &out
  89         if err := cmd.Run(); err != nil {
  90                 fmt.Println(time.Now(), "script error: ", err.Error(), string(out.Bytes()))
  91         }
  92 }
  93
  94 func main() {
  95         flag.Parse()
  96         timeout := *timeoutP
  97         verbose := *verboseP
  98         noncediff := uint64(*nonceDiff)
  99         var err error
 100         log.SetFlags(log.Ldate | log.Lmicroseconds | log.Lshortfile)
 101
 102         // Key decoding
 103         keyData, err := ioutil.ReadFile(*keyPath)
 104         if err != nil {
 105                 panic("Unable to read keyfile: " + err.Error())
 106         }
 107         if len(keyData) < 64 {
 108                 panic("Key must be 64 hex characters long")
 109         }
 110         keyDecoded, err := hex.DecodeString(string(keyData[0:64]))
 111         if err != nil {
 112                 panic("Unable to decode the key: " + err.Error())
 113         }
 114         key := new([KeySize]byte)
 115         copy(key[:], keyDecoded)
 116         keyDecoded = nil
 117         keyData = nil
 118
 119         // Interface listening
 120         maxIfacePktSize := *mtu - poly1305.TagSize - NonceSize
 121         log.Println("Max MTU", maxIfacePktSize, "on interface", *ifaceName)
 122         iface := NewTAP(*ifaceName)
 123         ethBuf := make([]byte, maxIfacePktSize)
 124         ethSink := make(chan int)
 125         ethSinkReady := make(chan bool)
 126         go func() {
 127                 var n int
 128                 var err error
 129                 for {
 130                         <-ethSinkReady
 131                         n, err = iface.Read(ethBuf)
 132                         if err != nil {
 133                                 panic(err)
 134                         }
 135                         ethSink <- n
 136                 }
 137         }()
 138         ethSinkReady <- true
 139
 140         // Network address parsing
 141         if (len(*bindAddr) > 1 && len(*remoteAddr) > 1) ||
 142                 (len(*bindAddr) == 0 && len(*remoteAddr) == 0) {
 143                 panic("Either -bind or -remote must be specified only")
 144         }
 145         var conn *net.UDPConn
 146         var remote *net.UDPAddr
 147         serverMode := false
 148         bindTo := "0.0.0.0:0"
 149
 150         if len(*bindAddr) > 1 {
 151                 bindTo = *bindAddr
 152                 serverMode = true
 153         }
 154
 155         bind, err := net.ResolveUDPAddr("udp", bindTo)
 156         if err != nil {
 157                 panic(err)
 158         }
 159         conn, err = net.ListenUDP("udp", bind)
 160         if err != nil {
 161                 panic(err)
 162         }
 163
 164         if len(*remoteAddr) > 1 {
 165                 remote, err = net.ResolveUDPAddr("udp", *remoteAddr)
 166                 if err != nil {
 167                         panic(err)
 168                 }
 169         }
 170
 171         udpBuf := make([]byte, *mtu)
 172         udpSink := make(chan *UDPPkt)
 173         udpSinkReady := make(chan bool)
 174         go func(conn *net.UDPConn) {
 175                 var n int
 176                 var addr *net.UDPAddr
 177                 var err error
 178                 for {
 179                         <-udpSinkReady
 180                         conn.SetReadDeadline(time.Now().Add(time.Second))
 181                         n, addr, err = conn.ReadFromUDP(udpBuf)
 182                         if err != nil {
 183                                 if verbose {
 184                                         fmt.Print("B")
 185                                 }
 186                                 udpSink <- nil
 187                         } else {
 188                                 udpSink <- &UDPPkt{addr, n}
 189                         }
 190                 }
 191         }(conn)
 192         udpSinkReady <- true
 193
 194         // Process packets
 195         var udpPkt *UDPPkt
 196         var udpPktData []byte
 197         var ethPktSize int
 198         var frame []byte
 199         var dataToSend []byte
 200         var addr string
 201         var peer *Peer
 202         var p *Peer
 203         var nonceRecv uint64
 204
 205         timeouts := 0
 206         bytes := 0
 207         states := make(map[string]*Handshake)
 208         nonce := make([]byte, NonceSize)
 209         keyAuth := new([KeySize]byte)
 210         tag := new([poly1305.TagSize]byte)
 211         buf := make([]byte, *mtu+S20BS)
 212         emptyKey := make([]byte, KeySize)
 213
 214         if !serverMode {
 215                 states[remote.String()] = HandshakeStart(conn, remote, key)
 216         }
 217
 218         heartbeat := time.Tick(time.Second * time.Duration(timeout/3))
 219         go func() { <-heartbeat }()
 220         heartbeatMark := []byte(HeartBeatMark)
 221
 222         termSignal := make(chan os.Signal, 1)
 223         signal.Notify(termSignal, os.Interrupt, os.Kill)
 224
 225         finished := false
 226         for {
 227                 if finished {
 228                         break
 229                 }
 230                 if !serverMode && bytes > MaxBytesPerKey {
 231                         states[remote.String()] = HandshakeStart(conn, remote, key)
 232                         bytes = 0
 233                 }
 234                 select {
 235                 case <-termSignal:
 236                         finished = true
 237                 case <-heartbeat:
 238                         go func() { ethSink <- -1 }()
 239                 case udpPkt = <-udpSink:
 240                         timeouts++
 241                         if !serverMode && timeouts >= timeout {
 242                                 finished = true
 243                         }
 244                         if udpPkt == nil {
 245                                 udpSinkReady <- true
 246                                 continue
 247                         }
 248                         udpPktData = udpBuf[:udpPkt.size]
 249                         if isValidHandshakePkt(udpPktData) {
 250                                 addr = udpPkt.addr.String()
 251                                 state, exists := states[addr]
 252                                 if serverMode {
 253                                         if !exists {
 254                                                 state = &Handshake{addr: udpPkt.addr}
 255                                                 states[addr] = state
 256                                         }
 257                                         p = state.Server(noncediff, conn, key, udpPktData)
 258                                 } else {
 259                                         if !exists {
 260                                                 fmt.Print("[HS?]")
 261                                                 udpSinkReady <- true
 262                                                 continue
 263                                         }
 264                                         p = state.Client(noncediff, conn, key, udpPktData)
 265                                 }
 266                                 if p != nil {
 267                                         fmt.Print("[HS-OK]")
 268                                         if peer == nil {
 269                                                 go ScriptCall(upPath)
 270                                         }
 271                                         peer = p
 272                                         delete(states, addr)
 273                                 }
 274                                 udpSinkReady <- true
 275                                 continue
 276                         }
 277                         if peer == nil {
 278                                 udpSinkReady <- true
 279                                 continue
 280                         }
 281                         nonceRecv, _ = binary.Uvarint(udpPktData[:8])
 282                         if nonceRecv < peer.nonceRecv-noncediff {
 283                                 fmt.Print("R")
 284                                 udpSinkReady <- true
 285                                 continue
 286                         }
 287                         copy(buf[:KeySize], emptyKey)
 288                         copy(tag[:], udpPktData[udpPkt.size-poly1305.TagSize:])
 289                         copy(buf[S20BS:], udpPktData[NonceSize:udpPkt.size-poly1305.TagSize])
 290                         salsa20.XORKeyStream(
 291                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 292                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 293                                 udpPktData[:NonceSize],
 294                                 peer.key,
 295                         )
 296                         copy(keyAuth[:], buf[:KeySize])
 297                         if !poly1305.Verify(tag, udpPktData[:udpPkt.size-poly1305.TagSize], keyAuth) {
 298                                 udpSinkReady <- true
 299                                 fmt.Print("T")
 300                                 continue
 301                         }
 302                         udpSinkReady <- true
 303                         peer.nonceRecv = nonceRecv
 304                         timeouts = 0
 305                         frame = buf[S20BS : S20BS+udpPkt.size-NonceSize-poly1305.TagSize]
 306                         bytes += len(frame)
 307                         if string(frame[0:HeartBeatSize]) == HeartBeatMark {
 308                                 continue
 309                         }
 310                         if _, err = iface.Write(frame); err != nil {
 311                                 log.Println("Error writing to iface: ", err)
 312                         }
 313                         if verbose {
 314                                 fmt.Print("r")
 315                         }
 316                 case ethPktSize = <-ethSink:
 317                         if ethPktSize > maxIfacePktSize {
 318                                 panic("Too large packet on interface")
 319                         }
 320                         if peer == nil {
 321                                 ethSinkReady <- true
 322                                 continue
 323                         }
 324                         peer.nonceOur = peer.nonceOur + 2
 325                         binary.PutUvarint(nonce, peer.nonceOur)
 326                         copy(buf[:KeySize], emptyKey)
 327                         if ethPktSize > -1 {
 328                                 copy(buf[S20BS:], ethBuf[:ethPktSize])
 329                                 ethSinkReady <- true
 330                         } else {
 331                                 copy(buf[S20BS:], heartbeatMark)
 332                                 ethPktSize = HeartBeatSize
 333                         }
 334                         salsa20.XORKeyStream(buf, buf, nonce, peer.key)
 335                         copy(buf[S20BS-NonceSize:S20BS], nonce)
 336                         copy(keyAuth[:], buf[:KeySize])
 337                         dataToSend = buf[S20BS-NonceSize : S20BS+ethPktSize]
 338                         poly1305.Sum(tag, dataToSend, keyAuth)
 339                         bytes += len(dataToSend)
 340                         if _, err = conn.WriteTo(append(dataToSend, tag[:]...), peer.addr); err != nil {
 341                                 log.Println("Error sending UDP", err)
 342                         }
 343                         if verbose {
 344                                 fmt.Print("w")
 345                         }
 346                 }
 347         }
 348         ScriptCall(downPath)
 349 }