govpn.go

   1 /*
   2 govpn -- simple 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 // 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         log.SetFlags(log.Ldate | log.Lmicroseconds | log.Lshortfile)
 100
 101         // Key decoding
 102         keyData, err := ioutil.ReadFile(*keyPath)
 103         if err != nil {
 104                 panic("Unable to read keyfile: " + err.Error())
 105         }
 106         if len(keyData) < 64 {
 107                 panic("Key must be 64 hex characters long")
 108         }
 109         keyDecoded, err := hex.DecodeString(string(keyData[0:64]))
 110         if err != nil {
 111                 panic("Unable to decode the key: " + err.Error())
 112         }
 113         key := new([KeySize]byte)
 114         copy(key[:], keyDecoded)
 115         keyDecoded = nil
 116         keyData = nil
 117
 118         // Interface listening
 119         maxIfacePktSize := *mtu - poly1305.TagSize - NonceSize
 120         log.Println("Max MTU", maxIfacePktSize, "on interface", *ifaceName)
 121         iface := NewTAP(*ifaceName)
 122         ethBuf := make([]byte, maxIfacePktSize)
 123         ethSink := make(chan int)
 124         ethSinkReady := make(chan bool)
 125         go func() {
 126                 for {
 127                         <-ethSinkReady
 128                         n, err := iface.Read(ethBuf)
 129                         if err != nil {
 130                                 panic(err)
 131                         }
 132                         ethSink <- n
 133                 }
 134         }()
 135         ethSinkReady <- true
 136
 137         // Network address parsing
 138         if (len(*bindAddr) > 1 && len(*remoteAddr) > 1) ||
 139                 (len(*bindAddr) == 0 && len(*remoteAddr) == 0) {
 140                 panic("Either -bind or -remote must be specified only")
 141         }
 142         var conn *net.UDPConn
 143         var remote *net.UDPAddr
 144         serverMode := false
 145         bindTo := "0.0.0.0:0"
 146
 147         if len(*bindAddr) > 1 {
 148                 bindTo = *bindAddr
 149                 serverMode = true
 150         }
 151
 152         bind, err := net.ResolveUDPAddr("udp", bindTo)
 153         if err != nil {
 154                 panic(err)
 155         }
 156         conn, err = net.ListenUDP("udp", bind)
 157         if err != nil {
 158                 panic(err)
 159         }
 160
 161         if len(*remoteAddr) > 1 {
 162                 remote, err = net.ResolveUDPAddr("udp", *remoteAddr)
 163                 if err != nil {
 164                         panic(err)
 165                 }
 166         }
 167
 168         udpBuf := make([]byte, *mtu)
 169         udpSink := make(chan *UDPPkt)
 170         udpSinkReady := make(chan bool)
 171         go func(conn *net.UDPConn) {
 172                 for {
 173                         <-udpSinkReady
 174                         conn.SetReadDeadline(time.Now().Add(time.Second))
 175                         n, addr, err := conn.ReadFromUDP(udpBuf)
 176                         if err != nil {
 177                                 if verbose {
 178                                         fmt.Print("B")
 179                                 }
 180                                 udpSink <- nil
 181                         } else {
 182                                 udpSink <- &UDPPkt{addr, n}
 183                         }
 184                 }
 185         }(conn)
 186         udpSinkReady <- true
 187
 188         // Process packets
 189         var udpPkt *UDPPkt
 190         var udpPktData []byte
 191         var ethPktSize int
 192         var frame []byte
 193         var addr string
 194         var peer *Peer
 195         var p *Peer
 196
 197         timeouts := 0
 198         bytes := 0
 199         states := make(map[string]*Handshake)
 200         nonce := make([]byte, NonceSize)
 201         keyAuth := new([KeySize]byte)
 202         tag := new([poly1305.TagSize]byte)
 203         buf := make([]byte, *mtu+S20BS)
 204         emptyKey := make([]byte, KeySize)
 205
 206         if !serverMode {
 207                 states[remote.String()] = HandshakeStart(conn, remote, key)
 208         }
 209
 210         heartbeat := time.Tick(time.Second * time.Duration(timeout/3))
 211         go func() { <-heartbeat }()
 212         heartbeatMark := []byte(HeartBeatMark)
 213
 214         termSignal := make(chan os.Signal, 1)
 215         signal.Notify(termSignal, os.Interrupt, os.Kill)
 216
 217         finished := false
 218         for {
 219                 if finished {
 220                         break
 221                 }
 222                 if !serverMode && bytes > MaxBytesPerKey {
 223                         states[remote.String()] = HandshakeStart(conn, remote, key)
 224                         bytes = 0
 225                 }
 226                 select {
 227                 case <-termSignal:
 228                         finished = true
 229                 case <-heartbeat:
 230                         go func() { ethSink <- -1 }()
 231                 case udpPkt = <-udpSink:
 232                         timeouts++
 233                         if !serverMode && timeouts >= timeout {
 234                                 finished = true
 235                         }
 236                         if udpPkt == nil {
 237                                 udpSinkReady <- true
 238                                 continue
 239                         }
 240                         udpPktData = udpBuf[:udpPkt.size]
 241                         if isValidHandshakePkt(udpPktData) {
 242                                 addr = udpPkt.addr.String()
 243                                 state, exists := states[addr]
 244                                 if serverMode {
 245                                         if !exists {
 246                                                 state = &Handshake{addr: udpPkt.addr}
 247                                                 states[addr] = state
 248                                         }
 249                                         p = state.Server(noncediff, conn, key, udpPktData)
 250                                 } else {
 251                                         if !exists {
 252                                                 fmt.Print("[HS?]")
 253                                                 udpSinkReady <- true
 254                                                 continue
 255                                         }
 256                                         p = state.Client(noncediff, conn, key, udpPktData)
 257                                 }
 258                                 if p != nil {
 259                                         fmt.Print("[HS-OK]")
 260                                         if peer == nil {
 261                                                 go ScriptCall(upPath)
 262                                         }
 263                                         peer = p
 264                                         delete(states, addr)
 265                                 }
 266                                 udpSinkReady <- true
 267                                 continue
 268                         }
 269                         if peer == nil {
 270                                 udpSinkReady <- true
 271                                 continue
 272                         }
 273                         nonceRecv, _ := binary.Uvarint(udpPktData[:8])
 274                         if nonceRecv < peer.nonceRecv-noncediff {
 275                                 fmt.Print("R")
 276                                 udpSinkReady <- true
 277                                 continue
 278                         }
 279                         copy(buf[:KeySize], emptyKey)
 280                         copy(tag[:], udpPktData[udpPkt.size-poly1305.TagSize:])
 281                         copy(buf[S20BS:], udpPktData[NonceSize:udpPkt.size-poly1305.TagSize])
 282                         salsa20.XORKeyStream(
 283                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 284                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 285                                 udpPktData[:NonceSize],
 286                                 peer.key,
 287                         )
 288                         copy(keyAuth[:], buf[:KeySize])
 289                         if !poly1305.Verify(tag, udpPktData[:udpPkt.size-poly1305.TagSize], keyAuth) {
 290                                 udpSinkReady <- true
 291                                 fmt.Print("T")
 292                                 continue
 293                         }
 294                         udpSinkReady <- true
 295                         peer.nonceRecv = nonceRecv
 296                         timeouts = 0
 297                         frame = buf[S20BS : S20BS+udpPkt.size-NonceSize-poly1305.TagSize]
 298                         bytes += len(frame)
 299                         if string(frame[0:HeartBeatSize]) == HeartBeatMark {
 300                                 continue
 301                         }
 302                         if _, err := iface.Write(frame); err != nil {
 303                                 log.Println("Error writing to iface: ", err)
 304                         }
 305                         if verbose {
 306                                 fmt.Print("r")
 307                         }
 308                 case ethPktSize = <-ethSink:
 309                         if ethPktSize > maxIfacePktSize {
 310                                 panic("Too large packet on interface")
 311                         }
 312                         if peer == nil {
 313                                 ethSinkReady <- true
 314                                 continue
 315                         }
 316                         peer.nonceOur = peer.nonceOur + 2
 317                         binary.PutUvarint(nonce, peer.nonceOur)
 318                         copy(buf[:KeySize], emptyKey)
 319                         if ethPktSize > -1 {
 320                                 copy(buf[S20BS:], ethBuf[:ethPktSize])
 321                                 ethSinkReady <- true
 322                         } else {
 323                                 copy(buf[S20BS:], heartbeatMark)
 324                                 ethPktSize = HeartBeatSize
 325                         }
 326                         salsa20.XORKeyStream(buf, buf, nonce, peer.key)
 327                         copy(buf[S20BS-NonceSize:S20BS], nonce)
 328                         copy(keyAuth[:], buf[:KeySize])
 329                         dataToSend := buf[S20BS-NonceSize : S20BS+ethPktSize]
 330                         poly1305.Sum(tag, dataToSend, keyAuth)
 331                         bytes += len(dataToSend)
 332                         if _, err := conn.WriteTo(append(dataToSend, tag[:]...), peer.addr); err != nil {
 333                                 log.Println("Error sending UDP", err)
 334                         }
 335                         if verbose {
 336                                 fmt.Print("w")
 337                         }
 338                 }
 339         }
 340         ScriptCall(downPath)
 341 }