Handshake negotiation functioning

src/constants.go

@@ -17,5 +17,9 @@ const (
 )
 
 const (
-	QueueOutboundSize = 1024
+	QueueOutboundSize      = 1024
+	QueueInboundSize       = 1024
+	QueueHandshakeSize     = 1024
+	QueueHandshakeBusySize = QueueHandshakeSize / 8
+	MinMessageSize         = MessageTransportSize
 )

src/device.go

@@ -23,7 +23,13 @@ type Device struct {
 	routingTable RoutingTable
 	indices      IndexTable
 	queue        struct {
-		encryption chan *QueueOutboundElement // parallel work queue
+		encryption chan *QueueOutboundElement
+		decryption chan *QueueInboundElement
+		handshake  chan QueueHandshakeElement
+		inbound    chan []byte // inbound queue for TUN
+	}
+	signal struct {
+		stop chan struct{}
 	}
 	peers map[NoisePublicKey]*Peer
 	mac   MacStateDevice
@@ -56,6 +62,7 @@ func NewDevice(tun TUNDevice, logLevel int) *Device {
 	defer device.mutex.Unlock()
 
 	device.log = NewLogger(logLevel)
+	device.mtu = tun.MTU()
 	device.peers = make(map[NoisePublicKey]*Peer)
 	device.indices.Init()
 	device.routingTable.Reset()
@@ -71,13 +78,22 @@ func NewDevice(tun TUNDevice, logLevel int) *Device {
 	// create queues
 
 	device.queue.encryption = make(chan *QueueOutboundElement, QueueOutboundSize)
+	device.queue.handshake = make(chan QueueHandshakeElement, QueueHandshakeSize)
+	device.queue.decryption = make(chan *QueueInboundElement, QueueInboundSize)
+
+	// prepare signals
+
+	device.signal.stop = make(chan struct{})
 
 	// start workers
 
 	for i := 0; i < runtime.NumCPU(); i += 1 {
 		go device.RoutineEncryption()
+		go device.RoutineDecryption()
+		go device.RoutineHandshake()
 	}
 	go device.RoutineReadFromTUN(tun)
+	go device.RoutineReceiveIncomming()
 	return device
 }
 
@@ -115,5 +131,6 @@ func (device *Device) RemoveAllPeers() {
 
 func (device *Device) Close() {
 	device.RemoveAllPeers()
+	close(device.signal.stop)
 	close(device.queue.encryption)
 }

src/handshake.go

@@ -3,7 +3,6 @@ package main
 import (
 	"bytes"
 	"encoding/binary"
-	"net"
 	"sync/atomic"
 	"time"
 )
@@ -24,14 +23,6 @@ func (peer *Peer) SendKeepAlive() bool {
 	return true
 }
 
-func StoppedTimer() *time.Timer {
-	timer := time.NewTimer(time.Hour)
-	if !timer.Stop() {
-		<-timer.C
-	}
-	return timer
-}
-
 /* Called when a new authenticated message has been send
  *
  * TODO: This might be done in a faster way
@@ -71,7 +62,7 @@ func (peer *Peer) RoutineHandshakeInitiator() {
 	device := peer.device
 	buffer := make([]byte, 1024)
 	logger := device.log.Debug
-	timeout := time.NewTimer(time.Hour)
+	timeout := stoppedTimer()
 
 	var work *QueueOutboundElement
 
@@ -129,13 +120,8 @@ func (peer *Peer) RoutineHandshakeInitiator() {
 
 				// set timeout
 
-				if !timeout.Stop() {
-					select {
-					case <-timeout.C:
-					default:
-					}
-				}
 				attempts += 1
+				stopTimer(timeout)
 				timeout.Reset(RekeyTimeout)
 				device.log.Debug.Println("Handshake initiation attempt", attempts, "queued for peer", peer.id)
 
@@ -163,45 +149,3 @@ func (peer *Peer) RoutineHandshakeInitiator() {
 
 	logger.Println("Routine, handshake initator, stopped for peer", peer.id)
 }
-
-/* Handles incomming packets related to handshake
- *
- *
- */
-func (device *Device) HandshakeWorker(queue chan struct {
-	msg     []byte
-	msgType uint32
-	addr    *net.UDPAddr
-}) {
-	for {
-		elem := <-queue
-
-		switch elem.msgType {
-		case MessageInitiationType:
-			if len(elem.msg) != MessageInitiationSize {
-				continue
-			}
-
-			// check for cookie
-
-			var msg MessageInitiation
-
-			binary.Read(nil, binary.LittleEndian, &msg)
-
-		case MessageResponseType:
-			if len(elem.msg) != MessageResponseSize {
-				continue
-			}
-
-			// check for cookie
-
-		case MessageCookieReplyType:
-			if len(elem.msg) != MessageCookieReplySize {
-				continue
-			}
-
-		default:
-			device.log.Error.Println("Invalid message type in handshake queue")
-		}
-	}
-}

src/misc.go

@@ -1,5 +1,9 @@
 package main
 
+import (
+	"time"
+)
+
 func min(a uint, b uint) uint {
 	if a > b {
 		return b
@@ -13,3 +17,18 @@ func sendSignal(c chan struct{}) {
 	default:
 	}
 }
+
+func stopTimer(timer *time.Timer) {
+	if !timer.Stop() {
+		select {
+		case <-timer.C:
+		default:
+		}
+	}
+}
+
+func stoppedTimer() *time.Timer {
+	timer := time.NewTimer(time.Hour)
+	stopTimer(timer)
+	return timer
+}

src/noise_protocol.go

@@ -6,6 +6,7 @@ import (
 	"golang.org/x/crypto/chacha20poly1305"
 	"golang.org/x/crypto/poly1305"
 	"sync"
+	"time"
 )
 
 const (
@@ -34,6 +35,13 @@ const (
 	MessageInitiationSize  = 148
 	MessageResponseSize    = 92
 	MessageCookieReplySize = 64
+	MessageTransportSize   = 16 + poly1305.TagSize // size of empty transport
+)
+
+const (
+	MessageTransportOffsetReceiver = 4
+	MessageTransportOffsetCounter  = 8
+	MessageTransportOffsetContent  = 16
 )
 
 /* Type is an 8-bit field, followed by 3 nul bytes,
@@ -55,7 +63,7 @@ type MessageInitiation struct {
 type MessageResponse struct {
 	Type      uint32
 	Sender    uint32
-	Reciever  uint32
+	Receiver  uint32
 	Ephemeral NoisePublicKey
 	Empty     [poly1305.TagSize]byte
 	Mac1      [blake2s.Size128]byte
@@ -64,7 +72,7 @@ type MessageResponse struct {
 
 type MessageTransport struct {
 	Type     uint32
-	Reciever uint32
+	Receiver uint32
 	Counter  uint64
 	Content  []byte
 }
@@ -292,7 +300,7 @@ func (device *Device) CreateMessageResponse(peer *Peer) (*MessageResponse, error
 	var msg MessageResponse
 	msg.Type = MessageResponseType
 	msg.Sender = handshake.localIndex
-	msg.Reciever = handshake.remoteIndex
+	msg.Receiver = handshake.remoteIndex
 
 	// create ephemeral key
 
@@ -302,6 +310,7 @@ func (device *Device) CreateMessageResponse(peer *Peer) (*MessageResponse, error
 	}
 	msg.Ephemeral = handshake.localEphemeral.publicKey()
 	handshake.mixHash(msg.Ephemeral[:])
+	handshake.mixKey(msg.Ephemeral[:])
 
 	func() {
 		ss := handshake.localEphemeral.sharedSecret(handshake.remoteEphemeral)
@@ -334,7 +343,7 @@ func (device *Device) ConsumeMessageResponse(msg *MessageResponse) *Peer {
 
 	// lookup handshake by reciever
 
-	lookup := device.indices.Lookup(msg.Reciever)
+	lookup := device.indices.Lookup(msg.Receiver)
 	handshake := lookup.handshake
 	if handshake == nil {
 		return nil
@@ -359,7 +368,7 @@ func (device *Device) ConsumeMessageResponse(msg *MessageResponse) *Peer {
 		// finish 3-way DH
 
 		hash = mixHash(handshake.hash, msg.Ephemeral[:])
-		chainKey = handshake.chainKey
+		chainKey = mixKey(handshake.chainKey, msg.Ephemeral[:])
 
 		func() {
 			ss := handshake.localEphemeral.sharedSecret(msg.Ephemeral)
@@ -380,6 +389,7 @@ func (device *Device) ConsumeMessageResponse(msg *MessageResponse) *Peer {
 		aead, _ := chacha20poly1305.New(key[:])
 		_, err := aead.Open(nil, ZeroNonce[:], msg.Empty[:], hash[:])
 		if err != nil {
+			device.log.Debug.Println("failed to open")
 			return false
 		}
 		hash = mixHash(hash, msg.Empty[:])
@@ -438,6 +448,7 @@ func (peer *Peer) NewKeyPair() *KeyPair {
 	keyPair.recv, _ = chacha20poly1305.New(recvKey[:])
 	keyPair.sendNonce = 0
 	keyPair.recvNonce = 0
+	keyPair.created = time.Now()
 
 	// remap index
 

src/peer.go

@@ -37,6 +37,7 @@ type Peer struct {
 	queue struct {
 		nonce    chan []byte                // nonce / pre-handshake queue
 		outbound chan *QueueOutboundElement // sequential ordering of work
+		inbound  chan *QueueInboundElement  // sequential ordering of work
 	}
 	mac MacStatePeer
 }
@@ -47,11 +48,10 @@ func (device *Device) NewPeer(pk NoisePublicKey) *Peer {
 	peer := new(Peer)
 	peer.mutex.Lock()
 	defer peer.mutex.Unlock()
-	peer.device = device
+
 	peer.mac.Init(pk)
-	peer.queue.outbound = make(chan *QueueOutboundElement, QueueOutboundSize)
+	peer.device = device
-	peer.queue.nonce = make(chan []byte, QueueOutboundSize)
+	peer.timer.sendKeepalive = stoppedTimer()
-	peer.timer.sendKeepalive = StoppedTimer()
 
 	// assign id for debugging
 
@@ -76,6 +76,12 @@ func (device *Device) NewPeer(pk NoisePublicKey) *Peer {
 	handshake.precomputedStaticStatic = device.privateKey.sharedSecret(handshake.remoteStatic)
 	handshake.mutex.Unlock()
 
+	// prepare queuing
+
+	peer.queue.nonce = make(chan []byte, QueueOutboundSize)
+	peer.queue.inbound = make(chan *QueueInboundElement, QueueInboundSize)
+	peer.queue.outbound = make(chan *QueueOutboundElement, QueueOutboundSize)
+
 	// prepare signaling
 
 	peer.signal.stop = make(chan struct{})
@@ -89,6 +95,7 @@ func (device *Device) NewPeer(pk NoisePublicKey) *Peer {
 	go peer.RoutineNonce()
 	go peer.RoutineHandshakeInitiator()
 	go peer.RoutineSequentialSender()
+	go peer.RoutineSequentialReceiver()
 
 	return peer
 }

src/receive.go

@@ -0,0 +1,404 @@
+package main
+
+import (
+	"bytes"
+	"encoding/binary"
+	"golang.org/x/crypto/chacha20poly1305"
+	"net"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+const (
+	ElementStateOkay = iota
+	ElementStateDropped
+)
+
+type QueueHandshakeElement struct {
+	msgType uint32
+	packet  []byte
+	source  *net.UDPAddr
+}
+
+type QueueInboundElement struct {
+	state   uint32
+	mutex   sync.Mutex
+	packet  []byte
+	counter uint64
+	keyPair *KeyPair
+}
+
+func (elem *QueueInboundElement) Drop() {
+	atomic.StoreUint32(&elem.state, ElementStateDropped)
+	elem.mutex.Unlock()
+}
+
+func (device *Device) RoutineReceiveIncomming() {
+	var packet []byte
+
+	debugLog := device.log.Debug
+	debugLog.Println("Routine, receive incomming, started")
+
+	errorLog := device.log.Error
+
+	for {
+
+		// check if stopped
+
+		select {
+		case <-device.signal.stop:
+			return
+		default:
+		}
+
+		// read next datagram
+
+		if packet == nil {
+			packet = make([]byte, 1<<16)
+		}
+
+		device.net.mutex.RLock()
+		conn := device.net.conn
+		device.net.mutex.RUnlock()
+
+		conn.SetReadDeadline(time.Now().Add(time.Second))
+
+		size, raddr, err := conn.ReadFromUDP(packet)
+		if err != nil {
+			continue
+		}
+		if size < MinMessageSize {
+			continue
+		}
+
+		// handle packet
+
+		packet = packet[:size]
+		msgType := binary.LittleEndian.Uint32(packet[:4])
+
+		func() {
+			switch msgType {
+
+			case MessageInitiationType, MessageResponseType:
+
+				// verify mac1
+
+				if !device.mac.CheckMAC1(packet) {
+					debugLog.Println("Received packet with invalid mac1")
+					return
+				}
+
+				// check if busy, TODO: refine definition of "busy"
+
+				busy := len(device.queue.handshake) > QueueHandshakeBusySize
+				if busy && !device.mac.CheckMAC2(packet, raddr) {
+					sender := binary.LittleEndian.Uint32(packet[4:8]) // "sender" follows "type"
+					reply, err := device.CreateMessageCookieReply(packet, sender, raddr)
+					if err != nil {
+						errorLog.Println("Failed to create cookie reply:", err)
+						return
+					}
+					writer := bytes.NewBuffer(packet[:0])
+					binary.Write(writer, binary.LittleEndian, reply)
+					packet = writer.Bytes()
+					_, err = device.net.conn.WriteToUDP(packet, raddr)
+					if err != nil {
+						debugLog.Println("Failed to send cookie reply:", err)
+					}
+					return
+				}
+
+				// add to handshake queue
+
+				device.queue.handshake <- QueueHandshakeElement{
+					msgType: msgType,
+					packet:  packet,
+					source:  raddr,
+				}
+
+			case MessageCookieReplyType:
+
+				// verify and update peer cookie state
+
+				if len(packet) != MessageCookieReplySize {
+					return
+				}
+
+				var reply MessageCookieReply
+				reader := bytes.NewReader(packet)
+				err := binary.Read(reader, binary.LittleEndian, &reply)
+				if err != nil {
+					debugLog.Println("Failed to decode cookie reply")
+					return
+				}
+				device.ConsumeMessageCookieReply(&reply)
+
+			case MessageTransportType:
+
+				debugLog.Println("DEBUG: Got transport")
+
+				// lookup key pair
+
+				if len(packet) < MessageTransportSize {
+					return
+				}
+
+				receiver := binary.LittleEndian.Uint32(
+					packet[MessageTransportOffsetReceiver:MessageTransportOffsetCounter],
+				)
+				value := device.indices.Lookup(receiver)
+				keyPair := value.keyPair
+				if keyPair == nil {
+					return
+				}
+
+				// check key-pair expiry
+
+				if keyPair.created.Add(RejectAfterTime).Before(time.Now()) {
+					return
+				}
+
+				// add to peer queue
+
+				peer := value.peer
+				work := new(QueueInboundElement)
+				work.packet = packet
+				work.keyPair = keyPair
+				work.state = ElementStateOkay
+				work.mutex.Lock()
+
+				// add to parallel decryption queue
+
+				func() {
+					for {
+						select {
+						case device.queue.decryption <- work:
+							return
+						default:
+							select {
+							case elem := <-device.queue.decryption:
+								elem.Drop()
+							default:
+							}
+						}
+					}
+				}()
+
+				// add to sequential inbound queue
+
+				func() {
+					for {
+						select {
+						case peer.queue.inbound <- work:
+							break
+						default:
+							select {
+							case elem := <-peer.queue.inbound:
+								elem.Drop()
+							default:
+							}
+						}
+					}
+				}()
+
+			default:
+				// unknown message type
+			}
+		}()
+	}
+}
+
+func (device *Device) RoutineDecryption() {
+	var elem *QueueInboundElement
+	var nonce [chacha20poly1305.NonceSize]byte
+
+	for {
+		select {
+		case elem = <-device.queue.decryption:
+		case <-device.signal.stop:
+			return
+		}
+
+		// check if dropped
+
+		state := atomic.LoadUint32(&elem.state)
+		if state != ElementStateOkay {
+			continue
+		}
+
+		// split message into fields
+
+		counter := binary.LittleEndian.Uint64(
+			elem.packet[MessageTransportOffsetCounter:MessageTransportOffsetContent],
+		)
+		content := elem.packet[MessageTransportOffsetContent:]
+
+		// decrypt with key-pair
+
+		var err error
+		binary.LittleEndian.PutUint64(nonce[4:], counter)
+		elem.packet, err = elem.keyPair.recv.Open(elem.packet[:0], nonce[:], content, nil)
+		if err != nil {
+			elem.Drop()
+			continue
+		}
+
+		// release to consumer
+
+		elem.counter = counter
+		elem.mutex.Unlock()
+	}
+}
+
+/* Handles incomming packets related to handshake
+ *
+ *
+ */
+func (device *Device) RoutineHandshake() {
+
+	logInfo := device.log.Info
+	logError := device.log.Error
+	logDebug := device.log.Debug
+
+	var elem QueueHandshakeElement
+
+	for {
+		select {
+		case elem = <-device.queue.handshake:
+		case <-device.signal.stop:
+			return
+		}
+
+		func() {
+
+			switch elem.msgType {
+			case MessageInitiationType:
+
+				// unmarshal
+
+				if len(elem.packet) != MessageInitiationSize {
+					return
+				}
+
+				var msg MessageInitiation
+				reader := bytes.NewReader(elem.packet)
+				err := binary.Read(reader, binary.LittleEndian, &msg)
+				if err != nil {
+					logError.Println("Failed to decode initiation message")
+					return
+				}
+
+				// consume initiation
+
+				peer := device.ConsumeMessageInitiation(&msg)
+				if peer == nil {
+					logInfo.Println(
+						"Recieved invalid initiation message from",
+						elem.source.IP.String(),
+						elem.source.Port,
+					)
+					return
+				}
+				logDebug.Println("Recieved valid initiation message for peer", peer.id)
+
+			case MessageResponseType:
+
+				// unmarshal
+
+				if len(elem.packet) != MessageResponseSize {
+					return
+				}
+
+				var msg MessageResponse
+				reader := bytes.NewReader(elem.packet)
+				err := binary.Read(reader, binary.LittleEndian, &msg)
+				if err != nil {
+					logError.Println("Failed to decode response message")
+					return
+				}
+
+				// consume response
+
+				peer := device.ConsumeMessageResponse(&msg)
+				if peer == nil {
+					logInfo.Println(
+						"Recieved invalid response message from",
+						elem.source.IP.String(),
+						elem.source.Port,
+					)
+					return
+				}
+				sendSignal(peer.signal.handshakeCompleted)
+				logDebug.Println("Recieved valid response message for peer", peer.id)
+				peer.NewKeyPair()
+				peer.SendKeepAlive()
+
+			default:
+				device.log.Error.Println("Invalid message type in handshake queue")
+			}
+
+		}()
+	}
+}
+
+func (peer *Peer) RoutineSequentialReceiver() {
+	var elem *QueueInboundElement
+
+	device := peer.device
+	logDebug := device.log.Debug
+
+	logDebug.Println("Routine, sequential receiver, started for peer", peer.id)
+
+	for {
+		// wait for decryption
+
+		select {
+		case <-peer.signal.stop:
+			return
+		case elem = <-peer.queue.inbound:
+		}
+		elem.mutex.Lock()
+
+		// check if dropped
+
+		logDebug.Println("MESSSAGE:", elem)
+
+		state := atomic.LoadUint32(&elem.state)
+		if state != ElementStateOkay {
+			continue
+		}
+
+		// check for replay
+
+		// check for keep-alive
+
+		if len(elem.packet) == 0 {
+			continue
+		}
+
+		// insert into inbound TUN queue
+
+		device.queue.inbound <- elem.packet
+	}
+
+}
+
+func (device *Device) RoutineWriteToTUN(tun TUNDevice) {
+	for {
+		var packet []byte
+
+		select {
+		case <-device.signal.stop:
+		case packet = <-device.queue.inbound:
+		}
+
+		device.log.Debug.Println("GOT:", packet)
+
+		size, err := tun.Write(packet)
+		device.log.Debug.Println("DEBUG:", size, err)
+		if err != nil {
+
+		}
+	}
+}

src/send.go

@@ -27,6 +27,7 @@ import (
  * workers release lock when they have completed work on the packet.
  */
 type QueueOutboundElement struct {
+	state   uint32
 	mutex   sync.Mutex
 	packet  []byte
 	nonce   uint64
@@ -59,6 +60,14 @@ func (peer *Peer) InsertOutbound(elem *QueueOutboundElement) {
 	}
 }
 
+func (elem *QueueOutboundElement) Drop() {
+	atomic.StoreUint32(&elem.state, ElementStateDropped)
+}
+
+func (elem *QueueOutboundElement) IsDropped() bool {
+	return atomic.LoadUint32(&elem.state) == ElementStateDropped
+}
+
 /* Reads packets from the TUN and inserts
  * into nonce queue for peer
  *
@@ -162,6 +171,8 @@ func (peer *Peer) RoutineNonce() {
 				}
 			}
 
+			logger.Println("PACKET:", packet)
+
 			// wait for key pair
 
 			for {
@@ -176,6 +187,7 @@ func (peer *Peer) RoutineNonce() {
 						break
 					}
 				}
+				logger.Println("Key pair:", keyPair)
 
 				sendSignal(peer.signal.handshakeBegin)
 				logger.Println("Waiting for key-pair, peer", peer.id)
@@ -205,10 +217,12 @@ func (peer *Peer) RoutineNonce() {
 				work := new(QueueOutboundElement) // TODO: profile, maybe use pool
 				work.keyPair = keyPair
 				work.packet = packet
-				work.nonce = atomic.AddUint64(&keyPair.sendNonce, 1)
+				work.nonce = atomic.AddUint64(&keyPair.sendNonce, 1) - 1
 				work.peer = peer
 				work.mutex.Lock()
 
+				logger.Println("WORK:", work)
+
 				packet = nil
 
 				// drop packets until there is space
@@ -219,9 +233,11 @@ func (peer *Peer) RoutineNonce() {
 						case peer.device.queue.encryption <- work:
 							return
 						default:
-							drop := <-peer.device.queue.encryption
+							select {
-							drop.packet = nil
+							case elem := <-peer.device.queue.encryption:
-							drop.mutex.Unlock()
+								elem.Drop()
+							default:
+							}
 						}
 					}
 				}()
@@ -241,18 +257,22 @@ func (peer *Peer) RoutineNonce() {
 func (device *Device) RoutineEncryption() {
 	var nonce [chacha20poly1305.NonceSize]byte
 	for work := range device.queue.encryption {
+		if work.IsDropped() {
+			continue
+		}
 
 		// pad packet
 
 		padding := device.mtu - len(work.packet)
 		if padding < 0 {
-			// drop
+			work.Drop()
-			work.packet = nil
+			continue
-			work.mutex.Unlock()
 		}
+
 		for n := 0; n < padding; n += 1 {
 			work.packet = append(work.packet, 0)
 		}
+		device.log.Debug.Println(work.packet)
 
 		// encrypt
 
@@ -288,6 +308,9 @@ func (peer *Peer) RoutineSequentialSender() {
 			logger.Println("Routine, sequential sender, stopped for peer", peer.id)
 			return
 		case work := <-peer.queue.outbound:
+			if work.IsDropped() {
+				continue
+			}
 			work.mutex.Lock()
 			func() {
 				if work.packet == nil {
@@ -310,10 +333,12 @@ func (peer *Peer) RoutineSequentialSender() {
 					return
 				}
 
-				logger.Println("Sending packet for peer", peer.id, work.packet)
+				logger.Println(work.packet)
 
 				_, err := device.net.conn.WriteToUDP(work.packet, peer.endpoint)
-				logger.Println("SEND:", peer.endpoint, err)
+				if err != nil {
+					return
+				}
 				atomic.AddUint64(&peer.tx_bytes, uint64(len(work.packet)))
 
 				// shift keep-alive timer
@@ -323,7 +348,6 @@ func (peer *Peer) RoutineSequentialSender() {
 					peer.timer.sendKeepalive.Reset(interval)
 				}
 			}()
-			work.mutex.Unlock()
 		}
 	}
 }

src/tun.go

@@ -4,5 +4,5 @@ type TUNDevice interface {
 	Read([]byte) (int, error)
 	Write([]byte) (int, error)
 	Name() string
-	MTU() uint
+	MTU() int
 }

src/tun_linux.go

@@ -24,14 +24,14 @@ const (
 type NativeTun struct {
 	fd   *os.File
 	name string
-	mtu  uint
+	mtu  int
 }
 
 func (tun *NativeTun) Name() string {
 	return tun.name
 }
 
-func (tun *NativeTun) MTU() uint {
+func (tun *NativeTun) MTU() int {
 	return tun.mtu
 }