feat: awg 3.1 features

* add RandomTrailers feature which appends random amount of bytes to the
end of each packet
* add DisableCookie feature which prohibits interface to send any cookie
replies

device/constants.go

@@ -24,6 +24,7 @@ const (
 	CookieRefreshTime       = time.Second * 120
 	HandshakeInitationRate  = time.Second / 50
 	PaddingMultiple         = 16
+	DefaultUdpWindow        = 500
 )
 
 const (

device/device.go

@@ -126,6 +126,9 @@ type Device struct {
 		keepaliveTimeoutSec AtomicUintRange
 		maxHandshakeAttemps AtomicUintRange
 	}
+
+	randomTrailers atomic.Bool
+	disableCookies atomic.Bool
 }
 
 // deviceState represents the state of a Device.

device/peer.go

@@ -57,6 +57,7 @@ type Peer struct {
 	cookieGenerator             CookieGenerator
 	trieEntries                 list.List
 	persistentKeepaliveInterval AtomicUintRange
+	udpWindow                   atomic.Uint32
 }
 
 func (device *Device) NewPeer(pk NoisePublicKey) (*Peer, error) {
@@ -79,6 +80,8 @@ func (device *Device) NewPeer(pk NoisePublicKey) (*Peer, error) {
 	// create peer
 	peer := new(Peer)
 
+	peer.udpWindow.Store(DefaultUdpWindow)
+
 	peer.cookieGenerator.Init(pk)
 	peer.device = device
 	peer.queue.outbound = newAutodrainingOutboundQueue(device)
@@ -283,6 +286,9 @@ func (peer *Peer) SetEndpointFromPacket(endpoint conn.Endpoint) {
 	if peer.endpoint.disableRoaming {
 		return
 	}
+	if peer.endpoint.val != endpoint {
+		peer.udpWindow.Store(DefaultUdpWindow)
+	}
 	peer.endpoint.clearSrcOnTx = false
 	peer.endpoint.val = endpoint
 }

device/receive.go

@@ -154,8 +154,12 @@ func (device *Device) RoutineReceiveIncoming(
 			}
 
 			// get message padding and type based on information from S1-S4 and H1-H4
-			msgType, padding := device.DeterminePacketTypeAndPadding(packet, MessageUnknownType, typeHash)
+			msgSize, msgType, padding := device.DeterminePacketTypeAndPadding(packet, typeHash)
+
 			packet = packet[padding:]
+			if msgType != MessageTransportType {
+				packet = packet[:msgSize]
+			}
 
 			if cip != nil {
 				applyHash(packet[:4], packet[:4], typeHash)
@@ -510,6 +514,11 @@ func (peer *Peer) RoutineSequentialReceiver(maxBatchSize int) {
 			}
 			rxBytesLen += uint64(len(elem.packet) + MinMessageSize)
 
+			udpWindow := elem.padding + MessageTransportHeaderSize + uint32(len(elem.packet))
+			if peer.udpWindow.Load() < udpWindow {
+				peer.udpWindow.Store(udpWindow)
+			}
+
 			if len(elem.packet) == 0 || elem.packet[0] == 0 {
 				device.log.Verbosef("%v - Receiving keepalive packet", peer)
 				continue
@@ -558,7 +567,7 @@ func (peer *Peer) RoutineSequentialReceiver(maxBatchSize int) {
 				continue
 			}
 
-			bufs = append(bufs, elem.buffer[int(elem.padding):int(elem.padding)+MessageTransportOffsetContent+len(elem.packet)])
+			bufs = append(bufs, elem.buffer[int(elem.padding):int(elem.padding)+MessageTransportHeaderSize+len(elem.packet)])
 		}
 
 		peer.rxBytes.Add(rxBytesLen)
@@ -592,57 +601,58 @@ func applyHash(dst, src, hash []byte) {
 	}
 }
 
-func (device *Device) DeterminePacketTypeAndPadding(packet []byte, expectedType uint32, typeHash []byte) (uint32, uint32) {
+func (device *Device) DeterminePacketTypeAndPadding(packet []byte, typeHash []byte) (int, uint32, uint32) {
 	var headerBytes [4]byte
+	var padding uint32
+	var header UintRange
+	var expectedSize int
+
 	size := len(packet)
+	randomTrailers := device.randomTrailers.Load()
 
-	if expectedType == MessageUnknownType || expectedType == MessageInitiationType {
-		padding := device.paddings.init.Load()
-		header := device.headers.init.Load()
+	padding = device.paddings.init.Load()
+	header = device.headers.init.Load()
+	expectedSize = int(padding) + MessageInitiationSize
 
-		if size == int(padding)+MessageInitiationSize {
-			applyHash(headerBytes[:], packet[padding:padding+4], typeHash)
-			if header.Contains(binary.LittleEndian.Uint32(headerBytes[:])) {
-				return MessageInitiationType, padding
-			}
+	if size == expectedSize || randomTrailers && size > expectedSize {
+		applyHash(headerBytes[:], packet[padding:padding+4], typeHash)
+		if header.Contains(binary.LittleEndian.Uint32(headerBytes[:])) {
+			return MessageInitiationSize, MessageInitiationType, padding
 		}
 	}
 
-	if expectedType == MessageUnknownType || expectedType == MessageResponseType {
-		padding := device.paddings.response.Load()
-		header := device.headers.response.Load()
+	padding = device.paddings.response.Load()
+	header = device.headers.response.Load()
+	expectedSize = int(padding) + MessageResponseSize
 
-		if size == int(padding)+MessageResponseSize {
-			applyHash(headerBytes[:], packet[padding:padding+4], typeHash)
-			if header.Contains(binary.LittleEndian.Uint32(headerBytes[:])) {
-				return MessageResponseType, padding
-			}
+	if size == expectedSize || randomTrailers && size > expectedSize {
+		applyHash(headerBytes[:], packet[padding:padding+4], typeHash)
+		if header.Contains(binary.LittleEndian.Uint32(headerBytes[:])) {
+			return MessageResponseSize, MessageResponseType, padding
 		}
 	}
 
-	if expectedType == MessageUnknownType || expectedType == MessageCookieReplyType {
-		padding := device.paddings.cookie.Load()
-		header := device.headers.cookie.Load()
+	padding = device.paddings.cookie.Load()
+	header = device.headers.cookie.Load()
+	expectedSize = int(padding) + MessageCookieReplySize
 
-		if size == int(padding)+MessageCookieReplySize {
-			applyHash(headerBytes[:], packet[padding:padding+4], typeHash)
-			if header.Contains(binary.LittleEndian.Uint32(headerBytes[:])) {
-				return MessageCookieReplyType, padding
-			}
+	if size == expectedSize || randomTrailers && size > expectedSize {
+		applyHash(headerBytes[:], packet[padding:padding+4], typeHash)
+		if header.Contains(binary.LittleEndian.Uint32(headerBytes[:])) {
+			return MessageCookieReplySize, MessageCookieReplyType, padding
 		}
 	}
 
-	if expectedType == MessageUnknownType || expectedType == MessageTransportType {
-		padding := device.paddings.transport.Load()
-		header := device.headers.transport.Load()
+	padding = device.paddings.transport.Load()
+	header = device.headers.transport.Load()
+	expectedSize = int(padding) + MessageTransportSize
 
-		if size >= int(padding)+MessageTransportHeaderSize {
-			applyHash(headerBytes[:], packet[padding:padding+4], typeHash)
-			if header.Contains(binary.LittleEndian.Uint32(headerBytes[:])) {
-				return MessageTransportType, padding
-			}
+	if size >= expectedSize {
+		applyHash(headerBytes[:], packet[padding:padding+4], typeHash)
+		if header.Contains(binary.LittleEndian.Uint32(headerBytes[:])) {
+			return MessageTransportSize, MessageTransportType, padding
 		}
 	}
 
-	return MessageUnknownType, 0
+	return 0, MessageUnknownType, 0
 }

device/send.go

@@ -146,8 +146,10 @@ func (peer *Peer) SendHandshakeInitiation(isRetry bool) error {
 
 	sendBuffer = append(sendBuffer, peer.device.JunkPackets()...)
 
-	padding := peer.device.paddings.init.Load()
-	buf := make([]byte, padding+MessageInitiationSize)
+	padding := int(peer.device.paddings.init.Load())
+	trailerLen := max(peer.randomTrailer(padding+MessageInitiationSize), 0)
+
+	buf := make([]byte, padding+MessageInitiationSize+trailerLen)
 
 	crypt := buf[:padding]
 	rand.Read(crypt)
@@ -168,6 +170,9 @@ func (peer *Peer) SendHandshakeInitiation(isRetry bool) error {
 		cip.XORKeyStream(packet, packet)
 	}
 
+	trailer := buf[padding+MessageInitiationSize:]
+	rand.Read(trailer)
+
 	sendBuffer = append(sendBuffer, buf)
 	err = peer.SendBuffers(sendBuffer)
 	if err != nil {
@@ -191,8 +196,10 @@ func (peer *Peer) SendHandshakeResponse() error {
 		return err
 	}
 
-	padding := peer.device.paddings.response.Load()
-	buf := make([]byte, padding+MessageResponseSize)
+	padding := int(peer.device.paddings.response.Load())
+	trailerLen := max(peer.randomTrailer(padding+MessageResponseSize), 0)
+
+	buf := make([]byte, padding+MessageResponseSize+trailerLen)
 
 	crypt := buf[:padding]
 	rand.Read(crypt)
@@ -220,6 +227,9 @@ func (peer *Peer) SendHandshakeResponse() error {
 		cip.XORKeyStream(packet, packet)
 	}
 
+	trailer := buf[padding+MessageResponseSize:]
+	rand.Read(trailer)
+
 	// TODO: allocation could be avoided
 	err = peer.SendBuffers([][]byte{buf})
 	if err != nil {
@@ -229,6 +239,11 @@ func (peer *Peer) SendHandshakeResponse() error {
 }
 
 func (device *Device) SendHandshakeCookie(initiatingElem *QueueHandshakeElement) error {
+	if device.disableCookies.Load() {
+		device.log.Verbosef("Sending cookie response blocked for %v due to disabled cookies", initiatingElem.endpoint.DstToString())
+		return nil
+	}
+
 	device.log.Verbosef("Sending cookie response for denied handshake message for %v", initiatingElem.endpoint.DstToString())
 
 	sender := binary.LittleEndian.Uint32(initiatingElem.packet[4:8])
@@ -245,8 +260,10 @@ func (device *Device) SendHandshakeCookie(initiatingElem *QueueHandshakeElement)
 		return err
 	}
 
-	padding := device.paddings.cookie.Load()
-	buf := make([]byte, padding+MessageCookieReplySize)
+	padding := int(device.paddings.cookie.Load())
+	trailerLen := max(device.randomTrailer(padding+MessageCookieReplySize), 0)
+
+	buf := make([]byte, padding+MessageCookieReplySize, trailerLen)
 
 	crypt := buf[:padding]
 	rand.Read(crypt)
@@ -263,6 +280,9 @@ func (device *Device) SendHandshakeCookie(initiatingElem *QueueHandshakeElement)
 		cip.XORKeyStream(packet, packet)
 	}
 
+	trailer := buf[padding+MessageCookieReplySize:]
+	rand.Read(trailer)
+
 	// TODO: allocation could be avoided
 	device.net.bind.Send([][]byte{buf}, initiatingElem.endpoint)
 	return nil
@@ -531,6 +551,29 @@ func (device *Device) randomPaddingAddition(packetSize, mtu int) int {
 	return add
 }
 
+func (device *Device) randomTrailer(packetSize int) int {
+	if !device.randomTrailers.Load() {
+		return -1
+	}
+
+	if DefaultUdpWindow < packetSize {
+		return 0
+	}
+	return int(fastrandn(uint32(DefaultUdpWindow - packetSize)))
+}
+
+func (peer *Peer) randomTrailer(packetSize int) int {
+	if !peer.device.randomTrailers.Load() {
+		return -1
+	}
+
+	udpWindow := int(peer.udpWindow.Load())
+	if udpWindow < packetSize {
+		return 0
+	}
+	return int(fastrandn(uint32(udpWindow - packetSize)))
+}
+
 /* Encrypts the elements in the queue
  * and marks them for sequential consumption (by releasing the mutex)
  *
@@ -544,6 +587,11 @@ func (device *Device) RoutineEncryption(id int) {
 
 	for elemsContainer := range device.queue.encryption.c {
 		for _, elem := range elemsContainer.elems {
+			udpWindow := elem.padding + MinMessageSize + uint32(len(elem.packet))
+			if elem.peer.udpWindow.Load() < udpWindow {
+				elem.peer.udpWindow.Store(udpWindow)
+			}
+
 			// fill crypto padding
 			crypt := elem.buffer[:elem.padding]
 			rand.Read(crypt)
@@ -563,6 +611,9 @@ func (device *Device) RoutineEncryption(id int) {
 			mtu := int(device.tun.mtu.Load())
 
 			paddingSize := device.randomPaddingAddition(packetSize, mtu)
+			if paddingSize < 0 {
+				paddingSize = elem.peer.randomTrailer(packetSize + MinMessageSize + int(elem.padding))
+			}
 			if paddingSize < 0 {
 				// pad content to multiple of 16
 				paddingSize = calculatePaddingSize(packetSize, mtu)

device/uapi.go

@@ -70,6 +70,18 @@ func (device *Device) IpcGetOperation(w io.Writer) error {
 		}
 		buf.WriteByte('\n')
 	}
+	boolf := func(prefix string, val bool) {
+		buf.Grow(3 + len(prefix))
+		buf.WriteString(prefix)
+		buf.WriteByte('=')
+		if val {
+			buf.WriteByte('1')
+		} else {
+			buf.WriteByte('0')
+		}
+		buf.WriteByte('\n')
+
+	}
 
 	func() {
 		// lock required resources
@@ -173,6 +185,8 @@ func (device *Device) IpcGetOperation(w io.Writer) error {
 		if rang := device.timings.maxHandshakeAttemps.Load(); !rang.IsZero() {
 			sendf("max_handshake_attempts=%s", rang.ToString())
 		}
+		boolf("random_trailers", device.randomTrailers.Load())
+		boolf("disable_cookies", device.disableCookies.Load())
 
 		for _, peer := range device.peers.keyMap {
 			// Serialize peer state.
@@ -513,6 +527,22 @@ func (device *Device) handleDeviceLine(ipcDev *ipcSetDevice, key, value string)
 		device.log.Verbosef("UAPI: Updating max handshake attempts")
 		device.timings.maxHandshakeAttemps.Store(rang)
 
+	case "random_trailers":
+		val, err := strconv.ParseBool(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse random trailers: %w", err)
+		}
+		device.log.Verbosef("UAPI: Updating random trailers")
+		device.randomTrailers.Store(val)
+
+	case "disable_cookies":
+		val, err := strconv.ParseBool(value)
+		if err != nil {
+			return ipcErrorf(ipc.IpcErrorInvalid, "failed to parse disable cookies: %w", err)
+		}
+		device.log.Verbosef("UAPI: Updating disable cookies")
+		device.disableCookies.Store(val)
+
 	default:
 		return ipcErrorf(ipc.IpcErrorInvalid, "invalid UAPI device key: %v", key)
 	}