1 files changed, 642 insertions, 0 deletions
diff --git a/receive.go b/receive.go
new file mode 100644
index 0000000..1f44df2
--- /dev/null
+++ b/receive.go
@@ -0,0 +1,642 @@
+package main
+
+import (
+	"bytes"
+	"encoding/binary"
+	"golang.org/x/crypto/chacha20poly1305"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+	"net"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+type QueueHandshakeElement struct {
+	msgType  uint32
+	packet   []byte
+	endpoint Endpoint
+	buffer   *[MaxMessageSize]byte
+}
+
+type QueueInboundElement struct {
+	dropped  int32
+	mutex    sync.Mutex
+	buffer   *[MaxMessageSize]byte
+	packet   []byte
+	counter  uint64
+	keyPair  *KeyPair
+	endpoint Endpoint
+}
+
+func (elem *QueueInboundElement) Drop() {
+	atomic.StoreInt32(&elem.dropped, AtomicTrue)
+}
+
+func (elem *QueueInboundElement) IsDropped() bool {
+	return atomic.LoadInt32(&elem.dropped) == AtomicTrue
+}
+
+func (device *Device) addToInboundQueue(
+	queue chan *QueueInboundElement,
+	element *QueueInboundElement,
+) {
+	for {
+		select {
+		case queue <- element:
+			return
+		default:
+			select {
+			case old := <-queue:
+				old.Drop()
+			default:
+			}
+		}
+	}
+}
+
+func (device *Device) addToDecryptionQueue(
+	queue chan *QueueInboundElement,
+	element *QueueInboundElement,
+) {
+	for {
+		select {
+		case queue <- element:
+			return
+		default:
+			select {
+			case old := <-queue:
+				// drop & release to potential consumer
+				old.Drop()
+				old.mutex.Unlock()
+			default:
+			}
+		}
+	}
+}
+
+func (device *Device) addToHandshakeQueue(
+	queue chan QueueHandshakeElement,
+	element QueueHandshakeElement,
+) {
+	for {
+		select {
+		case queue <- element:
+			return
+		default:
+			select {
+			case elem := <-queue:
+				device.PutMessageBuffer(elem.buffer)
+			default:
+			}
+		}
+	}
+}
+
+/* Receives incoming datagrams for the device
+ *
+ * Every time the bind is updated a new routine is started for
+ * IPv4 and IPv6 (separately)
+ */
+func (device *Device) RoutineReceiveIncoming(IP int, bind Bind) {
+
+	logDebug := device.log.Debug
+	logDebug.Println("Routine, receive incoming, IP version:", IP)
+
+	// receive datagrams until conn is closed
+
+	buffer := device.GetMessageBuffer()
+
+	var (
+		err      error
+		size     int
+		endpoint Endpoint
+	)
+
+	for {
+
+		// read next datagram
+
+		switch IP {
+		case ipv4.Version:
+			size, endpoint, err = bind.ReceiveIPv4(buffer[:])
+		case ipv6.Version:
+			size, endpoint, err = bind.ReceiveIPv6(buffer[:])
+		default:
+			panic("invalid IP version")
+		}
+
+		if err != nil {
+			return
+		}
+
+		if size < MinMessageSize {
+			continue
+		}
+
+		// check size of packet
+
+		packet := buffer[:size]
+		msgType := binary.LittleEndian.Uint32(packet[:4])
+
+		var okay bool
+
+		switch msgType {
+
+		// check if transport
+
+		case MessageTransportType:
+
+			// check size
+
+			if len(packet) < MessageTransportType {
+				continue
+			}
+
+			// lookup key pair
+
+			receiver := binary.LittleEndian.Uint32(
+				packet[MessageTransportOffsetReceiver:MessageTransportOffsetCounter],
+			)
+			value := device.indices.Lookup(receiver)
+			keyPair := value.keyPair
+			if keyPair == nil {
+				continue
+			}
+
+			// check key-pair expiry
+
+			if keyPair.created.Add(RejectAfterTime).Before(time.Now()) {
+				continue
+			}
+
+			// create work element
+
+			peer := value.peer
+			elem := &QueueInboundElement{
+				packet:   packet,
+				buffer:   buffer,
+				keyPair:  keyPair,
+				dropped:  AtomicFalse,
+				endpoint: endpoint,
+			}
+			elem.mutex.Lock()
+
+			// add to decryption queues
+
+			if peer.isRunning.Get() {
+				device.addToDecryptionQueue(device.queue.decryption, elem)
+				device.addToInboundQueue(peer.queue.inbound, elem)
+				buffer = device.GetMessageBuffer()
+			}
+
+			continue
+
+		// otherwise it is a fixed size & handshake related packet
+
+		case MessageInitiationType:
+			okay = len(packet) == MessageInitiationSize
+
+		case MessageResponseType:
+			okay = len(packet) == MessageResponseSize
+
+		case MessageCookieReplyType:
+			okay = len(packet) == MessageCookieReplySize
+		}
+
+		if okay {
+			device.addToHandshakeQueue(
+				device.queue.handshake,
+				QueueHandshakeElement{
+					msgType:  msgType,
+					buffer:   buffer,
+					packet:   packet,
+					endpoint: endpoint,
+				},
+			)
+			buffer = device.GetMessageBuffer()
+		}
+	}
+}
+
+func (device *Device) RoutineDecryption() {
+
+	var nonce [chacha20poly1305.NonceSize]byte
+
+	logDebug := device.log.Debug
+	logDebug.Println("Routine, decryption, started for device")
+
+	for {
+		select {
+		case <-device.signal.stop.Wait():
+			logDebug.Println("Routine, decryption worker, stopped")
+			return
+
+		case elem := <-device.queue.decryption:
+
+			// check if dropped
+
+			if elem.IsDropped() {
+				continue
+			}
+
+			// split message into fields
+
+			counter := elem.packet[MessageTransportOffsetCounter:MessageTransportOffsetContent]
+			content := elem.packet[MessageTransportOffsetContent:]
+
+			// expand nonce
+
+			nonce[0x4] = counter[0x0]
+			nonce[0x5] = counter[0x1]
+			nonce[0x6] = counter[0x2]
+			nonce[0x7] = counter[0x3]
+
+			nonce[0x8] = counter[0x4]
+			nonce[0x9] = counter[0x5]
+			nonce[0xa] = counter[0x6]
+			nonce[0xb] = counter[0x7]
+
+			// decrypt and release to consumer
+
+			var err error
+			elem.counter = binary.LittleEndian.Uint64(counter)
+			elem.packet, err = elem.keyPair.receive.Open(
+				content[:0],
+				nonce[:],
+				content,
+				nil,
+			)
+			if err != nil {
+				elem.Drop()
+			}
+			elem.mutex.Unlock()
+		}
+	}
+}
+
+/* Handles incoming packets related to handshake
+ */
+func (device *Device) RoutineHandshake() {
+
+	logInfo := device.log.Info
+	logError := device.log.Error
+	logDebug := device.log.Debug
+	logDebug.Println("Routine, handshake routine, started for device")
+
+	var temp [MessageHandshakeSize]byte
+	var elem QueueHandshakeElement
+
+	for {
+		select {
+		case elem = <-device.queue.handshake:
+		case <-device.signal.stop.Wait():
+			return
+		}
+
+		// handle cookie fields and ratelimiting
+
+		switch elem.msgType {
+
+		case MessageCookieReplyType:
+
+			// unmarshal packet
+
+			var reply MessageCookieReply
+			reader := bytes.NewReader(elem.packet)
+			err := binary.Read(reader, binary.LittleEndian, &reply)
+			if err != nil {
+				logDebug.Println("Failed to decode cookie reply")
+				return
+			}
+
+			// lookup peer from index
+
+			entry := device.indices.Lookup(reply.Receiver)
+
+			if entry.peer == nil {
+				continue
+			}
+
+			// consume reply
+
+			if peer := entry.peer; peer.isRunning.Get() {
+				peer.mac.ConsumeReply(&reply)
+			}
+
+			continue
+
+		case MessageInitiationType, MessageResponseType:
+
+			// check mac fields and ratelimit
+
+			if !device.mac.CheckMAC1(elem.packet) {
+				logDebug.Println("Received packet with invalid mac1")
+				continue
+			}
+
+			// endpoints destination address is the source of the datagram
+
+			srcBytes := elem.endpoint.DstToBytes()
+
+			if device.IsUnderLoad() {
+
+				// verify MAC2 field
+
+				if !device.mac.CheckMAC2(elem.packet, srcBytes) {
+
+					// construct cookie reply
+
+					logDebug.Println(
+						"Sending cookie reply to:",
+						elem.endpoint.DstToString(),
+					)
+
+					sender := binary.LittleEndian.Uint32(elem.packet[4:8])
+					reply, err := device.mac.CreateReply(elem.packet, sender, srcBytes)
+					if err != nil {
+						logError.Println("Failed to create cookie reply:", err)
+						continue
+					}
+
+					// marshal and send reply
+
+					writer := bytes.NewBuffer(temp[:0])
+					binary.Write(writer, binary.LittleEndian, reply)
+					device.net.bind.Send(writer.Bytes(), elem.endpoint)
+					if err != nil {
+						logDebug.Println("Failed to send cookie reply:", err)
+					}
+					continue
+				}
+
+				// check ratelimiter
+
+				if !device.rate.limiter.Allow(elem.endpoint.DstIP()) {
+					continue
+				}
+			}
+
+		default:
+			logError.Println("Invalid packet ended up in the handshake queue")
+			continue
+		}
+
+		// handle handshake initiation/response content
+
+		switch elem.msgType {
+		case MessageInitiationType:
+
+			// unmarshal
+
+			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")
+				continue
+			}
+
+			// consume initiation
+
+			peer := device.ConsumeMessageInitiation(&msg)
+			if peer == nil {
+				logInfo.Println(
+					"Received invalid initiation message from",
+					elem.endpoint.DstToString(),
+				)
+				continue
+			}
+
+			// update timers
+
+			peer.TimerAnyAuthenticatedPacketTraversal()
+			peer.TimerAnyAuthenticatedPacketReceived()
+
+			// update endpoint
+
+			peer.mutex.Lock()
+			peer.endpoint = elem.endpoint
+			peer.mutex.Unlock()
+
+			// create response
+
+			response, err := device.CreateMessageResponse(peer)
+			if err != nil {
+				logError.Println("Failed to create response message:", err)
+				continue
+			}
+
+			peer.TimerEphemeralKeyCreated()
+			peer.NewKeyPair()
+
+			logDebug.Println("Creating response message for", peer.String())
+
+			writer := bytes.NewBuffer(temp[:0])
+			binary.Write(writer, binary.LittleEndian, response)
+			packet := writer.Bytes()
+			peer.mac.AddMacs(packet)
+
+			// send response
+
+			err = peer.SendBuffer(packet)
+			if err == nil {
+				peer.TimerAnyAuthenticatedPacketTraversal()
+			} else {
+				logError.Println("Failed to send response to:", peer.String(), err)
+			}
+
+		case MessageResponseType:
+
+			// unmarshal
+
+			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")
+				continue
+			}
+
+			// consume response
+
+			peer := device.ConsumeMessageResponse(&msg)
+			if peer == nil {
+				logInfo.Println(
+					"Recieved invalid response message from",
+					elem.endpoint.DstToString(),
+				)
+				continue
+			}
+
+			// update endpoint
+
+			peer.mutex.Lock()
+			peer.endpoint = elem.endpoint
+			peer.mutex.Unlock()
+
+			logDebug.Println("Received handshake initiation from", peer)
+
+			peer.TimerEphemeralKeyCreated()
+
+			// update timers
+
+			peer.TimerAnyAuthenticatedPacketTraversal()
+			peer.TimerAnyAuthenticatedPacketReceived()
+			peer.TimerHandshakeComplete()
+
+			// derive key-pair
+
+			peer.NewKeyPair()
+			peer.SendKeepAlive()
+		}
+	}
+}
+
+func (peer *Peer) RoutineSequentialReceiver() {
+
+	defer peer.routines.stopping.Done()
+
+	device := peer.device
+
+	logInfo := device.log.Info
+	logError := device.log.Error
+	logDebug := device.log.Debug
+	logDebug.Println("Routine, sequential receiver, started for peer", peer.String())
+
+	peer.routines.starting.Done()
+
+	for {
+
+		select {
+
+		case <-peer.routines.stop.Wait():
+			logDebug.Println("Routine, sequential receiver, stopped for peer", peer.String())
+			return
+
+		case elem := <-peer.queue.inbound:
+
+			// wait for decryption
+
+			elem.mutex.Lock()
+
+			if elem.IsDropped() {
+				continue
+			}
+
+			// check for replay
+
+			if !elem.keyPair.replayFilter.ValidateCounter(elem.counter) {
+				continue
+			}
+
+			peer.TimerAnyAuthenticatedPacketTraversal()
+			peer.TimerAnyAuthenticatedPacketReceived()
+			peer.KeepKeyFreshReceiving()
+
+			// check if using new key-pair
+
+			kp := &peer.keyPairs
+			kp.mutex.Lock()
+			if kp.next == elem.keyPair {
+				peer.TimerHandshakeComplete()
+				if kp.previous != nil {
+					device.DeleteKeyPair(kp.previous)
+				}
+				kp.previous = kp.current
+				kp.current = kp.next
+				kp.next = nil
+			}
+			kp.mutex.Unlock()
+
+			// update endpoint
+
+			peer.mutex.Lock()
+			peer.endpoint = elem.endpoint
+			peer.mutex.Unlock()
+
+			// check for keep-alive
+
+			if len(elem.packet) == 0 {
+				logDebug.Println("Received keep-alive from", peer.String())
+				continue
+			}
+			peer.TimerDataReceived()
+
+			// verify source and strip padding
+
+			switch elem.packet[0] >> 4 {
+			case ipv4.Version:
+
+				// strip padding
+
+				if len(elem.packet) < ipv4.HeaderLen {
+					continue
+				}
+
+				field := elem.packet[IPv4offsetTotalLength : IPv4offsetTotalLength+2]
+				length := binary.BigEndian.Uint16(field)
+				if int(length) > len(elem.packet) || int(length) < ipv4.HeaderLen {
+					continue
+				}
+
+				elem.packet = elem.packet[:length]
+
+				// verify IPv4 source
+
+				src := elem.packet[IPv4offsetSrc : IPv4offsetSrc+net.IPv4len]
+				if device.routing.table.LookupIPv4(src) != peer {
+					logInfo.Println(
+						"IPv4 packet with disallowed source address from",
+						peer.String(),
+					)
+					continue
+				}
+
+			case ipv6.Version:
+
+				// strip padding
+
+				if len(elem.packet) < ipv6.HeaderLen {
+					continue
+				}
+
+				field := elem.packet[IPv6offsetPayloadLength : IPv6offsetPayloadLength+2]
+				length := binary.BigEndian.Uint16(field)
+				length += ipv6.HeaderLen
+				if int(length) > len(elem.packet) {
+					continue
+				}
+
+				elem.packet = elem.packet[:length]
+
+				// verify IPv6 source
+
+				src := elem.packet[IPv6offsetSrc : IPv6offsetSrc+net.IPv6len]
+				if device.routing.table.LookupIPv6(src) != peer {
+					logInfo.Println(
+						"IPv6 packet with disallowed source address from",
+						peer.String(),
+					)
+					continue
+				}
+
+			default:
+				logInfo.Println("Packet with invalid IP version from", peer.String())
+				continue
+			}
+
+			// write to tun device
+
+			offset := MessageTransportOffsetContent
+			atomic.AddUint64(&peer.stats.rxBytes, uint64(len(elem.packet)))
+			_, err := device.tun.device.Write(
+				elem.buffer[:offset+len(elem.packet)],
+				offset)
+			device.PutMessageBuffer(elem.buffer)
+			if err != nil {
+				logError.Println("Failed to write packet to TUN device:", err)
+			}
+		}
+	}
+}