EtherGuard-VPN/device/send.go

/* SPDX-License-Identifier: MIT
 *
 * Copyright (C) 2017-2020 WireGuard LLC. All Rights Reserved.
 */

package device

import (
	"bytes"
	"encoding/binary"
	"net"
	"sync"
	"sync/atomic"
	"time"

	"golang.org/x/crypto/chacha20poly1305"
	"golang.org/x/net/ipv4"
	"golang.org/x/net/ipv6"
)

/* Outbound flow
 *
 * 1. TUN queue
 * 2. Routing (sequential)
 * 3. Nonce assignment (sequential)
 * 4. Encryption (parallel)
 * 5. Transmission (sequential)
 *
 * The functions in this file occur (roughly) in the order in
 * which the packets are processed.
 *
 * Locking, Producers and Consumers
 *
 * The order of packets (per peer) must be maintained,
 * but encryption of packets happen out-of-order:
 *
 * The sequential consumers will attempt to take the lock,
 * workers release lock when they have completed work (encryption) on the packet.
 *
 * If the element is inserted into the "encryption queue",
 * the content is preceded by enough "junk" to contain the transport header
 * (to allow the construction of transport messages in-place)
 */

type QueueOutboundElement struct {
	dropped int32
	sync.Mutex
	buffer  *[MaxMessageSize]byte // slice holding the packet data
	packet  []byte                // slice of "buffer" (always!)
	nonce   uint64                // nonce for encryption
	keypair *Keypair              // keypair for encryption
	peer    *Peer                 // related peer
}

func (device *Device) NewOutboundElement() *QueueOutboundElement {
	elem := device.GetOutboundElement()
	elem.dropped = AtomicFalse
	elem.buffer = device.GetMessageBuffer()
	elem.Mutex = sync.Mutex{}
	elem.nonce = 0
	// keypair and peer were cleared (if necessary) by clearPointers.
	return elem
}

// clearPointers clears elem fields that contain pointers.
// This makes the garbage collector's life easier and
// avoids accidentally keeping other objects around unnecessarily.
// It also reduces the possible collateral damage from use-after-free bugs.
func (elem *QueueOutboundElement) clearPointers() {
	elem.buffer = nil
	elem.packet = nil
	elem.keypair = nil
	elem.peer = nil
}

func (elem *QueueOutboundElement) Drop() {
	atomic.StoreInt32(&elem.dropped, AtomicTrue)
}

func (elem *QueueOutboundElement) IsDropped() bool {
	return atomic.LoadInt32(&elem.dropped) == AtomicTrue
}

func addToNonceQueue(queue chan *QueueOutboundElement, elem *QueueOutboundElement, device *Device) {
	for {
		select {
		case queue <- elem:
			return
		default:
			select {
			case old := <-queue:
				device.PutMessageBuffer(old.buffer)
				device.PutOutboundElement(old)
			default:
			}
		}
	}
}

func addToOutboundAndEncryptionQueues(outboundQueue chan *QueueOutboundElement, encryptionQueue chan *QueueOutboundElement, elem *QueueOutboundElement) {
	select {
	case outboundQueue <- elem:
		select {
		case encryptionQueue <- elem:
			return
		default:
			elem.Drop()
			elem.peer.device.PutMessageBuffer(elem.buffer)
			elem.Unlock()
		}
	default:
		elem.peer.device.PutMessageBuffer(elem.buffer)
		elem.peer.device.PutOutboundElement(elem)
	}
}

/* Queues a keepalive if no packets are queued for peer
 */
func (peer *Peer) SendKeepalive() bool {
	peer.queue.RLock()
	defer peer.queue.RUnlock()
	if len(peer.queue.nonce) != 0 || peer.queue.packetInNonceQueueIsAwaitingKey.Get() || !peer.isRunning.Get() {
		return false
	}
	elem := peer.device.NewOutboundElement()
	elem.packet = nil
	select {
	case peer.queue.nonce <- elem:
		peer.device.log.Debug.Println(peer, "- Sending keepalive packet")
		return true
	default:
		peer.device.PutMessageBuffer(elem.buffer)
		peer.device.PutOutboundElement(elem)
		return false
	}
}

func (peer *Peer) SendHandshakeInitiation(isRetry bool) error {
	if !isRetry {
		atomic.StoreUint32(&peer.timers.handshakeAttempts, 0)
	}

	peer.handshake.mutex.RLock()
	if time.Since(peer.handshake.lastSentHandshake) < RekeyTimeout {
		peer.handshake.mutex.RUnlock()
		return nil
	}
	peer.handshake.mutex.RUnlock()

	peer.handshake.mutex.Lock()
	if time.Since(peer.handshake.lastSentHandshake) < RekeyTimeout {
		peer.handshake.mutex.Unlock()
		return nil
	}
	peer.handshake.lastSentHandshake = time.Now()
	peer.handshake.mutex.Unlock()

	peer.device.log.Debug.Println(peer, "- Sending handshake initiation")

	msg, err := peer.device.CreateMessageInitiation(peer)
	if err != nil {
		peer.device.log.Error.Println(peer, "- Failed to create initiation message:", err)
		return err
	}

	var buff [MessageInitiationSize]byte
	writer := bytes.NewBuffer(buff[:0])
	binary.Write(writer, binary.LittleEndian, msg)
	packet := writer.Bytes()
	peer.cookieGenerator.AddMacs(packet)

	peer.timersAnyAuthenticatedPacketTraversal()
	peer.timersAnyAuthenticatedPacketSent()

	err = peer.SendBuffer(packet)
	if err != nil {
		peer.device.log.Error.Println(peer, "- Failed to send handshake initiation:", err)
	}
	peer.timersHandshakeInitiated()

	return err
}

func (peer *Peer) SendHandshakeResponse() error {
	peer.handshake.mutex.Lock()
	peer.handshake.lastSentHandshake = time.Now()
	peer.handshake.mutex.Unlock()

	peer.device.log.Debug.Println(peer, "- Sending handshake response")

	response, err := peer.device.CreateMessageResponse(peer)
	if err != nil {
		peer.device.log.Error.Println(peer, "- Failed to create response message:", err)
		return err
	}

	var buff [MessageResponseSize]byte
	writer := bytes.NewBuffer(buff[:0])
	binary.Write(writer, binary.LittleEndian, response)
	packet := writer.Bytes()
	peer.cookieGenerator.AddMacs(packet)

	err = peer.BeginSymmetricSession()
	if err != nil {
		peer.device.log.Error.Println(peer, "- Failed to derive keypair:", err)
		return err
	}

	peer.timersSessionDerived()
	peer.timersAnyAuthenticatedPacketTraversal()
	peer.timersAnyAuthenticatedPacketSent()

	err = peer.SendBuffer(packet)
	if err != nil {
		peer.device.log.Error.Println(peer, "- Failed to send handshake response:", err)
	}
	return err
}

func (device *Device) SendHandshakeCookie(initiatingElem *QueueHandshakeElement) error {

	device.log.Debug.Println("Sending cookie response for denied handshake message for", initiatingElem.endpoint.DstToString())

	sender := binary.LittleEndian.Uint32(initiatingElem.packet[4:8])
	reply, err := device.cookieChecker.CreateReply(initiatingElem.packet, sender, initiatingElem.endpoint.DstToBytes())
	if err != nil {
		device.log.Error.Println("Failed to create cookie reply:", err)
		return err
	}

	var buff [MessageCookieReplySize]byte
	writer := bytes.NewBuffer(buff[:0])
	binary.Write(writer, binary.LittleEndian, reply)
	device.net.bind.Send(writer.Bytes(), initiatingElem.endpoint)
	return nil
}

func (peer *Peer) keepKeyFreshSending() {
	keypair := peer.keypairs.Current()
	if keypair == nil {
		return
	}
	nonce := atomic.LoadUint64(&keypair.sendNonce)
	if nonce > RekeyAfterMessages || (keypair.isInitiator && time.Since(keypair.created) > RekeyAfterTime) {
		peer.SendHandshakeInitiation(false)
	}
}

/* Reads packets from the TUN and inserts
 * into nonce queue for peer
 *
 * Obs. Single instance per TUN device
 */
func (device *Device) RoutineReadFromTUN() {

	logDebug := device.log.Debug
	logError := device.log.Error

	defer func() {
		logDebug.Println("Routine: TUN reader - stopped")
		device.state.stopping.Done()
	}()

	logDebug.Println("Routine: TUN reader - started")

	var elem *QueueOutboundElement

	for {
		if elem != nil {
			device.PutMessageBuffer(elem.buffer)
			device.PutOutboundElement(elem)
		}
		elem = device.NewOutboundElement()

		// read packet

		offset := MessageTransportHeaderSize
		size, err := device.tun.device.Read(elem.buffer[:], offset)

		if err != nil {
			if !device.isClosed.Get() {
				logError.Println("Failed to read packet from TUN device:", err)
				device.Close()
			}
			device.PutMessageBuffer(elem.buffer)
			device.PutOutboundElement(elem)
			return
		}

		if size == 0 || size > MaxContentSize {
			continue
		}

		elem.packet = elem.buffer[offset : offset+size]

		// lookup peer

		var peer *Peer
		switch elem.packet[0] >> 4 {
		case ipv4.Version:
			if len(elem.packet) < ipv4.HeaderLen {
				continue
			}
			dst := elem.packet[IPv4offsetDst : IPv4offsetDst+net.IPv4len]
			peer = device.allowedips.LookupIPv4(dst)

		case ipv6.Version:
			if len(elem.packet) < ipv6.HeaderLen {
				continue
			}
			dst := elem.packet[IPv6offsetDst : IPv6offsetDst+net.IPv6len]
			peer = device.allowedips.LookupIPv6(dst)

		default:
			logDebug.Println("Received packet with unknown IP version")
		}

		if peer == nil {
			continue
		}

		// insert into nonce/pre-handshake queue

		peer.queue.RLock()
		if peer.isRunning.Get() {
			if peer.queue.packetInNonceQueueIsAwaitingKey.Get() {
				peer.SendHandshakeInitiation(false)
			}
			addToNonceQueue(peer.queue.nonce, elem, device)
			elem = nil
		}
		peer.queue.RUnlock()
	}
}

func (peer *Peer) FlushNonceQueue() {
	select {
	case peer.signals.flushNonceQueue <- struct{}{}:
	default:
	}
}

/* Queues packets when there is no handshake.
 * Then assigns nonces to packets sequentially
 * and creates "work" structs for workers
 *
 * Obs. A single instance per peer
 */
func (peer *Peer) RoutineNonce() {
	var keypair *Keypair

	device := peer.device
	logDebug := device.log.Debug

	// We write to the encryption queue; keep it alive until we are done.
	device.queue.encryption.wg.Add(1)

	flush := func() {
		for {
			select {
			case elem := <-peer.queue.nonce:
				device.PutMessageBuffer(elem.buffer)
				device.PutOutboundElement(elem)
			default:
				return
			}
		}
	}

	defer func() {
		flush()
		logDebug.Println(peer, "- Routine: nonce worker - stopped")
		peer.queue.packetInNonceQueueIsAwaitingKey.Set(false)
		device.queue.encryption.wg.Done() // no more writes from us
		close(peer.queue.outbound)        // no more writes to this channel
		peer.routines.stopping.Done()
	}()

	logDebug.Println(peer, "- Routine: nonce worker - started")

NextPacket:
	for {
		peer.queue.packetInNonceQueueIsAwaitingKey.Set(false)

		select {
		case <-peer.routines.stop:
			return

		case <-peer.signals.flushNonceQueue:
			flush()
			continue NextPacket

		case elem, ok := <-peer.queue.nonce:

			if !ok {
				return
			}

			// make sure to always pick the newest key

			for {

				// check validity of newest key pair

				keypair = peer.keypairs.Current()
				if keypair != nil && atomic.LoadUint64(&keypair.sendNonce) < RejectAfterMessages {
					if time.Since(keypair.created) < RejectAfterTime {
						break
					}
				}
				peer.queue.packetInNonceQueueIsAwaitingKey.Set(true)

				// no suitable key pair, request for new handshake

				select {
				case <-peer.signals.newKeypairArrived:
				default:
				}

				peer.SendHandshakeInitiation(false)

				// wait for key to be established

				logDebug.Println(peer, "- Awaiting keypair")

				select {
				case <-peer.signals.newKeypairArrived:
					logDebug.Println(peer, "- Obtained awaited keypair")

				case <-peer.signals.flushNonceQueue:
					device.PutMessageBuffer(elem.buffer)
					device.PutOutboundElement(elem)
					flush()
					continue NextPacket

				case <-peer.routines.stop:
					device.PutMessageBuffer(elem.buffer)
					device.PutOutboundElement(elem)
					return
				}
			}
			peer.queue.packetInNonceQueueIsAwaitingKey.Set(false)

			// populate work element

			elem.peer = peer
			elem.nonce = atomic.AddUint64(&keypair.sendNonce, 1) - 1

			// double check in case of race condition added by future code

			if elem.nonce >= RejectAfterMessages {
				atomic.StoreUint64(&keypair.sendNonce, RejectAfterMessages)
				device.PutMessageBuffer(elem.buffer)
				device.PutOutboundElement(elem)
				continue NextPacket
			}

			elem.keypair = keypair
			elem.dropped = AtomicFalse
			elem.Lock()

			// add to parallel and sequential queue
			addToOutboundAndEncryptionQueues(peer.queue.outbound, device.queue.encryption.c, elem)
		}
	}
}

func calculatePaddingSize(packetSize, mtu int) int {
	lastUnit := packetSize
	if mtu == 0 {
		return ((lastUnit + PaddingMultiple - 1) & ^(PaddingMultiple - 1)) - lastUnit
	}
	if lastUnit > mtu {
		lastUnit %= mtu
	}
	paddedSize := ((lastUnit + PaddingMultiple - 1) & ^(PaddingMultiple - 1))
	if paddedSize > mtu {
		paddedSize = mtu
	}
	return paddedSize - lastUnit
}

/* Encrypts the elements in the queue
 * and marks them for sequential consumption (by releasing the mutex)
 *
 * Obs. One instance per core
 */
func (device *Device) RoutineEncryption() {

	var nonce [chacha20poly1305.NonceSize]byte

	logDebug := device.log.Debug

	defer logDebug.Println("Routine: encryption worker - stopped")
	logDebug.Println("Routine: encryption worker - started")

	for elem := range device.queue.encryption.c {

		// check if dropped

		if elem.IsDropped() {
			continue
		}

		// populate header fields

		header := elem.buffer[:MessageTransportHeaderSize]

		fieldType := header[0:4]
		fieldReceiver := header[4:8]
		fieldNonce := header[8:16]

		binary.LittleEndian.PutUint32(fieldType, MessageTransportType)
		binary.LittleEndian.PutUint32(fieldReceiver, elem.keypair.remoteIndex)
		binary.LittleEndian.PutUint64(fieldNonce, elem.nonce)

		// pad content to multiple of 16

		paddingSize := calculatePaddingSize(len(elem.packet), int(atomic.LoadInt32(&device.tun.mtu)))
		for i := 0; i < paddingSize; i++ {
			elem.packet = append(elem.packet, 0)
		}

		// encrypt content and release to consumer

		binary.LittleEndian.PutUint64(nonce[4:], elem.nonce)
		elem.packet = elem.keypair.send.Seal(
			header,
			nonce[:],
			elem.packet,
			nil,
		)
		elem.Unlock()
	}
}

/* Sequentially reads packets from queue and sends to endpoint
 *
 * Obs. Single instance per peer.
 * The routine terminates then the outbound queue is closed.
 */
func (peer *Peer) RoutineSequentialSender() {

	device := peer.device

	logDebug := device.log.Debug
	logError := device.log.Error

	defer logDebug.Println(peer, "- Routine: sequential sender - stopped")
	logDebug.Println(peer, "- Routine: sequential sender - started")

	for elem := range peer.queue.outbound {
		elem.Lock()
		if elem.IsDropped() {
			device.PutOutboundElement(elem)
			continue
		}
		if !peer.isRunning.Get() {
			// peer has been stopped; return re-usable elems to the shared pool.
			// This is an optimization only. It is possible for the peer to be stopped
			// immediately after this check, in which case, elem will get processed.
			// The timers and SendBuffer code are resilient to a few stragglers.
			// TODO(josharian): rework peer shutdown order to ensure
			// that we never accidentally keep timers alive longer than necessary.
			device.PutMessageBuffer(elem.buffer)
			device.PutOutboundElement(elem)
			continue
		}

		peer.timersAnyAuthenticatedPacketTraversal()
		peer.timersAnyAuthenticatedPacketSent()

		// send message and return buffer to pool

		err := peer.SendBuffer(elem.packet)
		if len(elem.packet) != MessageKeepaliveSize {
			peer.timersDataSent()
		}
		device.PutMessageBuffer(elem.buffer)
		device.PutOutboundElement(elem)
		if err != nil {
			logError.Println(peer, "- Failed to send data packet", err)
			continue
		}

		peer.keepKeyFreshSending()
	}
}