Update golang x/crypto dependencies (#2923)

vendor/golang.org/x/crypto/ssh/handshake.go

@@ -19,6 +19,11 @@ import (
 // messages are wrong when using ECDH.
 const debugHandshake = false
 
+// chanSize sets the amount of buffering SSH connections. This is
+// primarily for testing: setting chanSize=0 uncovers deadlocks more
+// quickly.
+const chanSize = 16
+
 // keyingTransport is a packet based transport that supports key
 // changes. It need not be thread-safe. It should pass through
 // msgNewKeys in both directions.
@@ -53,34 +58,65 @@ type handshakeTransport struct {
 	incoming  chan []byte
 	readError error
 
+	mu             sync.Mutex
+	writeError     error
+	sentInitPacket []byte
+	sentInitMsg    *kexInitMsg
+	pendingPackets [][]byte // Used when a key exchange is in progress.
+
+	// If the read loop wants to schedule a kex, it pings this
+	// channel, and the write loop will send out a kex
+	// message.
+	requestKex chan struct{}
+
+	// If the other side requests or confirms a kex, its kexInit
+	// packet is sent here for the write loop to find it.
+	startKex chan *pendingKex
+
 	// data for host key checking
-	hostKeyCallback func(hostname string, remote net.Addr, key PublicKey) error
+	hostKeyCallback HostKeyCallback
 	dialAddress     string
 	remoteAddr      net.Addr
 
-	readSinceKex uint64
+	// bannerCallback is non-empty if we are the client and it has been set in
+	// ClientConfig. In that case it is called during the user authentication
+	// dance to handle a custom server's message.
+	bannerCallback BannerCallback
 
-	// Protects the writing side of the connection
-	mu              sync.Mutex
-	cond            *sync.Cond
-	sentInitPacket  []byte
-	sentInitMsg     *kexInitMsg
-	writtenSinceKex uint64
-	writeError      error
+	// Algorithms agreed in the last key exchange.
+	algorithms *algorithms
+
+	readPacketsLeft uint32
+	readBytesLeft   int64
+
+	writePacketsLeft uint32
+	writeBytesLeft   int64
 
 	// The session ID or nil if first kex did not complete yet.
 	sessionID []byte
 }
 
+type pendingKex struct {
+	otherInit []byte
+	done      chan error
+}
+
 func newHandshakeTransport(conn keyingTransport, config *Config, clientVersion, serverVersion []byte) *handshakeTransport {
 	t := &handshakeTransport{
 		conn:          conn,
 		serverVersion: serverVersion,
 		clientVersion: clientVersion,
-		incoming:      make(chan []byte, 16),
-		config:        config,
+		incoming:      make(chan []byte, chanSize),
+		requestKex:    make(chan struct{}, 1),
+		startKex:      make(chan *pendingKex, 1),
+
+		config: config,
 	}
-	t.cond = sync.NewCond(&t.mu)
+	t.resetReadThresholds()
+	t.resetWriteThresholds()
+
+	// We always start with a mandatory key exchange.
+	t.requestKex <- struct{}{}
 	return t
 }
 
@@ -89,12 +125,14 @@ func newClientTransport(conn keyingTransport, clientVersion, serverVersion []byt
 	t.dialAddress = dialAddr
 	t.remoteAddr = addr
 	t.hostKeyCallback = config.HostKeyCallback
+	t.bannerCallback = config.BannerCallback
 	if config.HostKeyAlgorithms != nil {
 		t.hostKeyAlgorithms = config.HostKeyAlgorithms
 	} else {
 		t.hostKeyAlgorithms = supportedHostKeyAlgos
 	}
 	go t.readLoop()
+	go t.kexLoop()
 	return t
 }
 
@@ -102,6 +140,7 @@ func newServerTransport(conn keyingTransport, clientVersion, serverVersion []byt
 	t := newHandshakeTransport(conn, &config.Config, clientVersion, serverVersion)
 	t.hostKeys = config.hostKeys
 	go t.readLoop()
+	go t.kexLoop()
 	return t
 }
 
@@ -109,6 +148,20 @@ func (t *handshakeTransport) getSessionID() []byte {
 	return t.sessionID
 }
 
+// waitSession waits for the session to be established. This should be
+// the first thing to call after instantiating handshakeTransport.
+func (t *handshakeTransport) waitSession() error {
+	p, err := t.readPacket()
+	if err != nil {
+		return err
+	}
+	if p[0] != msgNewKeys {
+		return fmt.Errorf("ssh: first packet should be msgNewKeys")
+	}
+
+	return nil
+}
+
 func (t *handshakeTransport) id() string {
 	if len(t.hostKeys) > 0 {
 		return "server"
@@ -116,6 +169,20 @@ func (t *handshakeTransport) id() string {
 	return "client"
 }
 
+func (t *handshakeTransport) printPacket(p []byte, write bool) {
+	action := "got"
+	if write {
+		action = "sent"
+	}
+
+	if p[0] == msgChannelData || p[0] == msgChannelExtendedData {
+		log.Printf("%s %s data (packet %d bytes)", t.id(), action, len(p))
+	} else {
+		msg, err := decode(p)
+		log.Printf("%s %s %T %v (%v)", t.id(), action, msg, msg, err)
+	}
+}
+
 func (t *handshakeTransport) readPacket() ([]byte, error) {
 	p, ok := <-t.incoming
 	if !ok {
@@ -125,8 +192,10 @@ func (t *handshakeTransport) readPacket() ([]byte, error) {
 }
 
 func (t *handshakeTransport) readLoop() {
+	first := true
 	for {
-		p, err := t.readOnePacket()
+		p, err := t.readOnePacket(first)
+		first = false
 		if err != nil {
 			t.readError = err
 			close(t.incoming)
@@ -138,67 +207,217 @@ func (t *handshakeTransport) readLoop() {
 		t.incoming <- p
 	}
 
-	// If we can't read, declare the writing part dead too.
-	t.mu.Lock()
-	defer t.mu.Unlock()
-	if t.writeError == nil {
-		t.writeError = t.readError
-	}
-	t.cond.Broadcast()
+	// Stop writers too.
+	t.recordWriteError(t.readError)
+
+	// Unblock the writer should it wait for this.
+	close(t.startKex)
+
+	// Don't close t.requestKex; it's also written to from writePacket.
 }
 
-func (t *handshakeTransport) readOnePacket() ([]byte, error) {
-	if t.readSinceKex > t.config.RekeyThreshold {
-		if err := t.requestKeyChange(); err != nil {
-			return nil, err
+func (t *handshakeTransport) pushPacket(p []byte) error {
+	if debugHandshake {
+		t.printPacket(p, true)
+	}
+	return t.conn.writePacket(p)
+}
+
+func (t *handshakeTransport) getWriteError() error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return t.writeError
+}
+
+func (t *handshakeTransport) recordWriteError(err error) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if t.writeError == nil && err != nil {
+		t.writeError = err
+	}
+}
+
+func (t *handshakeTransport) requestKeyExchange() {
+	select {
+	case t.requestKex <- struct{}{}:
+	default:
+		// something already requested a kex, so do nothing.
+	}
+}
+
+func (t *handshakeTransport) resetWriteThresholds() {
+	t.writePacketsLeft = packetRekeyThreshold
+	if t.config.RekeyThreshold > 0 {
+		t.writeBytesLeft = int64(t.config.RekeyThreshold)
+	} else if t.algorithms != nil {
+		t.writeBytesLeft = t.algorithms.w.rekeyBytes()
+	} else {
+		t.writeBytesLeft = 1 << 30
+	}
+}
+
+func (t *handshakeTransport) kexLoop() {
+
+write:
+	for t.getWriteError() == nil {
+		var request *pendingKex
+		var sent bool
+
+		for request == nil || !sent {
+			var ok bool
+			select {
+			case request, ok = <-t.startKex:
+				if !ok {
+					break write
+				}
+			case <-t.requestKex:
+				break
+			}
+
+			if !sent {
+				if err := t.sendKexInit(); err != nil {
+					t.recordWriteError(err)
+					break
+				}
+				sent = true
+			}
 		}
+
+		if err := t.getWriteError(); err != nil {
+			if request != nil {
+				request.done <- err
+			}
+			break
+		}
+
+		// We're not servicing t.requestKex, but that is OK:
+		// we never block on sending to t.requestKex.
+
+		// We're not servicing t.startKex, but the remote end
+		// has just sent us a kexInitMsg, so it can't send
+		// another key change request, until we close the done
+		// channel on the pendingKex request.
+
+		err := t.enterKeyExchange(request.otherInit)
+
+		t.mu.Lock()
+		t.writeError = err
+		t.sentInitPacket = nil
+		t.sentInitMsg = nil
+
+		t.resetWriteThresholds()
+
+		// we have completed the key exchange. Since the
+		// reader is still blocked, it is safe to clear out
+		// the requestKex channel. This avoids the situation
+		// where: 1) we consumed our own request for the
+		// initial kex, and 2) the kex from the remote side
+		// caused another send on the requestKex channel,
+	clear:
+		for {
+			select {
+			case <-t.requestKex:
+				//
+			default:
+				break clear
+			}
+		}
+
+		request.done <- t.writeError
+
+		// kex finished. Push packets that we received while
+		// the kex was in progress. Don't look at t.startKex
+		// and don't increment writtenSinceKex: if we trigger
+		// another kex while we are still busy with the last
+		// one, things will become very confusing.
+		for _, p := range t.pendingPackets {
+			t.writeError = t.pushPacket(p)
+			if t.writeError != nil {
+				break
+			}
+		}
+		t.pendingPackets = t.pendingPackets[:0]
+		t.mu.Unlock()
 	}
 
+	// drain startKex channel. We don't service t.requestKex
+	// because nobody does blocking sends there.
+	go func() {
+		for init := range t.startKex {
+			init.done <- t.writeError
+		}
+	}()
+
+	// Unblock reader.
+	t.conn.Close()
+}
+
+// The protocol uses uint32 for packet counters, so we can't let them
+// reach 1<<32.  We will actually read and write more packets than
+// this, though: the other side may send more packets, and after we
+// hit this limit on writing we will send a few more packets for the
+// key exchange itself.
+const packetRekeyThreshold = (1 << 31)
+
+func (t *handshakeTransport) resetReadThresholds() {
+	t.readPacketsLeft = packetRekeyThreshold
+	if t.config.RekeyThreshold > 0 {
+		t.readBytesLeft = int64(t.config.RekeyThreshold)
+	} else if t.algorithms != nil {
+		t.readBytesLeft = t.algorithms.r.rekeyBytes()
+	} else {
+		t.readBytesLeft = 1 << 30
+	}
+}
+
+func (t *handshakeTransport) readOnePacket(first bool) ([]byte, error) {
 	p, err := t.conn.readPacket()
 	if err != nil {
 		return nil, err
 	}
 
-	t.readSinceKex += uint64(len(p))
-	if debugHandshake {
-		if p[0] == msgChannelData || p[0] == msgChannelExtendedData {
-			log.Printf("%s got data (packet %d bytes)", t.id(), len(p))
-		} else {
-			msg, err := decode(p)
-			log.Printf("%s got %T %v (%v)", t.id(), msg, msg, err)
-		}
+	if t.readPacketsLeft > 0 {
+		t.readPacketsLeft--
+	} else {
+		t.requestKeyExchange()
 	}
+
+	if t.readBytesLeft > 0 {
+		t.readBytesLeft -= int64(len(p))
+	} else {
+		t.requestKeyExchange()
+	}
+
+	if debugHandshake {
+		t.printPacket(p, false)
+	}
+
+	if first && p[0] != msgKexInit {
+		return nil, fmt.Errorf("ssh: first packet should be msgKexInit")
+	}
+
 	if p[0] != msgKexInit {
 		return p, nil
 	}
 
-	t.mu.Lock()
-
 	firstKex := t.sessionID == nil
 
-	err = t.enterKeyExchangeLocked(p)
-	if err != nil {
-		// drop connection
-		t.conn.Close()
-		t.writeError = err
+	kex := pendingKex{
+		done:      make(chan error, 1),
+		otherInit: p,
 	}
+	t.startKex <- &kex
+	err = <-kex.done
 
 	if debugHandshake {
 		log.Printf("%s exited key exchange (first %v), err %v", t.id(), firstKex, err)
 	}
 
-	// Unblock writers.
-	t.sentInitMsg = nil
-	t.sentInitPacket = nil
-	t.cond.Broadcast()
-	t.writtenSinceKex = 0
-	t.mu.Unlock()
-
 	if err != nil {
 		return nil, err
 	}
 
-	t.readSinceKex = 0
+	t.resetReadThresholds()
 
 	// By default, a key exchange is hidden from higher layers by
 	// translating it into msgIgnore.
@@ -213,61 +432,16 @@ func (t *handshakeTransport) readOnePacket() ([]byte, error) {
 	return successPacket, nil
 }
 
-// keyChangeCategory describes whether a key exchange is the first on a
-// connection, or a subsequent one.
-type keyChangeCategory bool
-
-const (
-	firstKeyExchange      keyChangeCategory = true
-	subsequentKeyExchange keyChangeCategory = false
-)
-
-// sendKexInit sends a key change message, and returns the message
-// that was sent. After initiating the key change, all writes will be
-// blocked until the change is done, and a failed key change will
-// close the underlying transport. This function is safe for
-// concurrent use by multiple goroutines.
-func (t *handshakeTransport) sendKexInit(isFirst keyChangeCategory) error {
-	var err error
-
+// sendKexInit sends a key change message.
+func (t *handshakeTransport) sendKexInit() error {
 	t.mu.Lock()
-	// If this is the initial key change, but we already have a sessionID,
-	// then do nothing because the key exchange has already completed
-	// asynchronously.
-	if !isFirst || t.sessionID == nil {
-		_, _, err = t.sendKexInitLocked(isFirst)
-	}
-	t.mu.Unlock()
-	if err != nil {
-		return err
-	}
-	if isFirst {
-		if packet, err := t.readPacket(); err != nil {
-			return err
-		} else if packet[0] != msgNewKeys {
-			return unexpectedMessageError(msgNewKeys, packet[0])
-		}
-	}
-	return nil
-}
-
-func (t *handshakeTransport) requestInitialKeyChange() error {
-	return t.sendKexInit(firstKeyExchange)
-}
-
-func (t *handshakeTransport) requestKeyChange() error {
-	return t.sendKexInit(subsequentKeyExchange)
-}
-
-// sendKexInitLocked sends a key change message. t.mu must be locked
-// while this happens.
-func (t *handshakeTransport) sendKexInitLocked(isFirst keyChangeCategory) (*kexInitMsg, []byte, error) {
-	// kexInits may be sent either in response to the other side,
-	// or because our side wants to initiate a key change, so we
-	// may have already sent a kexInit. In that case, don't send a
-	// second kexInit.
+	defer t.mu.Unlock()
 	if t.sentInitMsg != nil {
-		return t.sentInitMsg, t.sentInitPacket, nil
+		// kexInits may be sent either in response to the other side,
+		// or because our side wants to initiate a key change, so we
+		// may have already sent a kexInit. In that case, don't send a
+		// second kexInit.
+		return nil
 	}
 
 	msg := &kexInitMsg{
@@ -295,53 +469,65 @@ func (t *handshakeTransport) sendKexInitLocked(isFirst keyChangeCategory) (*kexI
 	packetCopy := make([]byte, len(packet))
 	copy(packetCopy, packet)
 
-	if err := t.conn.writePacket(packetCopy); err != nil {
-		return nil, nil, err
+	if err := t.pushPacket(packetCopy); err != nil {
+		return err
 	}
 
 	t.sentInitMsg = msg
 	t.sentInitPacket = packet
-	return msg, packet, nil
+
+	return nil
 }
 
 func (t *handshakeTransport) writePacket(p []byte) error {
-	t.mu.Lock()
-	defer t.mu.Unlock()
-
-	if t.writtenSinceKex > t.config.RekeyThreshold {
-		t.sendKexInitLocked(subsequentKeyExchange)
-	}
-	for t.sentInitMsg != nil && t.writeError == nil {
-		t.cond.Wait()
-	}
-	if t.writeError != nil {
-		return t.writeError
-	}
-	t.writtenSinceKex += uint64(len(p))
-
 	switch p[0] {
 	case msgKexInit:
 		return errors.New("ssh: only handshakeTransport can send kexInit")
 	case msgNewKeys:
 		return errors.New("ssh: only handshakeTransport can send newKeys")
-	default:
-		return t.conn.writePacket(p)
 	}
+
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if t.writeError != nil {
+		return t.writeError
+	}
+
+	if t.sentInitMsg != nil {
+		// Copy the packet so the writer can reuse the buffer.
+		cp := make([]byte, len(p))
+		copy(cp, p)
+		t.pendingPackets = append(t.pendingPackets, cp)
+		return nil
+	}
+
+	if t.writeBytesLeft > 0 {
+		t.writeBytesLeft -= int64(len(p))
+	} else {
+		t.requestKeyExchange()
+	}
+
+	if t.writePacketsLeft > 0 {
+		t.writePacketsLeft--
+	} else {
+		t.requestKeyExchange()
+	}
+
+	if err := t.pushPacket(p); err != nil {
+		t.writeError = err
+	}
+
+	return nil
 }
 
 func (t *handshakeTransport) Close() error {
 	return t.conn.Close()
 }
 
-// enterKeyExchange runs the key exchange. t.mu must be held while running this.
-func (t *handshakeTransport) enterKeyExchangeLocked(otherInitPacket []byte) error {
+func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error {
 	if debugHandshake {
 		log.Printf("%s entered key exchange", t.id())
 	}
-	myInit, myInitPacket, err := t.sendKexInitLocked(subsequentKeyExchange)
-	if err != nil {
-		return err
-	}
 
 	otherInit := &kexInitMsg{}
 	if err := Unmarshal(otherInitPacket, otherInit); err != nil {
@@ -352,20 +538,20 @@ func (t *handshakeTransport) enterKeyExchangeLocked(otherInitPacket []byte) erro
 		clientVersion: t.clientVersion,
 		serverVersion: t.serverVersion,
 		clientKexInit: otherInitPacket,
-		serverKexInit: myInitPacket,
+		serverKexInit: t.sentInitPacket,
 	}
 
 	clientInit := otherInit
-	serverInit := myInit
+	serverInit := t.sentInitMsg
 	if len(t.hostKeys) == 0 {
-		clientInit = myInit
-		serverInit = otherInit
+		clientInit, serverInit = serverInit, clientInit
 
-		magics.clientKexInit = myInitPacket
+		magics.clientKexInit = t.sentInitPacket
 		magics.serverKexInit = otherInitPacket
 	}
 
-	algs, err := findAgreedAlgorithms(clientInit, serverInit)
+	var err error
+	t.algorithms, err = findAgreedAlgorithms(clientInit, serverInit)
 	if err != nil {
 		return err
 	}
@@ -388,16 +574,16 @@ func (t *handshakeTransport) enterKeyExchangeLocked(otherInitPacket []byte) erro
 		}
 	}
 
-	kex, ok := kexAlgoMap[algs.kex]
+	kex, ok := kexAlgoMap[t.algorithms.kex]
 	if !ok {
-		return fmt.Errorf("ssh: unexpected key exchange algorithm %v", algs.kex)
+		return fmt.Errorf("ssh: unexpected key exchange algorithm %v", t.algorithms.kex)
 	}
 
 	var result *kexResult
 	if len(t.hostKeys) > 0 {
-		result, err = t.server(kex, algs, &magics)
+		result, err = t.server(kex, t.algorithms, &magics)
 	} else {
-		result, err = t.client(kex, algs, &magics)
+		result, err = t.client(kex, t.algorithms, &magics)
 	}
 
 	if err != nil {
@@ -409,7 +595,9 @@ func (t *handshakeTransport) enterKeyExchangeLocked(otherInitPacket []byte) erro
 	}
 	result.SessionID = t.sessionID
 
-	t.conn.prepareKeyChange(algs, result)
+	if err := t.conn.prepareKeyChange(t.algorithms, result); err != nil {
+		return err
+	}
 	if err = t.conn.writePacket([]byte{msgNewKeys}); err != nil {
 		return err
 	}
@@ -449,11 +637,9 @@ func (t *handshakeTransport) client(kex kexAlgorithm, algs *algorithms, magics *
 		return nil, err
 	}
 
-	if t.hostKeyCallback != nil {
-		err = t.hostKeyCallback(t.dialAddress, t.remoteAddr, hostKey)
-		if err != nil {
-			return nil, err
-		}
+	err = t.hostKeyCallback(t.dialAddress, t.remoteAddr, hostKey)
+	if err != nil {
+		return nil, err
 	}
 
 	return result, nil