Fix race between Conn.Close and Conn.Handshake

conn.go

@@ -74,13 +74,13 @@ type Conn struct {
 
 	handshakeCompletedSuccessfully atomic.Value
 	handshakeMutex                 sync.Mutex
+	handshakeDone                  chan struct{}
 
 	encryptedPackets []addrPkt
 
 	connectionClosedByUser bool
 	closeLock              sync.Mutex
 	closed                 *closer.Closer
-	handshakeLoopsFinished sync.WaitGroup
 
 	readDeadline  *deadline.Deadline
 	writeDeadline *deadline.Deadline
@@ -256,6 +256,12 @@ func (c *Conn) HandshakeContext(ctx context.Context) error {
 		return nil
 	}
 
+	handshakeDone := make(chan struct{})
+	defer close(handshakeDone)
+	c.closeLock.Lock()
+	c.handshakeDone = handshakeDone
+	c.closeLock.Unlock()
+
 	// rfc5246#section-7.4.3
 	// In addition, the hash and signature algorithms MUST be compatible
 	// with the key in the server's end-entity certificate.
@@ -405,7 +411,12 @@ func (c *Conn) Write(p []byte) (int, error) {
 // Close closes the connection.
 func (c *Conn) Close() error {
 	err := c.close(true) //nolint:contextcheck
-	c.handshakeLoopsFinished.Wait()
+	c.closeLock.Lock()
+	handshakeDone := c.handshakeDone
+	c.closeLock.Unlock()
+	if handshakeDone != nil {
+		<-handshakeDone
+	}
 	return err
 }
 
@@ -1026,7 +1037,6 @@ func (c *Conn) handshake(ctx context.Context, cfg *handshakeConfig, initialFligh
 
 	done := make(chan struct{})
 	ctxRead, cancelRead := context.WithCancel(context.Background())
-	c.cancelHandshakeReader = cancelRead
 	cfg.onFlightState = func(_ flightVal, s handshakeState) {
 		if s == handshakeFinished && !c.isHandshakeCompletedSuccessfully() {
 			c.setHandshakeCompletedSuccessfully()
@@ -1035,16 +1045,21 @@ func (c *Conn) handshake(ctx context.Context, cfg *handshakeConfig, initialFligh
 	}
 
 	ctxHs, cancel := context.WithCancel(context.Background())
+
+	c.closeLock.Lock()
 	c.cancelHandshaker = cancel
+	c.cancelHandshakeReader = cancelRead
+	c.closeLock.Unlock()
 
 	firstErr := make(chan error, 1)
 
-	c.handshakeLoopsFinished.Add(2)
+	var handshakeLoopsFinished sync.WaitGroup
+	handshakeLoopsFinished.Add(2)
 
 	// Handshake routine should be live until close.
 	// The other party may request retransmission of the last flight to cope with packet drop.
 	go func() {
-		defer c.handshakeLoopsFinished.Done()
+		defer handshakeLoopsFinished.Done()
 		err := c.fsm.Run(ctxHs, c, initialState)
 		if !errors.Is(err, context.Canceled) {
 			select {
@@ -1064,7 +1079,7 @@ func (c *Conn) handshake(ctx context.Context, cfg *handshakeConfig, initialFligh
 			// Force stop handshaker when the underlying connection is closed.
 			cancel()
 		}()
-		defer c.handshakeLoopsFinished.Done()
+		defer handshakeLoopsFinished.Done()
 		for {
 			if err := c.readAndBuffer(ctxRead); err != nil {
 				var e *alertError
@@ -1123,12 +1138,12 @@ func (c *Conn) handshake(ctx context.Context, cfg *handshakeConfig, initialFligh
 	case err := <-firstErr:
 		cancelRead()
 		cancel()
-		c.handshakeLoopsFinished.Wait()
+		handshakeLoopsFinished.Wait()
 		return c.translateHandshakeCtxError(err)
 	case <-ctx.Done():
 		cancelRead()
 		cancel()
-		c.handshakeLoopsFinished.Wait()
+		handshakeLoopsFinished.Wait()
 		return c.translateHandshakeCtxError(ctx.Err())
 	case <-done:
 		return nil
@@ -1146,8 +1161,13 @@ func (c *Conn) translateHandshakeCtxError(err error) error {
 }
 
 func (c *Conn) close(byUser bool) error {
-	c.cancelHandshaker()
-	c.cancelHandshakeReader()
+	c.closeLock.Lock()
+	cancelHandshaker := c.cancelHandshaker
+	cancelHandshakeReader := c.cancelHandshakeReader
+	c.closeLock.Unlock()
+
+	cancelHandshaker()
+	cancelHandshakeReader()
 
 	if c.isHandshakeCompletedSuccessfully() && byUser {
 		// Discard error from notify() to return non-error on the first user call of Close()

conn_test.go

@@ -3662,3 +3662,54 @@ func TestMultiHandshake(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestCloseDuringHandshake(t *testing.T) {
+	defer test.CheckRoutines(t)()
+	defer test.TimeOut(time.Second * 10).Stop()
+
+	serverCert, err := selfsign.GenerateSelfSigned()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for i := 0; i < 100; i++ {
+		_, cb := dpipe.Pipe()
+		server, err := Server(dtlsnet.PacketConnFromConn(cb), cb.RemoteAddr(), &Config{
+			Certificates: []tls.Certificate{serverCert},
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		waitChan := make(chan struct{})
+		go func() {
+			close(waitChan)
+			_ = server.Handshake()
+		}()
+
+		<-waitChan
+		if err = server.Close(); err != nil {
+			t.Fatal(err)
+		}
+	}
+}
+
+func TestCloseWithoutHandshake(t *testing.T) {
+	defer test.CheckRoutines(t)()
+	defer test.TimeOut(time.Second * 10).Stop()
+
+	serverCert, err := selfsign.GenerateSelfSigned()
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, cb := dpipe.Pipe()
+	server, err := Server(dtlsnet.PacketConnFromConn(cb), cb.RemoteAddr(), &Config{
+		Certificates: []tls.Certificate{serverCert},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err = server.Close(); err != nil {
+		t.Fatal(err)
+	}
+}