Drop invalid record silently during handshake

conn.go

@@ -1026,6 +1026,10 @@ func (c *Conn) handshake(ctx context.Context, cfg *handshakeConfig, initialFligh
 				} else {
 					switch {
 					case errors.Is(err, context.DeadlineExceeded), errors.Is(err, context.Canceled), errors.Is(err, io.EOF), errors.Is(err, net.ErrClosed):
+					case errors.Is(err, recordlayer.ErrInvalidPacketLength):
+						// Decode error must be silently discarded
+						// [RFC6347 Section-4.1.2.7]
+						continue
 					default:
 						if c.isHandshakeCompletedSuccessfully() {
 							// Keep read loop and pass the read error to Read()

conn_test.go

@@ -389,7 +389,7 @@ func TestHandshakeWithAlert(t *testing.T) {
 				clientErr <- err
 			}()
 
-			_, errServer := testServer(ctx, dtlsnet.PacketConnFromConn(cb), ca.RemoteAddr(), testCase.configServer, true)
+			_, errServer := testServer(ctx, dtlsnet.PacketConnFromConn(cb), cb.RemoteAddr(), testCase.configServer, true)
 			if !errors.Is(errServer, testCase.errServer) {
 				t.Fatalf("Server error exp(%v) failed(%v)", testCase.errServer, errServer)
 			}
@@ -402,6 +402,71 @@ func TestHandshakeWithAlert(t *testing.T) {
 	}
 }
 
+func TestHandshakeWithInvalidRecord(t *testing.T) {
+	// Limit runtime in case of deadlocks
+	lim := test.TimeOut(time.Second * 20)
+	defer lim.Stop()
+
+	// Check for leaking routines
+	report := test.CheckRoutines(t)
+	defer report()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	type result struct {
+		c   *Conn
+		err error
+	}
+	clientErr := make(chan result, 1)
+	ca, cb := dpipe.Pipe()
+	caWithInvalidRecord := &connWithCallback{Conn: ca}
+
+	var msgSeq atomic.Int32
+	// Send invalid record after first message
+	caWithInvalidRecord.onWrite = func(b []byte) {
+		if msgSeq.Add(1) == 2 {
+			if _, err := ca.Write([]byte{0x01, 0x02}); err != nil {
+				t.Fatal(err)
+			}
+		}
+	}
+	go func() {
+		client, err := testClient(ctx, dtlsnet.PacketConnFromConn(caWithInvalidRecord), caWithInvalidRecord.RemoteAddr(), &Config{
+			CipherSuites: []CipherSuiteID{TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256},
+		}, true)
+		clientErr <- result{client, err}
+	}()
+
+	server, errServer := testServer(ctx, dtlsnet.PacketConnFromConn(cb), cb.RemoteAddr(), &Config{
+		CipherSuites: []CipherSuiteID{TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256},
+	}, true)
+
+	errClient := <-clientErr
+
+	defer func() {
+		if server != nil {
+			if err := server.Close(); err != nil {
+				t.Fatal(err)
+			}
+		}
+
+		if errClient.c != nil {
+			if err := errClient.c.Close(); err != nil {
+				t.Fatal(err)
+			}
+		}
+	}()
+
+	if errServer != nil {
+		t.Fatalf("Server failed(%v)", errServer)
+	}
+
+	if errClient.err != nil {
+		t.Fatalf("Client failed(%v)", errClient.err)
+	}
+}
+
 func TestExportKeyingMaterial(t *testing.T) {
 	// Check for leaking routines
 	report := test.CheckRoutines(t)
@@ -3096,3 +3161,15 @@ func TestSkipHelloVerify(t *testing.T) {
 		t.Error(err)
 	}
 }
+
+type connWithCallback struct {
+	net.Conn
+	onWrite func([]byte)
+}
+
+func (c *connWithCallback) Write(b []byte) (int, error) {
+	if c.onWrite != nil {
+		c.onWrite(b)
+	}
+	return c.Conn.Write(b)
+}

pkg/protocol/recordlayer/errors.go

@@ -11,9 +11,11 @@ import (
 )
 
 var (
-	errBufferTooSmall             = &protocol.TemporaryError{Err: errors.New("buffer is too small")}                            //nolint:goerr113
-	errInvalidPacketLength        = &protocol.TemporaryError{Err: errors.New("packet length and declared length do not match")} //nolint:goerr113
-	errSequenceNumberOverflow     = &protocol.InternalError{Err: errors.New("sequence number overflow")}                        //nolint:goerr113
-	errUnsupportedProtocolVersion = &protocol.FatalError{Err: errors.New("unsupported protocol version")}                       //nolint:goerr113
-	errInvalidContentType         = &protocol.TemporaryError{Err: errors.New("invalid content type")}                           //nolint:goerr113
+	// ErrInvalidPacketLength is returned when the packet length too small or declared length do not match
+	ErrInvalidPacketLength = &protocol.TemporaryError{Err: errors.New("packet length and declared length do not match")} //nolint:goerr113
+
+	errBufferTooSmall             = &protocol.TemporaryError{Err: errors.New("buffer is too small")}      //nolint:goerr113
+	errSequenceNumberOverflow     = &protocol.InternalError{Err: errors.New("sequence number overflow")}  //nolint:goerr113
+	errUnsupportedProtocolVersion = &protocol.FatalError{Err: errors.New("unsupported protocol version")} //nolint:goerr113
+	errInvalidContentType         = &protocol.TemporaryError{Err: errors.New("invalid content type")}     //nolint:goerr113
 )

pkg/protocol/recordlayer/recordlayer.go

@@ -100,12 +100,12 @@
 
 	for offset := 0; len(buf) != offset; {
 		if len(buf)-offset <= FixedHeaderSize {
-			return nil, errInvalidPacketLength
+			return nil, ErrInvalidPacketLength
 		}
 
 		pktLen := (FixedHeaderSize + int(binary.BigEndian.Uint16(buf[offset+11:])))
 		if offset+pktLen > len(buf) {
-			return nil, errInvalidPacketLength
+			return nil, ErrInvalidPacketLength
 		}
 
 		out = append(out, buf[offset:offset+pktLen])
@@ -129,12 +129,12 @@
 			lenIdx += cidLength
 		}
 		if len(buf)-offset <= headerSize {
-			return nil, errInvalidPacketLength
+			return nil, ErrInvalidPacketLength
 		}
 
 		pktLen := (headerSize + int(binary.BigEndian.Uint16(buf[offset+lenIdx:])))
 		if offset+pktLen > len(buf) {
-			return nil, errInvalidPacketLength
+			return nil, ErrInvalidPacketLength
 		}
 
 		out = append(out, buf[offset:offset+pktLen])

pkg/protocol/recordlayer/recordlayer_test.go

@@ -39,12 +39,12 @@ func TestUDPDecode(t *testing.T) {
 		{
 			Name:      "Invalid packet length",
 			Data:      []byte{0x14, 0xfe},
-			WantError: errInvalidPacketLength,
+			WantError: ErrInvalidPacketLength,
 		},
 		{
 			Name:      "Packet declared invalid length",
 			Data:      []byte{0x14, 0xfe, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x12, 0x00, 0xFF, 0x01},
-			WantError: errInvalidPacketLength,
+			WantError: ErrInvalidPacketLength,
 		},
 	} {
 		dtlsPkts, err := UnpackDatagram(test.Data)