limit number of gaps in received StreamFrame data

fixes #159

protocol/server_parameters.go

@@ -59,6 +59,10 @@ const STKExpiryTimeSec = 24 * 60 * 60
 // TODO: decrease this value after dropping support for QUIC 33 and earlier
 const MaxTrackedSentPackets uint32 = 2000
 
+// MaxStreamFrameSorterGaps is the maximum number of gaps between received StreamFrames
+// prevents DOS attacks against the streamFrameSorter
+const MaxStreamFrameSorterGaps = 50
+
 // CryptoMaxParams is the upper limit for the number of parameters in a crypto message.
 // Value taken from Chrome.
 const CryptoMaxParams = 128

stream_frame_sorter.go

@@ -17,6 +17,7 @@ type streamFrameSorter struct {
 
 var (
 	errOverlappingStreamData           = qerr.Error(qerr.OverlappingStreamData, "")
+	errTooManyGapsInReceivedStreamData = errors.New("Too many gaps in received StreamFrame data")
 	errDuplicateStreamData             = errors.New("Overlapping Stream Data")
 	errEmptyStreamData                 = errors.New("Stream Data empty")
 )
@@ -93,6 +94,10 @@ func (s *streamFrameSorter) Push(frame *frames.StreamFrame) error {
 		return errDuplicateStreamData
 	}
 
+	if s.gaps.Len() > protocol.MaxStreamFrameSorterGaps {
+		return errTooManyGapsInReceivedStreamData
+	}
+
 	s.queuedFrames[frame.Offset] = frame
 	return nil
 }

stream_frame_sorter_test.go

@@ -395,6 +395,26 @@ var _ = Describe("StreamFrame sorter", func() {
 					compareGapValues(s.gaps, expectedGaps)
 				})
 			})
+
+			Context("DOS protection", func() {
+				It("errors when too many gaps are created", func() {
+					for i := 0; i < protocol.MaxStreamFrameSorterGaps; i++ {
+						f := &frames.StreamFrame{
+							Data:   []byte("foobar"),
+							Offset: protocol.ByteCount(i * 7),
+						}
+						err := s.Push(f)
+						Expect(err).ToNot(HaveOccurred())
+					}
+					Expect(s.gaps.Len()).To(Equal(protocol.MaxStreamFrameSorterGaps))
+					f := &frames.StreamFrame{
+						Data:   []byte("foobar"),
+						Offset: protocol.ByteCount(protocol.MaxStreamFrameSorterGaps*7) + 100,
+					}
+					err := s.Push(f)
+					Expect(err).To(MatchError(errTooManyGapsInReceivedStreamData))
+				})
+			})
 		})
 	})
 })