close connection when an abnormally large number of frames are queued (#4369)

Under normal circumstances, we should be able to send out control frames
right away, so we don't expect any queue to build up. To defend against
resource exhaustion attacks, we limit the control frame queue to 16384
elements.

connection.go

@@ -521,6 +521,9 @@ func (s *connection) run() error {
 
 runLoop:
 	for {
+		if s.framer.QueuedTooManyControlFrames() {
+			s.closeLocal(&qerr.TransportError{ErrorCode: InternalError})
+		}
 		// Close immediately if requested
 		select {
 		case closeErr = <-s.closeChan:

framer.go

@@ -21,9 +21,19 @@ type framer interface {
 	AppendStreamFrames([]ackhandler.StreamFrame, protocol.ByteCount, protocol.Version) ([]ackhandler.StreamFrame, protocol.ByteCount)
 
 	Handle0RTTRejection() error
+
+	// QueuedTooManyControlFrames says if the control frame queue exceeded its maximum queue length.
+	// This is a hack.
+	// It is easier to implement than propagating an error return value in QueueControlFrame.
+	// The correct solution would be to queue frames with their respective structs.
+	// See https://github.com/quic-go/quic-go/issues/4271 for the queueing of stream-related control frames.
+	QueuedTooManyControlFrames() bool
 }
 
-const maxPathResponses = 256
+const (
+	maxPathResponses = 256
+	maxControlFrames = 16 << 10
+)
 
 type framerI struct {
 	mutex sync.Mutex
@@ -33,9 +43,10 @@ type framerI struct {
 	activeStreams map[protocol.StreamID]struct{}
 	streamQueue   ringbuffer.RingBuffer[protocol.StreamID]
 
-	controlFrameMutex sync.Mutex
-	controlFrames     []wire.Frame
-	pathResponses     []*wire.PathResponseFrame
+	controlFrameMutex          sync.Mutex
+	controlFrames              []wire.Frame
+	pathResponses              []*wire.PathResponseFrame
+	queuedTooManyControlFrames bool
 }
 
 var _ framer = &framerI{}
@@ -73,6 +84,11 @@ func (f *framerI) QueueControlFrame(frame wire.Frame) {
 		f.pathResponses = append(f.pathResponses, pr)
 		return
 	}
+	// This is a hack.
+	if len(f.controlFrames) >= maxControlFrames {
+		f.queuedTooManyControlFrames = true
+		return
+	}
 	f.controlFrames = append(f.controlFrames, frame)
 }
 
@@ -105,6 +121,10 @@ func (f *framerI) AppendControlFrames(frames []ackhandler.Frame, maxLen protocol
 	return frames, length
 }
 
+func (f *framerI) QueuedTooManyControlFrames() bool {
+	return f.queuedTooManyControlFrames
+}
+
 func (f *framerI) AddActiveStream(id protocol.StreamID) {
 	f.mutex.Lock()
 	if _, ok := f.activeStreams[id]; !ok {

framer_test.go

@@ -109,6 +109,23 @@ var _ = Describe("Framer", func() {
 			Expect(fs).To(HaveLen(2))
 			Expect(length).To(Equal(ping.Length(version) + ncid.Length(version)))
 		})
+
+		It("detects when too many frames are queued", func() {
+			for i := 0; i < maxControlFrames-1; i++ {
+				framer.QueueControlFrame(&wire.PingFrame{})
+				framer.QueueControlFrame(&wire.PingFrame{})
+				Expect(framer.QueuedTooManyControlFrames()).To(BeFalse())
+				frames, _ := framer.AppendControlFrames([]ackhandler.Frame{}, 1, protocol.Version1)
+				Expect(frames).To(HaveLen(1))
+				Expect(framer.(*framerI).controlFrames).To(HaveLen(i + 1))
+			}
+			framer.QueueControlFrame(&wire.PingFrame{})
+			Expect(framer.QueuedTooManyControlFrames()).To(BeFalse())
+			Expect(framer.(*framerI).controlFrames).To(HaveLen(maxControlFrames))
+			framer.QueueControlFrame(&wire.PingFrame{})
+			Expect(framer.QueuedTooManyControlFrames()).To(BeTrue())
+			Expect(framer.(*framerI).controlFrames).To(HaveLen(maxControlFrames))
+		})
 	})
 
 	Context("handling PATH_RESPONSE frames", func() {