check transport parameters after 0-RTT resumption

connection.go

@@ -1665,6 +1665,14 @@ func (s *connection) handleTransportParameters(params *wire.TransportParameters)
 			ErrorMessage: err.Error(),
 		}
 	}
+
+	if s.perspective == protocol.PerspectiveClient && s.peerParams != nil && s.ConnectionState().Used0RTT && !params.ValidForUpdate(s.peerParams) {
+		return &qerr.TransportError{
+			ErrorCode:    qerr.ProtocolViolation,
+			ErrorMessage: "server sent reduced limits after accepting 0-RTT data",
+		}
+	}
+
 	s.peerParams = params
 	// On the client side we have to wait for handshake completion.
 	// During a 0-RTT connection, we are only allowed to use the new transport parameters for 1-RTT packets.

connection_test.go

@@ -3035,6 +3035,40 @@ var _ = Describe("Client Connection", func() {
 				ErrorMessage: "expected original_destination_connection_id to equal deadbeef, is decafbad",
 			})))
 		})
+
+		It("errors if the transport parameters contain reduced limits after knowing 0-RTT data is accepted by the server", func() {
+			conn.perspective = protocol.PerspectiveClient
+			conn.peerParams = &wire.TransportParameters{
+				ActiveConnectionIDLimit:        3,
+				InitialMaxData:                 0x5000,
+				InitialMaxStreamDataBidiLocal:  0x5000,
+				InitialMaxStreamDataBidiRemote: 1000,
+				InitialMaxStreamDataUni:        1000,
+				MaxBidiStreamNum:               500,
+				MaxUniStreamNum:                500,
+			}
+			params := &wire.TransportParameters{
+				OriginalDestinationConnectionID: destConnID,
+				InitialSourceConnectionID:       destConnID,
+				ActiveConnectionIDLimit:         3,
+				InitialMaxData:                  0x5000,
+				InitialMaxStreamDataBidiLocal:   0x5000,
+				InitialMaxStreamDataBidiRemote:  1000,
+				InitialMaxStreamDataUni:         1000,
+				MaxBidiStreamNum:                300,
+				MaxUniStreamNum:                 300,
+			}
+			expectClose(false, true)
+			processed := make(chan struct{})
+			tracer.EXPECT().ReceivedTransportParameters(params).Do(func(*wire.TransportParameters) { close(processed) })
+			cryptoSetup.EXPECT().ConnectionState().Return(handshake.ConnectionState{Used0RTT: true})
+			paramsChan <- params
+			Eventually(processed).Should(BeClosed())
+			Eventually(errChan).Should(Receive(MatchError(&qerr.TransportError{
+				ErrorCode:    qerr.ProtocolViolation,
+				ErrorMessage: "server sent reduced limits after accepting 0-RTT data",
+			})))
+		})
 	})
 
 	Context("handling potentially injected packets", func() {

internal/wire/transport_parameter_test.go

@@ -612,5 +612,93 @@ var _ = Describe("Transport Parameters", func() {
 				Expect(p.ValidFor0RTT(saved)).To(BeFalse())
 			})
 		})
+
+		Context("client checks the parameters after successfully sending 0-RTT data", func() {
+			var p TransportParameters
+			saved := &TransportParameters{
+				InitialMaxStreamDataBidiLocal:  1,
+				InitialMaxStreamDataBidiRemote: 2,
+				InitialMaxStreamDataUni:        3,
+				InitialMaxData:                 4,
+				MaxBidiStreamNum:               5,
+				MaxUniStreamNum:                6,
+				ActiveConnectionIDLimit:        7,
+			}
+
+			BeforeEach(func() {
+				p = *saved
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the InitialMaxStreamDataBidiLocal was reduced", func() {
+				p.InitialMaxStreamDataBidiLocal = saved.InitialMaxStreamDataBidiLocal - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the InitialMaxStreamDataBidiLocal was increased", func() {
+				p.InitialMaxStreamDataBidiLocal = saved.InitialMaxStreamDataBidiLocal + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the InitialMaxStreamDataBidiRemote was reduced", func() {
+				p.InitialMaxStreamDataBidiRemote = saved.InitialMaxStreamDataBidiRemote - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the InitialMaxStreamDataBidiRemote was increased", func() {
+				p.InitialMaxStreamDataBidiRemote = saved.InitialMaxStreamDataBidiRemote + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the InitialMaxStreamDataUni was reduced", func() {
+				p.InitialMaxStreamDataUni = saved.InitialMaxStreamDataUni - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the InitialMaxStreamDataUni was increased", func() {
+				p.InitialMaxStreamDataUni = saved.InitialMaxStreamDataUni + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the InitialMaxData was reduced", func() {
+				p.InitialMaxData = saved.InitialMaxData - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the InitialMaxData was increased", func() {
+				p.InitialMaxData = saved.InitialMaxData + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the MaxBidiStreamNum was reduced", func() {
+				p.MaxBidiStreamNum = saved.MaxBidiStreamNum - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the MaxBidiStreamNum was increased", func() {
+				p.MaxBidiStreamNum = saved.MaxBidiStreamNum + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the MaxUniStreamNum reduced", func() {
+				p.MaxUniStreamNum = saved.MaxUniStreamNum - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the MaxUniStreamNum was increased", func() {
+				p.MaxUniStreamNum = saved.MaxUniStreamNum + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+
+			It("rejects the parameters if the ActiveConnectionIDLimit reduced", func() {
+				p.ActiveConnectionIDLimit = saved.ActiveConnectionIDLimit - 1
+				Expect(p.ValidForUpdate(saved)).To(BeFalse())
+			})
+
+			It("doesn't reject the parameters if the ActiveConnectionIDLimit increased", func() {
+				p.ActiveConnectionIDLimit = saved.ActiveConnectionIDLimit + 1
+				Expect(p.ValidForUpdate(saved)).To(BeTrue())
+			})
+		})
 	})
 })

internal/wire/transport_parameters.go

@@ -481,6 +481,18 @@ func (p *TransportParameters) ValidFor0RTT(saved *TransportParameters) bool {
 		p.ActiveConnectionIDLimit == saved.ActiveConnectionIDLimit
 }
 
+// ValidForUpdate checks that the new transport parameters don't reduce limits after resuming a 0-RTT connection.
+// It is only used on the client side.
+func (p *TransportParameters) ValidForUpdate(saved *TransportParameters) bool {
+	return p.ActiveConnectionIDLimit >= saved.ActiveConnectionIDLimit &&
+		p.InitialMaxData >= saved.InitialMaxData &&
+		p.InitialMaxStreamDataBidiLocal >= saved.InitialMaxStreamDataBidiLocal &&
+		p.InitialMaxStreamDataBidiRemote >= saved.InitialMaxStreamDataBidiRemote &&
+		p.InitialMaxStreamDataUni >= saved.InitialMaxStreamDataUni &&
+		p.MaxBidiStreamNum >= saved.MaxBidiStreamNum &&
+		p.MaxUniStreamNum >= saved.MaxUniStreamNum
+}
+
 // String returns a string representation, intended for logging.
 func (p *TransportParameters) String() string {
 	logString := "&wire.TransportParameters{OriginalDestinationConnectionID: %s, InitialSourceConnectionID: %s, "