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ackhandler: detect ECN mangling (#4080)

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* ackhandler: detect ECN mangling

Mangling means that a path is re-marking all ECN-marked packets as CE.

* ackhandler: only detect ECN mangling once all testing packets were sent
This commit is contained in:
Marten Seemann
2023-09-12 13:18:33 +07:00
committed by GitHub
parent 2a8dc12a53
commit d52e9f35bc
5 changed files with 53 additions and 7 deletions
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23
internal/ackhandler/ecn.go
View File

@@ -218,7 +218,21 @@ func (e *ecnTracker) HandleNewlyAcked(packets []*packet, ect0, ect1, ecnce int64
return false
}
// update our counters
e.numAckedECT0 = ect0
e.numAckedECT1 = ect1
e.numAckedECNCE = ecnce
if e.state == ecnStateTesting || e.state == ecnStateUnknown {
// Detect mangling (a path remarking all ECN-marked testing packets as CE).
if e.numSentECT0+e.numSentECT1 == e.numAckedECNCE && e.numAckedECNCE >= numECNTestingPackets {
if e.tracer != nil {
e.tracer.ECNStateUpdated(logging.ECNStateFailed, logging.ECNFailedManglingDetected)
}
e.state = ecnStateFailed
return false
}
var ackedTestingPacket bool
for _, p := range packets {
if e.isTestingPacket(p.PacketNumber) {
@@ -236,12 +250,9 @@ func (e *ecnTracker) HandleNewlyAcked(packets []*packet, ect0, ect1, ecnce int64
}
}
// update our counters
e.numAckedECT0 = ect0
e.numAckedECT1 = ect1
e.numAckedECNCE = ecnce
return newECNCE > 0
// Don't trust CE marks before having confirmed ECN capability of the path.
// Otherwise, mangling would be misinterpreted as actual congestion.
return e.state == ecnStateCapable && newECNCE > 0
}
func (e *ecnTracker) ecnMarking(pn protocol.PacketNumber) protocol.ECN {

30
internal/ackhandler/ecn_test.go
View File

@@ -175,6 +175,36 @@ var _ = Describe("ECN tracker", func() {
Expect(ecnTracker.HandleNewlyAcked(getAckedPackets(4, 5, 6, 15), 3, 0, 2)).To(BeFalse())
})
It("detects ECN mangling", func() {
sendAllTestingPackets()
for i := 10; i < 20; i++ {
Expect(ecnTracker.Mode()).To(Equal(protocol.ECNNon))
ecnTracker.SentPacket(protocol.PacketNumber(i), protocol.ECNNon)
}
// ECN capability not confirmed yet, therefore CE marks are not regarded as congestion events
Expect(ecnTracker.HandleNewlyAcked(getAckedPackets(0, 1, 2, 3), 0, 0, 4)).To(BeFalse())
Expect(ecnTracker.HandleNewlyAcked(getAckedPackets(4, 5, 6, 10, 11, 12), 0, 0, 7)).To(BeFalse())
// With the next ACK, all testing packets will now have been marked CE.
tracer.EXPECT().ECNStateUpdated(logging.ECNStateFailed, logging.ECNFailedManglingDetected)
Expect(ecnTracker.HandleNewlyAcked(getAckedPackets(7, 8, 9, 13), 0, 0, 10)).To(BeFalse())
})
It("only detects ECN mangling after sending all testing packets", func() {
tracer.EXPECT().ECNStateUpdated(logging.ECNStateTesting, logging.ECNTriggerNoTrigger)
for i := 0; i < 9; i++ {
Expect(ecnTracker.Mode()).To(Equal(protocol.ECT0))
ecnTracker.SentPacket(protocol.PacketNumber(i), protocol.ECT0)
Expect(ecnTracker.HandleNewlyAcked(getAckedPackets(protocol.PacketNumber(i)), 0, 0, int64(i+1))).To(BeFalse())
}
// Send the last testing packet, and receive a
tracer.EXPECT().ECNStateUpdated(logging.ECNStateUnknown, logging.ECNTriggerNoTrigger)
Expect(ecnTracker.Mode()).To(Equal(protocol.ECT0))
ecnTracker.SentPacket(9, protocol.ECT0)
// This ACK now reports the last testing packets as CE as well.
tracer.EXPECT().ECNStateUpdated(logging.ECNStateFailed, logging.ECNFailedManglingDetected)
Expect(ecnTracker.HandleNewlyAcked(getAckedPackets(9), 0, 0, 10)).To(BeFalse())
})
It("declares congestion", func() {
sendAllTestingPackets()
for i := 10; i < 20; i++ {