diff options
Diffstat (limited to 'pkg/tcpip/transport/tcp/rcv.go')
| -rw-r--r-- | pkg/tcpip/transport/tcp/rcv.go | 78 |
1 files changed, 69 insertions, 9 deletions
diff --git a/pkg/tcpip/transport/tcp/rcv.go b/pkg/tcpip/transport/tcp/rcv.go index 8d9de9bf9..e90f9a7d9 100644 --- a/pkg/tcpip/transport/tcp/rcv.go +++ b/pkg/tcpip/transport/tcp/rcv.go @@ -16,6 +16,7 @@ package tcp import ( "container/heap" + "time" "gvisor.dev/gvisor/pkg/tcpip/header" "gvisor.dev/gvisor/pkg/tcpip/seqnum" @@ -38,6 +39,9 @@ type receiver struct { // shrinking it. rcvAcc seqnum.Value + // rcvWnd is the non-scaled receive window last advertised to the peer. + rcvWnd seqnum.Size + rcvWndScale uint8 closed bool @@ -47,13 +51,14 @@ type receiver struct { pendingBufSize seqnum.Size } -func newReceiver(ep *endpoint, irs seqnum.Value, rcvWnd seqnum.Size, rcvWndScale uint8) *receiver { +func newReceiver(ep *endpoint, irs seqnum.Value, rcvWnd seqnum.Size, rcvWndScale uint8, pendingBufSize seqnum.Size) *receiver { return &receiver{ ep: ep, rcvNxt: irs + 1, rcvAcc: irs.Add(rcvWnd + 1), + rcvWnd: rcvWnd, rcvWndScale: rcvWndScale, - pendingBufSize: rcvWnd, + pendingBufSize: pendingBufSize, } } @@ -72,14 +77,16 @@ func (r *receiver) acceptable(segSeq seqnum.Value, segLen seqnum.Size) bool { // getSendParams returns the parameters needed by the sender when building // segments to send. func (r *receiver) getSendParams() (rcvNxt seqnum.Value, rcvWnd seqnum.Size) { - // Calculate the window size based on the current buffer size. - n := r.ep.receiveBufferAvailable() - acc := r.rcvNxt.Add(seqnum.Size(n)) + // Calculate the window size based on the available buffer space. + receiveBufferAvailable := r.ep.receiveBufferAvailable() + acc := r.rcvNxt.Add(seqnum.Size(receiveBufferAvailable)) if r.rcvAcc.LessThan(acc) { r.rcvAcc = acc } - - return r.rcvNxt, r.rcvNxt.Size(r.rcvAcc) >> r.rcvWndScale + // Stash away the non-scaled receive window as we use it for measuring + // receiver's estimated RTT. + r.rcvWnd = r.rcvNxt.Size(r.rcvAcc) + return r.rcvNxt, r.rcvWnd >> r.rcvWndScale } // nonZeroWindow is called when the receive window grows from zero to nonzero; @@ -130,6 +137,21 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum // Update the segment that we're expecting to consume. r.rcvNxt = segSeq.Add(segLen) + // In cases of a misbehaving sender which could send more than the + // advertised window, we could end up in a situation where we get a + // segment that exceeds the window advertised. Instead of partially + // accepting the segment and discarding bytes beyond the advertised + // window, we accept the whole segment and make sure r.rcvAcc is moved + // forward to match r.rcvNxt to indicate that the window is now closed. + // + // In absence of this check the r.acceptable() check fails and accepts + // segments that should be dropped because rcvWnd is calculated as + // the size of the interval (rcvNxt, rcvAcc] which becomes extremely + // large if rcvAcc is ever less than rcvNxt. + if r.rcvAcc.LessThan(r.rcvNxt) { + r.rcvAcc = r.rcvNxt + } + // Trim SACK Blocks to remove any SACK information that covers // sequence numbers that have been consumed. TrimSACKBlockList(&r.ep.sack, r.rcvNxt) @@ -198,6 +220,39 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum return true } +// updateRTT updates the receiver RTT measurement based on the sequence number +// of the received segment. +func (r *receiver) updateRTT() { + // From: https://public.lanl.gov/radiant/pubs/drs/sc2001-poster.pdf + // + // A system that is only transmitting acknowledgements can still + // estimate the round-trip time by observing the time between when a byte + // is first acknowledged and the receipt of data that is at least one + // window beyond the sequence number that was acknowledged. + r.ep.rcvListMu.Lock() + if r.ep.rcvAutoParams.rttMeasureTime.IsZero() { + // New measurement. + r.ep.rcvAutoParams.rttMeasureTime = time.Now() + r.ep.rcvAutoParams.rttMeasureSeqNumber = r.rcvNxt.Add(r.rcvWnd) + r.ep.rcvListMu.Unlock() + return + } + if r.rcvNxt.LessThan(r.ep.rcvAutoParams.rttMeasureSeqNumber) { + r.ep.rcvListMu.Unlock() + return + } + rtt := time.Since(r.ep.rcvAutoParams.rttMeasureTime) + // We only store the minimum observed RTT here as this is only used in + // absence of a SRTT available from either timestamps or a sender + // measurement of RTT. + if r.ep.rcvAutoParams.rtt == 0 || rtt < r.ep.rcvAutoParams.rtt { + r.ep.rcvAutoParams.rtt = rtt + } + r.ep.rcvAutoParams.rttMeasureTime = time.Now() + r.ep.rcvAutoParams.rttMeasureSeqNumber = r.rcvNxt.Add(r.rcvWnd) + r.ep.rcvListMu.Unlock() +} + // handleRcvdSegment handles TCP segments directed at the connection managed by // r as they arrive. It is called by the protocol main loop. func (r *receiver) handleRcvdSegment(s *segment) { @@ -226,10 +281,9 @@ func (r *receiver) handleRcvdSegment(s *segment) { r.pendingBufUsed += s.logicalLen() s.incRef() heap.Push(&r.pendingRcvdSegments, s) + UpdateSACKBlocks(&r.ep.sack, segSeq, segSeq.Add(segLen), r.rcvNxt) } - UpdateSACKBlocks(&r.ep.sack, segSeq, segSeq.Add(segLen), r.rcvNxt) - // Immediately send an ack so that the peer knows it may // have to retransmit. r.ep.snd.sendAck() @@ -237,6 +291,12 @@ func (r *receiver) handleRcvdSegment(s *segment) { return } + // Since we consumed a segment update the receiver's RTT estimate + // if required. + if segLen > 0 { + r.updateRTT() + } + // By consuming the current segment, we may have filled a gap in the // sequence number domain that allows pending segments to be consumed // now. So try to do it. |