diff options
| -rw-r--r-- | pkg/tcpip/transport/tcp/snd.go | 94 |
1 files changed, 91 insertions, 3 deletions
diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go index d8cfe3115..a3018914b 100644 --- a/pkg/tcpip/transport/tcp/snd.go +++ b/pkg/tcpip/transport/tcp/snd.go @@ -41,6 +41,10 @@ const ( // nDupAckThreshold is the number of duplicate ACK's required // before fast-retransmit is entered. nDupAckThreshold = 3 + + // MaxRetries is the maximum number of probe retries sender does + // before timing out the connection, Linux default TCP_RETR2. + MaxRetries = 15 ) // ccState indicates the current congestion control state for this sender. @@ -138,6 +142,14 @@ type sender struct { // the first segment that was retransmitted due to RTO expiration. firstRetransmittedSegXmitTime time.Time `state:".(unixTime)"` + // zeroWindowProbing is set if the sender is currently probing + // for zero receive window. + zeroWindowProbing bool `state:"nosave"` + + // unackZeroWindowProbes is the number of unacknowledged zero + // window probes. + unackZeroWindowProbes uint32 `state:"nosave"` + closed bool writeNext *segment writeList segmentList @@ -479,10 +491,24 @@ func (s *sender) retransmitTimerExpired() bool { remaining = uto - elapsed } - if remaining <= 0 || s.rto >= MaxRTO { + // Always honor the user-timeout irrespective of whether the zero + // window probes were acknowledged. + // net/ipv4/tcp_timer.c::tcp_probe_timer() + if remaining <= 0 || s.unackZeroWindowProbes >= MaxRetries { return false } + if s.rto >= MaxRTO { + // RFC 1122 section: 4.2.2.17 + // A TCP MAY keep its offered receive window closed + // indefinitely. As long as the receiving TCP continues to + // send acknowledgments in response to the probe segments, the + // sending TCP MUST allow the connection to stay open. + if !(s.zeroWindowProbing && s.unackZeroWindowProbes == 0) { + return false + } + } + // Set new timeout. The timer will be restarted by the call to sendData // below. s.rto *= 2 @@ -533,6 +559,15 @@ func (s *sender) retransmitTimerExpired() bool { // information is usable after an RTO. s.ep.scoreboard.Reset() s.writeNext = s.writeList.Front() + + // RFC 1122 4.2.2.17: Start sending zero window probes when we still see a + // zero receive window after retransmission interval and we have data to + // send. + if s.zeroWindowProbing { + s.sendZeroWindowProbe() + return true + } + s.sendData() return true @@ -827,6 +862,34 @@ func (s *sender) handleSACKRecovery(limit int, end seqnum.Value) (dataSent bool) return dataSent } +func (s *sender) sendZeroWindowProbe() { + ack, win := s.ep.rcv.getSendParams() + s.unackZeroWindowProbes++ + // Send a zero window probe with sequence number pointing to + // the last acknowledged byte. + s.ep.sendRaw(buffer.VectorisedView{}, header.TCPFlagAck, s.sndUna-1, ack, win) + // Rearm the timer to continue probing. + s.resendTimer.enable(s.rto) +} + +func (s *sender) enableZeroWindowProbing() { + s.zeroWindowProbing = true + // We piggyback the probing on the retransmit timer with the + // current retranmission interval, as we may start probing while + // segment retransmissions. + if s.firstRetransmittedSegXmitTime.IsZero() { + s.firstRetransmittedSegXmitTime = time.Now() + } + s.resendTimer.enable(s.rto) +} + +func (s *sender) disableZeroWindowProbing() { + s.zeroWindowProbing = false + s.unackZeroWindowProbes = 0 + s.firstRetransmittedSegXmitTime = time.Time{} + s.resendTimer.disable() +} + // sendData sends new data segments. It is called when data becomes available or // when the send window opens up. func (s *sender) sendData() { @@ -875,6 +938,13 @@ func (s *sender) sendData() { s.ep.disableKeepaliveTimer() } + // If the sender has advertized zero receive window and we have + // data to be sent out, start zero window probing to query the + // the remote for it's receive window size. + if s.writeNext != nil && s.sndWnd == 0 { + s.enableZeroWindowProbing() + } + // Enable the timer if we have pending data and it's not enabled yet. if !s.resendTimer.enabled() && s.sndUna != s.sndNxt { s.resendTimer.enable(s.rto) @@ -1122,8 +1192,26 @@ func (s *sender) handleRcvdSegment(seg *segment) { // Stash away the current window size. s.sndWnd = seg.window - // Ignore ack if it doesn't acknowledge any new data. ack := seg.ackNumber + + // Disable zero window probing if remote advertizes a non-zero receive + // window. This can be with an ACK to the zero window probe (where the + // acknumber refers to the already acknowledged byte) OR to any previously + // unacknowledged segment. + if s.zeroWindowProbing && seg.window > 0 && + (ack == s.sndUna || (ack-1).InRange(s.sndUna, s.sndNxt)) { + s.disableZeroWindowProbing() + } + + // On receiving the ACK for the zero window probe, account for it and + // skip trying to send any segment as we are still probing for + // receive window to become non-zero. + if s.zeroWindowProbing && s.unackZeroWindowProbes > 0 && ack == s.sndUna { + s.unackZeroWindowProbes-- + return + } + + // Ignore ack if it doesn't acknowledge any new data. if (ack - 1).InRange(s.sndUna, s.sndNxt) { s.dupAckCount = 0 @@ -1143,7 +1231,7 @@ func (s *sender) handleRcvdSegment(seg *segment) { } // When an ack is received we must rearm the timer. - // RFC 6298 5.2 + // RFC 6298 5.3 s.resendTimer.enable(s.rto) // Remove all acknowledged data from the write list. |