diff options
Diffstat (limited to 'pkg/tcpip/transport/tcp/rcv.go')
| -rw-r--r-- | pkg/tcpip/transport/tcp/rcv.go | 37 |
1 files changed, 26 insertions, 11 deletions
diff --git a/pkg/tcpip/transport/tcp/rcv.go b/pkg/tcpip/transport/tcp/rcv.go index 5e0bfe585..bc920a03b 100644 --- a/pkg/tcpip/transport/tcp/rcv.go +++ b/pkg/tcpip/transport/tcp/rcv.go @@ -268,14 +268,7 @@ func (r *receiver) handleRcvdSegmentClosing(s *segment, state EndpointState, clo // If we are in one of the shutdown states then we need to do // additional checks before we try and process the segment. switch state { - case StateCloseWait: - // If the ACK acks something not yet sent then we send an ACK. - if r.ep.snd.sndNxt.LessThan(s.ackNumber) { - r.ep.snd.sendAck() - return true, nil - } - fallthrough - case StateClosing, StateLastAck: + case StateCloseWait, StateClosing, StateLastAck: if !s.sequenceNumber.LessThanEq(r.rcvNxt) { // Just drop the segment as we have // already received a FIN and this @@ -284,9 +277,31 @@ func (r *receiver) handleRcvdSegmentClosing(s *segment, state EndpointState, clo return true, nil } fallthrough - case StateFinWait1: - fallthrough - case StateFinWait2: + case StateFinWait1, StateFinWait2: + // If the ACK acks something not yet sent then we send an ACK. + // + // RFC793, page 37: If the connection is in a synchronized state, + // (ESTABLISHED, FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, + // TIME-WAIT), any unacceptable segment (out of window sequence number + // or unacceptable acknowledgment number) must elicit only an empty + // acknowledgment segment containing the current send-sequence number + // and an acknowledgment indicating the next sequence number expected + // to be received, and the connection remains in the same state. + // + // Just as on Linux, we do not apply this behavior when state is + // ESTABLISHED. + // Linux receive processing for all states except ESTABLISHED and + // TIME_WAIT is here where if the ACK check fails, we attempt to + // reply back with an ACK with correct seq/ack numbers. + // https://github.com/torvalds/linux/blob/v5.8/net/ipv4/tcp_input.c#L6186 + // The ESTABLISHED state processing is here where if the ACK check + // fails, we ignore the packet: + // https://github.com/torvalds/linux/blob/v5.8/net/ipv4/tcp_input.c#L5591 + if r.ep.snd.sndNxt.LessThan(s.ackNumber) { + r.ep.snd.sendAck() + return true, nil + } + // If we are closed for reads (either due to an // incoming FIN or the user calling shutdown(.., // SHUT_RD) then any data past the rcvNxt should |