[lwip-devel] [bug #20779] Keep-Alive and SYNs

[Oleg Tyshev]

Follow-up Comment #10, bug #20779 (project lwip):

I think, that in tcp_process() should be added SYN check for any state.
tcp_receive() is corect now only if sequence number of the packet outside of
the receive window. Otherwise it could be queued into out of sequence queue or
processed as data (by us tcplen = p->tot_len + ((flags & TCP_FIN || flags &
TCP_SYN)? 1: 0);)

for example instead

  case CLOSE_WAIT:
    /* FALLTHROUGH */
  case ESTABLISHED:
    accepted_inseq = tcp_receive(pcb);
    if ((flags & TCP_FIN) && accepted_inseq) { /* passive close */
      tcp_ack_now(pcb);
      pcb->state = CLOSE_WAIT;
    }
    break;

would be more correct following code

  case CLOSE_WAIT:
    /* FALLTHROUGH */
  case ESTABLISHED:
    if (flags & TCP_SYN) {
      tcp_ack_now(pcb);
    }
    else {
      accepted_inseq = tcp_receive(pcb);
      if ((flags & TCP_FIN) && accepted_inseq) { /* passive close */
        tcp_ack_now(pcb);
        pcb->state = CLOSE_WAIT;
      }
    }
    break;


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