[lwip-users] loopif bug ?

[Andreas Stenius]

Hi all,

I've run across a misshap with the loopif ( TCP only, not UDP ).
When connecting to 'localhost' using the loopif interface, the tcp packet is
processed on the
receiver side before the send process is completed, resulting in a reference
to NULL in tcp_process:

  case SYN_SENT:
    DEBUGF(TCP_INPUT_DEBUG, ("SYN-SENT: ackno %lu pcb->snd_nxt %lu unacked
%lu\n", ackno,
           pcb->snd_nxt, ntohl(pcb->unacked->tcphdr->seqno)));
    if(flags & (TCP_ACK | TCP_SYN) &&
       ackno == ntohl(pcb->unacked->tcphdr->seqno) + 1) {

Here, pcb->unacked is still NULL. It is set in tcp_output:

    tcp_output_segment(seg, pcb);
    pcb->snd_nxt = ntohl(seg->tcphdr->seqno) + TCP_TCPLEN(seg);
    if(TCP_SEQ_LT(pcb->snd_max, pcb->snd_nxt)) {
      pcb->snd_max = pcb->snd_nxt;
    }
    /* put segment on unacknowledged list if length > 0 */
    if(TCP_TCPLEN(seg) > 0) {
      seg->next = NULL;
      if(pcb->unacked == NULL) {
        pcb->unacked = seg;

But, tcp_output_segment is called first.


Didn't find any information regarding this in the mailinglist, so I wasn't
sure if you had noticed this yet ??


Thanks,
Andreas

------------------------------------------------
Andreas Stenius

E-mail     andreas.stenius AT device.se
Cell       +46 (0) 70 618 06 26
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Wireless Device AB
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