Re: [lwip-users] sending a RST when the connection is in a non-synchronized state(SYN-SENT, SYN-RECEIVED)

[Leon Woestenberg]

Olaf, Jan,

allow me some time to understand the patches and integrate them. Thanks!

I will create a new release if this applies.

Regards,

Leon.

On Mon, 2005-05-30 at 17:27, Olaf Peters wrote:
> Hi,
> 
> During TCP tests between lwIP 1.1.0 and Windows-XP I discovered that lwIP
> doesn't send a RST segment when the connection is in a non-synchronized
> state (SYN-SENT, SYN-RECEIVED) and an incoming segment acknowledges
> something not yet sent. See item 2 in the section "Reset Generation",
> RFC793, page 36.
> 
> I discovered this when I had a half open connection, i.e. I restarted my
> system when my app had an open connection with XP (so XP still thinks it is
> connected). In this half open connection state, my application on top of
> lwIP tried to connect to XP, and XP did send an ACK to me (see also
> figure-10 in RFC793). Anybody else did run into the same problem?
> 
> Olaf.
> 
> 
> Below are patches for the changes I applied to lwIP 1.1.0 to solve my
> problems, please have a look and comment:
> 
> 
> *** lwip-1.1.0-org/src/core/tcp_in.c  Wed Nov 24 17:05:42 2004
> --- lwip-1.1.0/src/core/tcp_in.c      Tue May 24 17:40:20 2005
> *************** tcp_process(struct tcp_pcb *pcb)
> *** 561,566 ****
> --- 562,579 ----
>         TCP_EVENT_CONNECTED(pcb, ERR_OK, err);
>         tcp_ack(pcb);
>       }
> +     else {
> +       /* When we received an ACK, we might deal with an half-open
> +          connection (the other side might be in a synchronized/connected
> +          state). Send a RST to bring the other side in a non-synchronized 
> +          state. */
> +       if (flags & TCP_ACK) {
> +          tcp_rst(ackno, seqno + tcplen, &(iphdr->dest), &(iphdr->src),
> +                  tcphdr->dest, tcphdr->src);
> +       }
> +     }
>       break;
>     case SYN_RCVD:
>       if (flags & TCP_ACK &&
> *************** tcp_process(struct tcp_pcb *pcb)
> *** 586,591 ****
> --- 599,613 ----
>           tcp_receive(pcb);
>           pcb->cwnd = pcb->mss;
>         }
> +       else {
> +         /* We received an ACK but with an incorrect ack number. Send a RST
> +            to inform the other side about this situation. */
> +         tcp_rst(ackno, seqno + tcplen, &(iphdr->dest), &(iphdr->src),
> +                 tcphdr->dest, tcphdr->src);
> +       }
>       }
>       break;
>     case CLOSE_WAIT:
> 
> 
> 
> 
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