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

[Oleg Tyshev]

URL:
  <http://savannah.nongnu.org/bugs/?20779>

                 Summary: Keep-Alive and SYNs
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: olegreen
            Submitted on: Tuesday 08/14/2007 at 09:43
                Category: TCP
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: 

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Details:

Hello All,

I will try to describe scenario

- Server listens on port 100, keep-alive is on.
- Client does connect to server from port 200. (Not ephemeral port, always
200)
- Successful connect
- No data exchange
...
- Client - power off
- Client - power on
- Client tries again to connect from port 200 to port 100. (SYNs)
- Server sees activity on connection and keep-alive expires never.

I have seen to tcp_process and tcp_receive in TCP state ESTABLISHED.
There is no check TCP_SYN flag.
I think it should be silently discarded, but without modification
(in)activity timer
(in tcp_process()
  /* Update the PCB (in)activity timer. */
  pcb->tmr = tcp_ticks;
  pcb->keep_cnt_sent = 0;)
It is discarded now too, but only due to sequence number without analyze
TCP_SYN flag.

Oleg Tyshev




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