Re: [lwip-users] Zero sstresh bug, proposed patch

[Kieran Mansley]

On Fri, 2007-06-08 at 10:35 +0200, Per-Henrik Lundblom wrote:
> Hi,
> 
> When heavily opening and closing the tcp receive window on one side of a
> TCP connection, I ran into the problem with the TCP sstresh value being
> set to 0 resulting in a stop of transmission. My interpretion of the
> TCP standards (carefully studying of TCP/IP Illustrated) is that sstresh
> never should be assigned a value less than one MSS. Adding zero value
> check to the code solved all the transmissions stops.
> 
> My proposed patch against 1.2.0 is:
> 
> --- lwip-1.2.0/src/core/tcp_in.c        2006-08-18 12:18:42.000000000
> +0200
> +++ lwip-1.2.0_patched/src/core/tcp_in.c        2007-06-08
> 10:24:42.451875000 +0200
> @@ -678,6 +678,9 @@
>                pcb->ssthresh = pcb->snd_wnd / 2;
>              else
>                pcb->ssthresh = pcb->cwnd / 2;
> +
> +            if (pcb->sstresh == 0)
> +              pcb->sstresh = pcb->mss;

If it shouldn't be less than 1 mss wouldn't this be better?

if (pcb->ssthresh < pcb->mss)
  pcb->ssthresh = pcb->mss

Either way, could you file a bug on savannah so that this gets tracked
and fixed?

Thanks

Kieran