Re: [lwip-devel] Bug in TCP ooseq FIN processing

[Kieran Mansley]

On Sat, 13 Dec 2003, Karl Jeacle wrote:
> There is a small bug in lwIP's TCP handling of out-of-sequence FIN segments.
>
> For me, this problem exhibits itself with my receiving application blocking
> forever on netconn_recv() despite the sender having closed the connection.
>
> The problem is caused when tcp_receive() checks to see if out-of-sequence
> segments are now in sequence. It checks if an ooseq segment was a FIN,
> but it does this incorrectly. Instead of looking at the flags on the
> ooseq segment itself, it uses the "flags" variable. But "flags" is set
> for the value of the current segment being processed by TCP, not the
> ooseq segment.  The fix in tcp_in.c is simple:
>
> 1024c1024
> <     if (flags & TCP_FIN) {
> ---
> >     if (TCPH_FLAGS(cseg->tcphdr) & TCP_FIN) {

Well spotted, and thanks for the fix.  Interestingly the relevant line in
my 0.5.2 based tree is:

if(TCPH_FLAGS(inseg.tcphdr) & TCP_FIN) {

inseg refers to the most recent segment received, so the bug exists there
too - the source has been changed, but the bug not spotted.

I'll check in a fix as soon as savannah is fully operational.

Kieran