Hi,
This calculation of the receive window has a logic error:
If win is 0 it will be overwritten by (rcv_adv - rcv_nxt). Thus, win
will be (rcv_adv - rcv_nxt) even if its below (sb_hiwat / 4).
We could just remove the dead (sb_hiwat / 4) code, or reorder the
conditions to keep the original feature.
OK?
bye,
Jan
Index: netinet/tcp_output.c
===================================================================
RCS file: /cvs/src/sys/netinet/tcp_output.c,v
retrieving revision 1.130
diff -u -p -r1.130 tcp_output.c
--- netinet/tcp_output.c 8 Feb 2021 19:37:15 -0000 1.130
+++ netinet/tcp_output.c 22 Jul 2021 12:33:13 -0000
@@ -812,12 +812,12 @@ send:
* Calculate receive window. Don't shrink window,
* but avoid silly window syndrome.
*/
- if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)tp->t_maxseg)
- win = 0;
if (win > (long)TCP_MAXWIN << tp->rcv_scale)
win = (long)TCP_MAXWIN << tp->rcv_scale;
if (win < (long)(int32_t)(tp->rcv_adv - tp->rcv_nxt))
win = (long)(int32_t)(tp->rcv_adv - tp->rcv_nxt);
+ if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)tp->t_maxseg)
+ win = 0;
if (flags & TH_RST)
win = 0;
th->th_win = htons((u_int16_t) (win>>tp->rcv_scale));
