On 22/07/21(Thu) 15:03, Jan Klemkow wrote: > 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).
Why is this a problem? > 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)); >
