svn commit: r336937 - head/sys/netinet

[Michael Tuexen]

Author: tuexen
Date: Mon Jul 30 21:13:42 2018
New Revision: 336937
URL: https://svnweb.freebsd.org/changeset/base/336937

Log:
  Send consistent SEG.WIN when using timewait codepath for TCP.
  
  When sending TCP segments from the timewait code path, a stored
  value of the last sent window is used. Use the same code for
  computing this in the timewait code path as in the main code
  path used in tcp_output() to avoiv inconsistencies.
  
  Reviewed by:		rrs@
  MFC after:		1 month
  Sponsored by:		Netflix, Inc.
  Differential Revision:	https://reviews.freebsd.org/D16503

Modified:
  head/sys/netinet/tcp_timewait.c

Modified: head/sys/netinet/tcp_timewait.c
==============================================================================
--- head/sys/netinet/tcp_timewait.c	Mon Jul 30 20:59:58 2018	(r336936)
+++ head/sys/netinet/tcp_timewait.c	Mon Jul 30 21:13:42 2018	(r336937)
@@ -230,6 +230,7 @@ tcp_twstart(struct tcpcb *tp)
 	struct tcptw twlocal, *tw;
 	struct inpcb *inp = tp->t_inpcb;
 	struct socket *so;
+	uint32_t recwin;
 	bool acknow, local;
 #ifdef INET6
 	bool isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
@@ -292,10 +293,16 @@ tcp_twstart(struct tcpcb *tp)
 	/*
 	 * Recover last window size sent.
 	 */
-	if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
-		tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale;
-	else
-		tw->last_win = 0;
+	so = inp->inp_socket;
+	recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
+	    (long)TCP_MAXWIN << tp->rcv_scale);
+	if (recwin < (so->so_rcv.sb_hiwat / 4) &&
+	    recwin < tp->t_maxseg)
+		recwin = 0;
+	if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
+	    recwin < (tp->rcv_adv - tp->rcv_nxt))
+		recwin = (tp->rcv_adv - tp->rcv_nxt);
+	tw->last_win = htons((u_short)(recwin >> tp->rcv_scale));
 
 	/*
 	 * Set t_recent if timestamps are used on the connection.
@@ -332,7 +339,6 @@ tcp_twstart(struct tcpcb *tp)
 	 * and might not be needed here any longer.
 	 */
 	tcp_discardcb(tp);
-	so = inp->inp_socket;
 	soisdisconnected(so);
 	tw->tw_so_options = so->so_options;
 	inp->inp_flags |= INP_TIMEWAIT;