svn commit: r347161 - stable/11/sys/netinet

[Michael Tuexen]

Author: tuexen
Date: Sun May  5 19:20:27 2019
New Revision: 347161
URL: https://svnweb.freebsd.org/changeset/base/347161

Log:
  MFC r336937:
  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 avoid inconsistencies.
  
  MFC r344148:
  Fix a byte ordering issue for the advertised receiver window in ACK
  segments sent in TIMEWAIT state, which I introduced in r336937.

Modified:
  stable/11/sys/netinet/tcp_timewait.c
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/sys/netinet/tcp_timewait.c
==============================================================================
--- stable/11/sys/netinet/tcp_timewait.c	Sun May  5 17:10:12 2019	(r347160)
+++ stable/11/sys/netinet/tcp_timewait.c	Sun May  5 19:20:27 2019	(r347161)
@@ -228,6 +228,7 @@ tcp_twstart(struct tcpcb *tp)
 	struct inpcb *inp = tp->t_inpcb;
 	int acknow;
 	struct socket *so;
+	uint32_t recwin;
 #ifdef INET6
 	int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
 #endif
@@ -294,10 +295,16 @@ 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 = (u_short)(recwin >> tp->rcv_scale);
 
 	/*
 	 * Set t_recent if timestamps are used on the connection.
@@ -334,7 +341,6 @@ tcp_twstart(struct tcpcb *tp)
 	 * and might not be needed here any longer.
 	 */
 	tcp_discardcb(tp);
-	so = inp->inp_socket;
 	soisdisconnected(so);
 	tw->tw_cred = crhold(so->so_cred);
 	SOCK_LOCK(so);