svn commit: r340774 - in head/sys/netinet: . tcp_stacks

[Michael Tuexen]

Author: tuexen
Date: Thu Nov 22 19:49:52 2018
New Revision: 340774
URL: https://svnweb.freebsd.org/changeset/base/340774

Log:
  Ensure that TCP RST-segments announce consistently a receiver window of
  zero. This was already done when sending them via tcp_respond().
  
  Reviewed by:		rrs@
  MFC after:		1 week
  Sponsored by:		Netflix, Inc.
  Differential Revision:	https://reviews.freebsd.org/D17949

Modified:
  head/sys/netinet/tcp_output.c
  head/sys/netinet/tcp_stacks/rack.c

Modified: head/sys/netinet/tcp_output.c
==============================================================================
--- head/sys/netinet/tcp_output.c	Thu Nov 22 18:59:05 2018	(r340773)
+++ head/sys/netinet/tcp_output.c	Thu Nov 22 19:49:52 2018	(r340774)
@@ -1172,14 +1172,18 @@ send:
 	/*
 	 * Calculate receive window.  Don't shrink window,
 	 * but avoid silly window syndrome.
+	 * If a RST segment is sent, advertise a window of zero.
 	 */
-	if (recwin < (so->so_rcv.sb_hiwat / 4) &&
-	    recwin < tp->t_maxseg)
+	if (flags & TH_RST) {
 		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);
-
+	} else {
+		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);
+	}
 	/*
 	 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
 	 * or <SYN,ACK>) segment itself is never scaled.  The <SYN,ACK>

Modified: head/sys/netinet/tcp_stacks/rack.c
==============================================================================
--- head/sys/netinet/tcp_stacks/rack.c	Thu Nov 22 18:59:05 2018	(r340773)
+++ head/sys/netinet/tcp_stacks/rack.c	Thu Nov 22 19:49:52 2018	(r340774)
@@ -8189,15 +8189,20 @@ send:
 	/*
 	 * Calculate receive window.  Don't shrink window, but avoid silly
 	 * window syndrome.
+	 * If a RST segment is sent, advertise a window of zero.
 	 */
-	if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
-	    recwin < (long)tp->t_maxseg)
+	if (flags & TH_RST) {
 		recwin = 0;
-	if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
-	    recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
-		recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
-	if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
-		recwin = (long)TCP_MAXWIN << tp->rcv_scale;
+	} else {
+		if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
+		    recwin < (long)tp->t_maxseg)
+			recwin = 0;
+		if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
+		    recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
+			recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
+		if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
+			recwin = (long)TCP_MAXWIN << tp->rcv_scale;
+	}
 
 	/*
 	 * According to RFC1323 the window field in a SYN (i.e., a <SYN> or