svn commit: r361340 - in stable/12/sys/netinet: . tcp_stacks

[Richard Scheffenegger]

Author: rscheff
Date: Thu May 21 19:41:25 2020
New Revision: 361340
URL: https://svnweb.freebsd.org/changeset/base/361340

Log:
  MFC r360479: Prevent premature shrinking of the scaled receive window
  
  which can cause a TCP client to use invalid or stale TCP sequence numbers for ACK packets.
  
  Packets with old sequence numbers are ignored and not used to update the send window size.
  This might cause the TCP session to hang indefinitely under some circumstances.
  
  Reported by:	Cui Cheng
  Reviewed by:	tuexen (mentor), rgrimes (mentor, blanket)
  Approved by:	tuexen (mentor), rgrimes (mentor, blanket)
  MFC after:	3 weeks
  Sponsored by:	NetApp, Inc.
  Differential Revision:	https://reviews.freebsd.org/D24515

Modified:
  stable/12/sys/netinet/tcp_output.c
  stable/12/sys/netinet/tcp_stacks/rack.c
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/sys/netinet/tcp_output.c
==============================================================================
--- stable/12/sys/netinet/tcp_output.c	Thu May 21 18:50:05 2020	(r361339)
+++ stable/12/sys/netinet/tcp_output.c	Thu May 21 19:41:25 2020	(r361340)
@@ -1206,8 +1206,11 @@ send:
 	if (flags & TH_SYN)
 		th->th_win = htons((u_short)
 				(min(sbspace(&so->so_rcv), TCP_MAXWIN)));
-	else
+	else {
+		/* Avoid shrinking window with window scaling. */
+		recwin = roundup2(recwin, 1 << tp->rcv_scale);
 		th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
+	}
 
 	/*
 	 * Adjust the RXWIN0SENT flag - indicate that we have advertised

Modified: stable/12/sys/netinet/tcp_stacks/rack.c
==============================================================================
--- stable/12/sys/netinet/tcp_stacks/rack.c	Thu May 21 18:50:05 2020	(r361339)
+++ stable/12/sys/netinet/tcp_stacks/rack.c	Thu May 21 19:41:25 2020	(r361340)
@@ -8355,8 +8355,11 @@ send:
 	if (flags & TH_SYN)
 		th->th_win = htons((u_short)
 		    (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
-	else
+	else {
+		/* Avoid shrinking window with window scaling. */
+		recwin = roundup2(recwin, 1 << tp->rcv_scale);
 		th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
+	}
 	/*
 	 * Adjust the RXWIN0SENT flag - indicate that we have advertised a 0
 	 * window.  This may cause the remote transmitter to stall.  This