From: friehm <friehm@openbsd.org>
Date: Mon, 17 Sep 2018 14:07:48 +0000 (+0000)
Subject: Do not acknowledge a received ack-only tcp packet that we would drop due to
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=af446eb323a81d8ed7c658886175000c1583d952;p=openbsd

Do not acknowledge a received ack-only tcp packet that we would drop due to
PAWS. Otherwise we could trigger a retransmit of the opposite party with another
wrong timestamp and produce loop. I have seen this with a buggy server which
messed up tcp timestamps.
Suggested by Prof. Jacobson for FreeBSD.

ok krw, bluhm, henning, mpi
---

diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index 899471dbbcc..0244e2907ab 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tcp_input.c,v 1.358 2018/07/23 21:14:00 bluhm Exp $	*/
+/*	$OpenBSD: tcp_input.c,v 1.359 2018/09/17 14:07:48 friehm Exp $	*/
 /*	$NetBSD: tcp_input.c,v 1.23 1996/02/13 23:43:44 christos Exp $	*/
 
 /*
@@ -1270,7 +1270,9 @@ trimthenstep6:
 		} else {
 			tcpstat_pkt(tcps_rcvduppack, tcps_rcvdupbyte, tlen);
 			tcpstat_inc(tcps_pawsdrop);
-			goto dropafterack;
+			if (tlen)
+				goto dropafterack;
+			goto drop;
 		}
 	}