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Relax overly-conservative TCP option parsing used by ipnat when 

hunting for an MSS option to clamp.  The previous code assumed that at least
one more byte of options (such as a TCPOPT_EOL) would follow the MSS
option; now, we allow the MSS option to end on the last byte of the
TCP header.

Packets have been observed "in the wild" with a TCP header length of
'6' (24 bytes.. 20 bytes fixed header, 4 bytes options) with a 4-byte
MSS option exactly filling the 4 bytes of options payload and no
following TCPOPT_EOL.

RFC793 is quite explicit that the EOL byte:

	" .. need only be used if the end of the options would not
	otherwise coincide with the end of the TCP header."
This commit is contained in:
sommerfeld 2002-09-24 14:14:25 +00:00
parent bddb0d021d
commit 17aee57321
1 changed files with 3 additions and 3 deletions
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6
sys/netinet/ip_nat.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: ip_nat.c,v 1.53 2002/09/19 08:12:52 martti Exp $ */
/* $NetBSD: ip_nat.c,v 1.54 2002/09/24 14:14:25 sommerfeld Exp $ */
/*
* Copyright (C) 1995-2001 by Darren Reed.
@ -112,7 +112,7 @@ extern struct ifnet vpnif;
#if !defined(lint)
#if defined(__NetBSD__)
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: ip_nat.c,v 1.53 2002/09/19 08:12:52 martti Exp $");
__KERNEL_RCSID(0, "$NetBSD: ip_nat.c,v 1.54 2002/09/24 14:14:25 sommerfeld Exp $");
#else
static const char sccsid[] = "@(#)ip_nat.c 1.11 6/5/96 (C) 1995 Darren Reed";
static const char rcsid[] = "@(#)Id: ip_nat.c,v 2.37.2.70 2002/08/28 12:45:48 darrenr Exp";
@ -1176,7 +1176,7 @@ tcp_mss_clamp(tcp, maxmss, fin, csump)
if (&cp[1] >= ep)
break;
advance = cp[1];
if (&cp[advance] >= ep)
if (&cp[advance] > ep)
break;
switch (opt) {
case TCPOPT_MAXSEG: