[netfilter-cvslog] r6737 - in trunk/iptables: extensions include/linux/netfilter_ipv6

kaber at netfilter.org kaber at netfilter.org
Tue Jan 16 15:19:21 CET 2007


Author: kaber at netfilter.org
Date: 2007-01-16 15:19:20 +0100 (Tue, 16 Jan 2007)
New Revision: 6737

Added:
   trunk/iptables/extensions/libip6t_TCPMSS.c
   trunk/iptables/extensions/libip6t_TCPMSS.man
   trunk/iptables/include/linux/netfilter_ipv6/ip6t_TCPMSS.h
Log:
Add ip6tables TCPMSS extension (Arnaud Ebalard <arno at natisbad.org>)

Kernel part will go in 2.6.21.


Added: trunk/iptables/extensions/libip6t_TCPMSS.c
===================================================================
--- trunk/iptables/extensions/libip6t_TCPMSS.c	                        (rev 0)
+++ trunk/iptables/extensions/libip6t_TCPMSS.c	2007-01-16 14:19:20 UTC (rev 6737)
@@ -0,0 +1,134 @@
+/* Shared library add-on to iptables to add TCPMSS target support.
+ *
+ * Copyright (c) 2000 Marc Boucher
+*/
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <getopt.h>
+
+#include <ip6tables.h>
+#include <linux/netfilter_ipv6/ip6_tables.h>
+#include <linux/netfilter_ipv6/ip6t_TCPMSS.h>
+
+struct mssinfo {
+	struct ip6t_entry_target t;
+	struct ip6t_tcpmss_info mss;
+};
+
+/* Function which prints out usage message. */
+static void
+help(void)
+{
+	printf(
+"TCPMSS target v%s mutually-exclusive options:\n"
+"  --set-mss value               explicitly set MSS option to specified value\n"
+"  --clamp-mss-to-pmtu           automatically clamp MSS value to (path_MTU - 60)\n",
+IPTABLES_VERSION);
+}
+
+static struct option opts[] = {
+	{ "set-mss", 1, 0, '1' },
+	{ "clamp-mss-to-pmtu", 0, 0, '2' },
+	{ 0 }
+};
+
+/* Initialize the target. */
+static void
+init(struct ip6t_entry_target *t, unsigned int *nfcache)
+{
+}
+
+/* Function which parses command options; returns true if it
+   ate an option */
+static int
+parse(int c, char **argv, int invert, unsigned int *flags,
+      const struct ip6t_entry *entry,
+      struct ip6t_entry_target **target)
+{
+	struct ip6t_tcpmss_info *mssinfo
+		= (struct ip6t_tcpmss_info *)(*target)->data;
+
+	switch (c) {
+		unsigned int mssval;
+
+	case '1':
+		if (*flags)
+			exit_error(PARAMETER_PROBLEM,
+			           "TCPMSS target: Only one option may be specified");
+		if (string_to_number(optarg, 0, 65535 - 60, &mssval) == -1)
+			exit_error(PARAMETER_PROBLEM, "Bad TCPMSS value `%s'", optarg);
+
+		mssinfo->mss = mssval;
+		*flags = 1;
+		break;
+
+	case '2':
+		if (*flags)
+			exit_error(PARAMETER_PROBLEM,
+			           "TCPMSS target: Only one option may be specified");
+		mssinfo->mss = IP6T_TCPMSS_CLAMP_PMTU;
+		*flags = 1;
+		break;
+
+	default:
+		return 0;
+	}
+
+	return 1;
+}
+
+static void
+final_check(unsigned int flags)
+{
+	if (!flags)
+		exit_error(PARAMETER_PROBLEM,
+		           "TCPMSS target: At least one parameter is required");
+}
+
+/* Prints out the targinfo. */
+static void
+print(const struct ip6t_ip6 *ip6,
+      const struct ip6t_entry_target *target,
+      int numeric)
+{
+	const struct ip6t_tcpmss_info *mssinfo =
+		(const struct ip6t_tcpmss_info *)target->data;
+	if(mssinfo->mss == IP6T_TCPMSS_CLAMP_PMTU)
+		printf("TCPMSS clamp to PMTU ");
+	else
+		printf("TCPMSS set %u ", mssinfo->mss);
+}
+
+/* Saves the union ip6t_targinfo in parsable form to stdout. */
+static void
+save(const struct ip6t_ip6 *ip, const struct ip6t_entry_target *target)
+{
+	const struct ip6t_tcpmss_info *mssinfo =
+		(const struct ip6t_tcpmss_info *)target->data;
+
+	if(mssinfo->mss == IP6T_TCPMSS_CLAMP_PMTU)
+		printf("--clamp-mss-to-pmtu ");
+	else
+		printf("--set-mss %u ", mssinfo->mss);
+}
+
+static struct ip6tables_target mss = {
+	.next		= NULL,
+	.name		= "TCPMSS",
+	.version	= IPTABLES_VERSION,
+	.size		= IP6T_ALIGN(sizeof(struct ip6t_tcpmss_info)),
+	.userspacesize	= IP6T_ALIGN(sizeof(struct ip6t_tcpmss_info)),
+	.help		= &help,
+	.init		= &init,
+	.parse		= &parse,
+	.final_check	= &final_check,
+	.print		= &print,
+	.save		= &save,
+	.extra_opts	= opts
+};
+
+void _init(void)
+{
+	register_target6(&mss);
+}

Added: trunk/iptables/extensions/libip6t_TCPMSS.man
===================================================================
--- trunk/iptables/extensions/libip6t_TCPMSS.man	                        (rev 0)
+++ trunk/iptables/extensions/libip6t_TCPMSS.man	2007-01-16 14:19:20 UTC (rev 6737)
@@ -0,0 +1,42 @@
+This target allows to alter the MSS value of TCP SYN packets, to control
+the maximum size for that connection (usually limiting it to your
+outgoing interface's MTU minus 60).  Of course, it can only be used
+in conjunction with
+.BR "-p tcp" .
+It is only valid in the
+.BR mangle
+table.
+.br
+This target is used to overcome criminally braindead ISPs or servers
+which block ICMPv6 Packet Too Big packets or are unable to send them.
+The symptoms of this problem are that everything works fine from your 
+Linux firewall/router, but machines behind it can never exchange large
+packets:
+.PD 0
+.RS 0.1i
+.TP 0.3i
+1)
+Web browsers connect, then hang with no data received.
+.TP
+2)
+Small mail works fine, but large emails hang.
+.TP
+3)
+ssh works fine, but scp hangs after initial handshaking.
+.RE
+.PD
+Workaround: activate this option and add a rule to your firewall
+configuration like:
+.nf
+ ip6tables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN \\
+             -j TCPMSS --clamp-mss-to-pmtu
+.fi
+.TP
+.BI "--set-mss " "value"
+Explicitly set MSS option to specified value.
+.TP
+.B "--clamp-mss-to-pmtu"
+Automatically clamp MSS value to (path_MTU - 60).
+.TP
+These options are mutually exclusive.
+

Added: trunk/iptables/include/linux/netfilter_ipv6/ip6t_TCPMSS.h
===================================================================
--- trunk/iptables/include/linux/netfilter_ipv6/ip6t_TCPMSS.h	                        (rev 0)
+++ trunk/iptables/include/linux/netfilter_ipv6/ip6t_TCPMSS.h	2007-01-16 14:19:20 UTC (rev 6737)
@@ -0,0 +1,10 @@
+#ifndef _IP6T_TCPMSS_H
+#define _IP6T_TCPMSS_H
+
+struct ip6t_tcpmss_info {
+	u_int16_t mss;
+};
+
+#define IP6T_TCPMSS_CLAMP_PMTU 0xffff
+
+#endif /*_IP6T_TCPMSS_H*/




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