This is a simple little iptables match that can be used to create the Strong
End System model, that router and other non-Linux customers expect. There
are management and other applications that use ping and expect to only get
a response when the interface with that address is up. Normally, a Linux
system will respond to a packet that arrives for any of the system addresses
independent of which link it arrives on.
The module can be used on the INPUT chain like:
# iptables -P INPUT DROP
# iptables -A INPUT -m strict -j ACCEPT
---
net/ipv4/devinet.c | 1
net/ipv4/netfilter/Kconfig | 12 ++++++++
net/ipv4/netfilter/Makefile | 1
net/ipv4/netfilter/ipt_strict.c | 56 ++++++++++++++++++++++++++++++++++++++++
4 files changed, 70 insertions(+)
--- a/net/ipv4/netfilter/Kconfig 2009-02-26 17:47:03.000000000 -0800
+++ b/net/ipv4/netfilter/Kconfig 2009-02-26 17:47:08.000000000 -0800
@@ -92,6 +92,18 @@ config IP_NF_MATCH_ECN
To compile it as a module, choose M here. If unsure, say N.
+config IP_NF_MATCH_STRICT
+ tristate '"strict end system" match support'
+ depends on NETFILTER_ADVANCED
+ help
+ This option adds a 'strict' match, which allows you to
+ match only packets that arrive with the destinaton address matching
+ an IP address on the incoming interface. This can be used to implement
+ Strong End System model as defined in Internet Host Requirements
+ (RFC1122).
+
+ To compile it as a module, choose M here. If unsure, say N.
+
config IP_NF_MATCH_TTL
tristate '"ttl" match support'
depends on NETFILTER_ADVANCED
--- a/net/ipv4/netfilter/Makefile 2009-02-26 17:46:37.000000000 -0800
+++ b/net/ipv4/netfilter/Makefile 2009-02-26 17:47:08.000000000 -0800
@@ -51,6 +51,7 @@ obj-$(CONFIG_IP_NF_SECURITY) += iptable_
obj-$(CONFIG_IP_NF_MATCH_ADDRTYPE) += ipt_addrtype.o
obj-$(CONFIG_IP_NF_MATCH_AH) += ipt_ah.o
obj-$(CONFIG_IP_NF_MATCH_ECN) += ipt_ecn.o
+obj-$(CONFIG_IP_NF_MATCH_STRICT) += ipt_strict.o
# targets
obj-$(CONFIG_IP_NF_TARGET_CLUSTERIP) += ipt_CLUSTERIP.o
--- a/net/ipv4/devinet.c 2009-02-26 17:46:37.000000000 -0800
+++ b/net/ipv4/devinet.c 2009-02-26 17:47:08.000000000 -0800
@@ -230,6 +230,7 @@ int inet_addr_onlink(struct in_device *i
rcu_read_unlock();
return 0;
}
+EXPORT_SYMBOL_GPL(inet_addr_onlink);
static void __inet_del_ifa(struct in_device *in_dev, struct in_ifaddr **ifap,
int destroy, struct nlmsghdr *nlh, u32 pid)
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ b/net/ipv4/netfilter/ipt_strict.c 2009-02-26 17:52:19.000000000 -0800
@@ -0,0 +1,56 @@
+/* IP tables module for matching packets not routed to incoming interface
+ *
+ * (C) 2009 by Stephen Hemminger <shemminger@xxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/in.h>
+#include <linux/ip.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/if.h>
+#include <linux/inetdevice.h>
+
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter_ipv4/ip_tables.h>
+
+MODULE_AUTHOR("Stephen Hemminger <shemminger@xxxxxxxxxx>");
+MODULE_DESCRIPTION("Xtables: Strict End System match");
+MODULE_LICENSE("GPL");
+
+static bool strict_mt(const struct sk_buff *skb, const struct xt_match_param *par)
+{
+ struct in_device *in_dev;
+ bool ret;
+
+ rcu_read_lock();
+ in_dev = __in_dev_get_rcu(skb->dev);
+ ret = (in_dev && inet_addr_onlink(in_dev, ip_hdr(skb)->daddr, 0));
+ rcu_read_unlock();
+
+ return ret;
+}
+
+static struct xt_match strict_mt_reg __read_mostly = {
+ .name = "strict",
+ .family = NFPROTO_IPV4,
+ .match = strict_mt,
+ .matchsize = 0,
+ .me = THIS_MODULE,
+};
+
+static int __init strict_mt_init(void)
+{
+ return xt_register_match(&strict_mt_reg);
+}
+
+static void __exit strict_mt_exit(void)
+{
+ xt_unregister_match(&strict_mt_reg);
+}
+
+module_init(strict_mt_init);
+module_exit(strict_mt_exit);
--
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