[PATCH 05/15] connection tracking helper for SLP

[Jiri Slaby]

From: Jiri Bohac <jbohac@xxxxxxx>

A simple connection tracking helper for SLP. Marks replies to a
SLP broadcast query as ESTABLISHED to allow them to pass through the
firewall.

Signed-off-by: Jiri Bohac <jbohac@xxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Cc: netfilter-devel@xxxxxxxxxxxxxxx
Cc: netfilter@xxxxxxxxxxxxxxx
Cc: coreteam@xxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Patrick McHardy <kaber@xxxxxxxxx>
Cc: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
---
 net/netfilter/Kconfig            |  15 +++++
 net/netfilter/Makefile           |   1 +
 net/netfilter/nf_conntrack_slp.c | 131 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 147 insertions(+)
 create mode 100644 net/netfilter/nf_conntrack_slp.c

diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 56d22ca..ec61b30 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -320,6 +320,21 @@ config NF_CONNTRACK_TFTP
 
 	  To compile it as a module, choose M here.  If unsure, say N.
 
+config NF_CONNTRACK_SLP
+	tristate "SLP protocol support"
+	depends on NF_CONNTRACK
+	depends on NETFILTER_ADVANCED
+	help
+	  SLP queries are sometimes sent as broadcast messages from an
+	  unprivileged port and responded to with unicast messages to the
+	  same port. This make them hard to firewall properly because connection
+	  tracking doesn't deal with broadcasts. This helper tracks locally
+	  originating broadcast SLP queries and the corresponding
+	  responses. It relies on correct IP address configuration, specifically
+	  netmask and broadcast address.
+
+	  To compile it as a module, choose M here.  If unsure, say N.
+
 config NF_CT_NETLINK
 	tristate 'Connection tracking netlink interface'
 	select NETFILTER_NETLINK
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index a1abf87..aa7d5f1 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -43,6 +43,7 @@ obj-$(CONFIG_NF_CONNTRACK_PPTP) += nf_conntrack_pptp.o
 obj-$(CONFIG_NF_CONNTRACK_SANE) += nf_conntrack_sane.o
 obj-$(CONFIG_NF_CONNTRACK_SIP) += nf_conntrack_sip.o
 obj-$(CONFIG_NF_CONNTRACK_TFTP) += nf_conntrack_tftp.o
+obj-$(CONFIG_NF_CONNTRACK_SLP) += nf_conntrack_slp.o
 
 nf_nat-y	:= nf_nat_core.o nf_nat_proto_unknown.o nf_nat_proto_common.o \
 		   nf_nat_proto_udp.o nf_nat_proto_tcp.o nf_nat_helper.o
diff --git a/net/netfilter/nf_conntrack_slp.c b/net/netfilter/nf_conntrack_slp.c
new file mode 100644
index 0000000..0174dd0
--- /dev/null
+++ b/net/netfilter/nf_conntrack_slp.c
@@ -0,0 +1,131 @@
+/*
+ *      NetBIOS name service broadcast connection tracking helper
+ *
+ *      (c) 2007 Jiri Bohac <jbohac@xxxxxxx>
+ *      (c) 2005 Patrick McHardy <kaber@xxxxxxxxx>
+ *
+ *      This program is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU General Public License
+ *      as published by the Free Software Foundation; either version
+ *      2 of the License, or (at your option) any later version.
+ */
+/*
+ *      This helper tracks locally originating NetBIOS name service
+ *      requests by issuing permanent expectations (valid until
+ *      timing out) matching all reply connections from the
+ *      destination network. The only NetBIOS specific thing is
+ *      actually the port number.
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/skbuff.h>
+#include <linux/netdevice.h>
+#include <linux/inetdevice.h>
+#include <linux/if_addr.h>
+#include <linux/in.h>
+#include <linux/ip.h>
+#include <linux/netfilter.h>
+#include <net/route.h>
+
+#include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_conntrack_helper.h>
+#include <net/netfilter/nf_conntrack_expect.h>
+
+#define SLP_PORT	427
+
+MODULE_AUTHOR("Jiri Bohac <jbohac@xxxxxxx>");
+MODULE_DESCRIPTION("SLP broadcast connection tracking helper");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("ip_conntrack_slp");
+
+static unsigned int timeout __read_mostly = 3;
+module_param(timeout, uint, 0400);
+MODULE_PARM_DESC(timeout, "timeout for master connection/replies in seconds");
+
+static int help(struct sk_buff *skb, unsigned int protoff,
+		struct nf_conn *ct, enum ip_conntrack_info ctinfo)
+{
+	struct nf_conntrack_expect *exp;
+	struct rtable *rt = skb_rtable(skb);
+	struct in_device *in_dev;
+	__be32 mask = 0;
+	__be32 src = 0;
+
+	/* we're only interested in locally generated packets */
+	if (skb->sk == NULL)
+		goto out;
+	if (rt == NULL || !(rt->rt_flags & (RTCF_MULTICAST|RTCF_BROADCAST)))
+		goto out;
+	if (CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
+		goto out;
+
+	rcu_read_lock();
+	in_dev = __in_dev_get_rcu(rt->dst.dev);
+	if (in_dev != NULL) {
+		for_primary_ifa(in_dev) {
+			/* this is a hack as slp uses multicast we can't match
+			 * the destination address to some broadcast address. So
+			 * just take the first one. Better would be to install
+			 * expectations for all addresses */
+			mask = ifa->ifa_mask;
+			src = ifa->ifa_broadcast;
+			break;
+		} endfor_ifa(in_dev);
+	}
+	rcu_read_unlock();
+
+	if (mask == 0 || src == 0)
+		goto out;
+
+	exp = nf_ct_expect_alloc(ct);
+	if (exp == NULL)
+		goto out;
+
+	exp->tuple                = ct->tuplehash[IP_CT_DIR_REPLY].tuple;
+	exp->tuple.src.u3.ip      = src;
+	exp->tuple.src.u.udp.port = htons(SLP_PORT);
+
+	exp->mask.src.u3.ip       = mask;
+	exp->mask.src.u.udp.port  = htons(0xFFFF);
+
+	exp->expectfn             = NULL;
+	exp->flags                = NF_CT_EXPECT_PERMANENT;
+	exp->class		  = NF_CT_EXPECT_CLASS_DEFAULT;
+	exp->helper               = NULL;
+
+	nf_ct_expect_related(exp);
+	nf_ct_expect_put(exp);
+
+	nf_ct_refresh(ct, skb, timeout * HZ);
+out:
+	return NF_ACCEPT;
+}
+
+static struct nf_conntrack_expect_policy exp_policy = {
+	.max_expected	= 1,
+};
+
+static struct nf_conntrack_helper helper __read_mostly = {
+	.name			= "slp",
+	.tuple.src.l3num	= AF_INET,
+	.tuple.src.u.udp.port	= __constant_htons(SLP_PORT),
+	.tuple.dst.protonum	= IPPROTO_UDP,
+	.me			= THIS_MODULE,
+	.help			= help,
+	.expect_policy		= &exp_policy,
+};
+
+static int __init nf_conntrack_slp_init(void)
+{
+	exp_policy.timeout = timeout;
+	return nf_conntrack_helper_register(&helper);
+}
+
+static void __exit nf_conntrack_slp_fini(void)
+{
+	nf_conntrack_helper_unregister(&helper);
+}
+
+module_init(nf_conntrack_slp_init);
+module_exit(nf_conntrack_slp_fini);
-- 
1.8.2.1

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