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Subject[PATCH 05/15] connection tracking helper for SLP
Date
From: Jiri Bohac <jbohac@suse.cz>

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@suse.cz>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: netfilter-devel@vger.kernel.org
Cc: netfilter@vger.kernel.org
Cc: coreteam@netfilter.org
Cc: netdev@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
---
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@suse.cz>
+ * (c) 2005 Patrick McHardy <kaber@trash.net>
+ *
+ * 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@suse.cz>");
+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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