1 /*
2  *      SNMP service broadcast connection tracking helper
3  *
4  *      (c) 2011 Jiri Olsa <jolsa@redhat.com>
5  *
6  *      This program is free software; you can redistribute it and/or
7  *      modify it under the terms of the GNU General Public License
8  *      as published by the Free Software Foundation; either version
9  *      2 of the License, or (at your option) any later version.
10  */
11 #include <linux/kernel.h>
12 #include <linux/module.h>
13 #include <linux/init.h>
14 #include <linux/in.h>
15 
16 #include <net/netfilter/nf_conntrack.h>
17 #include <net/netfilter/nf_conntrack_helper.h>
18 #include <net/netfilter/nf_conntrack_expect.h>
19 #include <linux/netfilter/nf_conntrack_snmp.h>
20 
21 #define SNMP_PORT	161
22 
23 MODULE_AUTHOR("Jiri Olsa <jolsa@redhat.com>");
24 MODULE_DESCRIPTION("SNMP service broadcast connection tracking helper");
25 MODULE_LICENSE("GPL");
26 MODULE_ALIAS_NFCT_HELPER("snmp");
27 
28 static unsigned int timeout __read_mostly = 30;
29 module_param(timeout, uint, 0400);
30 MODULE_PARM_DESC(timeout, "timeout for master connection/replies in seconds");
31 
32 int (*nf_nat_snmp_hook)(struct sk_buff *skb,
33 			unsigned int protoff,
34 			struct nf_conn *ct,
35 			enum ip_conntrack_info ctinfo);
36 EXPORT_SYMBOL_GPL(nf_nat_snmp_hook);
37 
38 static int snmp_conntrack_help(struct sk_buff *skb, unsigned int protoff,
39 			       struct nf_conn *ct,
40 			       enum ip_conntrack_info ctinfo)
41 {
42 	typeof(nf_nat_snmp_hook) nf_nat_snmp;
43 
44 	nf_conntrack_broadcast_help(skb, ct, ctinfo, timeout);
45 
46 	nf_nat_snmp = rcu_dereference(nf_nat_snmp_hook);
47 	if (nf_nat_snmp && ct->status & IPS_NAT_MASK)
48 		return nf_nat_snmp(skb, protoff, ct, ctinfo);
49 
50 	return NF_ACCEPT;
51 }
52 
53 static struct nf_conntrack_expect_policy exp_policy = {
54 	.max_expected	= 1,
55 };
56 
57 static struct nf_conntrack_helper helper __read_mostly = {
58 	.name			= "snmp",
59 	.tuple.src.l3num	= NFPROTO_IPV4,
60 	.tuple.src.u.udp.port	= cpu_to_be16(SNMP_PORT),
61 	.tuple.dst.protonum	= IPPROTO_UDP,
62 	.me			= THIS_MODULE,
63 	.help			= snmp_conntrack_help,
64 	.expect_policy		= &exp_policy,
65 };
66 
67 static int __init nf_conntrack_snmp_init(void)
68 {
69 	exp_policy.timeout = timeout;
70 	return nf_conntrack_helper_register(&helper);
71 }
72 
73 static void __exit nf_conntrack_snmp_fini(void)
74 {
75 	nf_conntrack_helper_unregister(&helper);
76 }
77 
78 module_init(nf_conntrack_snmp_init);
79 module_exit(nf_conntrack_snmp_fini);
80