1/* Amanda extension for TCP NAT alteration.
2 * (C) 2002 by Brian J. Murrell <netfilter@interlinx.bc.ca>
3 * based on a copy of HW's ip_nat_irc.c as well as other modules
4 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
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
12#include <linux/kernel.h>
13#include <linux/module.h>
14#include <linux/skbuff.h>
15#include <linux/udp.h>
16
17#include <net/netfilter/nf_conntrack_helper.h>
18#include <net/netfilter/nf_conntrack_expect.h>
19#include <net/netfilter/nf_nat_helper.h>
20#include <linux/netfilter/nf_conntrack_amanda.h>
21
22MODULE_AUTHOR("Brian J. Murrell <netfilter@interlinx.bc.ca>");
23MODULE_DESCRIPTION("Amanda NAT helper");
24MODULE_LICENSE("GPL");
25MODULE_ALIAS("ip_nat_amanda");
26
27static unsigned int help(struct sk_buff *skb,
28			 enum ip_conntrack_info ctinfo,
29			 unsigned int protoff,
30			 unsigned int matchoff,
31			 unsigned int matchlen,
32			 struct nf_conntrack_expect *exp)
33{
34	char buffer[sizeof("65535")];
35	u_int16_t port;
36	unsigned int ret;
37
38	/* Connection comes from client. */
39	exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
40	exp->dir = IP_CT_DIR_ORIGINAL;
41
42	/* When you see the packet, we need to NAT it the same as the
43	 * this one (ie. same IP: it will be TCP and master is UDP). */
44	exp->expectfn = nf_nat_follow_master;
45
46	/* Try to get same port: if not, try to change it. */
47	for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
48		int res;
49
50		exp->tuple.dst.u.tcp.port = htons(port);
51		res = nf_ct_expect_related(exp);
52		if (res == 0)
53			break;
54		else if (res != -EBUSY) {
55			port = 0;
56			break;
57		}
58	}
59
60	if (port == 0) {
61		nf_ct_helper_log(skb, exp->master, "all ports in use");
62		return NF_DROP;
63	}
64
65	sprintf(buffer, "%u", port);
66	ret = nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
67				       protoff, matchoff, matchlen,
68				       buffer, strlen(buffer));
69	if (ret != NF_ACCEPT) {
70		nf_ct_helper_log(skb, exp->master, "cannot mangle packet");
71		nf_ct_unexpect_related(exp);
72	}
73	return ret;
74}
75
76static void __exit nf_nat_amanda_fini(void)
77{
78	RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
79	synchronize_rcu();
80}
81
82static int __init nf_nat_amanda_init(void)
83{
84	BUG_ON(nf_nat_amanda_hook != NULL);
85	RCU_INIT_POINTER(nf_nat_amanda_hook, help);
86	return 0;
87}
88
89module_init(nf_nat_amanda_init);
90module_exit(nf_nat_amanda_fini);
91