nf_nat_amanda.c

 1// SPDX-License-Identifier: GPL-2.0-or-later
 2/* Amanda extension for TCP NAT alteration.
 3 * (C) 2002 by Brian J. Murrell <netfilter@interlinx.bc.ca>
 4 * based on a copy of HW's ip_nat_irc.c as well as other modules
 5 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
 6 */
 7
 8#include <linux/kernel.h>
 9#include <linux/module.h>
10#include <linux/skbuff.h>
11#include <linux/udp.h>
12
13#include <net/netfilter/nf_conntrack_helper.h>
14#include <net/netfilter/nf_conntrack_expect.h>
15#include <net/netfilter/nf_nat_helper.h>
16#include <linux/netfilter/nf_conntrack_amanda.h>
17
18#define NAT_HELPER_NAME "amanda"
19
20MODULE_AUTHOR("Brian J. Murrell <netfilter@interlinx.bc.ca>");
21MODULE_DESCRIPTION("Amanda NAT helper");
22MODULE_LICENSE("GPL");
23MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
24
25static struct nf_conntrack_nat_helper nat_helper_amanda =
26	NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
27
28static unsigned int help(struct sk_buff *skb,
29			 enum ip_conntrack_info ctinfo,
30			 unsigned int protoff,
31			 unsigned int matchoff,
32			 unsigned int matchlen,
33			 struct nf_conntrack_expect *exp)
34{
35	char buffer[sizeof("65535")];
36	u_int16_t port;
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	port = nf_nat_exp_find_port(exp, ntohs(exp->saved_proto.tcp.port));
48	if (port == 0) {
49		nf_ct_helper_log(skb, exp->master, "all ports in use");
50		return NF_DROP;
51	}
52
53	sprintf(buffer, "%u", port);
54	if (!nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
55				      protoff, matchoff, matchlen,
56				      buffer, strlen(buffer))) {
57		nf_ct_helper_log(skb, exp->master, "cannot mangle packet");
58		nf_ct_unexpect_related(exp);
59		return NF_DROP;
60	}
61	return NF_ACCEPT;
62}
63
64static void __exit nf_nat_amanda_fini(void)
65{
66	nf_nat_helper_unregister(&nat_helper_amanda);
67	RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
68	synchronize_rcu();
69}
70
71static int __init nf_nat_amanda_init(void)
72{
73	BUG_ON(nf_nat_amanda_hook != NULL);
74	nf_nat_helper_register(&nat_helper_amanda);
75	RCU_INIT_POINTER(nf_nat_amanda_hook, help);
76	return 0;
77}
78
79module_init(nf_nat_amanda_init);
80module_exit(nf_nat_amanda_fini);