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 
20 MODULE_AUTHOR("Brian J. Murrell <netfilter@interlinx.bc.ca>");
21 MODULE_DESCRIPTION("Amanda NAT helper");
22 MODULE_LICENSE("GPL");
23 MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
24 
25 static struct nf_conntrack_nat_helper nat_helper_amanda =
26 	NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
27 
help(struct sk_buff * skb,enum ip_conntrack_info ctinfo,unsigned int protoff,unsigned int matchoff,unsigned int matchlen,struct nf_conntrack_expect * exp)28 static 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 
nf_nat_amanda_fini(void)64 static 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 
nf_nat_amanda_init(void)71 static 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 
79 module_init(nf_nat_amanda_init);
80 module_exit(nf_nat_amanda_fini);
81