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 *
5 * This program is free software; you can redistribute it and/or
6 * modify it under the terms of the GNU General Public License
7 * as published by the Free Software Foundation; either version
8 * 2 of the License, or (at your option) any later version.
9 */
10
11 #include <linux/kernel.h>
12 #include <linux/module.h>
13 #include <linux/skbuff.h>
14 #include <linux/udp.h>
15
16 #include <net/netfilter/nf_nat_helper.h>
17 #include <net/netfilter/nf_nat_rule.h>
18 #include <net/netfilter/nf_conntrack_helper.h>
19 #include <net/netfilter/nf_conntrack_expect.h>
20 #include <linux/netfilter/nf_conntrack_amanda.h>
21
22 MODULE_AUTHOR("Brian J. Murrell <netfilter@interlinx.bc.ca>");
23 MODULE_DESCRIPTION("Amanda NAT helper");
24 MODULE_LICENSE("GPL");
25 MODULE_ALIAS("ip_nat_amanda");
26
help(struct sk_buff * skb,enum ip_conntrack_info ctinfo,unsigned int matchoff,unsigned int matchlen,struct nf_conntrack_expect * exp)27 static unsigned int help(struct sk_buff *skb,
28 enum ip_conntrack_info ctinfo,
29 unsigned int matchoff,
30 unsigned int matchlen,
31 struct nf_conntrack_expect *exp)
32 {
33 char buffer[sizeof("65535")];
34 u_int16_t port;
35 unsigned int ret;
36
37 /* Connection comes from client. */
38 exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
39 exp->dir = IP_CT_DIR_ORIGINAL;
40
41 /* When you see the packet, we need to NAT it the same as the
42 * this one (ie. same IP: it will be TCP and master is UDP). */
43 exp->expectfn = nf_nat_follow_master;
44
45 /* Try to get same port: if not, try to change it. */
46 for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
47 int res;
48
49 exp->tuple.dst.u.tcp.port = htons(port);
50 res = nf_ct_expect_related(exp);
51 if (res == 0)
52 break;
53 else if (res != -EBUSY) {
54 port = 0;
55 break;
56 }
57 }
58
59 if (port == 0)
60 return NF_DROP;
61
62 sprintf(buffer, "%u", port);
63 ret = nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
64 matchoff, matchlen,
65 buffer, strlen(buffer));
66 if (ret != NF_ACCEPT)
67 nf_ct_unexpect_related(exp);
68 return ret;
69 }
70
nf_nat_amanda_fini(void)71 static void __exit nf_nat_amanda_fini(void)
72 {
73 RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
74 synchronize_rcu();
75 }
76
nf_nat_amanda_init(void)77 static int __init nf_nat_amanda_init(void)
78 {
79 BUG_ON(nf_nat_amanda_hook != NULL);
80 RCU_INIT_POINTER(nf_nat_amanda_hook, help);
81 return 0;
82 }
83
84 module_init(nf_nat_amanda_init);
85 module_exit(nf_nat_amanda_fini);
86