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
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 protoff,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 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
nf_nat_amanda_fini(void)76 static void __exit nf_nat_amanda_fini(void)
77 {
78 RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
79 synchronize_rcu();
80 }
81
nf_nat_amanda_init(void)82 static 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
89 module_init(nf_nat_amanda_init);
90 module_exit(nf_nat_amanda_fini);
91