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 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, 0);
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 if (!nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
67 protoff, matchoff, matchlen,
68 buffer, strlen(buffer))) {
69 nf_ct_helper_log(skb, exp->master, "cannot mangle packet");
70 nf_ct_unexpect_related(exp);
71 return NF_DROP;
72 }
73 return NF_ACCEPT;
74 }
75
nf_nat_amanda_fini(void)76 static void __exit nf_nat_amanda_fini(void)
77 {
78 nf_nat_helper_unregister(&nat_helper_amanda);
79 RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
80 synchronize_rcu();
81 }
82
nf_nat_amanda_init(void)83 static int __init nf_nat_amanda_init(void)
84 {
85 BUG_ON(nf_nat_amanda_hook != NULL);
86 nf_nat_helper_register(&nat_helper_amanda);
87 RCU_INIT_POINTER(nf_nat_amanda_hook, help);
88 return 0;
89 }
90
91 module_init(nf_nat_amanda_init);
92 module_exit(nf_nat_amanda_fini);
93