1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* IRC extension for TCP NAT alteration.
3  *
4  * (C) 2000-2001 by Harald Welte <laforge@gnumonks.org>
5  * (C) 2004 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
6  * based on a copy of RR's ip_nat_ftp.c
7  */
8 
9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10 
11 #include <linux/module.h>
12 #include <linux/moduleparam.h>
13 #include <linux/tcp.h>
14 #include <linux/kernel.h>
15 
16 #include <net/netfilter/nf_nat.h>
17 #include <net/netfilter/nf_nat_helper.h>
18 #include <net/netfilter/nf_conntrack_helper.h>
19 #include <net/netfilter/nf_conntrack_expect.h>
20 #include <linux/netfilter/nf_conntrack_irc.h>
21 
22 #define NAT_HELPER_NAME "irc"
23 
24 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
25 MODULE_DESCRIPTION("IRC (DCC) NAT helper");
26 MODULE_LICENSE("GPL");
27 MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
28 
29 static struct nf_conntrack_nat_helper nat_helper_irc =
30 	NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
31 
help(struct sk_buff * skb,enum ip_conntrack_info ctinfo,unsigned int protoff,unsigned int matchoff,unsigned int matchlen,struct nf_conntrack_expect * exp)32 static unsigned int help(struct sk_buff *skb,
33 			 enum ip_conntrack_info ctinfo,
34 			 unsigned int protoff,
35 			 unsigned int matchoff,
36 			 unsigned int matchlen,
37 			 struct nf_conntrack_expect *exp)
38 {
39 	char buffer[sizeof("4294967296 65635")];
40 	struct nf_conn *ct = exp->master;
41 	union nf_inet_addr newaddr;
42 	u_int16_t port;
43 
44 	/* Reply comes from server. */
45 	newaddr = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3;
46 
47 	exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
48 	exp->dir = IP_CT_DIR_REPLY;
49 	exp->expectfn = nf_nat_follow_master;
50 
51 	/* Try to get same port: if not, try to change it. */
52 	for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
53 		int ret;
54 
55 		exp->tuple.dst.u.tcp.port = htons(port);
56 		ret = nf_ct_expect_related(exp, 0);
57 		if (ret == 0)
58 			break;
59 		else if (ret != -EBUSY) {
60 			port = 0;
61 			break;
62 		}
63 	}
64 
65 	if (port == 0) {
66 		nf_ct_helper_log(skb, ct, "all ports in use");
67 		return NF_DROP;
68 	}
69 
70 	/* strlen("\1DCC CHAT chat AAAAAAAA P\1\n")=27
71 	 * strlen("\1DCC SCHAT chat AAAAAAAA P\1\n")=28
72 	 * strlen("\1DCC SEND F AAAAAAAA P S\1\n")=26
73 	 * strlen("\1DCC MOVE F AAAAAAAA P S\1\n")=26
74 	 * strlen("\1DCC TSEND F AAAAAAAA P S\1\n")=27
75 	 *
76 	 * AAAAAAAAA: bound addr (1.0.0.0==16777216, min 8 digits,
77 	 *                        255.255.255.255==4294967296, 10 digits)
78 	 * P:         bound port (min 1 d, max 5d (65635))
79 	 * F:         filename   (min 1 d )
80 	 * S:         size       (min 1 d )
81 	 * 0x01, \n:  terminators
82 	 */
83 	/* AAA = "us", ie. where server normally talks to. */
84 	snprintf(buffer, sizeof(buffer), "%u %u", ntohl(newaddr.ip), port);
85 	pr_debug("inserting '%s' == %pI4, port %u\n",
86 		 buffer, &newaddr.ip, port);
87 
88 	if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
89 				      matchlen, buffer, strlen(buffer))) {
90 		nf_ct_helper_log(skb, ct, "cannot mangle packet");
91 		nf_ct_unexpect_related(exp);
92 		return NF_DROP;
93 	}
94 
95 	return NF_ACCEPT;
96 }
97 
nf_nat_irc_fini(void)98 static void __exit nf_nat_irc_fini(void)
99 {
100 	nf_nat_helper_unregister(&nat_helper_irc);
101 	RCU_INIT_POINTER(nf_nat_irc_hook, NULL);
102 	synchronize_rcu();
103 }
104 
nf_nat_irc_init(void)105 static int __init nf_nat_irc_init(void)
106 {
107 	BUG_ON(nf_nat_irc_hook != NULL);
108 	nf_nat_helper_register(&nat_helper_irc);
109 	RCU_INIT_POINTER(nf_nat_irc_hook, help);
110 	return 0;
111 }
112 
113 /* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
warn_set(const char * val,const struct kernel_param * kp)114 static int warn_set(const char *val, const struct kernel_param *kp)
115 {
116 	pr_info("kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
117 	return 0;
118 }
119 module_param_call(ports, warn_set, NULL, NULL, 0);
120 
121 module_init(nf_nat_irc_init);
122 module_exit(nf_nat_irc_fini);
123