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Linux/net/netfilter/nf_nat_irc.c

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  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 
 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 
 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 
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. */
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 

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