LXR linux/net/netfilter/nf_nat

   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
  24MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  25MODULE_DESCRIPTION("IRC (DCC) NAT helper");
  26MODULE_LICENSE("GPL");
  27MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
  28
  29static struct nf_conntrack_nat_helper nat_helper_irc =
  30        NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
  31
  32static 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
  98static 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
 105static 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. */
 114static 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}
 119module_param_call(ports, warn_set, NULL, NULL, 0);
 120
 121module_init(nf_nat_irc_init);
 122module_exit(nf_nat_irc_fini);
 123