linux/net/netfilter/nf_nat_amanda.c
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   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 *
   5 * This program is free software; you can redistribute it and/or
   6 * modify it under the terms of the GNU General Public License
   7 * as published by the Free Software Foundation; either version
   8 * 2 of the License, or (at your option) any later version.
   9 */
  10
  11#include <linux/kernel.h>
  12#include <linux/module.h>
  13#include <linux/skbuff.h>
  14#include <linux/udp.h>
  15
  16#include <net/netfilter/nf_conntrack_helper.h>
  17#include <net/netfilter/nf_conntrack_expect.h>
  18#include <net/netfilter/nf_nat_helper.h>
  19#include <linux/netfilter/nf_conntrack_amanda.h>
  20
  21MODULE_AUTHOR("Brian J. Murrell <netfilter@interlinx.bc.ca>");
  22MODULE_DESCRIPTION("Amanda NAT helper");
  23MODULE_LICENSE("GPL");
  24MODULE_ALIAS("ip_nat_amanda");
  25
  26static unsigned int help(struct sk_buff *skb,
  27                         enum ip_conntrack_info ctinfo,
  28                         unsigned int protoff,
  29                         unsigned int matchoff,
  30                         unsigned int matchlen,
  31                         struct nf_conntrack_expect *exp)
  32{
  33        char buffer[sizeof("65535")];
  34        u_int16_t port;
  35        unsigned int ret;
  36
  37        /* Connection comes from client. */
  38        exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  39        exp->dir = IP_CT_DIR_ORIGINAL;
  40
  41        /* When you see the packet, we need to NAT it the same as the
  42         * this one (ie. same IP: it will be TCP and master is UDP). */
  43        exp->expectfn = nf_nat_follow_master;
  44
  45        /* Try to get same port: if not, try to change it. */
  46        for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
  47                int res;
  48
  49                exp->tuple.dst.u.tcp.port = htons(port);
  50                res = nf_ct_expect_related(exp);
  51                if (res == 0)
  52                        break;
  53                else if (res != -EBUSY) {
  54                        port = 0;
  55                        break;
  56                }
  57        }
  58
  59        if (port == 0)
  60                return NF_DROP;
  61
  62        sprintf(buffer, "%u", port);
  63        ret = nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
  64                                       protoff, matchoff, matchlen,
  65                                       buffer, strlen(buffer));
  66        if (ret != NF_ACCEPT)
  67                nf_ct_unexpect_related(exp);
  68        return ret;
  69}
  70
  71static void __exit nf_nat_amanda_fini(void)
  72{
  73        RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
  74        synchronize_rcu();
  75}
  76
  77static int __init nf_nat_amanda_init(void)
  78{
  79        BUG_ON(nf_nat_amanda_hook != NULL);
  80        RCU_INIT_POINTER(nf_nat_amanda_hook, help);
  81        return 0;
  82}
  83
  84module_init(nf_nat_amanda_init);
  85module_exit(nf_nat_amanda_fini);
  86
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