net/ipv4/netfilter/nf_nat_amanda.c

   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_nat_helper.h>
  17 #include <net/netfilter/nf_nat_rule.h>
  18 #include <net/netfilter/nf_conntrack_helper.h>
  19 #include <net/netfilter/nf_conntrack_expect.h>
  20 #include <linux/netfilter/nf_conntrack_amanda.h>
  21
  22 MODULE_AUTHOR("Brian J. Murrell <netfilter@interlinx.bc.ca>");
  23 MODULE_DESCRIPTION("Amanda NAT helper");
  24 MODULE_LICENSE("GPL");
  25 MODULE_ALIAS("ip_nat_amanda");
  26
  27 static unsigned int help(struct sk_buff *skb,
  28                          enum ip_conntrack_info ctinfo,
  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                 exp->tuple.dst.u.tcp.port = htons(port);
  48                 if (nf_ct_expect_related(exp) == 0)
  49                         break;
  50         }
  51
  52         if (port == 0)
  53                 return NF_DROP;
  54
  55         sprintf(buffer, "%u", port);
  56         ret = nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
  57                                        matchoff, matchlen,
  58                                        buffer, strlen(buffer));
  59         if (ret != NF_ACCEPT)
  60                 nf_ct_unexpect_related(exp);
  61         return ret;
  62 }
  63
  64 static void __exit nf_nat_amanda_fini(void)
  65 {
  66         rcu_assign_pointer(nf_nat_amanda_hook, NULL);
  67         synchronize_rcu();
  68 }
  69
  70 static int __init nf_nat_amanda_init(void)
  71 {
  72         BUG_ON(nf_nat_amanda_hook != NULL);
  73         rcu_assign_pointer(nf_nat_amanda_hook, help);
  74         return 0;
  75 }
  76
  77 module_init(nf_nat_amanda_init);
  78 module_exit(nf_nat_amanda_fini);