net/ipv4/netfilter/ip_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  *      Module load syntax:
  11  *      insmod ip_nat_amanda.o
  12  */
  13
  14 #include <linux/kernel.h>
  15 #include <linux/module.h>
  16 #include <linux/netfilter.h>
  17 #include <linux/skbuff.h>
  18 #include <linux/ip.h>
  19 #include <linux/udp.h>
  20 #include <net/tcp.h>
  21 #include <net/udp.h>
  22
  23 #include <linux/netfilter_ipv4.h>
  24 #include <linux/netfilter_ipv4/ip_nat.h>
  25 #include <linux/netfilter_ipv4/ip_nat_helper.h>
  26 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  27 #include <linux/netfilter_ipv4/ip_conntrack_amanda.h>
  28
  29
  30 MODULE_AUTHOR("Brian J. Murrell <netfilter@interlinx.bc.ca>");
  31 MODULE_DESCRIPTION("Amanda NAT helper");
  32 MODULE_LICENSE("GPL");
  33
  34 static unsigned int help(struct sk_buff **pskb,
  35                          enum ip_conntrack_info ctinfo,
  36                          unsigned int matchoff,
  37                          unsigned int matchlen,
  38                          struct ip_conntrack_expect *exp)
  39 {
  40         char buffer[sizeof("65535")];
  41         u_int16_t port;
  42         unsigned int ret;
  43
  44         /* Connection comes from client. */
  45         exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  46         exp->dir = IP_CT_DIR_ORIGINAL;
  47
  48         /* When you see the packet, we need to NAT it the same as the
  49          * this one (ie. same IP: it will be TCP and master is UDP). */
  50         exp->expectfn = ip_nat_follow_master;
  51
  52         /* Try to get same port: if not, try to change it. */
  53         for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
  54                 exp->tuple.dst.u.tcp.port = htons(port);
  55                 if (ip_conntrack_expect_related(exp) == 0)
  56                         break;
  57         }
  58
  59         if (port == 0) {
  60                 ip_conntrack_expect_free(exp);
  61                 return NF_DROP;
  62         }
  63
  64         sprintf(buffer, "%u", port);
  65         ret = ip_nat_mangle_udp_packet(pskb, exp->master, ctinfo,
  66                                        matchoff, matchlen,
  67                                        buffer, strlen(buffer));
  68         if (ret != NF_ACCEPT)
  69                 ip_conntrack_unexpect_related(exp);
  70         return ret;
  71 }
  72
  73 static void __exit fini(void)
  74 {
  75         ip_nat_amanda_hook = NULL;
  76         /* Make sure noone calls it, meanwhile. */
  77         synchronize_net();
  78 }
  79
  80 static int __init init(void)
  81 {
  82         BUG_ON(ip_nat_amanda_hook);
  83         ip_nat_amanda_hook = help;
  84         return 0;
  85 }
  86
  87 module_init(init);
  88 module_exit(fini);