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_conntrack_helper.h>
  17 #include <net/netfilter/nf_conntrack_expect.h>
  18 #include <net/netfilter/nf_nat_helper.h>
  19 #include <net/netfilter/nf_nat_rule.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 protoff,
  30                          unsigned int matchoff,
  31                          unsigned int matchlen,
  32                          struct nf_conntrack_expect *exp)
  33 {
  34         char buffer[sizeof("65535")];
  35         u_int16_t port;
  36         unsigned int ret;
  37
  38         /* Connection comes from client. */
  39         exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  40         exp->dir = IP_CT_DIR_ORIGINAL;
  41
  42         /* When you see the packet, we need to NAT it the same as the
  43          * this one (ie. same IP: it will be TCP and master is UDP). */
  44         exp->expectfn = nf_nat_follow_master;
  45
  46         /* Try to get same port: if not, try to change it. */
  47         for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
  48                 int res;
  49
  50                 exp->tuple.dst.u.tcp.port = htons(port);
  51                 res = nf_ct_expect_related(exp);
  52                 if (res == 0)
  53                         break;
  54                 else if (res != -EBUSY) {
  55                         port = 0;
  56                         break;
  57                 }
  58         }
  59
  60         if (port == 0)
  61                 return NF_DROP;
  62
  63         sprintf(buffer, "%u", port);
  64         ret = nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
  65                                        protoff, matchoff, matchlen,
  66                                        buffer, strlen(buffer));
  67         if (ret != NF_ACCEPT)
  68                 nf_ct_unexpect_related(exp);
  69         return ret;
  70 }
  71
  72 static void __exit nf_nat_amanda_fini(void)
  73 {
  74         RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
  75         synchronize_rcu();
  76 }
  77
  78 static int __init nf_nat_amanda_init(void)
  79 {
  80         BUG_ON(nf_nat_amanda_hook != NULL);
  81         RCU_INIT_POINTER(nf_nat_amanda_hook, help);
  82         return 0;
  83 }
  84
  85 module_init(nf_nat_amanda_init);
  86 module_exit(nf_nat_amanda_fini);