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                 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                                        matchoff, matchlen,
  65                                        buffer, strlen(buffer));
  66         if (ret != NF_ACCEPT)
  67                 nf_ct_unexpect_related(exp);
  68         return ret;
  69 }
  70
  71 static void __exit nf_nat_amanda_fini(void)
  72 {
  73         RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
  74         synchronize_rcu();
  75 }
  76
  77 static 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
  84 module_init(nf_nat_amanda_init);
  85 module_exit(nf_nat_amanda_fini);