net/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  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #include <linux/kernel.h>
  13 #include <linux/module.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/udp.h>
  16
  17 #include <net/netfilter/nf_conntrack_helper.h>
  18 #include <net/netfilter/nf_conntrack_expect.h>
  19 #include <net/netfilter/nf_nat_helper.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
  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                 nf_ct_helper_log(skb, exp->master, "all ports in use");
  61                 return NF_DROP;
  62         }
  63
  64         sprintf(buffer, "%u", port);
  65         if (!nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
  66                                       protoff, matchoff, matchlen,
  67                                       buffer, strlen(buffer))) {
  68                 nf_ct_helper_log(skb, exp->master, "cannot mangle packet");
  69                 nf_ct_unexpect_related(exp);
  70                 return NF_DROP;
  71         }
  72         return NF_ACCEPT;
  73 }
  74
  75 static void __exit nf_nat_amanda_fini(void)
  76 {
  77         RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
  78         synchronize_rcu();
  79 }
  80
  81 static int __init nf_nat_amanda_init(void)
  82 {
  83         BUG_ON(nf_nat_amanda_hook != NULL);
  84         RCU_INIT_POINTER(nf_nat_amanda_hook, help);
  85         return 0;
  86 }
  87
  88 module_init(nf_nat_amanda_init);
  89 module_exit(nf_nat_amanda_fini);