net/netfilter/nf_nat_amanda.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Amanda extension for TCP NAT alteration.
   3  * (C) 2002 by Brian J. Murrell <netfilter@interlinx.bc.ca>
   4  * based on a copy of HW's ip_nat_irc.c as well as other modules
   5  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
   6  */
   7
   8 #include <linux/kernel.h>
   9 #include <linux/module.h>
  10 #include <linux/skbuff.h>
  11 #include <linux/udp.h>
  12
  13 #include <net/netfilter/nf_conntrack_helper.h>
  14 #include <net/netfilter/nf_conntrack_expect.h>
  15 #include <net/netfilter/nf_nat_helper.h>
  16 #include <linux/netfilter/nf_conntrack_amanda.h>
  17
  18 #define NAT_HELPER_NAME "amanda"
  19
  20 MODULE_AUTHOR("Brian J. Murrell <netfilter@interlinx.bc.ca>");
  21 MODULE_DESCRIPTION("Amanda NAT helper");
  22 MODULE_LICENSE("GPL");
  23 MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
  24
  25 static struct nf_conntrack_nat_helper nat_helper_amanda =
  26         NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
  27
  28 static unsigned int help(struct sk_buff *skb,
  29                          enum ip_conntrack_info ctinfo,
  30                          unsigned int protoff,
  31                          unsigned int matchoff,
  32                          unsigned int matchlen,
  33                          struct nf_conntrack_expect *exp)
  34 {
  35         char buffer[sizeof("65535")];
  36         u_int16_t port;
  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, 0);
  52                 if (res == 0)
  53                         break;
  54                 else if (res != -EBUSY) {
  55                         port = 0;
  56                         break;
  57                 }
  58         }
  59
  60         if (port == 0) {
  61                 nf_ct_helper_log(skb, exp->master, "all ports in use");
  62                 return NF_DROP;
  63         }
  64
  65         sprintf(buffer, "%u", port);
  66         if (!nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
  67                                       protoff, matchoff, matchlen,
  68                                       buffer, strlen(buffer))) {
  69                 nf_ct_helper_log(skb, exp->master, "cannot mangle packet");
  70                 nf_ct_unexpect_related(exp);
  71                 return NF_DROP;
  72         }
  73         return NF_ACCEPT;
  74 }
  75
  76 static void __exit nf_nat_amanda_fini(void)
  77 {
  78         nf_nat_helper_unregister(&nat_helper_amanda);
  79         RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
  80         synchronize_rcu();
  81 }
  82
  83 static int __init nf_nat_amanda_init(void)
  84 {
  85         BUG_ON(nf_nat_amanda_hook != NULL);
  86         nf_nat_helper_register(&nat_helper_amanda);
  87         RCU_INIT_POINTER(nf_nat_amanda_hook, help);
  88         return 0;
  89 }
  90
  91 module_init(nf_nat_amanda_init);
  92 module_exit(nf_nat_amanda_fini);