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Linux/net/netfilter/nf_nat_amanda.c

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  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);
 90 

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