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Linux/net/netfilter/nf_nat_amanda.c

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  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);
 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);
 93 

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