// SPDX-License-Identifier: GPL-2.0-or-later
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/* Amanda extension for TCP NAT alteration.
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* (C) 2002 by Brian J. Murrell <netfilter@interlinx.bc.ca>
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* based on a copy of HW's ip_nat_irc.c as well as other modules
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* (C) 2006-2012 Patrick McHardy <kaber@trash.net>
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/udp.h>
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#include <net/netfilter/nf_conntrack_helper.h>
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#include <net/netfilter/nf_conntrack_expect.h>
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#include <net/netfilter/nf_nat_helper.h>
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#include <linux/netfilter/nf_conntrack_amanda.h>
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#define NAT_HELPER_NAME "amanda"
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MODULE_AUTHOR("Brian J. Murrell <netfilter@interlinx.bc.ca>");
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MODULE_DESCRIPTION("Amanda NAT helper");
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MODULE_LICENSE("GPL");
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MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
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static struct nf_conntrack_nat_helper nat_helper_amanda =
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NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
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static unsigned int help(struct sk_buff *skb,
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enum ip_conntrack_info ctinfo,
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unsigned int protoff,
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unsigned int matchoff,
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unsigned int matchlen,
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struct nf_conntrack_expect *exp)
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{
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char buffer[sizeof("65535")];
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u_int16_t port;
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/* Connection comes from client. */
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exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
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exp->dir = IP_CT_DIR_ORIGINAL;
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/* When you see the packet, we need to NAT it the same as the
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* this one (ie. same IP: it will be TCP and master is UDP). */
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exp->expectfn = nf_nat_follow_master;
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/* Try to get same port: if not, try to change it. */
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for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
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int res;
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exp->tuple.dst.u.tcp.port = htons(port);
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res = nf_ct_expect_related(exp, 0);
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if (res == 0)
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break;
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else if (res != -EBUSY) {
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port = 0;
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break;
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}
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}
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if (port == 0) {
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nf_ct_helper_log(skb, exp->master, "all ports in use");
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return NF_DROP;
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}
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sprintf(buffer, "%u", port);
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if (!nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
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protoff, matchoff, matchlen,
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buffer, strlen(buffer))) {
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nf_ct_helper_log(skb, exp->master, "cannot mangle packet");
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nf_ct_unexpect_related(exp);
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return NF_DROP;
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}
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return NF_ACCEPT;
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}
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static void __exit nf_nat_amanda_fini(void)
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{
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nf_nat_helper_unregister(&nat_helper_amanda);
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RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
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synchronize_rcu();
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}
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static int __init nf_nat_amanda_init(void)
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{
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BUG_ON(nf_nat_amanda_hook != NULL);
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nf_nat_helper_register(&nat_helper_amanda);
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RCU_INIT_POINTER(nf_nat_amanda_hook, help);
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return 0;
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}
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module_init(nf_nat_amanda_init);
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module_exit(nf_nat_amanda_fini);
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