250 lines
7.2 KiB
C
250 lines
7.2 KiB
C
/* SIP extension for UDP NAT alteration.
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*
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* (C) 2005 by Christian Hentschel <chentschel@arnet.com.ar>
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* based on RR's ip_nat_ftp.c and other modules.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/ip.h>
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#include <linux/udp.h>
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#include <linux/netfilter_ipv4.h>
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#include <linux/netfilter_ipv4/ip_nat.h>
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#include <linux/netfilter_ipv4/ip_nat_helper.h>
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#include <linux/netfilter_ipv4/ip_conntrack_helper.h>
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#include <linux/netfilter_ipv4/ip_conntrack_sip.h>
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
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MODULE_DESCRIPTION("SIP NAT helper");
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#if 0
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#define DEBUGP printk
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#else
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#define DEBUGP(format, args...)
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#endif
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extern struct sip_header_nfo ct_sip_hdrs[];
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static unsigned int mangle_sip_packet(struct sk_buff **pskb,
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enum ip_conntrack_info ctinfo,
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struct ip_conntrack *ct,
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const char **dptr, size_t dlen,
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char *buffer, int bufflen,
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struct sip_header_nfo *hnfo)
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{
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unsigned int matchlen, matchoff;
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if (ct_sip_get_info(*dptr, dlen, &matchoff, &matchlen, hnfo) <= 0)
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return 0;
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if (!ip_nat_mangle_udp_packet(pskb, ct, ctinfo,
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matchoff, matchlen, buffer, bufflen))
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return 0;
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/* We need to reload this. Thanks Patrick. */
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*dptr = (*pskb)->data + (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
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return 1;
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}
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static unsigned int ip_nat_sip(struct sk_buff **pskb,
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enum ip_conntrack_info ctinfo,
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struct ip_conntrack *ct,
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const char **dptr)
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{
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enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
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char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
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unsigned int bufflen, dataoff;
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__be32 ip;
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__be16 port;
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dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
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ip = ct->tuplehash[!dir].tuple.dst.ip;
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port = ct->tuplehash[!dir].tuple.dst.u.udp.port;
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bufflen = sprintf(buffer, "%u.%u.%u.%u:%u", NIPQUAD(ip), ntohs(port));
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/* short packet ? */
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if (((*pskb)->len - dataoff) < (sizeof("SIP/2.0") - 1))
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return 0;
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/* Basic rules: requests and responses. */
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if (memcmp(*dptr, "SIP/2.0", sizeof("SIP/2.0") - 1) == 0) {
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const char *aux;
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if ((ctinfo) < IP_CT_IS_REPLY) {
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mangle_sip_packet(pskb, ctinfo, ct, dptr,
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(*pskb)->len - dataoff,
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buffer, bufflen,
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&ct_sip_hdrs[POS_CONTACT]);
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return 1;
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}
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if (!mangle_sip_packet(pskb, ctinfo, ct, dptr,
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(*pskb)->len - dataoff,
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buffer, bufflen, &ct_sip_hdrs[POS_VIA]))
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return 0;
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/* This search should ignore case, but later.. */
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aux = ct_sip_search("CSeq:", *dptr, sizeof("CSeq:") - 1,
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(*pskb)->len - dataoff);
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if (!aux)
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return 0;
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if (!ct_sip_search("REGISTER", aux, sizeof("REGISTER"),
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ct_sip_lnlen(aux, *dptr + (*pskb)->len - dataoff)))
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return 1;
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return mangle_sip_packet(pskb, ctinfo, ct, dptr,
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(*pskb)->len - dataoff,
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buffer, bufflen,
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&ct_sip_hdrs[POS_CONTACT]);
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}
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if ((ctinfo) < IP_CT_IS_REPLY) {
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if (!mangle_sip_packet(pskb, ctinfo, ct, dptr,
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(*pskb)->len - dataoff,
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buffer, bufflen, &ct_sip_hdrs[POS_VIA]))
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return 0;
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/* Mangle Contact if exists only. - watch udp_nat_mangle()! */
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mangle_sip_packet(pskb, ctinfo, ct, dptr, (*pskb)->len - dataoff,
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buffer, bufflen, &ct_sip_hdrs[POS_CONTACT]);
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return 1;
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}
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/* This mangle requests headers. */
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return mangle_sip_packet(pskb, ctinfo, ct, dptr,
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ct_sip_lnlen(*dptr,
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*dptr + (*pskb)->len - dataoff),
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buffer, bufflen, &ct_sip_hdrs[POS_REQ_HEADER]);
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}
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static int mangle_content_len(struct sk_buff **pskb,
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enum ip_conntrack_info ctinfo,
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struct ip_conntrack *ct,
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const char *dptr)
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{
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unsigned int dataoff, matchoff, matchlen;
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char buffer[sizeof("65536")];
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int bufflen;
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dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
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/* Get actual SDP lenght */
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if (ct_sip_get_info(dptr, (*pskb)->len - dataoff, &matchoff,
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&matchlen, &ct_sip_hdrs[POS_SDP_HEADER]) > 0) {
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/* since ct_sip_get_info() give us a pointer passing 'v='
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we need to add 2 bytes in this count. */
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int c_len = (*pskb)->len - dataoff - matchoff + 2;
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/* Now, update SDP lenght */
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if (ct_sip_get_info(dptr, (*pskb)->len - dataoff, &matchoff,
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&matchlen, &ct_sip_hdrs[POS_CONTENT]) > 0) {
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bufflen = sprintf(buffer, "%u", c_len);
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return ip_nat_mangle_udp_packet(pskb, ct, ctinfo,
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matchoff, matchlen,
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buffer, bufflen);
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}
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}
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return 0;
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}
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static unsigned int mangle_sdp(struct sk_buff **pskb,
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enum ip_conntrack_info ctinfo,
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struct ip_conntrack *ct,
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__be32 newip, u_int16_t port,
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const char *dptr)
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{
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char buffer[sizeof("nnn.nnn.nnn.nnn")];
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unsigned int dataoff, bufflen;
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dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
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/* Mangle owner and contact info. */
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bufflen = sprintf(buffer, "%u.%u.%u.%u", NIPQUAD(newip));
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if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
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buffer, bufflen, &ct_sip_hdrs[POS_OWNER]))
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return 0;
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if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
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buffer, bufflen, &ct_sip_hdrs[POS_CONNECTION]))
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return 0;
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/* Mangle media port. */
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bufflen = sprintf(buffer, "%u", port);
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if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
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buffer, bufflen, &ct_sip_hdrs[POS_MEDIA]))
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return 0;
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return mangle_content_len(pskb, ctinfo, ct, dptr);
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}
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/* So, this packet has hit the connection tracking matching code.
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Mangle it, and change the expectation to match the new version. */
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static unsigned int ip_nat_sdp(struct sk_buff **pskb,
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enum ip_conntrack_info ctinfo,
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struct ip_conntrack_expect *exp,
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const char *dptr)
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{
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struct ip_conntrack *ct = exp->master;
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enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
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__be32 newip;
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u_int16_t port;
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DEBUGP("ip_nat_sdp():\n");
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/* Connection will come from reply */
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newip = ct->tuplehash[!dir].tuple.dst.ip;
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exp->tuple.dst.ip = newip;
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exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port;
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exp->dir = !dir;
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/* When you see the packet, we need to NAT it the same as the
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this one. */
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exp->expectfn = ip_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.udp.port); port != 0; port++) {
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exp->tuple.dst.u.udp.port = htons(port);
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if (ip_conntrack_expect_related(exp) == 0)
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break;
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}
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if (port == 0)
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return NF_DROP;
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if (!mangle_sdp(pskb, ctinfo, ct, newip, port, dptr)) {
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ip_conntrack_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 fini(void)
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{
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ip_nat_sip_hook = NULL;
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ip_nat_sdp_hook = NULL;
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/* Make sure noone calls it, meanwhile. */
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synchronize_net();
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}
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static int __init init(void)
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{
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BUG_ON(ip_nat_sip_hook);
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BUG_ON(ip_nat_sdp_hook);
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ip_nat_sip_hook = ip_nat_sip;
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ip_nat_sdp_hook = ip_nat_sdp;
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return 0;
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}
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module_init(init);
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module_exit(fini);
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