[NETFILTER]: nf_conntrack/nf_nat: add SIP helper port

Add IPv4 and IPv6 capable nf_conntrack port of the SIP conntrack/NAT helper.
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netfilter/nf_conntrack_sip.h

+#ifndef __NF_CONNTRACK_SIP_H__
+#define __NF_CONNTRACK_SIP_H__
+#ifdef __KERNEL__
+
+#define SIP_PORT	5060
+#define SIP_TIMEOUT	3600
+
+enum sip_header_pos {
+	POS_REG_REQ_URI,
+	POS_REQ_URI,
+	POS_FROM,
+	POS_TO,
+	POS_VIA,
+	POS_CONTACT,
+	POS_CONTENT,
+	POS_MEDIA,
+	POS_OWNER_IP4,
+	POS_CONNECTION_IP4,
+	POS_OWNER_IP6,
+	POS_CONNECTION_IP6,
+	POS_SDP_HEADER,
+};
+
+extern unsigned int (*nf_nat_sip_hook)(struct sk_buff **pskb,
+				       enum ip_conntrack_info ctinfo,
+				       struct nf_conn *ct,
+				       const char **dptr);
+extern unsigned int (*nf_nat_sdp_hook)(struct sk_buff **pskb,
+				       enum ip_conntrack_info ctinfo,
+				       struct nf_conntrack_expect *exp,
+				       const char *dptr);
+
+extern int ct_sip_get_info(struct nf_conn *ct, const char *dptr, size_t dlen,
+			   unsigned int *matchoff, unsigned int *matchlen,
+			   enum sip_header_pos pos);
+extern int ct_sip_lnlen(const char *line, const char *limit);
+extern const char *ct_sip_search(const char *needle, const char *haystack,
+				 size_t needle_len, size_t haystack_len,
+				 int case_sensitive);
+#endif /* __KERNEL__ */
+#endif /* __NF_CONNTRACK_SIP_H__ */

net/ipv4/netfilter/Kconfig

@@ -555,6 +555,11 @@ config IP_NF_NAT_SIP
 	default IP_NF_NAT if IP_NF_SIP=y
 	default m if IP_NF_SIP=m
 
+config NF_NAT_SIP
+	tristate
+	depends on IP_NF_IPTABLES && NF_CONNTRACK && NF_NAT
+	default NF_NAT && NF_CONNTRACK_SIP
+
 # mangle + specific targets
 config IP_NF_MANGLE
 	tristate "Packet mangling"

net/ipv4/netfilter/Makefile

@@ -55,6 +55,7 @@ obj-$(CONFIG_NF_NAT_FTP) += nf_nat_ftp.o
 obj-$(CONFIG_NF_NAT_H323) += nf_nat_h323.o
 obj-$(CONFIG_NF_NAT_IRC) += nf_nat_irc.o
 obj-$(CONFIG_NF_NAT_PPTP) += nf_nat_pptp.o
+obj-$(CONFIG_NF_NAT_SIP) += nf_nat_sip.o
 
 # NAT protocols (nf_nat)
 obj-$(CONFIG_NF_NAT_PROTO_GRE) += nf_nat_proto_gre.o

net/ipv4/netfilter/nf_nat_sip.c

+/* SIP extension for UDP NAT alteration.
+ *
+ * (C) 2005 by Christian Hentschel <chentschel@arnet.com.ar>
+ * based on RR's ip_nat_ftp.c and other modules.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+#include <linux/udp.h>
+
+#include <net/netfilter/nf_nat.h>
+#include <net/netfilter/nf_nat_helper.h>
+#include <net/netfilter/nf_nat_rule.h>
+#include <net/netfilter/nf_conntrack_helper.h>
+#include <net/netfilter/nf_conntrack_expect.h>
+#include <linux/netfilter/nf_conntrack_sip.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
+MODULE_DESCRIPTION("SIP NAT helper");
+MODULE_ALIAS("ip_nat_sip");
+
+#if 0
+#define DEBUGP printk
+#else
+#define DEBUGP(format, args...)
+#endif
+
+struct addr_map {
+	struct {
+		char		src[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
+		char		dst[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
+		unsigned int	srclen, srciplen;
+		unsigned int	dstlen, dstiplen;
+	} addr[IP_CT_DIR_MAX];
+};
+
+static void addr_map_init(struct nf_conn *ct, struct addr_map *map)
+{
+	struct nf_conntrack_tuple *t;
+	enum ip_conntrack_dir dir;
+	unsigned int n;
+
+	for (dir = 0; dir < IP_CT_DIR_MAX; dir++) {
+		t = &ct->tuplehash[dir].tuple;
+
+		n = sprintf(map->addr[dir].src, "%u.%u.%u.%u",
+			    NIPQUAD(t->src.u3.ip));
+		map->addr[dir].srciplen = n;
+		n += sprintf(map->addr[dir].src + n, ":%u",
+			     ntohs(t->src.u.udp.port));
+		map->addr[dir].srclen = n;
+
+		n = sprintf(map->addr[dir].dst, "%u.%u.%u.%u",
+			    NIPQUAD(t->dst.u3.ip));
+		map->addr[dir].dstiplen = n;
+		n += sprintf(map->addr[dir].dst + n, ":%u",
+			     ntohs(t->dst.u.udp.port));
+		map->addr[dir].dstlen = n;
+	}
+}
+
+static int map_sip_addr(struct sk_buff **pskb, enum ip_conntrack_info ctinfo,
+			struct nf_conn *ct, const char **dptr, size_t dlen,
+			enum sip_header_pos pos, struct addr_map *map)
+{
+	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+	unsigned int matchlen, matchoff, addrlen;
+	char *addr;
+
+	if (ct_sip_get_info(ct, *dptr, dlen, &matchoff, &matchlen, pos) <= 0)
+		return 1;
+
+	if ((matchlen == map->addr[dir].srciplen ||
+	     matchlen == map->addr[dir].srclen) &&
+	    memcmp(*dptr + matchoff, map->addr[dir].src, matchlen) == 0) {
+		addr    = map->addr[!dir].dst;
+		addrlen = map->addr[!dir].dstlen;
+	} else if ((matchlen == map->addr[dir].dstiplen ||
+		    matchlen == map->addr[dir].dstlen) &&
+		   memcmp(*dptr + matchoff, map->addr[dir].dst, matchlen) == 0) {
+		addr    = map->addr[!dir].src;
+		addrlen = map->addr[!dir].srclen;
+	} else
+		return 1;
+
+	if (!nf_nat_mangle_udp_packet(pskb, ct, ctinfo,
+	                              matchoff, matchlen, addr, addrlen))
+		return 0;
+	*dptr = (*pskb)->data + (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
+	return 1;
+
+}
+
+static unsigned int ip_nat_sip(struct sk_buff **pskb,
+			       enum ip_conntrack_info ctinfo,
+			       struct nf_conn *ct,
+			       const char **dptr)
+{
+	enum sip_header_pos pos;
+	struct addr_map map;
+	int dataoff, datalen;
+
+	dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
+	datalen = (*pskb)->len - dataoff;
+	if (datalen < sizeof("SIP/2.0") - 1)
+		return NF_DROP;
+
+	addr_map_init(ct, &map);
+
+	/* Basic rules: requests and responses. */
+	if (strncmp(*dptr, "SIP/2.0", sizeof("SIP/2.0") - 1) != 0) {
+		/* 10.2: Constructing the REGISTER Request:
+		 *
+		 * The "userinfo" and "@" components of the SIP URI MUST NOT
+		 * be present.
+		 */
+		if (datalen >= sizeof("REGISTER") - 1 &&
+		    strncmp(*dptr, "REGISTER", sizeof("REGISTER") - 1) == 0)
+			pos = POS_REG_REQ_URI;
+		else
+			pos = POS_REQ_URI;
+
+		if (!map_sip_addr(pskb, ctinfo, ct, dptr, datalen, pos, &map))
+			return NF_DROP;
+	}
+
+	if (!map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_FROM, &map) ||
+	    !map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_TO, &map) ||
+	    !map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_VIA, &map) ||
+	    !map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_CONTACT, &map))
+		return NF_DROP;
+	return NF_ACCEPT;
+}
+
+static unsigned int mangle_sip_packet(struct sk_buff **pskb,
+				      enum ip_conntrack_info ctinfo,
+				      struct nf_conn *ct,
+				      const char **dptr, size_t dlen,
+				      char *buffer, int bufflen,
+				      enum sip_header_pos pos)
+{
+	unsigned int matchlen, matchoff;
+
+	if (ct_sip_get_info(ct, *dptr, dlen, &matchoff, &matchlen, pos) <= 0)
+		return 0;
+
+	if (!nf_nat_mangle_udp_packet(pskb, ct, ctinfo,
+	                              matchoff, matchlen, buffer, bufflen))
+		return 0;
+
+	/* We need to reload this. Thanks Patrick. */
+	*dptr = (*pskb)->data + (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
+	return 1;
+}
+
+static int mangle_content_len(struct sk_buff **pskb,
+			      enum ip_conntrack_info ctinfo,
+			      struct nf_conn *ct,
+			      const char *dptr)
+{
+	unsigned int dataoff, matchoff, matchlen;
+	char buffer[sizeof("65536")];
+	int bufflen;
+
+	dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
+
+	/* Get actual SDP lenght */
+	if (ct_sip_get_info(ct, dptr, (*pskb)->len - dataoff, &matchoff,
+	                    &matchlen, POS_SDP_HEADER) > 0) {
+
+		/* since ct_sip_get_info() give us a pointer passing 'v='
+		   we need to add 2 bytes in this count. */
+		int c_len = (*pskb)->len - dataoff - matchoff + 2;
+
+		/* Now, update SDP length */
+		if (ct_sip_get_info(ct, dptr, (*pskb)->len - dataoff, &matchoff,
+		                    &matchlen, POS_CONTENT) > 0) {
+
+			bufflen = sprintf(buffer, "%u", c_len);
+			return nf_nat_mangle_udp_packet(pskb, ct, ctinfo,
+							matchoff, matchlen,
+							buffer, bufflen);
+		}
+	}
+	return 0;
+}
+
+static unsigned int mangle_sdp(struct sk_buff **pskb,
+			       enum ip_conntrack_info ctinfo,
+			       struct nf_conn *ct,
+			       __be32 newip, u_int16_t port,
+			       const char *dptr)
+{
+	char buffer[sizeof("nnn.nnn.nnn.nnn")];
+	unsigned int dataoff, bufflen;
+
+	dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
+
+	/* Mangle owner and contact info. */
+	bufflen = sprintf(buffer, "%u.%u.%u.%u", NIPQUAD(newip));
+	if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
+	                       buffer, bufflen, POS_OWNER_IP4))
+		return 0;
+
+	if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
+	                       buffer, bufflen, POS_CONNECTION_IP4))
+		return 0;
+
+	/* Mangle media port. */
+	bufflen = sprintf(buffer, "%u", port);
+	if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
+	                       buffer, bufflen, POS_MEDIA))
+		return 0;
+
+	return mangle_content_len(pskb, ctinfo, ct, dptr);
+}
+
+/* So, this packet has hit the connection tracking matching code.
+   Mangle it, and change the expectation to match the new version. */
+static unsigned int ip_nat_sdp(struct sk_buff **pskb,
+			       enum ip_conntrack_info ctinfo,
+			       struct nf_conntrack_expect *exp,
+			       const char *dptr)
+{
+	struct nf_conn *ct = exp->master;
+	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+	__be32 newip;
+	u_int16_t port;
+
+	DEBUGP("ip_nat_sdp():\n");
+
+	/* Connection will come from reply */
+	newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
+
+	exp->tuple.dst.u3.ip = newip;
+	exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port;
+	exp->dir = !dir;
+
+	/* When you see the packet, we need to NAT it the same as the
+	   this one. */
+	exp->expectfn = nf_nat_follow_master;
+
+	/* Try to get same port: if not, try to change it. */
+	for (port = ntohs(exp->saved_proto.udp.port); port != 0; port++) {
+		exp->tuple.dst.u.udp.port = htons(port);
+		if (nf_conntrack_expect_related(exp) == 0)
+			break;
+	}
+
+	if (port == 0)
+		return NF_DROP;
+
+	if (!mangle_sdp(pskb, ctinfo, ct, newip, port, dptr)) {
+		nf_conntrack_unexpect_related(exp);
+		return NF_DROP;
+	}
+	return NF_ACCEPT;
+}
+
+static void __exit nf_nat_sip_fini(void)
+{
+	rcu_assign_pointer(nf_nat_sip_hook, NULL);
+	rcu_assign_pointer(nf_nat_sdp_hook, NULL);
+	synchronize_rcu();
+}
+
+static int __init nf_nat_sip_init(void)
+{
+	BUG_ON(rcu_dereference(nf_nat_sip_hook));
+	BUG_ON(rcu_dereference(nf_nat_sdp_hook));
+	rcu_assign_pointer(nf_nat_sip_hook, ip_nat_sip);
+	rcu_assign_pointer(nf_nat_sdp_hook, ip_nat_sdp);
+	return 0;
+}
+
+module_init(nf_nat_sip_init);
+module_exit(nf_nat_sip_fini);

net/netfilter/Kconfig

@@ -236,6 +236,18 @@ config NF_CONNTRACK_PPTP
 
 	  To compile it as a module, choose M here.  If unsure, say N.
 
+config NF_CONNTRACK_SIP
+	tristate "SIP protocol support (EXPERIMENTAL)"
+	depends on EXPERIMENTAL && NF_CONNTRACK
+	help
+	  SIP is an application-layer control protocol that can establish,
+	  modify, and terminate multimedia sessions (conferences) such as
+	  Internet telephony calls. With the ip_conntrack_sip and
+	  the nf_nat_sip modules you can support the protocol on a connection
+	  tracking/NATing firewall.
+
+	  To compile it as a module, choose M here.  If unsure, say N.
+
 config NF_CT_NETLINK
 	tristate 'Connection tracking netlink interface (EXPERIMENTAL)'
 	depends on EXPERIMENTAL && NF_CONNTRACK && NETFILTER_NETLINK

net/netfilter/Makefile

@@ -29,6 +29,7 @@ obj-$(CONFIG_NF_CONNTRACK_H323) += nf_conntrack_h323.o
 obj-$(CONFIG_NF_CONNTRACK_IRC) += nf_conntrack_irc.o
 obj-$(CONFIG_NF_CONNTRACK_NETBIOS_NS) += nf_conntrack_netbios_ns.o
 obj-$(CONFIG_NF_CONNTRACK_PPTP) += nf_conntrack_pptp.o
+obj-$(CONFIG_NF_CONNTRACK_SIP) += nf_conntrack_sip.o
 
 # generic X tables 
 obj-$(CONFIG_NETFILTER_XTABLES) += x_tables.o xt_tcpudp.o

net/netfilter/nf_conntrack_sip.c

+/* SIP extension for IP connection tracking.
+ *
+ * (C) 2005 by Christian Hentschel <chentschel@arnet.com.ar>
+ * based on RR's ip_conntrack_ftp.c and other modules.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/ctype.h>
+#include <linux/skbuff.h>
+#include <linux/inet.h>
+#include <linux/in.h>
+#include <linux/udp.h>
+
+#include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_conntrack_expect.h>
+#include <net/netfilter/nf_conntrack_helper.h>
+#include <linux/netfilter/nf_conntrack_sip.h>
+
+#if 0
+#define DEBUGP printk
+#else
+#define DEBUGP(format, args...)
+#endif
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
+MODULE_DESCRIPTION("SIP connection tracking helper");
+MODULE_ALIAS("ip_conntrack_sip");
+
+#define MAX_PORTS	8
+static unsigned short ports[MAX_PORTS];
+static int ports_c;
+module_param_array(ports, ushort, &ports_c, 0400);
+MODULE_PARM_DESC(ports, "port numbers of SIP servers");
+
+static unsigned int sip_timeout __read_mostly = SIP_TIMEOUT;
+module_param(sip_timeout, uint, 0600);
+MODULE_PARM_DESC(sip_timeout, "timeout for the master SIP session");
+
+unsigned int (*nf_nat_sip_hook)(struct sk_buff **pskb,
+				enum ip_conntrack_info ctinfo,
+				struct nf_conn *ct,
+				const char **dptr) __read_mostly;
+EXPORT_SYMBOL_GPL(nf_nat_sip_hook);
+
+unsigned int (*nf_nat_sdp_hook)(struct sk_buff **pskb,
+				enum ip_conntrack_info ctinfo,
+				struct nf_conntrack_expect *exp,
+				const char *dptr) __read_mostly;
+EXPORT_SYMBOL_GPL(nf_nat_sdp_hook);
+
+static int digits_len(struct nf_conn *, const char *, const char *, int *);
+static int epaddr_len(struct nf_conn *, const char *, const char *, int *);
+static int skp_digits_len(struct nf_conn *, const char *, const char *, int *);
+static int skp_epaddr_len(struct nf_conn *, const char *, const char *, int *);
+
+struct sip_header_nfo {
+	const char	*lname;
+	const char	*sname;
+	const char	*ln_str;
+	size_t		lnlen;
+	size_t		snlen;
+	size_t		ln_strlen;
+	int		case_sensitive;
+	int		(*match_len)(struct nf_conn *, const char *,
+				     const char *, int *);
+};
+
+static const struct sip_header_nfo ct_sip_hdrs[] = {
+	[POS_REG_REQ_URI] = { 	/* SIP REGISTER request URI */
+		.lname		= "sip:",
+		.lnlen		= sizeof("sip:") - 1,
+		.ln_str		= ":",
+		.ln_strlen	= sizeof(":") - 1,
+		.match_len	= epaddr_len,
+	},
+	[POS_REQ_URI] = { 	/* SIP request URI */
+		.lname		= "sip:",
+		.lnlen		= sizeof("sip:") - 1,
+		.ln_str		= "@",
+		.ln_strlen	= sizeof("@") - 1,
+		.match_len	= epaddr_len,
+	},
+	[POS_FROM] = {		/* SIP From header */
+		.lname		= "From:",
+		.lnlen		= sizeof("From:") - 1,
+		.sname		= "\r\nf:",
+		.snlen		= sizeof("\r\nf:") - 1,
+		.ln_str		= "sip:",
+		.ln_strlen	= sizeof("sip:") - 1,
+		.match_len	= skp_epaddr_len,
+	},
+	[POS_TO] = {		/* SIP To header */
+		.lname		= "To:",
+		.lnlen		= sizeof("To:") - 1,
+		.sname		= "\r\nt:",
+		.snlen		= sizeof("\r\nt:") - 1,
+		.ln_str		= "sip:",
+		.ln_strlen	= sizeof("sip:") - 1,
+		.match_len	= skp_epaddr_len
+	},
+	[POS_VIA] = { 		/* SIP Via header */
+		.lname		= "Via:",
+		.lnlen		= sizeof("Via:") - 1,
+		.sname		= "\r\nv:",
+		.snlen		= sizeof("\r\nv:") - 1, /* rfc3261 "\r\n" */
+		.ln_str		= "UDP ",
+		.ln_strlen	= sizeof("UDP ") - 1,
+		.match_len	= epaddr_len,
+	},
+	[POS_CONTACT] = { 	/* SIP Contact header */
+		.lname		= "Contact:",
+		.lnlen		= sizeof("Contact:") - 1,
+		.sname		= "\r\nm:",
+		.snlen		= sizeof("\r\nm:") - 1,
+		.ln_str		= "sip:",
+		.ln_strlen	= sizeof("sip:") - 1,
+		.match_len	= skp_epaddr_len
+	},
+	[POS_CONTENT] = { 	/* SIP Content length header */
+		.lname		= "Content-Length:",
+		.lnlen		= sizeof("Content-Length:") - 1,
+		.sname		= "\r\nl:",
+		.snlen		= sizeof("\r\nl:") - 1,
+		.ln_str		= ":",
+		.ln_strlen	= sizeof(":") - 1,
+		.match_len	= skp_digits_len
+	},
+	[POS_MEDIA] = {		/* SDP media info */
+		.case_sensitive	= 1,
+		.lname		= "\nm=",
+		.lnlen		= sizeof("\nm=") - 1,
+		.sname		= "\rm=",
+		.snlen		= sizeof("\rm=") - 1,
+		.ln_str		= "audio ",
+		.ln_strlen	= sizeof("audio ") - 1,
+		.match_len	= digits_len
+	},
+	[POS_OWNER_IP4] = {	/* SDP owner address*/
+		.case_sensitive	= 1,
+		.lname		= "\no=",
+		.lnlen		= sizeof("\no=") - 1,
+		.sname		= "\ro=",
+		.snlen		= sizeof("\ro=") - 1,
+		.ln_str		= "IN IP4 ",
+		.ln_strlen	= sizeof("IN IP4 ") - 1,
+		.match_len	= epaddr_len
+	},
+	[POS_CONNECTION_IP4] = {/* SDP connection info */
+		.case_sensitive	= 1,
+		.lname		= "\nc=",
+		.lnlen		= sizeof("\nc=") - 1,
+		.sname		= "\rc=",
+		.snlen		= sizeof("\rc=") - 1,
+		.ln_str		= "IN IP4 ",
+		.ln_strlen	= sizeof("IN IP4 ") - 1,
+		.match_len	= epaddr_len
+	},
+	[POS_OWNER_IP6] = {	/* SDP owner address*/
+		.case_sensitive	= 1,
+		.lname		= "\no=",
+		.lnlen		= sizeof("\no=") - 1,
+		.sname		= "\ro=",
+		.snlen		= sizeof("\ro=") - 1,
+		.ln_str		= "IN IP6 ",
+		.ln_strlen	= sizeof("IN IP6 ") - 1,
+		.match_len	= epaddr_len
+	},
+	[POS_CONNECTION_IP6] = {/* SDP connection info */
+		.case_sensitive	= 1,
+		.lname		= "\nc=",
+		.lnlen		= sizeof("\nc=") - 1,
+		.sname		= "\rc=",
+		.snlen		= sizeof("\rc=") - 1,
+		.ln_str		= "IN IP6 ",
+		.ln_strlen	= sizeof("IN IP6 ") - 1,
+		.match_len	= epaddr_len
+	},
+	[POS_SDP_HEADER] = { 	/* SDP version header */
+		.case_sensitive	= 1,
+		.lname		= "\nv=",
+		.lnlen		= sizeof("\nv=") - 1,
+		.sname		= "\rv=",
+		.snlen		= sizeof("\rv=") - 1,
+		.ln_str		= "=",
+		.ln_strlen	= sizeof("=") - 1,
+		.match_len	= digits_len
+	}
+};
+
+/* get line lenght until first CR or LF seen. */
+int ct_sip_lnlen(const char *line, const char *limit)
+{
+	const char *k = line;
+
+	while ((line <= limit) && (*line == '\r' || *line == '\n'))
+		line++;
+
+	while (line <= limit) {
+		if (*line == '\r' || *line == '\n')
+			break;
+		line++;
+	}
+	return line - k;
+}
+EXPORT_SYMBOL_GPL(ct_sip_lnlen);
+
+/* Linear string search, case sensitive. */
+const char *ct_sip_search(const char *needle, const char *haystack,
+			  size_t needle_len, size_t haystack_len,
+			  int case_sensitive)
+{
+	const char *limit = haystack + (haystack_len - needle_len);
+
+	while (haystack <= limit) {
+		if (case_sensitive) {
+			if (strncmp(haystack, needle, needle_len) == 0)
+				return haystack;
+		} else {
+			if (strnicmp(haystack, needle, needle_len) == 0)
+				return haystack;
+		}
+		haystack++;
+	}
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(ct_sip_search);
+
+static int digits_len(struct nf_conn *ct, const char *dptr,
+		      const char *limit, int *shift)
+{
+	int len = 0;
+	while (dptr <= limit && isdigit(*dptr)) {
+		dptr++;
+		len++;
+	}
+	return len;
+}
+
+/* get digits lenght, skiping blank spaces. */
+static int skp_digits_len(struct nf_conn *ct, const char *dptr,
+			  const char *limit, int *shift)
+{
+	for (; dptr <= limit && *dptr == ' '; dptr++)
+		(*shift)++;
+
+	return digits_len(ct, dptr, limit, shift);
+}
+
+static int parse_addr(struct nf_conn *ct, const char *cp, const char **endp,
+		      union nf_conntrack_address *addr, const char *limit)
+{
+	const char *end;
+	int family = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.l3num;
+	int ret = 0;
+
+	switch (family) {
+	case AF_INET:
+		ret = in4_pton(cp, limit - cp, (u8 *)&addr->ip, -1, &end);
+		break;
+	case AF_INET6:
+		ret = in6_pton(cp, limit - cp, (u8 *)&addr->ip6, -1, &end);
+		break;
+	default:
+		BUG();
+	}
+
+	if (ret == 0 || end == cp)
+		return 0;
+	if (endp)
+		*endp = end;
+	return 1;
+}
+
+/* skip ip address. returns its length. */
+static int epaddr_len(struct nf_conn *ct, const char *dptr,
+		      const char *limit, int *shift)
+{
+	union nf_conntrack_address addr;
+	const char *aux = dptr;
+
+	if (!parse_addr(ct, dptr, &dptr, &addr, limit)) {
+		DEBUGP("ip: %s parse failed.!\n", dptr);
+		return 0;
+	}
+
+	/* Port number */
+	if (*dptr == ':') {
+		dptr++;
+		dptr += digits_len(ct, dptr, limit, shift);
+	}
+	return dptr - aux;
+}
+
+/* get address length, skiping user info. */
+static int skp_epaddr_len(struct nf_conn *ct, const char *dptr,
+			  const char *limit, int *shift)
+{
+	int s = *shift;
+
+	for (; dptr <= limit && *dptr != '@'; dptr++)
+		(*shift)++;
+
+	if (*dptr == '@') {
+		dptr++;
+		(*shift)++;
+	} else
+		*shift = s;
+
+	return epaddr_len(ct, dptr, limit, shift);
+}
+
+/* Returns 0 if not found, -1 error parsing. */
+int ct_sip_get_info(struct nf_conn *ct,
+		    const char *dptr, size_t dlen,
+		    unsigned int *matchoff,
+		    unsigned int *matchlen,
+		    enum sip_header_pos pos)
+{
+	const struct sip_header_nfo *hnfo = &ct_sip_hdrs[pos];
+	const char *limit, *aux, *k = dptr;
+	int shift = 0;
+
+	limit = dptr + (dlen - hnfo->lnlen);
+
+	while (dptr <= limit) {
+		if ((strncmp(dptr, hnfo->lname, hnfo->lnlen) != 0) &&
+		    (strncmp(dptr, hnfo->sname, hnfo->snlen) != 0)) {
+			dptr++;
+			continue;
+		}
+		aux = ct_sip_search(hnfo->ln_str, dptr, hnfo->ln_strlen,
+		                    ct_sip_lnlen(dptr, limit),
+				    hnfo->case_sensitive);
+		if (!aux) {
+			DEBUGP("'%s' not found in '%s'.\n", hnfo->ln_str,
+			       hnfo->lname);
+			return -1;
+		}
+		aux += hnfo->ln_strlen;
+
+		*matchlen = hnfo->match_len(ct, aux, limit, &shift);
+		if (!*matchlen)
+			return -1;
+
+		*matchoff = (aux - k) + shift;
+
+		DEBUGP("%s match succeeded! - len: %u\n", hnfo->lname,
+		       *matchlen);
+		return 1;
+	}
+	DEBUGP("%s header not found.\n", hnfo->lname);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ct_sip_get_info);
+
+static int set_expected_rtp(struct sk_buff **pskb,
+			    struct nf_conn *ct,
+			    enum ip_conntrack_info ctinfo,
+			    union nf_conntrack_address *addr,
+			    __be16 port,
+			    const char *dptr)
+{
+	struct nf_conntrack_expect *exp;
+	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+	int family = ct->tuplehash[!dir].tuple.src.l3num;
+	int ret;
+	typeof(nf_nat_sdp_hook) nf_nat_sdp;
+
+	exp = nf_conntrack_expect_alloc(ct);
+	if (exp == NULL)
+		return NF_DROP;
+	nf_conntrack_expect_init(exp, family,
+				 &ct->tuplehash[!dir].tuple.src.u3, addr,
+				 IPPROTO_UDP, NULL, &port);
+
+	nf_nat_sdp = rcu_dereference(nf_nat_sdp_hook);
+	if (nf_nat_sdp && ct->status & IPS_NAT_MASK)
+		ret = nf_nat_sdp(pskb, ctinfo, exp, dptr);
+	else {
+		if (nf_conntrack_expect_related(exp) != 0)
+			ret = NF_DROP;
+		else
+			ret = NF_ACCEPT;
+	}
+	nf_conntrack_expect_put(exp);
+
+	return ret;
+}
+
+static int sip_help(struct sk_buff **pskb,
+		    unsigned int protoff,
+		    struct nf_conn *ct,
+		    enum ip_conntrack_info ctinfo)
+{
+	int family = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.l3num;
+	union nf_conntrack_address addr;
+	unsigned int dataoff, datalen;
+	const char *dptr;
+	int ret = NF_ACCEPT;
+	int matchoff, matchlen;
+	u_int16_t port;
+	enum sip_header_pos pos;
+	typeof(nf_nat_sip_hook) nf_nat_sip;
+
+	/* No Data ? */
+	dataoff = protoff + sizeof(struct udphdr);
+	if (dataoff >= (*pskb)->len)
+		return NF_ACCEPT;
+
+	nf_ct_refresh(ct, *pskb, sip_timeout * HZ);
+
+	if (!skb_is_nonlinear(*pskb))
+		dptr = (*pskb)->data + dataoff;
+	else {
+		DEBUGP("Copy of skbuff not supported yet.\n");
+		goto out;
+	}
+
+	nf_nat_sip = rcu_dereference(nf_nat_sip_hook);
+	if (nf_nat_sip && ct->status & IPS_NAT_MASK) {
+		if (!nf_nat_sip(pskb, ctinfo, ct, &dptr)) {
+			ret = NF_DROP;
+			goto out;
+		}
+	}
+
+	datalen = (*pskb)->len - dataoff;
+	if (datalen < sizeof("SIP/2.0 200") - 1)
+		goto out;
+
+	/* RTP info only in some SDP pkts */
+	if (memcmp(dptr, "INVITE", sizeof("INVITE") - 1) != 0 &&
+	    memcmp(dptr, "SIP/2.0 200", sizeof("SIP/2.0 200") - 1) != 0) {
+		goto out;
+	}
+	/* Get address and port from SDP packet. */
+	pos = family == AF_INET ? POS_CONNECTION_IP4 : POS_CONNECTION_IP6;
+	if (ct_sip_get_info(ct, dptr, datalen, &matchoff, &matchlen, pos) > 0) {
+
+		/* We'll drop only if there are parse problems. */
+		if (!parse_addr(ct, dptr + matchoff, NULL, &addr,
+			        dptr + datalen)) {
+			ret = NF_DROP;
+			goto out;
+		}
+		if (ct_sip_get_info(ct, dptr, datalen, &matchoff, &matchlen,
+		                    POS_MEDIA) > 0) {
+
+			port = simple_strtoul(dptr + matchoff, NULL, 10);
+			if (port < 1024) {
+				ret = NF_DROP;
+				goto out;
+			}
+			ret = set_expected_rtp(pskb, ct, ctinfo, &addr,
+					       htons(port), dptr);
+		}
+	}
+out:
+	return ret;
+}
+
+static struct nf_conntrack_helper sip[MAX_PORTS][2] __read_mostly;
+static char sip_names[MAX_PORTS][2][sizeof("sip-65535")] __read_mostly;
+
+static void nf_conntrack_sip_fini(void)
+{
+	int i, j;
+
+	for (i = 0; i < ports_c; i++) {
+		for (j = 0; j < 2; j++) {
+			if (sip[i][j].me == NULL)
+				continue;
+			nf_conntrack_helper_unregister(&sip[i][j]);
+		}
+	}
+}
+
+static int __init nf_conntrack_sip_init(void)
+{
+	int i, j, ret;
+	char *tmpname;
+
+	if (ports_c == 0)
+		ports[ports_c++] = SIP_PORT;
+
+	for (i = 0; i < ports_c; i++) {
+		memset(&sip[i], 0, sizeof(sip[i]));
+
+		sip[i][0].tuple.src.l3num = AF_INET;
+		sip[i][1].tuple.src.l3num = AF_INET6;
+		for (j = 0; j < 2; j++) {
+			sip[i][j].tuple.dst.protonum = IPPROTO_UDP;
+			sip[i][j].tuple.src.u.udp.port = htons(ports[i]);
+			sip[i][j].mask.src.l3num = 0xFFFF;
+			sip[i][j].mask.src.u.udp.port = htons(0xFFFF);
+			sip[i][j].mask.dst.protonum = 0xFF;
+			sip[i][j].max_expected = 2;
+			sip[i][j].timeout = 3 * 60; /* 3 minutes */
+			sip[i][j].me = THIS_MODULE;
+			sip[i][j].help = sip_help;
+
+			tmpname = &sip_names[i][j][0];
+			if (ports[i] == SIP_PORT)
+				sprintf(tmpname, "sip");
+			else
+				sprintf(tmpname, "sip-%u", i);
+			sip[i][j].name = tmpname;
+
+			DEBUGP("port #%u: %u\n", i, ports[i]);
+
+			ret = nf_conntrack_helper_register(&sip[i][j]);
+			if (ret) {
+				printk("nf_ct_sip: failed to register helper "
+				       "for pf: %u port: %u\n",
+				       sip[i][j].tuple.src.l3num, ports[i]);
+				nf_conntrack_sip_fini();
+				return ret;
+			}
+		}
+	}
+	return 0;
+}
+
+module_init(nf_conntrack_sip_init);
+module_exit(nf_conntrack_sip_fini);