// SPDX-License-Identifier: GPL-2.0-only

  /* 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.

   * (C) 2007 United Security Providers
   * (C) 2007, 2008 Patrick McHardy <kaber@trash.net>

   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #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 <linux/tcp.h>

  #include <linux/netfilter.h>

  #include <linux/netfilter_ipv4.h>
  #include <linux/netfilter_ipv6.h>

  
  #include <net/netfilter/nf_conntrack.h>

  #include <net/netfilter/nf_conntrack_core.h>

  #include <net/netfilter/nf_conntrack_expect.h>
  #include <net/netfilter/nf_conntrack_helper.h>

  #include <net/netfilter/nf_conntrack_zones.h>

  #include <linux/netfilter/nf_conntrack_sip.h>

  #define HELPER_NAME "sip"

  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
  MODULE_DESCRIPTION("SIP connection tracking helper");
  MODULE_ALIAS("ip_conntrack_sip");

  MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);

  
  #define MAX_PORTS	8
  static unsigned short ports[MAX_PORTS];

  static unsigned 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");

  static int sip_direct_signalling __read_mostly = 1;
  module_param(sip_direct_signalling, int, 0600);
  MODULE_PARM_DESC(sip_direct_signalling, "expect incoming calls from registrar "
  					"only (default 1)");

  static int sip_direct_media __read_mostly = 1;
  module_param(sip_direct_media, int, 0600);
  MODULE_PARM_DESC(sip_direct_media, "Expect Media streams between signalling "
  				   "endpoints only (default 1)");

  static int sip_external_media __read_mostly = 0;
  module_param(sip_external_media, int, 0600);
  MODULE_PARM_DESC(sip_external_media, "Expect Media streams between external "
  				     "endpoints (default 0)");

  const struct nf_nat_sip_hooks *nf_nat_sip_hooks;
  EXPORT_SYMBOL_GPL(nf_nat_sip_hooks);

  static int string_len(const struct nf_conn *ct, const char *dptr,
  		      const char *limit, int *shift)
  {
  	int len = 0;
  
  	while (dptr < limit && isalpha(*dptr)) {
  		dptr++;
  		len++;
  	}
  	return len;
  }

  static int digits_len(const struct nf_conn *ct, const char *dptr,

  		      const char *limit, int *shift)
  {
  	int len = 0;

  	while (dptr < limit && isdigit(*dptr)) {

  		dptr++;
  		len++;
  	}
  	return len;
  }

  static int iswordc(const char c)
  {
  	if (isalnum(c) || c == '!' || c == '"' || c == '%' ||

  	    (c >= '(' && c <= '+') || c == ':' || c == '<' || c == '>' ||

  	    c == '?' || (c >= '[' && c <= ']') || c == '_' || c == '`' ||

  	    c == '{' || c == '}' || c == '~' || (c >= '-' && c <= '/') ||
  	    c == '\'')

  		return 1;
  	return 0;
  }
  
  static int word_len(const char *dptr, const char *limit)
  {
  	int len = 0;
  	while (dptr < limit && iswordc(*dptr)) {
  		dptr++;
  		len++;
  	}
  	return len;
  }
  
  static int callid_len(const struct nf_conn *ct, const char *dptr,
  		      const char *limit, int *shift)
  {
  	int len, domain_len;
  
  	len = word_len(dptr, limit);
  	dptr += len;
  	if (!len || dptr == limit || *dptr != '@')
  		return len;
  	dptr++;
  	len++;
  
  	domain_len = word_len(dptr, limit);
  	if (!domain_len)
  		return 0;
  	return len + domain_len;
  }

  /* get media type + port length */
  static int media_len(const struct nf_conn *ct, const char *dptr,
  		     const char *limit, int *shift)
  {
  	int len = string_len(ct, dptr, limit, shift);
  
  	dptr += len;
  	if (dptr >= limit || *dptr != ' ')
  		return 0;
  	len++;
  	dptr++;
  
  	return len + digits_len(ct, dptr, limit, shift);
  }

  static int sip_parse_addr(const struct nf_conn *ct, const char *cp,
  			  const char **endp, union nf_inet_addr *addr,
  			  const char *limit, bool delim)

  {
  	const char *end;

  	int ret;

  	if (!ct)
  		return 0;

  	memset(addr, 0, sizeof(*addr));

  	switch (nf_ct_l3num(ct)) {

  	case AF_INET:
  		ret = in4_pton(cp, limit - cp, (u8 *)&addr->ip, -1, &end);

  		if (ret == 0)
  			return 0;

  		break;
  	case AF_INET6:

  		if (cp < limit && *cp == '[')
  			cp++;
  		else if (delim)
  			return 0;

  		ret = in6_pton(cp, limit - cp, (u8 *)&addr->ip6, -1, &end);

  		if (ret == 0)
  			return 0;
  
  		if (end < limit && *end == ']')
  			end++;
  		else if (delim)
  			return 0;

  		break;
  	default:
  		BUG();
  	}

  	if (endp)
  		*endp = end;
  	return 1;
  }
  
  /* skip ip address. returns its length. */

  static int epaddr_len(const struct nf_conn *ct, const char *dptr,

  		      const char *limit, int *shift)
  {

  	union nf_inet_addr addr;

  	const char *aux = dptr;

  	if (!sip_parse_addr(ct, dptr, &dptr, &addr, limit, true)) {

  		pr_debug("ip: %s parse failed.!
  ", 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(const struct nf_conn *ct, const char *dptr,

  			  const char *limit, int *shift)
  {

  	const char *start = dptr;

  	int s = *shift;

  	/* Search for @, but stop at the end of the line.
  	 * We are inside a sip: URI, so we don't need to worry about
  	 * continuation lines. */

  	while (dptr < limit &&

  	       *dptr != '@' && *dptr != '\r' && *dptr != '
  ') {

  		(*shift)++;

  		dptr++;
  	}

  	if (dptr < limit && *dptr == '@') {

  		dptr++;
  		(*shift)++;

  	} else {
  		dptr = start;

  		*shift = s;

  	}

  
  	return epaddr_len(ct, dptr, limit, shift);
  }

  /* Parse a SIP request line of the form:
   *
   * Request-Line = Method SP Request-URI SP SIP-Version CRLF
   *
   * and return the offset and length of the address contained in the Request-URI.
   */
  int ct_sip_parse_request(const struct nf_conn *ct,
  			 const char *dptr, unsigned int datalen,

  			 unsigned int *matchoff, unsigned int *matchlen,
  			 union nf_inet_addr *addr, __be16 *port)

  {

  	const char *start = dptr, *limit = dptr + datalen, *end;

  	unsigned int mlen;

  	unsigned int p;

  	int shift = 0;
  
  	/* Skip method and following whitespace */
  	mlen = string_len(ct, dptr, limit, NULL);
  	if (!mlen)
  		return 0;
  	dptr += mlen;
  	if (++dptr >= limit)
  		return 0;
  
  	/* Find SIP URI */

  	for (; dptr < limit - strlen("sip:"); dptr++) {

  		if (*dptr == '\r' || *dptr == '
  ')
  			return -1;

  		if (strncasecmp(dptr, "sip:", strlen("sip:")) == 0) {

  			dptr += strlen("sip:");

  			break;

  		}

  	}

  	if (!skp_epaddr_len(ct, dptr, limit, &shift))

  		return 0;

  	dptr += shift;

  	if (!sip_parse_addr(ct, dptr, &end, addr, limit, true))

  		return -1;
  	if (end < limit && *end == ':') {
  		end++;
  		p = simple_strtoul(end, (char **)&end, 10);
  		if (p < 1024 || p > 65535)
  			return -1;
  		*port = htons(p);
  	} else
  		*port = htons(SIP_PORT);
  
  	if (end == dptr)
  		return 0;
  	*matchoff = dptr - start;
  	*matchlen = end - dptr;

  	return 1;
  }
  EXPORT_SYMBOL_GPL(ct_sip_parse_request);

  /* SIP header parsing: SIP headers are located at the beginning of a line, but
   * may span several lines, in which case the continuation lines begin with a
   * whitespace character. RFC 2543 allows lines to be terminated with CR, LF or
   * CRLF, RFC 3261 allows only CRLF, we support both.
   *
   * Headers are followed by (optionally) whitespace, a colon, again (optionally)
   * whitespace and the values. Whitespace in this context means any amount of
   * tabs, spaces and continuation lines, which are treated as a single whitespace
   * character.

   *

   * Some headers may appear multiple times. A comma separated list of values is

   * equivalent to multiple headers.

   */
  static const struct sip_header ct_sip_hdrs[] = {

  	[SIP_HDR_CSEQ]			= SIP_HDR("CSeq", NULL, NULL, digits_len),

  	[SIP_HDR_FROM]			= SIP_HDR("From", "f", "sip:", skp_epaddr_len),
  	[SIP_HDR_TO]			= SIP_HDR("To", "t", "sip:", skp_epaddr_len),
  	[SIP_HDR_CONTACT]		= SIP_HDR("Contact", "m", "sip:", skp_epaddr_len),

  	[SIP_HDR_VIA_UDP]		= SIP_HDR("Via", "v", "UDP ", epaddr_len),
  	[SIP_HDR_VIA_TCP]		= SIP_HDR("Via", "v", "TCP ", epaddr_len),

  	[SIP_HDR_EXPIRES]		= SIP_HDR("Expires", NULL, NULL, digits_len),

  	[SIP_HDR_CONTENT_LENGTH]	= SIP_HDR("Content-Length", "l", NULL, digits_len),

  	[SIP_HDR_CALL_ID]		= SIP_HDR("Call-Id", "i", NULL, callid_len),

  };
  
  static const char *sip_follow_continuation(const char *dptr, const char *limit)

  {

  	/* Walk past newline */
  	if (++dptr >= limit)
  		return NULL;
  
  	/* Skip '
  ' in CR LF */
  	if (*(dptr - 1) == '\r' && *dptr == '
  ') {
  		if (++dptr >= limit)
  			return NULL;
  	}

  	/* Continuation line? */
  	if (*dptr != ' ' && *dptr != '\t')
  		return NULL;

  	/* skip leading whitespace */
  	for (; dptr < limit; dptr++) {
  		if (*dptr != ' ' && *dptr != '\t')
  			break;
  	}
  	return dptr;
  }
  
  static const char *sip_skip_whitespace(const char *dptr, const char *limit)
  {
  	for (; dptr < limit; dptr++) {

  		if (*dptr == ' ' || *dptr == '\t')

  			continue;
  		if (*dptr != '\r' && *dptr != '
  ')
  			break;
  		dptr = sip_follow_continuation(dptr, limit);

  		break;

  	}
  	return dptr;
  }
  
  /* Search within a SIP header value, dealing with continuation lines */
  static const char *ct_sip_header_search(const char *dptr, const char *limit,
  					const char *needle, unsigned int len)
  {
  	for (limit -= len; dptr < limit; dptr++) {
  		if (*dptr == '\r' || *dptr == '
  ') {
  			dptr = sip_follow_continuation(dptr, limit);
  			if (dptr == NULL)
  				break;

  			continue;
  		}

  		if (strncasecmp(dptr, needle, len) == 0)

  			return dptr;
  	}
  	return NULL;
  }
  
  int ct_sip_get_header(const struct nf_conn *ct, const char *dptr,
  		      unsigned int dataoff, unsigned int datalen,
  		      enum sip_header_types type,
  		      unsigned int *matchoff, unsigned int *matchlen)
  {
  	const struct sip_header *hdr = &ct_sip_hdrs[type];
  	const char *start = dptr, *limit = dptr + datalen;
  	int shift = 0;
  
  	for (dptr += dataoff; dptr < limit; dptr++) {
  		/* Find beginning of line */
  		if (*dptr != '\r' && *dptr != '
  ')
  			continue;
  		if (++dptr >= limit)
  			break;
  		if (*(dptr - 1) == '\r' && *dptr == '
  ') {
  			if (++dptr >= limit)
  				break;

  		}

  		/* Skip continuation lines */
  		if (*dptr == ' ' || *dptr == '\t')
  			continue;

  		/* Find header. Compact headers must be followed by a
  		 * non-alphabetic character to avoid mismatches. */
  		if (limit - dptr >= hdr->len &&

  		    strncasecmp(dptr, hdr->name, hdr->len) == 0)

  			dptr += hdr->len;
  		else if (hdr->cname && limit - dptr >= hdr->clen + 1 &&

  			 strncasecmp(dptr, hdr->cname, hdr->clen) == 0 &&

  			 !isalpha(*(dptr + hdr->clen)))

  			dptr += hdr->clen;
  		else
  			continue;

  		/* Find and skip colon */
  		dptr = sip_skip_whitespace(dptr, limit);
  		if (dptr == NULL)
  			break;
  		if (*dptr != ':' || ++dptr >= limit)
  			break;
  
  		/* Skip whitespace after colon */
  		dptr = sip_skip_whitespace(dptr, limit);
  		if (dptr == NULL)
  			break;
  
  		*matchoff = dptr - start;
  		if (hdr->search) {
  			dptr = ct_sip_header_search(dptr, limit, hdr->search,
  						    hdr->slen);
  			if (!dptr)
  				return -1;
  			dptr += hdr->slen;
  		}
  
  		*matchlen = hdr->match_len(ct, dptr, limit, &shift);
  		if (!*matchlen)
  			return -1;
  		*matchoff = dptr - start + shift;

  		return 1;
  	}

  	return 0;
  }

  EXPORT_SYMBOL_GPL(ct_sip_get_header);

  /* Get next header field in a list of comma separated values */

  static int ct_sip_next_header(const struct nf_conn *ct, const char *dptr,
  			      unsigned int dataoff, unsigned int datalen,
  			      enum sip_header_types type,
  			      unsigned int *matchoff, unsigned int *matchlen)
  {
  	const struct sip_header *hdr = &ct_sip_hdrs[type];
  	const char *start = dptr, *limit = dptr + datalen;
  	int shift = 0;
  
  	dptr += dataoff;
  
  	dptr = ct_sip_header_search(dptr, limit, ",", strlen(","));
  	if (!dptr)
  		return 0;
  
  	dptr = ct_sip_header_search(dptr, limit, hdr->search, hdr->slen);
  	if (!dptr)
  		return 0;
  	dptr += hdr->slen;
  
  	*matchoff = dptr - start;
  	*matchlen = hdr->match_len(ct, dptr, limit, &shift);
  	if (!*matchlen)
  		return -1;
  	*matchoff += shift;
  	return 1;
  }
  
  /* Walk through headers until a parsable one is found or no header of the
   * given type is left. */
  static int ct_sip_walk_headers(const struct nf_conn *ct, const char *dptr,
  			       unsigned int dataoff, unsigned int datalen,
  			       enum sip_header_types type, int *in_header,
  			       unsigned int *matchoff, unsigned int *matchlen)
  {
  	int ret;
  
  	if (in_header && *in_header) {
  		while (1) {
  			ret = ct_sip_next_header(ct, dptr, dataoff, datalen,
  						 type, matchoff, matchlen);
  			if (ret > 0)
  				return ret;
  			if (ret == 0)
  				break;
  			dataoff += *matchoff;
  		}
  		*in_header = 0;
  	}
  
  	while (1) {
  		ret = ct_sip_get_header(ct, dptr, dataoff, datalen,
  					type, matchoff, matchlen);
  		if (ret > 0)
  			break;
  		if (ret == 0)
  			return ret;
  		dataoff += *matchoff;
  	}
  
  	if (in_header)
  		*in_header = 1;
  	return 1;
  }
  
  /* Locate a SIP header, parse the URI and return the offset and length of
   * the address as well as the address and port themselves. A stream of
   * headers can be parsed by handing in a non-NULL datalen and in_header
   * pointer.
   */
  int ct_sip_parse_header_uri(const struct nf_conn *ct, const char *dptr,
  			    unsigned int *dataoff, unsigned int datalen,
  			    enum sip_header_types type, int *in_header,
  			    unsigned int *matchoff, unsigned int *matchlen,
  			    union nf_inet_addr *addr, __be16 *port)
  {
  	const char *c, *limit = dptr + datalen;
  	unsigned int p;
  	int ret;
  
  	ret = ct_sip_walk_headers(ct, dptr, dataoff ? *dataoff : 0, datalen,
  				  type, in_header, matchoff, matchlen);
  	WARN_ON(ret < 0);
  	if (ret == 0)
  		return ret;

  	if (!sip_parse_addr(ct, dptr + *matchoff, &c, addr, limit, true))

  		return -1;
  	if (*c == ':') {
  		c++;
  		p = simple_strtoul(c, (char **)&c, 10);
  		if (p < 1024 || p > 65535)
  			return -1;
  		*port = htons(p);
  	} else
  		*port = htons(SIP_PORT);
  
  	if (dataoff)
  		*dataoff = c - dptr;
  	return 1;
  }
  EXPORT_SYMBOL_GPL(ct_sip_parse_header_uri);

  static int ct_sip_parse_param(const struct nf_conn *ct, const char *dptr,
  			      unsigned int dataoff, unsigned int datalen,
  			      const char *name,
  			      unsigned int *matchoff, unsigned int *matchlen)
  {
  	const char *limit = dptr + datalen;
  	const char *start;
  	const char *end;
  
  	limit = ct_sip_header_search(dptr + dataoff, limit, ",", strlen(","));
  	if (!limit)
  		limit = dptr + datalen;
  
  	start = ct_sip_header_search(dptr + dataoff, limit, name, strlen(name));
  	if (!start)
  		return 0;
  	start += strlen(name);
  
  	end = ct_sip_header_search(start, limit, ";", strlen(";"));
  	if (!end)
  		end = limit;
  
  	*matchoff = start - dptr;
  	*matchlen = end - start;
  	return 1;
  }

  /* Parse address from header parameter and return address, offset and length */
  int ct_sip_parse_address_param(const struct nf_conn *ct, const char *dptr,
  			       unsigned int dataoff, unsigned int datalen,
  			       const char *name,
  			       unsigned int *matchoff, unsigned int *matchlen,

  			       union nf_inet_addr *addr, bool delim)

  {
  	const char *limit = dptr + datalen;
  	const char *start, *end;
  
  	limit = ct_sip_header_search(dptr + dataoff, limit, ",", strlen(","));
  	if (!limit)
  		limit = dptr + datalen;
  
  	start = ct_sip_header_search(dptr + dataoff, limit, name, strlen(name));
  	if (!start)
  		return 0;
  
  	start += strlen(name);

  	if (!sip_parse_addr(ct, start, &end, addr, limit, delim))

  		return 0;
  	*matchoff = start - dptr;
  	*matchlen = end - start;
  	return 1;
  }
  EXPORT_SYMBOL_GPL(ct_sip_parse_address_param);
  
  /* Parse numerical header parameter and return value, offset and length */
  int ct_sip_parse_numerical_param(const struct nf_conn *ct, const char *dptr,
  				 unsigned int dataoff, unsigned int datalen,
  				 const char *name,
  				 unsigned int *matchoff, unsigned int *matchlen,
  				 unsigned int *val)
  {
  	const char *limit = dptr + datalen;
  	const char *start;
  	char *end;
  
  	limit = ct_sip_header_search(dptr + dataoff, limit, ",", strlen(","));
  	if (!limit)
  		limit = dptr + datalen;
  
  	start = ct_sip_header_search(dptr + dataoff, limit, name, strlen(name));
  	if (!start)
  		return 0;
  
  	start += strlen(name);
  	*val = simple_strtoul(start, &end, 0);
  	if (start == end)
  		return 0;
  	if (matchoff && matchlen) {
  		*matchoff = start - dptr;
  		*matchlen = end - start;
  	}
  	return 1;
  }
  EXPORT_SYMBOL_GPL(ct_sip_parse_numerical_param);

  static int ct_sip_parse_transport(struct nf_conn *ct, const char *dptr,
  				  unsigned int dataoff, unsigned int datalen,
  				  u8 *proto)
  {
  	unsigned int matchoff, matchlen;
  
  	if (ct_sip_parse_param(ct, dptr, dataoff, datalen, "transport=",
  			       &matchoff, &matchlen)) {

  		if (!strncasecmp(dptr + matchoff, "TCP", strlen("TCP")))

  			*proto = IPPROTO_TCP;

  		else if (!strncasecmp(dptr + matchoff, "UDP", strlen("UDP")))

  			*proto = IPPROTO_UDP;
  		else
  			return 0;
  
  		if (*proto != nf_ct_protonum(ct))
  			return 0;
  	} else
  		*proto = nf_ct_protonum(ct);
  
  	return 1;
  }

  static int sdp_parse_addr(const struct nf_conn *ct, const char *cp,
  			  const char **endp, union nf_inet_addr *addr,
  			  const char *limit)
  {
  	const char *end;
  	int ret;
  
  	memset(addr, 0, sizeof(*addr));
  	switch (nf_ct_l3num(ct)) {
  	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)
  		return 0;
  	if (endp)
  		*endp = end;
  	return 1;
  }
  
  /* skip ip address. returns its length. */
  static int sdp_addr_len(const struct nf_conn *ct, const char *dptr,
  			const char *limit, int *shift)
  {
  	union nf_inet_addr addr;
  	const char *aux = dptr;
  
  	if (!sdp_parse_addr(ct, dptr, &dptr, &addr, limit)) {
  		pr_debug("ip: %s parse failed.!
  ", dptr);
  		return 0;
  	}
  
  	return dptr - aux;
  }

  /* SDP header parsing: a SDP session description contains an ordered set of
   * headers, starting with a section containing general session parameters,
   * optionally followed by multiple media descriptions.
   *
   * SDP headers always start at the beginning of a line. According to RFC 2327:
   * "The sequence CRLF (0x0d0a) is used to end a record, although parsers should
   * be tolerant and also accept records terminated with a single newline
   * character". We handle both cases.
   */

  static const struct sip_header ct_sdp_hdrs_v4[] = {
  	[SDP_HDR_VERSION]	= SDP_HDR("v=", NULL, digits_len),
  	[SDP_HDR_OWNER]		= SDP_HDR("o=", "IN IP4 ", sdp_addr_len),
  	[SDP_HDR_CONNECTION]	= SDP_HDR("c=", "IN IP4 ", sdp_addr_len),
  	[SDP_HDR_MEDIA]		= SDP_HDR("m=", NULL, media_len),
  };
  
  static const struct sip_header ct_sdp_hdrs_v6[] = {
  	[SDP_HDR_VERSION]	= SDP_HDR("v=", NULL, digits_len),
  	[SDP_HDR_OWNER]		= SDP_HDR("o=", "IN IP6 ", sdp_addr_len),
  	[SDP_HDR_CONNECTION]	= SDP_HDR("c=", "IN IP6 ", sdp_addr_len),
  	[SDP_HDR_MEDIA]		= SDP_HDR("m=", NULL, media_len),

  };
  
  /* Linear string search within SDP header values */
  static const char *ct_sdp_header_search(const char *dptr, const char *limit,
  					const char *needle, unsigned int len)
  {
  	for (limit -= len; dptr < limit; dptr++) {
  		if (*dptr == '\r' || *dptr == '
  ')
  			break;
  		if (strncmp(dptr, needle, len) == 0)
  			return dptr;
  	}
  	return NULL;
  }
  
  /* Locate a SDP header (optionally a substring within the header value),

   * optionally stopping at the first occurrence of the term header, parse

   * it and return the offset and length of the data we're interested in.
   */
  int ct_sip_get_sdp_header(const struct nf_conn *ct, const char *dptr,
  			  unsigned int dataoff, unsigned int datalen,
  			  enum sdp_header_types type,
  			  enum sdp_header_types term,
  			  unsigned int *matchoff, unsigned int *matchlen)
  {

  	const struct sip_header *hdrs, *hdr, *thdr;

  	const char *start = dptr, *limit = dptr + datalen;
  	int shift = 0;

  	hdrs = nf_ct_l3num(ct) == NFPROTO_IPV4 ? ct_sdp_hdrs_v4 : ct_sdp_hdrs_v6;
  	hdr = &hdrs[type];
  	thdr = &hdrs[term];

  	for (dptr += dataoff; dptr < limit; dptr++) {
  		/* Find beginning of line */
  		if (*dptr != '\r' && *dptr != '
  ')
  			continue;
  		if (++dptr >= limit)
  			break;
  		if (*(dptr - 1) == '\r' && *dptr == '
  ') {
  			if (++dptr >= limit)
  				break;
  		}
  
  		if (term != SDP_HDR_UNSPEC &&
  		    limit - dptr >= thdr->len &&

  		    strncasecmp(dptr, thdr->name, thdr->len) == 0)

  			break;
  		else if (limit - dptr >= hdr->len &&

  			 strncasecmp(dptr, hdr->name, hdr->len) == 0)

  			dptr += hdr->len;
  		else
  			continue;
  
  		*matchoff = dptr - start;
  		if (hdr->search) {
  			dptr = ct_sdp_header_search(dptr, limit, hdr->search,
  						    hdr->slen);
  			if (!dptr)
  				return -1;
  			dptr += hdr->slen;
  		}
  
  		*matchlen = hdr->match_len(ct, dptr, limit, &shift);
  		if (!*matchlen)
  			return -1;
  		*matchoff = dptr - start + shift;
  		return 1;
  	}
  	return 0;
  }
  EXPORT_SYMBOL_GPL(ct_sip_get_sdp_header);

  static int ct_sip_parse_sdp_addr(const struct nf_conn *ct, const char *dptr,
  				 unsigned int dataoff, unsigned int datalen,
  				 enum sdp_header_types type,
  				 enum sdp_header_types term,
  				 unsigned int *matchoff, unsigned int *matchlen,
  				 union nf_inet_addr *addr)
  {
  	int ret;
  
  	ret = ct_sip_get_sdp_header(ct, dptr, dataoff, datalen, type, term,
  				    matchoff, matchlen);
  	if (ret <= 0)
  		return ret;

  	if (!sdp_parse_addr(ct, dptr + *matchoff, NULL, addr,
  			    dptr + *matchoff + *matchlen))

  		return -1;
  	return 1;
  }

  static int refresh_signalling_expectation(struct nf_conn *ct,
  					  union nf_inet_addr *addr,

  					  u8 proto, __be16 port,

  					  unsigned int expires)

  {
  	struct nf_conn_help *help = nfct_help(ct);
  	struct nf_conntrack_expect *exp;

  	struct hlist_node *next;

  	int found = 0;

  	spin_lock_bh(&nf_conntrack_expect_lock);

  	hlist_for_each_entry_safe(exp, next, &help->expectations, lnode) {

  		if (exp->class != SIP_EXPECT_SIGNALLING ||
  		    !nf_inet_addr_cmp(&exp->tuple.dst.u3, addr) ||

  		    exp->tuple.dst.protonum != proto ||

  		    exp->tuple.dst.u.udp.port != port)
  			continue;

  		if (mod_timer_pending(&exp->timeout, jiffies + expires * HZ)) {
  			exp->flags &= ~NF_CT_EXPECT_INACTIVE;
  			found = 1;
  			break;
  		}

  	}

  	spin_unlock_bh(&nf_conntrack_expect_lock);

  	return found;
  }
  
  static void flush_expectations(struct nf_conn *ct, bool media)
  {
  	struct nf_conn_help *help = nfct_help(ct);
  	struct nf_conntrack_expect *exp;

  	struct hlist_node *next;

  	spin_lock_bh(&nf_conntrack_expect_lock);

  	hlist_for_each_entry_safe(exp, next, &help->expectations, lnode) {

  		if ((exp->class != SIP_EXPECT_SIGNALLING) ^ media)
  			continue;

  		if (!nf_ct_remove_expect(exp))

  			continue;

  		if (!media)
  			break;

  	}

  	spin_unlock_bh(&nf_conntrack_expect_lock);

  }

  static int set_expected_rtp_rtcp(struct sk_buff *skb, unsigned int protoff,
  				 unsigned int dataoff,

  				 const char **dptr, unsigned int *datalen,

  				 union nf_inet_addr *daddr, __be16 port,

  				 enum sip_expectation_classes class,

  				 unsigned int mediaoff, unsigned int medialen)

  {

  	struct nf_conntrack_expect *exp, *rtp_exp, *rtcp_exp;

  	enum ip_conntrack_info ctinfo;
  	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

  	struct net *net = nf_ct_net(ct);

  	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);

  	union nf_inet_addr *saddr;
  	struct nf_conntrack_tuple tuple;

  	int direct_rtp = 0, skip_expect = 0, ret = NF_DROP;

  	u_int16_t base_port;
  	__be16 rtp_port, rtcp_port;

  	const struct nf_nat_sip_hooks *hooks;

  	saddr = NULL;
  	if (sip_direct_media) {
  		if (!nf_inet_addr_cmp(daddr, &ct->tuplehash[dir].tuple.src.u3))
  			return NF_ACCEPT;
  		saddr = &ct->tuplehash[!dir].tuple.src.u3;

  	} else if (sip_external_media) {
  		struct net_device *dev = skb_dst(skb)->dev;
  		struct net *net = dev_net(dev);

  		struct flowi fl;

  		struct dst_entry *dst = NULL;

  		memset(&fl, 0, sizeof(fl));

  		switch (nf_ct_l3num(ct)) {
  			case NFPROTO_IPV4:

  				fl.u.ip4.daddr = daddr->ip;
  				nf_ip_route(net, &dst, &fl, false);

  				break;

  			case NFPROTO_IPV6:

  				fl.u.ip6.daddr = daddr->in6;
  				nf_ip6_route(net, &dst, &fl, false);

  				break;

  		}
  
  		/* Don't predict any conntracks when media endpoint is reachable
  		 * through the same interface as the signalling peer.
  		 */

  		if (dst) {
  			bool external_media = (dst->dev == dev);
  
  			dst_release(dst);
  			if (external_media)
  				return NF_ACCEPT;
  		}

  	}
  
  	/* We need to check whether the registration exists before attempting
  	 * to register it since we can see the same media description multiple
  	 * times on different connections in case multiple endpoints receive
  	 * the same call.

  	 *
  	 * RTP optimization: if we find a matching media channel expectation
  	 * and both the expectation and this connection are SNATed, we assume
  	 * both sides can reach each other directly and use the final
  	 * destination address from the expectation. We still need to keep
  	 * the NATed expectations for media that might arrive from the
  	 * outside, and additionally need to expect the direct RTP stream
  	 * in case it passes through us even without NAT.

  	 */
  	memset(&tuple, 0, sizeof(tuple));
  	if (saddr)
  		tuple.src.u3 = *saddr;

  	tuple.src.l3num		= nf_ct_l3num(ct);

  	tuple.dst.protonum	= IPPROTO_UDP;
  	tuple.dst.u3		= *daddr;
  	tuple.dst.u.udp.port	= port;

  	do {

  		exp = __nf_ct_expect_find(net, nf_ct_zone(ct), &tuple);

  		if (!exp || exp->master == ct ||
  		    nfct_help(exp->master)->helper != nfct_help(ct)->helper ||
  		    exp->class != class)
  			break;

  #if IS_ENABLED(CONFIG_NF_NAT)

  		if (!direct_rtp &&
  		    (!nf_inet_addr_cmp(&exp->saved_addr, &exp->tuple.dst.u3) ||

  		     exp->saved_proto.udp.port != exp->tuple.dst.u.udp.port) &&
  		    ct->status & IPS_NAT_MASK) {

  			*daddr			= exp->saved_addr;
  			tuple.dst.u3		= exp->saved_addr;

  			tuple.dst.u.udp.port	= exp->saved_proto.udp.port;
  			direct_rtp = 1;
  		} else

  #endif

  			skip_expect = 1;
  	} while (!skip_expect);

  	base_port = ntohs(tuple.dst.u.udp.port) & ~1;
  	rtp_port = htons(base_port);
  	rtcp_port = htons(base_port + 1);

  	if (direct_rtp) {

  		hooks = rcu_dereference(nf_nat_sip_hooks);
  		if (hooks &&
  		    !hooks->sdp_port(skb, protoff, dataoff, dptr, datalen,

  				     mediaoff, medialen, ntohs(rtp_port)))
  			goto err1;
  	}

  	if (skip_expect)

  		return NF_ACCEPT;

  	rtp_exp = nf_ct_expect_alloc(ct);
  	if (rtp_exp == NULL)
  		goto err1;

  	nf_ct_expect_init(rtp_exp, class, nf_ct_l3num(ct), saddr, daddr,

  			  IPPROTO_UDP, NULL, &rtp_port);
  
  	rtcp_exp = nf_ct_expect_alloc(ct);
  	if (rtcp_exp == NULL)
  		goto err2;

  	nf_ct_expect_init(rtcp_exp, class, nf_ct_l3num(ct), saddr, daddr,

  			  IPPROTO_UDP, NULL, &rtcp_port);

  	hooks = rcu_dereference(nf_nat_sip_hooks);
  	if (hooks && ct->status & IPS_NAT_MASK && !direct_rtp)
  		ret = hooks->sdp_media(skb, protoff, dataoff, dptr,
  				       datalen, rtp_exp, rtcp_exp,

  				       mediaoff, medialen, daddr);

  	else {

  		/* -EALREADY handling works around end-points that send
  		 * SDP messages with identical port but different media type,
  		 * we pretend expectation was set up.

  		 * It also works in the case that SDP messages are sent with
  		 * identical expect tuples but for different master conntracks.

  		 */

  		int errp = nf_ct_expect_related(rtp_exp,
  						NF_CT_EXP_F_SKIP_MASTER);

  
  		if (errp == 0 || errp == -EALREADY) {

  			int errcp = nf_ct_expect_related(rtcp_exp,
  						NF_CT_EXP_F_SKIP_MASTER);

  
  			if (errcp == 0 || errcp == -EALREADY)

  				ret = NF_ACCEPT;

  			else if (errp == 0)
  				nf_ct_unexpect_related(rtp_exp);

  		}

  	}

  	nf_ct_expect_put(rtcp_exp);
  err2:
  	nf_ct_expect_put(rtp_exp);
  err1:

  	return ret;
  }

  static const struct sdp_media_type sdp_media_types[] = {
  	SDP_MEDIA_TYPE("audio ", SIP_EXPECT_AUDIO),
  	SDP_MEDIA_TYPE("video ", SIP_EXPECT_VIDEO),

  	SDP_MEDIA_TYPE("image ", SIP_EXPECT_IMAGE),

  };
  
  static const struct sdp_media_type *sdp_media_type(const char *dptr,
  						   unsigned int matchoff,
  						   unsigned int matchlen)
  {
  	const struct sdp_media_type *t;
  	unsigned int i;
  
  	for (i = 0; i < ARRAY_SIZE(sdp_media_types); i++) {
  		t = &sdp_media_types[i];
  		if (matchlen < t->len ||
  		    strncmp(dptr + matchoff, t->name, t->len))
  			continue;
  		return t;
  	}
  	return NULL;
  }

  static int process_sdp(struct sk_buff *skb, unsigned int protoff,
  		       unsigned int dataoff,

  		       const char **dptr, unsigned int *datalen,
  		       unsigned int cseq)

  {
  	enum ip_conntrack_info ctinfo;
  	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

  	unsigned int matchoff, matchlen;

  	unsigned int mediaoff, medialen;
  	unsigned int sdpoff;
  	unsigned int caddr_len, maddr_len;

  	unsigned int i;

  	union nf_inet_addr caddr, maddr, rtp_addr;

  	const struct nf_nat_sip_hooks *hooks;

  	unsigned int port;

  	const struct sdp_media_type *t;
  	int ret = NF_ACCEPT;

  	hooks = rcu_dereference(nf_nat_sip_hooks);

  	/* Find beginning of session description */

  	if (ct_sip_get_sdp_header(ct, *dptr, 0, *datalen,

  				  SDP_HDR_VERSION, SDP_HDR_UNSPEC,

  				  &matchoff, &matchlen) <= 0)
  		return NF_ACCEPT;

  	sdpoff = matchoff;
  
  	/* The connection information is contained in the session description
  	 * and/or once per media description. The first media description marks
  	 * the end of the session description. */
  	caddr_len = 0;
  	if (ct_sip_parse_sdp_addr(ct, *dptr, sdpoff, *datalen,

  				  SDP_HDR_CONNECTION, SDP_HDR_MEDIA,

  				  &matchoff, &matchlen, &caddr) > 0)
  		caddr_len = matchlen;

  	mediaoff = sdpoff;
  	for (i = 0; i < ARRAY_SIZE(sdp_media_types); ) {
  		if (ct_sip_get_sdp_header(ct, *dptr, mediaoff, *datalen,
  					  SDP_HDR_MEDIA, SDP_HDR_UNSPEC,
  					  &mediaoff, &medialen) <= 0)
  			break;

  		/* Get media type and port number. A media port value of zero
  		 * indicates an inactive stream. */
  		t = sdp_media_type(*dptr, mediaoff, medialen);
  		if (!t) {
  			mediaoff += medialen;
  			continue;
  		}
  		mediaoff += t->len;
  		medialen -= t->len;

  		port = simple_strtoul(*dptr + mediaoff, NULL, 10);
  		if (port == 0)
  			continue;

  		if (port < 1024 || port > 65535) {
  			nf_ct_helper_log(skb, ct, "wrong port %u", port);

  			return NF_DROP;

  		}

  		/* The media description overrides the session description. */
  		maddr_len = 0;
  		if (ct_sip_parse_sdp_addr(ct, *dptr, mediaoff, *datalen,

  					  SDP_HDR_CONNECTION, SDP_HDR_MEDIA,

  					  &matchoff, &matchlen, &maddr) > 0) {
  			maddr_len = matchlen;
  			memcpy(&rtp_addr, &maddr, sizeof(rtp_addr));
  		} else if (caddr_len)
  			memcpy(&rtp_addr, &caddr, sizeof(rtp_addr));

  		else {
  			nf_ct_helper_log(skb, ct, "cannot parse SDP message");

  			return NF_DROP;

  		}

  		ret = set_expected_rtp_rtcp(skb, protoff, dataoff,
  					    dptr, datalen,

  					    &rtp_addr, htons(port), t->class,
  					    mediaoff, medialen);

  		if (ret != NF_ACCEPT) {
  			nf_ct_helper_log(skb, ct,
  					 "cannot add expectation for voice");

  			return ret;

  		}

  		/* Update media connection address if present */

  		if (maddr_len && hooks && ct->status & IPS_NAT_MASK) {
  			ret = hooks->sdp_addr(skb, protoff, dataoff,

  					      dptr, datalen, mediaoff,

  					      SDP_HDR_CONNECTION,
  					      SDP_HDR_MEDIA,

  					      &rtp_addr);

  			if (ret != NF_ACCEPT) {
  				nf_ct_helper_log(skb, ct, "cannot mangle SDP");

  				return ret;

  			}

  		}

  		i++;

  	}
  
  	/* Update session connection and owner addresses */

  	hooks = rcu_dereference(nf_nat_sip_hooks);
  	if (hooks && ct->status & IPS_NAT_MASK)
  		ret = hooks->sdp_session(skb, protoff, dataoff,
  					 dptr, datalen, sdpoff,
  					 &rtp_addr);

  
  	return ret;

  }

  static int process_invite_response(struct sk_buff *skb, unsigned int protoff,
  				   unsigned int dataoff,

  				   const char **dptr, unsigned int *datalen,
  				   unsigned int cseq, unsigned int code)
  {

  	enum ip_conntrack_info ctinfo;
  	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

  	struct nf_ct_sip_master *ct_sip_info = nfct_help_data(ct);

  	if ((code >= 100 && code <= 199) ||
  	    (code >= 200 && code <= 299))

  		return process_sdp(skb, protoff, dataoff, dptr, datalen, cseq);

  	else if (ct_sip_info->invite_cseq == cseq)

  		flush_expectations(ct, true);

  	return NF_ACCEPT;

  }

  static int process_update_response(struct sk_buff *skb, unsigned int protoff,
  				   unsigned int dataoff,

  				   const char **dptr, unsigned int *datalen,
  				   unsigned int cseq, unsigned int code)
  {

  	enum ip_conntrack_info ctinfo;
  	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

  	struct nf_ct_sip_master *ct_sip_info = nfct_help_data(ct);

  	if ((code >= 100 && code <= 199) ||
  	    (code >= 200 && code <= 299))

  		return process_sdp(skb, protoff, dataoff, dptr, datalen, cseq);

  	else if (ct_sip_info->invite_cseq == cseq)

  		flush_expectations(ct, true);

  	return NF_ACCEPT;

  }

  static int process_prack_response(struct sk_buff *skb, unsigned int protoff,
  				  unsigned int dataoff,

  				  const char **dptr, unsigned int *datalen,
  				  unsigned int cseq, unsigned int code)
  {

  	enum ip_conntrack_info ctinfo;
  	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

  	struct nf_ct_sip_master *ct_sip_info = nfct_help_data(ct);

  	if ((code >= 100 && code <= 199) ||
  	    (code >= 200 && code <= 299))

  		return process_sdp(skb, protoff, dataoff, dptr, datalen, cseq);

  	else if (ct_sip_info->invite_cseq == cseq)

  		flush_expectations(ct, true);

  	return NF_ACCEPT;

  }

  static int process_invite_request(struct sk_buff *skb, unsigned int protoff,
  				  unsigned int dataoff,

  				  const char **dptr, unsigned int *datalen,
  				  unsigned int cseq)
  {
  	enum ip_conntrack_info ctinfo;
  	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

  	struct nf_ct_sip_master *ct_sip_info = nfct_help_data(ct);

  	unsigned int ret;
  
  	flush_expectations(ct, true);

  	ret = process_sdp(skb, protoff, dataoff, dptr, datalen, cseq);

  	if (ret == NF_ACCEPT)

  		ct_sip_info->invite_cseq = cseq;

  	return ret;
  }

  static int process_bye_request(struct sk_buff *skb, unsigned int protoff,
  			       unsigned int dataoff,

  			       const char **dptr, unsigned int *datalen,
  			       unsigned int cseq)
  {
  	enum ip_conntrack_info ctinfo;
  	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

  	flush_expectations(ct, true);
  	return NF_ACCEPT;
  }
  
  /* Parse a REGISTER request and create a permanent expectation for incoming
   * signalling connections. The expectation is marked inactive and is activated
   * when receiving a response indicating success from the registrar.
   */

  static int process_register_request(struct sk_buff *skb, unsigned int protoff,
  				    unsigned int dataoff,

  				    const char **dptr, unsigned int *datalen,
  				    unsigned int cseq)
  {
  	enum ip_conntrack_info ctinfo;
  	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

  	struct nf_ct_sip_master *ct_sip_info = nfct_help_data(ct);

  	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);

  	unsigned int matchoff, matchlen;
  	struct nf_conntrack_expect *exp;
  	union nf_inet_addr *saddr, daddr;

  	const struct nf_nat_sip_hooks *hooks;

  	__be16 port;

  	u8 proto;

  	unsigned int expires = 0;
  	int ret;

  
  	/* Expected connections can not register again. */
  	if (ct->status & IPS_EXPECTED)
  		return NF_ACCEPT;
  
  	/* We must check the expiration time: a value of zero signals the
  	 * registrar to release the binding. We'll remove our expectation
  	 * when receiving the new bindings in the response, but we don't
  	 * want to create new ones.
  	 *
  	 * The expiration time may be contained in Expires: header, the
  	 * Contact: header parameters or the URI parameters.
  	 */
  	if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_EXPIRES,
  			      &matchoff, &matchlen) > 0)
  		expires = simple_strtoul(*dptr + matchoff, NULL, 10);
  
  	ret = ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen,
  				      SIP_HDR_CONTACT, NULL,
  				      &matchoff, &matchlen, &daddr, &port);

  	if (ret < 0) {
  		nf_ct_helper_log(skb, ct, "cannot parse contact");

  		return NF_DROP;

  	} else if (ret == 0)

  		return NF_ACCEPT;
  
  	/* We don't support third-party registrations */
  	if (!nf_inet_addr_cmp(&ct->tuplehash[dir].tuple.src.u3, &daddr))
  		return NF_ACCEPT;

  	if (ct_sip_parse_transport(ct, *dptr, matchoff + matchlen, *datalen,
  				   &proto) == 0)
  		return NF_ACCEPT;

  	if (ct_sip_parse_numerical_param(ct, *dptr,
  					 matchoff + matchlen, *datalen,

  					 "expires=", NULL, NULL, &expires) < 0) {
  		nf_ct_helper_log(skb, ct, "cannot parse expires");

  		return NF_DROP;

  	}

  
  	if (expires == 0) {
  		ret = NF_ACCEPT;
  		goto store_cseq;
  	}
  
  	exp = nf_ct_expect_alloc(ct);

  	if (!exp) {
  		nf_ct_helper_log(skb, ct, "cannot alloc expectation");

  		return NF_DROP;

  	}

  
  	saddr = NULL;
  	if (sip_direct_signalling)
  		saddr = &ct->tuplehash[!dir].tuple.src.u3;

  	nf_ct_expect_init(exp, SIP_EXPECT_SIGNALLING, nf_ct_l3num(ct),

  			  saddr, &daddr, proto, NULL, &port);

  	exp->timeout.expires = sip_timeout * HZ;
  	exp->helper = nfct_help(ct)->helper;
  	exp->flags = NF_CT_EXPECT_PERMANENT | NF_CT_EXPECT_INACTIVE;

  	hooks = rcu_dereference(nf_nat_sip_hooks);
  	if (hooks && ct->status & IPS_NAT_MASK)
  		ret = hooks->expect(skb, protoff, dataoff, dptr, datalen,
  				    exp, matchoff, matchlen);

  	else {

  		if (nf_ct_expect_related(exp, 0) != 0) {

  			nf_ct_helper_log(skb, ct, "cannot add expectation");

  			ret = NF_DROP;

  		} else

  			ret = NF_ACCEPT;
  	}
  	nf_ct_expect_put(exp);
  
  store_cseq:
  	if (ret == NF_ACCEPT)

  		ct_sip_info->register_cseq = cseq;

  	return ret;
  }

  static int process_register_response(struct sk_buff *skb, unsigned int protoff,
  				     unsigned int dataoff,

  				     const char **dptr, unsigned int *datalen,
  				     unsigned int cseq, unsigned int code)
  {
  	enum ip_conntrack_info ctinfo;
  	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

  	struct nf_ct_sip_master *ct_sip_info = nfct_help_data(ct);

  	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
  	union nf_inet_addr addr;
  	__be16 port;

  	u8 proto;

  	unsigned int matchoff, matchlen, coff = 0;

  	unsigned int expires = 0;
  	int in_contact = 0, ret;
  
  	/* According to RFC 3261, "UAs MUST NOT send a new registration until
  	 * they have received a final response from the registrar for the
  	 * previous one or the previous REGISTER request has timed out".
  	 *
  	 * However, some servers fail to detect retransmissions and send late
  	 * responses, so we store the sequence number of the last valid
  	 * request and compare it here.
  	 */

  	if (ct_sip_info->register_cseq != cseq)

  		return NF_ACCEPT;
  
  	if (code >= 100 && code <= 199)
  		return NF_ACCEPT;
  	if (code < 200 || code > 299)
  		goto flush;
  
  	if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_EXPIRES,
  			      &matchoff, &matchlen) > 0)
  		expires = simple_strtoul(*dptr + matchoff, NULL, 10);
  
  	while (1) {
  		unsigned int c_expires = expires;

  		ret = ct_sip_parse_header_uri(ct, *dptr, &coff, *datalen,

  					      SIP_HDR_CONTACT, &in_contact,
  					      &matchoff, &matchlen,
  					      &addr, &port);

  		if (ret < 0) {
  			nf_ct_helper_log(skb, ct, "cannot parse contact");

  			return NF_DROP;

  		} else if (ret == 0)

  			break;
  
  		/* We don't support third-party registrations */
  		if (!nf_inet_addr_cmp(&ct->tuplehash[dir].tuple.dst.u3, &addr))
  			continue;

  		if (ct_sip_parse_transport(ct, *dptr, matchoff + matchlen,
  					   *datalen, &proto) == 0)
  			continue;

  		ret = ct_sip_parse_numerical_param(ct, *dptr,
  						   matchoff + matchlen,
  						   *datalen, "expires=",
  						   NULL, NULL, &c_expires);

  		if (ret < 0) {
  			nf_ct_helper_log(skb, ct, "cannot parse expires");

  			return NF_DROP;

  		}

  		if (c_expires == 0)
  			break;

  		if (refresh_signalling_expectation(ct, &addr, proto, port,
  						   c_expires))

  			return NF_ACCEPT;
  	}
  
  flush:
  	flush_expectations(ct, false);

  	return NF_ACCEPT;
  }

  static const struct sip_handler sip_handlers[] = {

  	SIP_HANDLER("INVITE", process_invite_request, process_invite_response),

  	SIP_HANDLER("UPDATE", process_sdp, process_update_response),

  	SIP_HANDLER("ACK", process_sdp, NULL),
  	SIP_HANDLER("PRACK", process_sdp, process_prack_response),

  	SIP_HANDLER("BYE", process_bye_request, NULL),

  	SIP_HANDLER("REGISTER", process_register_request, process_register_response),

  };

  static int process_sip_response(struct sk_buff *skb, unsigned int protoff,
  				unsigned int dataoff,

  				const char **dptr, unsigned int *datalen)
  {

  	enum ip_conntrack_info ctinfo;
  	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

  	unsigned int matchoff, matchlen, matchend;
  	unsigned int code, cseq, i;

  
  	if (*datalen < strlen("SIP/2.0 200"))
  		return NF_ACCEPT;
  	code = simple_strtoul(*dptr + strlen("SIP/2.0 "), NULL, 10);

  	if (!code) {
  		nf_ct_helper_log(skb, ct, "cannot get code");

  		return NF_DROP;

  	}

  
  	if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CSEQ,

  			      &matchoff, &matchlen) <= 0) {
  		nf_ct_helper_log(skb, ct, "cannot parse cseq");

  		return NF_DROP;

  	}

  	cseq = simple_strtoul(*dptr + matchoff, NULL, 10);

  	if (!cseq && *(*dptr + matchoff) != '0') {

  		nf_ct_helper_log(skb, ct, "cannot get cseq");

  		return NF_DROP;

  	}

  	matchend = matchoff + matchlen + 1;

  
  	for (i = 0; i < ARRAY_SIZE(sip_handlers); i++) {

  		const struct sip_handler *handler;

  		handler = &sip_handlers[i];
  		if (handler->response == NULL)
  			continue;

  		if (*datalen < matchend + handler->len ||

  		    strncasecmp(*dptr + matchend, handler->method, handler->len))

  			continue;

  		return handler->response(skb, protoff, dataoff, dptr, datalen,

  					 cseq, code);

  	}
  	return NF_ACCEPT;
  }

  static int process_sip_request(struct sk_buff *skb, unsigned int protoff,
  			       unsigned int dataoff,

  			       const char **dptr, unsigned int *datalen)
  {

  	enum ip_conntrack_info ctinfo;
  	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);

  	struct nf_ct_sip_master *ct_sip_info = nfct_help_data(ct);
  	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);

  	unsigned int matchoff, matchlen;
  	unsigned int cseq, i;

  	union nf_inet_addr addr;
  	__be16 port;
  
  	/* Many Cisco IP phones use a high source port for SIP requests, but
  	 * listen for the response on port 5060.  If we are the local
  	 * router for one of these phones, save the port number from the
  	 * Via: header so that nf_nat_sip can redirect the responses to
  	 * the correct port.
  	 */
  	if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen,
  				    SIP_HDR_VIA_UDP, NULL, &matchoff,
  				    &matchlen, &addr, &port) > 0 &&
  	    port != ct->tuplehash[dir].tuple.src.u.udp.port &&
  	    nf_inet_addr_cmp(&addr, &ct->tuplehash[dir].tuple.src.u3))
  		ct_sip_info->forced_dport = port;

  
  	for (i = 0; i < ARRAY_SIZE(sip_handlers); i++) {

  		const struct sip_handler *handler;

  		handler = &sip_handlers[i];
  		if (handler->request == NULL)
  			continue;

  		if (*datalen < handler->len + 2 ||

  		    strncasecmp(*dptr, handler->method, handler->len))

  			continue;

  		if ((*dptr)[handler->len] != ' ' ||
  		    !isalpha((*dptr)[handler->len+1]))
  			continue;

  
  		if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CSEQ,

  				      &matchoff, &matchlen) <= 0) {
  			nf_ct_helper_log(skb, ct, "cannot parse cseq");

  			return NF_DROP;

  		}

  		cseq = simple_strtoul(*dptr + matchoff, NULL, 10);

  		if (!cseq && *(*dptr + matchoff) != '0') {

  			nf_ct_helper_log(skb, ct, "cannot get cseq");

  			return NF_DROP;

  		}

  		return handler->request(skb, protoff, dataoff, dptr, datalen,
  					cseq);

  	}
  	return NF_ACCEPT;
  }

  static int process_sip_msg(struct sk_buff *skb, struct nf_conn *ct,

  			   unsigned int protoff, unsigned int dataoff,
  			   const char **dptr, unsigned int *datalen)

  {

  	const struct nf_nat_sip_hooks *hooks;

  	int ret;

  	if (strncasecmp(*dptr, "SIP/2.0 ", strlen("SIP/2.0 ")) != 0)

  		ret = process_sip_request(skb, protoff, dataoff, dptr, datalen);

  	else

  		ret = process_sip_response(skb, protoff, dataoff, dptr, datalen);

  	if (ret == NF_ACCEPT && ct->status & IPS_NAT_MASK) {

  		hooks = rcu_dereference(nf_nat_sip_hooks);
  		if (hooks && !hooks->msg(skb, protoff, dataoff,
  					 dptr, datalen)) {

  			nf_ct_helper_log(skb, ct, "cannot NAT SIP message");

  			ret = NF_DROP;

  		}

  	}
  
  	return ret;
  }
  
  static int sip_help_tcp(struct sk_buff *skb, unsigned int protoff,
  			struct nf_conn *ct, enum ip_conntrack_info ctinfo)

  {

  	struct tcphdr *th, _tcph;

  	unsigned int dataoff, datalen;

  	unsigned int matchoff, matchlen, clen;
  	unsigned int msglen, origlen;
  	const char *dptr, *end;
  	s16 diff, tdiff = 0;

  	int ret = NF_ACCEPT;

  	bool term;

  
  	if (ctinfo != IP_CT_ESTABLISHED &&

  	    ctinfo != IP_CT_ESTABLISHED_REPLY)

  		return NF_ACCEPT;

  
  	/* No Data ? */

  	th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
  	if (th == NULL)
  		return NF_ACCEPT;
  	dataoff = protoff + th->doff * 4;

  	if (dataoff >= skb->len)

  		return NF_ACCEPT;

  	nf_ct_refresh(ct, skb, sip_timeout * HZ);

  	if (unlikely(skb_linearize(skb)))
  		return NF_DROP;

  	dptr = skb->data + dataoff;

  	datalen = skb->len - dataoff;

  	if (datalen < strlen("SIP/2.0 200"))

  		return NF_ACCEPT;

  	while (1) {
  		if (ct_sip_get_header(ct, dptr, 0, datalen,
  				      SIP_HDR_CONTENT_LENGTH,
  				      &matchoff, &matchlen) <= 0)
  			break;

  		clen = simple_strtoul(dptr + matchoff, (char **)&end, 10);
  		if (dptr + matchoff == end)
  			break;

  		term = false;
  		for (; end + strlen("\r
  \r
  ") <= dptr + datalen; end++) {
  			if (end[0] == '\r' && end[1] == '
  ' &&
  			    end[2] == '\r' && end[3] == '
  ') {
  				term = true;
  				break;
  			}
  		}
  		if (!term)

  			break;
  		end += strlen("\r
  \r
  ") + clen;
  
  		msglen = origlen = end - dptr;

  		if (msglen > datalen)
  			return NF_ACCEPT;

  		ret = process_sip_msg(skb, ct, protoff, dataoff,
  				      &dptr, &msglen);

  		/* process_sip_* functions report why this packet is dropped */

  		if (ret != NF_ACCEPT)
  			break;
  		diff     = msglen - origlen;
  		tdiff   += diff;
  
  		dataoff += msglen;
  		dptr    += msglen;
  		datalen  = datalen + diff - msglen;

  	}

  	if (ret == NF_ACCEPT && ct->status & IPS_NAT_MASK) {

  		const struct nf_nat_sip_hooks *hooks;
  
  		hooks = rcu_dereference(nf_nat_sip_hooks);
  		if (hooks)
  			hooks->seq_adjust(skb, protoff, tdiff);

  	}

  	return ret;

  }

  static int sip_help_udp(struct sk_buff *skb, unsigned int protoff,
  			struct nf_conn *ct, enum ip_conntrack_info ctinfo)
  {
  	unsigned int dataoff, datalen;
  	const char *dptr;
  
  	/* No Data ? */
  	dataoff = protoff + sizeof(struct udphdr);
  	if (dataoff >= skb->len)
  		return NF_ACCEPT;
  
  	nf_ct_refresh(ct, skb, sip_timeout * HZ);

  	if (unlikely(skb_linearize(skb)))
  		return NF_DROP;

  
  	dptr = skb->data + dataoff;
  	datalen = skb->len - dataoff;
  	if (datalen < strlen("SIP/2.0 200"))
  		return NF_ACCEPT;

  	return process_sip_msg(skb, ct, protoff, dataoff, &dptr, &datalen);

  }

  static struct nf_conntrack_helper sip[MAX_PORTS * 4] __read_mostly;

  static const struct nf_conntrack_expect_policy sip_exp_policy[SIP_EXPECT_MAX + 1] = {
  	[SIP_EXPECT_SIGNALLING] = {

  		.name		= "signalling",

  		.max_expected	= 1,
  		.timeout	= 3 * 60,
  	},
  	[SIP_EXPECT_AUDIO] = {

  		.name		= "audio",

  		.max_expected	= 2 * IP_CT_DIR_MAX,

  		.timeout	= 3 * 60,
  	},

  	[SIP_EXPECT_VIDEO] = {

  		.name		= "video",

  		.max_expected	= 2 * IP_CT_DIR_MAX,
  		.timeout	= 3 * 60,
  	},

  	[SIP_EXPECT_IMAGE] = {
  		.name		= "image",
  		.max_expected	= IP_CT_DIR_MAX,
  		.timeout	= 3 * 60,
  	},

  };

  static void __exit nf_conntrack_sip_fini(void)

  {

  	nf_conntrack_helpers_unregister(sip, ports_c * 4);

  }
  
  static int __init nf_conntrack_sip_init(void)
  {

  	int i, ret;

  	NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_sip_master));

  	if (ports_c == 0)
  		ports[ports_c++] = SIP_PORT;
  
  	for (i = 0; i < ports_c; i++) {

  		nf_ct_helper_init(&sip[4 * i], AF_INET, IPPROTO_UDP,
  				  HELPER_NAME, SIP_PORT, ports[i], i,
  				  sip_exp_policy, SIP_EXPECT_MAX, sip_help_udp,

  				  NULL, THIS_MODULE);

  		nf_ct_helper_init(&sip[4 * i + 1], AF_INET, IPPROTO_TCP,
  				  HELPER_NAME, SIP_PORT, ports[i], i,
  				  sip_exp_policy, SIP_EXPECT_MAX, sip_help_tcp,

  				  NULL, THIS_MODULE);

  		nf_ct_helper_init(&sip[4 * i + 2], AF_INET6, IPPROTO_UDP,
  				  HELPER_NAME, SIP_PORT, ports[i], i,
  				  sip_exp_policy, SIP_EXPECT_MAX, sip_help_udp,

  				  NULL, THIS_MODULE);

  		nf_ct_helper_init(&sip[4 * i + 3], AF_INET6, IPPROTO_TCP,
  				  HELPER_NAME, SIP_PORT, ports[i], i,
  				  sip_exp_policy, SIP_EXPECT_MAX, sip_help_tcp,

  				  NULL, THIS_MODULE);
  	}

  	ret = nf_conntrack_helpers_register(sip, ports_c * 4);
  	if (ret < 0) {
  		pr_err("failed to register helpers
  ");
  		return ret;

  	}
  	return 0;
  }
  
  module_init(nf_conntrack_sip_init);
  module_exit(nf_conntrack_sip_fini);