/* 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>
 *
 * 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 <linux/netfilter.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 <linux/netfilter/nf_conntrack_sip.h>

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("sip");

#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)");

unsigned int (*nf_nat_sip_hook)(struct sk_buff *skb,
                                const char **dptr,
                                unsigned int *datalen) __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_sip_hook);

unsigned int (*nf_nat_sip_expect_hook)(struct sk_buff *skb,
                                       const char **dptr,
                                       unsigned int *datalen,
                                       struct nf_conntrack_expect *exp,
                                       unsigned int matchoff,
                                       unsigned int matchlen) __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_sip_expect_hook);

unsigned int (*nf_nat_sdp_addr_hook)(struct sk_buff *skb,
                                     const char **dptr,
                                     unsigned int dataoff,
                                     unsigned int *datalen,
                                     enum sdp_header_types type,
                                     enum sdp_header_types term,
                                     const union nf_inet_addr *addr)
                                     __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_sdp_addr_hook);

unsigned int (*nf_nat_sdp_port_hook)(struct sk_buff *skb,
                                     const char **dptr,
                                     unsigned int *datalen,
                                     unsigned int matchoff,
                                     unsigned int matchlen,
                                     u_int16_t port) __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_sdp_port_hook);

unsigned int (*nf_nat_sdp_session_hook)(struct sk_buff *skb,
                                        const char **dptr,
                                        unsigned int dataoff,
                                        unsigned int *datalen,
                                        const union nf_inet_addr *addr)
                                        __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_sdp_session_hook);

unsigned int (*nf_nat_sdp_media_hook)(struct sk_buff *skb,
                                      const char **dptr,
                                      unsigned int *datalen,
                                      struct nf_conntrack_expect *rtp_exp,
                                      struct nf_conntrack_expect *rtcp_exp,
                                      unsigned int mediaoff,
                                      unsigned int medialen,
                                      union nf_inet_addr *rtp_addr)
                                      __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_sdp_media_hook);

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;
}

/* 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 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 = 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);
                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(const struct nf_conn *ct, const char *dptr,
                      const char *limit, int *shift)
{
        union nf_inet_addr addr;
        const char *aux = dptr;

        if (!parse_addr(ct, dptr, &dptr, &addr, limit)) {
                pr_debug("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(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 != '\n') {
                (*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 */
        limit -= strlen("sip:");
        for (; dptr < limit; dptr++) {
                if (*dptr == '\r' || *dptr == '\n')
                        return -1;
                if (strnicmp(dptr, "sip:", strlen("sip:")) == 0)
                        break;
        }
        if (!skp_epaddr_len(ct, dptr, limit, &shift))
                return 0;
        dptr += shift;

        if (!parse_addr(ct, dptr, &end, addr, limit))
                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 seperated 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]                   = SIP_HDR("Via", "v", "UDP ", epaddr_len),
        [SIP_HDR_EXPIRES]               = SIP_HDR("Expires", NULL, NULL, digits_len),
        [SIP_HDR_CONTENT_LENGTH]        = SIP_HDR("Content-Length", "l", NULL, digits_len),
};

static const char *sip_follow_continuation(const char *dptr, const char *limit)
{
        /* Walk past newline */
        if (++dptr >= limit)
                return NULL;

        /* Skip '\n' in CR LF */
        if (*(dptr - 1) == '\r' && *dptr == '\n') {
                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 == ' ')
                        continue;
                if (*dptr != '\r' && *dptr != '\n')
                        break;
                dptr = sip_follow_continuation(dptr, limit);
                if (dptr == NULL)
                        return NULL;
        }
        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 == '\n') {
                        dptr = sip_follow_continuation(dptr, limit);
                        if (dptr == NULL)
                                break;
                        continue;
                }

                if (strnicmp(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 != '\n')
                        continue;
                if (++dptr >= limit)
                        break;
                if (*(dptr - 1) == '\r' && *dptr == '\n') {
                        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 &&
                    strnicmp(dptr, hdr->name, hdr->len) == 0)
                        dptr += hdr->len;
                else if (hdr->cname && limit - dptr >= hdr->clen + 1 &&
                         strnicmp(dptr, hdr->cname, hdr->clen) == 0 &&
                         !isalpha(*(dptr + hdr->clen + 1)))
                        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 seperated 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 (!parse_addr(ct, dptr + *matchoff, &c, addr, limit))
                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);

/* 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)
{
        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 (!parse_addr(ct, start, &end, addr, limit))
                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);

/* 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[] = {
        [SDP_HDR_VERSION]               = SDP_HDR("v=", NULL, digits_len),
        [SDP_HDR_OWNER_IP4]             = SDP_HDR("o=", "IN IP4 ", epaddr_len),
        [SDP_HDR_CONNECTION_IP4]        = SDP_HDR("c=", "IN IP4 ", epaddr_len),
        [SDP_HDR_OWNER_IP6]             = SDP_HDR("o=", "IN IP6 ", epaddr_len),
        [SDP_HDR_CONNECTION_IP6]        = SDP_HDR("c=", "IN IP6 ", epaddr_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 == '\n')
                        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 occurence 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 *hdr = &ct_sdp_hdrs[type];
        const struct sip_header *thdr = &ct_sdp_hdrs[term];
        const char *start = dptr, *limit = dptr + datalen;
        int shift = 0;

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

                if (term != SDP_HDR_UNSPEC &&
                    limit - dptr >= thdr->len &&
                    strnicmp(dptr, thdr->name, thdr->len) == 0)
                        break;
                else if (limit - dptr >= hdr->len &&
                         strnicmp(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 (!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,
                                          __be16 port,
                                          unsigned int expires)
{
        struct nf_conn_help *help = nfct_help(ct);
        struct nf_conntrack_expect *exp;
        struct hlist_node *n, *next;
        int found = 0;

        spin_lock_bh(&nf_conntrack_lock);
        hlist_for_each_entry_safe(exp, n, next, &help->expectations, lnode) {
                if (exp->class != SIP_EXPECT_SIGNALLING ||
                    !nf_inet_addr_cmp(&exp->tuple.dst.u3, addr) ||
                    exp->tuple.dst.u.udp.port != port)
                        continue;
                if (!del_timer(&exp->timeout))
                        continue;
                exp->flags &= ~NF_CT_EXPECT_INACTIVE;
                exp->timeout.expires = jiffies + expires * HZ;
                add_timer(&exp->timeout);
                found = 1;
                break;
        }
        spin_unlock_bh(&nf_conntrack_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 *n, *next;

        spin_lock_bh(&nf_conntrack_lock);
        hlist_for_each_entry_safe(exp, n, next, &help->expectations, lnode) {
                if ((exp->class != SIP_EXPECT_SIGNALLING) ^ media)
                        continue;
                if (!del_timer(&exp->timeout))
                        continue;
                nf_ct_unlink_expect(exp);
                nf_ct_expect_put(exp);
                if (!media)
                        break;
        }
        spin_unlock_bh(&nf_conntrack_lock);
}

static int set_expected_rtp_rtcp(struct sk_buff *skb,
                                 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;
        typeof(nf_nat_sdp_port_hook) nf_nat_sdp_port;
        typeof(nf_nat_sdp_media_hook) nf_nat_sdp_media;

        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;
        }

        /* 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;

        rcu_read_lock();
        do {
                exp = __nf_ct_expect_find(net, &tuple);

                if (!exp || exp->master == ct ||
                    nfct_help(exp->master)->helper != nfct_help(ct)->helper ||
                    exp->class != class)
                        break;
#ifdef CONFIG_NF_NAT_NEEDED
                if (exp->tuple.src.l3num == AF_INET && !direct_rtp &&
                    (exp->saved_ip != exp->tuple.dst.u3.ip ||
                     exp->saved_proto.udp.port != exp->tuple.dst.u.udp.port) &&
                    ct->status & IPS_NAT_MASK) {
                        daddr->ip               = exp->saved_ip;
                        tuple.dst.u3.ip         = exp->saved_ip;
                        tuple.dst.u.udp.port    = exp->saved_proto.udp.port;
                        direct_rtp = 1;
                } else
#endif
                        skip_expect = 1;
        } while (!skip_expect);
        rcu_read_unlock();

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

        if (direct_rtp) {
                nf_nat_sdp_port = rcu_dereference(nf_nat_sdp_port_hook);
                if (nf_nat_sdp_port &&
                    !nf_nat_sdp_port(skb, 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);

        nf_nat_sdp_media = rcu_dereference(nf_nat_sdp_media_hook);
        if (nf_nat_sdp_media && ct->status & IPS_NAT_MASK && !direct_rtp)
                ret = nf_nat_sdp_media(skb, dptr, datalen, rtp_exp, rtcp_exp,
                                       mediaoff, medialen, daddr);
        else {
                if (nf_ct_expect_related(rtp_exp) == 0) {
                        if (nf_ct_expect_related(rtcp_exp) != 0)
                                nf_ct_unexpect_related(rtp_exp);
                        else
                                ret = NF_ACCEPT;
                }
        }
        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),
};

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,
                       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_conn_help *help = nfct_help(ct);
        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;
        unsigned int port;
        enum sdp_header_types c_hdr;
        const struct sdp_media_type *t;
        int ret = NF_ACCEPT;
        typeof(nf_nat_sdp_addr_hook) nf_nat_sdp_addr;
        typeof(nf_nat_sdp_session_hook) nf_nat_sdp_session;

        nf_nat_sdp_addr = rcu_dereference(nf_nat_sdp_addr_hook);
        c_hdr = nf_ct_l3num(ct) == AF_INET ? SDP_HDR_CONNECTION_IP4 :
                                             SDP_HDR_CONNECTION_IP6;

        /* 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,
                                  c_hdr, 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)
                        return NF_DROP;

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

                ret = set_expected_rtp_rtcp(skb, dptr, datalen,
                                            &rtp_addr, htons(port), t->class,
                                            mediaoff, medialen);
                if (ret != NF_ACCEPT)
                        return ret;

                /* Update media connection address if present */
                if (maddr_len && nf_nat_sdp_addr && ct->status & IPS_NAT_MASK) {
                        ret = nf_nat_sdp_addr(skb, dptr, mediaoff, datalen,
                                              c_hdr, SDP_HDR_MEDIA, &rtp_addr);
                        if (ret != NF_ACCEPT)
                                return ret;
                }
                i++;
        }

        /* Update session connection and owner addresses */
        nf_nat_sdp_session = rcu_dereference(nf_nat_sdp_session_hook);
        if (nf_nat_sdp_session && ct->status & IPS_NAT_MASK)
                ret = nf_nat_sdp_session(skb, dptr, sdpoff, datalen, &rtp_addr);

        if (ret == NF_ACCEPT && i > 0)
                help->help.ct_sip_info.invite_cseq = cseq;

        return ret;
}
static int process_invite_response(struct sk_buff *skb,
                                   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_conn_help *help = nfct_help(ct);

        if ((code >= 100 && code <= 199) ||
            (code >= 200 && code <= 299))
                return process_sdp(skb, dptr, datalen, cseq);
        else if (help->help.ct_sip_info.invite_cseq == cseq)
                flush_expectations(ct, true);
        return NF_ACCEPT;
}

static int process_update_response(struct sk_buff *skb,
                                   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_conn_help *help = nfct_help(ct);

        if ((code >= 100 && code <= 199) ||
            (code >= 200 && code <= 299))
                return process_sdp(skb, dptr, datalen, cseq);
        else if (help->help.ct_sip_info.invite_cseq == cseq)
                flush_expectations(ct, true);
        return NF_ACCEPT;
}

static int process_prack_response(struct sk_buff *skb,
                                  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_conn_help *help = nfct_help(ct);

        if ((code >= 100 && code <= 199) ||
            (code >= 200 && code <= 299))
                return process_sdp(skb, dptr, datalen, cseq);
        else if (help->help.ct_sip_info.invite_cseq == cseq)
                flush_expectations(ct, true);
        return NF_ACCEPT;
}

static int process_bye_request(struct sk_buff *skb,
                               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,
                                    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_conn_help *help = nfct_help(ct);
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
        unsigned int matchoff, matchlen;
        struct nf_conntrack_expect *exp;
        union nf_inet_addr *saddr, daddr;
        __be16 port;
        unsigned int expires = 0;
        int ret;
        typeof(nf_nat_sip_expect_hook) nf_nat_sip_expect;

        /* 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)
                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_numerical_param(ct, *dptr,
                                         matchoff + matchlen, *datalen,
                                         "expires=", NULL, NULL, &expires) < 0)
                return NF_DROP;

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

        exp = nf_ct_expect_alloc(ct);
        if (!exp)
                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, IPPROTO_UDP, NULL, &port);
        exp->timeout.expires = sip_timeout * HZ;
        exp->helper = nfct_help(ct)->helper;
        exp->flags = NF_CT_EXPECT_PERMANENT | NF_CT_EXPECT_INACTIVE;

        nf_nat_sip_expect = rcu_dereference(nf_nat_sip_expect_hook);
        if (nf_nat_sip_expect && ct->status & IPS_NAT_MASK)
                ret = nf_nat_sip_expect(skb, dptr, datalen, exp,
                                        matchoff, matchlen);
        else {
                if (nf_ct_expect_related(exp) != 0)
                        ret = NF_DROP;
                else
                        ret = NF_ACCEPT;
        }
        nf_ct_expect_put(exp);

store_cseq:
        if (ret == NF_ACCEPT)
                help->help.ct_sip_info.register_cseq = cseq;
        return ret;
}

static int process_register_response(struct sk_buff *skb,
                                     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_conn_help *help = nfct_help(ct);
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
        union nf_inet_addr addr;
        __be16 port;
        unsigned int matchoff, matchlen, dataoff = 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 (help->help.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, &dataoff, *datalen,
                                              SIP_HDR_CONTACT, &in_contact,
                                              &matchoff, &matchlen,
                                              &addr, &port);
                if (ret < 0)
                        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;

                ret = ct_sip_parse_numerical_param(ct, *dptr,
                                                   matchoff + matchlen,
                                                   *datalen, "expires=",
                                                   NULL, NULL, &c_expires);
                if (ret < 0)
                        return NF_DROP;
                if (c_expires == 0)
                        break;
                if (refresh_signalling_expectation(ct, &addr, 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_sdp, 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,
                                const char **dptr, unsigned int *datalen)
{
        enum ip_conntrack_info ctinfo;
        struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
        unsigned int matchoff, matchlen;
        unsigned int code, cseq, dataoff, i;

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

        if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CSEQ,
                              &matchoff, &matchlen) <= 0)
                return NF_DROP;
        cseq = simple_strtoul(*dptr + matchoff, NULL, 10);
        if (!cseq)
                return NF_DROP;
        dataoff = 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 < dataoff + handler->len ||
                    strnicmp(*dptr + dataoff, handler->method, handler->len))
                        continue;
                return handler->response(skb, dptr, datalen, cseq, code);
        }
        return NF_ACCEPT;
}

static int process_sip_request(struct sk_buff *skb,
                               const char **dptr, unsigned int *datalen)
{
        enum ip_conntrack_info ctinfo;
        struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
        unsigned int matchoff, matchlen;
        unsigned int cseq, i;

        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 ||
                    strnicmp(*dptr, handler->method, handler->len))
                        continue;

                if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CSEQ,
                                      &matchoff, &matchlen) <= 0)
                        return NF_DROP;
                cseq = simple_strtoul(*dptr + matchoff, NULL, 10);
                if (!cseq)
                        return NF_DROP;

                return handler->request(skb, dptr, datalen, cseq);
        }
        return NF_ACCEPT;
}

static int sip_help(struct sk_buff *skb,
                    unsigned int protoff,
                    struct nf_conn *ct,
                    enum ip_conntrack_info ctinfo)
{
        unsigned int dataoff, datalen;
        const char *dptr;
        int ret;
        typeof(nf_nat_sip_hook) nf_nat_sip;

        /* No Data ? */
        dataoff = protoff + sizeof(struct udphdr);
        if (dataoff >= skb->len)
                return NF_ACCEPT;

        nf_ct_refresh(ct, skb, sip_timeout * HZ);

        if (!skb_is_nonlinear(skb))
                dptr = skb->data + dataoff;
        else {
                pr_debug("Copy of skbuff not supported yet.\n");
                return NF_ACCEPT;
        }

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

        if (strnicmp(dptr, "SIP/2.0 ", strlen("SIP/2.0 ")) != 0)
                ret = process_sip_request(skb, &dptr, &datalen);
        else
                ret = process_sip_response(skb, &dptr, &datalen);

        if (ret == NF_ACCEPT && ct->status & IPS_NAT_MASK) {
                nf_nat_sip = rcu_dereference(nf_nat_sip_hook);
                if (nf_nat_sip && !nf_nat_sip(skb, &dptr, &datalen))
                        ret = NF_DROP;
        }

        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 const struct nf_conntrack_expect_policy sip_exp_policy[SIP_EXPECT_MAX + 1] = {
        [SIP_EXPECT_SIGNALLING] = {
                .max_expected   = 1,
                .timeout        = 3 * 60,
        },
        [SIP_EXPECT_AUDIO] = {
                .max_expected   = 2 * IP_CT_DIR_MAX,
                .timeout        = 3 * 60,
        },
        [SIP_EXPECT_VIDEO] = {
                .max_expected   = 2 * IP_CT_DIR_MAX,
                .timeout        = 3 * 60,
        },
};

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].expect_policy = sip_exp_policy;
                        sip[i][j].expect_class_max = SIP_EXPECT_MAX;
                        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;

                        pr_debug("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);