nf_conntrack_pptp.c

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/*
 * Connection tracking support for PPTP (Point to Point Tunneling Protocol).
 * PPTP is a a protocol for creating virtual private networks.
 * It is a specification defined by Microsoft and some vendors
 * working with Microsoft.  PPTP is built on top of a modified
 * version of the Internet Generic Routing Encapsulation Protocol.
 * GRE is defined in RFC 1701 and RFC 1702.  Documentation of
 * PPTP can be found in RFC 2637
 *
 * (C) 2000-2005 by Harald Welte <[email protected]>
 *
 * Development of this code funded by Astaro AG (http://www.astaro.com/)
 *
 * Limitations:
 *   - We blindly assume that control connections are always
 *     established in PNS->PAC direction.  This is a violation
 *     of RFFC2673
 *   - We can only support one single call within each session
 * TODO:
 *   - testing of incoming PPTP calls
 */

#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/in.h>
#include <linux/tcp.h>

#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_core.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_zones.h>
#include <linux/netfilter/nf_conntrack_proto_gre.h>
#include <linux/netfilter/nf_conntrack_pptp.h>

#define NF_CT_PPTP_VERSION "3.1"

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <[email protected]>");
MODULE_DESCRIPTION("Netfilter connection tracking helper module for PPTP");
MODULE_ALIAS("ip_conntrack_pptp");
MODULE_ALIAS_NFCT_HELPER("pptp");

static DEFINE_SPINLOCK(nf_pptp_lock);

int
(*nf_nat_pptp_hook_outbound)(struct sk_buff *skb,
                 struct nf_conn *ct, enum ip_conntrack_info ctinfo,
                 unsigned int protoff, struct PptpControlHeader *ctlh,
                 union pptp_ctrl_union *pptpReq) __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_outbound);

int
(*nf_nat_pptp_hook_inbound)(struct sk_buff *skb,
                struct nf_conn *ct, enum ip_conntrack_info ctinfo,
                unsigned int protoff, struct PptpControlHeader *ctlh,
                union pptp_ctrl_union *pptpReq) __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_inbound);

void
(*nf_nat_pptp_hook_exp_gre)(struct nf_conntrack_expect *expect_orig,
                struct nf_conntrack_expect *expect_reply)
                __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_exp_gre);

void
(*nf_nat_pptp_hook_expectfn)(struct nf_conn *ct,
                 struct nf_conntrack_expect *exp) __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_expectfn);

#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
/* PptpControlMessageType names */
const char *const pptp_msg_name[] = {
    "UNKNOWN_MESSAGE",
    "START_SESSION_REQUEST",
    "START_SESSION_REPLY",
    "STOP_SESSION_REQUEST",
    "STOP_SESSION_REPLY",
    "ECHO_REQUEST",
    "ECHO_REPLY",
    "OUT_CALL_REQUEST",
    "OUT_CALL_REPLY",
    "IN_CALL_REQUEST",
    "IN_CALL_REPLY",
    "IN_CALL_CONNECT",
    "CALL_CLEAR_REQUEST",
    "CALL_DISCONNECT_NOTIFY",
    "WAN_ERROR_NOTIFY",
    "SET_LINK_INFO"
};
EXPORT_SYMBOL(pptp_msg_name);
#endif

#define SECS *HZ
#define MINS * 60 SECS
#define HOURS * 60 MINS

#define PPTP_GRE_TIMEOUT        (10 MINS)
#define PPTP_GRE_STREAM_TIMEOUT     (5 HOURS)

static void pptp_expectfn(struct nf_conn *ct,
             struct nf_conntrack_expect *exp)
{
    struct net *net = nf_ct_net(ct);
    typeof(nf_nat_pptp_hook_expectfn) nf_nat_pptp_expectfn;
    pr_debug("increasing timeouts\n");

    /* increase timeout of GRE data channel conntrack entry */
    ct->proto.gre.timeout        = PPTP_GRE_TIMEOUT;
    ct->proto.gre.stream_timeout = PPTP_GRE_STREAM_TIMEOUT;

    /* Can you see how rusty this code is, compared with the pre-2.6.11
     * one? That's what happened to my shiny newnat of 2002 ;( -HW */

    rcu_read_lock();
    nf_nat_pptp_expectfn = rcu_dereference(nf_nat_pptp_hook_expectfn);
    if (nf_nat_pptp_expectfn && ct->master->status & IPS_NAT_MASK)
        nf_nat_pptp_expectfn(ct, exp);
    else {
        struct nf_conntrack_tuple inv_t;
        struct nf_conntrack_expect *exp_other;

        /* obviously this tuple inversion only works until you do NAT */
        nf_ct_invert_tuplepr(&inv_t, &exp->tuple);
        pr_debug("trying to unexpect other dir: ");
        nf_ct_dump_tuple(&inv_t);

        exp_other = nf_ct_expect_find_get(net, nf_ct_zone(ct), &inv_t);
        if (exp_other) {
            /* delete other expectation.  */
            pr_debug("found\n");
            nf_ct_unexpect_related(exp_other);
            nf_ct_expect_put(exp_other);
        } else {
            pr_debug("not found\n");
        }
    }
    rcu_read_unlock();
}

static int destroy_sibling_or_exp(struct net *net, struct nf_conn *ct,
                  const struct nf_conntrack_tuple *t)
{
    const struct nf_conntrack_tuple_hash *h;
    struct nf_conntrack_expect *exp;
    struct nf_conn *sibling;
    u16 zone = nf_ct_zone(ct);

    pr_debug("trying to timeout ct or exp for tuple ");
    nf_ct_dump_tuple(t);

    h = nf_conntrack_find_get(net, zone, t);
    if (h)  {
        sibling = nf_ct_tuplehash_to_ctrack(h);
        pr_debug("setting timeout of conntrack %p to 0\n", sibling);
        sibling->proto.gre.timeout    = 0;
        sibling->proto.gre.stream_timeout = 0;
        if (del_timer(&sibling->timeout))
            sibling->timeout.function((unsigned long)sibling);
        nf_ct_put(sibling);
        return 1;
    } else {
        exp = nf_ct_expect_find_get(net, zone, t);
        if (exp) {
            pr_debug("unexpect_related of expect %p\n", exp);
            nf_ct_unexpect_related(exp);
            nf_ct_expect_put(exp);
            return 1;
        }
    }
    return 0;
}

/* timeout GRE data connections */
static void pptp_destroy_siblings(struct nf_conn *ct)
{
    struct net *net = nf_ct_net(ct);
    const struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
    struct nf_conntrack_tuple t;

    nf_ct_gre_keymap_destroy(ct);

    /* try original (pns->pac) tuple */
    memcpy(&t, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, sizeof(t));
    t.dst.protonum = IPPROTO_GRE;
    t.src.u.gre.key = ct_pptp_info->pns_call_id;
    t.dst.u.gre.key = ct_pptp_info->pac_call_id;
    if (!destroy_sibling_or_exp(net, ct, &t))
        pr_debug("failed to timeout original pns->pac ct/exp\n");

    /* try reply (pac->pns) tuple */
    memcpy(&t, &ct->tuplehash[IP_CT_DIR_REPLY].tuple, sizeof(t));
    t.dst.protonum = IPPROTO_GRE;
    t.src.u.gre.key = ct_pptp_info->pac_call_id;
    t.dst.u.gre.key = ct_pptp_info->pns_call_id;
    if (!destroy_sibling_or_exp(net, ct, &t))
        pr_debug("failed to timeout reply pac->pns ct/exp\n");
}

/* expect GRE connections (PNS->PAC and PAC->PNS direction) */
static int exp_gre(struct nf_conn *ct, __be16 callid, __be16 peer_callid)
{
    struct nf_conntrack_expect *exp_orig, *exp_reply;
    enum ip_conntrack_dir dir;
    int ret = 1;
    typeof(nf_nat_pptp_hook_exp_gre) nf_nat_pptp_exp_gre;

    exp_orig = nf_ct_expect_alloc(ct);
    if (exp_orig == NULL)
        goto out;

    exp_reply = nf_ct_expect_alloc(ct);
    if (exp_reply == NULL)
        goto out_put_orig;

    /* original direction, PNS->PAC */
    dir = IP_CT_DIR_ORIGINAL;
    nf_ct_expect_init(exp_orig, NF_CT_EXPECT_CLASS_DEFAULT,
              nf_ct_l3num(ct),
              &ct->tuplehash[dir].tuple.src.u3,
              &ct->tuplehash[dir].tuple.dst.u3,
              IPPROTO_GRE, &peer_callid, &callid);
    exp_orig->expectfn = pptp_expectfn;

    /* reply direction, PAC->PNS */
    dir = IP_CT_DIR_REPLY;
    nf_ct_expect_init(exp_reply, NF_CT_EXPECT_CLASS_DEFAULT,
              nf_ct_l3num(ct),
              &ct->tuplehash[dir].tuple.src.u3,
              &ct->tuplehash[dir].tuple.dst.u3,
              IPPROTO_GRE, &callid, &peer_callid);
    exp_reply->expectfn = pptp_expectfn;

    nf_nat_pptp_exp_gre = rcu_dereference(nf_nat_pptp_hook_exp_gre);
    if (nf_nat_pptp_exp_gre && ct->status & IPS_NAT_MASK)
        nf_nat_pptp_exp_gre(exp_orig, exp_reply);
    if (nf_ct_expect_related(exp_orig) != 0)
        goto out_put_both;
    if (nf_ct_expect_related(exp_reply) != 0)
        goto out_unexpect_orig;

    /* Add GRE keymap entries */
    if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_ORIGINAL, &exp_orig->tuple) != 0)
        goto out_unexpect_both;
    if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_REPLY, &exp_reply->tuple) != 0) {
        nf_ct_gre_keymap_destroy(ct);
        goto out_unexpect_both;
    }
    ret = 0;

out_put_both:
    nf_ct_expect_put(exp_reply);
out_put_orig:
    nf_ct_expect_put(exp_orig);
out:
    return ret;

out_unexpect_both:
    nf_ct_unexpect_related(exp_reply);
out_unexpect_orig:
    nf_ct_unexpect_related(exp_orig);
    goto out_put_both;
}

static inline int
pptp_inbound_pkt(struct sk_buff *skb, unsigned int protoff,
         struct PptpControlHeader *ctlh,
         union pptp_ctrl_union *pptpReq,
         unsigned int reqlen,
         struct nf_conn *ct,
         enum ip_conntrack_info ctinfo)
{
    struct nf_ct_pptp_master *info = nfct_help_data(ct);
    u_int16_t msg;
    __be16 cid = 0, pcid = 0;
    typeof(nf_nat_pptp_hook_inbound) nf_nat_pptp_inbound;

    msg = ntohs(ctlh->messageType);
    pr_debug("inbound control message %s\n", pptp_msg_name[msg]);

    switch (msg) {
    case PPTP_START_SESSION_REPLY:
        /* server confirms new control session */
        if (info->sstate < PPTP_SESSION_REQUESTED)
            goto invalid;
        if (pptpReq->srep.resultCode == PPTP_START_OK)
            info->sstate = PPTP_SESSION_CONFIRMED;
        else
            info->sstate = PPTP_SESSION_ERROR;
        break;

    case PPTP_STOP_SESSION_REPLY:
        /* server confirms end of control session */
        if (info->sstate > PPTP_SESSION_STOPREQ)
            goto invalid;
        if (pptpReq->strep.resultCode == PPTP_STOP_OK)
            info->sstate = PPTP_SESSION_NONE;
        else
            info->sstate = PPTP_SESSION_ERROR;
        break;

    case PPTP_OUT_CALL_REPLY:
        /* server accepted call, we now expect GRE frames */
        if (info->sstate != PPTP_SESSION_CONFIRMED)
            goto invalid;
        if (info->cstate != PPTP_CALL_OUT_REQ &&
            info->cstate != PPTP_CALL_OUT_CONF)
            goto invalid;

        cid = pptpReq->ocack.callID;
        pcid = pptpReq->ocack.peersCallID;
        if (info->pns_call_id != pcid)
            goto invalid;
        pr_debug("%s, CID=%X, PCID=%X\n", pptp_msg_name[msg],
             ntohs(cid), ntohs(pcid));

        if (pptpReq->ocack.resultCode == PPTP_OUTCALL_CONNECT) {
            info->cstate = PPTP_CALL_OUT_CONF;
            info->pac_call_id = cid;
            exp_gre(ct, cid, pcid);
        } else
            info->cstate = PPTP_CALL_NONE;
        break;

    case PPTP_IN_CALL_REQUEST:
        /* server tells us about incoming call request */
        if (info->sstate != PPTP_SESSION_CONFIRMED)
            goto invalid;

        cid = pptpReq->icreq.callID;
        pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
        info->cstate = PPTP_CALL_IN_REQ;
        info->pac_call_id = cid;
        break;

    case PPTP_IN_CALL_CONNECT:
        /* server tells us about incoming call established */
        if (info->sstate != PPTP_SESSION_CONFIRMED)
            goto invalid;
        if (info->cstate != PPTP_CALL_IN_REP &&
            info->cstate != PPTP_CALL_IN_CONF)
            goto invalid;

        pcid = pptpReq->iccon.peersCallID;
        cid = info->pac_call_id;

        if (info->pns_call_id != pcid)
            goto invalid;

        pr_debug("%s, PCID=%X\n", pptp_msg_name[msg], ntohs(pcid));
        info->cstate = PPTP_CALL_IN_CONF;

        /* we expect a GRE connection from PAC to PNS */
        exp_gre(ct, cid, pcid);
        break;

    case PPTP_CALL_DISCONNECT_NOTIFY:
        /* server confirms disconnect */
        cid = pptpReq->disc.callID;
        pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
        info->cstate = PPTP_CALL_NONE;

        /* untrack this call id, unexpect GRE packets */
        pptp_destroy_siblings(ct);
        break;

    case PPTP_WAN_ERROR_NOTIFY:
    case PPTP_SET_LINK_INFO:
    case PPTP_ECHO_REQUEST:
    case PPTP_ECHO_REPLY:
        /* I don't have to explain these ;) */
        break;

    default:
        goto invalid;
    }

    nf_nat_pptp_inbound = rcu_dereference(nf_nat_pptp_hook_inbound);
    if (nf_nat_pptp_inbound && ct->status & IPS_NAT_MASK)
        return nf_nat_pptp_inbound(skb, ct, ctinfo,
                       protoff, ctlh, pptpReq);
    return NF_ACCEPT;

invalid:
    pr_debug("invalid %s: type=%d cid=%u pcid=%u "
         "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
         msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
         msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
         ntohs(info->pns_call_id), ntohs(info->pac_call_id));
    return NF_ACCEPT;
}

static inline int
pptp_outbound_pkt(struct sk_buff *skb, unsigned int protoff,
          struct PptpControlHeader *ctlh,
          union pptp_ctrl_union *pptpReq,
          unsigned int reqlen,
          struct nf_conn *ct,
          enum ip_conntrack_info ctinfo)
{
    struct nf_ct_pptp_master *info = nfct_help_data(ct);
    u_int16_t msg;
    __be16 cid = 0, pcid = 0;
    typeof(nf_nat_pptp_hook_outbound) nf_nat_pptp_outbound;

    msg = ntohs(ctlh->messageType);
    pr_debug("outbound control message %s\n", pptp_msg_name[msg]);

    switch (msg) {
    case PPTP_START_SESSION_REQUEST:
        /* client requests for new control session */
        if (info->sstate != PPTP_SESSION_NONE)
            goto invalid;
        info->sstate = PPTP_SESSION_REQUESTED;
        break;

    case PPTP_STOP_SESSION_REQUEST:
        /* client requests end of control session */
        info->sstate = PPTP_SESSION_STOPREQ;
        break;

    case PPTP_OUT_CALL_REQUEST:
        /* client initiating connection to server */
        if (info->sstate != PPTP_SESSION_CONFIRMED)
            goto invalid;
        info->cstate = PPTP_CALL_OUT_REQ;
        /* track PNS call id */
        cid = pptpReq->ocreq.callID;
        pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
        info->pns_call_id = cid;
        break;

    case PPTP_IN_CALL_REPLY:
        /* client answers incoming call */
        if (info->cstate != PPTP_CALL_IN_REQ &&
            info->cstate != PPTP_CALL_IN_REP)
            goto invalid;

        cid = pptpReq->icack.callID;
        pcid = pptpReq->icack.peersCallID;
        if (info->pac_call_id != pcid)
            goto invalid;
        pr_debug("%s, CID=%X PCID=%X\n", pptp_msg_name[msg],
             ntohs(cid), ntohs(pcid));

        if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
            /* part two of the three-way handshake */
            info->cstate = PPTP_CALL_IN_REP;
            info->pns_call_id = cid;
        } else
            info->cstate = PPTP_CALL_NONE;
        break;

    case PPTP_CALL_CLEAR_REQUEST:
        /* client requests hangup of call */
        if (info->sstate != PPTP_SESSION_CONFIRMED)
            goto invalid;
        /* FUTURE: iterate over all calls and check if
         * call ID is valid.  We don't do this without newnat,
         * because we only know about last call */
        info->cstate = PPTP_CALL_CLEAR_REQ;
        break;

    case PPTP_SET_LINK_INFO:
    case PPTP_ECHO_REQUEST:
    case PPTP_ECHO_REPLY:
        /* I don't have to explain these ;) */
        break;

    default:
        goto invalid;
    }

    nf_nat_pptp_outbound = rcu_dereference(nf_nat_pptp_hook_outbound);
    if (nf_nat_pptp_outbound && ct->status & IPS_NAT_MASK)
        return nf_nat_pptp_outbound(skb, ct, ctinfo,
                        protoff, ctlh, pptpReq);
    return NF_ACCEPT;

invalid:
    pr_debug("invalid %s: type=%d cid=%u pcid=%u "
         "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
         msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
         msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
         ntohs(info->pns_call_id), ntohs(info->pac_call_id));
    return NF_ACCEPT;
}

static const unsigned int pptp_msg_size[] = {
    [PPTP_START_SESSION_REQUEST]  = sizeof(struct PptpStartSessionRequest),
    [PPTP_START_SESSION_REPLY]    = sizeof(struct PptpStartSessionReply),
    [PPTP_STOP_SESSION_REQUEST]   = sizeof(struct PptpStopSessionRequest),
    [PPTP_STOP_SESSION_REPLY]     = sizeof(struct PptpStopSessionReply),
    [PPTP_OUT_CALL_REQUEST]       = sizeof(struct PptpOutCallRequest),
    [PPTP_OUT_CALL_REPLY]         = sizeof(struct PptpOutCallReply),
    [PPTP_IN_CALL_REQUEST]        = sizeof(struct PptpInCallRequest),
    [PPTP_IN_CALL_REPLY]          = sizeof(struct PptpInCallReply),
    [PPTP_IN_CALL_CONNECT]        = sizeof(struct PptpInCallConnected),
    [PPTP_CALL_CLEAR_REQUEST]     = sizeof(struct PptpClearCallRequest),
    [PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
    [PPTP_WAN_ERROR_NOTIFY]       = sizeof(struct PptpWanErrorNotify),
    [PPTP_SET_LINK_INFO]          = sizeof(struct PptpSetLinkInfo),
};

/* track caller id inside control connection, call expect_related */
static int
conntrack_pptp_help(struct sk_buff *skb, unsigned int protoff,
            struct nf_conn *ct, enum ip_conntrack_info ctinfo)

{
    int dir = CTINFO2DIR(ctinfo);
    const struct nf_ct_pptp_master *info = nfct_help_data(ct);
    const struct tcphdr *tcph;
    struct tcphdr _tcph;
    const struct pptp_pkt_hdr *pptph;
    struct pptp_pkt_hdr _pptph;
    struct PptpControlHeader _ctlh, *ctlh;
    union pptp_ctrl_union _pptpReq, *pptpReq;
    unsigned int tcplen = skb->len - protoff;
    unsigned int datalen, reqlen, nexthdr_off;
    int oldsstate, oldcstate;
    int ret;
    u_int16_t msg;

    /* don't do any tracking before tcp handshake complete */
    if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
        return NF_ACCEPT;

    nexthdr_off = protoff;
    tcph = skb_header_pointer(skb, nexthdr_off, sizeof(_tcph), &_tcph);
    BUG_ON(!tcph);
    nexthdr_off += tcph->doff * 4;
    datalen = tcplen - tcph->doff * 4;

    pptph = skb_header_pointer(skb, nexthdr_off, sizeof(_pptph), &_pptph);
    if (!pptph) {
        pr_debug("no full PPTP header, can't track\n");
        return NF_ACCEPT;
    }
    nexthdr_off += sizeof(_pptph);
    datalen -= sizeof(_pptph);

    /* if it's not a control message we can't do anything with it */
    if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
        ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
        pr_debug("not a control packet\n");
        return NF_ACCEPT;
    }

    ctlh = skb_header_pointer(skb, nexthdr_off, sizeof(_ctlh), &_ctlh);
    if (!ctlh)
        return NF_ACCEPT;
    nexthdr_off += sizeof(_ctlh);
    datalen -= sizeof(_ctlh);

    reqlen = datalen;
    msg = ntohs(ctlh->messageType);
    if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
        return NF_ACCEPT;
    if (reqlen > sizeof(*pptpReq))
        reqlen = sizeof(*pptpReq);

    pptpReq = skb_header_pointer(skb, nexthdr_off, reqlen, &_pptpReq);
    if (!pptpReq)
        return NF_ACCEPT;

    oldsstate = info->sstate;
    oldcstate = info->cstate;

    spin_lock_bh(&nf_pptp_lock);

    /* FIXME: We just blindly assume that the control connection is always
     * established from PNS->PAC.  However, RFC makes no guarantee */
    if (dir == IP_CT_DIR_ORIGINAL)
        /* client -> server (PNS -> PAC) */
        ret = pptp_outbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
                    ctinfo);
    else
        /* server -> client (PAC -> PNS) */
        ret = pptp_inbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
                       ctinfo);
    pr_debug("sstate: %d->%d, cstate: %d->%d\n",
         oldsstate, info->sstate, oldcstate, info->cstate);
    spin_unlock_bh(&nf_pptp_lock);

    return ret;
}

static const struct nf_conntrack_expect_policy pptp_exp_policy = {
    .max_expected   = 2,
    .timeout    = 5 * 60,
};

/* control protocol helper */
static struct nf_conntrack_helper pptp __read_mostly = {
    .name           = "pptp",
    .me         = THIS_MODULE,
    .data_len       = sizeof(struct nf_ct_pptp_master),
    .tuple.src.l3num    = AF_INET,
    .tuple.src.u.tcp.port   = cpu_to_be16(PPTP_CONTROL_PORT),
    .tuple.dst.protonum = IPPROTO_TCP,
    .help           = conntrack_pptp_help,
    .destroy        = pptp_destroy_siblings,
    .expect_policy      = &pptp_exp_policy,
};

static void nf_conntrack_pptp_net_exit(struct net *net)
{
    nf_ct_gre_keymap_flush(net);
}

static struct pernet_operations nf_conntrack_pptp_net_ops = {
    .exit = nf_conntrack_pptp_net_exit,
};

static int __init nf_conntrack_pptp_init(void)
{
    int rv;

    rv = nf_conntrack_helper_register(&pptp);
    if (rv < 0)
        return rv;
    rv = register_pernet_subsys(&nf_conntrack_pptp_net_ops);
    if (rv < 0)
        nf_conntrack_helper_unregister(&pptp);
    return rv;
}

static void __exit nf_conntrack_pptp_fini(void)
{
    nf_conntrack_helper_unregister(&pptp);
    unregister_pernet_subsys(&nf_conntrack_pptp_net_ops);
}

module_init(nf_conntrack_pptp_init);
module_exit(nf_conntrack_pptp_fini);