/*
   *  Point-to-Point Tunneling Protocol for Linux
   *
   *	Authors: Dmitry Kozlov <xeb@mail.ru>
   *
   *	This program is free software; you can redistribute it and/or
   *	modify it under the terms of the GNU General Public License
   *	as published by the Free Software Foundation; either version
   *	2 of the License, or (at your option) any later version.
   *
   */
  
  #include <linux/string.h>
  #include <linux/module.h>
  #include <linux/kernel.h>
  #include <linux/slab.h>
  #include <linux/errno.h>
  #include <linux/netdevice.h>
  #include <linux/net.h>
  #include <linux/skbuff.h>
  #include <linux/vmalloc.h>
  #include <linux/init.h>
  #include <linux/ppp_channel.h>
  #include <linux/ppp_defs.h>
  #include <linux/if_pppox.h>
  #include <linux/ppp-ioctl.h>
  #include <linux/notifier.h>
  #include <linux/file.h>
  #include <linux/in.h>
  #include <linux/ip.h>
  #include <linux/netfilter.h>
  #include <linux/netfilter_ipv4.h>
  #include <linux/rcupdate.h>
  #include <linux/spinlock.h>
  
  #include <net/sock.h>
  #include <net/protocol.h>
  #include <net/ip.h>
  #include <net/icmp.h>
  #include <net/route.h>
  #include <net/gre.h>
  
  #include <linux/uaccess.h>
  
  #define PPTP_DRIVER_VERSION "0.8.5"
  
  #define MAX_CALLID 65535
  
  static DECLARE_BITMAP(callid_bitmap, MAX_CALLID + 1);
  static struct pppox_sock __rcu **callid_sock;
  
  static DEFINE_SPINLOCK(chan_lock);
  
  static struct proto pptp_sk_proto __read_mostly;
  static const struct ppp_channel_ops pptp_chan_ops;
  static const struct proto_ops pptp_ops;
  
  #define PPP_LCP_ECHOREQ 0x09
  #define PPP_LCP_ECHOREP 0x0A
  #define SC_RCV_BITS	(SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
  
  #define MISSING_WINDOW 20
  #define WRAPPED(curseq, lastseq)\
  	((((curseq) & 0xffffff00) == 0) &&\
  	(((lastseq) & 0xffffff00) == 0xffffff00))
  
  #define PPTP_GRE_PROTO  0x880B
  #define PPTP_GRE_VER    0x1
  
  #define PPTP_GRE_FLAG_C	0x80
  #define PPTP_GRE_FLAG_R	0x40
  #define PPTP_GRE_FLAG_K	0x20
  #define PPTP_GRE_FLAG_S	0x10
  #define PPTP_GRE_FLAG_A	0x80
  
  #define PPTP_GRE_IS_C(f) ((f)&PPTP_GRE_FLAG_C)
  #define PPTP_GRE_IS_R(f) ((f)&PPTP_GRE_FLAG_R)
  #define PPTP_GRE_IS_K(f) ((f)&PPTP_GRE_FLAG_K)
  #define PPTP_GRE_IS_S(f) ((f)&PPTP_GRE_FLAG_S)
  #define PPTP_GRE_IS_A(f) ((f)&PPTP_GRE_FLAG_A)
  
  #define PPTP_HEADER_OVERHEAD (2+sizeof(struct pptp_gre_header))
  struct pptp_gre_header {
  	u8  flags;
  	u8  ver;
  	__be16 protocol;
  	__be16 payload_len;
  	__be16 call_id;
  	__be32 seq;
  	__be32 ack;
  } __packed;
  
  static struct pppox_sock *lookup_chan(u16 call_id, __be32 s_addr)
  {
  	struct pppox_sock *sock;
  	struct pptp_opt *opt;
  
  	rcu_read_lock();
  	sock = rcu_dereference(callid_sock[call_id]);
  	if (sock) {
  		opt = &sock->proto.pptp;
  		if (opt->dst_addr.sin_addr.s_addr != s_addr)
  			sock = NULL;
  		else
  			sock_hold(sk_pppox(sock));
  	}
  	rcu_read_unlock();
  
  	return sock;
  }
  
  static int lookup_chan_dst(u16 call_id, __be32 d_addr)
  {
  	struct pppox_sock *sock;
  	struct pptp_opt *opt;
  	int i;
  
  	rcu_read_lock();
  	i = 1;
  	for_each_set_bit_from(i, callid_bitmap, MAX_CALLID) {
  		sock = rcu_dereference(callid_sock[i]);
  		if (!sock)
  			continue;
  		opt = &sock->proto.pptp;
  		if (opt->dst_addr.call_id == call_id &&
  			  opt->dst_addr.sin_addr.s_addr == d_addr)
  			break;
  	}
  	rcu_read_unlock();
  
  	return i < MAX_CALLID;
  }
  
  static int add_chan(struct pppox_sock *sock)
  {
  	static int call_id;
  
  	spin_lock(&chan_lock);
  	if (!sock->proto.pptp.src_addr.call_id)	{
  		call_id = find_next_zero_bit(callid_bitmap, MAX_CALLID, call_id + 1);
  		if (call_id == MAX_CALLID) {
  			call_id = find_next_zero_bit(callid_bitmap, MAX_CALLID, 1);
  			if (call_id == MAX_CALLID)
  				goto out_err;
  		}
  		sock->proto.pptp.src_addr.call_id = call_id;
  	} else if (test_bit(sock->proto.pptp.src_addr.call_id, callid_bitmap))
  		goto out_err;
  
  	set_bit(sock->proto.pptp.src_addr.call_id, callid_bitmap);
  	rcu_assign_pointer(callid_sock[sock->proto.pptp.src_addr.call_id], sock);
  	spin_unlock(&chan_lock);
  
  	return 0;
  
  out_err:
  	spin_unlock(&chan_lock);
  	return -1;
  }
  
  static void del_chan(struct pppox_sock *sock)
  {
  	spin_lock(&chan_lock);
  	clear_bit(sock->proto.pptp.src_addr.call_id, callid_bitmap);
  	RCU_INIT_POINTER(callid_sock[sock->proto.pptp.src_addr.call_id], NULL);
  	spin_unlock(&chan_lock);
  	synchronize_rcu();
  }
  
  static int pptp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
  {
  	struct sock *sk = (struct sock *) chan->private;
  	struct pppox_sock *po = pppox_sk(sk);
  	struct pptp_opt *opt = &po->proto.pptp;
  	struct pptp_gre_header *hdr;
  	unsigned int header_len = sizeof(*hdr);
  	struct flowi4 fl4;
  	int islcp;
  	int len;
  	unsigned char *data;
  	__u32 seq_recv;
  
  
  	struct rtable *rt;
  	struct net_device *tdev;
  	struct iphdr  *iph;
  	int    max_headroom;
  
  	if (sk_pppox(po)->sk_state & PPPOX_DEAD)
  		goto tx_error;
  
  	rt = ip_route_output_ports(sock_net(sk), &fl4, NULL,
  				   opt->dst_addr.sin_addr.s_addr,
  				   opt->src_addr.sin_addr.s_addr,
  				   0, 0, IPPROTO_GRE,
  				   RT_TOS(0), 0);
  	if (IS_ERR(rt))
  		goto tx_error;
  
  	tdev = rt->dst.dev;
  
  	max_headroom = LL_RESERVED_SPACE(tdev) + sizeof(*iph) + sizeof(*hdr) + 2;
  
  	if (skb_headroom(skb) < max_headroom || skb_cloned(skb) || skb_shared(skb)) {
  		struct sk_buff *new_skb = skb_realloc_headroom(skb, max_headroom);
  		if (!new_skb) {
  			ip_rt_put(rt);
  			goto tx_error;
  		}
  		if (skb->sk)
  			skb_set_owner_w(new_skb, skb->sk);
  		consume_skb(skb);
  		skb = new_skb;
  	}
  
  	data = skb->data;
  	islcp = ((data[0] << 8) + data[1]) == PPP_LCP && 1 <= data[2] && data[2] <= 7;
  
  	/* compress protocol field */
  	if ((opt->ppp_flags & SC_COMP_PROT) && data[0] == 0 && !islcp)
  		skb_pull(skb, 1);
  
  	/* Put in the address/control bytes if necessary */
  	if ((opt->ppp_flags & SC_COMP_AC) == 0 || islcp) {
  		data = skb_push(skb, 2);
  		data[0] = PPP_ALLSTATIONS;
  		data[1] = PPP_UI;
  	}
  
  	len = skb->len;
  
  	seq_recv = opt->seq_recv;
  
  	if (opt->ack_sent == seq_recv)
  		header_len -= sizeof(hdr->ack);
  
  	/* Push down and install GRE header */
  	skb_push(skb, header_len);
  	hdr = (struct pptp_gre_header *)(skb->data);
  
  	hdr->flags       = PPTP_GRE_FLAG_K;
  	hdr->ver         = PPTP_GRE_VER;
  	hdr->protocol    = htons(PPTP_GRE_PROTO);
  	hdr->call_id     = htons(opt->dst_addr.call_id);
  
  	hdr->flags      |= PPTP_GRE_FLAG_S;
  	hdr->seq         = htonl(++opt->seq_sent);
  	if (opt->ack_sent != seq_recv)	{
  		/* send ack with this message */
  		hdr->ver |= PPTP_GRE_FLAG_A;
  		hdr->ack  = htonl(seq_recv);
  		opt->ack_sent = seq_recv;
  	}
  	hdr->payload_len = htons(len);
  
  	/*	Push down and install the IP header. */
  
  	skb_reset_transport_header(skb);
  	skb_push(skb, sizeof(*iph));
  	skb_reset_network_header(skb);
  	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
  	IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED | IPSKB_REROUTED);
  
  	iph =	ip_hdr(skb);
  	iph->version =	4;
  	iph->ihl =	sizeof(struct iphdr) >> 2;
  	if (ip_dont_fragment(sk, &rt->dst))
  		iph->frag_off	=	htons(IP_DF);
  	else
  		iph->frag_off	=	0;
  	iph->protocol = IPPROTO_GRE;
  	iph->tos      = 0;
  	iph->daddr    = fl4.daddr;
  	iph->saddr    = fl4.saddr;
  	iph->ttl      = ip4_dst_hoplimit(&rt->dst);
  	iph->tot_len  = htons(skb->len);
  
  	skb_dst_drop(skb);
  	skb_dst_set(skb, &rt->dst);
  
  	nf_reset(skb);
  
  	skb->ip_summed = CHECKSUM_NONE;
  	ip_select_ident(skb, NULL);
  	ip_send_check(iph);
  
  	ip_local_out(skb);
  	return 1;
  
  tx_error:
  	kfree_skb(skb);
  	return 1;
  }
  
  static int pptp_rcv_core(struct sock *sk, struct sk_buff *skb)
  {
  	struct pppox_sock *po = pppox_sk(sk);
  	struct pptp_opt *opt = &po->proto.pptp;
  	int headersize, payload_len, seq;
  	__u8 *payload;
  	struct pptp_gre_header *header;
  
  	if (!(sk->sk_state & PPPOX_CONNECTED)) {
  		if (sock_queue_rcv_skb(sk, skb))
  			goto drop;
  		return NET_RX_SUCCESS;
  	}
  
  	header = (struct pptp_gre_header *)(skb->data);
  	headersize  = sizeof(*header);
  
  	/* test if acknowledgement present */
  	if (PPTP_GRE_IS_A(header->ver)) {
  		__u32 ack;
  
  		if (!pskb_may_pull(skb, headersize))
  			goto drop;
  		header = (struct pptp_gre_header *)(skb->data);
  
  		/* ack in different place if S = 0 */
  		ack = PPTP_GRE_IS_S(header->flags) ? header->ack : header->seq;
  
  		ack = ntohl(ack);
  
  		if (ack > opt->ack_recv)
  			opt->ack_recv = ack;
  		/* also handle sequence number wrap-around  */
  		if (WRAPPED(ack, opt->ack_recv))
  			opt->ack_recv = ack;
  	} else {
  		headersize -= sizeof(header->ack);
  	}
  	/* test if payload present */
  	if (!PPTP_GRE_IS_S(header->flags))
  		goto drop;
  
  	payload_len = ntohs(header->payload_len);
  	seq         = ntohl(header->seq);
  
  	/* check for incomplete packet (length smaller than expected) */
  	if (!pskb_may_pull(skb, headersize + payload_len))
  		goto drop;
  
  	payload = skb->data + headersize;
  	/* check for expected sequence number */
  	if (seq < opt->seq_recv + 1 || WRAPPED(opt->seq_recv, seq)) {
  		if ((payload[0] == PPP_ALLSTATIONS) && (payload[1] == PPP_UI) &&
  				(PPP_PROTOCOL(payload) == PPP_LCP) &&
  				((payload[4] == PPP_LCP_ECHOREQ) || (payload[4] == PPP_LCP_ECHOREP)))
  			goto allow_packet;
  	} else {
  		opt->seq_recv = seq;
  allow_packet:
  		skb_pull(skb, headersize);
  
  		if (payload[0] == PPP_ALLSTATIONS && payload[1] == PPP_UI) {
  			/* chop off address/control */
  			if (skb->len < 3)
  				goto drop;
  			skb_pull(skb, 2);
  		}
  
  		if ((*skb->data) & 1) {
  			/* protocol is compressed */
  			skb_push(skb, 1)[0] = 0;
  		}
  
  		skb->ip_summed = CHECKSUM_NONE;
  		skb_set_network_header(skb, skb->head-skb->data);
  		ppp_input(&po->chan, skb);
  
  		return NET_RX_SUCCESS;
  	}
  drop:
  	kfree_skb(skb);
  	return NET_RX_DROP;
  }
  
  static int pptp_rcv(struct sk_buff *skb)
  {
  	struct pppox_sock *po;
  	struct pptp_gre_header *header;
  	struct iphdr *iph;
  
  	if (skb->pkt_type != PACKET_HOST)
  		goto drop;
  
  	if (!pskb_may_pull(skb, 12))
  		goto drop;
  
  	iph = ip_hdr(skb);
  
  	header = (struct pptp_gre_header *)skb->data;
  
  	if (ntohs(header->protocol) != PPTP_GRE_PROTO || /* PPTP-GRE protocol for PPTP */
  		PPTP_GRE_IS_C(header->flags) ||                /* flag C should be clear */
  		PPTP_GRE_IS_R(header->flags) ||                /* flag R should be clear */
  		!PPTP_GRE_IS_K(header->flags) ||               /* flag K should be set */
  		(header->flags&0xF) != 0)                      /* routing and recursion ctrl = 0 */
  		/* if invalid, discard this packet */
  		goto drop;
  
  	po = lookup_chan(htons(header->call_id), iph->saddr);
  	if (po) {
  		skb_dst_drop(skb);
  		nf_reset(skb);
  		return sk_receive_skb(sk_pppox(po), skb, 0);
  	}
  drop:
  	kfree_skb(skb);
  	return NET_RX_DROP;
  }
  
  static int pptp_bind(struct socket *sock, struct sockaddr *uservaddr,
  	int sockaddr_len)
  {
  	struct sock *sk = sock->sk;
  	struct sockaddr_pppox *sp = (struct sockaddr_pppox *) uservaddr;
  	struct pppox_sock *po = pppox_sk(sk);
  	struct pptp_opt *opt = &po->proto.pptp;
  	int error = 0;
  
  	lock_sock(sk);
  
  	opt->src_addr = sp->sa_addr.pptp;
  	if (add_chan(po))
  		error = -EBUSY;
  
  	release_sock(sk);
  	return error;
  }
  
  static int pptp_connect(struct socket *sock, struct sockaddr *uservaddr,
  	int sockaddr_len, int flags)
  {
  	struct sock *sk = sock->sk;
  	struct sockaddr_pppox *sp = (struct sockaddr_pppox *) uservaddr;
  	struct pppox_sock *po = pppox_sk(sk);
  	struct pptp_opt *opt = &po->proto.pptp;
  	struct rtable *rt;
  	struct flowi4 fl4;
  	int error = 0;
  
  	if (sp->sa_protocol != PX_PROTO_PPTP)
  		return -EINVAL;
  
  	if (lookup_chan_dst(sp->sa_addr.pptp.call_id, sp->sa_addr.pptp.sin_addr.s_addr))
  		return -EALREADY;
  
  	lock_sock(sk);
  	/* Check for already bound sockets */
  	if (sk->sk_state & PPPOX_CONNECTED) {
  		error = -EBUSY;
  		goto end;
  	}
  
  	/* Check for already disconnected sockets, on attempts to disconnect */
  	if (sk->sk_state & PPPOX_DEAD) {
  		error = -EALREADY;
  		goto end;
  	}
  
  	if (!opt->src_addr.sin_addr.s_addr || !sp->sa_addr.pptp.sin_addr.s_addr) {
  		error = -EINVAL;
  		goto end;
  	}
  
  	po->chan.private = sk;
  	po->chan.ops = &pptp_chan_ops;
  
  	rt = ip_route_output_ports(sock_net(sk), &fl4, sk,
  				   opt->dst_addr.sin_addr.s_addr,
  				   opt->src_addr.sin_addr.s_addr,
  				   0, 0,
  				   IPPROTO_GRE, RT_CONN_FLAGS(sk), 0);
  	if (IS_ERR(rt)) {
  		error = -EHOSTUNREACH;
  		goto end;
  	}
  	sk_setup_caps(sk, &rt->dst);
  
  	po->chan.mtu = dst_mtu(&rt->dst);
  	if (!po->chan.mtu)
  		po->chan.mtu = PPP_MRU;
  	ip_rt_put(rt);
  	po->chan.mtu -= PPTP_HEADER_OVERHEAD;
  
  	po->chan.hdrlen = 2 + sizeof(struct pptp_gre_header);
  	error = ppp_register_channel(&po->chan);
  	if (error) {
  		pr_err("PPTP: failed to register PPP channel (%d)
  ", error);
  		goto end;
  	}
  
  	opt->dst_addr = sp->sa_addr.pptp;
  	sk->sk_state = PPPOX_CONNECTED;
  
   end:
  	release_sock(sk);
  	return error;
  }
  
  static int pptp_getname(struct socket *sock, struct sockaddr *uaddr,
  	int *usockaddr_len, int peer)
  {
  	int len = sizeof(struct sockaddr_pppox);
  	struct sockaddr_pppox sp;
  
  	memset(&sp.sa_addr, 0, sizeof(sp.sa_addr));
  
  	sp.sa_family    = AF_PPPOX;
  	sp.sa_protocol  = PX_PROTO_PPTP;
  	sp.sa_addr.pptp = pppox_sk(sock->sk)->proto.pptp.src_addr;
  
  	memcpy(uaddr, &sp, len);
  
  	*usockaddr_len = len;
  
  	return 0;
  }
  
  static int pptp_release(struct socket *sock)
  {
  	struct sock *sk = sock->sk;
  	struct pppox_sock *po;
  	struct pptp_opt *opt;
  	int error = 0;
  
  	if (!sk)
  		return 0;
  
  	lock_sock(sk);
  
  	if (sock_flag(sk, SOCK_DEAD)) {
  		release_sock(sk);
  		return -EBADF;
  	}
  
  	po = pppox_sk(sk);
  	opt = &po->proto.pptp;
  	del_chan(po);
  
  	pppox_unbind_sock(sk);
  	sk->sk_state = PPPOX_DEAD;
  
  	sock_orphan(sk);
  	sock->sk = NULL;
  
  	release_sock(sk);
  	sock_put(sk);
  
  	return error;
  }
  
  static void pptp_sock_destruct(struct sock *sk)
  {
  	if (!(sk->sk_state & PPPOX_DEAD)) {
  		del_chan(pppox_sk(sk));
  		pppox_unbind_sock(sk);
  	}
  	skb_queue_purge(&sk->sk_receive_queue);
  }
  
  static int pptp_create(struct net *net, struct socket *sock)
  {
  	int error = -ENOMEM;
  	struct sock *sk;
  	struct pppox_sock *po;
  	struct pptp_opt *opt;
  
  	sk = sk_alloc(net, PF_PPPOX, GFP_KERNEL, &pptp_sk_proto);
  	if (!sk)
  		goto out;
  
  	sock_init_data(sock, sk);
  
  	sock->state = SS_UNCONNECTED;
  	sock->ops   = &pptp_ops;
  
  	sk->sk_backlog_rcv = pptp_rcv_core;
  	sk->sk_state       = PPPOX_NONE;
  	sk->sk_type        = SOCK_STREAM;
  	sk->sk_family      = PF_PPPOX;
  	sk->sk_protocol    = PX_PROTO_PPTP;
  	sk->sk_destruct    = pptp_sock_destruct;
  
  	po = pppox_sk(sk);
  	opt = &po->proto.pptp;
  
  	opt->seq_sent = 0; opt->seq_recv = 0xffffffff;
  	opt->ack_recv = 0; opt->ack_sent = 0xffffffff;
  
  	error = 0;
  out:
  	return error;
  }
  
  static int pptp_ppp_ioctl(struct ppp_channel *chan, unsigned int cmd,
  	unsigned long arg)
  {
  	struct sock *sk = (struct sock *) chan->private;
  	struct pppox_sock *po = pppox_sk(sk);
  	struct pptp_opt *opt = &po->proto.pptp;
  	void __user *argp = (void __user *)arg;
  	int __user *p = argp;
  	int err, val;
  
  	err = -EFAULT;
  	switch (cmd) {
  	case PPPIOCGFLAGS:
  		val = opt->ppp_flags;
  		if (put_user(val, p))
  			break;
  		err = 0;
  		break;
  	case PPPIOCSFLAGS:
  		if (get_user(val, p))
  			break;
  		opt->ppp_flags = val & ~SC_RCV_BITS;
  		err = 0;
  		break;
  	default:
  		err = -ENOTTY;
  	}
  
  	return err;
  }
  
  static const struct ppp_channel_ops pptp_chan_ops = {
  	.start_xmit = pptp_xmit,
  	.ioctl      = pptp_ppp_ioctl,
  };
  
  static struct proto pptp_sk_proto __read_mostly = {
  	.name     = "PPTP",
  	.owner    = THIS_MODULE,
  	.obj_size = sizeof(struct pppox_sock),
  };
  
  static const struct proto_ops pptp_ops = {
  	.family     = AF_PPPOX,
  	.owner      = THIS_MODULE,
  	.release    = pptp_release,
  	.bind       = pptp_bind,
  	.connect    = pptp_connect,
  	.socketpair = sock_no_socketpair,
  	.accept     = sock_no_accept,
  	.getname    = pptp_getname,
  	.poll       = sock_no_poll,
  	.listen     = sock_no_listen,
  	.shutdown   = sock_no_shutdown,
  	.setsockopt = sock_no_setsockopt,
  	.getsockopt = sock_no_getsockopt,
  	.sendmsg    = sock_no_sendmsg,
  	.recvmsg    = sock_no_recvmsg,
  	.mmap       = sock_no_mmap,
  	.ioctl      = pppox_ioctl,
  };
  
  static const struct pppox_proto pppox_pptp_proto = {
  	.create = pptp_create,
  	.owner  = THIS_MODULE,
  };
  
  static const struct gre_protocol gre_pptp_protocol = {
  	.handler = pptp_rcv,
  };
  
  static int __init pptp_init_module(void)
  {
  	int err = 0;
  	pr_info("PPTP driver version " PPTP_DRIVER_VERSION "
  ");
  
  	callid_sock = vzalloc((MAX_CALLID + 1) * sizeof(void *));
  	if (!callid_sock)
  		return -ENOMEM;
  
  	err = gre_add_protocol(&gre_pptp_protocol, GREPROTO_PPTP);
  	if (err) {
  		pr_err("PPTP: can't add gre protocol
  ");
  		goto out_mem_free;
  	}
  
  	err = proto_register(&pptp_sk_proto, 0);
  	if (err) {
  		pr_err("PPTP: can't register sk_proto
  ");
  		goto out_gre_del_protocol;
  	}
  
  	err = register_pppox_proto(PX_PROTO_PPTP, &pppox_pptp_proto);
  	if (err) {
  		pr_err("PPTP: can't register pppox_proto
  ");
  		goto out_unregister_sk_proto;
  	}
  
  	return 0;
  
  out_unregister_sk_proto:
  	proto_unregister(&pptp_sk_proto);
  out_gre_del_protocol:
  	gre_del_protocol(&gre_pptp_protocol, GREPROTO_PPTP);
  out_mem_free:
  	vfree(callid_sock);
  
  	return err;
  }
  
  static void __exit pptp_exit_module(void)
  {
  	unregister_pppox_proto(PX_PROTO_PPTP);
  	proto_unregister(&pptp_sk_proto);
  	gre_del_protocol(&gre_pptp_protocol, GREPROTO_PPTP);
  	vfree(callid_sock);
  }
  
  module_init(pptp_init_module);
  module_exit(pptp_exit_module);
  
  MODULE_DESCRIPTION("Point-to-Point Tunneling Protocol");
  MODULE_AUTHOR("D. Kozlov (xeb@mail.ru)");
  MODULE_LICENSE("GPL");