tun.c

/*
 *  TUN - Universal TUN/TAP device driver.
 *  Copyright (C) 1999-2002 Maxim Krasnyansky <maxk@qualcomm.com>
 *
 *  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.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 *  GNU General Public License for more details.
 *
 *  $Id: tun.c,v 1.15 2002/03/01 02:44:24 maxk Exp $
 */

/*
 *  Changes:
 *
 *  Mike Kershaw <dragorn@kismetwireless.net> 2005/08/14
 *    Add TUNSETLINK ioctl to set the link encapsulation
 *
 *  Mark Smith <markzzzsmith@yahoo.com.au>
 *    Use random_ether_addr() for tap MAC address.
 *
 *  Harald Roelle <harald.roelle@ifi.lmu.de>  2004/04/20
 *    Fixes in packet dropping, queue length setting and queue wakeup.
 *    Increased default tx queue length.
 *    Added ethtool API.
 *    Minor cleanups
 *
 *  Daniel Podlejski <underley@underley.eu.org>
 *    Modifications for 2.3.99-pre5 kernel.
 */

#define DRV_NAME	"tun"
#define DRV_VERSION	"1.6"
#define DRV_DESCRIPTION	"Universal TUN/TAP device driver"
#define DRV_COPYRIGHT	"(C) 1999-2004 Max Krasnyansky <maxk@qualcomm.com>"

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/fcntl.h>
#include <linux/init.h>
#include <linux/skbuff.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/miscdevice.h>
#include <linux/ethtool.h>
#include <linux/rtnetlink.h>
#include <linux/compat.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <linux/if_tun.h>
#include <linux/crc32.h>
#include <linux/nsproxy.h>
#include <linux/virtio_net.h>
#include <linux/rcupdate.h>
#include <net/net_namespace.h>
#include <net/netns/generic.h>
#include <net/rtnetlink.h>
#include <net/sock.h>

#include <asm/system.h>
#include <asm/uaccess.h>

/* Uncomment to enable debugging */
/* #define TUN_DEBUG 1 */

#ifdef TUN_DEBUG
static int debug;

#define DBG  if(tun->debug)printk
#define DBG1 if(debug==2)printk
#else
#define DBG( a... )
#define DBG1( a... )
#endif

#define FLT_EXACT_COUNT 8
struct tap_filter {
	unsigned int    count;    /* Number of addrs. Zero means disabled */
	u32             mask[2];  /* Mask of the hashed addrs */
	unsigned char	addr[FLT_EXACT_COUNT][ETH_ALEN];
};

struct tun_file {
	atomic_t count;
	struct tun_struct *tun;
	struct net *net;
};

struct tun_sock;

struct tun_struct {
	struct tun_file		*tfile;
	unsigned int 		flags;
	uid_t			owner;
	gid_t			group;

	struct net_device	*dev;
	struct fasync_struct	*fasync;

	struct tap_filter       txflt;
	struct socket		socket;
	struct socket_wq	wq;

	int			vnet_hdr_sz;

#ifdef TUN_DEBUG
	int debug;
#endif
};

struct tun_sock {
	struct sock		sk;
	struct tun_struct	*tun;
};

static inline struct tun_sock *tun_sk(struct sock *sk)
{
	return container_of(sk, struct tun_sock, sk);
}

static int tun_attach(struct tun_struct *tun, struct file *file)
{
	struct tun_file *tfile = file->private_data;
	int err;

	ASSERT_RTNL();

	netif_tx_lock_bh(tun->dev);

	err = -EINVAL;
	if (tfile->tun)
		goto out;

	err = -EBUSY;
	if (tun->tfile)
		goto out;

	err = 0;
	tfile->tun = tun;
	tun->tfile = tfile;
	tun->socket.file = file;
	dev_hold(tun->dev);
	sock_hold(tun->socket.sk);
	atomic_inc(&tfile->count);

out:
	netif_tx_unlock_bh(tun->dev);
	return err;
}

static void __tun_detach(struct tun_struct *tun)
{
	/* Detach from net device */
	netif_tx_lock_bh(tun->dev);
	tun->tfile = NULL;
	tun->socket.file = NULL;
	netif_tx_unlock_bh(tun->dev);

	/* Drop read queue */
	skb_queue_purge(&tun->socket.sk->sk_receive_queue);

	/* Drop the extra count on the net device */
	dev_put(tun->dev);
}

static void tun_detach(struct tun_struct *tun)
{
	rtnl_lock();
	__tun_detach(tun);
	rtnl_unlock();
}

static struct tun_struct *__tun_get(struct tun_file *tfile)
{
	struct tun_struct *tun = NULL;

	if (atomic_inc_not_zero(&tfile->count))
		tun = tfile->tun;

	return tun;
}

static struct tun_struct *tun_get(struct file *file)
{
	return __tun_get(file->private_data);
}

static void tun_put(struct tun_struct *tun)
{
	struct tun_file *tfile = tun->tfile;

	if (atomic_dec_and_test(&tfile->count))
		tun_detach(tfile->tun);
}

/* TAP filterting */
static void addr_hash_set(u32 *mask, const u8 *addr)
{
	int n = ether_crc(ETH_ALEN, addr) >> 26;
	mask[n >> 5] |= (1 << (n & 31));
}

static unsigned int addr_hash_test(const u32 *mask, const u8 *addr)
{
	int n = ether_crc(ETH_ALEN, addr) >> 26;
	return mask[n >> 5] & (1 << (n & 31));
}

static int update_filter(struct tap_filter *filter, void __user *arg)
{
	struct { u8 u[ETH_ALEN]; } *addr;
	struct tun_filter uf;
	int err, alen, n, nexact;

	if (copy_from_user(&uf, arg, sizeof(uf)))
		return -EFAULT;

	if (!uf.count) {
		/* Disabled */
		filter->count = 0;
		return 0;
	}

	alen = ETH_ALEN * uf.count;
	addr = kmalloc(alen, GFP_KERNEL);
	if (!addr)
		return -ENOMEM;

	if (copy_from_user(addr, arg + sizeof(uf), alen)) {
		err = -EFAULT;
		goto done;
	}

	/* The filter is updated without holding any locks. Which is
	 * perfectly safe. We disable it first and in the worst
	 * case we'll accept a few undesired packets. */
	filter->count = 0;
	wmb();

	/* Use first set of addresses as an exact filter */
	for (n = 0; n < uf.count && n < FLT_EXACT_COUNT; n++)
		memcpy(filter->addr[n], addr[n].u, ETH_ALEN);

	nexact = n;

	/* Remaining multicast addresses are hashed,
	 * unicast will leave the filter disabled. */
	memset(filter->mask, 0, sizeof(filter->mask));
	for (; n < uf.count; n++) {
		if (!is_multicast_ether_addr(addr[n].u)) {
			err = 0; /* no filter */
			goto done;
		}
		addr_hash_set(filter->mask, addr[n].u);
	}

	/* For ALLMULTI just set the mask to all ones.
	 * This overrides the mask populated above. */
	if ((uf.flags & TUN_FLT_ALLMULTI))
		memset(filter->mask, ~0, sizeof(filter->mask));

	/* Now enable the filter */
	wmb();
	filter->count = nexact;

	/* Return the number of exact filters */
	err = nexact;

done:
	kfree(addr);
	return err;
}

/* Returns: 0 - drop, !=0 - accept */
static int run_filter(struct tap_filter *filter, const struct sk_buff *skb)
{
	/* Cannot use eth_hdr(skb) here because skb_mac_hdr() is incorrect
	 * at this point. */
	struct ethhdr *eh = (struct ethhdr *) skb->data;
	int i;

	/* Exact match */
	for (i = 0; i < filter->count; i++)
		if (!compare_ether_addr(eh->h_dest, filter->addr[i]))
			return 1;

	/* Inexact match (multicast only) */
	if (is_multicast_ether_addr(eh->h_dest))
		return addr_hash_test(filter->mask, eh->h_dest);

	return 0;
}

/*
 * Checks whether the packet is accepted or not.
 * Returns: 0 - drop, !=0 - accept
 */
static int check_filter(struct tap_filter *filter, const struct sk_buff *skb)
{
	if (!filter->count)
		return 1;

	return run_filter(filter, skb);
}

/* Network device part of the driver */

static const struct ethtool_ops tun_ethtool_ops;

/* Net device detach from fd. */
static void tun_net_uninit(struct net_device *dev)
{
	struct tun_struct *tun = netdev_priv(dev);
	struct tun_file *tfile = tun->tfile;

	/* Inform the methods they need to stop using the dev.
	 */
	if (tfile) {
		wake_up_all(&tun->wq.wait);
		if (atomic_dec_and_test(&tfile->count))
			__tun_detach(tun);
	}
}

static void tun_free_netdev(struct net_device *dev)
{
	struct tun_struct *tun = netdev_priv(dev);

	sock_put(tun->socket.sk);
}

/* Net device open. */
static int tun_net_open(struct net_device *dev)
{
	netif_start_queue(dev);
	return 0;
}

/* Net device close. */
static int tun_net_close(struct net_device *dev)
{
	netif_stop_queue(dev);
	return 0;
}

/* Net device start xmit */
static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct tun_struct *tun = netdev_priv(dev);

	DBG(KERN_INFO "%s: tun_net_xmit %d\n", tun->dev->name, skb->len);

	/* Drop packet if interface is not attached */
	if (!tun->tfile)
		goto drop;

	/* Drop if the filter does not like it.
	 * This is a noop if the filter is disabled.
	 * Filter can be enabled only for the TAP devices. */
	if (!check_filter(&tun->txflt, skb))
		goto drop;

	if (tun->socket.sk->sk_filter &&
	    sk_filter(tun->socket.sk, skb))
		goto drop;

	if (skb_queue_len(&tun->socket.sk->sk_receive_queue) >= dev->tx_queue_len) {
		if (!(tun->flags & TUN_ONE_QUEUE)) {
			/* Normal queueing mode. */
			/* Packet scheduler handles dropping of further packets. */
			netif_stop_queue(dev);

			/* We won't see all dropped packets individually, so overrun
			 * error is more appropriate. */
			dev->stats.tx_fifo_errors++;
		} else {
			/* Single queue mode.
			 * Driver handles dropping of all packets itself. */
			goto drop;
		}
	}

	/* Orphan the skb - required as we might hang on to it
	 * for indefinite time. */
	skb_orphan(skb);

	/* Enqueue packet */
	skb_queue_tail(&tun->socket.sk->sk_receive_queue, skb);

	/* Notify and wake up reader process */
	if (tun->flags & TUN_FASYNC)
		kill_fasync(&tun->fasync, SIGIO, POLL_IN);
	wake_up_interruptible_poll(&tun->wq.wait, POLLIN |
				   POLLRDNORM | POLLRDBAND);
	return NETDEV_TX_OK;

drop:
	dev->stats.tx_dropped++;
	kfree_skb(skb);
	return NETDEV_TX_OK;
}

static void tun_net_mclist(struct net_device *dev)
{
	/*
	 * This callback is supposed to deal with mc filter in
	 * _rx_ path and has nothing to do with the _tx_ path.
	 * In rx path we always accept everything userspace gives us.
	 */
}

#define MIN_MTU 68
#define MAX_MTU 65535

static int
tun_net_change_mtu(struct net_device *dev, int new_mtu)
{
	if (new_mtu < MIN_MTU || new_mtu + dev->hard_header_len > MAX_MTU)
		return -EINVAL;
	dev->mtu = new_mtu;
	return 0;
}

static const struct net_device_ops tun_netdev_ops = {
	.ndo_uninit		= tun_net_uninit,
	.ndo_open		= tun_net_open,
	.ndo_stop		= tun_net_close,
	.ndo_start_xmit		= tun_net_xmit,
	.ndo_change_mtu		= tun_net_change_mtu,
};

static const struct net_device_ops tap_netdev_ops = {
	.ndo_uninit		= tun_net_uninit,
	.ndo_open		= tun_net_open,
	.ndo_stop		= tun_net_close,
	.ndo_start_xmit		= tun_net_xmit,
	.ndo_change_mtu		= tun_net_change_mtu,
	.ndo_set_multicast_list	= tun_net_mclist,
	.ndo_set_mac_address	= eth_mac_addr,
	.ndo_validate_addr	= eth_validate_addr,
};

/* Initialize net device. */
static void tun_net_init(struct net_device *dev)
{
	struct tun_struct *tun = netdev_priv(dev);

	switch (tun->flags & TUN_TYPE_MASK) {
	case TUN_TUN_DEV:
		dev->netdev_ops = &tun_netdev_ops;

		/* Point-to-Point TUN Device */
		dev->hard_header_len = 0;
		dev->addr_len = 0;
		dev->mtu = 1500;

		/* Zero header length */
		dev->type = ARPHRD_NONE;
		dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;
		dev->tx_queue_len = TUN_READQ_SIZE;  /* We prefer our own queue length */
		break;

	case TUN_TAP_DEV:
		dev->netdev_ops = &tap_netdev_ops;
		/* Ethernet TAP Device */
		ether_setup(dev);

		random_ether_addr(dev->dev_addr);

		dev->tx_queue_len = TUN_READQ_SIZE;  /* We prefer our own queue length */
		break;
	}
}

/* Character device part */

/* Poll */
static unsigned int tun_chr_poll(struct file *file, poll_table * wait)
{
	struct tun_file *tfile = file->private_data;
	struct tun_struct *tun = __tun_get(tfile);
	struct sock *sk;
	unsigned int mask = 0;

	if (!tun)
		return POLLERR;

	sk = tun->socket.sk;

	DBG(KERN_INFO "%s: tun_chr_poll\n", tun->dev->name);

	poll_wait(file, &tun->wq.wait, wait);

	if (!skb_queue_empty(&sk->sk_receive_queue))
		mask |= POLLIN | POLLRDNORM;

	if (sock_writeable(sk) ||
	    (!test_and_set_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags) &&
	     sock_writeable(sk)))
		mask |= POLLOUT | POLLWRNORM;

	if (tun->dev->reg_state != NETREG_REGISTERED)
		mask = POLLERR;

	tun_put(tun);
	return mask;
}

/* prepad is the amount to reserve at front.  len is length after that.
 * linear is a hint as to how much to copy (usually headers). */
static inline struct sk_buff *tun_alloc_skb(struct tun_struct *tun,
					    size_t prepad, size_t len,
					    size_t linear, int noblock)
{
	struct sock *sk = tun->socket.sk;
	struct sk_buff *skb;
	int err;

	/* Under a page?  Don't bother with paged skb. */
	if (prepad + len < PAGE_SIZE || !linear)
		linear = len;

	skb = sock_alloc_send_pskb(sk, prepad + linear, len - linear, noblock,
				   &err);
	if (!skb)
		return ERR_PTR(err);

	skb_reserve(skb, prepad);
	skb_put(skb, linear);
	skb->data_len = len - linear;
	skb->len += len - linear;

	return skb;
}

/* Get packet from user space buffer */
static __inline__ ssize_t tun_get_user(struct tun_struct *tun,
				       const struct iovec *iv, size_t count,
				       int noblock)
{
	struct tun_pi pi = { 0, cpu_to_be16(ETH_P_IP) };
	struct sk_buff *skb;
	size_t len = count, align = 0;
	struct virtio_net_hdr gso = { 0 };
	int offset = 0;

	if (!(tun->flags & TUN_NO_PI)) {
		if ((len -= sizeof(pi)) > count)
			return -EINVAL;

		if (memcpy_fromiovecend((void *)&pi, iv, 0, sizeof(pi)))
			return -EFAULT;
		offset += sizeof(pi);
	}

	if (tun->flags & TUN_VNET_HDR) {
		if ((len -= tun->vnet_hdr_sz) > count)
			return -EINVAL;

		if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
			return -EFAULT;

		if ((gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
		    gso.csum_start + gso.csum_offset + 2 > gso.hdr_len)
			gso.hdr_len = gso.csum_start + gso.csum_offset + 2;

		if (gso.hdr_len > len)
			return -EINVAL;
		offset += tun->vnet_hdr_sz;
	}

	if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {
		align = NET_IP_ALIGN;
		if (unlikely(len < ETH_HLEN ||
			     (gso.hdr_len && gso.hdr_len < ETH_HLEN)))
			return -EINVAL;
	}

	skb = tun_alloc_skb(tun, align, len, gso.hdr_len, noblock);
	if (IS_ERR(skb)) {
		if (PTR_ERR(skb) != -EAGAIN)
			tun->dev->stats.rx_dropped++;
		return PTR_ERR(skb);
	}

	if (skb_copy_datagram_from_iovec(skb, 0, iv, offset, len)) {
		tun->dev->stats.rx_dropped++;
		kfree_skb(skb);
		return -EFAULT;
	}

	if (gso.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
		if (!skb_partial_csum_set(skb, gso.csum_start,
					  gso.csum_offset)) {
			tun->dev->stats.rx_frame_errors++;
			kfree_skb(skb);
			return -EINVAL;
		}
	} else if (tun->flags & TUN_NOCHECKSUM)
		skb->ip_summed = CHECKSUM_UNNECESSARY;

	switch (tun->flags & TUN_TYPE_MASK) {
	case TUN_TUN_DEV:
		if (tun->flags & TUN_NO_PI) {
			switch (skb->data[0] & 0xf0) {
			case 0x40:
				pi.proto = htons(ETH_P_IP);
				break;
			case 0x60:
				pi.proto = htons(ETH_P_IPV6);
				break;
			default:
				tun->dev->stats.rx_dropped++;
				kfree_skb(skb);
				return -EINVAL;
			}
		}

		skb_reset_mac_header(skb);
		skb->protocol = pi.proto;
		skb->dev = tun->dev;
		break;
	case TUN_TAP_DEV:
		skb->protocol = eth_type_trans(skb, tun->dev);
		break;
	};

	if (gso.gso_type != VIRTIO_NET_HDR_GSO_NONE) {
		pr_debug("GSO!\n");
		switch (gso.gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
		case VIRTIO_NET_HDR_GSO_TCPV4:
			skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
			break;
		case VIRTIO_NET_HDR_GSO_TCPV6:
			skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
			break;
		case VIRTIO_NET_HDR_GSO_UDP:
			skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
			break;
		default:
			tun->dev->stats.rx_frame_errors++;
			kfree_skb(skb);
			return -EINVAL;
		}

		if (gso.gso_type & VIRTIO_NET_HDR_GSO_ECN)
			skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;

		skb_shinfo(skb)->gso_size = gso.gso_size;
		if (skb_shinfo(skb)->gso_size == 0) {
			tun->dev->stats.rx_frame_errors++;
			kfree_skb(skb);
			return -EINVAL;
		}

		/* Header must be checked, and gso_segs computed. */
		skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;
		skb_shinfo(skb)->gso_segs = 0;
	}

	netif_rx_ni(skb);

	tun->dev->stats.rx_packets++;
	tun->dev->stats.rx_bytes += len;

	return count;
}

static ssize_t tun_chr_aio_write(struct kiocb *iocb, const struct iovec *iv,
			      unsigned long count, loff_t pos)
{
	struct file *file = iocb->ki_filp;
	struct tun_struct *tun = tun_get(file);
	ssize_t result;

	if (!tun)
		return -EBADFD;

	DBG(KERN_INFO "%s: tun_chr_write %ld\n", tun->dev->name, count);

	result = tun_get_user(tun, iv, iov_length(iv, count),
			      file->f_flags & O_NONBLOCK);

	tun_put(tun);
	return result;
}

/* Put packet to the user space buffer */
static __inline__ ssize_t tun_put_user(struct tun_struct *tun,
				       struct sk_buff *skb,
				       const struct iovec *iv, int len)
{
	struct tun_pi pi = { 0, skb->protocol };
	ssize_t total = 0;

	if (!(tun->flags & TUN_NO_PI)) {
		if ((len -= sizeof(pi)) < 0)
			return -EINVAL;

		if (len < skb->len) {
			/* Packet will be striped */
			pi.flags |= TUN_PKT_STRIP;
		}

		if (memcpy_toiovecend(iv, (void *) &pi, 0, sizeof(pi)))
			return -EFAULT;
		total += sizeof(pi);
	}

	if (tun->flags & TUN_VNET_HDR) {
		struct virtio_net_hdr gso = { 0 }; /* no info leak */
		if ((len -= tun->vnet_hdr_sz) < 0)
			return -EINVAL;

		if (skb_is_gso(skb)) {
			struct skb_shared_info *sinfo = skb_shinfo(skb);

			/* This is a hint as to how much should be linear. */
			gso.hdr_len = skb_headlen(skb);
			gso.gso_size = sinfo->gso_size;
			if (sinfo->gso_type & SKB_GSO_TCPV4)
				gso.gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
			else if (sinfo->gso_type & SKB_GSO_TCPV6)
				gso.gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
			else if (sinfo->gso_type & SKB_GSO_UDP)
				gso.gso_type = VIRTIO_NET_HDR_GSO_UDP;
			else
				BUG();
			if (sinfo->gso_type & SKB_GSO_TCP_ECN)
				gso.gso_type |= VIRTIO_NET_HDR_GSO_ECN;
		} else
			gso.gso_type = VIRTIO_NET_HDR_GSO_NONE;

		if (skb->ip_summed == CHECKSUM_PARTIAL) {
			gso.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
			gso.csum_start = skb->csum_start - skb_headroom(skb);
			gso.csum_offset = skb->csum_offset;
		} /* else everything is zero */

		if (unlikely(memcpy_toiovecend(iv, (void *)&gso, total,
					       sizeof(gso))))
			return -EFAULT;
		total += tun->vnet_hdr_sz;
	}

	len = min_t(int, skb->len, len);

	skb_copy_datagram_const_iovec(skb, 0, iv, total, len);
	total += skb->len;

	tun->dev->stats.tx_packets++;
	tun->dev->stats.tx_bytes += len;

	return total;
}

static ssize_t tun_do_read(struct tun_struct *tun,
			   struct kiocb *iocb, const struct iovec *iv,
			   ssize_t len, int noblock)
{
	DECLARE_WAITQUEUE(wait, current);
	struct sk_buff *skb;
	ssize_t ret = 0;

	DBG(KERN_INFO "%s: tun_chr_read\n", tun->dev->name);

	add_wait_queue(&tun->wq.wait, &wait);
	while (len) {
		current->state = TASK_INTERRUPTIBLE;

		/* Read frames from the queue */
		if (!(skb=skb_dequeue(&tun->socket.sk->sk_receive_queue))) {
			if (noblock) {
				ret = -EAGAIN;
				break;
			}
			if (signal_pending(current)) {
				ret = -ERESTARTSYS;
				break;
			}
			if (tun->dev->reg_state != NETREG_REGISTERED) {
				ret = -EIO;
				break;
			}

			/* Nothing to read, let's sleep */
			schedule();
			continue;
		}
		netif_wake_queue(tun->dev);

		ret = tun_put_user(tun, skb, iv, len);
		kfree_skb(skb);
		break;
	}

	current->state = TASK_RUNNING;
	remove_wait_queue(&tun->wq.wait, &wait);

	return ret;
}

static ssize_t tun_chr_aio_read(struct kiocb *iocb, const struct iovec *iv,
			    unsigned long count, loff_t pos)
{
	struct file *file = iocb->ki_filp;
	struct tun_file *tfile = file->private_data;
	struct tun_struct *tun = __tun_get(tfile);
	ssize_t len, ret;

	if (!tun)
		return -EBADFD;
	len = iov_length(iv, count);
	if (len < 0) {
		ret = -EINVAL;
		goto out;
	}

	ret = tun_do_read(tun, iocb, iv, len, file->f_flags & O_NONBLOCK);
	ret = min_t(ssize_t, ret, len);
out:
	tun_put(tun);
	return ret;
}

static void tun_setup(struct net_device *dev)
{
	struct tun_struct *tun = netdev_priv(dev);

	tun->owner = -1;
	tun->group = -1;

	dev->ethtool_ops = &tun_ethtool_ops;
	dev->destructor = tun_free_netdev;
}

/* Trivial set of netlink ops to allow deleting tun or tap
 * device with netlink.
 */
static int tun_validate(struct nlattr *tb[], struct nlattr *data[])
{
	return -EINVAL;
}

static struct rtnl_link_ops tun_link_ops __read_mostly = {
	.kind		= DRV_NAME,
	.priv_size	= sizeof(struct tun_struct),
	.setup		= tun_setup,
	.validate	= tun_validate,
};

static void tun_sock_write_space(struct sock *sk)
{
	struct tun_struct *tun;
	wait_queue_head_t *wqueue;

	if (!sock_writeable(sk))
		return;

	if (!test_and_clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags))
		return;

	wqueue = sk_sleep(sk);
	if (wqueue && waitqueue_active(wqueue))
		wake_up_interruptible_sync_poll(wqueue, POLLOUT |
						POLLWRNORM | POLLWRBAND);

	tun = tun_sk(sk)->tun;
	kill_fasync(&tun->fasync, SIGIO, POLL_OUT);
}

static void tun_sock_destruct(struct sock *sk)
{
	free_netdev(tun_sk(sk)->tun->dev);
}

static int tun_sendmsg(struct kiocb *iocb, struct socket *sock,
		       struct msghdr *m, size_t total_len)
{
	struct tun_struct *tun = container_of(sock, struct tun_struct, socket);
	return tun_get_user(tun, m->msg_iov, total_len,
			    m->msg_flags & MSG_DONTWAIT);
}

static int tun_recvmsg(struct kiocb *iocb, struct socket *sock,
		       struct msghdr *m, size_t total_len,
		       int flags)
{
	struct tun_struct *tun = container_of(sock, struct tun_struct, socket);
	int ret;
	if (flags & ~(MSG_DONTWAIT|MSG_TRUNC))
		return -EINVAL;
	ret = tun_do_read(tun, iocb, m->msg_iov, total_len,
			  flags & MSG_DONTWAIT);
	if (ret > total_len) {
		m->msg_flags |= MSG_TRUNC;
		ret = flags & MSG_TRUNC ? ret : total_len;
	}
	return ret;
}

/* Ops structure to mimic raw sockets with tun */
static const struct proto_ops tun_socket_ops = {
	.sendmsg = tun_sendmsg,
	.recvmsg = tun_recvmsg,
};

static struct proto tun_proto = {
	.name		= "tun",
	.owner		= THIS_MODULE,
	.obj_size	= sizeof(struct tun_sock),
};

static int tun_flags(struct tun_struct *tun)
{
	int flags = 0;

	if (tun->flags & TUN_TUN_DEV)
		flags |= IFF_TUN;
	else
		flags |= IFF_TAP;

	if (tun->flags & TUN_NO_PI)
		flags |= IFF_NO_PI;

	if (tun->flags & TUN_ONE_QUEUE)
		flags |= IFF_ONE_QUEUE;

	if (tun->flags & TUN_VNET_HDR)
		flags |= IFF_VNET_HDR;

	return flags;
}

static ssize_t tun_show_flags(struct device *dev, struct device_attribute *attr,
			      char *buf)
{
	struct tun_struct *tun = netdev_priv(to_net_dev(dev));
	return sprintf(buf, "0x%x\n", tun_flags(tun));
}

static ssize_t tun_show_owner(struct device *dev, struct device_attribute *attr,
			      char *buf)
{
	struct tun_struct *tun = netdev_priv(to_net_dev(dev));
	return sprintf(buf, "%d\n", tun->owner);
}

static ssize_t tun_show_group(struct device *dev, struct device_attribute *attr,
			      char *buf)
{
	struct tun_struct *tun = netdev_priv(to_net_dev(dev));
	return sprintf(buf, "%d\n", tun->group);
}

static DEVICE_ATTR(tun_flags, 0444, tun_show_flags, NULL);
static DEVICE_ATTR(owner, 0444, tun_show_owner, NULL);
static DEVICE_ATTR(group, 0444, tun_show_group, NULL);

static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
{
	struct sock *sk;
	struct tun_struct *tun;
	struct net_device *dev;
	int err;

	dev = __dev_get_by_name(net, ifr->ifr_name);
	if (dev) {
		const struct cred *cred = current_cred();

		if (ifr->ifr_flags & IFF_TUN_EXCL)
			return -EBUSY;
		if ((ifr->ifr_flags & IFF_TUN) && dev->netdev_ops == &tun_netdev_ops)
			tun = netdev_priv(dev);
		else if ((ifr->ifr_flags & IFF_TAP) && dev->netdev_ops == &tap_netdev_ops)
			tun = netdev_priv(dev);
		else
			return -EINVAL;

		if (((tun->owner != -1 && cred->euid != tun->owner) ||
		     (tun->group != -1 && !in_egroup_p(tun->group))) &&
		    !capable(CAP_NET_ADMIN))
			return -EPERM;
		err = security_tun_dev_attach(tun->socket.sk);
		if (err < 0)
			return err;

		err = tun_attach(tun, file);
		if (err < 0)
			return err;
	}
	else {
		char *name;
		unsigned long flags = 0;

		if (!capable(CAP_NET_ADMIN))
			return -EPERM;
		err = security_tun_dev_create();
		if (err < 0)
			return err;

		/* Set dev type */
		if (ifr->ifr_flags & IFF_TUN) {
			/* TUN device */
			flags |= TUN_TUN_DEV;
			name = "tun%d";
		} else if (ifr->ifr_flags & IFF_TAP) {
			/* TAP device */
			flags |= TUN_TAP_DEV;
			name = "tap%d";
		} else
			return -EINVAL;

		if (*ifr->ifr_name)
			name = ifr->ifr_name;

		dev = alloc_netdev(sizeof(struct tun_struct), name,
				   tun_setup);
		if (!dev)
			return -ENOMEM;

		dev_net_set(dev, net);
		dev->rtnl_link_ops = &tun_link_ops;

		tun = netdev_priv(dev);
		tun->dev = dev;
		tun->flags = flags;
		tun->txflt.count = 0;
		tun->vnet_hdr_sz = sizeof(struct virtio_net_hdr);

		err = -ENOMEM;
		sk = sk_alloc(net, AF_UNSPEC, GFP_KERNEL, &tun_proto);
		if (!sk)
			goto err_free_dev;

		tun->socket.wq = &tun->wq;
		init_waitqueue_head(&tun->wq.wait);
		tun->socket.ops = &tun_socket_ops;
		sock_init_data(&tun->socket, sk);
		sk->sk_write_space = tun_sock_write_space;
		sk->sk_sndbuf = INT_MAX;

		tun_sk(sk)->tun = tun;

		security_tun_dev_post_create(sk);

		tun_net_init(dev);

		if (strchr(dev->name, '%')) {
			err = dev_alloc_name(dev, dev->name);
			if (err < 0)
				goto err_free_sk;
		}

		err = register_netdevice(tun->dev);
		if (err < 0)
			goto err_free_sk;

		if (device_create_file(&tun->dev->dev, &dev_attr_tun_flags) ||
		    device_create_file(&tun->dev->dev, &dev_attr_owner) ||
		    device_create_file(&tun->dev->dev, &dev_attr_group))
			printk(KERN_ERR "Failed to create tun sysfs files\n");

		sk->sk_destruct = tun_sock_destruct;

		err = tun_attach(tun, file);
		if (err < 0)
			goto failed;
	}

	DBG(KERN_INFO "%s: tun_set_iff\n", tun->dev->name);

	if (ifr->ifr_flags & IFF_NO_PI)
		tun->flags |= TUN_NO_PI;
	else
		tun->flags &= ~TUN_NO_PI;

	if (ifr->ifr_flags & IFF_ONE_QUEUE)
		tun->flags |= TUN_ONE_QUEUE;
	else
		tun->flags &= ~TUN_ONE_QUEUE;

	if (ifr->ifr_flags & IFF_VNET_HDR)
		tun->flags |= TUN_VNET_HDR;
	else
		tun->flags &= ~TUN_VNET_HDR;

	/* Make sure persistent devices do not get stuck in
	 * xoff state.
	 */
	if (netif_running(tun->dev))
		netif_wake_queue(tun->dev);

	strcpy(ifr->ifr_name, tun->dev->name);
	return 0;

 err_free_sk:
	sock_put(sk);
 err_free_dev:
	free_netdev(dev);
 failed:
	return err;
}

static int tun_get_iff(struct net *net, struct tun_struct *tun,
		       struct ifreq *ifr)
{
	DBG(KERN_INFO "%s: tun_get_iff\n", tun->dev->name);

	strcpy(ifr->ifr_name, tun->dev->name);

	ifr->ifr_flags = tun_flags(tun);

	return 0;
}

/* This is like a cut-down ethtool ops, except done via tun fd so no
 * privs required. */
static int set_offload(struct net_device *dev, unsigned long arg)
{
	unsigned int old_features, features;

	old_features = dev->features;
	/* Unset features, set them as we chew on the arg. */
	features = (old_features & ~(NETIF_F_HW_CSUM|NETIF_F_SG|NETIF_F_FRAGLIST
				    |NETIF_F_TSO_ECN|NETIF_F_TSO|NETIF_F_TSO6
				    |NETIF_F_UFO));

	if (arg & TUN_F_CSUM) {
		features |= NETIF_F_HW_CSUM|NETIF_F_SG|NETIF_F_FRAGLIST;
		arg &= ~TUN_F_CSUM;

		if (arg & (TUN_F_TSO4|TUN_F_TSO6)) {
			if (arg & TUN_F_TSO_ECN) {
				features |= NETIF_F_TSO_ECN;
				arg &= ~TUN_F_TSO_ECN;
			}
			if (arg & TUN_F_TSO4)
				features |= NETIF_F_TSO;
			if (arg & TUN_F_TSO6)
				features |= NETIF_F_TSO6;
			arg &= ~(TUN_F_TSO4|TUN_F_TSO6);
		}

		if (arg & TUN_F_UFO) {
			features |= NETIF_F_UFO;
			arg &= ~TUN_F_UFO;
		}
	}

	/* This gives the user a way to test for new features in future by
	 * trying to set them. */
	if (arg)
		return -EINVAL;

	dev->features = features;
	if (old_features != dev->features)
		netdev_features_change(dev);

	return 0;
}

static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
			    unsigned long arg, int ifreq_len)
{
	struct tun_file *tfile = file->private_data;
	struct tun_struct *tun;
	void __user* argp = (void __user*)arg;
	struct sock_fprog fprog;
	struct ifreq ifr;
	int sndbuf;
	int vnet_hdr_sz;
	int ret;

	if (cmd == TUNSETIFF || _IOC_TYPE(cmd) == 0x89)
		if (copy_from_user(&ifr, argp, ifreq_len))
			return -EFAULT;

	if (cmd == TUNGETFEATURES) {
		/* Currently this just means: "what IFF flags are valid?".
		 * This is needed because we never checked for invalid flags on
		 * TUNSETIFF. */
		return put_user(IFF_TUN | IFF_TAP | IFF_NO_PI | IFF_ONE_QUEUE |
				IFF_VNET_HDR,
				(unsigned int __user*)argp);
	}

	rtnl_lock();

	tun = __tun_get(tfile);
	if (cmd == TUNSETIFF && !tun) {
		ifr.ifr_name[IFNAMSIZ-1] = '\0';

		ret = tun_set_iff(tfile->net, file, &ifr);

		if (ret)
			goto unlock;

		if (copy_to_user(argp, &ifr, ifreq_len))
			ret = -EFAULT;
		goto unlock;
	}

	ret = -EBADFD;
	if (!tun)
		goto unlock;

	DBG(KERN_INFO "%s: tun_chr_ioctl cmd %d\n", tun->dev->name, cmd);

	ret = 0;
	switch (cmd) {
	case TUNGETIFF:
		ret = tun_get_iff(current->nsproxy->net_ns, tun, &ifr);
		if (ret)
			break;

		if (copy_to_user(argp, &ifr, ifreq_len))
			ret = -EFAULT;
		break;

	case TUNSETNOCSUM:
		/* Disable/Enable checksum */
		if (arg)
			tun->flags |= TUN_NOCHECKSUM;
		else
			tun->flags &= ~TUN_NOCHECKSUM;

		DBG(KERN_INFO "%s: checksum %s\n",
		    tun->dev->name, arg ? "disabled" : "enabled");
		break;

	case TUNSETPERSIST:
		/* Disable/Enable persist mode */
		if (arg)
			tun->flags |= TUN_PERSIST;
		else
			tun->flags &= ~TUN_PERSIST;

		DBG(KERN_INFO "%s: persist %s\n",
		    tun->dev->name, arg ? "enabled" : "disabled");
		break;

	case TUNSETOWNER:
		/* Set owner of the device */
		tun->owner = (uid_t) arg;

		DBG(KERN_INFO "%s: owner set to %d\n", tun->dev->name, tun->owner);
		break;

	case TUNSETGROUP:
		/* Set group of the device */
		tun->group= (gid_t) arg;

		DBG(KERN_INFO "%s: group set to %d\n", tun->dev->name, tun->group);
		break;

	case TUNSETLINK:
		/* Only allow setting the type when the interface is down */
		if (tun->dev->flags & IFF_UP) {
			DBG(KERN_INFO "%s: Linktype set failed because interface is up\n",
				tun->dev->name);
			ret = -EBUSY;
		} else {
			tun->dev->type = (int) arg;
			DBG(KERN_INFO "%s: linktype set to %d\n", tun->dev->name, tun->dev->type);
			ret = 0;
		}
		break;

#ifdef TUN_DEBUG
	case TUNSETDEBUG:
		tun->debug = arg;
		break;
#endif
	case TUNSETOFFLOAD:
		ret = set_offload(tun->dev, arg);
		break;

	case TUNSETTXFILTER:
		/* Can be set only for TAPs */
		ret = -EINVAL;
		if ((tun->flags & TUN_TYPE_MASK) != TUN_TAP_DEV)
			break;
		ret = update_filter(&tun->txflt, (void __user *)arg);
		break;

	case SIOCGIFHWADDR:
		/* Get hw addres */
		memcpy(ifr.ifr_hwaddr.sa_data, tun->dev->dev_addr, ETH_ALEN);
		ifr.ifr_hwaddr.sa_family = tun->dev->type;
		if (copy_to_user(argp, &ifr, ifreq_len))
			ret = -EFAULT;
		break;

	case SIOCSIFHWADDR:
		/* Set hw address */
		DBG(KERN_DEBUG "%s: set hw address: %pM\n",
			tun->dev->name, ifr.ifr_hwaddr.sa_data);

		ret = dev_set_mac_address(tun->dev, &ifr.ifr_hwaddr);
		break;

	case TUNGETSNDBUF:
		sndbuf = tun->socket.sk->sk_sndbuf;
		if (copy_to_user(argp, &sndbuf, sizeof(sndbuf)))
			ret = -EFAULT;
		break;

	case TUNSETSNDBUF:
		if (copy_from_user(&sndbuf, argp, sizeof(sndbuf))) {
			ret = -EFAULT;
			break;
		}

		tun->socket.sk->sk_sndbuf = sndbuf;
		break;

	case TUNGETVNETHDRSZ:
		vnet_hdr_sz = tun->vnet_hdr_sz;
		if (copy_to_user(argp, &vnet_hdr_sz, sizeof(vnet_hdr_sz)))
			ret = -EFAULT;
		break;

	case TUNSETVNETHDRSZ:
		if (copy_from_user(&vnet_hdr_sz, argp, sizeof(vnet_hdr_sz))) {
			ret = -EFAULT;
			break;
		}
		if (vnet_hdr_sz < (int)sizeof(struct virtio_net_hdr)) {
			ret = -EINVAL;
			break;
		}

		tun->vnet_hdr_sz = vnet_hdr_sz;
		break;

	case TUNATTACHFILTER:
		/* Can be set only for TAPs */
		ret = -EINVAL;
		if ((tun->flags & TUN_TYPE_MASK) != TUN_TAP_DEV)
			break;
		ret = -EFAULT;
		if (copy_from_user(&fprog, argp, sizeof(fprog)))
			break;

		ret = sk_attach_filter(&fprog, tun->socket.sk);
		break;

	case TUNDETACHFILTER:
		/* Can be set only for TAPs */
		ret = -EINVAL;
		if ((tun->flags & TUN_TYPE_MASK) != TUN_TAP_DEV)
			break;
		ret = sk_detach_filter(tun->socket.sk);
		break;

	default:
		ret = -EINVAL;
		break;
	}

unlock:
	rtnl_unlock();
	if (tun)
		tun_put(tun);
	return ret;
}

static long tun_chr_ioctl(struct file *file,
			  unsigned int cmd, unsigned long arg)
{
	return __tun_chr_ioctl(file, cmd, arg, sizeof (struct ifreq));
}

#ifdef CONFIG_COMPAT
static long tun_chr_compat_ioctl(struct file *file,
			 unsigned int cmd, unsigned long arg)
{
	switch (cmd) {
	case TUNSETIFF:
	case TUNGETIFF:
	case TUNSETTXFILTER:
	case TUNGETSNDBUF:
	case TUNSETSNDBUF:
	case SIOCGIFHWADDR:
	case SIOCSIFHWADDR:
		arg = (unsigned long)compat_ptr(arg);
		break;
	default:
		arg = (compat_ulong_t)arg;
		break;
	}

	/*
	 * compat_ifreq is shorter than ifreq, so we must not access beyond
	 * the end of that structure. All fields that are used in this
	 * driver are compatible though, we don't need to convert the
	 * contents.
	 */
	return __tun_chr_ioctl(file, cmd, arg, sizeof(struct compat_ifreq));
}
#endif /* CONFIG_COMPAT */

static int tun_chr_fasync(int fd, struct file *file, int on)
{
	struct tun_struct *tun = tun_get(file);
	int ret;

	if (!tun)
		return -EBADFD;

	DBG(KERN_INFO "%s: tun_chr_fasync %d\n", tun->dev->name, on);

	if ((ret = fasync_helper(fd, file, on, &tun->fasync)) < 0)
		goto out;

	if (on) {
		ret = __f_setown(file, task_pid(current), PIDTYPE_PID, 0);
		if (ret)
			goto out;
		tun->flags |= TUN_FASYNC;
	} else
		tun->flags &= ~TUN_FASYNC;
	ret = 0;
out:
	tun_put(tun);
	return ret;
}

static int tun_chr_open(struct inode *inode, struct file * file)
{
	struct tun_file *tfile;

	DBG1(KERN_INFO "tunX: tun_chr_open\n");

	tfile = kmalloc(sizeof(*tfile), GFP_KERNEL);
	if (!tfile)
		return -ENOMEM;
	atomic_set(&tfile->count, 0);
	tfile->tun = NULL;
	tfile->net = get_net(current->nsproxy->net_ns);
	file->private_data = tfile;
	return 0;
}

static int tun_chr_close(struct inode *inode, struct file *file)
{
	struct tun_file *tfile = file->private_data;
	struct tun_struct *tun;

	tun = __tun_get(tfile);
	if (tun) {
		struct net_device *dev = tun->dev;

		DBG(KERN_INFO "%s: tun_chr_close\n", dev->name);

		__tun_detach(tun);

		/* If desirable, unregister the netdevice. */
		if (!(tun->flags & TUN_PERSIST)) {
			rtnl_lock();
			if (dev->reg_state == NETREG_REGISTERED)
				unregister_netdevice(dev);
			rtnl_unlock();
		}
	}

	tun = tfile->tun;
	if (tun)
		sock_put(tun->socket.sk);

	put_net(tfile->net);
	kfree(tfile);

	return 0;
}

static const struct file_operations tun_fops = {
	.owner	= THIS_MODULE,
	.llseek = no_llseek,
	.read  = do_sync_read,
	.aio_read  = tun_chr_aio_read,
	.write = do_sync_write,
	.aio_write = tun_chr_aio_write,
	.poll	= tun_chr_poll,
	.unlocked_ioctl	= tun_chr_ioctl,
#ifdef CONFIG_COMPAT
	.compat_ioctl = tun_chr_compat_ioctl,
#endif
	.open	= tun_chr_open,
	.release = tun_chr_close,
	.fasync = tun_chr_fasync
};

static struct miscdevice tun_miscdev = {
	.minor = TUN_MINOR,
	.name = "tun",
	.nodename = "net/tun",
	.fops = &tun_fops,
};

/* ethtool interface */

static int tun_get_settings(struct net_device *dev, struct ethtool_cmd *cmd)
{
	cmd->supported		= 0;
	cmd->advertising	= 0;
	cmd->speed		= SPEED_10;
	cmd->duplex		= DUPLEX_FULL;
	cmd->port		= PORT_TP;
	cmd->phy_address	= 0;
	cmd->transceiver	= XCVR_INTERNAL;
	cmd->autoneg		= AUTONEG_DISABLE;
	cmd->maxtxpkt		= 0;
	cmd->maxrxpkt		= 0;
	return 0;
}

static void tun_get_drvinfo(struct net_device *dev, struct ethtool_drvinfo *info)
{
	struct tun_struct *tun = netdev_priv(dev);

	strcpy(info->driver, DRV_NAME);
	strcpy(info->version, DRV_VERSION);
	strcpy(info->fw_version, "N/A");

	switch (tun->flags & TUN_TYPE_MASK) {
	case TUN_TUN_DEV:
		strcpy(info->bus_info, "tun");
		break;
	case TUN_TAP_DEV:
		strcpy(info->bus_info, "tap");
		break;
	}
}

static u32 tun_get_msglevel(struct net_device *dev)
{
#ifdef TUN_DEBUG
	struct tun_struct *tun = netdev_priv(dev);
	return tun->debug;
#else
	return -EOPNOTSUPP;
#endif
}

static void tun_set_msglevel(struct net_device *dev, u32 value)
{
#ifdef TUN_DEBUG
	struct tun_struct *tun = netdev_priv(dev);
	tun->debug = value;
#endif
}

static u32 tun_get_link(struct net_device *dev)
{
	struct tun_struct *tun = netdev_priv(dev);
	return !!tun->tfile;
}

static u32 tun_get_rx_csum(struct net_device *dev)
{
	struct tun_struct *tun = netdev_priv(dev);
	return (tun->flags & TUN_NOCHECKSUM) == 0;
}

static int tun_set_rx_csum(struct net_device *dev, u32 data)
{
	struct tun_struct *tun = netdev_priv(dev);
	if (data)
		tun->flags &= ~TUN_NOCHECKSUM;
	else
		tun->flags |= TUN_NOCHECKSUM;
	return 0;
}

static const struct ethtool_ops tun_ethtool_ops = {
	.get_settings	= tun_get_settings,
	.get_drvinfo	= tun_get_drvinfo,
	.get_msglevel	= tun_get_msglevel,
	.set_msglevel	= tun_set_msglevel,
	.get_link	= tun_get_link,
	.get_rx_csum	= tun_get_rx_csum,
	.set_rx_csum	= tun_set_rx_csum
};


static int __init tun_init(void)
{
	int ret = 0;

	printk(KERN_INFO "tun: %s, %s\n", DRV_DESCRIPTION, DRV_VERSION);
	printk(KERN_INFO "tun: %s\n", DRV_COPYRIGHT);

	ret = rtnl_link_register(&tun_link_ops);
	if (ret) {
		printk(KERN_ERR "tun: Can't register link_ops\n");
		goto err_linkops;
	}

	ret = misc_register(&tun_miscdev);
	if (ret) {
		printk(KERN_ERR "tun: Can't register misc device %d\n", TUN_MINOR);
		goto err_misc;
	}
	return  0;
err_misc:
	rtnl_link_unregister(&tun_link_ops);
err_linkops:
	return ret;
}

static void tun_cleanup(void)
{
	misc_deregister(&tun_miscdev);
	rtnl_link_unregister(&tun_link_ops);
}

/* Get an underlying socket object from tun file.  Returns error unless file is
 * attached to a device.  The returned object works like a packet socket, it
 * can be used for sock_sendmsg/sock_recvmsg.  The caller is responsible for
 * holding a reference to the file for as long as the socket is in use. */
struct socket *tun_get_socket(struct file *file)
{
	struct tun_struct *tun;
	if (file->f_op != &tun_fops)
		return ERR_PTR(-EINVAL);
	tun = tun_get(file);
	if (!tun)
		return ERR_PTR(-EBADFD);
	tun_put(tun);
	return &tun->socket;
}
EXPORT_SYMBOL_GPL(tun_get_socket);

module_init(tun_init);
module_exit(tun_cleanup);
MODULE_DESCRIPTION(DRV_DESCRIPTION);
MODULE_AUTHOR(DRV_COPYRIGHT);
MODULE_LICENSE("GPL");
MODULE_ALIAS_MISCDEV(TUN_MINOR);