tun.c

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/*
 *  TUN - Universal TUN/TAP device driver.
 *  Copyright (C) 1999-2002 Maxim Krasnyansky <[email protected]>
 *
 *  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 <[email protected]> 2005/08/14
 *    Add TUNSETLINK ioctl to set the link encapsulation
 *
 *  Mark Smith <[email protected]>
 *    Use eth_random_addr() for tap MAC address.
 *
 *  Harald Roelle <[email protected]>  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 <[email protected]>
 *    Modifications for 2.3.99-pre5 kernel.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#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 <[email protected]>"

#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 <net/cls_cgroup.h>

#include <asm/uaccess.h>

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

#ifdef TUN_DEBUG
static int debug;

#define tun_debug(level, tun, fmt, args...)         \
do {                                \
    if (tun->debug)                     \
        netdev_printk(level, tun->dev, fmt, ##args);    \
} while (0)
#define DBG1(level, fmt, args...)               \
do {                                \
    if (debug == 2)                     \
        printk(level fmt, ##args);          \
} while (0)
#else
#define tun_debug(level, tun, fmt, args...)         \
do {                                \
    if (0)                          \
        netdev_printk(level, tun->dev, fmt, ##args);    \
} while (0)
#define DBG1(level, fmt, args...)               \
do {                                \
    if (0)                          \
        printk(level fmt, ##args);          \
} while (0)
#endif

#define GOODCOPY_LEN 128

#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;
    kuid_t          owner;
    kgid_t          group;

    struct net_device   *dev;
    netdev_features_t   set_features;
#define TUN_USER_FEATURES (NETIF_F_HW_CSUM|NETIF_F_TSO_ECN|NETIF_F_TSO| \
              NETIF_F_TSO6|NETIF_F_UFO)
    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;
    netif_carrier_on(tun->dev);
    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);
    netif_carrier_off(tun->dev);
    tun->tfile = 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 filtering */
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 (ether_addr_equal(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);

    BUG_ON(!test_bit(SOCK_EXTERNALLY_ALLOCATED, &tun->socket.flags));

    sk_release_kernel(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);

    tun_debug(KERN_INFO, tun, "tun_net_xmit %d\n", 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. */
    if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
        goto drop;
    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 netdev_features_t tun_net_fix_features(struct net_device *dev,
    netdev_features_t features)
{
    struct tun_struct *tun = netdev_priv(dev);

    return (features & tun->set_features) | (features & ~TUN_USER_FEATURES);
}
#ifdef CONFIG_NET_POLL_CONTROLLER
static void tun_poll_controller(struct net_device *dev)
{
    /*
     * Tun only receives frames when:
     * 1) the char device endpoint gets data from user space
     * 2) the tun socket gets a sendmsg call from user space
     * Since both of those are syncronous operations, we are guaranteed
     * never to have pending data when we poll for it
     * so theres nothing to do here but return.
     * We need this though so netpoll recognizes us as an interface that
     * supports polling, which enables bridge devices in virt setups to
     * still use netconsole
     */
    return;
}
#endif
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,
    .ndo_fix_features   = tun_net_fix_features,
#ifdef CONFIG_NET_POLL_CONTROLLER
    .ndo_poll_controller    = tun_poll_controller,
#endif
};

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_fix_features   = tun_net_fix_features,
    .ndo_set_rx_mode    = tun_net_mclist,
    .ndo_set_mac_address    = eth_mac_addr,
    .ndo_validate_addr  = eth_validate_addr,
#ifdef CONFIG_NET_POLL_CONTROLLER
    .ndo_poll_controller    = tun_poll_controller,
#endif
};

/* 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);
        dev->priv_flags &= ~IFF_TX_SKB_SHARING;

        eth_hw_addr_random(dev);

        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;

    tun_debug(KERN_INFO, tun, "tun_chr_poll\n");

    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 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;

    sock_update_classid(sk);

    /* 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;
}

/* set skb frags from iovec, this can move to core network code for reuse */
static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
                  int offset, size_t count)
{
    int len = iov_length(from, count) - offset;
    int copy = skb_headlen(skb);
    int size, offset1 = 0;
    int i = 0;

    /* Skip over from offset */
    while (count && (offset >= from->iov_len)) {
        offset -= from->iov_len;
        ++from;
        --count;
    }

    /* copy up to skb headlen */
    while (count && (copy > 0)) {
        size = min_t(unsigned int, copy, from->iov_len - offset);
        if (copy_from_user(skb->data + offset1, from->iov_base + offset,
                   size))
            return -EFAULT;
        if (copy > size) {
            ++from;
            --count;
            offset = 0;
        } else
            offset += size;
        copy -= size;
        offset1 += size;
    }

    if (len == offset1)
        return 0;

    while (count--) {
        struct page *page[MAX_SKB_FRAGS];
        int num_pages;
        unsigned long base;
        unsigned long truesize;

        len = from->iov_len - offset;
        if (!len) {
            offset = 0;
            ++from;
            continue;
        }
        base = (unsigned long)from->iov_base + offset;
        size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
        if (i + size > MAX_SKB_FRAGS)
            return -EMSGSIZE;
        num_pages = get_user_pages_fast(base, size, 0, &page[i]);
        if (num_pages != size) {
            for (i = 0; i < num_pages; i++)
                put_page(page[i]);
            return -EFAULT;
        }
        truesize = size * PAGE_SIZE;
        skb->data_len += len;
        skb->len += len;
        skb->truesize += truesize;
        atomic_add(truesize, &skb->sk->sk_wmem_alloc);
        while (len) {
            int off = base & ~PAGE_MASK;
            int size = min_t(int, len, PAGE_SIZE - off);
            __skb_fill_page_desc(skb, i, page[i], off, size);
            skb_shinfo(skb)->nr_frags++;
            /* increase sk_wmem_alloc */
            base += size;
            len -= size;
            i++;
        }
        offset = 0;
        ++from;
    }
    return 0;
}

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

    if (!(tun->flags & TUN_NO_PI)) {
        if ((len -= sizeof(pi)) > total_len)
            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) > total_len)
            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;
    }

    if (msg_control)
        zerocopy = true;

    if (zerocopy) {
        /* Userspace may produce vectors with count greater than
         * MAX_SKB_FRAGS, so we need to linearize parts of the skb
         * to let the rest of data to be fit in the frags.
         */
        if (count > MAX_SKB_FRAGS) {
            copylen = iov_length(iv, count - MAX_SKB_FRAGS);
            if (copylen < offset)
                copylen = 0;
            else
                copylen -= offset;
        } else
                copylen = 0;
        /* There are 256 bytes to be copied in skb, so there is enough
         * room for skb expand head in case it is used.
         * The rest of the buffer is mapped from userspace.
         */
        if (copylen < gso.hdr_len)
            copylen = gso.hdr_len;
        if (!copylen)
            copylen = GOODCOPY_LEN;
    } else
        copylen = len;

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

    if (zerocopy)
        err = zerocopy_sg_from_iovec(skb, iv, offset, count);
    else
        err = skb_copy_datagram_from_iovec(skb, 0, iv, offset, len);

    if (err) {
        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;
        }
    }

    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;
    }

    /* copy skb_ubuf_info for callback when skb has no error */
    if (zerocopy) {
        skb_shinfo(skb)->destructor_arg = msg_control;
        skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
    }

    netif_rx_ni(skb);

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

    return total_len;
}

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;

    tun_debug(KERN_INFO, tun, "tun_chr_write %ld\n", count);

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

    tun_put(tun);
    return result;
}

/* Put packet to the user space buffer */
static 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 {
                pr_err("unexpected GSO type: "
                       "0x%x, gso_size %d, hdr_len %d\n",
                       sinfo->gso_type, gso.gso_size,
                       gso.hdr_len);
                print_hex_dump(KERN_ERR, "tun: ",
                           DUMP_PREFIX_NONE,
                           16, 1, skb->head,
                           min((int)gso.hdr_len, 64), true);
                WARN_ON_ONCE(1);
                return -EINVAL;
            }
            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_checksum_start_offset(skb);
            gso.csum_offset = skb->csum_offset;
        } else if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
            gso.flags = VIRTIO_NET_HDR_F_DATA_VALID;
        } /* 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;

    tun_debug(KERN_INFO, tun, "tun_chr_read\n");

    if (unlikely(!noblock))
        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;
    if (unlikely(!noblock))
        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 = INVALID_UID;
    tun->group = INVALID_GID;

    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_control, m->msg_iov, total_len,
                m->msg_iovlen, 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;
}

static int tun_release(struct socket *sock)
{
    if (sock->sk)
        sock_put(sock->sk);
    return 0;
}

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

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 uid_valid(tun->owner)?
        sprintf(buf, "%u\n",
            from_kuid_munged(current_user_ns(), tun->owner)):
        sprintf(buf, "-1\n");
}

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 gid_valid(tun->group) ?
        sprintf(buf, "%u\n",
            from_kgid_munged(current_user_ns(), tun->group)):
        sprintf(buf, "-1\n");
}

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 (((uid_valid(tun->owner) && !uid_eq(cred->euid, tun->owner)) ||
             (gid_valid(tun->group) && !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);
        set_bit(SOCK_EXTERNALLY_ALLOCATED, &tun->socket.flags);

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

        sk_change_net(sk, net);
        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;
        sock_set_flag(sk, SOCK_ZEROCOPY);

        tun_sk(sk)->tun = tun;

        security_tun_dev_post_create(sk);

        tun_net_init(dev);

        dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
            TUN_USER_FEATURES;
        dev->features = dev->hw_features;

        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))
            pr_err("Failed to create tun sysfs files\n");

        sk->sk_destruct = tun_sock_destruct;

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

    tun_debug(KERN_INFO, tun, "tun_set_iff\n");

    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:
    tun_free_netdev(dev);
 err_free_dev:
    free_netdev(dev);
 failed:
    return err;
}

static int tun_get_iff(struct net *net, struct tun_struct *tun,
               struct ifreq *ifr)
{
    tun_debug(KERN_INFO, tun, "tun_get_iff\n");

    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 tun_struct *tun, unsigned long arg)
{
    netdev_features_t features = 0;

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

    tun->set_features = features;
    netdev_update_features(tun->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;
    kuid_t owner;
    kgid_t group;
    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;
    } else {
        memset(&ifr, 0, sizeof(ifr));
    }
    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;

    tun_debug(KERN_INFO, tun, "tun_chr_ioctl cmd %d\n", 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 */

        /* [unimplemented] */
        tun_debug(KERN_INFO, tun, "ignored: set checksum %s\n",
              arg ? "disabled" : "enabled");
        break;

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

        tun_debug(KERN_INFO, tun, "persist %s\n",
              arg ? "enabled" : "disabled");
        break;

    case TUNSETOWNER:
        /* Set owner of the device */
        owner = make_kuid(current_user_ns(), arg);
        if (!uid_valid(owner)) {
            ret = -EINVAL;
            break;
        }
        tun->owner = owner;
        tun_debug(KERN_INFO, tun, "owner set to %d\n",
              from_kuid(&init_user_ns, tun->owner));
        break;

    case TUNSETGROUP:
        /* Set group of the device */
        group = make_kgid(current_user_ns(), arg);
        if (!gid_valid(group)) {
            ret = -EINVAL;
            break;
        }
        tun->group = group;
        tun_debug(KERN_INFO, tun, "group set to %d\n",
              from_kgid(&init_user_ns, tun->group));
        break;

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

#ifdef TUN_DEBUG
    case TUNSETDEBUG:
        tun->debug = arg;
        break;
#endif
    case TUNSETOFFLOAD:
        ret = set_offload(tun, 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 address */
        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 */
        tun_debug(KERN_DEBUG, tun, "set hw address: %pM\n",
              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;

    tun_debug(KERN_INFO, tun, "tun_chr_fasync %d\n", 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;

        tun_debug(KERN_INFO, tun, "tun_chr_close\n");

        __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;
    ethtool_cmd_speed_set(cmd, 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);

    strlcpy(info->driver, DRV_NAME, sizeof(info->driver));
    strlcpy(info->version, DRV_VERSION, sizeof(info->version));

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


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

    pr_info("%s, %s\n", DRV_DESCRIPTION, DRV_VERSION);
    pr_info("%s\n", DRV_COPYRIGHT);

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

    ret = misc_register(&tun_miscdev);
    if (ret) {
        pr_err("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);
MODULE_ALIAS("devname:net/tun");