net: trans_start cleanups
[safe/jmp/linux-2.6] / drivers / net / tun.c
index 5f7842e..dbdfb1f 100644 (file)
@@ -44,7 +44,6 @@
 #include <linux/kernel.h>
 #include <linux/major.h>
 #include <linux/slab.h>
-#include <linux/smp_lock.h>
 #include <linux/poll.h>
 #include <linux/fcntl.h>
 #include <linux/init.h>
@@ -54,6 +53,7 @@
 #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>
@@ -61,6 +61,7 @@
 #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>
@@ -103,14 +104,14 @@ struct tun_struct {
        uid_t                   owner;
        gid_t                   group;
 
-       struct sk_buff_head     readq;
-
        struct net_device       *dev;
        struct fasync_struct    *fasync;
 
        struct tap_filter       txflt;
-       struct sock             *sk;
        struct socket           socket;
+       struct socket_wq        wq;
+
+       int                     vnet_hdr_sz;
 
 #ifdef TUN_DEBUG
        int debug;
@@ -130,17 +131,10 @@ static inline struct tun_sock *tun_sk(struct sock *sk)
 static int tun_attach(struct tun_struct *tun, struct file *file)
 {
        struct tun_file *tfile = file->private_data;
-       const struct cred *cred = current_cred();
        int err;
 
        ASSERT_RTNL();
 
-       /* Check permissions */
-       if (((tun->owner != -1 && cred->euid != tun->owner) ||
-            (tun->group != -1 && !in_egroup_p(tun->group))) &&
-               !capable(CAP_NET_ADMIN))
-               return -EPERM;
-
        netif_tx_lock_bh(tun->dev);
 
        err = -EINVAL;
@@ -154,8 +148,9 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
        err = 0;
        tfile->tun = tun;
        tun->tfile = tfile;
+       tun->socket.file = file;
        dev_hold(tun->dev);
-       sock_hold(tun->sk);
+       sock_hold(tun->socket.sk);
        atomic_inc(&tfile->count);
 
 out:
@@ -168,10 +163,11 @@ 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->readq);
+       skb_queue_purge(&tun->socket.sk->sk_receive_queue);
 
        /* Drop the extra count on the net device */
        dev_put(tun->dev);
@@ -330,7 +326,7 @@ static void tun_net_uninit(struct net_device *dev)
        /* Inform the methods they need to stop using the dev.
         */
        if (tfile) {
-               wake_up_all(&tun->socket.wait);
+               wake_up_all(&tun->wq.wait);
                if (atomic_dec_and_test(&tfile->count))
                        __tun_detach(tun);
        }
@@ -340,7 +336,7 @@ static void tun_free_netdev(struct net_device *dev)
 {
        struct tun_struct *tun = netdev_priv(dev);
 
-       sock_put(tun->sk);
+       sock_put(tun->socket.sk);
 }
 
 /* Net device open. */
@@ -374,7 +370,11 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
        if (!check_filter(&tun->txflt, skb))
                goto drop;
 
-       if (skb_queue_len(&tun->readq) >= dev->tx_queue_len) {
+       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. */
@@ -390,14 +390,18 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
                }
        }
 
+       /* Orphan the skb - required as we might hang on to it
+        * for indefinite time. */
+       skb_orphan(skb);
+
        /* Enqueue packet */
-       skb_queue_tail(&tun->readq, skb);
-       dev->trans_start = jiffies;
+       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(&tun->socket.wait);
+       wake_up_interruptible_poll(&tun->wq.wait, POLLIN |
+                                  POLLRDNORM | POLLRDBAND);
        return NETDEV_TX_OK;
 
 drop:
@@ -492,13 +496,13 @@ static unsigned int tun_chr_poll(struct file *file, poll_table * wait)
        if (!tun)
                return POLLERR;
 
-       sk = tun->sk;
+       sk = tun->socket.sk;
 
        DBG(KERN_INFO "%s: tun_chr_poll\n", tun->dev->name);
 
-       poll_wait(file, &tun->socket.wait, wait);
+       poll_wait(file, &tun->wq.wait, wait);
 
-       if (!skb_queue_empty(&tun->readq))
+       if (!skb_queue_empty(&sk->sk_receive_queue))
                mask |= POLLIN | POLLRDNORM;
 
        if (sock_writeable(sk) ||
@@ -519,7 +523,7 @@ 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->sk;
+       struct sock *sk = tun->socket.sk;
        struct sk_buff *skb;
        int err;
 
@@ -561,7 +565,7 @@ static __inline__ ssize_t tun_get_user(struct tun_struct *tun,
        }
 
        if (tun->flags & TUN_VNET_HDR) {
-               if ((len -= sizeof(gso)) > count)
+               if ((len -= tun->vnet_hdr_sz) > count)
                        return -EINVAL;
 
                if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
@@ -573,7 +577,7 @@ static __inline__ ssize_t tun_get_user(struct tun_struct *tun,
 
                if (gso.hdr_len > len)
                        return -EINVAL;
-               offset += sizeof(gso);
+               offset += tun->vnet_hdr_sz;
        }
 
        if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {
@@ -716,7 +720,7 @@ static __inline__ ssize_t tun_put_user(struct tun_struct *tun,
 
        if (tun->flags & TUN_VNET_HDR) {
                struct virtio_net_hdr gso = { 0 }; /* no info leak */
-               if ((len -= sizeof(gso)) < 0)
+               if ((len -= tun->vnet_hdr_sz) < 0)
                        return -EINVAL;
 
                if (skb_is_gso(skb)) {
@@ -747,13 +751,13 @@ static __inline__ ssize_t tun_put_user(struct tun_struct *tun,
                if (unlikely(memcpy_toiovecend(iv, (void *)&gso, total,
                                               sizeof(gso))))
                        return -EFAULT;
-               total += sizeof(gso);
+               total += tun->vnet_hdr_sz;
        }
 
        len = min_t(int, skb->len, len);
 
        skb_copy_datagram_const_iovec(skb, 0, iv, total, len);
-       total += len;
+       total += skb->len;
 
        tun->dev->stats.tx_packets++;
        tun->dev->stats.tx_bytes += len;
@@ -761,34 +765,23 @@ static __inline__ ssize_t tun_put_user(struct tun_struct *tun,
        return total;
 }
 
-static ssize_t tun_chr_aio_read(struct kiocb *iocb, const struct iovec *iv,
-                           unsigned long count, loff_t pos)
+static ssize_t tun_do_read(struct tun_struct *tun,
+                          struct kiocb *iocb, const struct iovec *iv,
+                          ssize_t len, int noblock)
 {
-       struct file *file = iocb->ki_filp;
-       struct tun_file *tfile = file->private_data;
-       struct tun_struct *tun = __tun_get(tfile);
        DECLARE_WAITQUEUE(wait, current);
        struct sk_buff *skb;
-       ssize_t len, ret = 0;
-
-       if (!tun)
-               return -EBADFD;
+       ssize_t ret = 0;
 
        DBG(KERN_INFO "%s: tun_chr_read\n", tun->dev->name);
 
-       len = iov_length(iv, count);
-       if (len < 0) {
-               ret = -EINVAL;
-               goto out;
-       }
-
-       add_wait_queue(&tun->socket.wait, &wait);
+       add_wait_queue(&tun->wq.wait, &wait);
        while (len) {
                current->state = TASK_INTERRUPTIBLE;
 
                /* Read frames from the queue */
-               if (!(skb=skb_dequeue(&tun->readq))) {
-                       if (file->f_flags & O_NONBLOCK) {
+               if (!(skb=skb_dequeue(&tun->socket.sk->sk_receive_queue))) {
+                       if (noblock) {
                                ret = -EAGAIN;
                                break;
                        }
@@ -813,8 +806,29 @@ static ssize_t tun_chr_aio_read(struct kiocb *iocb, const struct iovec *iv,
        }
 
        current->state = TASK_RUNNING;
-       remove_wait_queue(&tun->socket.wait, &wait);
+       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;
@@ -824,8 +838,6 @@ static void tun_setup(struct net_device *dev)
 {
        struct tun_struct *tun = netdev_priv(dev);
 
-       skb_queue_head_init(&tun->readq);
-
        tun->owner = -1;
        tun->group = -1;
 
@@ -851,6 +863,7 @@ static struct rtnl_link_ops tun_link_ops __read_mostly = {
 static void tun_sock_write_space(struct sock *sk)
 {
        struct tun_struct *tun;
+       wait_queue_head_t *wqueue;
 
        if (!sock_writeable(sk))
                return;
@@ -858,18 +871,51 @@ static void tun_sock_write_space(struct sock *sk)
        if (!test_and_clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags))
                return;
 
-       if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
-               wake_up_interruptible_sync(sk->sk_sleep);
+       wqueue = sk_sleep(sk);
+       if (wqueue && waitqueue_active(wqueue))
+               wake_up_interruptible_sync_poll(wqueue, POLLOUT |
+                                               POLLWRNORM | POLLWRBAND);
 
-       tun = container_of(sk, struct tun_sock, sk)->tun;
+       tun = tun_sk(sk)->tun;
        kill_fasync(&tun->fasync, SIGIO, POLL_OUT);
 }
 
 static void tun_sock_destruct(struct sock *sk)
 {
-       free_netdev(container_of(sk, struct tun_sock, sk)->tun->dev);
+       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,
@@ -931,6 +977,8 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 
        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)
@@ -940,6 +988,14 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
                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;
@@ -948,10 +1004,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
                char *name;
                unsigned long flags = 0;
 
-               err = -EINVAL;
-
                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) {
@@ -963,7 +1020,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
                        flags |= TUN_TAP_DEV;
                        name = "tap%d";
                } else
-                       goto failed;
+                       return -EINVAL;
 
                if (*ifr->ifr_name)
                        name = ifr->ifr_name;
@@ -980,19 +1037,23 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
                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;
 
-               init_waitqueue_head(&tun->socket.wait);
+               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;
-               container_of(sk, struct tun_sock, sk)->tun = tun;
+               tun_sk(sk)->tun = tun;
+
+               security_tun_dev_post_create(sk);
 
                tun_net_init(dev);
 
@@ -1110,18 +1171,20 @@ static int set_offload(struct net_device *dev, unsigned long arg)
        return 0;
 }
 
-static long tun_chr_ioctl(struct file *file, unsigned int cmd,
-                         unsigned long arg)
+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, sizeof ifr))
+               if (copy_from_user(&ifr, argp, ifreq_len))
                        return -EFAULT;
 
        if (cmd == TUNGETFEATURES) {
@@ -1144,7 +1207,7 @@ static long tun_chr_ioctl(struct file *file, unsigned int cmd,
                if (ret)
                        goto unlock;
 
-               if (copy_to_user(argp, &ifr, sizeof(ifr)))
+               if (copy_to_user(argp, &ifr, ifreq_len))
                        ret = -EFAULT;
                goto unlock;
        }
@@ -1162,7 +1225,7 @@ static long tun_chr_ioctl(struct file *file, unsigned int cmd,
                if (ret)
                        break;
 
-               if (copy_to_user(argp, &ifr, sizeof(ifr)))
+               if (copy_to_user(argp, &ifr, ifreq_len))
                        ret = -EFAULT;
                break;
 
@@ -1236,7 +1299,7 @@ static long tun_chr_ioctl(struct file *file, unsigned int cmd,
                /* 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, sizeof ifr))
+               if (copy_to_user(argp, &ifr, ifreq_len))
                        ret = -EFAULT;
                break;
 
@@ -1249,7 +1312,7 @@ static long tun_chr_ioctl(struct file *file, unsigned int cmd,
                break;
 
        case TUNGETSNDBUF:
-               sndbuf = tun->sk->sk_sndbuf;
+               sndbuf = tun->socket.sk->sk_sndbuf;
                if (copy_to_user(argp, &sndbuf, sizeof(sndbuf)))
                        ret = -EFAULT;
                break;
@@ -1260,7 +1323,46 @@ static long tun_chr_ioctl(struct file *file, unsigned int cmd,
                        break;
                }
 
-               tun->sk->sk_sndbuf = sndbuf;
+               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:
@@ -1275,6 +1377,41 @@ unlock:
        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);
@@ -1285,7 +1422,6 @@ static int tun_chr_fasync(int fd, struct file *file, int on)
 
        DBG(KERN_INFO "%s: tun_chr_fasync %d\n", tun->dev->name, on);
 
-       lock_kernel();
        if ((ret = fasync_helper(fd, file, on, &tun->fasync)) < 0)
                goto out;
 
@@ -1298,7 +1434,6 @@ static int tun_chr_fasync(int fd, struct file *file, int on)
                tun->flags &= ~TUN_FASYNC;
        ret = 0;
 out:
-       unlock_kernel();
        tun_put(tun);
        return ret;
 }
@@ -1306,7 +1441,7 @@ out:
 static int tun_chr_open(struct inode *inode, struct file * file)
 {
        struct tun_file *tfile;
-       cycle_kernel_lock();
+
        DBG1(KERN_INFO "tunX: tun_chr_open\n");
 
        tfile = kmalloc(sizeof(*tfile), GFP_KERNEL);
@@ -1332,7 +1467,7 @@ static int tun_chr_close(struct inode *inode, struct file *file)
 
                __tun_detach(tun);
 
-               /* If desireable, unregister the netdevice. */
+               /* If desirable, unregister the netdevice. */
                if (!(tun->flags & TUN_PERSIST)) {
                        rtnl_lock();
                        if (dev->reg_state == NETREG_REGISTERED)
@@ -1343,7 +1478,7 @@ static int tun_chr_close(struct inode *inode, struct file *file)
 
        tun = tfile->tun;
        if (tun)
-               sock_put(tun->sk);
+               sock_put(tun->socket.sk);
 
        put_net(tfile->net);
        kfree(tfile);
@@ -1359,7 +1494,10 @@ static const struct file_operations tun_fops = {
        .write = do_sync_write,
        .aio_write = tun_chr_aio_write,
        .poll   = tun_chr_poll,
-       .unlocked_ioctl = tun_chr_ioctl,
+       .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
@@ -1368,7 +1506,7 @@ static const struct file_operations tun_fops = {
 static struct miscdevice tun_miscdev = {
        .minor = TUN_MINOR,
        .name = "tun",
-       .devnode = "net/tun",
+       .nodename = "net/tun",
        .fops = &tun_fops,
 };
 
@@ -1489,6 +1627,23 @@ static void tun_cleanup(void)
        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);