+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;
+ 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;
+ if (tfile->tun)
+ goto out;
+
+ err = -EBUSY;
+ if (tun->tfile)
+ goto out;
+
+ err = 0;
+ tfile->tun = tun;
+ tun->tfile = tfile;
+ dev_hold(tun->dev);
+ atomic_inc(&tfile->count);
+
+out:
+ netif_tx_unlock_bh(tun->dev);
+ return err;
+}
+
+static void __tun_detach(struct tun_struct *tun)
+{
+ struct tun_file *tfile = tun->tfile;
+
+ /* Detach from net device */
+ netif_tx_lock_bh(tun->dev);
+ tfile->tun = NULL;
+ tun->tfile = NULL;
+ netif_tx_unlock_bh(tun->dev);
+
+ /* Drop read queue */
+ skb_queue_purge(&tun->readq);
+
+ /* 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);
+}
+