tun: Introduce tun_file

Currently the tun code suffers from only having a single word of
data that exists for the entire life of the tun file descriptor.

This results in peculiar holding of references to the network namespace
as well as races between free_netdevice and tun_chr_close.

Fix this by introducing tun_file which will hold the per file state.
For the moment it still holds just a single word so the differences
are all logic changes with no changes in semantics.
Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -87,9 +87,13 @@ struct tap_filter {
 	unsigned char	addr[FLT_EXACT_COUNT][ETH_ALEN];
 };
 
+struct tun_file {
+	struct tun_struct *tun;
+};
+
 struct tun_struct {
+	struct tun_file		*tfile;
 	unsigned int 		flags;
-	int			attached;
 	uid_t			owner;
 	gid_t			group;
 
@@ -108,14 +112,15 @@ struct tun_struct {
 
 static int tun_attach(struct tun_struct *tun, struct file *file)
 {
+	struct tun_file *tfile = file->private_data;
 	const struct cred *cred = current_cred();
 
 	ASSERT_RTNL();
 
-	if (file->private_data)
+	if (tfile->tun)
 		return -EINVAL;
 
-	if (tun->attached)
+	if (tun->tfile)
 		return -EBUSY;
 
 	/* Check permissions */
@@ -124,13 +129,41 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
 		!capable(CAP_NET_ADMIN))
 		return -EPERM;
 
-	file->private_data = tun;
-	tun->attached = 1;
+	tfile->tun = tun;
+	tun->tfile = tfile;
 	get_net(dev_net(tun->dev));
 
 	return 0;
 }
 
+static void __tun_detach(struct tun_struct *tun)
+{
+	struct tun_file *tfile = tun->tfile;
+
+	/* Detach from net device */
+	tfile->tun = NULL;
+	tun->tfile = NULL;
+	put_net(dev_net(tun->dev));
+
+	/* Drop read queue */
+	skb_queue_purge(&tun->readq);
+}
+
+static struct tun_struct *__tun_get(struct tun_file *tfile)
+{
+	return tfile->tun;
+}
+
+static struct tun_struct *tun_get(struct file *file)
+{
+	return __tun_get(file->private_data);
+}
+
+static void tun_put(struct tun_struct *tun)
+{
+	/* Noop for now */
+}
+
 /* TAP filterting */
 static void addr_hash_set(u32 *mask, const u8 *addr)
 {
@@ -261,7 +294,7 @@ static int tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 	DBG(KERN_INFO "%s: tun_net_xmit %d\n", tun->dev->name, skb->len);
 
 	/* Drop packet if interface is not attached */
-	if (!tun->attached)
+	if (!tun->tfile)
 		goto drop;
 
 	/* Drop if the filter does not like it.
@@ -378,7 +411,7 @@ static void tun_net_init(struct net_device *dev)
 /* Poll */
 static unsigned int tun_chr_poll(struct file *file, poll_table * wait)
 {
-	struct tun_struct *tun = file->private_data;
+	struct tun_struct *tun = tun_get(file);
 	unsigned int mask = POLLOUT | POLLWRNORM;
 
 	if (!tun)
@@ -391,6 +424,7 @@ static unsigned int tun_chr_poll(struct file *file, poll_table * wait)
 	if (!skb_queue_empty(&tun->readq))
 		mask |= POLLIN | POLLRDNORM;
 
+	tun_put(tun);
 	return mask;
 }
 
@@ -575,14 +609,18 @@ static __inline__ ssize_t tun_get_user(struct tun_struct *tun, struct iovec *iv,
 static ssize_t tun_chr_aio_write(struct kiocb *iocb, const struct iovec *iv,
 			      unsigned long count, loff_t pos)
 {
-	struct tun_struct *tun = iocb->ki_filp->private_data;
+	struct tun_struct *tun = tun_get(iocb->ki_filp);
+	ssize_t result;
 
 	if (!tun)
 		return -EBADFD;
 
 	DBG(KERN_INFO "%s: tun_chr_write %ld\n", tun->dev->name, count);
 
-	return tun_get_user(tun, (struct iovec *) iv, iov_length(iv, count));
+	result = tun_get_user(tun, (struct iovec *) iv, iov_length(iv, count));
+
+	tun_put(tun);
+	return result;
 }
 
 /* Put packet to the user space buffer */
@@ -655,7 +693,7 @@ 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_struct *tun = file->private_data;
+	struct tun_struct *tun = tun_get(file);
 	DECLARE_WAITQUEUE(wait, current);
 	struct sk_buff *skb;
 	ssize_t len, ret = 0;
@@ -666,8 +704,10 @@ static ssize_t tun_chr_aio_read(struct kiocb *iocb, const struct iovec *iv,
 	DBG(KERN_INFO "%s: tun_chr_read\n", tun->dev->name);
 
 	len = iov_length(iv, count);
-	if (len < 0)
-		return -EINVAL;
+	if (len < 0) {
+		ret = -EINVAL;
+		goto out;
+	}
 
 	add_wait_queue(&tun->read_wait, &wait);
 	while (len) {
@@ -698,6 +738,8 @@ static ssize_t tun_chr_aio_read(struct kiocb *iocb, const struct iovec *iv,
 	current->state = TASK_RUNNING;
 	remove_wait_queue(&tun->read_wait, &wait);
 
+out:
+	tun_put(tun);
 	return ret;
 }
 
@@ -822,7 +864,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 
 static int tun_get_iff(struct net *net, struct file *file, struct ifreq *ifr)
 {
-	struct tun_struct *tun = file->private_data;
+	struct tun_struct *tun = tun_get(file);
 
 	if (!tun)
 		return -EBADFD;
@@ -847,6 +889,7 @@ static int tun_get_iff(struct net *net, struct file *file, struct ifreq *ifr)
 	if (tun->flags & TUN_VNET_HDR)
 		ifr->ifr_flags |= IFF_VNET_HDR;
 
+	tun_put(tun);
 	return 0;
 }
 
@@ -893,7 +936,7 @@ static int set_offload(struct net_device *dev, unsigned long arg)
 static int tun_chr_ioctl(struct inode *inode, struct file *file,
 			 unsigned int cmd, unsigned long arg)
 {
-	struct tun_struct *tun = file->private_data;
+	struct tun_struct *tun;
 	void __user* argp = (void __user*)arg;
 	struct ifreq ifr;
 	int ret;
@@ -902,6 +945,16 @@ static int tun_chr_ioctl(struct inode *inode, struct file *file,
 		if (copy_from_user(&ifr, argp, sizeof ifr))
 			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);
+	}
+
+	tun = tun_get(file);
 	if (cmd == TUNSETIFF && !tun) {
 		int err;
 
@@ -919,28 +972,21 @@ static int tun_chr_ioctl(struct inode *inode, struct file *file,
 		return 0;
 	}
 
-	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);
-	}
 
 	if (!tun)
 		return -EBADFD;
 
 	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, file, &ifr);
 		if (ret)
-			return ret;
+			break;
 
 		if (copy_to_user(argp, &ifr, sizeof(ifr)))
-			return -EFAULT;
+			ret = -EFAULT;
 		break;
 
 	case TUNSETNOCSUM:
@@ -992,7 +1038,7 @@ static int tun_chr_ioctl(struct inode *inode, struct file *file,
 			ret = 0;
 		}
 		rtnl_unlock();
-		return ret;
+		break;
 
 #ifdef TUN_DEBUG
 	case TUNSETDEBUG:
@@ -1003,24 +1049,25 @@ static int tun_chr_ioctl(struct inode *inode, struct file *file,
 		rtnl_lock();
 		ret = set_offload(tun->dev, arg);
 		rtnl_unlock();
-		return ret;
+		break;
 
 	case TUNSETTXFILTER:
 		/* Can be set only for TAPs */
+		ret = -EINVAL;
 		if ((tun->flags & TUN_TYPE_MASK) != TUN_TAP_DEV)
-			return -EINVAL;
+			break;
 		rtnl_lock();
 		ret = update_filter(&tun->txflt, (void __user *)arg);
 		rtnl_unlock();
-		return ret;
+		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, sizeof ifr))
-			return -EFAULT;
-		return 0;
+			ret = -EFAULT;
+		break;
 
 	case SIOCSIFHWADDR:
 		/* Set hw address */
@@ -1030,18 +1077,19 @@ static int tun_chr_ioctl(struct inode *inode, struct file *file,
 		rtnl_lock();
 		ret = dev_set_mac_address(tun->dev, &ifr.ifr_hwaddr);
 		rtnl_unlock();
-		return ret;
-
+		break;
 	default:
-		return -EINVAL;
+		ret = -EINVAL;
+		break;
 	};
 
-	return 0;
+	tun_put(tun);
+	return ret;
 }
 
 static int tun_chr_fasync(int fd, struct file *file, int on)
 {
-	struct tun_struct *tun = file->private_data;
+	struct tun_struct *tun = tun_get(file);
 	int ret;
 
 	if (!tun)
@@ -1063,40 +1111,44 @@ static int tun_chr_fasync(int fd, struct file *file, int on)
 	ret = 0;
 out:
 	unlock_kernel();
+	tun_put(tun);
 	return ret;
 }
 
 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");
-	file->private_data = NULL;
+
+	tfile = kmalloc(sizeof(*tfile), GFP_KERNEL);
+	if (!tfile)
+		return -ENOMEM;
+	tfile->tun = NULL;
+	file->private_data = tfile;
 	return 0;
 }
 
 static int tun_chr_close(struct inode *inode, struct file *file)
 {
-	struct tun_struct *tun = file->private_data;
+	struct tun_file *tfile = file->private_data;
+	struct tun_struct *tun = __tun_get(tfile);
 
-	if (!tun)
-		return 0;
 
+	if (tun) {
 		DBG(KERN_INFO "%s: tun_chr_close\n", tun->dev->name);
 
 		rtnl_lock();
+		__tun_detach(tun);
 
-	/* Detach from net device */
-	file->private_data = NULL;
-	tun->attached = 0;
-	put_net(dev_net(tun->dev));
-
-	/* Drop read queue */
-	skb_queue_purge(&tun->readq);
-
+		/* If desireable, unregister the netdevice. */
 		if (!(tun->flags & TUN_PERSIST))
 			unregister_netdevice(tun->dev);
 
 		rtnl_unlock();
+	}
+
+	kfree(tfile);
 
 	return 0;
 }
@@ -1177,7 +1229,7 @@ static void tun_set_msglevel(struct net_device *dev, u32 value)
 static u32 tun_get_link(struct net_device *dev)
 {
 	struct tun_struct *tun = netdev_priv(dev);
-	return tun->attached;
+	return !!tun->tfile;
 }
 
 static u32 tun_get_rx_csum(struct net_device *dev)