Bluetooth: vhci: Fix race at creating hci device

commit c7c999cb upstream.

hci_vhci driver creates a hci device object dynamically upon each
HCI_VENDOR_PKT write.  Although it checks the already created object
and returns an error, it's still racy and may build multiple hci_dev
objects concurrently when parallel writes are performed, as the device
tracks only a single hci_dev object.

This patch introduces a mutex to protect against the concurrent device
creations.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/bluetooth/hci_vhci.c

@@ -50,6 +50,7 @@ struct vhci_data {
 	wait_queue_head_t read_wait;
 	struct sk_buff_head readq;
 
+	struct mutex open_mutex;
 	struct delayed_work open_timeout;
 };
 
@@ -95,11 +96,14 @@ static int vhci_send_frame(struct hci_dev *hdev, struct sk_buff *skb)
 	return 0;
 }
 
-static int vhci_create_device(struct vhci_data *data, __u8 dev_type)
+static int __vhci_create_device(struct vhci_data *data, __u8 dev_type)
 {
 	struct hci_dev *hdev;
 	struct sk_buff *skb;
 
+	if (data->hdev)
+		return -EBADFD;
+
 	skb = bt_skb_alloc(4, GFP_KERNEL);
 	if (!skb)
 		return -ENOMEM;
@@ -140,6 +144,17 @@ static int vhci_create_device(struct vhci_data *data, __u8 dev_type)
 	return 0;
 }
 
+static int vhci_create_device(struct vhci_data *data, __u8 opcode)
+{
+	int err;
+
+	mutex_lock(&data->open_mutex);
+	err = __vhci_create_device(data, opcode);
+	mutex_unlock(&data->open_mutex);
+
+	return err;
+}
+
 static inline ssize_t vhci_get_user(struct vhci_data *data,
 				    const struct iovec *iov,
 				    unsigned long count)
@@ -185,11 +200,6 @@ static inline ssize_t vhci_get_user(struct vhci_data *data,
 	case HCI_VENDOR_PKT:
 		cancel_delayed_work_sync(&data->open_timeout);
 
-		if (data->hdev) {
-			kfree_skb(skb);
-			return -EBADFD;
-		}
-
 		dev_type = *((__u8 *) skb->data);
 		skb_pull(skb, 1);
 
@@ -318,6 +328,7 @@ static int vhci_open(struct inode *inode, struct file *file)
 	skb_queue_head_init(&data->readq);
 	init_waitqueue_head(&data->read_wait);
 
+	mutex_init(&data->open_mutex);
 	INIT_DELAYED_WORK(&data->open_timeout, vhci_open_timeout);
 
 	file->private_data = data;