Hi Takashi,
> 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.
>
> Cc: <sta...@vger.kernel.org>
> Signed-off-by: Takashi Iwai <ti...@suse.de>
> ---
> drivers/bluetooth/hci_vhci.c | 22 ++++++++++++++++------
> 1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/bluetooth/hci_vhci.c b/drivers/bluetooth/hci_vhci.c
> index f67ea1c090cb..39230f30f544 100644
> --- a/drivers/bluetooth/hci_vhci.c
> +++ b/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;
> };
>
> @@ -87,7 +88,7 @@ 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 opcode)
> +static int __vhci_create_device(struct vhci_data *data, __u8 opcode)
> {
> struct hci_dev *hdev;
> struct sk_buff *skb;
> @@ -151,6 +152,19 @@ static int vhci_create_device(struct vhci_data *data,
> __u8 opcode)
> return 0;
> }
>
> +static int vhci_create_device(struct vhci_data *data, __u8 opcode)
> +{
> + int err;
> +
> + mutex_lock(&data->open_mutex);
> + if (data->hdev)
> + err = -EBADFD;
> + else
> + err = __vhci_create_device(data, opcode);
> + mutex_unlock(&data->open_mutex);
> + return err;
> +}
> +
> static inline ssize_t vhci_get_user(struct vhci_data *data,
> struct iov_iter *from)
> {
> @@ -191,11 +205,6 @@ 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;
> - }
> -
why not just have the mutex around this block and the vhci_create_device in the
timeout. Wouldn't that achieve exactly the same.
Since when you actually remove this check, then you still can create another
hci_dev by just writing another vendor packet. That is actually something we
want to avoid.
> opcode = *((__u8 *) skb->data);
> skb_pull(skb, 1);
>
> @@ -320,6 +329,7 @@ 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;
Regards
Marcel
