On Wed, 20 Apr 2016 15:16:57 +0200,
Marcel Holtmann wrote:
>
> 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: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> > ---
> > 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.
It's just a matter of taste :) I prefer avoiding the duplicated
codes; instead of open-coding mutex_lock/unlock and data->hdev check
in two places, do it in the common helper. If you prefer other way,
I'm fine with it. Just let me know. I'll resubmit the patch.
> 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.
No, it won't happen. The removal of data->hdev in the above is merely
moving the check into the mutex protection in vhci_create_device().
thanks,
Takashi
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