Re: [PATCH v3] media: uvcvideo: Fix race condition with usb_kill_urb

From: Laurent Pinchart
Date: Wed Dec 14 2022 - 08:30:09 EST

Hi Ricardo,

On Wed, Dec 14, 2022 at 01:44:56PM +0100, Ricardo Ribalda wrote:
> On Wed, 14 Dec 2022 at 13:41, Laurent Pinchart wrote:
> > On Wed, Dec 14, 2022 at 12:18:52PM +0100, Ricardo Ribalda wrote:
> > > usb_kill_urb warranties that all the handlers are finished when it
> > > returns, but does not protect against threads that might be handling
> > > asynchronously the urb.
> > >
> > > For UVC, the function uvc_ctrl_status_event_async() takes care of
> > > control changes asynchronously.
> > >
> > > If the code is executed in the following order:
> > >
> > > CPU 0 CPU 1
> > > ===== =====
> > > uvc_status_complete()
> > > uvc_status_stop()
> > > uvc_ctrl_status_event_work()
> > > uvc_status_start() -> FAIL
> > > Then uvc_status_start will keep failing and this error will be shown:
> > >
> > > <4>[ 5.540139] URB 0000000000000000 submitted while active
> > > drivers/usb/core/urb.c:378 usb_submit_urb+0x4c3/0x528
> > >
> > > Let's improve the current situation, by not re-submiting the urb if
> > > we are stopping the status event. Also process the queued work
> > > (if any) during stop.
> > >
> > > CPU 0 CPU 1
> > > ===== =====
> > > uvc_status_complete()
> > > uvc_status_stop()
> > > uvc_status_start()
> > > uvc_ctrl_status_event_work() -> FAIL
> > >
> > > Hopefully, with the usb layer protection this should be enough to cover
> > > all the cases.
> > >
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
> > > Reviewed-by: Yunke Cao <yunkec@xxxxxxxxxxxx>
> > > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> > > ---
> > > uvc: Fix race condition on uvc
> > >
> > > Make sure that all the async work is finished when we stop the status urb.
> > >
> > > To: Yunke Cao <yunkec@xxxxxxxxxxxx>
> > > To: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> > > To: Max Staudt <mstaudt@xxxxxxxxxx>
> > > To: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> > > To: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
> > > Cc: linux-media@xxxxxxxxxxxxxxx
> > > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > > ---
> > > Changes in v3:
> > > - Remove the patch for dev->status, makes more sense in another series, and makes
> > > the zero day less nervous.
> > > - Update reviewed-by (thanks Yunke!).
> > > - Link to v2: https://lore.kernel.org/r/20221212-uvc-race-v2-0-54496cc3b8ab@xxxxxxxxxxxx
> > >
> > > Changes in v2:
> > > - Add a patch for not kalloc dev->status
> > > - Redo the logic mechanism, so it also works with suspend (Thanks Yunke!)
> > > - Link to v1: https://lore.kernel.org/r/20221212-uvc-race-v1-0-c52e1783c31d@xxxxxxxxxxxx
> > > ---
> > > drivers/media/usb/uvc/uvc_ctrl.c | 3 +++
> > > drivers/media/usb/uvc/uvc_status.c | 6 ++++++
> > > drivers/media/usb/uvc/uvcvideo.h | 1 +
> > > 3 files changed, 10 insertions(+)
> > >
> > > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > > index c95a2229f4fa..5160facc8e20 100644
> > > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > > @@ -1442,6 +1442,9 @@ static void uvc_ctrl_status_event_work(struct work_struct *work)
> > >
> > > uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
> > >
> > > + if (dev->flush_status)
> > > + return;
> > > +
> > > /* Resubmit the URB. */
> > > w->urb->interval = dev->int_ep->desc.bInterval;
> > > ret = usb_submit_urb(w->urb, GFP_KERNEL);
> > > diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
> > > index 7518ffce22ed..09a5802dc974 100644
> > > --- a/drivers/media/usb/uvc/uvc_status.c
> > > +++ b/drivers/media/usb/uvc/uvc_status.c
> > > @@ -304,10 +304,16 @@ int uvc_status_start(struct uvc_device *dev, gfp_t flags)
> > > if (dev->int_urb == NULL)
> > > return 0;
> > >
> > > + dev->flush_status = false;
> > > return usb_submit_urb(dev->int_urb, flags);
> > > }
> > >
> > > void uvc_status_stop(struct uvc_device *dev)
> > > {
> > > + struct uvc_ctrl_work *w = &dev->async_ctrl;
> > > +
> > > + dev->flush_status = true;
> > > usb_kill_urb(dev->int_urb);
> >
> > Isn't this still racy ?
>
> Indeed...
>
> I could add a mutex just for flush_status
>
> what do you think?

It may be possible to avoid that. I'm giving it a try.

> >
> > CPU0 CPU1
> > ==== ====
> >
> > uvc_status_stop() uvc_ctrl_status_event_work()
> > { {
> > if (dev->flush_status)
> > return;
> >
> > dev->flush_status = true;
> > usb_kill_urb(dev->int_urb);
> >
> > /* Resubmit the URB. */
> > w->urb->interval = dev->int_ep->desc.bInterval;
> > ret = usb_submit_urb(w->urb, GFP_KERNEL);
> > }
> >
> > if (cancel_work_sync(&w->work))
> > uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
> > }
> >
> > uvc_status_start() will then return an error, right ?
> >
> > > + if (cancel_work_sync(&w->work))
> > > + uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
> > > }
> > > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > > index df93db259312..6a9b72d6789e 100644
> > > --- a/drivers/media/usb/uvc/uvcvideo.h
> > > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > > @@ -560,6 +560,7 @@ struct uvc_device {
> > > struct usb_host_endpoint *int_ep;
> > > struct urb *int_urb;
> > > u8 *status;
> > > + bool flush_status;
> > > struct input_dev *input;
> > > char input_phys[64];
> > >
> > >
> > > ---
> > > base-commit: 0ec5a38bf8499f403f81cb81a0e3a60887d1993c
> > > change-id: 20221212-uvc-race-09276ea68bf8

--
Regards,

Laurent Pinchart