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

[Ricardo Ribalda]

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. 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
there are no users on the system.

Also add a flag that is clear during stop, that will capture this
situation:

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 it 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")
Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
To: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
To: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Cc: linux-media@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 drivers/media/usb/uvc/uvc_ctrl.c   | 9 +++++++++
 drivers/media/usb/uvc/uvc_status.c | 1 +
 drivers/media/usb/uvc/uvcvideo.h   | 2 ++
 3 files changed, 12 insertions(+)

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index c95a2229f4fa..0634a4baa2e9 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -1442,12 +1442,20 @@ static void uvc_ctrl_status_event_work(struct work_struct *work)
 
 	uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
 
+	mutex_lock(&dev->lock);
+	if (!dev->users || !dev->resubmit_urb) {
+		mutex_unlock(&dev->lock);
+		return;
+	}
+
 	/* Resubmit the URB. */
 	w->urb->interval = dev->int_ep->desc.bInterval;
 	ret = usb_submit_urb(w->urb, GFP_KERNEL);
 	if (ret < 0)
 		dev_err(&dev->udev->dev,
 			"Failed to resubmit status URB (%d).\n", ret);
+	dev->resubmit_urb = false;
+	mutex_unlock(&dev->lock);
 }
 
 bool uvc_ctrl_status_event_async(struct urb *urb, struct uvc_video_chain *chain,
@@ -1466,6 +1474,7 @@ bool uvc_ctrl_status_event_async(struct urb *urb, struct uvc_video_chain *chain,
 	w->chain = chain;
 	w->ctrl = ctrl;
 
+	dev->resubmit_urb = true;
 	schedule_work(&w->work);
 
 	return true;
diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
index 7518ffce22ed..3cc6e1dfaf01 100644
--- a/drivers/media/usb/uvc/uvc_status.c
+++ b/drivers/media/usb/uvc/uvc_status.c
@@ -310,4 +310,5 @@ int uvc_status_start(struct uvc_device *dev, gfp_t flags)
 void uvc_status_stop(struct uvc_device *dev)
 {
 	usb_kill_urb(dev->int_urb);
+	dev->resubmit_urb = false;
 }
diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index df93db259312..9e6a52008ce5 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -539,6 +539,8 @@ struct uvc_device {
 
 	struct mutex lock;		/* Protects users */
 	unsigned int users;
+	bool resubmit_urb;
+
 	atomic_t nmappings;
 
 	/* Video control interface */

---
base-commit: 0ec5a38bf8499f403f81cb81a0e3a60887d1993c
change-id: 20221212-uvc-race-09276ea68bf8

Best regards,
-- 
Ricardo Ribalda <ribalda@xxxxxxxxxxxx>