[PATCH v2 2/4] media: uvcvideo: Do not set an async control owned by other fh

[Ricardo Ribalda]

If a file handle is waiting for a response from an async control, avoid
that other file handle operate with it.

Without this patch, the first file handle will never get the event
associated with that operation, which can lead to endless loops in
applications. Eg:
If an application A wants to change the zoom and to know when the
operation has completed:
it will open the video node, subscribe to the zoom event, change the
control and wait for zoom to finish.
If before the zoom operation finishes, another application B changes
the zoom, the first app A will loop forever.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
 drivers/media/usb/uvc/uvc_ctrl.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index b6af4ff92cbd..3f8ae35cb3bc 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -1955,6 +1955,10 @@ int uvc_ctrl_set(struct uvc_fh *handle,
 	if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR))
 		return -EACCES;
 
+	/* Other file handle is waiting a response from this async control. */
+	if (ctrl->handle && ctrl->handle != handle)
+		return -EBUSY;
+
 	/* Clamp out of range values. */
 	switch (mapping->v4l2_type) {
 	case V4L2_CTRL_TYPE_INTEGER:

-- 
2.47.0.338.g60cca15819-goog