V4L/DVB: v4l2-dev: fix memory leak

Since commit b4028437
the 'driver_data' field resides in device's struct device_private
which may be allocated by dev_set_drvdata() if device_private
struct was not allocated previously.

dev_set_drvdata() is used in video_set_drvdata() to set
the driver's private data pointer in v4l2 drivers. Setting
the private data _before_ registering the v4l2 device results
in a memory leak since __video_register_device() also calls
video_set_drvdata(), but after zeroing the device structure.
Thus, the reference to the previously allocated device_private
struct goes lost and a new device_private will be allocated.

All v4l drivers which call video_set_drvdata() _before_
calling video_register_device() are affected. The patch fixes
__video_register_device() to preserve previously allocated
device_private reference.

Caught by kmemleak.
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/v4l2-dev.c

@@ -410,7 +410,7 @@ static int __video_register_device(struct video_device *vdev, int type, int nr,
 	int minor_offset = 0;
 	int minor_cnt = VIDEO_NUM_DEVICES;
 	const char *name_base;
-	void *priv = video_get_drvdata(vdev);
+	void *priv = vdev->dev.p;
 
 	/* A minor value of -1 marks this video device as never
 	   having been registered */
@@ -536,9 +536,9 @@ static int __video_register_device(struct video_device *vdev, int type, int nr,
 
 	/* Part 4: register the device with sysfs */
 	memset(&vdev->dev, 0, sizeof(vdev->dev));
-	/* The memset above cleared the device's drvdata, so
+	/* The memset above cleared the device's device_private, so
 	   put back the copy we made earlier. */
-	video_set_drvdata(vdev, priv);
+	vdev->dev.p = priv;
 	vdev->dev.class = &video_class;
 	vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor);
 	if (vdev->parent)