media: v4l2-dev/ioctl: require non-zero device_caps, verify sane querycap results

Now that all V4L2 drivers set device_caps in struct video_device, we can add
a check for this to ensure all future drivers fill this in.

Also verify that when the querycap ioctl is called the driver didn't mess
with the device_caps value and that capabilities is a superset of device_caps.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
[hverkuil-cisco@xs4all.nl: fix too-long line]
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/v4l2-core/v4l2-dev.c

@@ -859,6 +859,9 @@ int __video_register_device(struct video_device *vdev,
 	/* the v4l2_dev pointer MUST be present */
 	if (WARN_ON(!vdev->v4l2_dev))
 		return -EINVAL;
+	/* the device_caps field MUST be set */
+	if (WARN_ON(!vdev->device_caps))
+		return -EINVAL;
 
 	/* v4l2_fh support */
 	spin_lock_init(&vdev->fh_lock);

drivers/media/v4l2-core/v4l2-ioctl.c

@@ -1057,14 +1057,19 @@ static int v4l_querycap(const struct v4l2_ioctl_ops *ops,
 
 	ret = ops->vidioc_querycap(file, fh, cap);
 
-	cap->capabilities |= V4L2_CAP_EXT_PIX_FORMAT;
 	/*
-	 * Drivers MUST fill in device_caps, so check for this and
-	 * warn if it was forgotten.
+	 * Drivers must not change device_caps, so check for this and
+	 * warn if this happened.
+	 */
+	WARN_ON(cap->device_caps != vfd->device_caps);
+	/*
+	 * Check that capabilities is a superset of
+	 * vfd->device_caps | V4L2_CAP_DEVICE_CAPS
 	 */
-	WARN(!(cap->capabilities & V4L2_CAP_DEVICE_CAPS) ||
-		!cap->device_caps, "Bad caps for driver %s, %x %x",
-		cap->driver, cap->capabilities, cap->device_caps);
+	WARN_ON((cap->capabilities &
+		 (vfd->device_caps | V4L2_CAP_DEVICE_CAPS)) !=
+		(vfd->device_caps | V4L2_CAP_DEVICE_CAPS));
+	cap->capabilities |= V4L2_CAP_EXT_PIX_FORMAT;
 	cap->device_caps |= V4L2_CAP_EXT_PIX_FORMAT;
 
 	return ret;