media: uvcvideo: Check controls flags before accessing them

We can figure out if reading/writing a set of controls can fail without
accessing them by checking their flags.

This way we can honor the API closer:

If an error is found when validating the list of controls passed with
VIDIOC_G_EXT_CTRLS, then error_idx shall be set to ctrls->count to
indicate to userspace that no actual hardware was touched.

Fixes v4l2-compliance:
Control ioctls (Input 0):
		warn: v4l2-test-controls.cpp(765): g_ext_ctrls(0) invalid error_idx 0
                fail: v4l2-test-controls.cpp(645): invalid error index write only control
        test VIDIOC_G/S/TRY_EXT_CTRLS: FAIL

Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index 2cc2ff0d0cae..18c315b52ef5 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -1042,6 +1042,28 @@ static int uvc_query_v4l2_class(struct uvc_video_chain *chain, u32 req_id,
 	return 0;
 }
 
+int uvc_ctrl_is_accessible(struct uvc_video_chain *chain, u32 v4l2_id,
+			   bool read)
+{
+	struct uvc_control_mapping *mapping;
+	struct uvc_control *ctrl;
+
+	if (__uvc_query_v4l2_class(chain, v4l2_id, 0) >= 0)
+		return -EACCES;
+
+	ctrl = uvc_find_control(chain, v4l2_id, &mapping);
+	if (!ctrl)
+		return -EINVAL;
+
+	if (!(ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR) && read)
+		return -EACCES;
+
+	if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR) && !read)
+		return -EACCES;
+
+	return 0;
+}
+
 static const char *uvc_map_get_name(const struct uvc_control_mapping *map)
 {
 	const char *name;