[PATCH v5 04/13] media: uvcvideo: Check controls flags before accessing them

[Ricardo Ribalda <ribalda@xxxxxxxxxxxx>]

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

Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
 drivers/media/usb/uvc/uvc_v4l2.c | 69 +++++++++++++++++++++++---------
 1 file changed, 51 insertions(+), 18 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
index 157310c0ca87..e956d833ed84 100644
--- a/drivers/media/usb/uvc/uvc_v4l2.c
+++ b/drivers/media/usb/uvc/uvc_v4l2.c
@@ -1040,31 +1040,54 @@ static int uvc_ioctl_s_ctrl(struct file *file, void *fh,
 	return 0;
 }
 
-static int uvc_ioctl_g_ext_ctrls(struct file *file, void *fh,
-				 struct v4l2_ext_controls *ctrls)
+static int uvc_ctrl_check_access(struct uvc_video_chain *chain,
+				 struct v4l2_ext_controls *ctrls, bool read)
 {
-	struct uvc_fh *handle = fh;
-	struct uvc_video_chain *chain = handle->chain;
 	struct v4l2_ext_control *ctrl = ctrls->controls;
 	unsigned int i;
-	int ret;
+	int ret = 0;
 
-	if (ctrls->which == V4L2_CTRL_WHICH_DEF_VAL) {
-		for (i = 0; i < ctrls->count; ++ctrl, ++i) {
-			struct v4l2_queryctrl qc = { .id = ctrl->id };
+	for (i = 0; i < ctrls->count; ++ctrl, ++i) {
+		struct v4l2_queryctrl qc = { .id = ctrl->id };
 
-			ret = uvc_query_v4l2_ctrl(chain, &qc);
-			if (ret < 0) {
-				ctrls->error_idx = i;
-				return ret;
-			}
+		ret = uvc_query_v4l2_ctrl(chain, &qc);
+		if (ret < 0)
+			break;
 
+		if (ctrls->which == V4L2_CTRL_WHICH_DEF_VAL) {
 			ctrl->value = qc.default_value;
+			continue;
 		}
 
-		return 0;
+		if (qc.flags & V4L2_CTRL_FLAG_WRITE_ONLY && read) {
+			ret = -EACCES;
+			break;
+		}
+
+		if (qc.flags & V4L2_CTRL_FLAG_READ_ONLY && !read) {
+			ret = -EACCES;
+			break;
+		}
 	}
 
+	ctrls->error_idx = ctrls->count;
+
+	return ret;
+}
+
+static int uvc_ioctl_g_ext_ctrls(struct file *file, void *fh,
+				 struct v4l2_ext_controls *ctrls)
+{
+	struct uvc_fh *handle = fh;
+	struct uvc_video_chain *chain = handle->chain;
+	struct v4l2_ext_control *ctrl = ctrls->controls;
+	unsigned int i;
+	int ret;
+
+	ret = uvc_ctrl_check_access(chain, ctrls, true);
+	if (ret < 0 || ctrls->which == V4L2_CTRL_WHICH_DEF_VAL)
+		return ret;
+
 	ret = uvc_ctrl_begin(chain);
 	if (ret < 0)
 		return ret;
@@ -1092,10 +1115,6 @@ static int uvc_ioctl_s_try_ext_ctrls(struct uvc_fh *handle,
 	unsigned int i;
 	int ret;
 
-	/* Default value cannot be changed */
-	if (ctrls->which == V4L2_CTRL_WHICH_DEF_VAL)
-		return -EINVAL;
-
 	ret = uvc_ctrl_begin(chain);
 	if (ret < 0)
 		return ret;
@@ -1121,6 +1140,16 @@ static int uvc_ioctl_s_ext_ctrls(struct file *file, void *fh,
 				 struct v4l2_ext_controls *ctrls)
 {
 	struct uvc_fh *handle = fh;
+	struct uvc_video_chain *chain = handle->chain;
+	int ret;
+
+	/* Default value cannot be changed */
+	if (ctrls->which == V4L2_CTRL_WHICH_DEF_VAL)
+		return -EINVAL;
+
+	ret = uvc_ctrl_check_access(chain, ctrls, false);
+	if (ret < 0)
+		return ret;
 
 	return uvc_ioctl_s_try_ext_ctrls(handle, ctrls, true);
 }
@@ -1130,6 +1159,10 @@ static int uvc_ioctl_try_ext_ctrls(struct file *file, void *fh,
 {
 	struct uvc_fh *handle = fh;
 
+	/* Default value cannot be changed */
+	if (ctrls->which == V4L2_CTRL_WHICH_DEF_VAL)
+		return -EINVAL;
+
 	return uvc_ioctl_s_try_ext_ctrls(handle, ctrls, false);
 }
 
-- 
2.31.0.rc2.261.g7f71774620-goog