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>

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;

drivers/media/usb/uvc/uvc_v4l2.c

@@ -1003,6 +1003,26 @@ static int uvc_ioctl_query_ext_ctrl(struct file *file, void *fh,
 	return 0;
 }
 
+static int uvc_ctrl_check_access(struct uvc_video_chain *chain,
+				 struct v4l2_ext_controls *ctrls,
+				 unsigned long ioctl)
+{
+	struct v4l2_ext_control *ctrl = ctrls->controls;
+	unsigned int i;
+	int ret = 0;
+
+	for (i = 0; i < ctrls->count; ++ctrl, ++i) {
+		ret = uvc_ctrl_is_accessible(chain, ctrl->id,
+					    ioctl == VIDIOC_G_EXT_CTRLS);
+		if (ret)
+			break;
+	}
+
+	ctrls->error_idx = ioctl == VIDIOC_TRY_EXT_CTRLS ? i : ctrls->count;
+
+	return ret;
+}
+
 static int uvc_ioctl_g_ext_ctrls(struct file *file, void *fh,
 				 struct v4l2_ext_controls *ctrls)
 {
@@ -1012,6 +1032,10 @@ static int uvc_ioctl_g_ext_ctrls(struct file *file, void *fh,
 	unsigned int i;
 	int ret;
 
+	ret = uvc_ctrl_check_access(chain, ctrls, VIDIOC_G_EXT_CTRLS);
+	if (ret < 0)
+		return ret;
+
 	if (ctrls->which == V4L2_CTRL_WHICH_DEF_VAL) {
 		for (i = 0; i < ctrls->count; ++ctrl, ++i) {
 			struct v4l2_queryctrl qc = { .id = ctrl->id };
@@ -1048,13 +1072,17 @@ static int uvc_ioctl_g_ext_ctrls(struct file *file, void *fh,
 
 static int uvc_ioctl_s_try_ext_ctrls(struct uvc_fh *handle,
 				     struct v4l2_ext_controls *ctrls,
-				     bool commit)
+				     unsigned long ioctl)
 {
 	struct v4l2_ext_control *ctrl = ctrls->controls;
 	struct uvc_video_chain *chain = handle->chain;
 	unsigned int i;
 	int ret;
 
+	ret = uvc_ctrl_check_access(chain, ctrls, ioctl);
+	if (ret < 0)
+		return ret;
+
 	ret = uvc_ctrl_begin(chain);
 	if (ret < 0)
 		return ret;
@@ -1063,14 +1091,15 @@ static int uvc_ioctl_s_try_ext_ctrls(struct uvc_fh *handle,
 		ret = uvc_ctrl_set(handle, ctrl);
 		if (ret < 0) {
 			uvc_ctrl_rollback(handle);
-			ctrls->error_idx = commit ? ctrls->count : i;
+			ctrls->error_idx = ioctl == VIDIOC_S_EXT_CTRLS ?
+						    ctrls->count : i;
 			return ret;
 		}
 	}
 
 	ctrls->error_idx = 0;
 
-	if (commit)
+	if (ioctl == VIDIOC_S_EXT_CTRLS)
 		return uvc_ctrl_commit(handle, ctrls->controls, ctrls->count);
 	else
 		return uvc_ctrl_rollback(handle);
@@ -1081,7 +1110,7 @@ static int uvc_ioctl_s_ext_ctrls(struct file *file, void *fh,
 {
 	struct uvc_fh *handle = fh;
 
-	return uvc_ioctl_s_try_ext_ctrls(handle, ctrls, true);
+	return uvc_ioctl_s_try_ext_ctrls(handle, ctrls, VIDIOC_S_EXT_CTRLS);
 }
 
 static int uvc_ioctl_try_ext_ctrls(struct file *file, void *fh,
@@ -1089,7 +1118,7 @@ static int uvc_ioctl_try_ext_ctrls(struct file *file, void *fh,
 {
 	struct uvc_fh *handle = fh;
 
-	return uvc_ioctl_s_try_ext_ctrls(handle, ctrls, false);
+	return uvc_ioctl_s_try_ext_ctrls(handle, ctrls, VIDIOC_TRY_EXT_CTRLS);
 }
 
 static int uvc_ioctl_querymenu(struct file *file, void *fh,

drivers/media/usb/uvc/uvcvideo.h

@@ -901,6 +901,8 @@ static inline int uvc_ctrl_rollback(struct uvc_fh *handle)
 
 int uvc_ctrl_get(struct uvc_video_chain *chain, struct v4l2_ext_control *xctrl);
 int uvc_ctrl_set(struct uvc_fh *handle, struct v4l2_ext_control *xctrl);
+int uvc_ctrl_is_accessible(struct uvc_video_chain *chain, u32 v4l2_id,
+			   bool read);
 
 int uvc_xu_ctrl_query(struct uvc_video_chain *chain,
 		      struct uvc_xu_control_query *xqry);