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From 90712c1a495c2aa4b10dd8127fdd7f1a0cd9ef00 Mon Sep 17 00:00:00 2001
From: Jacopo Mondi <jacopo@jmondi.org>
Date: Tue, 7 Apr 2020 17:21:57 +0200
Subject: [PATCH] media: v4l2-dev: Add
 v4l2_device_register_ro_subdev_node()

Add to the V4L2 core a function to register device nodes for video
subdevices in read-only mode.

Registering a device node in read-only mode is useful to expose to
userspace the current sub-device configuration, without allowing
application to change it by using the V4L2 subdevice ioctls.

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
---
 drivers/media/v4l2-core/v4l2-device.c |  7 ++--
 drivers/media/v4l2-core/v4l2-subdev.c | 19 ++++++++++
 include/media/v4l2-dev.h              |  7 ++++
 include/media/v4l2-device.h           | 50 ++++++++++++++++++++++++---
 4 files changed, 77 insertions(+), 6 deletions(-)

--- a/drivers/media/v4l2-core/v4l2-device.c
+++ b/drivers/media/v4l2-core/v4l2-device.c
@@ -189,7 +189,8 @@ static void v4l2_device_release_subdev_n
        kfree(vdev);
 }
 
-int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
+int __v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev,
+                                       bool read_only)
 {
        struct video_device *vdev;
        struct v4l2_subdev *sd;
@@ -218,6 +219,8 @@ int v4l2_device_register_subdev_nodes(st
                vdev->fops = &v4l2_subdev_fops;
                vdev->release = v4l2_device_release_subdev_node;
                vdev->ctrl_handler = sd->ctrl_handler;
+               if (read_only)
+                       set_bit(V4L2_FL_SUBDEV_RO_DEVNODE, &vdev->flags);
                err = __video_register_device(vdev, VFL_TYPE_SUBDEV, -1, 1,
                                              sd->owner);
                if (err < 0) {
@@ -255,7 +258,7 @@ clean_up:
 
        return err;
 }
-EXPORT_SYMBOL_GPL(v4l2_device_register_subdev_nodes);
+EXPORT_SYMBOL_GPL(__v4l2_device_register_subdev_nodes);
 
 void v4l2_device_unregister_subdev(struct v4l2_subdev *sd)
 {
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -331,6 +331,7 @@ static long subdev_do_ioctl(struct file
        struct v4l2_fh *vfh = file->private_data;
 #if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
        struct v4l2_subdev_fh *subdev_fh = to_v4l2_subdev_fh(vfh);
+       bool ro_subdev = test_bit(V4L2_FL_SUBDEV_RO_DEVNODE, &vdev->flags);
        int rval;
 #endif
 
@@ -453,6 +454,9 @@ static long subdev_do_ioctl(struct file
        case VIDIOC_SUBDEV_S_FMT: {
                struct v4l2_subdev_format *format = arg;
 
+               if (format->which != V4L2_SUBDEV_FORMAT_TRY && ro_subdev)
+                       return -EPERM;
+
                memset(format->reserved, 0, sizeof(format->reserved));
                memset(format->format.reserved, 0, sizeof(format->format.reserved));
                return v4l2_subdev_call(sd, pad, set_fmt, subdev_fh->pad, format);
@@ -480,6 +484,9 @@ static long subdev_do_ioctl(struct file
                struct v4l2_subdev_crop *crop = arg;
                struct v4l2_subdev_selection sel;
 
+               if (crop->which != V4L2_SUBDEV_FORMAT_TRY && ro_subdev)
+                       return -EPERM;
+
                memset(crop->reserved, 0, sizeof(crop->reserved));
                memset(&sel, 0, sizeof(sel));
                sel.which = crop->which;
@@ -521,6 +528,9 @@ static long subdev_do_ioctl(struct file
        case VIDIOC_SUBDEV_S_FRAME_INTERVAL: {
                struct v4l2_subdev_frame_interval *fi = arg;
 
+               if (ro_subdev)
+                       return -EPERM;
+
                memset(fi->reserved, 0, sizeof(fi->reserved));
                return v4l2_subdev_call(sd, video, s_frame_interval, arg);
        }
@@ -544,6 +554,9 @@ static long subdev_do_ioctl(struct file
        case VIDIOC_SUBDEV_S_SELECTION: {
                struct v4l2_subdev_selection *sel = arg;
 
+               if (sel->which != V4L2_SUBDEV_FORMAT_TRY && ro_subdev)
+                       return -EPERM;
+
                memset(sel->reserved, 0, sizeof(sel->reserved));
                return v4l2_subdev_call(
                        sd, pad, set_selection, subdev_fh->pad, sel);
@@ -580,6 +593,9 @@ static long subdev_do_ioctl(struct file
                return v4l2_subdev_call(sd, video, g_dv_timings, arg);
 
        case VIDIOC_SUBDEV_S_DV_TIMINGS:
+               if (ro_subdev)
+                       return -EPERM;
+
                return v4l2_subdev_call(sd, video, s_dv_timings, arg);
 
        case VIDIOC_SUBDEV_G_STD:
@@ -588,6 +604,9 @@ static long subdev_do_ioctl(struct file
        case VIDIOC_SUBDEV_S_STD: {
                v4l2_std_id *std = arg;
 
+               if (ro_subdev)
+                       return -EPERM;
+
                return v4l2_subdev_call(sd, video, s_std, *std);
        }
 
--- a/include/media/v4l2-dev.h
+++ b/include/media/v4l2-dev.h
@@ -82,11 +82,18 @@ struct v4l2_ctrl_handler;
  *     but the old crop API will still work as expected in order to preserve
  *     backwards compatibility.
  *     Never set this flag for new drivers.
+ * @V4L2_FL_SUBDEV_RO_DEVNODE:
+ *     indicates that the video device node is registered in read-only mode.
+ *     The flag only applies to device nodes registered for sub-devices, it is
+ *     set by the core when the sub-devices device nodes are registered with
+ *     v4l2_device_register_ro_subdev_nodes() and used by the sub-device ioctl
+ *     handler to restrict access to some ioctl calls.
  */
 enum v4l2_video_device_flags {
        V4L2_FL_REGISTERED              = 0,
        V4L2_FL_USES_V4L2_FH            = 1,
        V4L2_FL_QUIRK_INVERTED_CROP     = 2,
+       V4L2_FL_SUBDEV_RO_DEVNODE       = 3,
 };
 
 /* Priority helper functions */
--- a/include/media/v4l2-device.h
+++ b/include/media/v4l2-device.h
@@ -174,14 +174,56 @@ int __must_check v4l2_device_register_su
 void v4l2_device_unregister_subdev(struct v4l2_subdev *sd);
 
 /**
- * v4l2_device_register_subdev_nodes - Registers device nodes for all subdevs
- *     of the v4l2 device that are marked with
- *     the %V4L2_SUBDEV_FL_HAS_DEVNODE flag.
+ * __v4l2_device_register_ro_subdev_nodes - Registers device nodes for
+ *      all subdevs of the v4l2 device that are marked with the
+ *      %V4L2_SUBDEV_FL_HAS_DEVNODE flag.
  *
  * @v4l2_dev: pointer to struct v4l2_device
+ * @read_only: subdevices read-only flag. True to register the subdevices
+ *     device nodes in read-only mode, false to allow full access to the
+ *     subdevice userspace API.
  */
 int __must_check
-v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev);
+__v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev,
+                                   bool read_only);
+
+/**
+ * v4l2_device_register_subdev_nodes - Registers subdevices device nodes with
+ *     unrestricted access to the subdevice userspace operations
+ *
+ * Internally calls __v4l2_device_register_subdev_nodes(). See its documentation
+ * for more details.
+ *
+ * @v4l2_dev: pointer to struct v4l2_device
+ */
+static inline int __must_check
+v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
+{
+#if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
+       return __v4l2_device_register_subdev_nodes(v4l2_dev, false);
+#else
+       return 0;
+#endif
+}
+
+/**
+ * v4l2_device_register_ro_subdev_nodes - Registers subdevices device nodes
+ *     in read-only mode
+ *
+ * Internally calls __v4l2_device_register_subdev_nodes(). See its documentation
+ * for more details.
+ *
+ * @v4l2_dev: pointer to struct v4l2_device
+ */
+static inline int __must_check
+v4l2_device_register_ro_subdev_nodes(struct v4l2_device *v4l2_dev)
+{
+#if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
+       return __v4l2_device_register_subdev_nodes(v4l2_dev, true);
+#else
+       return 0;
+#endif
+}
 
 /**
  * v4l2_subdev_notify - Sends a notification to v4l2_device.