Re: [PATCH 06/12] platform/wmi: use generic driver_override infrastructure

[Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>]

On Tue, 24 Mar 2026, Danilo Krummrich wrote:

> When a driver is probed through __driver_attach(), the bus' match()
> callback is called without the device lock held, thus accessing the
> driver_override field without a lock, which can cause a UAF.
> 
> Fix this by using the driver-core driver_override infrastructure taking
> care of proper locking internally.
> 
> Note that calling match() from __driver_attach() without the device lock
> held is intentional. [1]
> 
> Link: 
> https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@xxxxxxxxxx/ [1]
> Reported-by: Gui-Dong Han <hanguidong02@xxxxxxxxx>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220789
> Fixes: 12046f8c77e0 ("platform/x86: wmi: Add driver_override support")
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> ---
>  drivers/platform/wmi/core.c | 36 +++++-------------------------------
>  include/linux/wmi.h         |  4 ----
>  2 files changed, 5 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/platform/wmi/core.c b/drivers/platform/wmi/core.c
> index b8e6b9a421c6..750e3619724e 100644
> --- a/drivers/platform/wmi/core.c
> +++ b/drivers/platform/wmi/core.c
> @@ -842,39 +842,11 @@ static ssize_t expensive_show(struct device *dev,
>  }
>  static DEVICE_ATTR_RO(expensive);
>  
> -static ssize_t driver_override_show(struct device *dev, struct 
> device_attribute *attr,
> -                                 char *buf)
> -{
> -     struct wmi_device *wdev = to_wmi_device(dev);
> -     ssize_t ret;
> -
> -     device_lock(dev);
> -     ret = sysfs_emit(buf, "%s\n", wdev->driver_override);
> -     device_unlock(dev);
> -
> -     return ret;
> -}
> -
> -static ssize_t driver_override_store(struct device *dev, struct 
> device_attribute *attr,
> -                                  const char *buf, size_t count)
> -{
> -     struct wmi_device *wdev = to_wmi_device(dev);
> -     int ret;
> -
> -     ret = driver_set_override(dev, &wdev->driver_override, buf, count);
> -     if (ret < 0)
> -             return ret;
> -
> -     return count;
> -}
> -static DEVICE_ATTR_RW(driver_override);
> -
>  static struct attribute *wmi_attrs[] = {
>       &dev_attr_modalias.attr,
>       &dev_attr_guid.attr,
>       &dev_attr_instance_count.attr,
>       &dev_attr_expensive.attr,
> -     &dev_attr_driver_override.attr,
>       NULL
>  };
>  ATTRIBUTE_GROUPS(wmi);
> @@ -943,7 +915,6 @@ static void wmi_dev_release(struct device *dev)
>  {
>       struct wmi_block *wblock = dev_to_wblock(dev);
>  
> -     kfree(wblock->dev.driver_override);
>       kfree(wblock);
>  }
>  
> @@ -952,10 +923,12 @@ static int wmi_dev_match(struct device *dev, const 
> struct device_driver *driver)
>       const struct wmi_driver *wmi_driver = to_wmi_driver(driver);
>       struct wmi_block *wblock = dev_to_wblock(dev);
>       const struct wmi_device_id *id = wmi_driver->id_table;
> +     int ret;
>  
>       /* When driver_override is set, only bind to the matching driver */
> -     if (wblock->dev.driver_override)
> -             return !strcmp(wblock->dev.driver_override, driver->name);
> +     ret = device_match_driver_override(dev, driver);
> +     if (ret >= 0)
> +             return ret;
>  
>       if (id == NULL)
>               return 0;
> @@ -1076,6 +1049,7 @@ static struct class wmi_bus_class = {
>  static const struct bus_type wmi_bus_type = {
>       .name = "wmi",
>       .dev_groups = wmi_groups,
> +     .driver_override = true,
>       .match = wmi_dev_match,
>       .uevent = wmi_dev_uevent,
>       .probe = wmi_dev_probe,
> diff --git a/include/linux/wmi.h b/include/linux/wmi.h
> index 75cb0c7cfe57..14fb644e1701 100644
> --- a/include/linux/wmi.h
> +++ b/include/linux/wmi.h
> @@ -18,16 +18,12 @@
>   * struct wmi_device - WMI device structure
>   * @dev: Device associated with this WMI device
>   * @setable: True for devices implementing the Set Control Method
> - * @driver_override: Driver name to force a match; do not set directly,
> - *                because core frees it; use driver_set_override() to
> - *                set or clear it.
>   *
>   * This represents WMI devices discovered by the WMI driver core.
>   */
>  struct wmi_device {
>       struct device dev;
>       bool setable;
> -     const char *driver_override;
>  };
>  
>  /**
> 

Hi,

I tried applying this to platform-drivers tree but it failed to compile so 
I ended up dropping the changed.

-- 
 i.