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

Ilpo Järvinen
2026-03-31T15:02:56Z

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@kernel.org/ [1]
> Reported-by: Gui-Dong Han <hanguidong02@gmail.com>
> 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@kernel.org>
> ---
> 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.