Re: [PATCH 08/12] vdpa: use generic driver_override infrastructure

[Eugenio Perez Martin <eperezma@redhat.com>]

On Tue, Mar 24, 2026 at 2:00 AM Danilo Krummrich <dakr@kernel.org> 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: 539fec78edb4 ("vdpa: add driver_override support")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
>  drivers/vdpa/vdpa.c  | 48 +++++---------------------------------------
>  include/linux/vdpa.h |  4 ----
>  2 files changed, 5 insertions(+), 47 deletions(-)
>

Consolidate this logic is great, thanks!

> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> index 34874beb0152..caf0ee5d6856 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -67,57 +67,20 @@ static void vdpa_dev_remove(struct device *d)
>
>  static int vdpa_dev_match(struct device *dev, const struct device_driver *drv)
>  {
> -       struct vdpa_device *vdev = dev_to_vdpa(dev);
> +       int ret;
>
>         /* Check override first, and if set, only use the named driver */
> -       if (vdev->driver_override)
> -               return strcmp(vdev->driver_override, drv->name) == 0;
> +       ret = device_match_driver_override(dev, drv);
> +       if (ret >= 0)
> +               return ret;
>
>         /* Currently devices must be supported by all vDPA bus drivers */
>         return 1;

Nit: Maybe all of this can be replaced by
abs(device_match_driver_override(dev,drv))? Or maybe we're putting too
much in the same line.

Either way,

Acked-by: Eugenio Pérez <eperezma@redhat.com>

Thanks!




>  }
>
> -static ssize_t driver_override_store(struct device *dev,
> -                                    struct device_attribute *attr,
> -                                    const char *buf, size_t count)
> -{
> -       struct vdpa_device *vdev = dev_to_vdpa(dev);
> -       int ret;
> -
> -       ret = driver_set_override(dev, &vdev->driver_override, buf, count);
> -       if (ret)
> -               return ret;
> -
> -       return count;
> -}
> -
> -static ssize_t driver_override_show(struct device *dev,
> -                                   struct device_attribute *attr, char *buf)
> -{
> -       struct vdpa_device *vdev = dev_to_vdpa(dev);
> -       ssize_t len;
> -
> -       device_lock(dev);
> -       len = sysfs_emit(buf, "%s\n", vdev->driver_override);
> -       device_unlock(dev);
> -
> -       return len;
> -}
> -static DEVICE_ATTR_RW(driver_override);
> -
> -static struct attribute *vdpa_dev_attrs[] = {
> -       &dev_attr_driver_override.attr,
> -       NULL,
> -};
> -
> -static const struct attribute_group vdpa_dev_group = {
> -       .attrs  = vdpa_dev_attrs,
> -};
> -__ATTRIBUTE_GROUPS(vdpa_dev);
> -
>  static const struct bus_type vdpa_bus = {
>         .name  = "vdpa",
> -       .dev_groups = vdpa_dev_groups,
> +       .driver_override = true,
>         .match = vdpa_dev_match,
>         .probe = vdpa_dev_probe,
>         .remove = vdpa_dev_remove,
> @@ -132,7 +95,6 @@ static void vdpa_release_dev(struct device *d)
>                 ops->free(vdev);
>
>         ida_free(&vdpa_index_ida, vdev->index);
> -       kfree(vdev->driver_override);
>         kfree(vdev);
>  }
>
> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> index 2bfe3baa63f4..782c42d25db1 100644
> --- a/include/linux/vdpa.h
> +++ b/include/linux/vdpa.h
> @@ -72,9 +72,6 @@ struct vdpa_mgmt_dev;
>   * struct vdpa_device - representation of a vDPA device
>   * @dev: underlying device
>   * @vmap: the metadata passed to upper layer to be used for mapping
> - * @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.
>   * @config: the configuration ops for this device.
>   * @map: the map ops for this device
>   * @cf_lock: Protects get and set access to configuration layout.
> @@ -90,7 +87,6 @@ struct vdpa_mgmt_dev;
>  struct vdpa_device {
>         struct device dev;
>         union virtio_map vmap;
> -       const char *driver_override;
>         const struct vdpa_config_ops *config;
>         const struct virtio_map_ops *map;
>         struct rw_semaphore cf_lock; /* Protects get/set config */
> --
> 2.53.0
>