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

Eugenio Perez Martin
2026-03-25T10:18:24Z

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
>