[PATCH 1/2] cxl: fix possible null-ptr-deref in cxl_guest_init_afu|adapter()

[Andrew Donnellan]

On Fri, 2022-11-11 at 22:54 +0800, Yang Yingliang wrote:
> If device_register() fails in cxl_register_afu|adapter(), the device
> is not added, device_unregister() can not be called in the error
> path,
> otherwise it will cause a null-ptr-deref because of removing not
> added
> device.
> 
> As comment of device_register() says, it should use put_device() to
> give
> up the reference in the error path. So split device_unregister() into
> device_del() and put_device(), then goes to put dev when register
> fails.

The comment around device_add() is relevant too:

  Rule of thumb is: if device_add() succeeds, you should call
  device_del() when you want to get rid of it. If device_add() has
  *not* succeeded, use *only* put_device() to drop the reference count.

> 
> Fixes: 14baf4d9c739 ("cxl: Add guest-specific code")
> Signed-off-by: Yang Yingliang <yangyingliang at huawei.com>

Thanks for the fix!

Acked-by: Andrew Donnellan <ajd at linux.ibm.com>

> ---
>  drivers/misc/cxl/guest.c | 24 ++++++++++++++----------
>  1 file changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/misc/cxl/guest.c b/drivers/misc/cxl/guest.c
> index 375f692ae9d6..fb95a2d5cef4 100644
> --- a/drivers/misc/cxl/guest.c
> +++ b/drivers/misc/cxl/guest.c
> @@ -965,10 +965,10 @@ int cxl_guest_init_afu(struct cxl *adapter, int
> slice, struct device_node *afu_n
>          * if it returns an error!
>          */
>         if ((rc = cxl_register_afu(afu)))
> -               goto err_put1;
> +               goto err_put_dev;
>  
>         if ((rc = cxl_sysfs_afu_add(afu)))
> -               goto err_put1;
> +               goto err_del_dev;
>  
>         /*
>          * pHyp doesn't expose the programming models supported by
> the
> @@ -984,7 +984,7 @@ int cxl_guest_init_afu(struct cxl *adapter, int
> slice, struct device_node *afu_n
>                 afu->modes_supported = CXL_MODE_DIRECTED;
>  
>         if ((rc = cxl_afu_select_best_mode(afu)))
> -               goto err_put2;
> +               goto err_remove_sysfs;
>  
>         adapter->afu[afu->slice] = afu;
>  
> @@ -1004,10 +1004,12 @@ int cxl_guest_init_afu(struct cxl *adapter,
> int slice, struct device_node *afu_n
>  
>         return 0;
>  
> -err_put2:
> +err_remove_sysfs:
>         cxl_sysfs_afu_remove(afu);
> -err_put1:
> -       device_unregister(&afu->dev);
> +err_del_dev:
> +       device_del(&afu->dev);
> +err_put_dev:
> +       put_device(&afu->dev);
>         free = false;
>         guest_release_serr_irq(afu);
>  err2:
> @@ -1141,18 +1143,20 @@ struct cxl *cxl_guest_init_adapter(struct
> device_node *np, struct platform_devic
>          * even if it returns an error!
>          */
>         if ((rc = cxl_register_adapter(adapter)))
> -               goto err_put1;
> +               goto err_put_dev;
>  
>         if ((rc = cxl_sysfs_adapter_add(adapter)))
> -               goto err_put1;
> +               goto err_del_dev;
>  
>         /* release the context lock as the adapter is configured */
>         cxl_adapter_context_unlock(adapter);
>  
>         return adapter;
>  
> -err_put1:
> -       device_unregister(&adapter->dev);
> +err_del_dev:
> +       device_del(&adapter->dev);
> +err_put_dev:
> +       put_device(&adapter->dev);
>         free = false;
>         cxl_guest_remove_chardev(adapter);
>  err1:

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd at linux.ibm.com   IBM Australia Limited