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

[Frederic Barrat <fbarrat@linux.ibm.com>]

On 11/11/2022 15:54, 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.
> 
> Fixes: 14baf4d9c739 ("cxl: Add guest-specific code")
> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
> ---


Thanks for fixing it!
At first, I was slightly uneasy about calling device_del() and 
put_device() directly, i.e. it would be better not to worry about what's 
under the hood of device_unregister(). But 1) I don't see how else to 
fix it and 2) more importantly, I looked at the history of 
device_unregister() to see how frequently it changed. I can now rest 
easy :-)

Acked-by: Frederic Barrat <fbarrat@linux.ibm.com>

   Fred



>   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: