linux-kernel - Re: [PATCH v2] driver: uio: fix possible memory leak and use-after-free in __uio_register

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Date:   Mon, 7 Jan 2019 17:13:15 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     liujian <liujian56@...wei.com>
Cc:     michal.simek@...inx.com, hamish.martin@...iedtelesis.co.nz,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] driver: uio: fix possible memory leak and
 use-after-free in __uio_register_device

On Fri, Jan 04, 2019 at 10:19:08PM +0800, liujian wrote:
> 'idev' is malloced in __uio_register_device() and leak free it before
> leaving from the uio_get_minor() error handing case, it will cause
> memory leak.
> 
> Also, in uio_dev_add_attributes() error handing case, idev is used after
> device_unregister(), in which 'idev' has been released, touch idev cause
> use-after-free.
> 
> Fixes: a93e7b331568 ("uio: Prevent device destruction while fds are open")
> Fixes: e6789cd3dfb5 ("uio: Simplify uio error path by using devres functions")
> Signed-off-by: liujian <liujian56@...wei.com>
> Reviewed-by: Hamish Martin <hamish.martin@...iedtelesis.co.nz>
> ---
> v1->v2:
> change git log and fix code
> 
>  drivers/uio/uio.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
> index 1313422..be2a943 100644
> --- a/drivers/uio/uio.c
> +++ b/drivers/uio/uio.c
> @@ -940,9 +940,12 @@ int __uio_register_device(struct module *owner,
>  	atomic_set(&idev->event, 0);
>  
>  	ret = uio_get_minor(idev);
> -	if (ret)
> +	if (ret) {
> +		kfree(idev);
>  		return ret;
> +	}
>  
> +	device_initialize(&idev->dev);
>  	idev->dev.devt = MKDEV(uio_major, idev->minor);
>  	idev->dev.class = &uio_class;
>  	idev->dev.parent = parent;
> @@ -953,7 +956,7 @@ int __uio_register_device(struct module *owner,
>  	if (ret)
>  		goto err_device_create;
>  
> -	ret = device_register(&idev->dev);
> +	ret = device_add(&idev->dev);
>  	if (ret)
>  		goto err_device_create;
>  
> @@ -985,9 +988,10 @@ int __uio_register_device(struct module *owner,
>  err_request_irq:
>  	uio_dev_del_attributes(idev);
>  err_uio_dev_add_attributes:
> -	device_unregister(&idev->dev);
> +	device_del(&idev->dev);
>  err_device_create:
>  	uio_free_minor(idev);
> +	put_device(&idev->dev);

device_del() and then put_device()?  I don't think that's a correct
error cleanup path do you?

Please fix one thing at a time here also, this should be a a patch
series, right?

thanks,

greg k-h