linux-kernel - Re: [PATCH] auxdisplay: ht16k33: fix potential user-after-free on module unload

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Date:   Mon, 11 Feb 2019 08:26:19 +0100
From:   Robin van der Gracht <robin@...tonic.nl>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     Sven Van Asbroeck <thesven73@...il.com>, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Sebastian Reichel <sre@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] auxdisplay: ht16k33: fix potential user-after-free on
 module unload

On Sat, 9 Feb 2019 01:15:22 +0100
Miguel Ojeda <miguel.ojeda.sandonis@...il.com> wrote:

> On module unload/remove, we need to ensure that work does not run
> after we have freed resources. Concretely, cancel_delayed_work()
> may return while the callback function is still running.
> 
> From kernel/workqueue.c:
> 
>     The work callback function may still be running on return,
>     unless it returns true and the work doesn't re-arm itself.
>     Explicitly flush or use cancel_delayed_work_sync() to wait on it.
> 
> Link: https://lore.kernel.org/lkml/20190204220952.30761-1-TheSven73@googlemail.com/
> Reported-by: Sven Van Asbroeck <thesven73@...il.com>
> Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
> ---
>  drivers/auxdisplay/ht16k33.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/auxdisplay/ht16k33.c b/drivers/auxdisplay/ht16k33.c
> index a43276c76fc6..21393ec3b9a4 100644
> --- a/drivers/auxdisplay/ht16k33.c
> +++ b/drivers/auxdisplay/ht16k33.c
> @@ -509,7 +509,7 @@ static int ht16k33_remove(struct i2c_client *client)
>  	struct ht16k33_priv *priv = i2c_get_clientdata(client);
>  	struct ht16k33_fbdev *fbdev = &priv->fbdev;
>  
> -	cancel_delayed_work(&fbdev->work);
> +	cancel_delayed_work_sync(&fbdev->work);
>  	unregister_framebuffer(fbdev->info);
>  	framebuffer_release(fbdev->info);
>  	free_page((unsigned long) fbdev->buffer);

Looks good

Acked-by: Robin van der Gracht <robin@...tonic.nl>