linux-kernel - Re: [PATCH 1/3] fbdev: Prevent possible use-after-free in fb

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Date:   Thu, 5 May 2022 09:31:18 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-fbdev@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Helge Deller <deller@....de>, dri-devel@...ts.freedesktop.org,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH 1/3] fbdev: Prevent possible use-after-free in
 fb_release()



Am 04.05.22 um 23:56 schrieb Javier Martinez Canillas:
> From: Daniel Vetter <daniel.vetter@...ll.ch>
> 
> Most fbdev drivers have issues with the fb_info lifetime, because call to
> framebuffer_release() from their driver's .remove callback, rather than
> doing from fbops.fb_destroy callback.
> 
> Doing that will destroy the fb_info too early, while references to it may
> still exist, leading to a use-after-free error.
> 
> To prevent this, check the fb_info reference counter when attempting to
> kfree the data structure in framebuffer_release(). That will leak it but
> at least will prevent the mentioned error.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

> ---
> 
>   drivers/video/fbdev/core/fbsysfs.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c
> index 26892940c213..82e31a2d845e 100644
> --- a/drivers/video/fbdev/core/fbsysfs.c
> +++ b/drivers/video/fbdev/core/fbsysfs.c
> @@ -80,6 +80,10 @@ void framebuffer_release(struct fb_info *info)
>   {
>   	if (!info)
>   		return;
> +
> +	if (WARN_ON(refcount_read(&info->count)))
> +		return;
> +
>   	kfree(info->apertures);
>   	kfree(info);
>   }

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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