linux-kernel - Re: [PATCH] fbdev: efifb: Fix a use-after-free due early fb

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Date:   Fri, 6 May 2022 18:50:16 +0200
From:   Andrzej Hajda <andrzej.hajda@...el.com>
To:     Javier Martinez Canillas <javierm@...hat.com>,
        <linux-kernel@...r.kernel.org>
CC:     Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        <intel-gfx@...ts.freedesktop.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Helge Deller <deller@....de>, Peter Jones <pjones@...hat.com>,
        "Thomas Zimmermann" <tzimmermann@...e.de>,
        <dri-devel@...ts.freedesktop.org>, <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH] fbdev: efifb: Fix a use-after-free due early fb_info
 cleanup



On 06.05.2022 15:22, Javier Martinez Canillas wrote:
> Commit d258d00fb9c7 ("fbdev: efifb: Cleanup fb_info in .fb_destroy rather
> than .remove") attempted to fix a use-after-free error due driver freeing
> the fb_info in the .remove handler instead of doing it in .fb_destroy.
>
> But ironically that change introduced yet another use-after-free since the
> fb_info was still used after the free.
>
> This should fix for good by freeing the fb_info at the end of the handler.
>
> Fixes: d258d00fb9c7 ("fbdev: efifb: Cleanup fb_info in .fb_destroy rather than .remove")
> Reported-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> Reported-by: Andrzej Hajda <andrzej.hajda@...el.com>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> ---

Reviewed-by: Andrzej Hajda <andrzej.hajda@...el.com>

Regards
Andrzej
>
>   drivers/video/fbdev/efifb.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c
> index cfa3dc0b4eee..b3d5f884c544 100644
> --- a/drivers/video/fbdev/efifb.c
> +++ b/drivers/video/fbdev/efifb.c
> @@ -259,12 +259,12 @@ static void efifb_destroy(struct fb_info *info)
>   			memunmap(info->screen_base);
>   	}
>   
> -	framebuffer_release(info);
> -
>   	if (request_mem_succeeded)
>   		release_mem_region(info->apertures->ranges[0].base,
>   				   info->apertures->ranges[0].size);
>   	fb_dealloc_cmap(&info->cmap);
> +
> +	framebuffer_release(info);
>   }
>   
>   static const struct fb_ops efifb_ops = {