linux-kernel - Re: [PATCH v2 4/4] fbdev: vesafb: Cleanup fb_info in .fb

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Date:   Thu, 5 May 2022 13:51:41 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        Helge Deller <deller@....de>, dri-devel@...ts.freedesktop.org,
        linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v2 4/4] fbdev: vesafb: Cleanup fb_info in .fb_destroy
 rather than .remove



Am 05.05.22 um 13:31 schrieb Javier Martinez Canillas:
> The driver is calling framebuffer_release() in its .remove callback, but
> this will cause the struct fb_info to be freed too early. Since it could
> be that a reference is still hold to it if user-space opened the fbdev.
> 
> This would lead to a use-after-free error if the framebuffer device was
> unregistered but later a user-space process tries to close the fbdev fd.
> 
> The correct thing to do is to only unregister the framebuffer in the
> driver's .remove callback, but do any cleanup in the fb_ops.fb_destroy.
> 
> Suggested-by: Daniel Vetter <daniel.vetter@...ll.ch>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>

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

> ---
> 
> Changes in v2:
> - Also do the change for vesafb (Thomas Zimmermann).
> 
>   drivers/video/fbdev/vesafb.c | 14 +++++++++++---
>   1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c
> index df6de5a9dd4c..1f03a449e505 100644
> --- a/drivers/video/fbdev/vesafb.c
> +++ b/drivers/video/fbdev/vesafb.c
> @@ -179,6 +179,10 @@ static int vesafb_setcolreg(unsigned regno, unsigned red, unsigned green,
>   	return err;
>   }
>   
> +/*
> + * fb_ops.fb_destroy is called by the last put_fb_info() call at the end
> + * of unregister_framebuffer() or fb_release(). Do any cleanup here.
> + */
>   static void vesafb_destroy(struct fb_info *info)
>   {
>   	struct vesafb_par *par = info->par;
> @@ -187,7 +191,13 @@ static void vesafb_destroy(struct fb_info *info)
>   	arch_phys_wc_del(par->wc_cookie);
>   	if (info->screen_base)
>   		iounmap(info->screen_base);
> +
> +	if (((struct vesafb_par *)(info->par))->region)
> +		release_region(0x3c0, 32);
> +
>   	release_mem_region(info->apertures->ranges[0].base, info->apertures->ranges[0].size);
> +
> +	framebuffer_release(info);
>   }
>   
>   static struct fb_ops vesafb_ops = {
> @@ -484,10 +494,8 @@ static int vesafb_remove(struct platform_device *pdev)
>   {
>   	struct fb_info *info = platform_get_drvdata(pdev);
>   
> +	/* vesafb_destroy takes care of info cleanup */
>   	unregister_framebuffer(info);
> -	if (((struct vesafb_par *)(info->par))->region)
> -		release_region(0x3c0, 32);
> -	framebuffer_release(info);
>   
>   	return 0;
>   }

-- 
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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