Re: [PATCH 3/3] fbdev/efifb: Cleanup fb_info in .fb_destroy rather than .remove

[Thomas Zimmermann <tzimmermann@suse.de>]

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Am 04.05.22 um 23:58 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@ffwll.ch>
> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>

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

> ---
> 
>   drivers/video/fbdev/efifb.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c
> index ea42ba6445b2..cfa3dc0b4eee 100644
> --- a/drivers/video/fbdev/efifb.c
> +++ b/drivers/video/fbdev/efifb.c
> @@ -243,6 +243,10 @@ static void efifb_show_boot_graphics(struct fb_info *info)
>   static inline void efifb_show_boot_graphics(struct fb_info *info) {}
>   #endif
>   
> +/*
> + * 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 efifb_destroy(struct fb_info *info)
>   {
>   	if (efifb_pci_dev)
> @@ -254,6 +258,9 @@ static void efifb_destroy(struct fb_info *info)
>   		else
>   			memunmap(info->screen_base);
>   	}
> +
> +	framebuffer_release(info);
> +
>   	if (request_mem_succeeded)
>   		release_mem_region(info->apertures->ranges[0].base,
>   				   info->apertures->ranges[0].size);
> @@ -620,9 +627,9 @@ static int efifb_remove(struct platform_device *pdev)
>   {
>   	struct fb_info *info = platform_get_drvdata(pdev);
>   
> +	/* efifb_destroy takes care of info cleanup */
>   	unregister_framebuffer(info);
>   	sysfs_remove_groups(&pdev->dev.kobj, efifb_groups);
> -	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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