linux-kernel - Re: [PATCH 2/2] fbdev: Make fb_release() return -ENODEV if fbdev was unregistered

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Message-ID: <193c9eef-af13-219c-e5e0-2cc9469bf562@suse.de>
Date:   Mon, 2 May 2022 15:20:23 +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, Helge Deller <deller@....de>,
        Zheyu Ma <zheyuma97@...il.com>,
        Changcheng Deng <deng.changcheng@....com.cn>,
        dri-devel@...ts.freedesktop.org, Maxime Ripard <maxime@...no.tech>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Alex Deucher <alexander.deucher@....com>,
        Sam Ravnborg <sam@...nborg.org>,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH 2/2] fbdev: Make fb_release() return -ENODEV if fbdev was
 unregistered



Am 02.05.22 um 15:09 schrieb Javier Martinez Canillas:
> A reference to the framebuffer device struct fb_info is stored in the file
> private data, but this reference could no longer be valid and must not be
> accessed directly. Instead, the file_fb_info() accessor function must be
> used since it does sanity checking to make sure that the fb_info is valid.
> 
> This can happen for example if the fbdev driver was one that is using a
> framebuffer provided by the system firmware. In that case, the fbdev core
> could unregister the framebuffer device if a real video driver is probed.
> 
> Reported-by: Maxime Ripard <maxime@...no.tech>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>

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

This seems like the correct thing to do in any case. Thanks for the 
patch. Before merging, you should also add

Fixes: 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced 
removal")
Reported-by: Junxiao Chang <junxiao.chang@...el.com>

Best regards
Thomas

> ---
> 
>   drivers/video/fbdev/core/fbmem.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 20d8929df79f..d68097105f93 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1439,7 +1439,10 @@ fb_release(struct inode *inode, struct file *file)
>   __acquires(&info->lock)
>   __releases(&info->lock)
>   {
> -	struct fb_info * const info = file->private_data;
> +	struct fb_info * const info = file_fb_info(file);
> +
> +	if (!info)
> +		return -ENODEV;
>   
>   	lock_fb_info(info);
>   	if (info->fbops->fb_release)

-- 
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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