linux-kernel - Re: [PATCH v2] fbdev: Make fb_release() return -ENODEV if fbdev was unregistered

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Message-ID: <e3ce080c-8ef8-f838-d4a8-b10cd5d5c172@redhat.com>
Date:   Tue, 3 May 2022 17:28:09 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Maxime Ripard <maxime@...no.tech>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Junxiao Chang <junxiao.chang@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        Changcheng Deng <deng.changcheng@....com.cn>,
        Daniel Vetter <daniel@...ll.ch>,
        Hans de Goede <hdegoede@...hat.com>,
        Helge Deller <deller@....de>, Sam Ravnborg <sam@...nborg.org>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Zack Rusin <zackr@...are.com>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Zheyu Ma <zheyuma97@...il.com>,
        Zhouyi Zhou <zhouzhouyi@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v2] fbdev: Make fb_release() return -ENODEV if fbdev was
 unregistered

On 5/2/22 15:50, Javier Martinez Canillas wrote:
> 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 registered framebuffer device is for a
> driver that just uses a framebuffer provided by the system firmware. In
> that case, the fbdev core would unregister the framebuffer device when a
> real video driver is probed and ask to remove conflicting framebuffers.
> 
> The bug has been present for a long time but commit 27599aacbaef ("fbdev:
> Hot-unplug firmware fb devices on forced removal") unmasked it since the
> fbdev core started unregistering the framebuffers' devices associated.
> 
> Fixes: 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced removal")
> Reported-by: Maxime Ripard <maxime@...no.tech>
> Reported-by: Junxiao Chang <junxiao.chang@...el.com>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
> ---
Applied to drm-misc (drm-misc-fixes).

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat