linux-kernel - Re: [PATCH] fbdev/xen-fbfront: Assign fb

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Message-ID: <Zt_zvt3VXwim_DwS@macbook.local>
Date: Tue, 10 Sep 2024 09:22:38 +0200
From: Roger Pau Monné <roger.pau@...rix.com>
To: Jason Andryuk <jandryuk@...il.com>
Cc: Helge Deller <deller@....de>, Thomas Zimmermann <tzimmermann@...e.de>,
	Arnd Bergmann <arnd@...db.de>, Sam Ravnborg <sam@...nborg.org>,
	xen-devel@...ts.xenproject.org,
	Jason Andryuk <jason.andryuk@....com>,
	Arthur Borsboom <arthurborsboom@...il.com>, stable@...r.kernel.org,
	linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fbdev/xen-fbfront: Assign fb_info->device

On Mon, Sep 09, 2024 at 10:09:16PM -0400, Jason Andryuk wrote:
> From: Jason Andryuk <jason.andryuk@....com>
> 
> Probing xen-fbfront faults in video_is_primary_device().  The passed-in
> struct device is NULL since xen-fbfront doesn't assign it and the
> memory is kzalloc()-ed.  Assign fb_info->device to avoid this.
> 
> This was exposed by the conversion of fb_is_primary_device() to
> video_is_primary_device() which dropped a NULL check for struct device.
> 
> Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
> Reported-by: Arthur Borsboom <arthurborsboom@...il.com>
> Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=LkXWeiSiTKsDY-cOe8QksWhFvcCneOKfrKd0ZajA@mail.gmail.com/
> Tested-by: Arthur Borsboom <arthurborsboom@...il.com>
> CC: stable@...r.kernel.org
> Signed-off-by: Jason Andryuk <jason.andryuk@....com>

Reviewed-by: Roger Pau Monné <roger.pau@...rix.com>

> ---
> The other option would be to re-instate the NULL check in
> video_is_primary_device()

I do think this is needed, or at least an explanation.  The commit
message in f178e96de7f0 doesn't mention anything about
video_is_primary_device() not allowing being passed a NULL device
(like it was possible with fb_is_primary_device()).

Otherwise callers of video_is_primary_device() would need to be
adjusted to check for device != NULL.

Thanks, Roger.