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Date:   Thu, 10 Feb 2022 17:26:18 -0800
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Zhouyi Zhou <zhouzhouyi@gmail.com>
Cc:     daniel@ffwll.ch, deller@gmx.de, sam@ravnborg.org,
        linux@roeck-us.net, willy@infradead.org,
        linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, rcu@vger.kernel.org,
        pmenzel@molgen.mpg.de
Subject: Re: [PATCH linux-next] video: fbdev: fbmem: fix pointer reference to
 null device field
Message-ID: <20220211012618.GA4285@paulmck-ThinkPad-P17-Gen-1>
Reply-To: paulmck@kernel.org
References: <20220210065824.368355-1-zhouzhouyi@gmail.com>
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On Thu, Feb 10, 2022 at 02:58:24PM +0800, Zhouyi Zhou wrote:
> In function do_remove_conflicting_framebuffers, if device is NULL, there
> will be null pointer reference. The patch add a check to the if expression.
> 
> Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
> ---
> Dear Linux folks
> 
> I discover this bug in the PowerPC VM provided by
> Open source lab of Oregon State University:
> 
> https://lkml.org/lkml/2022/2/8/1145
> 
> I found that the root cause of null device field is in offb_init_fb:
> info = framebuffer_alloc(sizeof(u32) * 16, NULL);
> 
> I have tested the patch in the PowerPC VM. Hope my patch can be correct.

This looks plausible to me, but I am quite unfamiliar with this code.

						Thanx, Paul

> Many Thanks
> Zhouyi
> --
>  drivers/video/fbdev/core/fbmem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 34d6bb1bf82e..422b1fc01722 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1579,7 +1579,7 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
>  			 * If it's not a platform device, at least print a warning. A
>  			 * fix would add code to remove the device from the system.
>  			 */
> -			if (dev_is_platform(device)) {
> +			if (device && dev_is_platform(device)) {
>  				registered_fb[i]->forced_out = true;
>  				platform_device_unregister(to_platform_device(device));
>  			} else {
> -- 
> 2.25.1
>