linux-kernel - Re: [PATCH] fbdev: pxafb: Fix use after free vulnerability in pxafb

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Message-ID: <7baab3f7-1185-473d-83a7-07ad49a4130a@gmx.de>
Date: Wed, 11 Sep 2024 19:38:26 +0200
From: Helge Deller <deller@....de>
To: Kaixin Wang <kxwang23@...udan.edu.cn>
Cc: 21210240012@...udan.edu.cn, 21302010073@...udan.edu.cn,
 linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, kuninori.morimoto.gx@...esas.com,
 laurent.pinchart@...asonboard.com
Subject: Re: [PATCH] fbdev: pxafb: Fix use after free vulnerability in
 pxafb_driver Driver Due to Race Condition

On 9/11/24 16:29, Kaixin Wang wrote:
> In the pxafb_probe function, it calls the pxafb_init_fbinfo function,
> after which &fbi->task is associated with pxafb_task. Moreover,
> within this pxafb_init_fbinfo function, the pxafb_blank function
> within the &pxafb_ops struct is capable of scheduling work.
>
> If we remove the module which will call pxafb_remove to make cleanup,
> it will call unregister_framebuffer function which can call
> do_unregister_framebuffer to free fbi->fb through
> put_fb_info(fb_info), while the work mentioned above will be used.
> The sequence of operations that may lead to a UAF bug is as follows:
>
> CPU0                                                CPU1
>
>                                     | pxafb_task
> pxafb_remove                       |
> unregister_framebuffer(info)       |
> do_unregister_framebuffer(fb_info) |
> put_fb_info(fb_info)               |
> // free fbi->fb                    | set_ctrlr_state(fbi, state)
>                                     | __pxafb_lcd_power(fbi, 0)
>                                     | fbi->lcd_power(on, &fbi->fb.var)
>                                     | //use fbi->fb
>
> Fix it by ensuring that the work is canceled before proceeding
> with the cleanup in pxafb_remove.
>
> Note that only root user can remove the driver at runtime.
>
> Signed-off-by: Kaixin Wang <kxwang23@...udan.edu.cn>
> ---
>   drivers/video/fbdev/pxafb.c | 1 +
>   1 file changed, 1 insertion(+)

I've added the patch to the fbdev git tree, but changed the title to:
"fbdev: pxafb: Fix possible use after free in pxafb_task()"

Thanks!
Helge