Re: [PATCH] fbdev: pxafb: Fix use after free vulnerability in pxafb_driver Driver Due to Race Condition

[Kaixin Wang]

At 2024-09-12 01:38:26, "Helge Deller" <deller@xxxxxx> wrote:
>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@xxxxxxxxxxxxxx>
>> ---
>>   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
>
>


Thanks for the review! I appreciate the adjustment to the patch title to make it more precise.

Best regards,
Kaixin Wang