linux-kernel - Re: Bug report: greybus/interface.c: use-after-free bug in gb_interface

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Date: Tue, 16 Apr 2024 06:49:43 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: sicong <congei42@....com>
Cc: johan@...nel.org, elder@...nel.org, greybus-dev@...ts.linaro.org,
	linux-kernel@...r.kernel.org
Subject: Re: Bug report: greybus/interface.c: use-after-free bug in
 gb_interface_release due to race condition

On Tue, Apr 16, 2024 at 11:00:25AM +0800, sicong wrote:
> greybus/interface.c: use-after-free bug in gb_interface_release due to
> race condition.
> 
> In gb_interface_create, &intf->mode_switch_completion is bound with 
> gb_interface_mode_switch_work. Then it will be started by 
> gb_interface_request_mode_switch. Here is the code.
> if (!queue_work(system_long_wq, &intf->mode_switch_work)) {
> 	...
> }
> 
> If we call gb_interface_release to make cleanup, there may be an 
> unfinished work. This function will call kfree to free the object 
> "intf". However, if gb_interface_mode_switch_work is scheduled to 
> run after kfree, it may cause use-after-free error as 
> gb_interface_mode_switch_work will use the object "intf". 
> The possible execution flow that may lead to the issue is as follows:
> 
> CPU0                            CPU1
> 
>                             |   gb_interface_create
>                             |   gb_interface_request_mode_switch
> gb_interface_release        |
> kfree(intf) (free)          |
>                             |   gb_interface_mode_switch_work
>                             |   mutex_lock(&intf->mutex) (use)   
> 
> This bug may be fixed by adding the following code before kfree.
> cancel_work_sync(&intf->mode_switch_work);

Wonderful, please submit a patch with this information and we will be
glad to review it.

thanks,

greg k-h