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

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Date: Tue, 16 Apr 2024 11:00:25 +0800 (CST)
From: sicong <congei42@....com>
To: johan@...nel.org, elder@...nel.org, gregkh@...uxfoundation.org
Cc: greybus-dev@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Bug report: greybus/interface.c: use-after-free bug in
 gb_interface_release due to race condition

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);

Best regards,
Sicong Huang