Re: [PATCH v5] usb: gadget: udc: renesas_usb3: Fix use after free bug in renesas_usb3_remove due to race condition

[Greg KH]

On Thu, Mar 16, 2023 at 11:56:45PM +0800, Zheng Wang wrote:
> In renesas_usb3_probe, &usb3->role_work is bound with
> renesas_usb3_role_work. renesas_usb3_start will be called
> to start the work.

You have a full 72 columns to write in, please use them :)

> 
> If we remove the driver which will call usbhs_remove, there may be
> an unfinished work. The possible sequence is as follows:
> 
> Fix it by canceling the work before cleanup in the renesas_usb3_remove.
> 
> CPU0                  CPU1
> 
>                     |renesas_usb3_role_work
> renesas_usb3_remove |
> usb_role_switch_unregister  |
> device_unregister   |
> kfree(sw)  	     |
> free usb3->role_sw  |
>                     |   usb_role_switch_set_role
>                     |   //use usb3->role_sw

Why can't this be written so it looks better:

 CPU0                         CPU1

                            | renesas_usb3_role_work
 renesas_usb3_remove        |
 usb_role_switch_unregister |
 device_unregister          |
 kfree(sw)  	            |
 free usb3->role_sw         |
                            |  usb_role_switch_set_role
                            |  // use usb3->role_sw

Note that removing a driver is a root-only operation, and should never
happen so please also say that.

thanks,

greg k-h