[v7] usb: gadget: udc: renesas_usb3: Fix use after free bug in renesas_usb3_remove due to race condition

In renesas_usb3_probe, role_work is bound with renesas_usb3_role_work.
renesas_usb3_start will be called to start the work.

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.

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

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

This bug was found by static analysis.

Fixes: 39facfa01c9f ("usb: gadget: udc: renesas_usb3: Add register of usb role switch")
Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
---
v7:
- add more details about how the bug was found suggested by Shuah
v6:
- beautify the format and add note suggested by Greg KH
v5:
- fix typo
v4:
- add Reviewed-by label and resubmit v4 suggested by Greg KH
v3:
- modify the commit message to make it clearer suggested by Yoshihiro Shimoda
v2:
- fix typo, use clearer commit message and only cancel the UAF-related work suggested by Yoshihiro Shimoda
---
 drivers/usb/gadget/udc/renesas_usb3.c | 1 +
 1 file changed, 1 insertion(+)

On Fri, Mar 17, 2023 at 02:08:50AM +0800, Zheng Wang wrote:
> In renesas_usb3_probe, role_work is bound with renesas_usb3_role_work.
> renesas_usb3_start will be called to start the work.
> 
> 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.
> 
> Note that removing a driver is a root-only operation, and should never
> happen.
> 
> 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

This still isn't working :(

Greg KH <gregkh@linuxfoundation.org> 于2023年3月17日周五 03:07写道：
>
> On Fri, Mar 17, 2023 at 02:08:50AM +0800, Zheng Wang wrote:
> > In renesas_usb3_probe, role_work is bound with renesas_usb3_role_work.
> > renesas_usb3_start will be called to start the work.
> >
> > 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.
> >
> > Note that removing a driver is a root-only operation, and should never
> > happen.
> >
> > 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
>
> This still isn't working :(
>
Sorry I haven't read your advice when submiting this version of patch.

Best Regards,
Zheng