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

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

[Zheng Wang]

In renesas_usb3_probe, &usb3->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.

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

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>
---
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(+)

diff --git a/drivers/usb/gadget/udc/renesas_usb3.c b/drivers/usb/gadget/udc/renesas_usb3.c
index bee6bceafc4f..a301af66bd91 100644
--- a/drivers/usb/gadget/udc/renesas_usb3.c
+++ b/drivers/usb/gadget/udc/renesas_usb3.c
@@ -2661,6 +2661,7 @@ static int renesas_usb3_remove(struct platform_device *pdev)
 	debugfs_remove_recursive(usb3->dentry);
 	device_remove_file(&pdev->dev, &dev_attr_role);
 
+	cancel_work_sync(&usb3->role_work);
 	usb_role_switch_unregister(usb3->role_sw);
 
 	usb_del_gadget_udc(&usb3->gadget);
-- 
2.25.1

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

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

[Zheng Hacker]

Greg KH <gregkh@linuxfoundation.org> 于2023年3月17日周五 00:23写道：
>
> 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 :)
>

Thanks for your kind reminder. I'll fix the format in the next version.

> >
> > 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:

Sorry, I'll beautify the format next time.

>
>  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.
>
Get it.

Best regards,
Zheng

> thanks,
>
> greg k-h