RE: [PATCH v9] usb: gadget: udc: renesas_usb3: Fix use after free bug in renesas_usb3_remove due to race condition

[Yoshihiro Shimoda]

Hi Zheng,

> From: Zheng Wang <zyytlz.wz@xxxxxxx>, Sent: Friday, March 17, 2023 6:55 PM
> 
> 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:
> 
> 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
> 
> The usb3->role_sw could be freed under such circumstance and use in usb_role_switch_set_role.

The checkpatch.pl said:
---
./scripts/checkpatch.pl this.patch
WARNING: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#75:
The usb3->role_sw could be freed under such circumstance and use in usb_role_switch_set_role.

total: 0 errors, 1 warnings, 7 lines checked
---

> This bug was found by static analysis. And note that removing a driver is a root-only operation, and should never
> happen in normal case. But the attacker can directly remove the device which will also triggering remove function.

I think you should fix them about 75 chars per line) too.

And, I don't know why "attacker" is related to this issue.
I think "the root user" is better than "attacker".

Best regards,
Yoshihiro Shimoda

> Fix it by canceling the work before cleanup in the renesas_usb3_remove.
> 
> Fixes: 39facfa01c9f ("usb: gadget: udc: renesas_usb3: Add register of usb role switch")
> Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
> Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> ---
> v9:
> - append with more information suggested by Greg KH
> v8:
> - replace | with spaces to make line up suggested by Greg KH
> 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(+)
> 
> 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