linux-kernel - RE: [PATCH] usb: gadget: udc: renesas_usb3: Fix use after free bug in renesas_usb3

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Date:   Fri, 10 Mar 2023 04:56:31 +0000
From:   Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To:     Zheng Wang <zyytlz.wz@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        Biju Das <biju.das.jz@...renesas.com>,
        "phil.edworthy@...esas.com" <phil.edworthy@...esas.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hackerzheng666@...il.com" <hackerzheng666@...il.com>,
        "1395428693sheep@...il.com" <1395428693sheep@...il.com>,
        "alex000young@...il.com" <alex000young@...il.com>
Subject: RE: [PATCH]  usb: gadget: udc: renesas_usb3: Fix use after free bug
 in renesas_usb3_remove due to race condition

Hi Zheng,

> From: Zheng Wang, Sent: Friday, March 10, 2023 4:30 AM
> 
> 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 module which will call renesas_usb3_remove
>   to make cleanup, there may be a unfinished work. The possible
>   sequence is as follows:

Thank you for the patch!
I think we should remove double spaces like below. (Also "an" unfinished):

-----
If we remove the module which will call renesas_usb3_remove
to make cleanup, 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                  CPUc1

s/CPUc1/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

Adding a blank line here is better, I think.

> Fixes: 39facfa01c9f ("usb: gadget: udc: renesas_usb3: Add register of usb role switch")
> Signed-off-by: Zheng Wang <zyytlz.wz@....com>
> ---
>  drivers/usb/gadget/udc/renesas_usb3.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/gadget/udc/renesas_usb3.c b/drivers/usb/gadget/udc/renesas_usb3.c
> index bee6bceafc4f..23b5f1706d25 100644
> --- a/drivers/usb/gadget/udc/renesas_usb3.c
> +++ b/drivers/usb/gadget/udc/renesas_usb3.c
> @@ -2658,6 +2658,8 @@ static int renesas_usb3_remove(struct platform_device *pdev)
>  {
>  	struct renesas_usb3 *usb3 = platform_get_drvdata(pdev);
> 
> +	cancel_work_sync(&usb3->extcon_work);

IIUC, this work is not related to the issue.
But, what do you think?
If so, adding this should be a separate patch with the following Fixes tag:

Fixes: 3b68e7ca3888 ("usb: gadget: udc: renesas_usb3: add extcon support")

Best regards,
Yoshihiro Shimoda

> +	cancel_work_sync(&usb3->role_work);
>  	debugfs_remove_recursive(usb3->dentry);
>  	device_remove_file(&pdev->dev, &dev_attr_role);
> 
> --
> 2.25.1