linux-kernel - Re: [PATCH v9] usb: gadget: udc: renesas_usb3: Fix use after free bug in renesas_usb3

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Date:   Sat, 18 Mar 2023 15:40:10 +0800
From:   Zheng Hacker <hackerzheng666@...il.com>
To:     Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
Cc:     Zheng Wang <zyytlz.wz@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "skhan@...uxfoundation.org" <skhan@...uxfoundation.org>,
        "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>,
        "1395428693sheep@...il.com" <1395428693sheep@...il.com>,
        "alex000young@...il.com" <alex000young@...il.com>
Subject: Re: [PATCH v9] usb: gadget: udc: renesas_usb3: Fix use after free bug
 in renesas_usb3_remove due to race condition

Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com> 于2023年3月17日周五 20:19写道：
>
> Hi Zheng,
>
> > From: Zheng Wang <zyytlz.wz@....com>, 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".
>

Thanks for your detailed check and advice. I'll apply it in the next verion.

Best regards,
Zheng

> 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@....com>
> > Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
> > ---
> > 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
>