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From:   Zheng Hacker <hackerzheng666@gmail.com>
Date:   Thu, 13 Apr 2023 23:35:17 +0800
Message-ID: <CAJedcCyeM2a79i0=ffKwdKfnQayo7svhTTEth2ka6K9np0Ztiw@mail.gmail.com>
Subject: Re: [PATCH] misc: hisi_hikey_usb: Fix use after free bug in
 hisi_hikey_usb_remove due to race condition
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Yongqin Liu <yongqin.liu@linaro.org>,
        John Stultz <jstultz@google.com>,
        Zheng Wang <zyytlz.wz@163.com>,
        Sumit Semwal <sumit.semwal@linaro.org>, arnd@arndb.de,
        linux-kernel@vger.kernel.org, 1395428693sheep@gmail.com,
        alex000young@gmail.com, Mauro Carvalho Chehab <mchehab@kernel.org>
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Greg KH <gregkh@linuxfoundation.org> =E4=BA=8E2023=E5=B9=B44=E6=9C=8813=E6=
=97=A5=E5=91=A8=E5=9B=9B 20:48=E5=86=99=E9=81=93=EF=BC=9A
>
> On Thu, Apr 13, 2023 at 07:12:07PM +0800, Zheng Hacker wrote:
> > Yongqin Liu <yongqin.liu@linaro.org> =E4=BA=8E2023=E5=B9=B44=E6=9C=8813=
=E6=97=A5=E5=91=A8=E5=9B=9B 18:55=E5=86=99=E9=81=93=EF=BC=9A
> > >
> > > Hi, Zheng
> > >
> > > On Thu, 13 Apr 2023 at 16:08, Zheng Hacker <hackerzheng666@gmail.com>=
 wrote:
> > > >
> > > > Friendly ping about the bug.
> > >
> > > Sorry, wasn't aware of this message before,
> > >
> > > Could you please help share the instructions to reproduce the problem
> > > this change fixes?
> > >
> >
> > Hi Yongqin,
> >
> > Thanks for your reply. This bug is found by static analysis. There is n=
o PoC.
> >
> > >From my personal experience, triggering race condition bugs stably in
> > the kernel needs some tricks.
> > For example, you can insert some sleep-time code to slow down the
> > thread until the related object is freed.
> > Besides, you can use gdb to control the time window. Also, there are
> > some other tricks as [1] said.
> >
> > As for the reproduction, this attack vector requires that the attacker
> > can physically access the device.
> > When he/she unplugs the usb, the remove function is triggered, and if
> > the set callback is invoked, there might be a race condition.
>
> How does the removal of the USB device trigger a platform device
> removal?

Sorry I made a mistake. The USB device usually calls disconnect
callback when it's unpluged.
What I want to express here is When the driver-related device(here
it's USB GPIO Hub) was removed, the remove function is triggered.
>
> Are you sure this can be triggered by some other way other than manually
> unloading the driver?

As I didn't make a PoC, I'm not 100 percent sure about that.

Best regards,
Zheng

>
> thanks,
>
> greg k-h