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From:   Zheng Hacker <hackerzheng666@gmail.com>
Date:   Tue, 18 Apr 2023 21:18:13 +0800
Message-ID: <CAJedcCwow9sTEzZpiqmmcEDZ0XFLauA_tVBTJf5MfpadC1M+cQ@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:     Yongqin Liu <yongqin.liu@linaro.org>
Cc:     Greg KH <gregkh@linuxfoundation.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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Yongqin Liu <yongqin.liu@linaro.org> =E4=BA=8E2023=E5=B9=B44=E6=9C=8818=E6=
=97=A5=E5=91=A8=E4=BA=8C 01:31=E5=86=99=E9=81=93=EF=BC=9A
>
> Hi, Zheng
>
> Sorry for the late reply.
>
> I tested this change with Android build based on the ACK
> android-mainline branch.
> The hisi_hikey_usb module could not be removed with error like this:
>     console:/ # rmmod -f hisi_hikey_usb
>     rmmod: failed to unload hisi_hikey_usb: Try again
>     1|console:/ #
> Sorry I am not able to reproduce any problem without this commit,
> but I do not see any problem with this change applied either.
>
> If there is any specific things you want to check, please feel free let m=
e know
>

Hi Yongqin,

Thanks for your testing. I have no more questions about the issue.

Best regards,
Zheng

> Thanks,
> Yongqin Liu
>
>
> On Fri, 14 Apr 2023 at 00:46, Zheng Hacker <hackerzheng666@gmail.com> wro=
te:
> >
> > Greg KH <gregkh@linuxfoundation.org> =E4=BA=8E2023=E5=B9=B44=E6=9C=8813=
=E6=97=A5=E5=91=A8=E5=9B=9B 23:56=E5=86=99=E9=81=93=EF=BC=9A
> > >
> > > On Thu, Apr 13, 2023 at 11:35:17PM +0800, Zheng Hacker wrote:
> > > > 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@gm=
ail.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. Th=
ere is no PoC.
> > > > > >
> > > > > > >From my personal experience, triggering race condition bugs st=
ably in
> > > > > > the kernel needs some tricks.
> > > > > > For example, you can insert some sleep-time code to slow down t=
he
> > > > > > thread until the related object is freed.
> > > > > > Besides, you can use gdb to control the time window. Also, ther=
e are
> > > > > > some other tricks as [1] said.
> > > > > >
> > > > > > As for the reproduction, this attack vector requires that the a=
ttacker
> > > > > > 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.
> > >
> > > Yes, but you are changing the platform device disconnect, not the USB
> > > device disconnect.
> > >
> > > > 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.
> > >
> > > And is this a patform device on a USB device?  If so, that's a bigger
> > > problem that we need to fix as that is not allowed.
> >
> > No this is not a platform  device on a USB device.
> >
> > >
> > > But in looking at the code, it does not seem to be that at all, this =
is
> > > just a "normal" platform device.  So how can it ever be removed from =
the
> > > system?  (and no, unloading the driver doesn't count, that can never
> > > happen on a normal machine.)
> > >
> >
> > Yes, I finally figured out your meaning. I know it's hard to unplug
> > the platform device
> > directly. All I want to express is that it's a theoretical method
> > except  rmmod. I think it's better to fix the bug. But if the
> > developers think it's practically impossible, I think there's no need
> > to take further action.
> >
> > Sorry for wasting your time and thanks for your explanation.
> >
> > Best regards,
> > Zheng
> >
> > > thanks,
> > >
> > > greg k-h
>
>
>
> --
> Best Regards,
> Yongqin Liu
> ---------------------------------------------------------------
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