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In-Reply-To: <2023041308-unvisited-slinky-a56f@gregkh>
From:   Zheng Hacker <hackerzheng666@gmail.com>
Date:   Fri, 14 Apr 2023 00:46:08 +0800
Message-ID: <CAJedcCxzGbUSj0nh4xYp8P2zhYSM31CGi2fGE+9VJt7mkg6h4g@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 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@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 pro=
blem
> > > > > this change fixes?
> > > > >
> > > >
> > > > Hi Yongqin,
> > > >
> > > > Thanks for your reply. This bug is found by static analysis. There =
is no 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 ar=
e
> > > > some other tricks as [1] said.
> > > >
> > > > As for the reproduction, this attack vector requires that the attac=
ker
> > > > 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