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Date:   Thu, 13 Apr 2023 17:56:06 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Zheng Hacker <hackerzheng666@gmail.com>
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>
Subject: Re: [PATCH] misc: hisi_hikey_usb: Fix use after free bug in
 hisi_hikey_usb_remove due to race condition
Message-ID: <2023041308-unvisited-slinky-a56f@gregkh>
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On Thu, Apr 13, 2023 at 11:35:17PM +0800, Zheng Hacker wrote:
> Greg KH <gregkh@linuxfoundation.org> 于2023年4月13日周四 20:48写道：
> >
> > On Thu, Apr 13, 2023 at 07:12:07PM +0800, Zheng Hacker wrote:
> > > Yongqin Liu <yongqin.liu@linaro.org> 于2023年4月13日周四 18:55写道：
> > > >
> > > > 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 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 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.

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.

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.)

thanks,

greg k-h