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From:   Yongqin Liu <yongqin.liu@linaro.org>
Date:   Fri, 21 Apr 2023 23:42:24 +0800
Message-ID: <CAMSo37Vse=gVqC_2LU44YzOepXpy909kSDSQjebb0zyk-b27kg@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:     Zheng Hacker <hackerzheng666@gmail.com>
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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HI, Zheng

Thanks for the explanation!
BTW, from what I tested, I am OK to have this change merged.

Thanks,
Yongqin Liu
On Fri, 21 Apr 2023 at 10:35, Zheng Hacker <hackerzheng666@gmail.com> wrote=
:
>
> Yongqin Liu <yongqin.liu@linaro.org> =E4=BA=8E2023=E5=B9=B44=E6=9C=8820=
=E6=97=A5=E5=91=A8=E5=9B=9B 14:31=E5=86=99=E9=81=93=EF=BC=9A
> >
> > Hi, Zheng
> >
> > BTW, I just see cancel_delayed_work_sync is used in
> > the drivers/usb/common/usb-conn-gpio.c usb_conn_remove function.
> >     https://android.googlesource.com/kernel/common/+/refs/heads/android=
-mainline/drivers/usb/common/usb-conn-gpio.c#274
> >
> > I know nothing about the cancel_delayed_work_sync and cancel_work_sync
> > functions,
> > just for your information in case cancel_delayed_work_sync might be
> > better to be used here.
> >
>
> HI Yongqin,
>
> Thanks for your kind reminder. The cancel_delayed_work_sync is used
> with INIT_DELAYED_WORK and queue_delayed_work.
> This is used to start a work after some time while schedule_work means
> start it immediately.
>
> In this case, the &hisi_hikey_usb->work is initialized with INIT_WORK
> and scheduled with schedule_work. So I think we'd better use
> cancel_work_sync here. I'm also not so familiar with the code. If
> there's something wrong with it, please feel free to let me know.
>
> Best regards,
> Zheng
>
>
> > Thanks,
> > Yongqin Liu
> > On Tue, 18 Apr 2023 at 21:18, Zheng Hacker <hackerzheng666@gmail.com> w=
rote:
> > >
> > > Yongqin Liu <yongqin.liu@linaro.org> =E4=BA=8E2023=E5=B9=B44=E6=9C=88=
18=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 me 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.co=
m> wrote:
> > > > >
> > > > > 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 wrot=
e:
> > > > > > > > > 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 <hackerzheng=
666@gmail.com> wrote:
> > > > > > > > > > >
> > > > > > > > > > > Friendly ping about the bug.
> > > > > > > > > >
> > > > > > > > > > Sorry, wasn't aware of this message before,
> > > > > > > > > >
> > > > > > > > > > Could you please help share the instructions to reprodu=
ce the problem
> > > > > > > > > > this change fixes?
> > > > > > > > > >
> > > > > > > > >
> > > > > > > > > Hi Yongqin,
> > > > > > > > >
> > > > > > > > > Thanks for your reply. This bug is found by static analys=
is. There is no PoC.
> > > > > > > > >
> > > > > > > > > >From my personal experience, triggering race condition b=
ugs 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 trigg=
ered, and if
> > > > > > > > > the set callback is invoked, there might be a race condit=
ion.
> > > > > > > >
> > > > > > > > How does the removal of the USB device trigger a platform d=
evice
> > > > > > > > removal?
> > > > > > >
> > > > > > > Sorry I made a mistake. The USB device usually calls disconne=
ct
> > > > > > > callback when it's unpluged.
> > > > > >
> > > > > > Yes, but you are changing the platform device disconnect, not t=
he 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 trigge=
red.
> > > > > >
> > > > > > 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 unpl=
ug
> > > > > 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
> > > > ---------------------------------------------------------------
> > > > #mailing list
> > > > linaro-android@lists.linaro.org
> > > > http://lists.linaro.org/mailman/listinfo/linaro-android
> >
> >
> >
> > --
> > Best Regards,
> > Yongqin Liu
> > ---------------------------------------------------------------
> > #mailing list
> > linaro-android@lists.linaro.org
> > http://lists.linaro.org/mailman/listinfo/linaro-android


--=20
Best Regards,
Yongqin Liu
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