Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <Pine.LNX.4.44L0.1908011359580.1305-100000@iolanthe.rowland.org> <1565095011.8136.20.camel@suse.com>
In-Reply-To: <1565095011.8136.20.camel@suse.com>
From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Tue, 6 Aug 2019 14:50:50 +0200
Message-ID: <CAAeHK+wyvJbi08ruuOn1qF0O1Jubz_BhZz5wXdNg4Vy5XeyQmw@mail.gmail.com>
Subject: Re: KASAN: use-after-free Read in device_release_driver_internal
To:     Oliver Neukum <oneukum@suse.com>
Cc:     Alan Stern <stern@rowland.harvard.edu>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        syzbot <syzbot+1b2449b7b5dc240d107a@syzkaller.appspotmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>
Content-Type: multipart/mixed; boundary="000000000000dd87f8058f7246cd"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

--000000000000dd87f8058f7246cd
Content-Type: text/plain; charset="UTF-8"

On Tue, Aug 6, 2019 at 2:36 PM Oliver Neukum <oneukum@suse.com> wrote:
>
> Am Donnerstag, den 01.08.2019, 14:47 -0400 schrieb Alan Stern:
> >
> > I think this must be caused by an unbalanced refcount.  That is,
> > something must drop one more reference to the device than it takes.
> > That would explain why the invalid access occurs inside a single
> > bus_remove_device() call, between the klist_del() and
> > device_release_driver().
> >
> > The kernel log indicates that the device was probed by rndis_wlan,
> > rndis_host, and cdc_acm, all of which got errors because of the
> > device's bogus descriptors.  Probably one of them is messing up the
> > refcount.
>
> Hi,
>
> you made me look at cdc-acm. I suspect
>
> cae2bc768d176bfbdad7035bbcc3cdc973eb7984 ("usb: cdc-acm: Decrement tty port's refcount if probe() fail")
>
> is buggy decrementing the refcount on the interface in destroy()
> even before the refcount is increased.
>
> Unfortunately I cannot tell from the bug report how many and which
> interfaces the emulated test device has. Hence it is unclear to me,
> when exactly probe() would fail cdc-acm.
>
> If you agree. I am attaching a putative fix.

Let's see if it fixes the issue.

#syz fix: https://github.com/google/kasan.git 6a3599ce

>
>         Regards
>                 Oliver

--000000000000dd87f8058f7246cd
Content-Type: text/x-patch; charset="US-ASCII"; 
	name="0001-usb-cdc-acm-make-sure-a-refcount-is-taken-early-enou.patch"
Content-Disposition: attachment; 
	filename="0001-usb-cdc-acm-make-sure-a-refcount-is-taken-early-enou.patch"
Content-Transfer-Encoding: base64
Content-ID: <f_jyztngtt0>
X-Attachment-Id: f_jyztngtt0
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--000000000000dd87f8058f7246cd--