From: Alan Stern <stern@rowland.harvard.edu>
To: Oliver Neukum <oneukum@suse.com>
Cc: Andrey Konovalov <andreyknvl@google.com>,
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>
Subject: Re: KASAN: use-after-free Read in device_release_driver_internal
Date: Tue, 6 Aug 2019 10:19:37 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1908061009450.1571-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <1565095011.8136.20.camel@suse.com>
On Tue, 6 Aug 2019, Oliver Neukum 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.
Only one interface (numbered 234!).
> If you agree. I am attaching a putative fix.
Your patch adds a line saying:
> + usb_get_intf(acm->control); /* undone in destroy() */
but I don't see any destroy() function in that source file. Did you
mean acm_port_destruct()?
In any case, I don't know if this missing "get" would cause the
problem, but it might well.
Alan Stern
next prev parent reply other threads:[~2019-08-06 14:19 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-23 14:28 KASAN: use-after-free Read in device_release_driver_internal syzbot
2019-08-01 16:01 ` Andrey Konovalov
2019-08-01 18:47 ` Alan Stern
2019-08-06 12:36 ` Oliver Neukum
2019-08-06 12:50 ` Andrey Konovalov
2019-08-07 13:38 ` Oliver Neukum
2019-08-07 13:44 ` Andrey Konovalov
2019-08-07 13:44 ` Andrey Konovalov
2019-08-07 13:45 ` Andrey Konovalov
2019-08-07 14:13 ` syzbot
2019-08-07 13:56 ` syzbot
2019-08-07 17:40 ` Alan Stern
2019-08-07 17:51 ` syzbot
2019-08-07 18:05 ` Alan Stern
2019-08-07 18:23 ` syzbot
2019-08-07 18:31 ` Alan Stern
2019-08-08 12:27 ` Andrey Konovalov
2019-08-08 12:43 ` Dmitry Vyukov
2019-08-08 13:03 ` Andrey Konovalov
2019-08-08 13:59 ` Alan Stern
2019-08-13 12:42 ` Andrey Konovalov
2019-08-13 13:22 ` Oliver Neukum
2019-08-13 13:24 ` Andrey Konovalov
2019-08-13 15:16 ` Greg KH
2019-08-13 13:59 ` Andrey Konovalov
2019-08-06 14:19 ` Alan Stern [this message]
2019-08-06 14:25 ` Oliver Neukum
2019-08-06 15:33 ` Oliver Neukum
2019-08-07 13:46 ` Andrey Konovalov
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