linux-kernel - Re: [PATCH 1/1] usb: cdc-acm: Fix acm_tty_hangup() vs. acm_tty

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Date:	Thu, 5 Jan 2012 12:14:18 -0800
From:	Greg KH <greg@...ah.com>
To:	Thilo-Alexander Ginkel <thilo@...kel.com>
Cc:	oliver@...kum.name, gregkh@...e.de, jhovold@...il.com,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] usb: cdc-acm: Fix acm_tty_hangup() vs.
 acm_tty_close() race

On Sun, Dec 25, 2011 at 10:43:09PM +0100, Thilo-Alexander Ginkel wrote:
> Hi there,
> 
> On Sat, Dec 17, 2011 at 10:55, Thilo-Alexander Ginkel <thilo@...kel.com> wrote:
> > There is a race condition involving acm_tty_hangup() and acm_tty_close() where
> > hangup() would attempt to access tty->driver_data without proper locking and
> > NULL checking after close() has potentially already set it to NULL.
> > One possibility to (sporadically) trigger this behavior is to perform a
> > suspend/resume cycle with a running WWAN data connection.
> >
> > This patch addresses the issue by introducing a NULL check for
> > tty->driver_data in acm_tty_hangup() protected by open_mutex and exiting
> > gracefully when hangup() is invoked on a device that has already been closed.
> 
> just wondering: Is there any chance that this patch will make it into
> 3.3? I would really appreciate that as the bug it fixes is pretty
> annoying (and potentially causes data loss when the laptop locks up on
> resume) and I am sure that I am not the only one affected by it (at
> least all Lenovo T420s with an Ericsson F5521gw WWAN modem should be
> similarly affected).
> 
> If you would like to see any changes to the code or commit message
> before considering the patch for inclusion, please let me know.

As this isn't going to be an issue with 3.3 (from what I can tell, the
code is correctly reworked in the patch set queued up for 3.3), I'll
submit this for only the 3.2 and older kernel -stable releases, as that
is the only place this should be relevant for.

thanks,

greg k-h
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