From: Thilo-Alexander Ginkel <thilo@ginkel.com>
Date: Sat, 17 Dec 2011 09:55:10 +0000 (+0100)
Subject: usb: cdc-acm: Fix acm_tty_hangup() vs. acm_tty_close() race
X-Git-Tag: v3.2.1~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f9fd8d6232137e255fc9409a81cf282817472b6f;p=pandora-kernel.git

usb: cdc-acm: Fix acm_tty_hangup() vs. acm_tty_close() race

[Not upstream as it was fixed differently for 3.3 with a much more
"intrusive" rework of the driver - gregkh]

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.

Signed-off-by: Thilo-Alexander Ginkel <thilo@ginkel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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