linux-kernel - Re: [PATCH] USB: cdc-acm: fix possible null pointer in acm_tty

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20110809104323.412b6282@lxorguk.ukuu.org.uk>
Date:	Tue, 9 Aug 2011 10:43:23 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Vincent Palatin <vpalatin@...omium.org>
Cc:	Oliver Neukum <oliver@...kum.name>,
	Greg Kroah-Hartman <gregkh@...e.de>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: cdc-acm: fix possible null pointer in
 acm_tty_hangup

On Mon,  8 Aug 2011 15:38:20 -0700
Vincent Palatin <vpalatin@...omium.org> wrote:

> Sometimes, acm_tty_hangup and acm_tty_close are called concurrently.
> This results in acm pointer being null in acm_tty_hangup and panics when
> it is dereferenced.

This is definitely not the way to attack the problem.

The tty port hangup and close logic will do all the needed locking and do
it right. The big problem here is touching tty->driver_data. If you have
a block of memory that is tied to the tty object lifetime it needs to get
destroyed when the tty object is destroyed not as close/hangup or you
still leave races.

Take a look at

	tty_port_close
	tty_port_hangup

and in particular for port internal sychronization of open/close/hangup
once only events at

	port->ops->activate
	port->ops->shutdown
	port->ops->destruct

and for a tty lifetime object

	tty->ops->shutdown

Alan
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/