linux-kernel - Re: BUG: tty: memory corruption through tty_release/tty_ldisc

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Date:	Thu, 16 May 2013 09:47:44 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Alexander Holler <holler@...oftware.de>
CC:	linux-kernel@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Marcel Holtmann <marcel@...tmann.org>,
	Gustavo Padovan <gustavo@...ovan.org>,
	Johan Hedberg <johan.hedberg@...il.com>,
	linux-bluetooth@...r.kernel.org
Subject: Re: BUG: tty: memory corruption through tty_release/tty_ldisc_release

On 05/16/2013 02:45 AM, Alexander Holler wrote:
> Hello,
>
> after some pain because the "big step" (ecbbfd4) happened while the support for my AMD CPU was broken and thus git bisect hit a series of kernels which didn't boot, I've finally found the cause for a memory corruption: tty_ldisc_release().
>
> What happens is the following:
>
> tty_port is self-destructing, that means it destroys itself in tty_port.c:tty_port_destructor() when the last reference is gone. E.g. in case of rfcomm this happens with the call to tty->ops->close() in tty_io.c:tty_release().
>
> The problem here is that tty_io.c:tty_release() calls tty_ldisc.c:tty_ldisc_release() which uses the tty_port to flush the ldisc work queues.
>
> In the best case this hits a BUG() in cancel_work_sync() but often it just causes a memory corruption without a BUG() got hit before.

Hi Alexander,

Actually, the problem is that tty->ops->close() shouldn't be
the last kref on the port.

It doesn't look to me like device removal is being handled
properly.

Regards,
Peter Hurley

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