linux-kernel - Re: [PATCH] pty: fix use after free of tty->driver

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Date:	Tue, 15 Dec 2015 12:36:50 -0800
From:	Peter Hurley <peter@...leysoftware.com>
To:	"Herton R. Krzesinski" <herton@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>
Subject: Re: [PATCH] pty: fix use after free of tty->driver_data

On 12/15/2015 12:34 PM, Herton R. Krzesinski wrote:
> On Tue, Dec 15, 2015 at 11:52:14AM -0800, Peter Hurley wrote:
>> On 12/15/2015 11:23 AM, Herton R. Krzesinski wrote:
>>> On Tue, Dec 15, 2015 at 04:05:09PM -0200, Herton R. Krzesinski wrote:
>>>> On Tue, Dec 15, 2015 at 09:36:26AM -0800, Peter Hurley wrote:
>>>>>
>>>>>
>>>>>> Signed-off-by: Herton R. Krzesinski <herton@...hat.com>
>>>>>> Cc: <stable@...r.kernel.org>
>>>>>
>>>>> Afaict, the stable tag goes back to the original implementation.
>>>>> Did you research how far back the /dev/tty alias problem goes?
>>>>
>>>> Hmm no. I did cc stable because the first report I got about this issue
>>>> was on RHEL 7 with 3.10 based kernel, so this issue goes far back
>>>> some releases that are still supported and similar code is there.
>>>>
>>>> On a quick check on a 2.6.32 kernel, things were very different,
>>>> tty_release_dev() called directly devpts_kill_index with inode
>>>> from the same file being closed. I'll check more and adjust the tag.
>>>
>>> FYI, checked here and the problem should start with 3.8, after commit
>>> fa2ecfc5a68d85624bbd84f7d010860776b7e602 devpts_kill_index was moved
>>> to pty.c/pty_unix98_shutdown
>>>
>>
>> istm this goes back to multi-instance devpts support added in 2.6.28.
>>
>> Before then, there was no inode parameter because there was only
>> one devpts instance and the idas were global.
> 
> Yeah, I'm not ruling out problems with devpts instances prior to 3.8, where to
> me the wrong inode will be given in the final close with /dev/tty case, when the
> ptmx is on a different instance other than the main ptmx instance (
> pts_sb_from_inode will choose the "root"/main devpts instance, as the /dev/tty
> inode usually is inode tied to devtmpfs mount at /dev). Both fa2ecfc5a68d85624b
> and the new fix could be backported to 3.7 and as far as 2.6.28 perhaps, not
> sure if anything else will be needed, however may not be worth the trouble.

I think a 2.6.28 tag is sufficient.

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