linux-kernel - Re: [PATCH] TTY: do not reset master's packet mode

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Date:	Wed, 20 Feb 2013 17:40:34 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Karel Zak <kzak@...hat.com>
CC:	gregkh@...uxfoundation.org, alan@...ux.intel.com,
	jirislaby@...il.com, linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Bryan Mason <bmason@...hat.com>
Subject: Re: [PATCH] TTY: do not reset master's packet mode

On 02/20/2013 02:19 PM, Karel Zak wrote:
> On Tue, Jan 15, 2013 at 11:26:22PM +0100, Jiri Slaby wrote:
>> Now that login from util-linux is forced to drop all references to a
>> TTY which it wants to hangup (to reach reference count 1) we are
>> seeing issues with telnet. When login closes its last reference to the
>> slave PTY, it also resets packet mode on the *master* side. And we
>> have a race here.
> 
> [...]
> 
>> By this I am resurrecting an old bug, see References. We are hitting
>> it regularly now, i.e. with updated util-linux, ergo login.
>>
>> Here, I am changing a behavior introduced back in 2.1 times. It would
>> better have a long time testing before goes upstream.
> 
>  It would be nice to found a quick way how to resolve this problem,
>  because telnet+login is broken now... and for end users it seems like
>  a regression.

Oh, the patch is in the TTY tree and I suppose it will go to 3.9-rc1
(and to stable as we will get to same later -rc -- to have some testing).

>  Maybe the requirement (patch) to close all references to TTY before
>  hangup should reverted or we can make an exception in login(1) code to
>  keep TTY open when login(1) is executed with -h (as used by telned).

If we reverted the patch in login, we would have to revert also a patch
in the TTY which closes a window allowing you to crash a kernel at will
(in fact that patch disallows multiple opens when hanging up a terminal.
IOW only the one to hang the terminal is allowed to have it opened.)

-- 
js
suse labs
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