linux-kernel - Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup

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Message-ID: <AC547146-B027-4AE2-9B26-111F0180C0B9@zytor.com>
Date:	Mon, 11 Apr 2016 13:16:42 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	security@...ian.org, "security@...nel.org" <security@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	"security@...ntu.com >> security" <security@...ntu.com>,
	Peter Hurley <peter@...leysoftware.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Willy Tarreau <w@....eu>,
	Aurelien Jarno <aurelien@...el32.net>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Jann Horn <jann@...jh.net>, Greg KH <greg@...ah.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.com>, Florian Weimer <fw@...eb.enyo.de>
Subject: Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup

On April 11, 2016 1:12:22 PM PDT, Andy Lutomirski <luto@...capital.net> wrote:
>On Sat, Apr 9, 2016 at 6:27 PM, Linus Torvalds
><torvalds@...ux-foundation.org> wrote:
>>
>> On Apr 9, 2016 5:45 PM, "Andy Lutomirski" <luto@...capital.net>
>wrote:
>>>
>>>
>>> What we *do* want to do, though, is to prevent the following:
>>
>> I don't see the point. Why do you bring up this insane scenario that
>nobody
>> can possibly care about?
>>
>> So you actually have any reason to believe somebody does that?
>>
>> I already asked about that earlier, and the silence was deafening.
>
>I have no idea, but I'm generally uncomfortable with magical things
>that bypass normal security policy.
>
>That being said, here's an idea for fixing this, at least in the long
>run.  Add a new devpts mount option "no_ptmx_redirect" that turns off
>this behavior for the super in question.  That is, opening /dev/ptmx
>if "pts/ptmx" points to something with no_ptmx_redirect set will fail.
>Distros shipping new kernels could be encouraged to (finally!) make
>/dev/ptmx a symlink and set this option.
>
>We just might be able to get away with spelling that option
>"newinstance".

What about the idea of making the bind mount automatic?
-- 
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