From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1755123AbcDKU0o (ORCPT <rfc822;w@1wt.eu>);
	Mon, 11 Apr 2016 16:26:44 -0400
Received: from [198.137.202.10] ([198.137.202.10]:47228 "EHLO mail.zytor.com"
	rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP
	id S1752104AbcDKU0n (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 11 Apr 2016 16:26:43 -0400
User-Agent: K-9 Mail for Android
In-Reply-To: <CALCETrUQ_Oad61dYvPpYFxDBT++jhZoAT3e4n4yiu22iTNcxNQ@mail.gmail.com>
References: <878u0s3orx.fsf_-_@x220.int.ebiederm.org> <1459819769-30387-1-git-send-email-ebiederm@xmission.com> <CA+55aFwv7d8XfeN8KvYaVcSs7V9XoHtS-1cqtkG4gF4yJwB5nA@mail.gmail.com> <87twjcorwg.fsf@x220.int.ebiederm.org> <20160409140909.42315e6d@lxorguk.ukuu.org.uk> <83FE8CD2-C0A2-4ADB-AEBD-8DD89AD4F88A@zytor.com> <87bn5ij0x1.fsf@x220.int.ebiederm.org> <78205895-E11D-417F-91DC-4BCA0B61A122@zytor.com> <CA+55aFyB7y8TfQ=_EvMAFONS6oSPs=uY88f+S6n_QWh4MkKTHg@mail.gmail.com> <FC521A3F-4BEB-427E-AE8E-CA54C0128AA3@zytor.com> <CA+55aFw62q5bjNiK7Q9dEQQEDZs5fbUxNPxDq376OZJ6JKT=Rg@mail.gmail.com> <CALCETrUZ=QVZbTCr3gvhSd2-j_U4R02y5fCxbddG_HsQdnuBkw@mail.gmail.com> <CA+55aFzs00iDkYhvFCq=AZMVcNL0+oZT4SeimTeVurJq=5ZS3A@mail.gmail.com> <CALCETrUQ_Oad61dYvPpYFxDBT++jhZoAT3e4n4yiu22iTNcxNQ@mail.gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain;
 charset=UTF-8
Subject: Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Mon, 11 Apr 2016 13:16:42 -0700
To: Andy Lutomirski <luto@amacapital.net>,
        Linus Torvalds <torvalds@linux-foundation.org>
CC: security@debian.org, "security@kernel.org" <security@kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "security@ubuntu.com >> security" <security@ubuntu.com>,
        Peter Hurley <peter@hurleysoftware.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Serge Hallyn <serge.hallyn@ubuntu.com>, Willy Tarreau <w@1wt.eu>,
        Aurelien Jarno <aurelien@aurel32.net>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Jann Horn <jann@thejh.net>, Greg KH <greg@kroah.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jiri Slaby <jslaby@suse.com>, Florian Weimer <fw@deneb.enyo.de>
Message-ID: <AC547146-B027-4AE2-9B26-111F0180C0B9@zytor.com>
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On April 11, 2016 1:12:22 PM PDT, Andy Lutomirski <luto@amacapital.net> wrote:
>On Sat, Apr 9, 2016 at 6:27 PM, Linus Torvalds
><torvalds@linux-foundation.org> wrote:
>>
>> On Apr 9, 2016 5:45 PM, "Andy Lutomirski" <luto@amacapital.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?
-- 
Sent from my Android device with K-9 Mail. Please excuse brevity and formatting.