linux-kernel - Re: [PATCH PLACEHOLDER 1/3] fs/exec: "always

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Message-ID: <CABqD9hZCpFM4fN9p3vmnGeLVbvoDtTgbiovz=RsSkjH6sv=xBQ@mail.gmail.com>
Date:	Thu, 12 Jan 2012 19:37:07 -0600
From:	Will Drewry <wad@...omium.org>
To:	Andrew Lutomirski <luto@....edu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, keescook@...omium.org,
	john.johansen@...onical.com, serge.hallyn@...onical.com,
	coreyb@...ux.vnet.ibm.com, pmoore@...hat.com, eparis@...hat.com,
	djm@...drot.org, segoon@...nwall.com, rostedt@...dmis.org,
	jmorris@...ei.org, scarybeasts@...il.com, avi@...hat.com,
	penberg@...helsinki.fi, viro@...iv.linux.org.uk, mingo@...e.hu,
	akpm@...ux-foundation.org, khilman@...com, borislav.petkov@....com,
	amwang@...hat.com, oleg@...hat.com, ak@...ux.intel.com,
	eric.dumazet@...il.com, gregkh@...e.de, dhowells@...hat.com,
	daniel.lezcano@...e.fr, linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com, corbet@....net,
	alan@...rguk.ukuu.org.uk
Subject: Re: [PATCH PLACEHOLDER 1/3] fs/exec: "always_unprivileged" patch

On Thu, Jan 12, 2012 at 7:11 PM, Andrew Lutomirski <luto@....edu> wrote:
> (Also, preventing dropping of privileges will probably make a patch
> more complicted -- I'll have to find and update all the places that
> allow dropping privileges.)

An alternative approach might be that the restricted bit drops all
privileges that allows privilege changes in either direction.  E.g.,
- set restricted bit
-- adds a check anywhere MNT_NOSUID is
-- sets securebit to SECURE_NOROOT|..LOCKED
-- drops CAP_SETUID, CAP_DAC_OVERRIDE, ...
-- set the caps bounding set to the minimum the restricted bit allows

That may deviate from the intent (by re-using caps), but it could keep some
of the privilege transition checking code the same.

Just a thought,
will
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