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

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Message-ID: <CAObL_7Fr-yV33jobSa3g_WqVJar-5x5oQM0t8GJxcLFsuBhLtg@mail.gmail.com>
Date:	Thu, 12 Jan 2012 17:41:33 -0800
From:	Andrew Lutomirski <luto@....edu>
To:	Will Drewry <wad@...omium.org>
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 5:37 PM, Will Drewry <wad@...omium.org> wrote:
> 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.

I'm not sure it'll be much of a simplification.  The entire patch is
45 lines right now :)  I'll test it and send it out.

FWIW, though, it breaks apparmor (intentionally).  Can any of you
either explain what *should* happen or (better) volunteer to fix it?
It should be about three lines of code for someone who understands
what's going on.  I don't have an apparmor system, so I can't really
test it.

--Andy

>
> Just a thought,
> will
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