linux-kernel - Re: [PATCH] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

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Date:	Sat, 14 Jan 2012 08:04:34 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Eric Paris <eparis@...hat.com>
Cc:	jamie@...reable.org, torvalds@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, oleg@...hat.com, wad@...omium.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, 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, luto@....edu, mingo@...e.hu,
	akpm@...ux-foundation.org, khilman@...com, borislav.petkov@....com,
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	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
Subject: Re: [PATCH] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from
 granting privs

On Sat, Jan 14, 2012 at 7:17 AM, Eric Paris <eparis@...hat.com> wrote:
> -----Original Message-----
> From: Jamie Lokier [jamie@...reable.org]

> Andy Lutomirski wrote:
>
>> Is the current exec_no_trans check enough for you?  With my patch,
>> selinux can already block the execve if it wants.  (The policy is the
>> same as it would be if a program explicitly asked to run the new
>> executable with an unchanged security context.)  I'd be happy to fail
>> the exec in AppArmor, and then maybe AppArmor will change its mind
>> if/when users get annoyed :)
>
> Does SELinux block if userspace does exec entirely in userspace using
> mmap() and not execve()?  If not, why is execve() allowed to be different?
>
> Yes, we do (or can, and usually do in policy)
>

By blocking open, read, mmap, or mprotect?  And, more to the point, why?

I've always found it weird/annoying that selinux blocks things that
can neither be used to gain privilege nor to DoS the system.
Certainly a fully confined selinux program can emulate the execution
of anything it can read -- it just might be slow.

--Andy
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