linux-kernel - Re: [PATCH v2 0/4] PR_SET_NO_NEW

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Date:	Mon, 16 Jan 2012 15:49:07 -0500
From:	Colin Walters <walters@...bum.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Casey Schaufler <casey@...aufler-ca.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jamie Lokier <jamie@...reable.org>,
	Will Drewry <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, 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 v2 0/4] PR_SET_NO_NEW_PRIVS, unshare, and chroot

On Sun, 2012-01-15 at 16:37 -0800, Andy Lutomirski wrote:
> To make the no_new_privs discussion more concrete, here is an updated
> series that is actually useful.  It adds PR_SET_NO_NEW_PRIVS

I think it'd be clearer to call it PR_SET_NOSUID - basically it should
match the semantics for MS_NOSUID mounts, as if on every exec()
thereafter the target binary was on a nosuid filesystem.

You might then change this flag to only take effect on a later exec(),
which would solve your race condition for the hypothetical PAM module.

>  with the
> same semantics as before (plus John Johansen's AppArmor fix and with
> improved bisectability).  It then allows some unshare flags 

What's the rationale behind the unshare subset?  Did you actually
analyze any setuid binaries found on Debian/Fedora etc. and determined
that e.g. CLONE_NEWNET was problematic for some reason?

I actually want CLONE_NEWNET for my build tool, so I can be sure the
arbitrary code I'm executing as part of the build at least isn't
downloading more new code.


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