linux-kernel - Re: [PATCH 4/4] Allow unprivileged chroot when safe

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Date:	Tue, 17 Jan 2012 08:31:58 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Oleg Nesterov <oleg@...hat.com>
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,
	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 4/4] Allow unprivileged chroot when safe

On Tue, Jan 17, 2012 at 8:23 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 01/15, Andy Lutomirski wrote:
>>
>> Chroot can easily be used to subvert setuid programs.  If no_new_privs,
>> then setuid programs don't gain any privilege, so allow chroot.
>>
>> ...
>>
>> +     if (!(current->no_new_privs && !is_chrooted) &&
>> +         !capable(CAP_SYS_CHROOT))
>
> I must have missed something. How no_new_privs can help if fs->users != 1 ?

Whoops.  That needs fixing.

--Andy
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