linux-kernel - Re: [RFC] Implement ambient capability set.

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Message-ID: <CALCETrU+u1yL3TsOVRKqRV6c=vXY1CU2V0xc2cgjabM1ys8DBw@mail.gmail.com>
Date:	Wed, 4 Feb 2015 14:29:55 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Christoph Lameter <cl@...ux.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	"Andrew G. Morgan" <morgan@...nel.org>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Jonathan Corbet <corbet@....net>,
	Aaron Jones <aaronmdjones@...il.com>,
	"Ted Ts'o" <tytso@....edu>,
	LSM List <linux-security-module@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...uxfoundation.org>
Subject: Re: [RFC] Implement ambient capability set.

On Wed, Feb 4, 2015 at 1:57 PM, Christoph Lameter <cl@...ux.com> wrote:
> On Wed, 4 Feb 2015, Andy Lutomirski wrote:
>
>> But someone will want to run *bash* as an untrusted user with, say,
>> CAP_NET_BIND permitted and ambient.  Then that user has a non-empty
>> ambient set, and they can run a setuid-root program, and who knows
>> what will go wrong?  Requiring no_new_privs would prevent this type of
>> failure entirely.
>>
>> If we need to relax that later, it's easy, I think.  The rule's not
>> that convoluted, and there's precedent for having new fancy features
>> require setting no_new_privs first.
>
> It would make the patch pointless. The case of having to run a setuid root
> prpgrams from a shell that has the caps enabled is a routine thing for
> testing etc.
>

That's unfortunate.  In that case, we need to figure out what happens
when you run such a setuid root program.  I think the answer should be
that pA gets cleared, and that pA also gets cleared if you run a
program that has file caps.

--Andy
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