linux-kernel - Re: [PATCH] Smack: replace capable() with ns

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Message-ID: <55B7A996.8010704@schaufler-ca.com>
Date:	Tue, 28 Jul 2015 09:11:02 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	Sungbae Yoo <sungbae.yoo@...sung.com>,
	'Lukasz Pawelczyk' <l.pawelczyk@...sung.com>,
	'James Morris' <james.l.morris@...cle.com>,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH] Smack: replace capable() with ns_capable()

On 7/28/2015 8:06 AM, Serge E. Hallyn wrote:
> On Tue, Jul 28, 2015 at 07:36:30AM -0700, Casey Schaufler wrote:
>> On 7/26/2015 6:27 PM, Sungbae Yoo wrote:
>>> So, Do you agree to allow the process to change its own labels?
>> No. This requires CAP_MAC_ADMIN. Smack is mandatory access control.
>> Being in a namespace (as they are implemented today) is not sufficient.
> "requires CAP_MAC_ADMIN" should probably read "requires
> CAP_MAC_ADMIN against initial user namespace."  Any unprivileged
> user can unshare a user_ns and get CAP_MAC_ADMIN.

As you say. Since the inode's xattrs are common you need
privilege relative to the initial namespace.

>
> I'm terribly sorry I'm not yet caught up on the smack-lsm thread.
> But intuitively I'd think that you'd want a way for smack policy
> to say "this label is allowed to create a user-ns which will be
> allowed to CAP_MAC_ADMIN", so then smack_capable() can use that
> information to cleanly deny CAP_MAC_ADMIN in namespaces.
>
> -serge
>

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