linux-kernel - Re: [PATCH v2] xattr: Enable security.capability in user namespaces

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Date:   Fri, 14 Jul 2017 07:04:19 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:     "Theodore Ts'o" <tytso@....edu>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        containers@...ts.linux-foundation.org, lkp@...org,
        linux-kernel@...r.kernel.org, zohar@...ux.vnet.ibm.com,
        tycho@...ker.com, James.Bottomley@...senPartnership.com,
        vgoyal@...hat.com, christian.brauner@...lbox.org,
        amir73il@...il.com, linux-security-module@...r.kernel.org,
        casey@...aufler-ca.com
Subject: Re: [PATCH v2] xattr: Enable security.capability in user namespaces

Stefan Berger <stefanb@...ux.vnet.ibm.com> writes:

> On 07/13/2017 08:38 PM, Eric W. Biederman wrote:
>> Stefan Berger <stefanb@...ux.vnet.ibm.com> writes:
>>
>>> On 07/13/2017 01:49 PM, Eric W. Biederman wrote:
>>>
>>>> My big question right now is can you implement Ted's suggested
>>>> restriction.  Only one security.foo or secuirty.foo@... attribute ?
>>> We need to raw-list the xattrs and do the check before writing them. I am fairly sure this can be done.
>>>
>>> So now you want to allow security.foo and one security.foo@...=<> or just a single one security.foo(@[[:print:]]*)?
>>>
>> The latter.
>
> That case would prevent a container user from overriding the xattr on
> the host. Is that what we want?

Most definitely.  If a more privileged use has set secure.capable that
is better.  

> For limiting the number of xattrs and
> getting that functionality (override IMA signature for example) the
> former seems better...

I don't know about IMA.  But my feeling is that we will only be dealing
with a single signing key, so I don't see how having multiple IMA xattrs
make sense.  Could you explain that to me?

> For the former I now have the topmost patch here:
> https://github.com/stefanberger/linux/commits/xattr_for_userns.v3

Thank you.

Eric