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

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Date:   Fri, 14 Jul 2017 12:35:56 -0500
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        Mimi Zohar <zohar@...ibm.com>
Cc:     "Serge E. Hallyn" <serge@...lyn.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Theodore Ts'o <tytso@....edu>,
        containers@...ts.linux-foundation.org, lkp@...org,
        linux-kernel@...r.kernel.org, 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

Quoting Stefan Berger (stefanb@...ux.vnet.ibm.com):
> On 07/14/2017 09:34 AM, Serge E. Hallyn wrote:
> >Quoting Stefan Berger (stefanb@...ux.vnet.ibm.com):
> >>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? For limiting the number of xattrs
> >Not really.  If the file is owned by a uid mapped into the container,
> >then the container root can chown the file which will clear the file
> >capability, after which he can set a new one.  If the file is not
> >owned by a uid mapped into the container, then container root could
> >not set a filecap anyway.
> 
> Let's say I installed a container where all files are signed and
> thus have security.ima. Now for some reason I want to re-sign some
> or all files inside that container. How would I do that ? Would I
> need to get rid of security.ima first, possibly by copying each
> file, deleting the original file, and renaming the copied file to
> the original name, or should I just be able to write out a new
> signature, thus creating security.ima@...=1000 besides the
> security.ima ?
> 
>    Stefan

Hi Mimi,

what do you think makes most sense for IMA?

-serge