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Date:   Mon, 8 Jul 2019 13:51:05 -0400
From:   Richard Guy Briggs <rgb@redhat.com>
To:     Paul Moore <paul@paul-moore.com>
Cc:     Tycho Andersen <tycho@tycho.ws>,
        containers@lists.linux-foundation.org, linux-api@vger.kernel.org,
        Linux-Audit Mailing List <linux-audit@redhat.com>,
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        sgrubb@redhat.com, omosnace@redhat.com, dhowells@redhat.com,
        simo@redhat.com, Eric Paris <eparis@parisplace.org>,
        Serge Hallyn <serge@hallyn.com>, ebiederm@xmission.com,
        nhorman@tuxdriver.com
Subject: Re: [PATCH ghak90 V6 02/10] audit: add container id
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On 2019-05-29 11:29, Paul Moore wrote:
> On Wed, May 29, 2019 at 10:57 AM Tycho Andersen <tycho@tycho.ws> wrote:
> >
> > On Mon, Apr 08, 2019 at 11:39:09PM -0400, Richard Guy Briggs wrote:
> > > It is not permitted to unset the audit container identifier.
> > > A child inherits its parent's audit container identifier.
> >
> > ...
> >
> > >  /**
> > > + * audit_set_contid - set current task's audit contid
> > > + * @contid: contid value
> > > + *
> > > + * Returns 0 on success, -EPERM on permission failure.
> > > + *
> > > + * Called (set) from fs/proc/base.c::proc_contid_write().
> > > + */
> > > +int audit_set_contid(struct task_struct *task, u64 contid)
> > > +{
> > > +     u64 oldcontid;
> > > +     int rc = 0;
> > > +     struct audit_buffer *ab;
> > > +     uid_t uid;
> > > +     struct tty_struct *tty;
> > > +     char comm[sizeof(current->comm)];
> > > +
> > > +     task_lock(task);
> > > +     /* Can't set if audit disabled */
> > > +     if (!task->audit) {
> > > +             task_unlock(task);
> > > +             return -ENOPROTOOPT;
> > > +     }
> > > +     oldcontid = audit_get_contid(task);
> > > +     read_lock(&tasklist_lock);
> > > +     /* Don't allow the audit containerid to be unset */
> > > +     if (!audit_contid_valid(contid))
> > > +             rc = -EINVAL;
> > > +     /* if we don't have caps, reject */
> > > +     else if (!capable(CAP_AUDIT_CONTROL))
> > > +             rc = -EPERM;
> > > +     /* if task has children or is not single-threaded, deny */
> > > +     else if (!list_empty(&task->children))
> > > +             rc = -EBUSY;
> > > +     else if (!(thread_group_leader(task) && thread_group_empty(task)))
> > > +             rc = -EALREADY;
> > > +     read_unlock(&tasklist_lock);
> > > +     if (!rc)
> > > +             task->audit->contid = contid;
> > > +     task_unlock(task);
> > > +
> > > +     if (!audit_enabled)
> > > +             return rc;
> >
> > ...but it is allowed to change it (assuming
> > capable(CAP_AUDIT_CONTROL), of course)? Seems like this might be more
> > immediately useful since we still live in the world of majority
> > privileged containers if we didn't allow changing it, in addition to
> > un-setting it.
> 
> The idea is that only container orchestrators should be able to
> set/modify the audit container ID, and since setting the audit
> container ID can have a significant effect on the records captured
> (and their routing to multiple daemons when we get there) modifying
> the audit container ID is akin to modifying the audit configuration
> which is why it is gated by CAP_AUDIT_CONTROL.  The current thinking
> is that you would only change the audit container ID from one
> set/inherited value to another if you were nesting containers, in
> which case the nested container orchestrator would need to be granted
> CAP_AUDIT_CONTROL (which everyone to date seems to agree is a workable
> compromise).  We did consider allowing for a chain of nested audit
> container IDs, but the implications of doing so are significant
> (implementation mess, runtime cost, etc.) so we are leaving that out
> of this effort.

We had previously discussed the idea of restricting
orchestrators/engines from only being able to set the audit container
identifier on their own descendants, but it was discarded.  I've added a
check to ensure this is now enforced.

I've also added a check to ensure that a process can't set its own audit
container identifier and that if the identifier is already set, then the
orchestrator/engine must be in a descendant user namespace from the
orchestrator that set the previously inherited audit container
identifier.

> From a practical perspective, un-setting the audit container ID is
> pretty much the same as changing it from one set value to another so
> most of the above applies to that case as well.
> 
> -- 
> paul moore
> www.paul-moore.com

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635