Re: [PATCH ghak90 V7 14/21] audit: contid check descendancy and nesting

[Richard Guy Briggs]

On 2019-10-10 20:40, Paul Moore wrote:
> On Wed, Sep 18, 2019 at 9:26 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> > ?fixup! audit: convert to contid list to check for orch/engine ownership
> 
> ?
> 
> > Require the target task to be a descendant of the container
> > orchestrator/engine.
> >
> > You would only change the audit container ID from one set or inherited
> > value to another if you were nesting containers.
> >
> > If changing the contid, the container orchestrator/engine must be a
> > descendant and not same orchestrator as the one that set it so it is not
> > possible to change the contid of another orchestrator's container.
> 
> Did you mean to say that the container orchestrator must be an
> ancestor of the target, and the same orchestrator as the one that set
> the target process' audit container ID?

Not quite, the first half yes, but the second half: if it was already
set by that orchestrator, it can't be set again.  If it is a different
orchestrator that is a descendant of the orchestrator that set it, then
allow the action.

> Or maybe I'm missing something about what you are trying to do?

Does that help clarify it?

> > Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> > ---
> >  kernel/audit.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++-------
> >  1 file changed, 62 insertions(+), 8 deletions(-)
> >
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > index 9ce7a1ec7a92..69fe1e9af7cb 100644
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c
> > @@ -2560,6 +2560,39 @@ static struct task_struct *audit_cont_owner(struct task_struct *tsk)
> >  }
> >
> >  /*
> > + * task_is_descendant - walk up a process family tree looking for a match
> > + * @parent: the process to compare against while walking up from child
> > + * @child: the process to start from while looking upwards for parent
> > + *
> > + * Returns 1 if child is a descendant of parent, 0 if not.
> > + */
> > +static int task_is_descendant(struct task_struct *parent,
> > +                             struct task_struct *child)
> > +{
> > +       int rc = 0;
> > +       struct task_struct *walker = child;
> > +
> > +       if (!parent || !child)
> > +               return 0;
> > +
> > +       rcu_read_lock();
> > +       if (!thread_group_leader(parent))
> > +               parent = rcu_dereference(parent->group_leader);
> > +       while (walker->pid > 0) {
> > +               if (!thread_group_leader(walker))
> > +                       walker = rcu_dereference(walker->group_leader);
> > +               if (walker == parent) {
> > +                       rc = 1;
> > +                       break;
> > +               }
> > +               walker = rcu_dereference(walker->real_parent);
> > +       }
> > +       rcu_read_unlock();
> > +
> > +       return rc;
> > +}
> > +
> > +/*
> >   * audit_set_contid - set current task's audit contid
> >   * @task: target task
> >   * @contid: contid value
> > @@ -2587,22 +2620,43 @@ int audit_set_contid(struct task_struct *task, u64 contid)
> >         oldcontid = audit_get_contid(task);
> >         read_lock(&tasklist_lock);
> >         /* Don't allow the contid to be unset */
> > -       if (!audit_contid_valid(contid))
> > +       if (!audit_contid_valid(contid)) {
> >                 rc = -EINVAL;
> > +               goto unlock;
> > +       }
> >         /* Don't allow the contid to be set to the same value again */
> > -       else if (contid == oldcontid) {
> > +       if (contid == oldcontid) {
> >                 rc = -EADDRINUSE;
> > +               goto unlock;
> > +       }
> >         /* if we don't have caps, reject */
> > -       else if (!capable(CAP_AUDIT_CONTROL))
> > +       if (!capable(CAP_AUDIT_CONTROL)) {
> >                 rc = -EPERM;
> > -       /* if task has children or is not single-threaded, deny */
> > -       else if (!list_empty(&task->children))
> > +               goto unlock;
> > +       }
> > +       /* if task has children, deny */
> > +       if (!list_empty(&task->children)) {
> >                 rc = -EBUSY;
> > -       else if (!(thread_group_leader(task) && thread_group_empty(task)))
> > +               goto unlock;
> > +       }
> > +       /* if task is not single-threaded, deny */
> > +       if (!(thread_group_leader(task) && thread_group_empty(task))) {
> >                 rc = -EALREADY;
> > -       /* if contid is already set, deny */
> > -       else if (audit_contid_set(task))
> > +               goto unlock;
> > +       }
> > +       /* if task is not descendant, block */
> > +       if (task == current) {
> > +               rc = -EBADSLT;
> > +               goto unlock;
> > +       }
> > +       if (!task_is_descendant(current, task)) {
> > +               rc = -EXDEV;
> > +               goto unlock;
> > +       }
> > +       /* only allow contid setting again if nesting */
> > +       if (audit_contid_set(task) && current == audit_cont_owner(task))
> >                 rc = -ECHILD;
> > +unlock:
> >         read_unlock(&tasklist_lock);
> >         if (!rc) {
> >                 struct audit_cont *oldcont = audit_cont(task);
> 
> --
> paul moore
> www.paul-moore.com

- RGB

--
Richard Guy Briggs <rgb@xxxxxxxxxx>
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