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

[Paul Moore <paul@paul-moore.com>]

On Wed, Sep 18, 2019 at 9:26 PM Richard Guy Briggs <rgb@redhat.com> 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?

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

> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> ---
>  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