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    SubjectRe: [PATCH ghak90 V7 14/21] audit: contid check descendancy and nesting
    On 2019-10-10 20:40, Paul Moore wrote:
    > 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?

    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@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

    - 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

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