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Message-ID: <20191024220814.pid5ql6kvyr4ianb@madcap2.tricolour.ca>
Date: Thu, 24 Oct 2019 18:08:14 -0400
From: Richard Guy Briggs <rgb@...hat.com>
To: Paul Moore <paul@...l-moore.com>
Cc: containers@...ts.linux-foundation.org, linux-api@...r.kernel.org,
Linux-Audit Mailing List <linux-audit@...hat.com>,
linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
sgrubb@...hat.com, omosnace@...hat.com, dhowells@...hat.com,
simo@...hat.com, Eric Paris <eparis@...isplace.org>,
Serge Hallyn <serge@...lyn.com>, ebiederm@...ssion.com,
nhorman@...driver.com, Dan Walsh <dwalsh@...hat.com>,
mpatel@...hat.com
Subject: Re: [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@...hat.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@...hat.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@...hat.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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