Re: [RFC PATCH ghak90 (was ghak32) V3 07/10] audit: add support for containerid to network namespaces

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

On Tue, Jul 24, 2018 at 10:06 AM Richard Guy Briggs <rgb@redhat.com> wrote:
> On 2018-07-20 18:14, Paul Moore wrote:
> > On Wed, Jun 6, 2018 at 1:03 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> > > Audit events could happen in a network namespace outside of a task
> > > context due to packets received from the net that trigger an auditing
> > > rule prior to being associated with a running task.  The network
> > > namespace could in use by multiple containers by association to the
> > > tasks in that network namespace.  We still want a way to attribute
> > > these events to any potential containers.  Keep a list per network
> > > namespace to track these audit container identifiiers.
> > >
> > > Add/increment the audit container identifier on:
> > > - initial setting of the audit container identifier via /proc
> > > - clone/fork call that inherits an audit container identifier
> > > - unshare call that inherits an audit container identifier
> > > - setns call that inherits an audit container identifier
> > > Delete/decrement the audit container identifier on:
> > > - an inherited audit container identifier dropped when child set
> > > - process exit
> > > - unshare call that drops a net namespace
> > > - setns call that drops a net namespace
> > >
> > > See: https://github.com/linux-audit/audit-kernel/issues/92
> > > See: https://github.com/linux-audit/audit-testsuite/issues/64
> > > See: https://github.com/linux-audit/audit-kernel/wiki/RFE-Audit-Container-ID
> > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > > ---
> > >  include/linux/audit.h | 23 ++++++++++++++++
> > >  kernel/audit.c        | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  kernel/auditsc.c      |  5 ++++
> > >  kernel/nsproxy.c      |  4 +++
> > >  4 files changed, 104 insertions(+)

...

> > > +                       }
> > > +       if (!found)
> > > +               return;
> > > +       list_del(&cont->list);
> > > +       if (refcount_dec_and_test(&cont->refcount))
> > > +               kfree(cont);
> >
> > Don't you want to dec_and_test first and only remove it from the list
> > if there are no other references?
>
> I don't think so.  Let me try to describe it in prose to see if I
> understood this properly and see if this makes more sense: I want to
> remove this audit_contid list member from this net's audit_contid list
> and decrement unconditionally this member's refcount so it knows there
> is one less thing pointing at it and when there is no longer anything
> pointing at it, free it.

Yep, sorry, my mistake, I was thinking the other way around (netns
going away) ... which actually, this patchset doesn't handle that does
it (I don't see any new code in audit_net_exit())?  Is is in a later
patch?  If so, it really should be in the same patch as this code to
prevent bisect nasties.

-- 
paul moore
www.paul-moore.com