Re: [PATCH ghak90 V7 06/21] audit: contid limit of 32k imposed to avoid DoS

[Paul Moore]

On Fri, Sep 27, 2019 at 8:52 AM Neil Horman <nhorman@xxxxxxxxxxxxx> wrote:
> On Wed, Sep 18, 2019 at 09:22:23PM -0400, Richard Guy Briggs wrote:
> > Set an arbitrary limit on the number of audit container identifiers to
> > limit abuse.
> >
> > Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> > ---
> >  kernel/audit.c | 8 ++++++++
> >  kernel/audit.h | 4 ++++
> >  2 files changed, 12 insertions(+)
> >
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > index 53d13d638c63..329916534dd2 100644
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c

...

> > @@ -2465,6 +2472,7 @@ int audit_set_contid(struct task_struct *task, u64 contid)
> >                               newcont->owner = current;
> >                               refcount_set(&newcont->refcount, 1);
> >                               list_add_rcu(&newcont->list, &audit_contid_hash[h]);
> > +                             audit_contid_count++;
> >                       } else {
> >                               rc = -ENOMEM;
> >                               goto conterror;
> > diff --git a/kernel/audit.h b/kernel/audit.h
> > index 162de8366b32..543f1334ba47 100644
> > --- a/kernel/audit.h
> > +++ b/kernel/audit.h
> > @@ -219,6 +219,10 @@ static inline int audit_hash_contid(u64 contid)
> >       return (contid & (AUDIT_CONTID_BUCKETS-1));
> >  }
> >
> > +extern int audit_contid_count;
> > +
> > +#define AUDIT_CONTID_COUNT   1 << 16
> > +
>
> Just to ask the question, since it wasn't clear in the changelog, what
> abuse are you avoiding here?  Ostensibly you should be able to create as
> many container ids as you have space for, and the simple creation of
> container ids doesn't seem like the resource strain I would be concerned
> about here, given that an orchestrator can still create as many
> containers as the system will otherwise allow, which will consume
> significantly more ram/disk/etc.

I've got a similar question.  Up to this point in the patchset, there
is a potential issue of hash bucket chain lengths and traversing them
with a spinlock held, but it seems like we shouldn't be putting an
arbitrary limit on audit container IDs unless we have a good reason
for it.  If for some reason we do want to enforce a limit, it should
probably be a tunable value like a sysctl, or similar.

--
paul moore
www.paul-moore.com