[kernel-hardening] Re: [RFC] ipc: introduce shm_rmid_forced sysctl

[Vasiliy Kulikov <segoon@openwall.com>]

On Mon, Jul 04, 2011 at 17:08 +0200, Oleg Nesterov wrote:
> On 06/22, Vasiliy Kulikov wrote:
> >
> > +void exit_shm(struct task_struct *task)
> > +{
> > +	struct nsproxy *nsp = task->nsproxy;
> > +	struct ipc_namespace *ns;
> > +
> > +	if (!nsp)
> > +		return;
> > +	ns = nsp->ipc_ns;
> > +	if (!ns || !ns->shm_rmid_forced)
> 
> This looks confusing, imho. How it is possible that ->nsproxy or
> ->ipc_ns is NULL?

I spotted the same checking logic in other places.  I don't know whether
it is redundant, I guess it can happen when the namespace is dying.
Probably it cannot happed inside of task do_exit(), only for extern
observers.


> > +		return;
> > +
> > +	/* Destroy all already created segments, but not mapped yet */
> > +	down_write(&shm_ids(ns).rw_mutex);
> > +	idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_current, ns);
> >  	up_write(&shm_ids(ns).rw_mutex);
> 
> Again, I do not pretend I understand ipc/, but it seems we can check
> ns->ipc_ids[].in_use != 0 before the slow path, no?

Looks like you're right.  Given it is do_exit(), the boost is
significant.

I'll send the patch for this thing and the locking part.


Thank you!

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments