Re: [PATCH v2] taskstats: don't allow duplicate entries in listener mode

[Vasiliy Kulikov <segoon@openwall.com>]

On Tue, Jun 21, 2011 at 15:49 -0700, Andrew Morton wrote:
> On Thu, 16 Jun 2011 19:55:59 +0400
> Vasiliy Kulikov <segoon@openwall.com> wrote:
> 
> > Currently a single process may register exit handlers unlimited times.
> > It may lead to a bloated listeners chain and very slow process terminations.
> > E.g. after 10KK sent TASKSTATS_CMD_ATTR_REGISTER_CPUMASKs ~300 Mb of
> > kernel memory is stolen for the handlers chain and "time id" shows 2-7
> > seconds instead of normal 0.003.  It makes it possible to exhaust all
> > kernel memory and to eat much of CPU time by triggerring numerous exits
> > on a single CPU.
> > 
> > The patch limits the number of times a single process may register
> > itself on a single CPU to one.
> > 
> > One little issue is kept unfixed - as taskstats_exit() is called before
> > exit_files() in do_exit(), the orphaned listener entry (if it was not
> > explicitly deregistered) is kept until the next someone's exit() and
> > implicit deregistration in send_cpu_listeners().  So, if a process
> > registered itself as a listener exits and the next spawned process gets
> > the same pid, it would inherit taskstats attributes.
> 
> ow. That's an unprivileged operation, isn't it?

Yes.


Thanks,

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