Re: [local DoS] Re: Linux 2.6.24-rc4

[Ingo Molnar <mingo@elte.hu>]

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> 
> 
> On Tue, 4 Dec 2007, Luiz Fernando N. Capitulino wrote:
> >
> > 	sched_rr_get_interval(1, NULL);
> 
> Looks like we have a zero "cfs_rq->load.weight".
> 
> Ingo? Both sched_slice() and __sched_slice() do a divide by the 
> runqueue weight, and at least dequeue_task_fair() explicitly checks 
> for that being zero, so clearly zero is a possible value. Hmm?

yeah, i can reproduce this crash too.

The problem is on SMP: if sched_rr_get_interval() gets a task from an 
otherwise idle runqueue, then rq->load.weight is 0. Normally 
sched_slice() is only used on a busy runqueue. So the correct fixup site 
is not in sched_slice() but in sys_sched_rr_get_interval() - i'm working 
on the right fix, i hope to be able to send a pull request in a few 
minutes.

	Ingo