On Thu, Sep 15, 2016 at 02:19:38PM -0500, Josh Poimboeuf wrote:
> On Thu, Sep 15, 2016 at 11:41:25AM -0700, Andy Lutomirski wrote:
> > I also wouldn't mind trying to do something to prevent ever dumping
> > the stack of an actively running task. It's definitely safe to dump:
> > - current
> > - any task that's stopped via ptrace, etc
> > - any task on the current CPU if running atomically enough that the
> > task can't migrate (which probably covers the nasty NMI cases, I hope)
> > What's *not* safe AFAIK is /proc/PID/stack. I don't know if we can
> > somehow fix that short of actually sending an interrupt or NMI to
> > freeze the task if it's running. I'm also not sure it's worth
> > worrying about it.
> Yeah, I proposed a fix for /proc/PID/stack a while back:
> My idea was to use task_rq_lock() to lock the runqueue and then check
> tsk->on_cpu. I think Peter wasn't too keen on it.
That basically allows a DoS on the scheduler, since a user can run tasks
on every cpu (through sys_sched_setaffinity()). Then doing while (1) cat
/proc/$PID/stack would saturate the rq->lock on every CPU.
The more tasks the merrier.