Re: /proc/sys/kernel/pid_max issues

[Ingo Molnar]

* Albert Cahalan <albert@xxxxxxxxxxxx> wrote:

> > > I'd much prefer LRU allocation. There are
> > > lots of system calls that take PID values.
> > > All such calls are hazardous. They're pretty
> > > much broken by design.
> > 
> > this is a pretty sweeping assertion. Would you
> > care to mention a few examples of such hazards?
> 
> kill(12345,9)
> setpriority(PRIO_PROCESS,12345,-20)
> sched_setscheduler(12345, SCHED_FIFO, &sp)
> 
> Prior to the call being handled, the process may
> die and be replaced. Some random innocent process,
> or a not-so-innocent one, will get acted upon by
> mistake. This is broken and dangerous.

easy to fix: SIGSTOP the task, check it's really
the one you want and then do the setpriority / 
setscheduler call and SIGCONT it. Any privileged
code that is about to spread some of its privileges
via asynchronous system-calls need to be careful.

	Ingo
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