On Sun, 2016-09-18 at 17:05 +0200, Jann Horn wrote:
> This ensures that self_privunit_id ("privilege unit ID") is only shared by
> processes that share the mm_struct and the signal_struct; not just
> spatially, but also temporally. In other words, if you do execve() or
> clone() without CLONE_THREAD, you get a new privunit_id that has never been
> used before.
[...]
> +void increment_privunit_counter(void)
> +{
> +	BUILD_BUG_ON(NR_CPUS > (1 << 16));
> +	current->self_privunit_id = this_cpu_add_return(exec_counter, NR_CPUS);
> +}
[...]

This will wrap incorrectly if NR_CPUS is not a power of 2 (which is
unusual but allowed).

Ben.
 
-- 
Ben Hutchings
Klipstein's 4th Law of Prototyping and Production:
                                    A fail-safe circuit will destroy
others.