KASAN: use-after-free Read in task_is_descendant

[Oleg Nesterov]

On 10/25, Oleg Nesterov wrote:
>
> As I said below, please ignore ptracer_exception_found(), another caller for now,
> perhaps it needs some changes too. I even have a vague feeling that I have already
> blamed this function some time ago...

Heh, yes, 3 years ago ;)

https://lore.kernel.org/lkml/20150106184427.GA18153@redhat.com/

I can't understand my email today, but note that I tried to point out that
task_is_descendant() can dereference the freed mem.

And yes, task_is_descendant() is overcompicated for no reason, afaics.

Oleg.