Re: [PATCH v2 2/2] pidfd: change pidfd_send_signal() to respect PIDFD_THREAD

[Oleg Nesterov <oleg@redhat.com>]

On 02/16, Christian Brauner wrote:
>
> > SI_USER means that the target can trust the values of si_pid/si_uid
> > in siginfo.
>
> Bah, what an annoying nonsense. I see that this can be used to emulate
> stuff like SI_TIMER and SI_ASYNCIO. But I very much doubt the value of
> e.g., emulating SI_DETHREAD. Maybe I'm missing something very obvious.

I don't understand...

SI_USER/SI_TKILL means that the signal comes from the userspace (kill/etc),
but siginfo was filled by the kernel so the receiver can trust it.

> So wouldn't be better of just writing this as?
>
> if ((task_pid(current) != pid || type > PIDTYPE_TGID) &&
>     (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL))
>         goto err;
>
> So that we don't have to repeat the same exercise if we extend this to
> anything above PIDTYPE_PGID?

Heh ;)

I swear, this is how I wrote it originally, but then for some reason I
thought it would raise the questions, so I changed it to check PIDTYPE_PGID.

IOW, sure, I agree.

Oleg.