linux-kernel - Re: [PATCH v2 2/2] pidfd: change pidfd_send_signal() to respect PIDFD

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Date: Fri, 16 Feb 2024 15:46:20 +0100
From: Christian Brauner <brauner@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Andy Lutomirski <luto@...capital.net>, 
	"Eric W. Biederman" <ebiederm@...ssion.com>, Tycho Andersen <tycho@...ho.pizza>, linux-api@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] pidfd: change pidfd_send_signal() to respect
 PIDFD_THREAD

> 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.
In any case, thanks for keeping me honest:

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?