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

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Date: Fri, 9 Feb 2024 11:28:17 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Christian Brauner <brauner@...nel.org>
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] pidfd: change pidfd_send_signal() to respect PIDFD_THREAD

On 02/08, Oleg Nesterov wrote:
>
> Is prepare_kill_siginfo() correct when we send a signal to the child
> pid namespace? si_pid = task_tgid_vnr(current) doesn't look right

Yes, but iiuc send_signal_locked() should fixup si_pid/si_uid, so it
is not buggy.

> And why do we need it at all? Can't sys_kill() and pidfd_send_signal()
> just use SEND_SIG_NOINFO?

Probably yes. And even do_tkill() can use SEND_SIG_NOINFO if we change
__send_signal_locked() to check the type before ".si_code = SI_USER".
but then TP_STORE_SIGINFO() needs some changes...

I'll try to do this later, I do not want to mix this change with the
PIDFD_THREAD changes.

Oleg.