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

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Date: Wed, 14 Feb 2024 13:36:56 +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 v2 2/2] pidfd: change pidfd_send_signal() to respect
 PIDFD_THREAD

On 02/10, Oleg Nesterov wrote:
>
> On 02/10, Christian Brauner wrote:
> >
> > +	if (type == PIDFD_SIGNAL_PROCESS_GROUP)
> > +		ret = kill_pgrp_info(sig, &kinfo, pid);
>
> I guess you meant
>
> 	if (type == PIDTYPE_PGID)
>
> other than that,
>
> Reviewed-by: Oleg Nesterov <oleg@...hat.com>

Yes, but there is another thing I hadn't thought of...

sys_pidfd_send_signal() does

	/* Only allow sending arbitrary signals to yourself. */
	ret = -EPERM;
	if ((task_pid(current) != pid) &&
	    (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL))
		goto err;

and I am not sure that task_pid(current) == pid should allow
the "arbitrary signals" if PIDFD_SIGNAL_PROCESS_GROUP.

Perhaps

	/* Only allow sending arbitrary signals to yourself. */
	ret = -EPERM;
	if ((task_pid(current) != pid || type == PIDTYPE_PGID) &&
	    (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL)
		goto err;

?

Oleg.