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

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Date: Fri, 16 Feb 2024 14:06:25 +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 02/16, Christian Brauner wrote:
>
> On Wed, Feb 14, 2024 at 01:36:56PM +0100, Oleg Nesterov wrote:
> >
> > 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;
>
> Honestly, we should probably just do:
>
> if (kinfo->si_code != SI_USER)
>         goto err

Hmm. This doesn't look right. The purpose of the current check is to
forbid SI_TKILL and si_code >= 0, and SI_USER == 0.

SI_USER means that the target can trust the values of si_pid/si_uid
in siginfo.

> +		if (kinfo.si_code != SI_USER)
>  			goto err;

See above...

Oleg.