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Date: Fri, 16 Feb 2024 14:06:25 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Christian Brauner <brauner@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Tycho Andersen <tycho@tycho.pizza>, linux-api@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/2] pidfd: change pidfd_send_signal() to respect
 PIDFD_THREAD
Message-ID: <20240216130625.GA8723@redhat.com>
References: <20240209-radeln-untrennbar-9d4ae05aa4cc@brauner>
 <20240209155644.GD3282@redhat.com>
 <20240210-abfinden-beimessen-2dbfea59b0da@brauner>
 <20240210123033.GA27557@redhat.com>
 <20240210-dackel-getan-619c70fefa62@brauner>
 <20240210131518.GC27557@redhat.com>
 <20240210-chihuahua-hinzog-3945b6abd44a@brauner>
 <20240210165133.GD27557@redhat.com>
 <20240214123655.GB16265@redhat.com>
 <20240216-albern-aufwiegen-1de327c7dafd@brauner>
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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.