Received-SPF: pass (google.com: domain of linux-kernel+bounces-69140-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Date: Fri, 16 Feb 2024 19:12:14 +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: <20240216181214.GA10393@redhat.com>
References: <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>
 <20240216130625.GA8723@redhat.com>
 <20240216-ohnedies-improvisieren-58edcc102b6a@brauner>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240216-ohnedies-improvisieren-58edcc102b6a@brauner>
User-Agent: Mutt/1.5.24 (2015-08-30)

On 02/16, Christian Brauner wrote:
>
> > 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.

I don't understand...

SI_USER/SI_TKILL means that the signal comes from the userspace (kill/etc),
but siginfo was filled by the kernel so the receiver can trust it.

> 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?

Heh ;)

I swear, this is how I wrote it originally, but then for some reason I
thought it would raise the questions, so I changed it to check PIDTYPE_PGID.

IOW, sure, I agree.

Oleg.