linux-kernel - Re: [PATCH 0/3 v2] seccomp: improve handling of SECCOMP_IOCTL_NOTIF

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Date: Mon, 24 Jun 2024 17:19:06 -0700
From: Andrei Vagin <avagin@...gle.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Kees Cook <keescook@...omium.org>, Andy Lutomirski <luto@...capital.net>, 
	Will Drewry <wad@...omium.org>, Christian Brauner <brauner@...nel.org>, linux-kernel@...r.kernel.org, 
	Tycho Andersen <tandersen@...flix.com>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 0/3 v2] seccomp: improve handling of SECCOMP_IOCTL_NOTIF_RECV

On Thu, May 23, 2024 at 2:35 AM Oleg Nesterov <oleg@...hat.com> wrote:
>
> On 05/23, Andrei Vagin wrote:
> >
> > This patch set addresses two problems with the SECCOMP_IOCTL_NOTIF_RECV
> > ioctl:
> > * it doesn't return when the seccomp filter becomes unused (all tasks
> >   have exited).
> > * EPOLLHUP is triggered not when a task exits, but rather when its zombie
> >   is collected.
>
> It seems that 2/3 also fixes another minor problem.
>
> Suppose that a group leader installs the new filter without
> SECCOMP_FILTER_FLAG_TSYNC, exits, and becomes a zombie. It can't be
> released until all its sub-threads exit.
>
> After that, without 2/3, SECCOMP_FILTER_FLAG_TSYNC from any other thread
> can never succeed, seccomp_can_sync_threads() will check a zombie leader
> and is_ancestor() will fail.
>
> Right?

It is right. I can introduce a self test for this case too, but let's
do that in a separate patch set.

>
> Oleg.
>