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

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Message-ID: <20240523093334.GD15163@redhat.com>
Date: Thu, 23 May 2024 11:33:35 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Andrei Vagin <avagin@...gle.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 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?

Oleg.