linux-kernel - Re: [PATCH 2/3] seccomp: release task filters when the task exits

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Date: Thu, 23 May 2024 11:00:04 +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 2/3] seccomp: release task filters when the task exits

On 05/23, Andrei Vagin wrote:
>
> Previously, seccomp filters were released in release_task(), which
> required the process to exit and its zombie to be collected. However,
> exited threads/processes can't trigger any seccomp events, making it
> more logical to release filters upon task exits.
>
> This adjustment simplifies scenarios where a parent is tracing its child
> process. The parent process can now handle all events from a seccomp
> listening descriptor and then call wait to collect a child zombie.
>
> seccomp_filter_release takes the siglock to avoid races with
> seccomp_sync_threads. There was an idea to bypass taking the lock by
> checking PF_EXITING, but it can be set without holding siglock if
> threads have SIGNAL_GROUP_EXIT. This means it can happen concurently
> with seccomp_filter_release.
>
> Signed-off-by: Andrei Vagin <avagin@...gle.com>
> ---
>  kernel/exit.c    |  3 ++-
>  kernel/seccomp.c | 22 ++++++++++++++++------
>  2 files changed, 18 insertions(+), 7 deletions(-)

Reviewed-by: Oleg Nesterov <oleg@...hat.com>