linux-kernel - Re: [PATCH] pid: allow pidfds for reaped tasks

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Date:   Fri, 11 Aug 2023 13:47:11 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <brauner@...nel.org>
Cc:     David Rheinsberg <david@...dahead.eu>,
        linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        Kees Cook <keescook@...omium.org>,
        Alexander Mikhalitsyn <alexander@...alicyn.com>,
        Luca Boccassi <bluca@...ian.org>
Subject: Re: [PATCH] pid: allow pidfds for reaped tasks

As I said, I am not sure I understand the problem. And I know nothing
about net/ but...

On 08/07, Christian Brauner wrote:
>
> > SO_PEERPIDFD returns `EINVAL` if the peer-task was already reaped,
> > but returns a stale pidfd if the task is reaped immediately after the
> > respective alive-check.

after the quick grep it seems that SO_PEERPIDFD can simply use
__pidfd_prepare() ? We know that sk->sk_peer_pid was initialized with
task_tgid(current) and thus we know it is (was) a valid TGID pid.

The same is probably true for scm->pid and scm_pidfd_recv()...

But again, I am not familiar with this code, I can be wrong.

Oleg.