linux-kernel - Re: [PATCH 1/2] seccomp: notify user trap about unused filter

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Message-ID: <202005271537.75548B6@keescook>
Date:   Wed, 27 May 2020 15:37:58 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Tycho Andersen <tycho@...ho.ws>,
        Matt Denton <mpdenton@...gle.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Jann Horn <jannh@...gle.com>, Chris Palmer <palmer@...gle.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Robert Sesek <rsesek@...gle.com>,
        Jeffrey Vander Stoep <jeffv@...gle.com>,
        Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH 1/2] seccomp: notify user trap about unused filter

On Thu, May 28, 2020 at 12:05:32AM +0200, Christian Brauner wrote:
> The main question also is, is there precedence where the kernel just
> closes the file descriptor for userspace behind it's back? I'm not sure
> I've heard of this before. That's not how that works afaict; it's also
> not how we do pidfds. We don't just close the fd when the task
> associated with it goes away, we notify and then userspace can close.

But there's a mapping between pidfd and task struct that is separate
from task struct itself, yes? I.e. keeping a pidfd open doesn't pin
struct task in memory forever, right?

-- 
Kees Cook