linux-kernel - Re: [PATCH 1/6] cgroup: Use open-time credentials for process migraton perm checks

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Message-ID: <CAHk-=wiCZgpVjF2PNkx5V+Kuhr--1iX1yaYcOoxPsc2n2Zuhpg@mail.gmail.com>
Date:   Fri, 10 Dec 2021 09:41:52 -0800
From:   Linus Torvalds <torvalds@...uxfoundation.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Michal Koutny <mkoutny@...e.com>, Jens Axboe <axboe@...nel.dk>,
        Kees Cook <keescook@...omium.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jim Newsome <jnewsome@...project.org>,
        Alexey Gladkov <legion@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jann Horn <jannh@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Security Officers <security@...nel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH 1/6] cgroup: Use open-time credentials for process
 migraton perm checks

On Thu, Dec 9, 2021 at 1:47 PM Tejun Heo <tj@...nel.org> wrote:
>
> +       saved_cred = override_creds(of->file->f_cred);
>         ret = cgroup_attach_permissions(src_cgrp, dst_cgrp,
>                                         of->file->f_path.dentry->d_sb, threadgroup);
> +       revert_creds(saved_cred);

I'm not happy about adding another override_creds/revert_creds pair,
but looking at what that thing ends up doing I don't see a better
alternative - no sane way to pass in explicit creds due to the way
that "descend to common parent, use inode_permission" thing works.

So it's not pretty, and I don't love it, but I don't see a better
solution either.

            Linus