Date:   Thu, 9 Dec 2021 14:44:19 +0100
From:   Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
To:     Tejun Heo <tj@kernel.org>
Cc:     Linus Torvalds <torvalds@linuxfoundation.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jens Axboe <axboe@kernel.dk>,
        Kees Cook <keescook@chromium.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jim Newsome <jnewsome@torproject.org>,
        Alexey Gladkov <legion@kernel.org>,
        Security Officers <security@kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Jann Horn <jannh@google.com>,
        Christian Brauner <christian.brauner@ubuntu.com>
Subject: Re: [PATCH] exit: Retain nsproxy for exit_task_work() work entries
Message-ID: <20211209134419.GA17186@blackbody.suse.cz>
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On Wed, Dec 08, 2021 at 01:07:54PM -1000, Tejun Heo <tj@kernel.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);
> +					of->file->f_path.dentry->d_sb,
> +					threadgroup, ctx->ns);
> +	revert_creds(saved_cred);

I wonder now whether such a wrap shouldn't also be around cgroup_kill()
too (+ replacement of send_sig() with group_send_sig_info() [1])?

This shouldn't break the use case of passing cgroup kill fd to a less
privileged task for (auto)destruction purposes but on the other hand it
would prevent subverting the fd to a more privileged confused task to
kill otherwise disallowed processes.

Thanks,
Michal

[1] https://lore.kernel.org/r/m1v97x6niq.fsf@fess.ebiederm.org/