linux-kernel - Re: [RFC PATCH v1 2/6] proc: Add allowlist to control access to procfs files

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Date:   Wed, 25 Jan 2023 15:36:42 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alexey Gladkov <legion@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, containers@...ts.linux.dev,
        linux-fsdevel@...r.kernel.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Val Cowan <vcowan@...hat.com>
Subject: Re: [RFC PATCH v1 2/6] proc: Add allowlist to control access to
 procfs files

On Wed, 25 Jan 2023 16:28:49 +0100 Alexey Gladkov <legion@...nel.org> wrote:

> If, after creating a container and mounting procfs, the system
> configuration may change and new files may appear in procfs. Files
> including writable root or any other users.
> 
> In most cases, it is known in advance which files in procfs the user
> needs in the container. It is much easier to control the list of what
> you want than to control the list of unwanted files.
> 
> To do this, subset=allowlist is added to control the visibility of
> static files in procfs (not process pids). After that, the control file
> /proc/allowlist appears in the root of the filesystem. This file
> contains a list of files and directories that will be visible in this
> vmountpoint. Immediately after mount, this file contains only one
> name - the name of the file itself.
> 
> The admin can add names, read this file to get the current state of the
> allowlist. The file behaves almost like a regular file. Changes are
> applied when the file is closed.

"the admin" is a bit vague.  Precisely which capabilities are required
for this?

> To prevent changes to allowlist, admin should remove its name from the
> list of allowed files. After this change, the file will disappear.