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

From: Alexey Gladkov <legion@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	containers@lists.linux.dev, linux-fsdevel@vger.kernel.org,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>,
	Val Cowan <vcowan@redhat.com>
Subject: Re: [RFC PATCH v1 2/6] proc: Add allowlist to control access to procfs files
Date: Thu, 26 Jan 2023 12:13:36 +0100	[thread overview]
Message-ID: <Y9JgYPHebozyuTTe@example.org> (raw)
In-Reply-To: <20230125153642.db8c733f5b21e27d3aa80b7d@linux-foundation.org>

On Wed, Jan 25, 2023 at 03:36:42PM -0800, Andrew Morton wrote:
> On Wed, 25 Jan 2023 16:28:49 +0100 Alexey Gladkov <legion@kernel.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?

In this commit, the admin is the one with CAP_SYS_ADMIN. You're right,
I'll fix the commit message.

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

-- 
Rgrds, legion