Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 20 Jan 2022 15:23:04 +0300
From:   Alexey Dobriyan <adobriyan@gmail.com>
To:     Christian Brauner <brauner@kernel.org>
Cc:     viro@zeniv.linux.org.uk, ebiederm@xmission.com,
        akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, stephen.s.brennan@oracle.com,
        legion@kernel.org, cyphar@cyphar.com
Subject: Re: [PATCH v2] proc: "mount -o lookup=" support
Message-ID: <YelUKIOjLd7A9XQN@localhost.localdomain>
References: <YegysyqL3LvljK66@localhost.localdomain>
 <20220119162423.eqbyefywhtzm22tr@wittgenstein>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20220119162423.eqbyefywhtzm22tr@wittgenstein>
Precedence: bulk

On Wed, Jan 19, 2022 at 05:24:23PM +0100, Christian Brauner wrote:
> On Wed, Jan 19, 2022 at 06:48:03PM +0300, Alexey Dobriyan wrote:
> > From 61376c85daab50afb343ce50b5a97e562bc1c8d3 Mon Sep 17 00:00:00 2001
> > From: Alexey Dobriyan <adobriyan@gmail.com>
> > Date: Mon, 22 Nov 2021 20:41:06 +0300
> > Subject: [PATCH 1/1] proc: "mount -o lookup=..." support
> > 
> > Docker implements MaskedPaths configuration option
> > 
> > 	https://github.com/estesp/docker/blob/9c15e82f19b0ad3c5fe8617a8ec2dddc6639f40a/oci/defaults.go#L97
> > 
> > to disable certain /proc files. It overmounts them with /dev/null.
> > 
> > Implement proper mount option which selectively disables lookup/readdir
> > in the top level /proc directory so that MaskedPaths doesn't need
> > to be updated as time goes on.
> 
> I might've missed this when this was sent the last time so maybe it was
> clearly explained in an earlier thread: What's the reason this needs to
> live in the kernel?
> 
> The MaskedPaths entry is optional so runtimes aren't required to block
> anything by default and this mostly makes sense for workloads that run
> privileged.
> 
> In addition MaskedPaths is a generic option which allows to hide any
> existing path, not just proc. Even in the very docker-specific defaults
> /sys/firmware is covered.

MaskedPaths is not future proof, new entries might pop up and nobody
will update the MaskedPaths list.

> I do see clear value in the subset= and hidepid= options. They are
> generally useful independent of opinionated container workloads. I don't
> see the same for lookup=.

The value is if you get /proc/cpuinfo you get everything else
but you might not want everything else given that "everything else"
changes over time.

> An alternative I find more sensible is to add a new value for subset=
> that hides anything(?) that only global root should have read/write
> access too.