netdev - Re: [PATCH ghak90 V7 20/21] audit: add capcontid to set contid outside init_user

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Date:   Thu, 31 Oct 2019 19:37:47 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Steve Grubb <sgrubb@...hat.com>
Cc:     Richard Guy Briggs <rgb@...hat.com>,
        containers@...ts.linux-foundation.org, linux-api@...r.kernel.org,
        Linux-Audit Mailing List <linux-audit@...hat.com>,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
        omosnace@...hat.com, dhowells@...hat.com, simo@...hat.com,
        Eric Paris <eparis@...isplace.org>,
        Serge Hallyn <serge@...lyn.com>, ebiederm@...ssion.com,
        nhorman@...driver.com, Dan Walsh <dwalsh@...hat.com>,
        mpatel@...hat.com
Subject: Re: [PATCH ghak90 V7 20/21] audit: add capcontid to set contid
 outside init_user_ns

On Thu, Oct 31, 2019 at 10:51 AM Steve Grubb <sgrubb@...hat.com> wrote:
> On Wednesday, October 30, 2019 6:03:20 PM EDT Richard Guy Briggs wrote:
> > > Also, for the record, removing the audit loginuid from procfs is not
> > > something to take lightly, if at all; like it or not, it's part of the
> > > kernel API.
>
> It can also be used by tools to iterate processes related to one user or
> session. I use this in my Intrusion Prevention System which will land in
> audit user space at some point in the future.

Let's try to stay focused on the audit container ID functionality; I
fear if we start bringing in other unrelated issues we are never going
to land these patches.

> > Oh, I'm quite aware of how important this change is and it was discussed
> > with Steve Grubb who saw the concern and value of considering such a
> > disruptive change.
>
> Actually, I advocated for syscall. I think the gist of Eric's idea was that /
> proc is the intersection of many nasty problems. By relying on it, you can't
> simplify the API to reduce the complexity.

I guess complexity is relative in a sense, but reading and writing a
number from a file in procfs seems awfully simple to me.

> Almost no program actually needs
> access to /proc. ps does. But almost everything else is happy without it. For
> example, when you setup chroot jails, you may have to add /dev/random or /
> dev/null, but almost never /proc. What does force you to add /proc is any
> entry point daemon like sshd because it needs to set the loginuid. If we
> switch away from /proc, then sshd or crond will no longer /require/ procfs to
> be available which again simplifies the system design.

It's not that simple, there are plenty of container use cases beyond
ps which require procfs:

Most LSM aware applications require procfs to view and manage some LSM
state (e.g. /proc/self/attr).

System containers, containers that run their own init/systemd/etc.,
require a working procfs.

Nested container orchestrators often run in system containers, which
require a working procfs (see above).

I'm sure there are plenty others, but these are the ones that came
immediately to mind.

-- 
paul moore
www.paul-moore.com