linux-kernel - Re: [RFC][PATCH 0/9] Make containers kernel objects

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Date:   Tue, 23 May 2017 16:30:19 +0100
From:   David Howells <dhowells@...hat.com>
To:     Colin Walters <walters@...bum.org>
Cc:     dhowells@...hat.com, Djalal Harouni <tixxdz@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Jeff Layton <jlayton@...hat.com>, trondmy@...marydata.com,
        Miklos Szeredi <mszeredi@...hat.com>,
        linux-nfs@...r.kernel.org,
        "linux-kernel" <linux-kernel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>
Subject: Re: [RFC][PATCH 0/9] Make containers kernel objects

Colin Walters <walters@...bum.org> wrote:

> Why not drop the upcall model in favor of having userspace monitor events
> via a (more efficient) protocol and react to them on its own?

 (1) That's not necessarily more efficient.  You now have the overhead of a
     permanently running userspace daemon in every relevant namespace
     combination.

 (2) You then have to work out how to route to the appropriate daemon.

> It's just generally more flexible

Actually, it's less flexible.  You can't easily get at the caller's
namespaces.

> and avoids all of those issues like replicating the seccomp configuration,
> etc.

So does my container implementation.

> Something like inotify/signalfd could be a precedent around having a read()/poll()able
> fd.  /proc/keys-requests ?
>
> Then if you create a new user namespace, and open /proc/keys-requests, the
> kernel will always write to that instead of calling /sbin/request-key.

That's not good enough.  You're basically making it one daemon per user
namespace and ignoring all the other namespaces.

[Also note that the kernel would have to paste a temporary authorisation key
 into the daemon's session keyring for each key that requires instantiation].

David