Date: Wed, 18 Nov 2015 09:05:12 -0600
From: Seth Forshee <seth.forshee@canonical.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Austin S Hemmelgarn <ahferroin7@gmail.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        linux-bcache@vger.kernel.org, dm-devel@redhat.com,
        linux-raid@vger.kernel.org, linux-mtd@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org,
        selinux@tycho.nsa.gov, Serge Hallyn <serge.hallyn@canonical.com>,
        Andy Lutomirski <luto@amacapital.net>, linux-kernel@vger.kernel.org,
        "Theodore Ts'o" <tytso@mit.edu>
Subject: Re: [PATCH v3 0/7] User namespace mount updates
Message-ID: <20151118150512.GE134139@ubuntu-hedt>
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 <20151117175506.GW22011@ZenIV.linux.org.uk>
 <564B79B1.3040207@gmail.com>
 <20151117191606.GC108807@ubuntu-hedt>
 <564B941A.2070601@gmail.com>
 <20151117213255.GE108807@ubuntu-hedt>
 <564C6DD4.6090308@gmail.com>
 <20151118142238.GB134139@ubuntu-hedt>
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On Wed, Nov 18, 2015 at 02:58:18PM +0000, Al Viro wrote:
> On Wed, Nov 18, 2015 at 08:22:38AM -0600, Seth Forshee wrote:
> 
> > But it still requires the admin set it up that way, no? And aren't
> > privileges required to set up those devices in the first place?
> > 
> > I'm not saying that it wouldn't be a good idea to lock down the backing
> > stores for those types of devices too, just that it isn't something that
> > a regular user could exploit without an admin doing something to
> > facilitate it.
> 
> Sigh...  If it boils down to "all admins within all containers must be
> trusted not to try and break out" (along with "roothole in any container
> escalates to kernel-mode code execution on host"), then what the fuck
> is the *point* of bothering with containers, userns, etc. in the first
> place?  If your model is basically "you want isolation, just use kvm",
> fine, but where's the place for userns in all that?
> 
> And if you are talking about the _host_ admin, then WTF not have him just
> mount what's needed as part of setup and to hell with mounting those
> inside the container?

Yes, the host admin. I'm not talking about trusting the admin inside the
container at all.

>From my perspective the idea is essentially to allow mounting with fuse
or with ext4 using "mount -o loop ..." within a container.

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