linux-kernel - Re: [PATCH v3 0/7] User namespace mount updates

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Message-ID: <20151118150512.GE134139@ubuntu-hedt>
Date:	Wed, 18 Nov 2015 09:05:12 -0600
From:	Seth Forshee <seth.forshee@...onical.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Austin S Hemmelgarn <ahferroin7@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-bcache@...r.kernel.org, dm-devel@...hat.com,
	linux-raid@...r.kernel.org, linux-mtd@...ts.infradead.org,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andy Lutomirski <luto@...capital.net>,
	linux-kernel@...r.kernel.org, Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH v3 0/7] User namespace mount updates

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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