linux-ext4 - Re: generic question: user-only directory w/o root access

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Date:	Thu, 4 Jun 2015 13:29:15 +0200 (CEST)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
cc:	"U.Mutlu" <for-gmane@...luit.com>, linux-ext4@...r.kernel.org
Subject: Re: generic question: user-only directory w/o root access

On Wed, 3 Jun 2015, Theodore Ts'o wrote:

> Date: Wed, 3 Jun 2015 21:44:52 -0400
> From: Theodore Ts'o <tytso@....edu>
> To: U.Mutlu <for-gmane@...luit.com>
> Cc: linux-ext4@...r.kernel.org
> Subject: Re: generic question: user-only directory w/o root access
> 
> On Mon, Jun 01, 2015 at 12:45:22AM +0200, U.Mutlu wrote:
> > A private directory (or private mountpoint) for the user only
> > (or for an application running under that 'user'-account).
> > 
> > The rationale behind this is: there are many system programs,
> > and other programs running with root rights. The user cannot know
> > them all and so cannot trust them. This includes also admins and the root
> > user itself.
> > 
> > The idea is to have a truly private directory or a private mountpoint
> > where by default nobody else has access to it, incl. root,
> > unless the owner grants access to others.
> 
> A user can't protect herself from root.  For one thing, root can
> modify the kernel, or install a module that runs arbitrary code inside
> the kernel context.  If you can insert or run arbitrary kernel code,
> you can do *anything*.  You can extract the user's encryption key; you
> can mess with arbitrary namespaces.  Root can use ptrace to muck with
> a running process.  Etc., etc., etc.
> 
> > So, my wish is to mount an encrypted virtual HD to a mountpoint,
> > and nobody else shall have access to it, especially not root or
> > any program with root rights.
> > 
> > Does anybody know of such an open-source solution for Linux?
> 
> No, just as there is no open-source solution for a perpetual motion
> machine...
> 
> Ultimately, the user has to trust the hardware and the firmware on it,
> the kernel, root, whoever is building the kernel (i.e., if you are
> using Debian and using the Debian kernel, you have to trust the people
> who build the Debian kernel, the Debian ftpmasters and so on).
> 
>     	      	     	     	 		   - Ted

Everything Ted mentioned is true. However there are ways to prevent
application and daemons running under root privileges doing harmful
things. Using Selinux is one of the ways
(https://en.wikipedia.org/wiki/Security-Enhanced_Linux).

However note that it'll still require you to trust your hardware,
kernel, whoever has a root access and to some extent the
applications as well because since it will protect you from someone
exploiting a bug in the application it will not fully protect you
from intentionally malicious application (because again, as a root
user you *can* do anything).

-Lukas

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