Date:	Fri, 5 Jun 2015 21:24:51 +0200
From:	"U.Mutlu" <for-gmane@...luit.com>
To:	linux-ext4@...r.kernel.org
Subject: Re: generic question: user-only directory w/o root access

Theodore Ts'o wrote on 06/05/2015 04:14 PM:
> On Thu, Jun 04, 2015 at 03:24:06PM +0200, U.Mutlu wrote:
>> I use a truecrypt container with ext2 on it and now use the mentioned
>> private namespace-mount, because only that single application (running
>> under its own user account) shall have access to the mountpoint,
>> root by default has no access to it, and yes as you both pointed out
>> root can overcome this, but then he would need to restart the machine.
>> But then he cannot mount the encrypted volume :-) [not using any automount],
>> so, imo that solution looks to me rock solid, and that was what I was
>> looking for when I started the thread here.
>
> I wouldn't count out a sufficiently clever root user.  At the very
> minimum, root could replace the kernel and wait for the system to
> reboot under normal circumstances.  The root user could load a kernel
> module (or replace an existing kernel module) that gives him access to
> *any* namespace, or extract *any* key, or read from *any* userspace
> process.
>
> If there are any shared files used by both the container and rest of
> the system (i.e., if the container only contains the data files and
> uses /usr/bin and /bin and /lib from the rest of the system), then
> root could replace one of these executables or shared libaries which
> would then used by the container.  If you are using kvm in the
> "secure" container, root could insert mailware into the kvm binary.
>
> If you are using a secure boot system (i.e., using UEFI bios with your
> own firmware public/private key pair), and then use a kernel signed by
> your BIOS key, and then use signed modules, and then use SELinux to
> try to add more fences to prevent unauthorized changes to binaries,
> you can make things more secure.
>
> But your original statement talked about trying to protect against all
> root users, and that's what was so concerning.  Listing all of the
> authorized users may very well be a very large list.  Consider that on
> a Debian system, this includes all of the people authorized to upload
> packages to the debian-security repository (or the equivalent for
> Fedora, SuSE, etc.)
>
> This is why a lot of people who hear words like "rock solid" will
> start assuming that the speaker either doesn't know what he or she is
> talking about, and/or is a snake oil salesperson.  :-)
>
> Regards,
>
> 						- Ted

Dear Ted,
true, the dangers and challenges are high. The solution I finally
found took me unfortunately a long time to find it, and I know of
no other open-source solution to achieve what I described,
because of the unfortunate 'root is king and user is nobody' mentality
and reality we have.
But as described, in some security environments the user needs
a truly private space on the system where nobody else has access to.

I'm just a concerned admin seeking a practical solution to
the challenging problem IMO we all face nowadays regarding
data security and integrity.

If you have any other or further ideas on how such a security goal
could be realized or improved upon under a stock Linux distribution,
let me know pls, I'm open for all suggestions.

I think the filesystem could indeed implement such a "user-only" directory,
because the FUSE-API wrapper showed me that it is indeed possible
to implement that idea. I would suggest to add this feature to ext4,
and that new feature could be a real game-changer (yes, I know another
bold statement) in IT security.

Thx
Uenal


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