linux-kernel - Re: [PATCH 0/7] Initial support for user namespace owned mounts

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Date:	Wed, 15 Jul 2015 18:08:56 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Casey Schaufler <casey@...aufler-ca.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Seth Forshee <seth.forshee@...onical.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	LSM List <linux-security-module@...r.kernel.org>,
	SELinux-NSA <selinux@...ho.nsa.gov>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] Initial support for user namespace owned mounts

On Wed, Jul 15, 2015 at 3:39 PM, Casey Schaufler <casey@...aufler-ca.com> wrote:
> On 7/15/2015 2:06 PM, Eric W. Biederman wrote:
>> Casey Schaufler <casey@...aufler-ca.com> writes:
>
>> The first step needs to be not trusting those labels and treating such
>> filesystems as filesystems without label support.  I hope that is Seth
>> has implemented.
>
> A filesystem with Smack labels gets mounted in a namespace. The labels
> are ignored. Instead, the filesystem defaults (potentially specified as
> mount options smackfsdef="something", but usually the floor label ("_"))
> are used, giving the user the ability to read everything and (usually)
> change nothing. This is both dangerous (unintended read access to files)
> and pointless (can't make changes).

I don't get it.

If I mount an unprivileged filesystem, then either the contents were
put there *by me*, in which case letting me access them are fine, or
(with Seth's patches and then some) I control the backing store, in
which case I can do whatever I want regardless of what LSM thinks.

So I don't see the problem.  Why would Smack or any other LSM care at
all, unless it wants to prevent me from mounting the fs in the first
place?

--Andy
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