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From: Andy Lutomirski <luto@amacapital.net>
Date: Wed, 15 Jul 2015 18:08:56 -0700
Message-ID: <CALCETrVCNQPVr-hg_pqd2J_LeWtRJs3LRsbbE+fifo4sat+FQQ@mail.gmail.com>
Subject: Re: [PATCH 0/7] Initial support for user namespace owned mounts
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
        Seth Forshee <seth.forshee@canonical.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        LSM List <linux-security-module@vger.kernel.org>,
        SELinux-NSA <selinux@tycho.nsa.gov>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Wed, Jul 15, 2015 at 3:39 PM, Casey Schaufler <casey@schaufler-ca.com> wrote:
> On 7/15/2015 2:06 PM, Eric W. Biederman wrote:
>> Casey Schaufler <casey@schaufler-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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