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

From: Al Viro <viro@ZenIV.linux.org.uk>
To: Austin S Hemmelgarn <ahferroin7@gmail.com>
Cc: Seth Forshee <seth.forshee@canonical.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	linux-bcache@vger.kernel.org, dm-devel@redhat.com,
	linux-raid@vger.kernel.org, linux-mtd@lists.infradead.org,
	linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov,
	Serge Hallyn <serge.hallyn@canonical.com>,
	Andy Lutomirski <luto@amacapital.net>,
	linux-kernel@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH v3 0/7] User namespace mount updates
Date: Tue, 17 Nov 2015 21:05:42 +0000	[thread overview]
Message-ID: <20151117210542.GY22011@ZenIV.linux.org.uk> (raw)
In-Reply-To: <564B9074.5030305@gmail.com>

On Tue, Nov 17, 2015 at 03:39:16PM -0500, Austin S Hemmelgarn wrote:

> >This is absolutely insane, no matter how much LSM snake oil you slatter on
> >the whole thing.  All of a sudden you are exposing a huge attack surface
> >in the place where it would hurt most and as the consolation we are offered
> >basically "Ted is willing to fix holes when they are found".
> For the context of static image attacks, anything that's found
> _needs_ to be fixed regardless, and unless you can find some way to
> actually prevent attacks on mounted filesystems that doesn't involve
> a complete re-write of the filesystem drivers, then there's not much
> we can do about it.  Yes, unprivileged mounts expose an attack
> surface, but so does userspace access to the network stack, and so
> do a lot of other features that are considered essential in a modern
> general purpose operating system.

"X is exposes an attack surface.  Y exposes a diferent attack surface.
Y is considered important.  Therefore X is important enough to implement it"

Right...