[PATCH v3 0/7] User namespace mount updates

[Al Viro]

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...