[PATCH v3 0/7] User namespace mount updates

[Al Viro]

On Tue, Nov 17, 2015 at 10:39:03AM -0600, Seth Forshee wrote:
> Hi Eric,
> 
> Here's another update to my patches for user namespace mounts, based on
> your for-testing branch. These patches add safeguards necessary to allow
> unprivileged mounts and update SELinux and Smack to safely handle
> device-backed mounts from unprivileged users.
> 
> The v2 posting received very little in the way of feedback, so changes
> are minimal. I've made a trivial style change to the Smack changes at
> Casey's request, and I've added Stephen's ack for the SELinux changes.

Would you mind explaining which filesystem types do you plan to allow?
SELinux and the rest of Linux S&M bunch do fuck-all for attacks via
handcrafted fs image fed to the code in fs driver that does not expect
a given kind of inconsistencies.

As it is, validation of on-disk metadata is not particularly strong;
what's more, protection against concurrent malicious *changes* of
fs image (via direct writes by root) is simply inexistent.

So what is that about?