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

[Seth Forshee <seth.forshee@canonical.com>]

On Tue, Nov 17, 2015 at 05:05:56PM +0000, Al Viro wrote:
> 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?

The first target is fuse, which won't be vulnerable to those attacks.

Shortly after that I plan to follow with support for ext4. I've been
fuzzing ext4 for a while now and it has held up well, and I'm currently
working on hand-crafted attacks. Ted has commented privately (to others,
not to me personally) that he will fix bugs for such attacks, though I
haven't seen any public comments to that effect.

Seth