[PATCH v4 4/7] fs: Limit file caps to the user namespace of the super block

[Seth Forshee]

On Thu, Sep 24, 2015 at 04:59:35PM -0500, Eric W. Biederman wrote:
> Seth Forshee <seth.forshee at canonical.com> writes:
> 
> > Capability sets attached to files must be ignored except in the
> > user namespaces where the mounter is privileged, i.e. s_user_ns
> > and its descendants. Otherwise a vector exists for gaining
> > privileges in namespaces where a user is not already privileged.
> >
> > Add a new helper function, in_user_ns(), to test whether a user
> > namespace is the same as or a descendant of another namespace.
> > Use this helper to determine whether a file's capability set
> > should be applied to the caps constructed during exec.
> 
> No issues with this but given that we always pass current_user_ns()
> we may want to simplify the users of in_user_ns by renaming it
> current_in_user_ns() and hard codeing current_user_ns().

Sure, if that's what you prefer then I'll change it.

Seth