simplified security.nscapability xattr

This can only be set by root in his own namespace, and will
only be respected by namespaces with that same root kuid
mapped as root, or namespaces descended from it.

This allows a simple setxattr to work, allows tar/untar to
work, and allows us to tar in one namespace and untar in
another while preserving the capability, without risking
leaking privilege into a parent namespace.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
4 files changed