In the embedded world there are often situations
  where libraries are updated from a variety of sources,
  for a variety of reasons, and with any number of
  security characteristics. These differences
  might include privilege required for a given library
  provided interface to function properly, as occurs
  from time to time in graphics libraries. There are
  also cases where it is important to limit use of
  libraries based on the provider of the library and
  the security aware application may make choices
  based on that criteria.

  These issues are addressed by providing an additional
  Smack label that may optionally be assigned to an object,
  the SMACK64MMAP attribute. An mmap operation is allowed
  if there is no such attribute.

  If there is a SMACK64MMAP attribute the mmap is permitted
  only if a subject with that label has all of the access
  permitted a subject with the current task label.

  Security aware applications may from time to time
  wish to reduce their "privilege" to avoid accidental use
  of privilege. One case where this arises is the
  environment in which multiple sources provide libraries
  to perform the same functions. An application may know
  that it should eschew services made available from a
  particular vendor, or of a particular version.

  In support of this a secondary list of Smack rules has
  been added that is local to the task. This list is
  consulted only in the case where the global list has
  approved access. It can only further restrict access.
  Unlike the global last, if no entry is found on the
  local list access is granted. An application can add
  entries to its own list by writing to /smack/load-self.

  The changes appear large as they involve refactoring
  the list handling to accomodate there being more
  than one rule list.
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>