Bring in fix from FreeBSD/cperciva:

Bring in fix from FreeBSD/cperciva:
  Log:
  If we are going to
  1. Copy a NULL-terminated string into a fixed-length buffer, and
  2. copyout that buffer to userland,
  we really ought to
  0. Zero the entire buffer
  first.

  Security: FreeBSD-SA-05:08.kmem

Thanks to Colin Percival for notifying us!