MFC r358992:

MFC r358992:

  kern_jail: missing \0 termination check on osrelease parameter

  If a user spplies a non-\0 terminated osrelease parameter reading it back
  may disclose kernel memory.
  This is a problem in case of nested jails (children.max > 0, which is not
  the default).  Otherwise root outside the jail has access to kernel memory
  by other means and root inside a jail cannot create a child jail.

  Add the proper \0 check at the end of a supplied osrelease parameter and
  make sure any copies of the field will be \0-terminated.

  Submitted by:	Hans Christian Woithe (chwoithe yahoo.com)