illumos-gate: Missing authorization in illumos zonestatd allows local users to disrupt zonestat and enumerate running zones

A missing authorization check in the illumos zones statistics daemon (zonestatd) allows a local user in any zone to disrupt zonestat in other zones and to determine which zones are running. The zonestatd door server procedure, zsd_server() in usr/src/cmd/zonestat/zonestatd/zonestatd.c, handles the ZSD_CMD_NEW_ZONE command, which is intended to be sent by zoneadmd, without checking the caller's credentials. Because the zonestatd door is accessible to all users in every zone, an unprivileged user can send this command with an arbitrary zone ID, causing zonestatd to re-create its door file in that zone, so that new zonestat requests in that zone can fail while the file is replaced. The time taken to handle the command also reveals whether a given zone ID belongs to a running zone. The flaw has existed since 2010 (illumos-gate commit efd4c9b6), and affects any illumos distribution prior to illumos-gate commit 865b58d2.