Double free in OmniOS and SmartOS ipmgmtd allows local users to crash the daemon

A double free in the IP management daemon (ipmgmtd) of OmniOS and SmartOS allows a local user to crash the daemon. When authorizing a door request that modifies interface configuration, ipmgmt_handler() in usr/src/cmd/cmd-inet/lib/ipmgmtd/ipmgmt_door.c frees the caller's credential with ucred_free() immediately after reading the user ID, and frees it a second time on the error path if the authorization check fails. An unprivileged local user who does not hold the solaris.network.interface.config authorization can send such a request, for example IPMGMT_CMD_RESETIF, to the ipmgmtd door, causing ipmgmtd to abort; repeated requests place the svc:/network/ip-interface-management service into maintenance, preventing IP interface configuration. The early free was introduced in 2014 to support lx-branded zones (OmniOS commit 4c170900) and is not present in upstream illumos-gate. It affects OmniOS r151020 and later, and SmartOS, prior to the fix.