The man page for
jail says that
allow.sysvipc enables "System V primitives [to] share a single namespace across the host and jail environments..." thus "... processes within a jail would be able to communicate with ... processes outside of the jail, and in other jails."
What are the practical security implications of this? The most extreme interpretation would imply that when using this option, there is little effective security within the entire jail infrastucture. (If processes can interfere with and communicate with other processes on the host and other jails then why bother with the jail at all?)