The mac_portacl policy allows administrators to administratively limit binding to local UDP and TCP ports via the sysctl(8) interface.
In order to enable the mac_portacl policy, MAC policy must be enforced on sockets (see mac(4)), and the port(s) protected by mac_portacl must not be included in the range specified by the net.inet.ip.portrange.reservedlow and net.inet.ip.portrange.reservedhigh sysctl(8) MIBs.
The mac_portacl policy only affects ports explicitly bound by a user process (either for a listen/outgoing TCP socket, or a send/receive UDP socket). This policy will not limit ports bound implicitly for outgoing connections where the process has not explicitly selected a port: these are automatically selected by the IP stack.
When mac_portacl is enabled, it will control binding access to ports up to the port number set in the security.mac.portacl.port_high sysctl(8) variable. By default, all attempts to bind to mac_portacl controlled ports will fail if not explicitly allowed by the port access control list, though binding by the superuser will be allowed, if the sysctl(8) variable security.mac.portacl.suser_exempt is set to a non-zero value.
The following sysctl(8) MIBs are available for fine-tuning the enforcement of this MAC policy. All sysctl(8) variables, except security.mac.portacl.rules, can also be set as loader(8) tunables in loader.conf(5).