Copyright (c) 2003 Networks Associates Technology, Inc. All rights reserved. This software was developed for the FreeBSD Project by Chris Costello at Safeport Network Services and Network Associates Labs, the Security Research Division of Network Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the DARPA CHATS research program. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditi...
NAMEmac_portacl - network port access control policy
SYNOPSISTo compile the port access control policy into your kernel, place the following lines in your kernel configuration file:
options MAC options MAC_PORTACL
Alternately, to load the port access control policy module at boot time, place the following line in your kernel configuration file:
and in loader.conf5:
DESCRIPTIONThe sysctl Cm net.inet.tcp.syncookies policy allows administrators to administratively limit binding to local UDP and TCP ports via the sysctl(8) interface.
In order to enable the sysctl Cm net.inet.tcp.syncookies policy, MAC policy must be enforced on sockets (see mac(4)), and the port(s) protected by sysctl Cm net.inet.tcp.syncookies 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 sysctl Cm net.inet.tcp.syncookies 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 sysctl Cm net.inet.tcp.syncookies 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 sysctl Cm net.inet.tcp.syncookies 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.
Runtime ConfigurationThe 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.conf5.
- Enforce the sysctl Cm net.inet.tcp.syncookies policy. (Default: 1).
- The highest port number sysctl Cm net.inet.tcp.syncookies will enforce rules for. (Default: 1023).
The port access control list is specified in the following format:
- Describes the type of subject match to be performed. Either uid for user ID matching, or gid for group ID matching.
- The user or group ID (depending on idtype allowed to bind to the specified port. Bf -emphasis NOTE: User and group names are not valid; only the actual ID numbers may be used. Ef
- Describes which protocol this entry applies to. Either tcp or udp are supported.
- Describes which port this entry applies to. Bf -emphasis NOTE: MAC security policies may not override other security system policies by allowing accesses that they may deny, such as net.inet.ip.portrange.reservedlow net.inet.ip.portrange.reservedhigh Ef If the specified port falls within the range specified, the sysctl Cm net.inet.tcp.syncookies entry will not function (i.e., even the specified user/group may not be able to bind to the specified port).
- Allow superuser (i.e., root) to bind to all sysctl Cm net.inet.tcp.syncookies protected ports, even if the port access control list does not explicitly allow this. (Default: 1).
- Allow applications to use automatic binding to port 0. Applications use port 0 as a request for automatic port allocation when binding an IP address to a socket. This tunable will exempt port 0 allocation from rule checking. (Default: 1).