MAC_PORTACL(4)

NAME
mac_portacl - network port access control policy

SYNOPSIS
To 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:

options MAC

and in loader.conf(5):

    mac_portacl_load="YES"

DESCRIPTION
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.

  Runtime Configuration
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).

security.mac.portacl.enabled
    Enforce the mac_portacl policy. (Default: 1).

security.mac.portacl.port_high
    The highest port number mac_portacl will enforce rules for. (Default: 1023).

security.mac.portacl.rules
    The port access control list is specified in the following format:

        idtype:id:protocol:port[,idtype:id:protocol:port,...]

    idtype
        Describes the type of subject match to be performed. Either uid for user ID matching, or gid for group ID matching.

    id  The user or group ID (depending on idtype) allowed to bind to the specified port. NOTE: User and group names are not valid; only the actual ID numbers may be used.

    protocol
        Describes which protocol this entry applies to. Either tcp or udp are supported.

    port
        Describes which port this entry applies to. 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. If the specified port falls within the range specified, the mac_portacl entry will not function (i.e., even the specified user/group may not be able to bind to the specified port).

security.mac.portacl.suser_exempt
    Allow superuser (i.e., root) to bind to all mac_portacl protected ports, even if the port access control list does not explicitly allow this. (Default: 1).

security.mac.portacl.autoport_exempt
    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).

SEE ALSO
mac(3), ip(4), mac_biba(4), mac_bsdextended(4), mac_ifoff(4), mac_mls(4), mac_none(4), mac_partition(4), mac_seeotheruids(4), mac_test(4), mac(9)

HISTORY
MAC first appeared in FreeBSD 5.0 and mac_portacl first appeared in FreeBSD 5.1.

AUTHORS
This software was contributed to the FreeBSD Project by NAI 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.