mac_portacl — network port access control policy

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.

Debian                                          December 9, 2004                                  MAC_PORTACL(4)

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.reservedhighsysctl(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_highsysctl(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.

RuntimeConfiguration
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:Userandgroupnamesarenotvalid;onlytheactualIDnumbersmaybeused.protocol Describes which protocol this entry applies to. Either tcp or udp are supported.

port Describes which port this entry applies to. NOTE:MACsecuritypoliciesmaynotoverrideothersecuritysystempoliciesbyallowingaccessesthattheymaydeny,suchasnet.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).

History

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

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:

             optionsMACoptionsMAC_PORTACL

       Alternately, to load the port access control policy module at boot time, place the following line in your
       kernel configuration file:

             optionsMAC

       and in loader.conf(5):

             mac_portacl_load="YES"