Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
MAC_PORTACL(4)         FreeBSD Kernel Interfaces Manual         MAC_PORTACL(4)

     mac_portacl -- network port access control policy

     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):


     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 enforce-
     ment of this MAC policy.  All sysctl(8) variables, except
     security.mac.portacl.rules, can also be set as loader(8) tunables in

             Enforce the mac_portacl policy.  (Default: 1).

             The highest port number mac_portacl will enforce rules for.
             (Default: 1023).

             The port access control list is specified in the following for-


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

             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 sys-
                       tem 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

             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).

             Allow applications to use automatic binding to port 0.  Applica-
             tions 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).

     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)

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

     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.

FreeBSD 6.2                    December 9, 2004                    FreeBSD 6.2


Want to link to this manual page? Use this URL:

home | help