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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 pro‐
cess (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
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 for‐
mat:
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 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
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. 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)
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.