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mac - Mandatory Access Control


MAC Labels
MAC Support for UFS2 File Systems
Policy Enforcement
Setting MAC Labels
Programming With MAC
Runtime Configuration
See Also


.Cd "options MAC"



The Mandatory Access Control, or MAC, framework allows administrators to finely control system security by providing for a loadable security policy architecture. It is important to note that due to its nature, MAC security policies may only restrict access relative to one another and the base system policy; they cannot override traditional Unix security provisions such as file permissions and superuser checks.

Currently, the following MAC policy modules are shipped with
.Fx :

Name Description Labeling "Load time"
mac_biba 4 "Biba integrity policy" yes boot only
mac_bsdextended 4 "File system firewall" no any time
mac_ifoff 4 "Interface silencing" no any time
mac_lomac 4 "Low-Watermark MAC policy" yes boot only
mac_mls 4 "Confidentiality policy" yes boot only
mac_none 4 "Sample no-op policy" no any time
mac_partition 4 "Process partition policy" yes any time
mac_portacl 4 "Port bind(2) access control" no any time
mac_seeotheruids 4 "See-other-UIDs policy" no any time
mac_test 4 "MAC testing policy" no any time

MAC Labels

Each system subject (processes, sockets, etc.) and each system object (file system objects, sockets, etc.) can carry with it a MAC label. MAC labels contain data in an arbitrary format taken into consideration in making access control decisions for a given operation. Most MAC labels on system subjects and objects can be modified directly or indirectly by the system administrator. The format for a given policy’s label may vary depending on the type of object or subject being labeled. More information on the format for MAC labels can be found in the maclabel(7) man page.

MAC Support for UFS2 File Systems

By default, file system enforcement of labeled MAC policies relies on a single file system label (see "MAC Labels") in order to make access control decisions for all the files in a particular file system. With some policies, this configuration may not allow administrators to take full advantage of features. In order to enable support for labeling files on an individual basis for a particular file system, the "multilabel" flag must be enabled on the file system. To set the "multilabel" flag, drop to single-user mode and unmount the file system, then execute the following command:

"tunefs -l enable" filesystem

where filesystem is either the mount point (in fstab(5)) or the special file (in /dev) corresponding to the file system on which to enable multilabel support.

Policy Enforcement

MAC can be configured to enforce only specific portions of policies (see "Runtime Configuration"). Policy enforcement is divided into the following areas of the system:
"File System" File system mounts, modifying directories, modifying files, etc.
KLD Loading, unloading, and retrieving statistics on loaded kernel modules
Network Network interfaces, bpf(4), packet delivery and transmission, interface configuration ( ioctl 2, ifconfig(8))
Pipes Creation of and operation on pipe(2) objects
Processes Debugging (e.g. ktrace(2)), process visibility (ps(1)), process execution (execve(2)), signalling (kill(2))
Sockets Creation of and operation on socket(2) objects
System Kernel environment (kenv(1)), system accounting (acct(2)), reboot(2), settimeofday(2), swapon(2), sysctl(3), nfsd 8 -related operations
VM mmap 2 -ed files

Setting MAC Labels

From the command line, each type of system object has its own means for setting and modifying its MAC policy label.
"Subject/Object" "Utility"
"File system object" setfmac 8, setfsmac(8)
"Network interface" ifconfig(8)
"TTY (by login class)" login.conf(5)
"User (by login class)" login.conf(5)

Additionally, the su(1) and setpmac(8) utilities can be used to run a command with a different process label than the shell’s current label.

Programming With MAC

MAC security enforcement itself is transparent to application programs, with the exception that some programs may need to be aware of additional errno(2) returns from various system calls.

The interface for retrieving, handling, and setting policy labels is documented in the mac(3) man page.

Runtime Configuration

The following sysctl(8) MIBs are available for fine-tuning the enforcement of MAC policies. Unless specifically noted, all MIBs default to 1 (that is, all areas are enforced by default):
security.mac.enforce_fs Enforce MAC policies for file system accesses.
security.mac.enforce_kld Enforce MAC policies on kld(4).
security.mac.enforce_network Enforce MAC policies on network interfaces.
security.mac.enforce_pipe Enforce MAC policies on pipes.
security.mac.enforce_process Enforce MAC policies between system processes (e.g. ps(1), ktrace(2)).
security.mac.enforce_socket Enforce MAC policies on sockets.
security.mac.enforce_system Enforce MAC policies on system-related items (e.g. kenv(1), acct(2), reboot(2)).
security.mac.enforce_vm Enforce MAC policies on mmap(2) and mprotect(2).


mac(3), mac_biba(4), mac_bsdextended(4), mac_ifoff(4), mac_lomac(4), mac_mls(4), mac_none(4), mac_partition(4), mac_portacl(4), mac_seeotheruids(4), mac_test(4), login.conf(5), maclabel(7), getfmac(8), getpmac(8), setfmac(8), setpmac(8), mac(9)
.Rs "Mandatory Access Control"





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