BSM Service (Reference)

This chapter describes the important components of the BSM service, which are the auditing subsystem and the device allocation mechanism.

The auditing mechanism helps you detect potential security breaches by revealing suspicious or abnormal patterns of system usage. The auditing mechanism also provides a means to trace suspect actions back to a particular user, thus serving as a deterrent. If users know that their activities are likely to be audited, they might be less likely to attempt malicious activities.

The following is a list of the reference information in this chapter.

• Audit Commands

• Audit Service Files

• Audit Administration Profiles

• Audit Classes and Their Audit Flags

• Audit Policies

• Process Audit Characteristics

• Audit Trail

• Naming Conventions for Audit Files

• Audit Record Structure

• Audit Token Formats

• Device Allocation Reference

For an overview of auditing, see Chapter 20, BSM (Overview). For planning suggestions, see Chapter 21, Audit Planning. For procedures to configure auditing at your site, see Chapter 22, Managing the BSM Service (Tasks).

Audit Commands

This section provides information about the commands that are used with the auditing service.

The Audit Daemon

The following list summarizes what the audit daemon, auditd, does.

• auditd opens and closes audit log files in the directories that are specified in the audit_control file, in the order in which they are specified.

• auditd reads audit data from the kernel and writes the data to an audit log file.

• auditd executes the audit_warn script when the audit directories fill past limits that are specified in the audit_control file. The script, by default, sends warnings to the audit_warn mail alias and to the console.

• By default, when all audit directories are full, processes that generate audit records are suspended. In addition, the auditd command writes a message to the console and to the audit_warn mail alias. The audit policy can be reconfigured with the auditconfig command. At this point, only the system administrator fix the auditing mechanism. The administrator can log in to write audit files to tape, can delete audit files from the system, and can do other cleanup.

The auditd daemon can be started automatically when the machine is brought up to multiuser mode, or you can start it from the command line. When the audit daemon is started, it determines the amount of free space necessary for audit log files.

The daemon uses the list of audit directories in the audit_control file as possible locations for creating audit files. The audit daemon maintains a pointer into this list of directories, starting with the first directory. Every time the audit daemon needs to create an audit file, it puts the file into the first available directory in the list. The list starts at the audit daemon's current pointer. You can reset the pointer to the beginning of the list by running the audit -s command. The audit -n command instructs the daemon to switch to a new audit file. The new file is created in the same directory as the current file.

The audit Command

The audit command controls the actions of the audit daemon. The audit command can do the following tasks:

• Enable and disable auditing

• Reset the audit daemon

• Adjust the auditing preselection mask on the local machine

• Write audit records to a different audit log file

See the audit(1M) man page for a discussion of the available options.

The bsmrecord Command

The bsmrecord command displays the format of audit events that are defined in the /etc/security/audit_event file. The output includes the event's audit ID, audit class, audit flag, and the record's tokens in order. With no option, the bsmrecord output displays well in a terminal window. With the -h option, the output is suitable for viewing in a browser. See How to Display Audit Record Formats for examples of its use. For more information, see the bsmrecord(1M) man page.

The auditreduce Command

Use the auditreduce command to merge audit records from one or more input audit files. The command can also be used to perform a post selection of audit records. See the auditreduce(1M) man page. To merge the entire audit trail, run this command on the audit server. The audit server is the machine that mounts all the audit file systems for the installation.

The auditreduce command enables you to track all auditable actions on multiple machines from a single location. The command can read the logical combination of all audit files as a single audit trail. You must identically configure all machines at a site for auditing, and create servers and local directories for the audit log files. The auditreduce command ignores how the records were generated or where they are stored. Without options, the auditreduce command merges audit records from all the audit files in all of the subdirectories in the audit root directory. Typically, /etc/security/audit is the audit root directory. The auditreduce command sends the merge result to standard output. You can also place the result into a single, chronologically ordered output file. The file contains binary data.

The auditreduce command also can select particular types of records for analysis. The merging functions and selecting functions of the auditreduce command are logically independent. auditreduce captures data from the input files as the records are read, before the files are merged and then written to disk.

The praudit command makes the binary output of the auditreduce command readable.

By specifying options to the auditreduce command, you can also do the following:

• Request audit records that were generated by only certain audit flags

• Request audit records that were generated by one particular user

• Request audit records that were generated on specific dates

With no arguments, auditreduce checks the subdirectories within the /etc/security/audit directory, the default audit root directory. The command checks for a files directory in which the start-time.end-time.hostname files reside. The auditreduce command is very useful when audit data resides in separate directories. Figure 23-1 illustrates audit data in separate directories for different hosts. Figure 23-2) illustrates audit data in separate directories for different audit servers.

Figure 23-1 Audit Trail Storage Sorted by Host

Figure 23-2 Audit Trail Storage Sorted by Server

If the partition for /etc/security/audit is very small, you might not store audit data in the default directory. You can pass the auditreduce command another directory by using the -R option:

# auditreduce -R /var/audit-alt 

You can also specify a particular subdirectory by using the -S option:

# auditreduce -S /var/audit-alt/host1 

You can direct auditreduce to process only certain audit log files by specifying them as command arguments:

# auditreduce /var/audit/egret/files/2001*.2001*egret

For other options and additional examples, see the auditreduce(1M) man page.