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The audit facility provides an audit pipe facility for applications requiring direct access to live BSM audit data for the purposes of real-time monitoring. Audit pipes are available via a clonable special device, /dev/auditpipe, subject to the permissions on the device node, and provide a "tee" of the audit event stream. As the device is clonable, more than one instance of the device may be opened at a time; each device instance will provide independent access to all records.
The audit pipe device provides discrete BSM audit records; if the read buffer passed by the application is too small to hold the next record in the sequence, it will be dropped. Unlike audit data written to the audit trail, the reliability of record delivery is not guaranteed. In particular, when an audit pipe queue fills, records will be dropped. Audit pipe devices are blocking by default, but support non-blocking I/O, asynchronous I/O using SIGIO, and polled operation via select(2) and poll(2).
Applications may choose to track the global audit trail, or configure local preselection parameters independent of the global audit trail parameters.
|AUDITPIPE_GET_QLEN||Query the current number of records available for reading on the pipe.|
|AUDITPIPE_GET_QLIMIT||Retrieve the current maximum number of records that may be queued for reading on the pipe.|
|AUDITPIPE_SET_QLIMIT||Set the current maximum number of records that may be queued for reading on the pipe. The new limit must fall between the queue limit minimum and queue limit maximum queryable using the following two ioctls.|
|AUDITPIPE_GET_QLIMIT_MIN||Query the lowest possible maximum number of records that may be queued for reading on the pipe.|
|AUDITPIPE_GET_QLIMIT_MAX||Query the highest possible maximum number of records that may be queued for reading on the pipe.|
|AUDITPIPE_FLUSH||Flush all outstanding records on the audit pipe; useful after setting initial preselection properties to delete records queued during the configuration process which may not match the interests of the user process.|
|Query the maximum size of an audit record, which is a useful minimum size for a user space buffer intended to hold audit records read from the audit pipe.|
The following ioctls configure the preselection mode on an audit pipe:
|Return the current preselect mode on the audit pipe. The ioctl argument should be of type int.|
|Set the current preselection mode on the audit pipe. The ioctl argument should be of type int.|
Possible preselection mode values are:
|Use the global audit trail preselection parameters to select records for the audit pipe.|
|Use local audit pipe preselection; this model is similar to the global audit trail configuration model, consisting of global flags and naflags parameters, as well as a set of per-auid masks. These parameters are configured using further ioctls.|
After changing the audit pipe preselection mode, records selected under earlier preselection configuration may still be in the audit pipe queue. The application may flush the current record queue after changing the configuration to remove possibly undesired records.
|AUDITPIPE_GET_PRESELECT_FLAGS||Retrieve the current default preselection flags for attributable events on the pipe. These flags correspond to the flags field in audit_control(5). The ioctl argument should be of type u_int.|
|AUDITPIPE_SET_PRESELECT_FLAGS||Set the current default preselection flags for attributable events on the pipe. These flags correspond to the flags field in audit_control(5). The ioctl argument should be of type u_int.|
|Retrieve the current default preselection flags for non-attributable events on the pipe. These flags correspond to the naflags field in audit_control(5). The ioctl argument should be of type u_int.|
|Set the current default preselection flags for non-attributable events on the pipe. These flags correspond to the naflags field in audit_control(5). The ioctl argument should be of type u_int.|
|AUDITPIPE_GET_PRESELECT_AUID||Query the current preselection masks for a specific auid on the pipe. The ioctl argument should be of type struct auditpipe_ioctl_preselect. The auid to query is specified via the ap_auid field of type au_id_t; the mask will be returned via ap_mask of type au_mask_t.|
|AUDITPIPE_SET_PRESELECT_AUID||Set the current preselection masks for a specific auid on the pipe. Arguments are identical to AUDITPIPE_GET_PRESELECT_AUID, except that the caller should properly initialize the ap_mask field to hold the desired preselection mask.|
|Delete the current preselection mask for a specific auid on the pipe. Once called, events associated with the specified auid will use the default flags mask. The ioctl argument should be of type au_id_t.|
|AUDITPIPE_FLUSH_PRESELECT_AUID||Delete all auid specific preselection specifications.|
Support for kernel audit first appeared in FreeBSD 6.2 .
The Basic Security Module (BSM) interface to audit records and audit event stream format were defined by Sun Microsystems.
The configurable preselection mechanism mirrors the selection model present for the global audit trail. It might be desirable to provided a more flexible selection model.
The per-pipe audit event queue is fifo, with drops occurring if either the user thread provides in sufficient for the record on the queue head, or on enqueue if there is insufficient room. It might be desirable to support partial reads of records, which would be more compatible with buffered I/O as implemented in system libraries, and to allow applications to select which records are dropped, possibly in the style of preselection.
|AUDITPIPE (4)||May 5, 2006|
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|“||A computer would deserve to be called intelligent if it could deceive a human into believing that it was human.||”|
|— Alan Turing|