.\"-
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.\" Copyright (c) 2019 Robert N. M. Watson
.\"
.\" This software was developed by BAE Systems, the University of Cambridge
.\" Computer Laboratory, and Memorial University under DARPA/AFRL contract
.\" FA8650-15-C-7558 ("CADETS"), as part of the DARPA Transparent Computing
.\" (TC) research program.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
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.Dd April 28, 2019
.Dt DTRACE_AUDIT 4
.Os
.Sh NAME
.Nm dtrace_audit
.Nd A DTrace provider for tracing
.Xr audit 4
events
.Sh SYNOPSIS
.Fn audit:event:aue_*:commit "char *eventname" "struct audit_record *ar"
.Fn audit:event:aue_*:bsm "char *eventname" "struct audit_record *ar" "const void *" "size_t"
.Pp
To compile this module into the kernel, place the following in your kernel
configuration file:
.Bd -literal -offset indent
.Cd "options DTAUDIT"
.Ed
.Pp
Alternatively, to load the module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
dtaudit_load="YES"
.Ed
.Sh DESCRIPTION
The DTrace
.Nm dtaudit
provider allows users to trace events in the kernel security auditing
subsystem,
.Xr audit 4 .
.Xr audit 4
provides detailed logging of a configurable set of security-relevant system
calls, including key arguments (such as file paths) and return values that are
copied race-free as the system call proceeds.
The
.Nm dtaudit
provider allows DTrace scripts to selectively enable in-kernel audit-record
capture for system calls, and then access those records in either the
in-kernel format or BSM format (\c
.Xr audit.log 5 )
when the system call completes.
While the in-kernel audit record data structure is subject to change as the
kernel changes over time, it is a much more friendly interface for use in D
scripts than either those available via the DTrace system-call provider or the
BSM trail itself.
.Ss Configuration
The
.Nm dtaudit
provider relies on
.Xr audit 4
being compiled into the kernel.
.Nm dtaudit
probes become available only once there is an event-to-name mapping installed
in the kernel, normally done by
.Xr auditd 8
during the boot process, if audit is enabled in
.Xr rc.conf 5 :
.Bd -literal -offset indent
auditd_enable="YES"
.Ed
.Pp
If
.Nm dtaudit
probes are required earlier in boot -- for example, in single-user mode -- or
without enabling
.Xr audit 4 ,
they can be preloaded in the boot loader by adding this line to
.Xr loader.conf 5 .
.Bd -literal -offset indent
audit_event_load="YES"
.Ed
.Ss Probes
The
.Fn audit:event:aue_*:commit
probes fire synchronously during system-call return, giving access to two
arguments: a
.Vt char *
audit event name, and
the
.Vt struct audit_record *
in-kernel audit record.
Because the probe fires in system-call return, the user thread has not yet
regained control, and additional information from the thread and process
remains available for capture by the script.
.Pp
The
.Fn audit:event:aue_*:bsm
probes fire asynchronously from system-call return, following BSM conversion
and just prior to being written to disk, giving access to four arguments: a
.Vt char *
audit event name, the
.Vt struct audit_record *
in-kernel audit record, a
.Vt const void *
pointer to the converted BSM record, and a
.Vt size_t
for the length of the BSM record.
.Sh IMPLEMENTATION NOTES
When a set of
.Nm dtaudit
probes are registered, corresponding in-kernel audit records will be captured
and their probes will fire regardless of whether the
.Xr audit 4
subsystem itself would have captured the record for the purposes of writing it
to the audit trail, or for delivery to a
.Xr auditpipe 4 .
In-kernel audit records allocated only because of enabled
.Xr dtaudit 4
probes will not be unnecessarily written to the audit trail or enabled pipes.
.Sh SEE ALSO
.Xr dtrace 1 ,
.Xr audit 4 ,
.Xr audit.log 5 ,
.Xr loader.conf 5 ,
.Xr rc.conf 5 ,
.Xr auditd 8
.Sh HISTORY
The
.Nm dtaudit
provider first appeared in
.Fx 12.0 .
.Sh AUTHORS
This software and this manual page were developed by BAE Systems, the
University of Cambridge Computer Laboratory, and Memorial University under
DARPA/AFRL contract
.Pq FA8650-15-C-7558
.Pq Do CADETS Dc ,
as part of the DARPA Transparent Computing (TC) research program.
The
.Nm dtaudit
provider and this manual page were written by
.An Robert Watson Aq Mt rwatson@FreeBSD.org .
.Sh BUGS
Because
.Xr audit 4
maintains its primary event-to-name mapping database in userspace, that
database must be loaded into the kernel before
.Nm dtaudit
probes become available.
.Pp
.Nm dtaudit
is only able to provide access to system-call audit events, not the full
scope of userspace events, such as those relating to login, password change,
and so on.