man/man4/dtrace_audit.4

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.\" Copyright (c) 2019 Robert N. M. Watson
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.\" 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.
.\"
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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.