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AUSEARCH-EXPRESSION(5) Linux Audit AUSEARCH-EXPRESSION(5)
NAME
ausearch-expression - audit search expression format
OVERVIEW
This man page describes the format of "ausearch expressions". Parsing and evaluation of
these expressions is provided by libauparse and is common to applications that use this
library.
LEXICAL STRUCTURE
White space (ASCII space, tab and new-line characters) between tokens is ignored. The
following tokens are recognized:
Punctuation
( ) \
Logical operators
! && ||
Comparison operators
< <= == > >= !== i= i!= r= r!=
Unquoted strings
Any non-empty sequence of ASCII letters, digits, and the _ symbol.
Quoted strings
A sequence of characters surrounded by the " quotes. The \ character starts an
escape sequence. The only defined escape sequences are \\ and \". The semantics
of other escape sequences is undefined.
Regexps
A sequence of characters surrounded by the / characters. The \ character starts an
escape sequence. The only defined escape sequences are \\ and \/. The semantics
of other escape sequences is undefined.
Anywhere an unquoted string is valid, a quoted string is valid as well, and vice versa.
In particular, field names may be specified using quoted strings, and field values may be
specified using unquoted strings.
EXPRESSION SYNTAX
The primary expression has one of the following forms:
field comparison-operator value
\regexp string-or-regexp
field is either a string, which specifies the first field with that name within the cur-
rent audit record, or the \ escape character followed by a string, which specifies a vir-
tual field with the specified name (virtual fields are defined in a later section).
field is a string. operator specifies the comparison to perform
r= r!= Get the "raw" string of field, and compare it to value. For fields in audit
records, the "raw" string is the exact string stored in the audit record (with all
escaping and unprintable character encoding left alone); applications can read the
"raw" string using auparse_get_field_str(3). Each virtual field may define a "raw"
string. If field is not present or does not define a "raw" string, the result of
the comparison is false (regardless of the operator).
i= i!= Get the "interpreted" string of field, and compare it to value. For fields in
audit records, the "interpreted" string is an "user-readable" interpretation of the
field value; applications can read the "interpreted" string using auparse_inter-
pret_field(3). Each virtual field may define an "interpreted" string. If field is
not present or does not define an "interpreted" string, the result of the compari-
son is false (regardless of the operator).
< <= == > >= !==
Evaluate the "value" of field, and compare it to value. A "value" may be defined
for any field or virtual field, but no "value" is currently defined for any audit
record field. The rules of parsing value for comparing it with the "value" of
field are specific for each field. If field is not present, the result of the com-
parison is false (regardless of the operator). If field does not define a "value",
an error is reported when parsing the expression.
In the special case of \regexp regexp-or-string, the current audit record is taken as a
string (without interpreting field values), and matched against regexp-or-string. regexp-
or-string is an extended regular expression, using a string or regexp token (in other
words, delimited by " or /).
If E1 and E2 are valid expressions, then ! E1, E1 && E2, and E1 || E2 are valid expres-
sions as well, with the usual C semantics and evaluation priorities. Note that ! field
op value is interpreted as !(field op value), not as (!field) op value.
VIRTUAL FIELDS
The following virtual fields are defined:
\timestamp
The value is the timestamp of the current event. value must be formatted as:
ts:seconds.milli
where seconds and milli are decimal numbers specifying the seconds and milliseconds
part of the timestamp, respectively.
\timestamp_ex
This is similar to \timestamp but also includes the event's serial number. value
must be formatted as:
ts:seconds.milli:serial
where serial is a decimal number specifying the event's serial number.
\record_type
The value is the type of the current record. value is either the record type name,
or a decimal number specifying the type.
SEMANTICS
The expression as a whole applies to a single record. The expression is true for a speci-
fied event if it is true for any record associated with the event.
EXAMPLES
As a demonstration of the semantics of handling missing fields, the following expression
is true if field is present:
(field r= "") || (field r!= "")
and the same expression surrounded by !( and ) is true if field is not present.
FUTURE DIRECTIONS
New escape sequences for quoted strings may be defined.
For currently defined virtual fields that do not define a "raw" or "interpreted" string,
the definition may be added. Therefore, don't rely on the fact that comparing the "raw"
or "interpreted" string of the field with any value is false.
New formats of value constants for the \timestamp virtual field may be added.
AUTHOR
Miloslav Trmac
Red Hat Feb 2008 AUSEARCH-EXPRESSION(5)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
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