This filter was introduced in MariaDB MaxScale 2.1.
With the masking filter it is possible to obfuscate the returned value of a particular column.
For instance, suppose there is a table person that, among other columns, contains the column ssn where the social security number of a person is stored.
With the masking filter it is possible to specify that when the ssn field is queried, a masked value is returned unless the user making the query is a specific one. That is, when making the query
> SELECT name, ssn FROM person;
instead of getting the real result, as in
+-------+-------------+
+ name | ssn |
+-------+-------------+
| Alice | 721-07-4426 |
| Bob | 435-22-3267 |
...
the ssn would be masked, as in
+-------+-------------+
+ name | ssn |
+-------+-------------+
| Alice | XXX-XX-XXXX |
| Bob | XXX-XX-XXXX |
...
From MaxScale 2.3 onwards, the masking filter will reject statements that use functions in conjunction with columns that should be masked. Allowing function usage provides a way for circumventing the masking, unless a firewall filter is separately configured and installed.
Please see the configuration parameter prevent_function_usage for how to change the default behaviour.
The masking filter can only be used for masking columns of the following
types: BINARY, VARBINARY, CHAR, VARCHAR, BLOB, TINYBLOB,
MEDIUMBLOB, LONGBLOB, TEXT, TINYTEXT, MEDIUMTEXT, LONGTEXT,
ENUM and SET. If the type of the column is something else, then no
masking will be performed.
Currently, the masking filter can only work on packets whose payload is less
than 16MB. If the masking filter encounters a packet whose payload is exactly
that, thus indicating a situation where the payload is delivered in multiple
packets, the value of the parameter large_payloads specifies how the masking
filter should handle the situation.
The masking filter is taken into use with the following kind of configuration setup.
[Mask-SSN]
type=filter
module=masking
rules=...
[SomeService]
type=service
...
filters=Mask-SSN
The masking filter has one mandatory parameter - rules.
Specifies the path of the file where the masking rules are stored. A relative path is interpreted relative to the module configuration directory of MariaDB MaxScale. The default module configuration directory is /etc/maxscale.modules.d.
rules=/path/to/rules-file
With this optional parameter the masking filter can be instructed to log a warning if a masking rule matches a column that is not of one of the allowed types.
The values that can be used are never and always, with never being
the default.
warn_type_mismatch=always
This optional parameter specifies how the masking filter should treat
payloads larger than 16MB, that is, payloads that are delivered in
multiple MySQL protocol packets.
The values that can be used are ignore, which means that columns in
such payloads are not masked, and abort, which means that if such
payloads are encountered, the client connection is closed. The default
is abort.
Note that the aborting behaviour is applied only to resultsets that contain columns that should be masked. There are no limitations on resultsets that do not contain such columns.
large_payload=ignore
This optional parameter specifies how the masking filter should behave if a column that should be masked, is used in conjunction with some function. As the masking filter works only on the basis of the information in the returned result-set, if the name of a column is not present in the result-set, then the masking filter cannot mask a value. This means that the masking filter bascially can be bypassed with a query like:
SELECT CONCAT(masked_column) FROM tbl;
If the value of prevent_function_usage is true, then all
statements that contain functions referring to masked columns will
be rejected. As that means that also queries using potentially
harmless functions, such as LENGTH(masked_column), are rejected
as well, this feature can be turned off. In that case, the firewall
filter should be setup to allow or reject the use of certain functions.
prevent_function_usage=false
The default value is true.
The masking rules are expressed as a JSON object.
The top-level object is expected to contain a key rules whose
value is an array of rule objects.
{
"rules": [ ... ]
}
Each rule in the rules array is a JSON object, expected to
contain the keys replace, with, applies_to and
exempted. The two former ones are obligatory and the two
latter ones optional.
{
"rules": [
{
"replace": { ... },
"with": { ... },
"applies_to": [ ... ],
"exempted": [ ... ]
}
]
}
The value of this key is an object that specifies the column
whose values should be masked. The object must contain the key
column and may contain the keys table and database. The
value of these keys must be a string.
If only column is specified, then a column with that name
matches irrespective of the table and database. If table
is specified, then the column matches only if it is in a table
with the specified name, and if database is specified when
the column matches only if it is in a database with the
specified name.
{
"rules": [
{
"replace": {
"database": "db1",
"table": "person",
"column": "ssn"
},
"with": { ... },
"applies_to": [ ... ],
"exempted": [ ... ]
}
]
}
NOTE If a rule contains a table/database then if the resultset
does not contain table/database information, it will always be
considered a match if the column matches. For instance, given the
rule above, if there is a table person2, also containing an ssn
field, then a query like
SELECT ssn FROM person2;
will not return masked values, but a query like
SELECT ssn FROM person UNION SELECT ssn FROM person2;
will only return masked values, even if the ssn values from
person2 in principle should not be masked. The same effect is
observed even with a non-sensical query like
SELECT ssn FROM person2 UNION SELECT ssn FROM person2;
even if nothing from person2 should be masked. The reason is that
as the resultset contains no table information, the values must be
masked if the column name matches, as otherwise the masking could
easily be circumvented with a query like
SELECT ssn FROM person UNION SELECT ssn FROM person;
The optional key match makes partial replacement of the original
value possible: only the matched part would be replaced
with the fill character.
The match value must be a valid pcre2 regular expression.
"replace": {
"column": "ssn",
"match": "(123)"
},
"with": {
"fill": "X#"
}
The obfuscate rule allows the obfuscation of the value by passing it through an obfuscation algorithm. Current solution uses a nonreversible obfuscation approach.
However, note that although it is in principle impossible to obtain the original value from the obfuscated one, if the range of possible original values is limited, it is straightforward to figure out the possible original values by running all possible values through the obfuscation algortihm and then comparing the results.
The minimal configuration is:
"obfuscate": {
"column": "name"
}
Output example for Db field name = 'remo'
SELECT name from db1.tbl1;`
+------+
| name |
+------+
| $-~) |
+------+
The value of this key is an object that specifies what the value of the matched
column should be replaced with for the replace rule. Currently, the object
is expected to contain either the key value or the key fill.
The value of both must be a string with length greater than zero.
If both keys are specified, value takes precedence.
If fill is not specified, the default X is used as its value.
If value is specified, then its value is used to replace the actual value
verbatim and the length of the specified value must match the actual returned
value (from the server) exactly. If the lengths do not match, the value of
fill is used to mask the actual value.
When the value of fill (fill-value) is used for masking the returned value,
the fill-value is used as many times as necessary to match the length of the
return value. If required, only a part of the fill-value may be used in the end
of the mask value to get the lengths to match.
{
"rules": [
{
"replace": {
"column": "ssn"
},
"with": {
"value": "XXX-XX-XXXX"
},
"applies_to": [ ... ],
"exempted": [ ... ]
},
{
"replace": {
"column": "age"
},
"with": {
"fill": "*"
},
"applies_to": [ ... ],
"exempted": [ ... ]
},
{
"replace": {
"column": "creditcard"
},
"with": {
"value": "1234123412341234",
"fill": "0"
},
"applies_to": [ ... ],
"exempted": [ ... ]
},
]
}
With this optional key, whose value must be an array of strings,
it can be specified what users the rule is applied to. Each string
should be a MariaDB account string, that is, % is a wildcard.
{
"rules": [
{
"replace": { ... },
"with": { ... },
"applies_to": [ "'alice'@'host'", "'bob'@'%'" ],
"exempted": [ ... ]
}
]
}
If this key is not specified, then the masking is performed for all
users, except the ones exempted using the key exempted.
With this optional key, whose value must be an array of strings,
it can be specified what users the rule is not applied to. Each
string should be a MariaDB account string, that is, % is a wildcard.
{
"rules": [
{
"replace": { ... },
"with": { ... },
"applies_to": [ ... ],
"exempted": [ "'admin'" ]
}
]
}
Read Module Commands documentation for details about module commands.
The masking filter supports the following module commands.
Reload the rules from the rules file. The new rules are taken into use only if the loading succeeds without any errors.
MaxScale> call command masking reload MyMaskingFilter
MyMaskingFilter refers to a particular filter section in the
MariaDB MaxScale configuration file.
In the following we configure a masking filter MyMasking that should always log a
warning if a masking rule matches a column that is of a type that cannot be masked,
and that should abort the client connection if a resultset package is larger than
16MB. The rules for the masking filter are in the file masking_rules.json.
[MyMasking]
type=filter
module=masking
warn_type_mismatch=always
large_payload=abort
rules=masking_rules.json
[MyService]
type=service
...
filters=MyMasking
The rules specify that the data of a column whose name is ssn, should
be replaced with the string 012345-ABCD. If the length of the data is
not exactly the same as the length of the replacement value, then the
data should be replaced with as many X characters as needed.
{
"rules": [
{
"replace": {
"column": "ssn"
},
"with": {
"value": "012345-ABCD",
"fill": "X"
}
}
]
}