Impala Authorization

Authorization determines which users are allowed to access which resources, and what operations they are allowed to perform. You use Apache Ranger to enable and manage authorization in Impala.

Supported Ranger Features in Impala

  • Resource-based and tag-based authorization policies
  • Resource-based and tag-based column masking

Unsupported Ranger Features in Impala

  • Row-level filtering

Using Resource-based Authorization Policies for Impala

In the Ranger Service Manager, you can use the Hadoop SQL preloaded resource-based and tag-based services and policies to authorize access to Impala:

Ranger service manager

You can configure services for Impala as described in Using Ranger to Provide Authorization in CDP.

For example, you can edit the all-global policy for an Impala user:

Global policy impala user

For information about using tag-based policies, see Tag-based column masking in Hive with Ranger policies.

Privilege Model

You set up privileges through the GRANT and REVOKE statements in either Impala or Hive. Then both components use those same privileges automatically.

By default, when authorization is not enabled, Impala does all read and write operations with the privileges of the impala user, which is suitable for a development/test environment but not for a secure production environment. When authorization is enabled, Impala uses the OS user ID of the user who runs impala-shell or other client programs, and associates various privileges with each user.

Privileges can be granted on different resources in the schema and are associated with a level in the resource hierarchy. A privilege on a particular resource automatically inherits the same privilege of its parent.

The resource hierarchy is:

Server
    URI
    Database
        Table
            Column
        Function

The table-level privileges apply to views as well. Anywhere you specify a table name, you can specify a view name instead.

You can specify privileges for individual columns.

The table below lists the minimum level of privileges and the scope required to execute SQL statements in Impala. The following notations are used:
  • The SERVER resource type in Ranger implies all databases, all tables, all columns, all UDFs, and all URLs.
  • ANY denotes the CREATE, ALTER, DROP, SELECT, INSERT, or REFRESH privilege.
  • ALL privilege denotes the SELECT, INSERT, CREATE, ALTER, DROP, and REFRESH privileges.
  • VIEW_METADATA privilege denotes the SELECT, INSERT, or REFRESH privileges.
  • The parent levels of the specified scope are implicitly supported. For example, if a privilege is listed with the TABLE scope, the same privilege granted on DATABASE and SERVER will allow the user to execute that specific SQL statement on TABLE.

For example, to be able to execute CREATE VIEW, you need the CREATE privilege on the database and the SELECT privilege on the source table.

SQL Statement Privileges Object Type /

Resource Type

SELECT SELECT TABLE
WITH SELECT SELECT TABLE
EXPLAIN SELECT SELECT TABLE
INSERT INSERT TABLE
EXPLAIN INSERT INSERT TABLE
TRUNCATE INSERT TABLE
LOAD INSERT TABLE
ALL URI
CREATE DATABASE CREATE SERVER
CREATE DATABASE LOCATION CREATE SERVER
ALL URI
CREATE TABLE CREATE DATABASE
CREATE TABLE LIKE CREATE DATABASE
VIEW_METADATA TABLE
CREATE TABLE AS SELECT CREATE DATABASE
INSERT DATABASE
SELECT TABLE
EXPLAIN CREATE TABLE AS SELECT CREATE DATABASE
INSERT DATABASE
SELECT TABLE
CREATE TABLE LOCATION CREATE TABLE
ALL URI
CREATE VIEW CREATE DATABASE
SELECT TABLE
ALTER DATABASE SET OWNER ALL WITH GRANT DATABASE
ALTER TABLE ALL TABLE
ALTER TABLE SET LOCATION ALL TABLE
ALL URI
ALTER TABLE RENAME CREATE DATABASE
ALL TABLE
ALTER TABLE SET OWNER ALL WITH GRANT TABLE
ALTER VIEW ALL TABLE
SELECT TABLE
ALTER VIEW RENAME CREATE DATABASE
ALL TABLE
ALTER VIEW SET OWNER ALL WITH GRANT VIEW
DROP DATABASE ALL DATABASE
DROP TABLE ALL TABLE
DROP VIEW ALL TABLE
CREATE FUNCTION CREATE DATABASE
ALL URI
DROP FUNCTION ALL DATABASE
COMPUTE STATS ALL TABLE
DROP STATS ALL TABLE
INVALIDATE METADATA REFRESH SERVER
INVALIDATE METADATA <table> REFRESH TABLE
REFRESH <table> REFRESH TABLE
REFRESH AUTHORIZATION REFRESH SERVER
REFRESH FUNCTIONS REFRESH DATABASE
COMMENT ON DATABASE ALL DATABASE
COMMENT ON TABLE ALL TABLE
COMMENT ON VIEW ALL TABLE
COMMENT ON COLUMN ALL TABLE
DESCRIBE DATABASE VIEW_METADATA DATABASE
DESCRIBE <table/view>

If the user has the SELECT privilege at the COLUMN level, only the columns the user has access will show.

VIEW_METADATA TABLE
SELECT COLUMN
USE ANY TABLE
SHOW DATABASES ANY TABLE
SHOW TABLES ANY TABLE
SHOW FUNCTIONS VIEW_METADATA DATABASE
SHOW PARTITIONS VIEW_METADATA TABLE
SHOW TABLE STATS VIEW_METADATA TABLE
SHOW COLUMN STATS VIEW_METADATA TABLE
SHOW FILES VIEW_METADATA TABLE
SHOW CREATE TABLE VIEW_METADATA TABLE
SHOW CREATE VIEW VIEW_METADATA TABLE
SHOW CREATE FUNCTION VIEW_METADATA DATABASE
SHOW RANGE PARTITIONS (Kudu only) VIEW_METADATA TABLE
UPDATE (Kudu only) ALL TABLE
EXPLAIN UPDATE (Kudu only) ALL TABLE
UPSERT (Kudu only) ALL TABLE
WITH UPSERT (Kudu only) ALL TABLE
EXPLAIN UPSERT (Kudu only) ALL TABLE
DELETE (Kudu only) ALL TABLE
EXPLAIN DELETE (Kudu only) ALL TABLE

The privileges not listed in the table above will be silently ignored by Impala.

Changing Privileges in Impala

Privileges are managed via the GRANT and REVOKE SQL statements that require the Ranger service enabled.

Privileges can be also managed in Ranger UI. Especially, for attribute-based access control, Ranger UI is required to manage authorization.

Impala authorization policies are listed in the Hive service section in Ranger UI.

REFRESH AUTHORIZATION is not required when you make the changes to privileges within Impala. The changes are automatically propagated.

Changing Privileges from Outside of Impala

If you make a change to privileges in Ranger from outside of Impala, e.g. adding a user, removing a user, modifying privileges, there are two options to propagate the change:

  • Use the ranger.plugin.hive.policy.pollIntervalMs property to specify how often to do a Ranger refresh. The property is specified in ranger-hive-security.xml in the conf directory under your Impala home directory.
  • Run the REFRESH AUTHORIZATION statement to force a refresh.

Granting Privileges on URI

URIs represent the file paths you specify as part of statements such as CREATE EXTERNAL TABLE and LOAD DATA. Typically, you specify what look like UNIX paths, but these locations can also be prefixed with hdfs:// to make clear that they are really URIs. To set privileges for a URI, specify the name of a directory, and the privilege applies to all the files in that directory and any directories underneath it.

URIs must start with hdfs://, s3a://, adl://, or file://. If a URI starts with an absolute path, the path will be appended to the default filesystem prefix. For example, if you specify:
GRANT ALL ON URI '/tmp';
The above statement effectively becomes the following where the default filesystem is HDFS.
GRANT ALL ON URI 'hdfs://localhost:20500/tmp';
When defining URIs for HDFS, you must also specify the NameNode. For example:
GRANT ALL ON URI file:///path/to/dir TO <principal>
          GRANT ALL ON URI hdfs://namenode:port/path/to/dir TO <principal>

Object Ownership

Object ownership for tables, views and databases is enabled by default in Impala.

To define owner specific privileges, go to Ranger UI and define appropriate policies on the {OWNER} user.

The CREATE statements implicitly make the user running the statement the owner of the object. For example, if User A creates a database, foo, via the CREATE DATABASE statement, User A now owns the foo database and is authorized to perform any operation on the foo database.

An ownership can be transferred to another user or role via the ALTER DATABASE, ALTER TABLE, or ALTER VIEW with the SET OWNER clause.

Ranger Column Masking for Impala

Ranger column masking hides sensitive columnar data in Impala query output. For example, you can define a policy that reveals only the first or last four characters of column data. Column masking is enabled by default. To disable column masking, modify the following configuration property in all coordinators:
--enable_column_masking=false
This flag might be removed in a future release. The Impala behavior mimics Hive behavior with respect to column masking.
The following table lists all Impala-supported, built-in mask types for defining column masking in a policy using the Ranger REST API or Ranger UI:
Type Name Description Transformer
MASK Redact Replace lowercase with 'x', uppercase with 'X', digits with '0' mask({col})
MASK_SHOW_LAST_4 Partial mask: show last 4 Show last 4 characters; replace rest with 'x' mask_show_last_n({col}, 4, 'x', 'x', 'x', -1, '1')
MASK_SHOW_FIRST_4 Partial mask: show first 4 Show first 4 characters; replace rest with 'x' mask_show_first_n({col}, 4, 'x', 'x', 'x', -1, '1')
MASK_HASH Hash Hash the value mask_hash({col})
MASK_NULL Nullify Replace with NULL N/A
MASK_NONE Unmasked (retain original value) No masking N/A
MASK_DATE_SHOW_YEAR Date: show only year Date: show only year mask({col}, 'x', 'x', 'x', -1, '1', 1, 0, -1)
CUSTOM Custom Custom N/A
The table includes the mask name as it appears in the Ranger UI.

Ranger Column Masking Limitations in Impala

  • Column masking introduces unused columns during the query analysis and, consequently, additional SELECT privileges checks on all columns of the masked table.
  • Impala might produce more than one audit log entry for a column involved in a column masking policy under all of these conditions: the column appears in multiple places in a query, the query is rewritten, or the query is re-analyzed.
  • Column masking policies, shared between Hive and Impala, might be affected by SQL/UDF differences between Hive and Impala, as shown in the following example.

    For instance, UTF-8 strings containing non-ASCII characters are not guaranteed to work properly. Suppose a column masking policy masks the last two characters of a string: s => mask_last_n(s, 2, 'x', 'x', 'x', 'x'). Applying this policy, Hive properly masks SQL引擎 to SQLxx, but the Impala masking produces SQL引�xx because each Chinese character is encoded in 3 bytes. Impala and Hive do not handle different lengths in the same way.

Limitations on Mask Functions

The mask functions in Hive are implemented through GenericUDFs. Even though Impala users can call Hive UDFs, Impala does not yet support Hive GenericUDFs, so you cannot use Hive's mask functions in Impala. However, Impala has builtin mask functions that are implemented through overloads. In Impala, when using mask functions, not all parameter combinations are supported. These mask functions are introduced in Impala 3.4

The following list includes all the implemented overloads.

  • Overloads used by Ranger default masking policies,
  • Overloads with simple arguments,
  • Overload with all arguments in int type for full functionality. Char argument needs to be converted to their ASCII value.

To list the available overloads, use the following query:

show functions in _impala_builtins like "mask*";