Hive SQL Syntax for Use with Sentry

Sentry permissions can be configured through GRANT and REVOKE statements issued either interactively or programmatically through the HiveServer2 SQL command line interface, Beeline (documentation available here). The syntax described below is very similar to the GRANT and REVOKE commands that are available in well-established relational database systems.

In HUE, the Sentry Admin that creates roles and grants privileges must belong to a group that has ALL privileges on the server. For example, you can create a role for the group that contains the hive or impala user, and grant ALL ON SERVER .. WITH GRANT OPTION to that role:

CREATE ROLE <admin role>;
GRANT ALL ON SERVER <server1> TO ROLE <admin role> WITH GRANT OPTION;
GRANT ROLE <admin role> TO GROUP <hive>;

Sentry supports column-level authorization with the SELECT privilege. Information about column-level authorization is in the Column-level Authorization section of this page.

See the sections below for details about the supported statements and privileges:

Column-level Authorization
CREATE ROLE Statement
DROP ROLE Statement
GRANT ROLE Statement
REVOKE ROLE Statement
GRANT <Privilege> Statement
GRANT <Privilege> ON URIs (HDFS and S3A)
REVOKE <Privilege> Statement
GRANT <Privilege> ... WITH GRANT OPTION
SET ROLE Statement
SHOW Statement
Example: Using Grant/Revoke Statements to Match an Existing Policy File

Column-level Authorization

Sentry allows you to assign the SELECT privilege on a subset of columns in a table.

The following command grants a role the SELECT privilege on a column:

GRANT SELECT <column name> ON TABLE <table name> TO ROLE <role name>;

The following command can be used to revoke the SELECT privilege on a column:

REVOKE SELECT <column name> ON TABLE <table name> FROM ROLE <role name>;

Any new columns added to a table will be inaccessible by default, until explicitly granted access.

Actions allowed for users with SELECT privilege on a column:

Users whose roles have been granted the SELECT privilege on columns only, can perform operations which explicitly refer to those columns. Some examples are:

```
SELECT <column name> FROM TABLE <table name>;
```
In this case, Sentry will first check to see if the user has the required privileges to access the table. It will then further check to see whether the user has the SELECT privilege to access the column(s).
```
SELECT COUNT <column name> FROM TABLE <table name>;
```
Users are also allowed to use the COUNT function to return the number of values in the column.

SELECT <column name> FROM TABLE <table name> WHERE <column name> <operator> GROUP BY <column name>;

The above command will work as long as you refer only to columns to which you already have access.

To list the column(s) to which the current user has SELECT access:

SHOW COLUMNS (FROM|IN) <table name> [(FROM|IN) <database name>];

Exceptions:

If a user has SELECT access to all columns in a table, the following command will work. Note that this is an exception, not the norm. In all other cases, SELECT on all columns does not allow you to perform table-level operations.
```
SELECT * FROM TABLE <table name>;
```

Limitations:

Column-level privileges can only be applied to tables, not partitions or views.
HDFS-Sentry Sync: With HDFS-Sentry sync enabled, even if a user has been granted access to all columns of a table, they will not have access to the corresponding HDFS data files. This is because Sentry does not consider SELECT on all columns equivalent to explicitly being granted SELECT on the table.
Column-level access control for access from Spark SQL is not supported by the HDFS-Sentry plug-in.

CREATE ROLE Statement

The CREATE ROLE statement creates a role to which privileges can be granted. Privileges can be granted to roles, which can then be assigned to users. A user that has been assigned a role will only be able to exercise the privileges of that role.

Only users that have administrative privileges can create or drop roles. By default, the hive, impala and hue users have admin privileges in Sentry.

CREATE ROLE <role name>;

Note that role names are case-insensitive.

DROP ROLE Statement

The DROP ROLE statement can be used to remove a role from the database. Once dropped, the role will be revoked for all users to whom it was previously assigned. Queries that are already executing will not be affected. However, since Hive checks user privileges before executing each query, active user sessions in which the role has already been enabled will be affected.

DROP ROLE <role name>;

GRANT ROLE Statement

The GRANT ROLE statement can be used to grant roles to groups. Only Sentry admin users can grant roles to a group.

GRANT ROLE <role name> [, <role name>]
    TO GROUP <group name> [,GROUP <group name>]

Sentry only allows you to grant roles to groups that have alphanumeric characters and underscores (_) in the group name. If the group name contains a non-alphanumeric character that is not an underscore, you can put the group name in backticks (`) to execute the command. For example, Sentry will return an error for the following command:

GRANT ROLE test TO GROUP test-group;

To grant a role to this group, put the group name in backticks:

GRANT ROLE test TO GROUP `test-group`;

The following command, which contains an underscore, is also acceptable:

GRANT ROLE test TO GROUP test_group;

Operating system group names must be in lowercase letters. Although group names are case-insensitive to Sentry, Sentry modifies capital letters within group names to be lowercase. For example, Sentry will change TestGroup to testgroup. It is not possible to disable this normalization. Therefore, group information within the environment must be in lowercase letters.

REVOKE ROLE Statement

The REVOKE ROLE statement can be used to revoke roles from groups. Only Sentry admin users can revoke the role from a group.

REVOKE ROLE <role name> [, <role name>]
    FROM GROUP <group name> [,GROUP <group name>]

GRANT <Privilege> Statement

Use the GRANT <Privilege> statement to grant privileges on an object to a role. The statement uses the following syntax:

GRANT
    <privilege> [, <privilege> ]
    ON <object type> <object name>
    TO ROLE <role name> [,ROLE <role name>]

You can grant the SELECT privilege on specific columns of a table. For example:

GRANT SELECT <column name> ON TABLE <table name> TO ROLE <role name>;

GRANT <Privilege> ON URIs (HDFS and S3A)

If the GRANT for Sentry URI does not specify the complete scheme, or the URI mentioned in Hive DDL statements does not have a scheme, Sentry automatically completes the URI by applying the default scheme based on the HDFS configuration provided in the fs.defaultFS property. Using the same HDFS configuration, Sentry can also auto-complete URIs in case the URI is missing a scheme and an authority component.

When a user attempts to access a URI, Sentry will check to see if the user has the required privileges. During the authorization check, if the URI is incomplete, Sentry will complete the URI using the default HDFS scheme. Note that Sentry does not check URI schemes for completion when they are being used to grant privileges. This is because users can GRANT privileges on URIs that do not have a complete scheme or do not already exist on the filesystem.

For example, in CDH 5.8 and later, the following CREATE EXTERNAL TABLE statement works even though the statement does not include the URI scheme.

GRANT ALL ON URI 'hdfs://namenode:XXX/path/to/table' TO ROLE <role name>;
CREATE EXTERNAL TABLE foo LOCATION 'namenode:XXX/path/to/table' TO ROLE <role name>;

Similarly, the following CREATE EXTERNAL TABLE statement works even though it is missing scheme and authority components.

GRANT ALL ON URI 'hdfs://namenode:XXX/path/to/table' TO ROLE <role name>;
CREATE EXTERNAL TABLE foo LOCATION
  '/path/to/table'

Since Sentry supports both HDFS and Amazon S3, in CDH 5.8 and later, Cloudera recommends that you specify the fully qualified URI in GRANT statements to avoid confusion. If the underlying storage is a mix of S3 and HDFS, the risk of granting the wrong privileges increases. The following are examples of fully qualified URIs:

HDFS: hdfs://host:port/path/to/hdfs/table
S3: s3a://host:port/path/to/s3/table

REVOKE <Privilege> Statement

You can use the REVOKE <Privilege> statement to revoke previously-granted privileges that a role has on an object.

REVOKE
    <privilege> [, <privilege> ]
    ON <object type> <object name>
    FROM ROLE <role name> [,ROLE <role name>]

For example, you can revoke previously-granted SELECT privileges on specific columns of a table with the following statement:

REVOKE SELECT <column name> ON TABLE <table name> FROM ROLE <role name>;

GRANT <Privilege> ... WITH GRANT OPTION

You can delegate granting and revoking privileges to other roles. For example, a role that is granted a privilege WITH GRANT OPTION can GRANT/REVOKE the same privilege to/from other roles. Hence, if a role has the ALL privilege on a database and the WITH GRANT OPTION set, users granted that role can execute GRANT/REVOKE statements only for that database or child tables of the database.

GRANT
    <privilege>
    ON <object type> <object name>
    TO ROLE <role name>
    WITH GRANT OPTION

Only a role with GRANT option on a specific privilege or its parent privilege can revoke that privilege from other roles. Once the following statement is executed, all privileges with and without grant option are revoked.

REVOKE
    <privilege>
    ON <object type> <object name>
    FROM ROLE <role name>

Hive does not currently support revoking only the WITH GRANT OPTION from a privilege previously granted to a role. To remove the WITH GRANT OPTION, revoke the privilege and grant it again without the WITH GRANT OPTION flag.

SET ROLE Statement

Sentry enforces restrictions on queries based on the roles and privileges that the user has. A user can have multiple roles and a role can have multiple privileges.

The SET ROLE command enforces restrictions at the role level, not at the user level. When you use the SET ROLE command to make a role active, the role becomes current for the session. If a role is not current for the session, it is inactive and the user does not have the privileges assigned to that role. A user can only use the SET ROLE command for roles that have been granted to the user.

To list the roles that are current for the user, use the SHOW CURRENT ROLES command. By default, all roles that are assigned to the user are current.

You can use the following SET ROLE commands:

SET ROLE NONE: Makes all roles for the user inactive. When no role is current, the user does not have any privileges and cannot execute a query.
SET ROLE ALL: Makes all roles that have been granted to the user active. All privileges assigned to those roles are applied. When the user executes a query, the query is filtered based on those privileges.
SET ROLE role name: Makes a single role active. The privileges assigned to that role are applied. When the user executes a query, the query is filtered based on the privileges assigned to that role.

SHOW Statement

To list the database(s) for which the current user has database, table, or column-level access:
```
SHOW DATABASES;
```
To list the table(s) for which the current user has table or column-level access:
```
SHOW TABLES;
```

To list the column(s) to which the current user has SELECT access:

SHOW COLUMNS (FROM|IN) <table name> [(FROM|IN) <database name>];

To list all the roles in the system (only for sentry admin users):
```
SHOW ROLES;
```
To list all the roles in effect for the current user session:
```
SHOW CURRENT ROLES;
```
To list all the roles assigned to the given group name (only allowed for Sentry admin users and others users that are part of the group specified by group name):
```
SHOW ROLE GRANT GROUP group name;
```
The SHOW statement can also be used to list the privileges that have been granted to a role or all the grants given to a role for a particular object.
To list all the grants for the given <role name> (only allowed for Sentry admin users and other users that have been granted the role specified by <role name>). The following command will also list any column-level privileges:
```
SHOW GRANT ROLE <role name>;
```
To list all the grants for a role on the given <object name> (only allowed for Sentry admin users and other users that have been granted the role specified by <role name>). The following command will also list any column-level privileges:
```
SHOW GRANT ROLE <role name> on <object type> <object name>;
```

Example: Using Grant/Revoke Statements to Match an Existing Policy File

Here is a sample policy file:

[groups]
# Assigns each Hadoop group to its set of roles  
manager = analyst_role, junior_analyst_role 
analyst = analyst_role 
jranalyst = junior_analyst_role 
customers_admin = customers_admin_role 
admin = admin_role  

[roles] # The UIRs below define a landing skid which
# the user can use to import or export data from the system. 
# Since the server runs as the user "hive" files in that directory 
# must either have the group hive and read/write set or 
# be world read/write. 
analyst_role = server=server1->db=analyst1, \     
    server=server1->db=jranalyst1->table=*->action=select         
    server=server1->uri=hdfs://ha-nn-uri/landing/analyst1 
junior_analyst_role = server=server1->db=jranalyst1, \     
    server=server1->uri=hdfs://ha-nn-uri/landing/jranalyst1  

# Implies everything on server1. 
admin_role = server=server1

The following sections show how you can use the new GRANT statements to assign privileges to roles (and assign roles to groups) to match the sample policy file above.

Grant privileges to analyst_role:

CREATE ROLE analyst_role;
GRANT ALL ON DATABASE analyst1 TO ROLE analyst_role;
GRANT SELECT ON DATABASE jranalyst1 TO ROLE analyst_role;
GRANT ALL ON URI 'hdfs://ha-nn-uri/landing/analyst1' \
TO ROLE analyst_role;

Grant privileges to junior_analyst_role:

CREATE ROLE junior_analyst_role;
GRANT ALL ON DATABASE jranalyst1 TO ROLE junior_analyst_role;
GRANT ALL ON URI 'hdfs://ha-nn-uri/landing/jranalyst1' \
TO ROLE junior_analyst_role;

Grant privileges to admin_role:

CREATE ROLE admin_role;
GRANT ALL ON SERVER server1 TO ROLE admin_role;

Grant roles to groups:

GRANT ROLE admin_role TO GROUP admin;
GRANT ROLE analyst_role TO GROUP analyst;
GRANT ROLE jranalyst_role TO GROUP jranalyst;

Sentry Debugging and Failure Scenarios

Synchronizing HDFS ACLs and Sentry Permissions