Managing permissions in Parallel Data Warehouse

This article describes the requirements and options for managing database permissions for SQL Server PDW.

Database Engine Permission Basics

Database Engine permissions on SQL Server PDW are managed at the server level through logins, and at the database level through database users and user-defined database roles.

Logins
Logins are individual user accounts for logging on to the SQL Server PDW. SQL Server PDW supports logins using Windows Authentication and SQL Server authentication. Windows Authentication logins can be Windows users or Windows groups from any domain that is trusted by SQL Server PDW. SQL Server Authentication logins are defined and authenticated by SQL Server PDW and must be created by specifying a password.

Members of the sysadmin fixed server role (such as the sa login) can connect to a database without having being mapped to a database user. They are mapped to the dbo user. The owner of the database is also mapped as the dbo user.

Server Roles
There are four special server roles with a set of preconfigured roles that provide convenient group of server-level permissions. The sysadmin, MediumRC, LargeRC, and XLargeRCfixed server roles are the only server roles currently implemented in SQL Server PDW. The sa login is the only member of the sysadmin fixed server role, and additional logins cannot be added to the sysadmin role. Logins can be granted the CONTROL SERVER permission, which is similar, though not identical, to the sysadmin fixed server role. Use ALTER SERVER ROLE to add members to the other server roles. SQL Server PDW does not support user-defined server roles.

Database Users
Logins are granted access to a database by creating a database user in a database and mapping that database user to a login. Typically the database user name is the same as the login name, though it does not have to be the same. Each database user maps to a single login. A login can be mapped to only one user in a database, but can be mapped as a database user in several different databases.

Fixed Database Roles
Fixed database roles are a set of preconfigured roles that provide convenient group of database-level permissions. Database users and user-defined database roles can be added to the fixed database roles using the sp_addrolemember procedure. For more information about fixed database roles, see Fixed Database Roles.

User-defined Database Roles
Users with the CREATE ROLE permission can create new user-defined database roles to represent groups of users with common permissions. Typically permissions are granted or denied to the entire role, simplifying permissions management and monitoring.

Permissions are granted to security principals (logins, users, and roles) by using the GRANT statement. Permissions are explicitly denied by using the DENY command. A previously granted or denied permission is removed by using the REVOKE statement. Permissions are cumulative, with the user receiving all the permissions granted to the user, login, and any group memberships; however any permission denial overrides all grants.

The following example represents a common and recommended method of configuring permissions.

  1. If using Windows Authentication, create a login for each Windows user or Windows group who will connect to SQL Server PDW. If using SQL Server Authentication, create a login for each person who will connect to SQL Server PDW.

  2. Create a database user for each login in all necessary databases.

  3. Create one or more user-defined database roles, each representing a similar function. For example financial analyst, and sales analyst.

  4. Add database users to one or more user-defined database roles.

  5. Grant permissions to the user-defined database roles.

Logins are server-level objects and can be listed by viewing sys.server_principals. Only server-level permissions can be granted to server principals.

Users and database roles are database-level objects and can be listed by viewing sys.database_principals. Only database-level permissions can be granted to database principals.

Default Permissions

The following list describes the default permissions:

  • When a login is created by usings CREATE LOGIN statement, the login receives the CONNECT SQL permission allowing the login to connect to the SQL Server PDW.

  • When a database user is created by using the CREATE USER statement, the user receives the CONNECT ON DATABASE::<database_name> permission, allowing the login to connect to that database as a user.

  • All principals, including the PUBLIC role, have no explicit or implicit permissions by default because implicit permissions are inherited from explicit permissions. Therefore, when no explicit permissions are present, there can also be no implicit permissions.

  • When a login becomes the owner of an object or database, the login always has all permissions on the object or database. The ownership permissions are not visible as explicit permissions. The GRANT, REVOKE, and DENY statements have no effect on ownership permissions. Ownership can be changed by using the ALTER AUTHORIZATION statement.

  • The sa login has all permissions on the appliance. Similar to ownership permissions, the sa permissions cannot be changed and are not visible as explicit permissions. The GRANT, REVOKE, and DENY statements have no effect on sa permissions.

  • The PUBLIC server role receives no permissions by default and does not inherit permissions from other server roles. The PUBLIC server role can be given explicit permissions with the GRANT, REVOKE, and DENY statements.

  • Transactions do not require permissions. All principals can run the BEGIN TRANSACTION, COMMIT, and ROLLBACK transaction commands. However, a principal must have the appropriate permissions to run each statement within the transaction.

  • The USE statement does not require permissions. All principals can run the USE statement on any database, however to access a database they must have a user principal in the database or the guest user must be enabled.

The PUBLIC Role

All new appliance logins automatically belong to the PUBLIC role. The PUBLIC server role has the following characteristics:

  • The PUBLIC server role has no permissions by default.

  • All principals are members of the PUBLIC server role, and the PUBLIC server role is not a member of another server role.

  • The PUBLIC server role cannot inherit implicit permissions. Any permissions given to the PUBLIC role must be explicitly granted.

Determining Permissions

Whether or not a login has permission to perform a specific action depends on the permissions granted or denied to login, user, and roles the user is a member of. Server-level permissions (such as CREATE LOGIN and VIEW SERVER STATE) are available to server-level principals (logins). Database-level permissions (such as SELECT from a table or EXECUTE on a procedure) are available to database-level principals (users and database roles).

Implicit and Explicit Permissions

An explicit permission is a GRANT or DENY permission given to a principal by a GRANT or DENY statement. Database-level permissions are listed in the sys.database_permissions view. Server-level permissions are listed in the sys.server_permissions view.

An implicit permission is a GRANT or DENY permission that a principal (login or server role) has inherited. A permission can be inherited in the following ways.

  • A principal can inherit a permission from a role if the principal is a member of the role even if the principal does not have an explicit GRANT or DENY permission.

  • A principal can inherit a permission on a subordinate object (such as a table) if the principal has a permission on one of the objects parent scopes (such as the schema of the table or the permission on the entire database).

  • A principal can inherit a permission by having a permission that includes a subordinate permission. For example the ALTER ANY USER permission includes the both the CREATE USER and the ALTER ON USER:: permissions.

Determining Permissions When Performing Actions

The process of determining which permission to assign to a principal is complex. The complexity occurs when determining implicit permissions because principals can be members of multiple roles and permissions can be passed through multiple levels in the role hierarchy.

The following list describes general rules for determining permissions:

  • Ownership implies permission.

    An object owner has all permissions on the object. Likewise, a database owner has all permissions on the database and all permissions on the objects in the database. These permissions cannot be changed.

  • Permissions can be inherited across multiple levels in the hierarchy of server role memberships.

    For example, suppose you have the following situation:

    • Login David is a member of database role PerfAnalysts.

    • PerfAnalysts is a member of database role Production.

    • David and PerfAnalysts have no SELECT permission on the Customer table. The permission was either revoked or never explicitly granted.

    • Production has SELECT permission on the Customer table.

    In this case, PerfAnalysts will inherit GRANT permission on the Customer table from Production, and David will inherit GRANT permission on the Customer table from Production.

  • DENY overrides GRANT when permissions conflict.

    For example, suppose login David has no permissions on the Customer table and is a member of two database roles –dbgroup1, which has DENY permission on the Customer table, and dbgroup2, which has GRANT permission on the Customer table. In this case, David will inherit the DENY permission on the Customer table. This is the case whether the roles gained their permissions explicitly or implicitly.

Auditing Permissions

To research the permissions of a user check the following.

  • Execute the following query to determine which logins are system administrators.

    SELECT SPLogins.name, 'is a member of ', SPRoles.name   
    FROM sys.server_role_members AS SRM   
    JOIN sys.server_principals AS SPRoles   
        ON SRM.role_principal_id = SPRoles.principal_id   
    JOIN sys.server_principals AS SPLogins   
        ON SRM.member_principal_id = SPLogins.principal_id;  
    
  • Execute the following query to determine which logins have been granted explicit permissions.

    SELECT name, 'has the ', state_desc , permission_name, ' permission'  
    FROM sys.server_permissions AS SP  
    JOIN sys.server_principals AS SPRoles   
        ON SP.grantee_principal_id = SPRoles.principal_id;  
    
  • Execute the following query in a user database to determine which database users are members of a database role.

    SELECT DPUsers.name, 'is a member of ', DPRoles.name    
    FROM sys.database_role_members AS DRM  
    JOIN sys.database_principals AS DPRoles   
        ON DRM.role_principal_id = DPRoles.principal_id  
    JOIN sys.database_principals AS DPUsers  
        ON DRM.member_principal_id = DPUsers.principal_id;  
    
  • Execute the following query in a user database to determine which database users and roles have been granted or denied specific permissions. You will have to query additional views such as sys.objects and sys.schemas to identify the items described with the major_id.

    SELECT DPUsers.name, 'has the ', permission_name,   
    'permission on the item described as class = ', class, 'id = ', major_id  
    FROM sys.database_permissions AS DP  
    JOIN sys.database_principals AS DPUsers  
        ON DP.grantee_principal_id = DPUsers.principal_id;  
    

Database Permissions Best Practices

  • Grant permissions at the most granular level that is practical. Granting permissions at the table or view level permissions could become unmanageable. But granting permissions at the database level could be too permissive. If the database is designed with schemas to define work boundaries, perhaps the granting permission to the schema is an appropriate compromise between the table level and the database level.

  • Grant permissions to roles, rather than to users or logins. Managing rights by using roles instead of users makes it easy to quickly grant or revoke a set of permissions for a user or login by moving them into or out of the role. When a function passes from one person to another, the permissions can remain intact at the role level while the role membership changes.

  • Grant permissions to roles based on job function, and on higher-level group roles that combine the job function roles based on the company group performing the actions.

  • Every end user should have a unique login. Do not allow users to share logins. Providing a login for each user ensures an audit trail and simplifies permission management.

Fixed Database Roles

SQL Server provides pre-configured (fixed) database-level roles to help you manage the permissions on a server. The pre-configured roles are fixed in that you cannot change the permissions assigned to them. User-defined database roles can also be created. You can change the permissions assigned to user-defined database roles.

Roles are security principals that group other principals. Database roles are database-wide in their permissions scope. Database users and other database roles can be added as members of database roles. The fixed database roles cannot be added to each other. (Roles are like groups in the Windows operating system.)

There are 9 fixed database roles.

  • db_owner

  • db_securityadmin

  • db_accessadmin

  • db_backupoperator

  • db_ddladmin

  • db_datawriter

  • db_datareader

  • db_denydatawriter

  • db_denydatareader

Permissions of the Fixed Database Roles

The system of fixed server roles and fixed database roles is a legacy system originated in the 1980's. Fixed roles are still supported and are useful in environments where there are few users and the security needs are simple. Beginning with SQL Server 2005, a more detailed system of granting permission was created. This new system is more granular, providing many more options for both granting and denying permissions. The extra complexity of the more granular system makes it harder to learn, but most enterprise systems should grant permissions instead of using the fixed roles. The following chart shows the permissions that are associated with each fixed database role. All permissions in this SQL Server graphic are not available (or necessary) in APS.

APS security fixed database roles

Fixed Server Roles

Fixed server roles are created automatically by SQL Server. SQL Server PDW has a limited implementation of SQL Server fixed server roles. Only the sysadmin and public have user logins as members. The setupadmin and dbcreator roles are used internally by SQL Server PDW. Additional members cannot be added or removed from any role.

sysadmin Fixed Server Role

Members of the sysadmin fixed server role can perform any activity in the server. The sa login is the only member of the sysadmin fixed server role. Additional logins cannot be added to the sysadmin fixed server role. Granting the CONTROL SERVER permission approximates membership in the sysadmin fixed server role. The following example grants the CONTROL SERVER permission to a login named Fay.

USE master;  
GO  
GRANT CONTROL SERVER TO Fay;  

Important

The CONTROL SERVER permission provides nearly complete control of SQL Server PDW. Whenever possible, provide more granular permissions to logins instead. For example, consider granting the VIEW SERVER STATE, ALTER ANY LOGIN, VIEW ANY DATABASE, or CREATE ANY DATABASE permissions.

public Server Role

Every login that can connect to SQL Server PDW is a member of the public server role. All logins inherit the permissions granted to public on any object. Only assign public permissions on an object when you want the object to be available to all users. You cannot change membership in the public role.

Note

public is implemented differently than other roles. Because all server principals are members of public, the membership of the public role is not listed in the sys.server_role_members DMV.

Fixed Server Roles vs. Granting Permissions

The system of fixed server roles and fixed database roles is a legacy system originated in the 1980's. Fixed roles are still supported and are useful in environments where there are few users and the security needs are simple. Beginning with SQL Server 2005, a more detailed system of granting permission was created. This new system is more granular, providing many more options for both granting and denying permissions. The extra complexity of the more granular system makes it harder to learn, but most enterprise systems should grant permissions instead of using the fixed roles.