Nov 21, 2016

Security Features of SQL Server on Linux


This guide will walk you through some of the security tasks if you are running SQL Server on Linux. These are not unique or specific to Linux, but it helps to give you an idea of areas to investigate further.







Note
The following examples use the AdventureWorks2014 sample database. For instructions on how to obtain and install this sample database, see Restore a SQL Server database from Windows to Linux.

Create a login and a database user

Grant others access to SQL Server by creating a login in the master database using the CREATE LOGIN statement. For example:

CREATE LOGIN Larry WITH PASSWORD = '************';
Note
Always use a strong password in place of the asterisks above.
Logins can connect to SQL Server and have access (with limited permissions) to the master database. To connect to a user-database, a login needs a corresponding identity at the database level, called a database user. 

Users are specific to each database and must be separately created in each database to grant them access. The following example moves you into the AdventureWorks2014 database, and then uses the CREATE USER statement to create a user named Larry that is associated with the login named Larry. 

Though the login and the user are related (mapped to each other), they are different objects. The login is a server-level principle. The user is a database-level principal.

USE AdventureWorks2014;
GO
CREATE USER Larry;
GO
  • A SQL Server administrator account can connect to any database and can create more logins and users in any database.
  • When someone creates a database they become the database owner, which can connect to that database. Database owners can create more users.
Later you can authorize other logins to create a more logins by granting them the ALTER ANY LOGIN permission. Inside a database, you can authorize other users to create more users by granting them the ALTER ANY USER permission. For example:

GRANT ALTER ANY LOGIN TO Larry;   
GO   

USE AdventureWorks2014;   
GO   
GRANT ALTER ANY USER TO Jerry;    
GO
Now the login Jerry can create more logins, and the user Jerry can create more users.

Granting access with least privileges

The first people to connect to a user-database will be the administrator and database owner accounts. However these users have all the the permissions available on the database. This is more permission than most users should have.

When you are just getting started, you can assign some general categories of permissions by using the built-in fixed database roles. For example, the db_datareader fixed database role can read all tables in the database, but make no changes. Grant membership in a fixed database role by using the ALTER ROLE statement. The following example add the user Jerry to the db_datareaderfixed database role.

USE AdventureWorks2014;   
GO   

ALTER ROLE db_datareader ADD MEMBER Jerry;
Later, when you are ready to configure more precise access to your data (highly recommended), create your own user-defined database roles using CREATE ROLE statement. Then assign specific granular permissions to you custom roles.

For example, the following statements create a database role named Sales, grants the Salesgroup the ability to see, update, and delete rows from the Orders table, and then adds the user Jerry to the Sales role.

CREATE ROLE Sales;   
GRANT SELECT ON Object::Sales TO Orders;   
GRANT UPDATE ON Object::Sales TO Orders;   
GRANT DELETE ON Object::Sales TO Orders;   
ALTER ROLE Sales ADD MEMBER Jerry;

Configure row-level security

Row-Level Security enables you to restrict access to rows in a database based on the user executing a query. This feature is useful for scenarios like ensuring that customers can only access their own data or that workers can only access data that is pertinent to their department.

The steps below walk through setting up two Users with different row-level access to the Sales.SalesOrderHeader table.

Create two user accounts to test the row level security:

USE AdventureWorks2014;   
GO   

CREATE USER Manager WITHOUT LOGIN;     

CREATE USER SalesPerson280 WITHOUT LOGIN;
Grant read access on the Sales.SalesOrderHeader table to both users:

GRANT SELECT ON Sales.SalesOrderHeader TO Manager;      
GRANT SELECT ON Sales.SalesOrderHeader TO SalesPerson280;
Create a new schema and inline table-valued function. The function returns 1 when a row in the SalesPersonID column matches the ID of a SalesPerson login or if the user executing the query is the Manager user.

CREATE SCHEMA Security;   
GO   

CREATE FUNCTION Security.fn_securitypredicate(@SalesPersonID AS int)     
    RETURNS TABLE   
WITH SCHEMABINDING   
AS     
   RETURN SELECT 1 AS fn_securitypredicate_result    
WHERE ('SalesPerson' + CAST(@SalesPersonId as VARCHAR(16)) = USER_NAME())     
    OR (USER_NAME() = 'Manager');
Create a security policy adding the function as both a filter and a block predicate on the table:

CREATE SECURITY POLICY SalesFilter   
ADD FILTER PREDICATE Security.fn_securitypredicate(SalesPersonID)    
  ON Sales.SalesOrderHeader,   
ADD BLOCK PREDICATE Security.fn_securitypredicate(SalesPersonID)    
  ON Sales.SalesOrderHeader   
WITH (STATE = ON);
Execute the following to query the SalesOrderHeader table as each user. Verify that SalesPerson280 only sees the 95 rows from their own sales and that the Manager can see all the rows in the table.

EXECUTE AS USER = 'SalesPerson280';   
SELECT * FROM Sales.SalesOrderHeader;    
REVERT; 

EXECUTE AS USER = 'Manager';   
SELECT * FROM Sales.SalesOrderHeader;   
REVERT;
Alter the security policy to disable the policy. Now both users can access all rows.

ALTER SECURITY POLICY SalesFilter   
WITH (STATE = OFF);

Enable dynamic data masking

Dynamic Data Masking enables you to limit the exposure of sensitive data to users of an application by fully or partially masking certain columns.

Use an ALTER TABLE statement to add a masking function to the EmailAddress column in the Person.EmailAddress table:

USE AdventureWorks2014;
GO
ALTER TABLE Person.EmailAddress    
ALTER COLUMN EmailAddress    
ADD MASKED WITH (FUNCTION = 'email()');
Create a new user TestUser with SEELCT permission on the table, then execute a query as TestUser to view the masked data:

CREATE USER TestUser WITHOUT LOGIN;   
GRANT SELECT ON Person.EmailAddress TO TestUser;    

EXECUTE AS USER = 'TestUser';   
SELECT EmailAddressID, EmailAddress FROM Person.EmailAddress;       
REVERT;
Verify that the masking function changes the email address in the first record from:

EmailAddressIDEmailAddress
1ken0@adventure-works.com
into
EmailAddressIDEmailAddress
1kXXX@XXXX.com

Enable Transparent Data Encryption

One threat to your database is the risk that someone will steal the database files off of your hard-drive. This could happen with an intrusion that gets elevated access to your system, through the actions of a problem employee, or by theft of the computer containing the files (such as a laptop).

Transparent Data Encryption (TDE) encrypts the data files as they are stored on the hard drive. The master database of the SQL Server database engine has the encryption key, so that the database engine can manipulate the data. The database files cannot be read without access to the key. High-level administrators can manage, backup, and recreate the key, so the database can be moved, but only by selected people. When TDE is configured, the tempdb database is also automatically encrypted.

Since the Database Engine can read the data, Transparent Data Encryption does not protect against unauthorized access by administrators of the computer who can directly read memory, or access SQL Server through an administrator account.

Configure TDE

  • Create a master key
  • Create or obtain a certificate protected by the master key
  • Create a database encryption key and protect it by the certificate
  • Set the database to use encryption
Configuring TDE requires CONTROL permission on the master database and CONTROL permission on the user database. Typically an administrator configures TDE.

The following example illustrates encrypting and decrypting the AdventureWorks2014 database using a certificate installed on the server named MyServerCert.

USE master;  
GO  

CREATE MASTER KEY ENCRYPTION BY PASSWORD = '**********';  
GO  

CREATE CERTIFICATE MyServerCert WITH SUBJECT = 'My Database Encryption Key Certificate';  
GO  

USE AdventureWorks2014;  
GO

CREATE DATABASE ENCRYPTION KEY  
WITH ALGORITHM = AES_256  
ENCRYPTION BY SERVER CERTIFICATE MyServerCert;  
GO

ALTER DATABASE AdventureWorks2014  
SET ENCRYPTION ON;
To remove TDE, execute ALTER DATABASE AdventureWorks2014 SET ENCRYPTION OFF;

The encryption and decryption operations are scheduled on background threads by SQL Server. You can view the status of these operations using the catalog views and dynamic management views in the list that appears later in this topic.

Configure backup encryption

SQL Server has the ability to encrypt the data while creating a backup. By specifying the encryption algorithm and the encryptor (a certificate or asymmetric key) when creating a backup, you can create an encrypted backup file.

The following example creates a certificate, and then creates a backup protected by the certificate.






USE master;  
GO  
CREATE CERTIFICATE BackupEncryptCert   
   WITH SUBJECT = 'Database backups';  
GO 
BACKUP DATABASE [AdventureWorks2014]  
TO DISK = N'/var/opt/mssql/backups/AdventureWorks2014.bak'  
WITH  
  COMPRESSION,  
  ENCRYPTION   
   (  
   ALGORITHM = AES_256,  
   SERVER CERTIFICATE = BackupEncryptCert  
   ),  
  STATS = 10  
GO

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