Apply Row-Level Security to all tables — helper script

Developing multi-tenant applications with Row-Level Security (RLS) just got a little easier. This post makes available a script that will automatically apply an RLS predicate to all tables in a database.

Applications with multi-tenant databases, including those using Elastic Scale for sharding, commonly have a “TenantId” column in every table to indicate which rows belong to each tenant. As described in Building More Secure Middle-Tier Applications with Azure SQL Database using Row-Level Security, the recommended approach for filtering out rows that don’t belong to a tenant querying the database is to create an RLS security policy that filters out rows whose TenantId doesn’t match the current value of CONTEXT_INFO. However, for large applications with perhaps hundreds of tables, it can be tedious to write out “ADD FILTER PREDICATE…” for every table when creating or altering the RLS security policy.

To streamline this common RLS use case, we’ve created a helper stored procedure to automatically generate a security policy that adds a filter predicate on all tables with a TenantId column. See below for syntax and three common usage examples.

Script available here: http://rlssamples.codeplex.com/SourceControl/latest#RLS-Auto-Enable.sql

 

Syntax:

CREATE PROCEDURE dbo.sp_enable_rls_auto (
/* The type for the tenant ID column. It could be short, int or bigint. */
@rlsColType sysname,

/* The name for the tenant ID column. All tables that match the column name & type will be affected. */
@rlsColName sysname,

/* The schema name where the policy will be applied.
If null (default), the policy will be applied to tables in all schemas in the database. */
@applyToSchema sysname = null,

/* Set to 1 to disable all existing policies that affect the identified target tables.
If set to 0 (default), this function will fail if there is an existing policy on any of these tables. */
@deactivateExistingPolicies bit = 0,

/* Schema name for new RLS objects. If it does not exist, it will be created. */
@rlsSchemaName sysname = N'rls',

/* The name of an existing function in the RLS schema that will be used as the predicate.
If null (default), a new function will be created with a simple CONTEXT_INFO = tenant ID filter. */
@rlsPredicateFunctionName sysname = null,

/* Set to 1 to allow CONTEXT_INFO = null to have access to all rows. Default is 0.
Not applicable if @rlsPredicateFunctionName is set with a custom predicate function. */
@isNullAdmin bit = 0,

/* If @isNullAdmin = 1, set to 1 to optimize the CONTEXT_INFO = null disjunction into a range query.
Not applicable if @rlsPredicateFunctionName is set with a custom predicate function.
Note that on Azure SQL Database, CONTEXT_INFO is pre-populated with a unique connection GUID (not null),
so you must execute SET CONTEXT_INFO 0x to reset it to null for this 'admin' mode to work. */
@isNullAdminOptimized bit = 1,

/* If set, the predicate function will allow only this user to access rows.
Use only for middle-tier scenarios, where this is the shared application user name.
Not applicable if @rlsPredicateFunctionName is set with a custom predicate function. */
@restrictedToAppUserName sysname = null,

/* Set to 1 to print the commands (on by default). */
@printCommands bit = 1,

/* Set to 1 to execute the commands (off by default). */
@runCommands bit = 0
)

 

Examples:

Example 1: Typical CONTEXT_INFO usage

Generate a security policy that adds a new filter predicate (using CONTEXT_INFO as described in Building More Secure Middle-Tier Applications with Azure SQL Database using Row-Level Security) on all tables with a “TenantId” column of type “int.” Only allow access to “AppUser,” the shared application user in our app’s connection string. If CONTEXT_INFO is null, filter all rows by default.

EXEC sp_enable_rls_auto
@rlsColType = 'int',
@rlsColName = 'TenantId',
@applyToSchema = null,
@deactivateExistingPolicies = 1,
@rlsSchemaName = N'rls',
@rlsPredicateFunctionName = null,
@isNullAdmin = 0,
@isNullAdminOptimized = 0,
@restrictedToAppUserName = 'AppUser',
@printCommands = 1,
@runCommands = 0 -- set to 1 to execute output
go

Sample output:

CREATE FUNCTION [rls].[fn_predicate_TenantId_2015-03-30T17:36:51.010](@TenantId [int] )
RETURNS TABLE
WITH SCHEMABINDING
AS
RETURN SELECT 1 AS fn_accessResult
WHERE
DATABASE_PRINCIPAL_ID() = DATABASE_PRINCIPAL_ID ('AppUser')
AND CONVERT([int], CONVERT(varbinary(4), CONTEXT_INFO())) = @TenantId
go

CREATE SECURITY POLICY [rls].[secpol_TenantId_2015-03-30T17:36:51.073]
ADD FILTER PREDICATE [rls].[fn_predicate_TenantId_2015-03-30T17:36:51.010]([TenantId]) ON [dbo].[Sales],
ADD FILTER PREDICATE [rls].[fn_predicate_TenantId_2015-03-30T17:36:51.010]([TenantId]) ON [dbo].[Products],
ADD FILTER PREDICATE [rls].[fn_predicate_TenantId_2015-03-30T17:36:51.010]([TenantId]) ON [dbo].[PriceHistory],
ADD FILTER PREDICATE [rls].[fn_predicate_TenantId_2015-03-30T17:36:51.010]([TenantId]) ON [dbo].[OrderDetails]
go


Example 2: Custom predicate function

Generate a security policy that adds a custom predicate function as a filter predicate on all tables with a “TenantId” column of type “int.” 

CREATE FUNCTION rls.customTenantAccessPredicate(@TenantId int)
RETURNS TABLE
WITH SCHEMABINDING
AS
RETURN SELECT 1 AS accessResult WHERE
(
DATABASE_PRINCIPAL_ID() = DATABASE_PRINCIPAL_ID('AppUser') -- shared app user
AND CONVERT(int, CONVERT(varbinary(4), CONTEXT_INFO())) = @TenantId
)
OR
DATABASE_PRINCIPAL_ID() = DATABASE_PRINCIPAL_ID('ReportUser') -- reporting user can see all rows
go

EXEC sp_enable_rls_auto
@rlsColType = 'int',
@rlsColName = 'TenantId',
@applyToSchema = null,
@deactivateExistingPolicies = 1,
@rlsSchemaName = N'rls',
@rlsPredicateFunctionName = N'customTenantAccessPredicate',
@isNullAdmin = 0, -- n/a
@isNullAdminOptimized = 0, -- n/a
@restrictedToAppUserName = null, -- n/a
@printCommands = 1,
@runCommands = 0 -- set to 1 to execute output
go

Sample output:

CREATE SECURITY POLICY [rls].[secpol_TenantId_2015-03-30T18:22:14.213]
ADD FILTER PREDICATE [rls].[customTenantAccessPredicate]([TenantId]) ON [dbo].[Sales],
ADD FILTER PREDICATE [rls].[customTenantAccessPredicate]([TenantId]) ON [dbo].[Products],
ADD FILTER PREDICATE [rls].[customTenantAccessPredicate]([TenantId]) ON [dbo].[PriceHistory],
ADD FILTER PREDICATE [rls].[customTenantAccessPredicate]([TenantId]) ON [dbo].[OrderDetails]
go


Example 3: Optimized “superuser” if CONTEXT_INFO is null

Same as Example 1, but if CONTEXT_INFO is null, make all rows visible to the application and utilize the performance optimization for disjunctions described in Row-Level Security for Middle-Tier Apps – Using Disjunctions in the Predicate.

EXEC sp_enable_rls_auto
@rlsColType = 'int',
@rlsColName = 'TenantId',
@applyToSchema = null,
@deactivateExistingPolicies = 1,
@rlsSchemaName = N'rls',
@rlsPredicateFunctionName = null,
@isNullAdmin = 1,
@isNullAdminOptimized = 1,
@restrictedToAppUserName = 'AppUser',
@printCommands = 1,
@runCommands = 0 -- set to 1 to execute output
go

Sample output:

CREATE FUNCTION [rls].[int_lo_2015-03-30T18:30:46.993]() RETURNS [int]
WITH SCHEMABINDING
AS BEGIN
RETURN CASE WHEN context_info() is null THEN
-2147483648 ELSE
convert([int], convert(varbinary(4), context_info())) END
END
go

CREATE FUNCTION [rls].[int_hi_2015-03-30T18:30:46.993]() RETURNS [int]
WITH SCHEMABINDING
AS BEGIN
RETURN CASE WHEN context_info() is null THEN
2147483647 ELSE
convert([int], convert(varbinary(4), context_info())) END
END
go

CREATE FUNCTION [rls].[fn_predicate_TenantId_2015-03-30T18:30:46.993](@TenantId [int] )
RETURNS TABLE
WITH SCHEMABINDING
AS
RETURN SELECT 1 AS fn_accessResult
WHERE
DATABASE_PRINCIPAL_ID() = DATABASE_PRINCIPAL_ID ('AppUser') AND (
(@TenantId BETWEEN [rls].[int_lo_2015-03-30T18:30:46.993]() AND [rls].[int_hi_2015-03-30T18:30:46.993]())
go

CREATE SECURITY POLICY [rls].[secpol_TenantId_2015-03-30T18:30:47.047]
ADD FILTER PREDICATE [rls].[fn_predicate_TenantId_2015-03-30T18:30:46.993]([TenantId]) ON [dbo].[Sales],
ADD FILTER PREDICATE [rls].[fn_predicate_TenantId_2015-03-30T18:30:46.993]([TenantId]) ON [dbo].[Products],
ADD FILTER PREDICATE [rls].[fn_predicate_TenantId_2015-03-30T18:30:46.993]([TenantId]) ON [dbo].[PriceHistory],
ADD FILTER PREDICATE [rls].[fn_predicate_TenantId_2015-03-30T18:30:46.993]([TenantId]) ON [dbo].[OrderDetails]
go