SQL xp_create_subdir for non-admin - sql-server

Question

I'd like to give a non-admin the ability to create folders on the SQL server's local hard disk using xp_create_subdir. Reason - need to create a folder structure so that manufacturing equipment can FTP large files. Meta data for the files is stored in SQL.
Server is SQL 2016 Express. OS is Windows 10 Pro.
I've found lots of explanations of how to get this to work but can't figure out what I'm missing. Using the SA account I've created a stored procedure like this:
use [DBname]
CREATE PROCEDURE dbo.usp_CreateDirectory
#directoryFullPath varchar(500)
WITH EXECUTE AS owner
AS
BEGIN
SET NOCOUNT ON;
EXEC master.dbo.xp_create_subdir #directoryFullPath;
END
GO
GRANT EXECUTE ON dbo.usp_CreateDirectory TO [TestUser]
GO
Code to run the stored procedure:
DECLARE #RC int
DECLARE #directoryFullPath varchar(500)
set #directoryFullPath = 'd:\FTP_Root\2020\08\22\'
EXECUTE #RC = dbo.usp_CreateDirectory
#directoryFullPath
GO
In Windows I've given NT Service\MSSQL${InstanceName} full access to d:\FTP_Root\
What am I missing? Running xp_create_subdir 'C:\FTP_Root\2020\08\22' in MSSMS works fine.
Running the stored procedure as SA or the non-admin TestUser gives this result:
Msg 229, Level 14, State 5, Procedure xp_create_subdir, Line 1 [Batch
Start Line 2] The EXECUTE permission was denied on the object
'xp_create_subdir', database 'mssqlsystemresource', schema 'sys'.

Answer 1

I found this on another site: https://www.sqlservercentral.com/forums/topic/xp_create_subdir-for-non-sysadmins
The headlines here are two main points
Although this post is old,
In order to solve this issue, you should make sure that your database is Trustworthy - since the SP xp_create_subdir is on different DB
You still need to set "with Execute as 'dbo'
alter database [DBNAME] set trustworthy on
- Guy-456224
And DO understand the security ramifications of using SET TRUSTWORTHY ON. It may not be a problem or... it may. "It Depends" but you won't know until you read about it.
- Jeff Moden
I completely agree with Jeff on this one. If you remotely care about security, understand what the TRUSTWORTHY setting does before adjusting it.
I think the larger question here is to ask why SQL Server needs to create the directory? Powershell could both query the database for the Directory Path and create the Directory. You could have a SQL Server Agent job that will execute this under the security context of either a SQL Server Proxy account, or the SQL Agent service account (I would pick the proxy account personally, but that's just me).