I am deploying a database in postgreSQL and I created a user that just will be able to execute certain functions.
I revoked all privileges from the user i just created and granted connect privileges executing:
REVOKE ALL PRIVILEGES ON DATABASE <database> FROM my_user;
REVOKE ALL PRIVILEGES ON SCHEMA public TO my_user;
GRANT CONNECT ON DATABASE <database> TO my_user;
But when i connect to the database with this user, i am able to read all table structures and all function source codes. Is there a way to hide it from this user?
I take the chance to make another question: I want to just execute functions (which may include select, insert or update on database tables) with this user, but I don't want to grant privileges on select, update or delete on tables.
I am using "SECURITY DEFINER" and then I grant execution, but I think it may be a little insecure. Am I right? is there any other way to do it?
Thanks in Advance.
Lamis
There's no way to hide the system catalogues from a user in PostgreSQL. If a user can't access the catalogues then they can't locate any other database objects.
If you really can't afford to let them see the structure of the db, you'll need to prevent them connecting. Build some sort of middle layer with a simple API that calls the db.
SECURITY DEFINER is the standard way to provide limited access at a higher privilege level. You have to be careful with any function arguments that can end up in a dynamic query though. That's the same "bobby tables" issue as with any dynamic sql building though.
How about
REVOKE SELECT ON pg_namespace FROM my_user;
REVOKE SELECT ON pg_catalog.pg_database FROM my_user;
You won't be able to see anything, but you'll be able to make queries if you know the namespace and table name.
Related
Goal
Create a database with three users and restrict their privileges (I'm just thinking out loud, so my user separation is also open to correction):
Superuser - this user allows for the very initial provisioning of the database. Create the application database, create the other users, set their privileges. Default postgres superuser works for me, so this one is done.
Administrator - this user has access only to the database that was created during provisioning. Administrator can CRUD all data in all tables, and can also CRUD tables, etc. "Superuser for only this database" type of situation. When the application is being updated, the administrator is the user used by automated tooling to handle database migrations.
App user - this user is ultimately the one who supports the web app's functionality. Note this has nothing to do with users on web pages etc - this is the user the server leverages to run queries, insert and remove data. I explicitly do not want this user to be able to modify permissions of anything, nor create/destroy tables or indices or anything structural.
What I've tried
First off, looking at the (generally excellent) PostgreSQL documentation, the page on Grant pretty much leaves me cross-eyed. After spending a few hours reading about PostgreSQL roles and privileges I'm generally confused. I think with a bit more work I'll be able to nail down what I want for the admin user, but I'm pretty stuck on the "app user". I've gotten about this far (naming and passwords are all just placeholders):
$ psql -U postgres
postgres=# CREATE USER "app-admin" WITH PASSWORD 'password';
CREATE ROLE
postgres=# CREATE USER "app-user" WITH PASSWORD 'password';
CREATE ROLE
postgres=# CREATE DATABASE "test-database" WITH OWNER "app-admin";
CREATE DATABASE
postgres=# \c "test-database"
You are now connected to database "test-database" as user "postgres".
test-database=# DROP SCHEMA "public";
DROP SCHEMA
test-database=# CREATE SCHEMA "app" AUTHORIZATION "app-admin";
CREATE SCHEMA
And here's where I get unsure. I feel like the answer I'm trying to avoid is "revoke everything by default then enumerate all the privileges you'll need at all the different levels on all the different objects". I'm trying to avoid that because I straight up don't know what I need there. If that ends up being the answer, then I'll just have to hunker down and read a bunch more, but generally when I start going down paths like that I've missed something.
Issues
How do I restrict privileges for app-user so they are unable to modify any structural data (e.g. cannot add or destroy tables) but are able to connect and do anything with rows (row level security is not even on my radar). Is this general model of privileges not really in sync with what PostgreSQL expects? I feel like I'm missing something if I have to walk through every option on that "grant" page to accomplish something like this - whether it be my motivation for doing it in the first place or the means by which I'm going about it.
Context
I'm trying to build my first end-to-end web application. I've done enough general software development and web app development, now I'm trying to understand the pieces that I generally take for granted day to day. I'm trying to set up a PostgreSQL server while keeping the principle of least privilege in mind.
Side-quest
I haven't seen this done on web apps where I have simply joined the development team, although they're generally small and not heavily used. Does doing this actually accomplish anything? Does anyone have compelling reasons for why to do something like this, or why it's a bad or ineffective idea? My assumption was that if I ultimately ended up with a SQL injection vulnerability, this would mitigate the damage because the database user would have limited access. Is that misguided?
Neat articles I've found on the subject:
http://www.ibm.com/developerworks/opensource/library/os-postgresecurity/index.html
PDF WARNING: https://wiki.postgresql.org/images/d/d1/Managing_rights_in_postgresql.pdf
https://www.digitalocean.com/community/tutorials/how-to-use-roles-and-manage-grant-permissions-in-postgresql-on-a-vps--2
http://blog.2ndquadrant.com/auditing-users-and-roles-in-postgresql/
I'll answer your “side-quest” question first:
you are completely right with your worries and concerns, and everybody who designs an application should think about the same things. Everything else is sloppy and careless.
To mitigate the damage that can be caused by a successful SQL injection attack, you should definitely employ the principle of least privilege.
It should be quite simple to set up a system that matches your requirements.
I'll use the object names from your exaple, except that I'll use underscores instead of minuses. It is good practive to use only lower case letters, underscores and numbers in object names, since it will make your life easier.
/* create the database */
\c postgres postgres
CREATE DATABASE test_database WITH OWNER app_admin;
\c test_database postgres
/* drop public schema; other, less invasive option is to
REVOKE ALL ON SCHEMA public FROM PUBLIC */
DROP SCHEMA public;
/* create an application schema */
CREATE SCHEMA app AUTHORIZATION app_admin;
/* further operations won't need superuser access */
\c test_database app_admin
/* allow app_user to access, but not create objects in the schema */
GRANT USAGE ON SCHEMA app TO app_user;
/* PUBLIC should not be allowed to execute functions created by app_admin */
ALTER DEFAULT PRIVILEGES FOR ROLE app_admin
REVOKE EXECUTE ON FUNCTIONS FROM PUBLIC;
/* assuming that app_user should be allowed to do anything
with data in all tables in that schema, allow access for all
objects that app_admin will create there */
ALTER DEFAULT PRIVILEGES FOR ROLE app_admin IN SCHEMA app
GRANT SELECT, INSERT, UPDATE, DELETE ON TABLES TO app_user;
ALTER DEFAULT PRIVILEGES FOR ROLE app_admin IN SCHEMA app
GRANT SELECT, USAGE ON SEQUENCES TO app_user;
ALTER DEFAULT PRIVILEGES FOR ROLE app_admin IN SCHEMA app
GRANT EXECUTE ON FUNCTIONS TO app_user;
But if you take the principle of least seriously, you should grant table permissions individually and e.g. not allow app_user to DELETE and UPDATE data in tables where there is no need for the user to do so.
For Web Applications, I split the permissions into three roles, where each role inherits from its predecessor.
Read Only - Used for SELECT queries and function calls
Insert - Used for INSERT statements
Update and Delete - These are used mostly for Administration, as the public facing front-end application does not usually modify or deletes data
That way, even if some hacker manages to do SQL Injection he is limited to the permissions of the role that is used, usually only SELECT or INSERT.
My web applications usually do not need the more intrusive permissions like CREATE, DROP, TRUNCATE, etc., so I don't GRANT those permissions to web apps.
In the rare instances where the the second role needs to update or delete something, I either give it permission for that specific table, or put the code in a function that is created with SECURITY DEFINER.
/** role_read is read-only with SELECT and EXECUTE */
CREATE ROLE role_read;
/** role_read_add adds INSERT */
CREATE ROLE role_read_add;
/** role_read_add_modify adds UPDATE and DELETE */
CREATE ROLE role_read_add_modify;
GRANT USAGE ON SCHEMA <schema> TO role_read;
/** for existing objects */
GRANT SELECT ON ALL TABLES IN SCHEMA <schema> TO role_read;
GRANT SELECT ON ALL SEQUENCES IN SCHEMA <schema> TO role_read;
GRANT EXECUTE ON ALL FUNCTIONS IN SCHEMA <schema> TO role_read;
/** for future objects */
ALTER DEFAULT PRIVILEGES IN SCHEMA <schema>
GRANT SELECT ON TABLES TO role_read;
ALTER DEFAULT PRIVILEGES IN SCHEMA <schema>
GRANT SELECT ON SEQUENCES TO role_read;
/** role_read_add inherits from role_read */
GRANT role_read TO role_read_add;
/** for existing objects */
GRANT INSERT ON ALL TABLES IN SCHEMA <schema> TO role_read_add;
GRANT ALL ON ALL SEQUENCES IN SCHEMA <schema> TO role_read;
/** for future objects */
ALTER DEFAULT PRIVILEGES IN SCHEMA <schema>
GRANT INSERT ON TABLES TO role_read_add;
ALTER DEFAULT PRIVILEGES IN SCHEMA <schema>
GRANT ALL ON SEQUENCES TO role_read_add;
/** role_read_add_modify inherits from role_read_add */
GRANT role_read_add TO role_read_add_modify;
/** for existing objects */
GRANT UPDATE, DELETE ON ALL TABLES IN SCHEMA <schema>
TO role_read_add_modify;
/** for future objects */
ALTER DEFAULT PRIVILEGES IN SCHEMA <schema>
GRANT UPDATE, DELETE ON TABLES TO role_read_add_modify;
I am learning oracle and PL/SQL. I have created a database called "PRACTICE" and created a user called "MITHRA" by connecting as a SYS.
My question is i want to grant privileges to the user "MITHRA" for the specific database "PRACTICE". The user "MITHRA" can able to do all activities like create, drop, alter etc.. only in "PRACTICE" database.
Please suggest me how to do this.
Oracle can only host one database so what you are asking for will essentially grant root privileges to this user, including drop database. This should be avoided on production from obvious reasons.
So in order to grant full access to user mithra:
Connect as sys and run the following command -
Grant dba to mithra;
That should give the user mithra all possible privileges for that database.
You can also use the grant command the grant any distinct privileges.
Just to be sure that we speak in the same terms.
Is the "PRACTICE" database or schema? If it is DATABASE then you should grant DBA, if it is schema then Oracle does not have statements to grant rights to schemas (only system and object priveleges). Reading your question makes me think that you come from MSSQL where you can grant to a specific user gratns to specific database, in Oracle it is a little bit different - to make an analogy - you do not have databases but schemas.
What is the best way to prevent changes to a database or verify the integrity of this, so that it can not be altered from an application created for this database.
assuming you have a username and password to access the database permits reading - writing.
requirements:
The user has write permissions
Do not depend on a particular system like (MySQL, Oracle, SQL Server)
solution I'm looking for is not based on the user's permissions on the database
Most modern databases allow you to grant reading and writing permissions but while disallowing DDL commands like ALTER TABLE.
Do not give users that should not alter the DB structure permission to execute DDL.
If by "Alter" you mean change any data rows, rather than the database structure, you can grant the user only SELECT rights.
The user or account that your application uses must be granted permissions from the database server. Typically permissions include things like:
Select
Insert
Update
Delete
Alter
Drop
Only give the user account the permissions needed; in other words, don't grant Alter permission, and the application (or anyone using the same login) won't be able to alter tables.
Two strategies: 1) if you are running SQL Server, Oracle, DB2, etc, you can configure permissions so users are reader/writer by default (which means no alter permissions). 2) you can periodically check to see if someone has changed the data structure or even set up a DB trigger to detect changes and record who/when, etc (depends on your DB platform)
Please advice how to restrict user access to mssql: just connect and execute only specific list of functions or stored procedures. The problem is that default 'public' role is giving more rights than needed - list databases, get user list etc.
How to close as much as possile (deny all) and after that open only what is allowed?
Real situation is the following: partner site asked not to get data through xml webservice but have direct connection to mssql and I am going to make a table function for them or stored procedure with parameters, but want to hide everything what is going on inside server.
Thanks.
You can deny them permissions they will not need. For instance, you can DENY VIEW ANY DATABASE so that they cannot see other databases on the server. There are lots of options available through the DENY facility (so many that they have separate pages for those that apply at the server level, and those that apply at the database level).
Just:
DENY VIEW ANY DATABASE to <user> --Run in master
and
DENY VIEW DEFINTION to <user> -- run in the database you've given them connect permission
should be sufficient that they cannot see anything, or select from any tables. Then you just need to explicitly grant them the permissions you want them to have.
I am using LinqToSQL and a trusted connection to handle database selects/updates/inserts/deletes. In the past I have always used stored procedures and only granted execute permission to the Application Pool identity for the particular sproc in the database. This is my first LinqToSql project (and I really love how much it helps). I would prefer not to grant dbo access to the application pool identity to get LinqToSql to work (but if that is recommended then I don't mind). What type of permissions can I grant to the Application Pool identity so that LinqToSql will have the minimum permissions? Or should I just go with dbo permissions and be done with it?
As per KristoferA's answer this is the permissions I granted the application pool identity in the database:
EXEC sp_addrolemember 'db_datareader', 'app_pool_identity'
EXEC sp_addrolemember 'db_datawriter', 'app_pool_identity'
Not exactly the same level of security as only granting execute permissions to the necessary sprocs but I am very good with it considering the huge development gains I have achieved just by using Linq2SQL. And it is better than granting the full dbo access.
db_datareader and db_datawriter is enough if you just want to read and write data without messing around with schema changes and stuff...
LinqToSQL creates dynamically generated SQL. As such, it needs full access to the data manipulation language commands (insert, update, delete). Your application account should not need access to data definition language commands (create, drop, alter, etc.).