New to Pg from MS SQL side where to restrict access simply grant EXE permission to Functions and SPs. So created a user/role, set its search_path to a dedicated schema of a database, grant EXECUTE ON ALL FUNCTIONS IN SCHEMA myschema. Tried execute a function got
permission denied for schema myschema
Ok, grant usage on schema myschema to role. The function does a select ... from mytable so now
permission denied for table mytable
To grant SELECT on my table? Wait, purpose of this function is to restrict the role from exploring tables.
Your situation is: User a owns a table mytable in a schema myschema. User b initially has no permissions on either. Now you want to allow b limited access to mytable. Granting SELECT on the table would be too much — you want to grant access only through a special function myfunction.
Then you need a function that does not run with the permissions of the caller (SECURITY INVOKER), which would be the default, but with the permissions of the function owner (SECURITY DEFINER). Then user a should run:
CREATE FUNCTION public.read_mytable(...) RETURNS ...
LANGUAGE ...
/* runs with the privileges of the owner */
SECURITY DEFINER
/* important: force "search_path" to a fixed order */
SET search_path = pg_catalog,pg_temp
AS $$...$$;
/* by default, everybody can execute a function */
REVOKE EXECUTE ON FUNCTION public.read_mytable FROM PUBLIC;
GRANT EXECUTE ON FUNCTION public.read_mytable TO b;
Note that I created the function in schema public, to which b has access (don't forget to REVOKE CREATE ON SCHEMA public FROM PUBLIC;!).
Setting a search_path for user b is not enough, since this can always be changed dynamically with the SET command. You don't want b to run a privilege escalation attack.
Related
I don't want to execute the stored procedure with admin privileges or with the instance owner. I am looking for the minimum permissions required to execute an undocumented stored procedure called SYSPROC.DB2LK_GENERATE_DDL for extracting the DDL statements from a DB2 database.
For example: I tried with SELECT and EXCEUTE permissions but it's not working:
db2 grant SELECT on SYSTOOLS.DB2LOOK_INFO to user devuser
db2 grant execute on procedure SYSPROC.DB2LK_GENERATE_DDL to user devuser`
You should call this routine once as some administrative user with appropriate privileges to create necessary objects implicitly in the database.
Grant the following privileges to your user afterwards.
grant usage on sequence SYSTOOLS.DB2LOOK_TOKEN to user myuser;
grant select on table SYSTOOLS.DB2LOOK_INFO_V to user myuser;
grant select, update, delete, insert on table SYSTOOLS.DB2LOOK_INFO to user myuser;
So I am having an issue that I wanted to clear up. I am granting access to a user in postgres, but I only want that user to be able to execute functions.
I have the following code:
GRANT USAGE ON SCHEMA not_public TO test_id;
GRANT USAGE ON SCHEMA public TO test_id;
GRANT EXECUTE ON FUNCTION testFunction TO web_reporting_id;
When this is ran, though, and I try to run the function under that user, I get a permissions error on the first table the function tries to read from.
I know some db languages you only need to grant permissions for the functions/procedures and not the underlying objects. In postgres, do I need to grant permissions on the tables too? Or do I need to update my grant scripts?
Thanks!
Normally, functions run with the privileges of the user calling them, so all SQL statements in them will be executed by that user.
You could define the function as SECURITY DEFINER to have it run with the privileges of the function owner, but then you must use the SET clause of CREATE FUNCTION to fix the search_path for the duration of the function execution for security reasons.
Also note that by default, everybody (PUBLIC) has execute privileges on functions, so you might want to revoke that.
I am experiencing a weird and (to me) inexplicable behaviour related to DEFAULT PRIVILEGES. It seems default privileges cannot be revoked just for a specific schema once they have been granted database-wide.
I am currently testing this with PostgreSQL 10.5 on CentOS.
Let's say there are 3 users:
admin Owner of the database. Used to manipulate the STRUCTURE of the database (CREATE, DROP, TRUNCATE...)
manager Used for DATA manipulation (INSERT, UPDATE, DELETE)
reader Used to read DATA (basically SELECT)
The idea is that:
admin will be the owner of the database and all the objects contained into it
manager will be used for data manipulation across all schemas but public (only user admin can modify data in public schema)
reader will be able to read everything.
To make things easier, this will rely on default privileges, so that newly created objects (schemas, tables, views, functions, etc.) will all have the correct permissions.
This is the first time I am trying something like that instead of a fine-grained permissions policy based on multiple users for all different schemas and apparently this setup should be very straightforward.
It turns out I am missing something.
Here is a simple test script. User admin is the owner of db database and all those commands are issued being connected to it as admin:
-- 1. User manager inherits from user "reader"
GRANT reader TO manager;
-- 2. Allow connections to the database to our users, but not PUBLIC
REVOKE ALL ON DATABASE db FROM PUBLIC;
GRANT CONNECT ON DATABASE db TO reader;
-- 3. Revoke default privileges from PUBLIC
ALTER DEFAULT PRIVILEGES REVOKE ALL ON SCHEMAS FROM PUBLIC;
ALTER DEFAULT PRIVILEGES REVOKE ALL ON TABLES FROM PUBLIC;
ALTER DEFAULT PRIVILEGES REVOKE ALL ON SEQUENCES FROM PUBLIC;
ALTER DEFAULT PRIVILEGES REVOKE ALL ON FUNCTIONS FROM PUBLIC;
-- 4. Grant default reading privileges to user "reader"
ALTER DEFAULT PRIVILEGES GRANT USAGE ON SCHEMAS TO reader;
ALTER DEFAULT PRIVILEGES GRANT SELECT ON TABLES TO reader;
ALTER DEFAULT PRIVILEGES GRANT SELECT ON SEQUENCES TO reader;
ALTER DEFAULT PRIVILEGES GRANT EXECUTE ON FUNCTIONS TO reader;
-- 5. Grant Defauly writing privileges to user "manager"
ALTER DEFAULT PRIVILEGES GRANT INSERT, UPDATE, DELETE ON TABLES TO manager;
ALTER DEFAULT PRIVILEGES GRANT USAGE ON SEQUENCES TO manager;
-- 6. Reinit "public" schema
DROP SCHEMA public;
CREATE SCHEMA public;
-- 7. HERE COMES THE WEIRD STUFF, the two following statements don't have any effect at all
ALTER DEFAULT PRIVILEGES IN SCHEMA public REVOKE INSERT, UPDATE, DELETE ON TABLES FROM manager;
ALTER DEFAULT PRIVILEGES IN SCHEMA public REVOKE USAGE ON SEQUENCES FROM manager;
This can be easily verified like that:
-- Execute as user "admin":
CREATE TABLE public.t (id serial PRIMARY KEY, dummy integer)
-- Execute as user "manager" (it should not be allowed, but it is!)
DELETE FROM public.t;
I know I could circumvent this using some trigger functions, but the point of the question is whether this is something normal and expected, some sort of bug or am I missing something?
I have been thinking about it and the most elegant solution I could come up with relies on an Event Trigger.
Of course it does not answer my question directly, meaning that I am still wondering why default privileges cannot be used like that, but at least this meets the initial requirement of set-and-forget that default privileges would have provided.
Create a function that revokes unwanted privileges and returns an event_trigger:
CREATE FUNCTION reset_privileges() RETURNS event_trigger AS $$
BEGIN
IF EXISTS (SELECT true FROM pg_event_trigger_ddl_commands() WHERE schema_name = 'public') THEN
REVOKE INSERT, UPDATE, DELETE ON ALL TABLES IN SCHEMA public FROM manager;
REVOKE USAGE ON ALL SEQUENCES IN SCHEMA public FROM manager;
END IF;
END;
$$ LANGUAGE plpgsql;
Create an actual EVENT TRIGGER (This requires superuser privileges!):
CREATE EVENT TRIGGER reset_public_schema_privileges
ON ddl_command_end WHEN TAG IN (
'CREATE TABLE',
'CREATE TABLE AS',
'CREATE VIEW',
'CREATE MATERIALIZED VIEW',
'CREATE FUNCTION'
) EXECUTE PROCEDURE reset_privileges();
The function checks whether the newly created object(s) are in the public schema and eventually revokes all the unwanted privileges from the user manager.
It does not even bother to filter those objects, but rather it revokes the privileges for ALL TABLEs, VIEWs and FUNCTIONs in the public schema. Of course it can be easily customised using the object_identity field provided by pg_event_trigger_ddl_commands and a more refined logic inside the function.
According to the manual for ALTER DEFAULT PRIVILEGES:
Default privileges that are specified per-schema are added to whatever the global default privileges are for the particular object type. This means you cannot revoke privileges per-schema if they are granted globally (either by default, or according to a previous ALTER DEFAULT PRIVILEGES command that did not specify a schema). Per-schema REVOKE is only useful to reverse the effects of a previous per-schema GRANT.
(This is even more explicit in the examples given on that manual page.)
So I think what is happening is that in step 5 of your script, you are setting the default privilege to grant DELETE on the tables of all schemas (as a global default):
ALTER DEFAULT PRIVILEGES GRANT INSERT, UPDATE, DELETE ON TABLES TO manager;
But in step 7 you are revoking from the public schema specifically. This revocation has no effect on the global grant, so the DELETE (and other) privileges will still be granted:
ALTER DEFAULT PRIVILEGES IN SCHEMA public REVOKE INSERT, UPDATE, DELETE ON TABLES FROM manager;
I think I would either (a) bite the bullet and add default privileges for each schema (which isn't "fire-and-forget" but is more explicit) or (b) challenge why I need the public schema to exist, aiming to remove it to simplify this situation.
I ran into a peculiar problem with my database that I haven't been able to solve since yesterday.
So I created a user that has access to the function "write_match_history()" and access to the table "match_history," and I can use this user to query match history as well as write to it directly using sql. However, when I try to run "write_match_history," I get the following error:
error: error: permission denied for relation match_history
Here are the accesses I've granted to this user:
drop OWNED by d_write;
drop user if exists d_write;
create user d_write with encrypted password 'supersecret';
grant execute on function write_match_history(a,b,c,d,e,f) to d_write;
grant usage on schema d to d_write;
grant insert on table d.match_history to d_write;
grant select on table d.match_history to d_write;
grant select on all SEQUENCES in SCHEME d to d_write;
grant insert on all tables in schema d to d_write;
grant select on all talbes in schema d to d_write;
These permissions are everything I've tried so far. Let me know if you need more information.
Thanks!
Well, what is the owner of the function write_match_history(a,b,c,d,e,f). Do it allow to insert/update on table match_history. If not, please try it. I think the problem is here.
I have been looking for this for years and I have tried everything on the web with no success.
I am able to do it in MSSQL, but I didn´t find a way to do it in PostgreSQL.
What I want to achieve is just create a role with login that cannot create, drop or alter databases, functions, tables or anything else. Just select specific functions.
For example, if I have a table called costumer and two functions called return_customers() and return_time() I just want a role with login that are able to select return_customers() and select return_time(). Nothing more than that.
Thank you very much for supporting this useful web site!
Execute this connected to the database you want to configure.
-- Create the user.
CREATE ROLE somebody WITH LOGIN PASSWORD '...';
-- Prevent all authenticated users from being able to use the database,
-- unless they have been explicitly granted permission.
REVOKE ALL PRIVILEGES ON DATABASE foo FROM PUBLIC;
REVOKE ALL PRIVILEGES ON ALL TABLES IN SCHEMA public FROM PUBLIC;
REVOKE ALL PRIVILEGES ON ALL FUNCTIONS IN SCHEMA public FROM PUBLIC;
REVOKE ALL PRIVILEGES ON ALL SEQUENCES IN SCHEMA public FROM PUBLIC;
-- Allow the user to only use the specified functions.
GRANT CONNECT ON DATABASE foo TO somebody;
GRANT EXECUTE ON FUNCTION return_customers(), return_time() TO somebody;
If you have more schemas than "public" then you will need to add those to the two REVOKE ALL PRIVILEGES ON ALL ... statements.
Do not forget that the functions must have been created with SECURITY DEFINER or this user will still be unable to execute them, as the contents of the function will be executed with the permissions of this user, instead of the user who created the function.
See:
CREATE FUNCTION particularly SECURITY DEFINER
GRANT both for adding users to roles and for assigning access rights to tables, sequences, etc
REVOKE
CREATE ROLE