Postgresql – Reg: Default Privileges on PostgreSQL Schemas

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I have a situation where many users can create database objects across all the available schema.

There is a generic user pg_dump_user used for by all the developers to dump the whole database to their local db whenever required. So this user should have read access to all the database objects.

To achieve this, I have tried setting the default privilege at schema level as well as at the user level.

–Default privileges set for each schema

ALTER DEFAULT PRIVILEGES IN SCHEMA xyz GRANT SELECT ON TABLES to ro_user';

–Default privileges set for each user 

ALTER DEFAULT PRIVILEGES FOR ROLE abc_user GRANT SELECT ON TABLES to ro_user' ;

Even though above setup is there, after certain times these are getting vanished as the new objects created are not accessible by ro_user.

Any pointer on this would help, my aim is just to achieve select access for all the objects current and future for a user so as to do pg_dump.

Best Answer

The documentation about ALTER DEFAULT PRIVILEGES tells you a possible reason - it is not that clearly described, though.

Let's see, what is said:

You can change default privileges only for objects that will be created by yourself or by roles that you are a member of.

This means that the default privileges defined by this statement applies only to objects that are created by you (or the role you are a member of). Let's see this in action!

alice's schema

First, we are logged in as alice. Then, in a newly created schema, we create a table and grant some rights to bob:

SELECT current_user;
 current_user 
──────────────
 alice


SHOW search_path ;
 search_path  
──────────────
 test, public

CREATE SCHEMA alicetest;

ALTER DEFAULT PRIVILEGES 
    FOR ROLE alice 
    IN SCHEMA alicetest 
    GRANT ALL ON TABLES TO alice;

GRANT SELECT ON alicetest.a TO bob; 
-- this I do only for showing the privileges - 
-- the owner has by default ALL and is not shown by \dp

\dp alicetest.a
                             Access privileges
  Schema   │ Name │ Type  │  Access privileges  │ Column access privileges 
───────────┼──────┼───────┼─────────────────────┼──────────────────────────
 alicetest │ a    │ table │ alice=arwdDxt/alice↵│ 
           │      │       │ bob=r/alice         │

alice now has all rights on her table, as expected.

bob' table in the same schema

Now, after obtaining access to this schema, bob tries to create a table:

SELECT current_user;
 current_user 
──────────────
 bob

CREATE TABLE alicetest.b (id integer);

GRANT SELECT ON alicetest.b TO alice;

\dp alicetest.b
                            Access privileges
  Schema   │ Name │ Type  │ Access privileges │ Column access privileges 
───────────┼──────┼───────┼───────────────────┼──────────────────────────
 alicetest │ b    │ table │ bob=arwdDxt/bob  ↵│ 
           │      │       │ alice=r/bob       │

As you can see, despite creating the table in alice's schema where she set the default privileges, bob's table doesn't have all those permissions. This happens because alice is not a member of bob.

Let's check this membership thing, too, and try to define default privileges by alice again, this time for another role:

ALTER DEFAULT PRIVILEGES 
    FOR ROLE charlie 
    IN SCHEMA alicetest 
    GRANT ALL ON TABLES TO alice;
ERROR:  must be member of role "charlie"

So, some mighty enough user grants her a membership in charlie, then she tries again, with success:

ALTER DEFAULT PRIVILEGES 
    FOR ROLE charlie 
    IN SCHEMA alicetest 
    GRANT ALL ON TABLES TO alice;
ALTER DEFAULT PRIVILEGES

charlie's round

Then charlie creates a new table:

CREATE TABLE alicetest.c (id integer);

And the privileges:

\dp alicetest.c
                               Access privileges
  Schema   │ Name │ Type  │    Access privileges    │ Column access privileges 
───────────┼──────┼───────┼─────────────────────────┼──────────────────────────
 alicetest │ c    │ table │ charlie=arwdDxt/charlie↵│ 
           │      │       │ alice=arwdDxt/charlie   │

As you see, alice, as a member of charlie, gets her access to this table.

To answer your question,

I guess you defined the default privileges for yourself (alice in the example), but you developers act as a bunch of bobs here, not getting the necessary privileges. One way to get around this (as we do it at work) is to do a 

SET ROLE TO schema_owner;

every time before creating a new object in the schema. This should be a role that all developers are a member of (otherwise you'd get an error).

NOTE that \dp is a psql command.

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