Thread: Grant read-only access to exactly one database amongst many

Hi all,

I have a postgresql 15 instance with two databases in it, and I have a need to grant read-only access to one of those
databasesto a given user. 

To do this I created a dedicated role for readonly access to the database db1:

CREATE ROLE "dv_read_db1"
GRANT CONNECT ON DATABASE db1 TO dv_read_db1
GRANT USAGE ON SCHEMA public TO “dv_read_db1"
GRANT SELECT ON ALL TABLES IN SCHEMA public TO “dv_read_db1"
ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO “dv_read_db1"

CREATE USER minfrin LOGIN;
GRANT dv_read_db1 TO minfrin;

On the surface this works, I get readonly access to db1.

Trouble is, I can create tables in db1 which is write access. I can also connect to db2 (bad), and I can enumerate the
tablesin db2 (bad), although the queries of the contents say access is denied. 

I appears the mechanism I am using above has insecure side effects.

What is the way to grant read only access to a single database, without exposing other databases, and being futureproof
againstfuture features offering potential write access to a read only user? 

Regards,
Graham
—

Graham Leggett <minfrin@sharp.fm> writes:
> Trouble is, I can create tables in db1 which is write access. I can also connect to db2 (bad), and I can enumerate
thetables in db2 (bad), although the queries of the contents say access is denied. 

You need to read the docs about default privileges: see about
halfway down

https://www.postgresql.org/docs/15/ddl-priv.html

where it says "PostgreSQL grants privileges on some types of objects
to PUBLIC by default ...".  In this case I think you likely need to
revoke the default public CREATE privilege on schema public in db1,
and revoke the default public CONNECT privilege on database db2.

            regards, tom lane

Also, how do you handle the race condition between the time a database db3 is created, and the the time all readonly users have their access revoked to db3?