fix: prevent non-superuser roles from dropping supabase_privileged_role (#2150)

Add supabase_privileged_role to supautils.reserved_roles so non-superusers
with CREATEROLE cannot drop it on PG 15, where PG's native ADMIN OPTION
check (introduced in PG 16) does not apply.

PG 16+ requires ADMIN OPTION to drop a non-superuser role:
https://github.com/postgres/postgres/blame/REL_16_STABLE/src/backend/commands/user.c#L1175

This check is absent in PG 15:
https://github.com/postgres/postgres/blob/REL_15_STABLE/src/backend/commands/user.c#L986

Fixes: https://linear.app/supabase/issue/PSQL-1205

Author: utkarash2991

ansible/files/postgresql_config/supautils.conf.j2

@@ -12,5 +12,5 @@ supautils.privileged_extensions_superuser = 'supabase_admin'
 supautils.privileged_role = 'supabase_privileged_role'
 supautils.privileged_role_allowed_configs = 'auto_explain.*, deadlock_timeout, log_lock_waits, log_min_duration_statement, log_min_messages, log_parameter_max_length, log_replication_commands, log_statement, log_temp_files, pg_net.batch_size, pg_net.ttl, pg_stat_statements.*, pgaudit.log, pgaudit.log_catalog, pgaudit.log_client, pgaudit.log_level, pgaudit.log_relation, pgaudit.log_rows, pgaudit.log_statement, pgaudit.log_statement_once, pgaudit.role, pgrst.*, plan_filter.*, safeupdate.enabled, session_replication_role, track_functions, track_io_timing, wal_compression'
 supautils.reserved_memberships = 'pg_read_server_files, pg_write_server_files, pg_execute_server_program, supabase_admin, supabase_auth_admin, supabase_storage_admin, supabase_read_only_user, supabase_realtime_admin, supabase_replication_admin, supabase_etl_admin, dashboard_user, pgbouncer, authenticator'
-supautils.reserved_roles = 'supabase_admin, supabase_auth_admin, supabase_storage_admin, supabase_read_only_user, supabase_realtime_admin, supabase_replication_admin, supabase_etl_admin, dashboard_user, pgbouncer, service_role*, authenticator*, authenticated*, anon*'
+supautils.reserved_roles = 'supabase_admin, supabase_auth_admin, supabase_storage_admin, supabase_read_only_user, supabase_realtime_admin, supabase_replication_admin, supabase_etl_admin, dashboard_user, pgbouncer, service_role*, authenticator*, authenticated*, anon*, supabase_privileged_role'
 supautils.hint_roles = 'anon, authenticated, service_role'

nix/tests/expected/supautils_reserved_roles.out

@@ -0,0 +1,17 @@
+-- verify non-superuser postgres role cannot drop supabase_privileged_role
+BEGIN;
+-- Switch to the postgres role (non-superuser) to test supautils behavior
+SET ROLE postgres;
+-- SAVEPOINT is needed to recover from the expected error and continue the transaction
+SAVEPOINT before_drop;
+DROP ROLE supabase_privileged_role;
+ERROR:  "supabase_privileged_role" is a reserved role, only superusers can modify it
+ROLLBACK TO SAVEPOINT before_drop;
+RESET ROLE;
+SELECT rolname FROM pg_roles WHERE rolname = 'supabase_privileged_role';
+         rolname          
+--------------------------
+ supabase_privileged_role
+(1 row)
+
+ROLLBACK;

nix/tests/sql/supautils_reserved_roles.sql

@@ -0,0 +1,16 @@
+-- verify non-superuser postgres role cannot drop supabase_privileged_role
+BEGIN;
+
+-- Switch to the postgres role (non-superuser) to test supautils behavior
+SET ROLE postgres;
+
+-- SAVEPOINT is needed to recover from the expected error and continue the transaction
+SAVEPOINT before_drop;
+DROP ROLE supabase_privileged_role;
+ROLLBACK TO SAVEPOINT before_drop;
+
+RESET ROLE;
+
+SELECT rolname FROM pg_roles WHERE rolname = 'supabase_privileged_role';
+
+ROLLBACK;