Backport: Ban role pg_signal_backend from more superuser backend types.

src/backend/storage/ipc/signalfuncs.c

@@ -72,8 +72,13 @@ pg_signal_backend(int pid, int sig, char *msg)
 		return SIGNAL_BACKEND_ERROR;
 	}
 
-	/* Only allow superusers to signal superuser-owned backends. */
-	if (superuser_arg(proc->roleId) && !superuser())
+	/*
+	 * Only allow superusers to signal superuser-owned backends.  Any process
+	 * not advertising a role might have the importance of a superuser-owned
+	 * backend, so treat it that way.
+	 */
+	if ((!OidIsValid(proc->roleId) || superuser_arg(proc->roleId)) &&
+		!superuser())
 		return SIGNAL_BACKEND_NOSUPERUSER;
 
 	/* Users can signal backends they have role membership in. */

src/test/regress/expected/privileges.out

@@ -1926,6 +1926,24 @@ SELECT * FROM pg_largeobject LIMIT 0;
 SET SESSION AUTHORIZATION regress_priv_user1;
 SELECT * FROM pg_largeobject LIMIT 0;			-- to be denied
 ERROR:  permission denied for table pg_largeobject
+-- pg_signal_backend can't signal superusers
+RESET SESSION AUTHORIZATION;
+BEGIN;
+CREATE OR REPLACE FUNCTION terminate_nothrow(pid int) RETURNS bool
+	LANGUAGE plpgsql SECURITY DEFINER SET client_min_messages = error AS $$
+BEGIN
+	RETURN pg_terminate_backend($1);
+EXCEPTION WHEN OTHERS THEN
+	RETURN false;
+END$$;
+ALTER FUNCTION terminate_nothrow OWNER TO pg_signal_backend;
+SELECT backend_type FROM pg_stat_activity
+WHERE CASE WHEN COALESCE(usesysid, 10) = 10 THEN terminate_nothrow(pid) END;
+ backend_type 
+--------------
+(0 rows)
+
+ROLLBACK;
 -- test pg_database_owner
 RESET SESSION AUTHORIZATION;
 GRANT pg_database_owner TO regress_priv_user1;

src/test/regress/sql/privileges.sql

@@ -1208,6 +1208,21 @@ TABLE information_schema.enabled_roles;
 INSERT INTO datdba_only DEFAULT VALUES;
 ROLLBACK;
 
+-- pg_signal_backend can't signal superusers
+RESET SESSION AUTHORIZATION;
+BEGIN;
+CREATE OR REPLACE FUNCTION terminate_nothrow(pid int) RETURNS bool
+	LANGUAGE plpgsql SECURITY DEFINER SET client_min_messages = error AS $$
+BEGIN
+	RETURN pg_terminate_backend($1);
+EXCEPTION WHEN OTHERS THEN
+	RETURN false;
+END$$;
+ALTER FUNCTION terminate_nothrow OWNER TO pg_signal_backend;
+SELECT backend_type FROM pg_stat_activity
+WHERE CASE WHEN COALESCE(usesysid, 10) = 10 THEN terminate_nothrow(pid) END;
+ROLLBACK;
+
 -- test default ACLs
 \c -