Backport: Ban role pg_signal_backend from more superuser backend types.

src/backend/storage/ipc/signalfuncs.c

@@ -52,7 +52,6 @@ static int
 pg_signal_backend(int pid, int sig, char *msg)
 {
 	PGPROC	   *proc = BackendPidGetProc(pid);
-	LocalPgBackendStatus *local_beentry;
 
 	/*
 	 * BackendPidGetProc returns NULL if the pid isn't valid; but by the time
@@ -73,34 +72,14 @@ pg_signal_backend(int pid, int sig, char *msg)
 		return SIGNAL_BACKEND_ERROR;
 	}
 
-	local_beentry = pgstat_fetch_stat_local_beentry_by_pid(pid);
-
-	/* Only allow superusers to signal superuser-owned backends. */
-	if (superuser_arg(proc->roleId) && !superuser())
-	{
-		Oid role;
-		char * appname;
-
-		if (local_beentry == NULL) {
-			return SIGNAL_BACKEND_NOSUPERUSER;
-		}
-
-		role = get_role_oid("mdb_admin", true /*if nodoby created mdb_admin role in this database*/);
-		appname = local_beentry->backendStatus.st_appname;
-
-		// only allow mdb_admin to kill su queries
-		if (!is_member_of_role(GetUserId(), role)) {
-			return SIGNAL_BACKEND_NOSUPERUSER;
-		}
-
-		if (local_beentry->backendStatus.st_backendType == B_AUTOVAC_WORKER) {
-			// ok
-		} else if (appname != NULL && strcmp(appname, "MDB") == 0) {
-			// ok
-		} else {
-			return SIGNAL_BACKEND_NOSUPERUSER;
-		}
-	}
+	/*
+	 * 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. */
 	if (!has_privs_of_role(GetUserId(), proc->roleId) &&

src/test/regress/expected/privileges.out

@@ -1986,6 +1986,24 @@ TABLE information_schema.enabled_roles;
 
 INSERT INTO datdba_only DEFAULT VALUES;
 ERROR:  permission denied for table datdba_only
+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;
+ backend_type 
+--------------
+(0 rows)
+
 ROLLBACK;
 -- test default ACLs
 \c -

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 -