Refuse auth attempts for progressively longer periods on failed attempts up to a maximum of 10mins

src/stratifier.c

@@ -185,6 +185,8 @@ struct user_instance {
 
 	bool authorised; /* Has this username ever been authorised? */
 	time_t auth_time;
+	time_t failed_authtime; /* Last time this username failed to authorise */
+	int auth_backoff; /* How long to reject any auth attempts since last failure */
 };
 
 /* Combined data from workers with the same workername */
@@ -2165,6 +2167,7 @@ static user_instance_t *generate_user(ckpool_t *ckp, stratum_instance_t *client,
 	if (!user) {
 		/* New user instance. Secondary user id will be NULL */
 		user = ckzalloc(sizeof(user_instance_t));
+		user->auth_backoff = 3; /* Set initial backoff to 3 seconds */
 		strcpy(user->username, username);
 		new_instance = true;
 		user->id = sdata->user_instance_id++;
@@ -2385,8 +2388,17 @@ static json_t *parse_authorise(stratum_instance_t *client, json_t *params_val, j
 	ts_realtime(&now);
 	client->start_time = now.tv_sec;
 	strcpy(client->address, address);
-
 	client->workername = strdup(buf);
+	if (user_instance->failed_authtime) {
+		time_t now_t = time(NULL);
+
+		if (now_t < user_instance->failed_authtime + user_instance->auth_backoff) {
+			LOGNOTICE("Client %ld worker %s rate limited due to failed auth attempts",
+				  client->id, buf);
+			client->dropped = true;
+			goto out;
+		}
+	}
 	if (CKP_STANDALONE(ckp))
 		ret = true;
 	else {
@@ -2413,9 +2425,15 @@ static json_t *parse_authorise(stratum_instance_t *client, json_t *params_val, j
 		inc_worker(ckp, user_instance);
 		LOGNOTICE("Authorised client %ld worker %s as user %s", client->id, buf,
 			  user_instance->username);
+		user_instance->auth_backoff = 3; /* Reset auth backoff time */
 	} else {
 		LOGNOTICE("Client %ld worker %s failed to authorise as user %s", client->id, buf,
 			  user_instance->username);
+		user_instance->failed_authtime = time(NULL);
+		user_instance->auth_backoff <<= 1;
+		/* Cap backoff time to 10 mins */
+		if (user_instance->auth_backoff > 600)
+			user_instance->auth_backoff = 600;
 	}
 out:
 	return json_boolean(ret);