Fix zero-count divide overflow bug in RateLimiterController (#461)

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/controller/RateLimiterController.java

@@ -44,6 +44,21 @@ public class RateLimiterController implements TrafficShapingController {
 
     @Override
     public boolean canPass(Node node, int acquireCount, boolean prioritized) {
+        /*
+            1. Pass when acquire count is less or equal than 0
+            2. Reject when count is less or equal than 0.
+               Otherwise,the costTime will be max of long and waitTime will overflow in some cases.
+               This will lead to pass of following request.It's dangerous!!!
+         */
+
+        if (acquireCount <= 0) {
+            return true;
+        }
+
+        if (count <= 0) {
+            return false;
+        }
+
         long currentTime = TimeUtil.currentTimeMillis();
         // Calculate the interval between every two requests.
         long costTime = Math.round(1.0 * (acquireCount) / count * 1000);

sentinel-core/src/test/java/com/alibaba/csp/sentinel/slots/block/flow/controller/RateLimiterControllerTest.java

@@ -15,6 +15,7 @@
  */
 package com.alibaba.csp.sentinel.slots.block.flow.controller;
 
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Mockito.mock;
 
@@ -25,7 +26,6 @@ import org.junit.Test;
 
 import com.alibaba.csp.sentinel.util.TimeUtil;
 import com.alibaba.csp.sentinel.node.Node;
-import com.alibaba.csp.sentinel.slots.block.flow.controller.RateLimiterController;
 
 /**
  * @author jialiang.linjl
@@ -85,4 +85,14 @@ public class RateLimiterControllerTest {
 
     }
 
+    @Test
+    public void testPaceController_zeroattack() throws InterruptedException {
+        RateLimiterController paceController = new RateLimiterController(500, 0d);
+        Node node = mock(Node.class);
+
+        for (int i = 0; i < 2; i++) {
+            assertFalse(paceController.canPass(node, 1));
+            assertTrue(paceController.canPass(node, 0));
+        }
+    }
 }