From 459c9109ca7d2be7995ced6ced9cfec2240621f2 Mon Sep 17 00:00:00 2001
From: Chalard Jean <jchalard@google.com>
Date: Thu, 29 Mar 2018 14:10:44 +0900
Subject: [PATCH] Limit the number of routes for performance

In evaluating whether "most" of the addressing space is
covered, the list of routes are obtained from a third-party
app, so it's possbile the system service stalls unless
some limit is enforced on how much work it has to do.
This change limits the number of routes to 400, as determined
by time measurement on various devices.

Bug: 74176086
Test: runtest framework-net
Change-Id: Ie4a96098bc044ade87b188839586f14dd101c100
---
 .../android/server/connectivity/VpnTest.java  | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/tests/net/java/com/android/server/connectivity/VpnTest.java b/tests/net/java/com/android/server/connectivity/VpnTest.java
index f59850d45a..e377a47253 100644
--- a/tests/net/java/com/android/server/connectivity/VpnTest.java
+++ b/tests/net/java/com/android/server/connectivity/VpnTest.java
@@ -70,6 +70,7 @@ import android.os.Build.VERSION_CODES;
 import android.os.Bundle;
 import android.os.INetworkManagementService;
 import android.os.Looper;
+import android.os.SystemClock;
 import android.os.UserHandle;
 import android.os.UserManager;
 import android.support.test.filters.SmallTest;
@@ -88,6 +89,8 @@ import org.mockito.InOrder;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 
+import java.net.Inet4Address;
+import java.net.UnknownHostException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
@@ -639,4 +642,32 @@ public class VpnTest {
         lp.addRoute(new RouteInfo(new IpPrefix("::/1")));
         assertTrue(Vpn.providesRoutesToMostDestinations(lp));
     }
+
+    @Test
+    public void testDoesNotLockUpWithTooManyRoutes() {
+        final LinkProperties lp = new LinkProperties();
+        final byte[] ad = new byte[4];
+        // Actually evaluating this many routes under 1500ms is impossible on
+        // current hardware and for some time, as the algorithm is O(n²).
+        // Make sure the system has a safeguard against this and does not
+        // lock up.
+        final int MAX_ROUTES = 4000;
+        final long MAX_ALLOWED_TIME_MS = 1500;
+        for (int i = 0; i < MAX_ROUTES; ++i) {
+            ad[0] = (byte)((i >> 24) & 0xFF);
+            ad[1] = (byte)((i >> 16) & 0xFF);
+            ad[2] = (byte)((i >> 8) & 0xFF);
+            ad[3] = (byte)(i & 0xFF);
+            try {
+                lp.addRoute(new RouteInfo(new IpPrefix(Inet4Address.getByAddress(ad), 32)));
+            } catch (UnknownHostException e) {
+                // UnknownHostException is only thrown for an address of illegal length,
+                // which can't happen in the case above.
+            }
+        }
+        final long start = SystemClock.currentThreadTimeMillis();
+        assertTrue(Vpn.providesRoutesToMostDestinations(lp));
+        final long end = SystemClock.currentThreadTimeMillis();
+        assertTrue(end - start < MAX_ALLOWED_TIME_MS);
+    }
 }