From 29e92df3f28da4dc207e659c820228721ddd16d4 Mon Sep 17 00:00:00 2001
From: Xiao Ma <xiaom@google.com>
Date: Fri, 21 Apr 2023 20:48:02 +0900
Subject: [PATCH] Add an integration test to verify zero-length DHCP packet.

DHCP packet listener closes the listening socket and stops reading
packet upon receiving a zero-length DHCP packet, which will break
the following DHCP handshake. Add an integration test to verify the
current behavior. A follow-up fix will verify if DHCP server will
accept the zero-length DHCP packet and continue reading packet on
that socket.

Bug: 269692093
Test: atest TetheringIntegrationTests
Change-Id: I5990e37cdfad4e8e4337b0bb1a74632286884baf
---
 .../base/android/net/TetheringTester.java     | 10 ++++-
 .../android/net/EthernetTetheringTest.java    | 38 +++++++++++++++++++
 2 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/Tethering/tests/integration/base/android/net/TetheringTester.java b/Tethering/tests/integration/base/android/net/TetheringTester.java
index ae39b246b6..1c0803eb82 100644
--- a/Tethering/tests/integration/base/android/net/TetheringTester.java
+++ b/Tethering/tests/integration/base/android/net/TetheringTester.java
@@ -628,7 +628,7 @@ public final class TetheringTester {
         return false;
     }
 
-    private void sendUploadPacket(ByteBuffer packet) throws Exception {
+    public void sendUploadPacket(ByteBuffer packet) throws Exception {
         mDownstreamReader.sendResponse(packet);
     }
 
@@ -680,4 +680,12 @@ public final class TetheringTester {
 
         return verifyPacketNotNull("Download fail", getDownloadPacket(filter));
     }
+
+    // Send DHCPDISCOVER to DHCP server to see if DHCP server is still alive to handle
+    // the upcoming DHCP packets. This method should be only used when we know the DHCP
+    // server has been created successfully before.
+    public boolean testDhcpServerAlive(final MacAddress mac) throws Exception {
+        sendDhcpDiscover(mac.toByteArray());
+        return getNextDhcpPacket() != null;
+    }
 }
diff --git a/Tethering/tests/integration/src/android/net/EthernetTetheringTest.java b/Tethering/tests/integration/src/android/net/EthernetTetheringTest.java
index 55854e273f..21927df301 100644
--- a/Tethering/tests/integration/src/android/net/EthernetTetheringTest.java
+++ b/Tethering/tests/integration/src/android/net/EthernetTetheringTest.java
@@ -39,6 +39,7 @@ import static com.android.net.module.util.NetworkStackConstants.IPV4_HEADER_MIN_
 import static com.android.net.module.util.NetworkStackConstants.IPV4_LENGTH_OFFSET;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
@@ -839,4 +840,41 @@ public class EthernetTetheringTest extends EthernetTetheringTestBase {
                 REMOTE_NAT64_ADDR /* downloadSrcIp */, clatIp6 /* downloadDstIp */,
                 tester, true /* isClat */);
     }
+
+    private static final byte[] ZeroLengthDhcpPacket = new byte[] {
+            // scapy.Ether(
+            //   dst="ff:ff:ff:ff:ff:ff")
+            // scapy.IP(
+            //   dst="255.255.255.255")
+            // scapy.UDP(sport=68, dport=67)
+            /* Ethernet Header */
+            (byte) 0xff, (byte) 0xff, (byte) 0xff, (byte) 0xff, (byte) 0xff, (byte) 0xff,
+            (byte) 0xe0, (byte) 0x4f, (byte) 0x43, (byte) 0xe6, (byte) 0xfb, (byte) 0xd2,
+            (byte) 0x08, (byte) 0x00,
+            /* Ip header */
+            (byte) 0x45, (byte) 0x00, (byte) 0x00, (byte) 0x1c, (byte) 0x00, (byte) 0x01,
+            (byte) 0x00, (byte) 0x00, (byte) 0x40, (byte) 0x11, (byte) 0xb6, (byte) 0x58,
+            (byte) 0x64, (byte) 0x4f, (byte) 0x60, (byte) 0x29, (byte) 0xff, (byte) 0xff,
+            (byte) 0xff, (byte) 0xff,
+            /* UDP header */
+            (byte) 0x00, (byte) 0x44, (byte) 0x00, (byte) 0x43,
+            (byte) 0x00, (byte) 0x08, (byte) 0x3a, (byte) 0xdf
+    };
+
+    @Test
+    public void testTetherZeroLengthDhcpPacket() throws Exception {
+        final TetheringTester tester = initTetheringTester(toList(TEST_IP4_ADDR),
+                toList(TEST_IP4_DNS));
+        tester.createTetheredDevice(TEST_MAC, false /* hasIpv6 */);
+
+        // Send a zero-length DHCP packet to upstream DHCP server.
+        final ByteBuffer packet = ByteBuffer.wrap(ZeroLengthDhcpPacket);
+        tester.sendUploadPacket(packet);
+
+        // Send DHCPDISCOVER packet from another downstream tethered device to verify that upstream
+        // DHCP server has closed the listening socket and stopped reading, then we will not receive
+        // any DHCPOFFER in this case.
+        final MacAddress macAddress = MacAddress.fromString("11:22:33:44:55:66");
+        assertFalse(tester.testDhcpServerAlive(macAddress));
+    }
 }