Don't crash if the PREF64 expires when IpClient is stopped.

Currently the code does not cancel the PREF64 alarm when IpClient
is stopped. If the alarm fires when IpClient has disconnected, it
will call updatePref64 with a null prefix, which will crash.

Ensure that the alarm is cancelled when IpClient is stopped.

Bug: 153694684
Bug: 155559286
Test: new unit tests
Change-Id: I397eb36c1a8ecf1324de33e720577fe2e4e07056

2 files changed, 32 insertions, 4 deletions

diff --git a/src/android/net/ip/IpClientLinkObserver.java b/src/android/net/ip/IpClientLinkObserver.java
index dc58e7b..ee7f18b 100644
--- a/src/android/net/ip/IpClientLinkObserver.java
+++ b/src/android/net/ip/IpClientLinkObserver.java
@@ -238,6 +238,7 @@ public class IpClientLinkObserver implements NetworkObserver {
         // while interfaceDnsServerInfo() is being called, we'll end up with no DNS servers in
         // mLinkProperties, as desired.
         mDnsServerRepository = new DnsServerRepository(mConfig.minRdnssLifetime);
+        mNetlinkMonitor.clearAlarms();
         mLinkProperties.clear();
         mLinkProperties.setInterfaceName(mInterfaceName);
     }
@@ -281,18 +282,27 @@ public class IpClientLinkObserver implements NetworkObserver {
             mIfindex = ifindex;
         }
 
+        void clearAlarms() {
+            cancelPref64Alarm();
+        }
+
         private final AlarmManager.OnAlarmListener mExpirePref64Alarm = () -> {
+            // Ignore the alarm if cancelPref64Alarm has already been called.
+            //
             // TODO: in the rare case where the alarm fires and posts the lambda to the handler
             // thread while we are processing an RA that changes the lifetime of the same prefix,
             // this code will run anyway even if the alarm is rescheduled or cancelled. If the
-            // lifetime in the RA is zero this doesn't matter (we just harmlessly cancel the alarm
-            // one extra time) but if the lifetime is nonzero then the prefix will be added and
-            // immediately removed by this code.
+            // lifetime in the RA is zero this code will correctly do nothing, but if the lifetime
+            // is nonzero then the prefix will be added and immediately removed by this code.
+            if (mNat64PrefixExpiry == 0) return;
             updatePref64(mShim.getNat64Prefix(mLinkProperties),
                     mNat64PrefixExpiry, mNat64PrefixExpiry);
         };
 
         private void cancelPref64Alarm() {
+            // Clear the expiry in case the alarm just fired and has not been processed yet.
+            if (mNat64PrefixExpiry == 0) return;
+            mNat64PrefixExpiry = 0;
             mAlarmManager.cancel(mExpirePref64Alarm);
         }
 
@@ -342,7 +352,6 @@ public class IpClientLinkObserver implements NetworkObserver {
                 schedulePref64Alarm();
             } else {
                 mShim.setNat64Prefix(mLinkProperties, null);
-                mNat64PrefixExpiry = 0;
                 cancelPref64Alarm();
             }
 
diff --git a/tests/integration/src/android/net/ip/IpClientIntegrationTest.java b/tests/integration/src/android/net/ip/IpClientIntegrationTest.java
index 225f598..4a3f445 100644
--- a/tests/integration/src/android/net/ip/IpClientIntegrationTest.java
+++ b/tests/integration/src/android/net/ip/IpClientIntegrationTest.java
@@ -1527,6 +1527,25 @@ public class IpClientIntegrationTest {
         mIpc.getHandler().post(() -> lastAlarm.onAlarm());
         expectAlarmCancelled(inOrder, pref64Alarm);
         expectNat64PrefixUpdate(inOrder, null);
+
+        // Re-announce the prefix.
+        pref64 = new StructNdOptPref64(prefix, 600).toByteBuffer();
+        ra = buildRaPacket(pio, rdnss, pref64);
+        mPacketReader.sendResponse(ra);
+        final OnAlarmListener clearAlarm = expectAlarmSet(inOrder, "PREF64", 600);
+        expectNat64PrefixUpdate(inOrder, prefix);
+        reset(mCb, mAlarm);
+
+        // Check that the alarm is cancelled when IpClient is stopped.
+        mIpc.stop();
+        HandlerUtilsKt.waitForIdle(mIpc.getHandler(), TEST_TIMEOUT_MS);
+        expectAlarmCancelled(inOrder, clearAlarm);
+        expectNat64PrefixUpdate(inOrder, null);
+
+        // Check that even if the alarm was already in the message queue while it was cancelled, it
+        // is safely ignored.
+        mIpc.getHandler().post(() -> clearAlarm.onAlarm());
+        HandlerUtilsKt.waitForIdle(mIpc.getHandler(), TEST_TIMEOUT_MS);
     }
 
     private void addIpAddressAndWaitForIt(final String iface) throws Exception {