Support dropping RDNSS options with a low lifetime.

Some routers have been known to use RDNSS lifetimes of 10
seconds(!). This causes APF filters to be set to very low
lifetimes, which substantially impacts battery life.

There are two parts to this:
1. Ignore low RDNSS option lifetimes for the purpose of
   calculating APF filter lifetimes.
2. Do not add DNS servers to the repository if their lifetimes
   are too low.

If we do #1 without #2, the servers will expire because APF will
drop the RAs that refresh them, potentially causing outages or
disconnections.

The behaviour is enabled by default starting from R and can be
enabled on all builds using a flag.

Bug: 66928272
Test: New unit test passes
Change-Id: Ib2e2555026da3e81ea3d50767a30092413b4e4f5

1 files changed, 29 insertions, 1 deletions

diff --git a/src/android/net/ip/IpClient.java b/src/android/net/ip/IpClient.java
index 9f1f17c..8808ee2 100644
--- a/src/android/net/ip/IpClient.java
+++ b/src/android/net/ip/IpClient.java
@@ -18,6 +18,7 @@ package android.net.ip;
 
 import static android.net.RouteInfo.RTN_UNICAST;
 import static android.net.shared.IpConfigurationParcelableUtil.toStableParcelable;
+import static android.provider.DeviceConfig.NAMESPACE_CONNECTIVITY;
 
 import static com.android.server.util.PermissionUtil.enforceNetworkStackCallingPermission;
 
@@ -42,7 +43,9 @@ import android.net.metrics.IpManagerEvent;
 import android.net.shared.InitialConfiguration;
 import android.net.shared.ProvisioningConfiguration;
 import android.net.util.InterfaceParams;
+import android.net.util.NetworkStackUtils;
 import android.net.util.SharedLog;
+import android.os.Build;
 import android.os.ConditionVariable;
 import android.os.IBinder;
 import android.os.Message;
@@ -65,6 +68,7 @@ import com.android.internal.util.Preconditions;
 import com.android.internal.util.State;
 import com.android.internal.util.StateMachine;
 import com.android.internal.util.WakeupMessage;
+import com.android.networkstack.apishim.ShimUtils;
 import com.android.server.NetworkObserverRegistry;
 import com.android.server.NetworkStackService.NetworkStackServiceManager;
 
@@ -313,9 +317,15 @@ public class IpClient extends StateMachine {
     // IpClient shares a handler with DhcpClient: commands must not overlap
     public static final int DHCPCLIENT_CMD_BASE = 1000;
 
+    // Settings and default values.
     private static final int MAX_LOG_RECORDS = 500;
     private static final int MAX_PACKET_RECORDS = 100;
 
+    @VisibleForTesting
+    static final String CONFIG_MIN_RDNSS_LIFETIME = "ipclient_min_rdnss_lifetime";
+    private static final int DEFAULT_MIN_RDNSS_LIFETIME =
+            ShimUtils.isReleaseOrDevelopmentApiAbove(Build.VERSION_CODES.Q) ? 120 : 0;
+
     private static final boolean NO_CALLBACKS = false;
     private static final boolean SEND_CALLBACKS = true;
 
@@ -355,6 +365,9 @@ public class IpClient extends StateMachine {
     private final IpConnectivityLog mMetricsLog = new IpConnectivityLog();
     private final InterfaceController mInterfaceCtrl;
 
+    // Ignore nonzero RDNSS option lifetimes below this value. 0 = disabled.
+    private final int mMinRdnssLifetimeSec;
+
     private InterfaceParams mInterfaceParams;
 
     /**
@@ -411,6 +424,14 @@ public class IpClient extends StateMachine {
                 NetworkStackIpMemoryStore ipMemoryStore) {
             return new DhcpClient.Dependencies(ipMemoryStore);
         }
+
+        /**
+         * Read an integer DeviceConfig property.
+         */
+        public int getDeviceConfigPropertyInt(String name, int defaultValue) {
+            return NetworkStackUtils.getDeviceConfigPropertyInt(NAMESPACE_CONNECTIVITY, name,
+                    defaultValue);
+        }
     }
 
     public IpClient(Context context, String ifName, IIpClientCallbacks callback,
@@ -449,9 +470,15 @@ public class IpClient extends StateMachine {
         mNetd = deps.getNetd(mContext);
         mInterfaceCtrl = new InterfaceController(mInterfaceName, mNetd, mLog);
 
+        mMinRdnssLifetimeSec = mDependencies.getDeviceConfigPropertyInt(
+                CONFIG_MIN_RDNSS_LIFETIME, DEFAULT_MIN_RDNSS_LIFETIME);
+
+        IpClientLinkObserver.Configuration config = new IpClientLinkObserver.Configuration(
+                mMinRdnssLifetimeSec);
+
         mLinkObserver = new IpClientLinkObserver(
                 mInterfaceName,
-                () -> sendMessage(EVENT_NETLINK_LINKPROPERTIES_CHANGED)) {
+                () -> sendMessage(EVENT_NETLINK_LINKPROPERTIES_CHANGED), config) {
             @Override
             public void onInterfaceAdded(String iface) {
                 super.onInterfaceAdded(iface);
@@ -1500,6 +1527,7 @@ public class IpClient extends StateMachine {
             // Get the Configuration for ApfFilter from Context
             apfConfig.ieee802_3Filter = ApfCapabilities.getApfDrop8023Frames();
             apfConfig.ethTypeBlackList = ApfCapabilities.getApfEtherTypeBlackList();
+            apfConfig.minRdnssLifetimeSec = mMinRdnssLifetimeSec;
             mApfFilter = ApfFilter.maybeCreate(mContext, apfConfig, mInterfaceParams, mCallback);
             // TODO: investigate the effects of any multicast filtering racing/interfering with the
             // rest of this IP configuration startup.