Extract DNS setting logic into DnsManager class

In future, managing DNS-over-TLS hostname lookup and netd programming
can be encapsulated here.

Test: as follows
    - built
    - flashed
    - booted
    - runtest frameworks-net passes
Bug: 64133961
Change-Id: I47ccfa99c30c780524c45c4af605e720ccba34a0

services/core/java/com/android/server/ConnectivityService.java

@@ -130,6 +130,7 @@ import com.android.internal.util.WakeupMessage;
 import com.android.internal.util.XmlUtils;
 import com.android.server.am.BatteryStatsService;
 import com.android.server.connectivity.DataConnectionStats;
+import com.android.server.connectivity.DnsManager;
 import com.android.server.connectivity.IpConnectivityMetrics;
 import com.android.server.connectivity.KeepaliveTracker;
 import com.android.server.connectivity.LingerMonitor;
@@ -232,8 +233,6 @@ public class ConnectivityService extends IConnectivityManager.Stub
     // 0 is full bad, 100 is full good
     private int mDefaultInetConditionPublished = 0;
 
-    private int mNumDnsEntries;
-
     private boolean mTestMode;
     private static ConnectivityService sServiceInstance;
 
@@ -407,6 +406,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
     final private InternalHandler mHandler;
     /** Handler used for incoming {@link NetworkStateTracker} events. */
     final private NetworkStateTrackerHandler mTrackerHandler;
+    private final DnsManager mDnsManager;
 
     private boolean mSystemReady;
     private Intent mInitialBroadcast;
@@ -857,6 +857,8 @@ public class ConnectivityService extends IConnectivityManager.Stub
         mMultinetworkPolicyTracker = createMultinetworkPolicyTracker(
                 mContext, mHandler, () -> rematchForAvoidBadWifiUpdate());
         mMultinetworkPolicyTracker.start();
+
+        mDnsManager = new DnsManager(mContext, mNetd, mSystemProperties);
     }
 
     private Tethering makeTethering() {
@@ -1803,24 +1805,6 @@ public class ConnectivityService extends IConnectivityManager.Stub
         }
     }
 
-    private void flushVmDnsCache() {
-        /*
-         * Tell the VMs to toss their DNS caches
-         */
-        Intent intent = new Intent(Intent.ACTION_CLEAR_DNS_CACHE);
-        intent.addFlags(Intent.FLAG_RECEIVER_REPLACE_PENDING);
-        /*
-         * Connectivity events can happen before boot has completed ...
-         */
-        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
-        final long ident = Binder.clearCallingIdentity();
-        try {
-            mContext.sendBroadcastAsUser(intent, UserHandle.ALL);
-        } finally {
-            Binder.restoreCallingIdentity(ident);
-        }
-    }
-
     @Override
     public int getRestoreDefaultNetworkDelay(int networkType) {
         String restoreDefaultNetworkDelayStr = mSystemProperties.get(
@@ -4558,41 +4542,17 @@ public class ConnectivityService extends IConnectivityManager.Stub
             return;  // no updating necessary
         }
 
+        final NetworkAgentInfo defaultNai = getDefaultNetwork();
+        final boolean isDefaultNetwork = (defaultNai != null && defaultNai.network.netId == netId);
+
         Collection<InetAddress> dnses = newLp.getDnsServers();
         if (DBG) log("Setting DNS servers for network " + netId + " to " + dnses);
         try {
-            mNetd.setDnsConfigurationForNetwork(
+            mDnsManager.setDnsConfigurationForNetwork(
-                    netId, NetworkUtils.makeStrings(dnses), newLp.getDomains());
+                    netId, dnses, newLp.getDomains(), isDefaultNetwork);
         } catch (Exception e) {
             loge("Exception in setDnsConfigurationForNetwork: " + e);
         }
-        final NetworkAgentInfo defaultNai = getDefaultNetwork();
-        if (defaultNai != null && defaultNai.network.netId == netId) {
-            setDefaultDnsSystemProperties(dnses);
-        }
-        flushVmDnsCache();
-    }
-
-    private void setDefaultDnsSystemProperties(Collection<InetAddress> dnses) {
-        int last = 0;
-        for (InetAddress dns : dnses) {
-            ++last;
-            setNetDnsProperty(last, dns.getHostAddress());
-        }
-        for (int i = last + 1; i <= mNumDnsEntries; ++i) {
-            setNetDnsProperty(i, "");
-        }
-        mNumDnsEntries = last;
-    }
-
-    private void setNetDnsProperty(int which, String value) {
-        final String key = "net.dns" + which;
-        // Log and forget errors setting unsupported properties.
-        try {
-            mSystemProperties.set(key, value);
-        } catch (Exception e) {
-            Log.e(TAG, "Error setting unsupported net.dns property: ", e);
-        }
     }
 
     private String getNetworkPermission(NetworkCapabilities nc) {
@@ -4865,7 +4825,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
         notifyLockdownVpn(newNetwork);
         handleApplyDefaultProxy(newNetwork.linkProperties.getHttpProxy());
         updateTcpBufferSizes(newNetwork);
-        setDefaultDnsSystemProperties(newNetwork.linkProperties.getDnsServers());
+        mDnsManager.setDefaultDnsSystemProperties(newNetwork.linkProperties.getDnsServers());
     }
 
     private void processListenRequests(NetworkAgentInfo nai, boolean capabilitiesChanged) {

services/core/java/com/android/server/connectivity/DnsManager.java

@@ -0,0 +1,226 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.server.connectivity;
+
+import static android.net.ConnectivityManager.PRIVATE_DNS_DEFAULT_MODE;
+import static android.net.ConnectivityManager.PRIVATE_DNS_MODE_OPPORTUNISTIC;
+import static android.net.ConnectivityManager.PRIVATE_DNS_MODE_PROVIDER_HOSTNAME;
+import static android.provider.Settings.Global.DNS_RESOLVER_MIN_SAMPLES;
+import static android.provider.Settings.Global.DNS_RESOLVER_MAX_SAMPLES;
+import static android.provider.Settings.Global.DNS_RESOLVER_SAMPLE_VALIDITY_SECONDS;
+import static android.provider.Settings.Global.DNS_RESOLVER_SUCCESS_THRESHOLD_PERCENT;
+import static android.provider.Settings.Global.PRIVATE_DNS_MODE;
+import static android.provider.Settings.Global.PRIVATE_DNS_SPECIFIER;
+
+import android.content.ContentResolver;
+import android.content.Context;
+import android.content.Intent;
+import android.net.NetworkUtils;
+import android.os.Binder;
+import android.os.INetworkManagementService;
+import android.os.Handler;
+import android.os.UserHandle;
+import android.provider.Settings;
+import android.text.TextUtils;
+import android.util.Slog;
+
+import com.android.server.connectivity.MockableSystemProperties;
+
+import java.net.InetAddress;
+import java.util.Collection;
+
+
+/**
+ * Encapsulate the management of DNS settings for networks.
+ *
+ * This class it NOT designed for concurrent access. Furthermore, all non-static
+ * methods MUST be called from ConnectivityService's thread.
+ *
+ * @hide
+ */
+public class DnsManager {
+    private static final String TAG = DnsManager.class.getSimpleName();
+
+    /* Defaults for resolver parameters. */
+    private static final int DNS_RESOLVER_DEFAULT_SAMPLE_VALIDITY_SECONDS = 1800;
+    private static final int DNS_RESOLVER_DEFAULT_SUCCESS_THRESHOLD_PERCENT = 25;
+    private static final int DNS_RESOLVER_DEFAULT_MIN_SAMPLES = 8;
+    private static final int DNS_RESOLVER_DEFAULT_MAX_SAMPLES = 64;
+
+    private final Context mContext;
+    private final ContentResolver mContentResolver;
+    private final INetworkManagementService mNMS;
+    private final MockableSystemProperties mSystemProperties;
+
+    private int mNumDnsEntries;
+    private int mSampleValidity;
+    private int mSuccessThreshold;
+    private int mMinSamples;
+    private int mMaxSamples;
+    private String mPrivateDnsMode;
+    private String mPrivateDnsSpecifier;
+
+    public DnsManager(Context ctx, INetworkManagementService nms, MockableSystemProperties sp) {
+        mContext = ctx;
+        mContentResolver = mContext.getContentResolver();
+        mNMS = nms;
+        mSystemProperties = sp;
+
+        // TODO: Create and register ContentObservers to track every setting
+        // used herein, posting messages to respond to changes.
+    }
+
+    public boolean isPrivateDnsInStrictMode() {
+        return !TextUtils.isEmpty(mPrivateDnsMode) &&
+               mPrivateDnsMode.startsWith(PRIVATE_DNS_MODE_PROVIDER_HOSTNAME) &&
+               !TextUtils.isEmpty(mPrivateDnsSpecifier);
+    }
+
+    public void setDnsConfigurationForNetwork(
+            int netId, Collection<InetAddress> servers, String domains, boolean isDefaultNetwork) {
+        updateParametersSettings();
+        updatePrivateDnsSettings();
+
+        final String[] serverStrs = NetworkUtils.makeStrings(servers);
+        final String[] domainStrs = (domains == null) ? new String[0] : domains.split(" ");
+        final int[] params = { mSampleValidity, mSuccessThreshold, mMinSamples, mMaxSamples };
+        final boolean useTls = shouldUseTls(mPrivateDnsMode);
+        // TODO: Populate tlsHostname once it's decided how the hostname's IP
+        // addresses will be resolved:
+        //
+        //     [1] network-provided DNS servers are included here with the
+        //         hostname and netd will use the network-provided servers to
+        //         resolve the hostname and fix up its internal structures, or
+        //
+        //     [2] network-provided DNS servers are included here without the
+        //         hostname, the ConnectivityService layer resolves the given
+        //         hostname, and then reconfigures netd with this information.
+        //
+        // In practice, there will always be a need for ConnectivityService or
+        // the captive portal app to use the network-provided services to make
+        // some queries. This argues in favor of [1], in concert with another
+        // mechanism, perhaps setting a high bit in the netid, to indicate
+        // via existing DNS APIs which set of servers (network-provided or
+        // non-network-provided private DNS) should be queried.
+        final String tlsHostname = "";
+        try {
+            mNMS.setDnsConfigurationForNetwork(
+                    netId, serverStrs, domainStrs, params, useTls, tlsHostname);
+        } catch (Exception e) {
+            Slog.e(TAG, "Error setting DNS configuration: " + e);
+            return;
+        }
+
+        // TODO: netd should listen on [::1]:53 and proxy queries to the current
+        // default network, and we should just set net.dns1 to ::1, not least
+        // because applications attempting to use net.dns resolvers will bypass
+        // the privacy protections of things like DNS-over-TLS.
+        if (isDefaultNetwork) setDefaultDnsSystemProperties(servers);
+        flushVmDnsCache();
+    }
+
+    public void setDefaultDnsSystemProperties(Collection<InetAddress> dnses) {
+        int last = 0;
+        for (InetAddress dns : dnses) {
+            ++last;
+            setNetDnsProperty(last, dns.getHostAddress());
+        }
+        for (int i = last + 1; i <= mNumDnsEntries; ++i) {
+            setNetDnsProperty(i, "");
+        }
+        mNumDnsEntries = last;
+    }
+
+    private void flushVmDnsCache() {
+        /*
+         * Tell the VMs to toss their DNS caches
+         */
+        final Intent intent = new Intent(Intent.ACTION_CLEAR_DNS_CACHE);
+        intent.addFlags(Intent.FLAG_RECEIVER_REPLACE_PENDING);
+        /*
+         * Connectivity events can happen before boot has completed ...
+         */
+        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
+        final long ident = Binder.clearCallingIdentity();
+        try {
+            mContext.sendBroadcastAsUser(intent, UserHandle.ALL);
+        } finally {
+            Binder.restoreCallingIdentity(ident);
+        }
+    }
+
+    private void updatePrivateDnsSettings() {
+        mPrivateDnsMode = getStringSetting(PRIVATE_DNS_MODE);
+        mPrivateDnsSpecifier = getStringSetting(PRIVATE_DNS_SPECIFIER);
+    }
+
+    private void updateParametersSettings() {
+        mSampleValidity = getIntSetting(
+                DNS_RESOLVER_SAMPLE_VALIDITY_SECONDS,
+                DNS_RESOLVER_DEFAULT_SAMPLE_VALIDITY_SECONDS);
+        if (mSampleValidity < 0 || mSampleValidity > 65535) {
+            Slog.w(TAG, "Invalid sampleValidity=" + mSampleValidity + ", using default=" +
+                    DNS_RESOLVER_DEFAULT_SAMPLE_VALIDITY_SECONDS);
+            mSampleValidity = DNS_RESOLVER_DEFAULT_SAMPLE_VALIDITY_SECONDS;
+        }
+
+        mSuccessThreshold = getIntSetting(
+                DNS_RESOLVER_SUCCESS_THRESHOLD_PERCENT,
+                DNS_RESOLVER_DEFAULT_SUCCESS_THRESHOLD_PERCENT);
+        if (mSuccessThreshold < 0 || mSuccessThreshold > 100) {
+            Slog.w(TAG, "Invalid successThreshold=" + mSuccessThreshold + ", using default=" +
+                    DNS_RESOLVER_DEFAULT_SUCCESS_THRESHOLD_PERCENT);
+            mSuccessThreshold = DNS_RESOLVER_DEFAULT_SUCCESS_THRESHOLD_PERCENT;
+        }
+
+        mMinSamples = getIntSetting(DNS_RESOLVER_MIN_SAMPLES, DNS_RESOLVER_DEFAULT_MIN_SAMPLES);
+        mMaxSamples = getIntSetting(DNS_RESOLVER_MAX_SAMPLES, DNS_RESOLVER_DEFAULT_MAX_SAMPLES);
+        if (mMinSamples < 0 || mMinSamples > mMaxSamples || mMaxSamples > 64) {
+            Slog.w(TAG, "Invalid sample count (min, max)=(" + mMinSamples + ", " + mMaxSamples +
+                    "), using default=(" + DNS_RESOLVER_DEFAULT_MIN_SAMPLES + ", " +
+                    DNS_RESOLVER_DEFAULT_MAX_SAMPLES + ")");
+            mMinSamples = DNS_RESOLVER_DEFAULT_MIN_SAMPLES;
+            mMaxSamples = DNS_RESOLVER_DEFAULT_MAX_SAMPLES;
+        }
+    }
+
+    private String getStringSetting(String which) {
+        return Settings.Global.getString(mContentResolver, which);
+    }
+
+    private int getIntSetting(String which, int dflt) {
+        return Settings.Global.getInt(mContentResolver, which, dflt);
+    }
+
+    private void setNetDnsProperty(int which, String value) {
+        final String key = "net.dns" + which;
+        // Log and forget errors setting unsupported properties.
+        try {
+            mSystemProperties.set(key, value);
+        } catch (Exception e) {
+            Slog.e(TAG, "Error setting unsupported net.dns property: ", e);
+        }
+    }
+
+    private static boolean shouldUseTls(String mode) {
+        if (TextUtils.isEmpty(mode)) {
+            mode = PRIVATE_DNS_DEFAULT_MODE;
+        }
+        return mode.equals(PRIVATE_DNS_MODE_OPPORTUNISTIC) ||
+               mode.startsWith(PRIVATE_DNS_MODE_PROVIDER_HOSTNAME);
+    }
+}

tests/net/java/com/android/server/ConnectivityServiceTest.java

@@ -3505,7 +3505,7 @@ public class ConnectivityServiceTest {
         mCellNetworkAgent = new MockNetworkAgent(TRANSPORT_CELLULAR);
         waitForIdle();
         verify(mNetworkManagementService, never()).setDnsConfigurationForNetwork(
-                anyInt(), any(), any());
+                anyInt(), any(), any(), any(), anyBoolean(), anyString());
 
         final LinkProperties cellLp = new LinkProperties();
         cellLp.setInterfaceName("test_rmnet_data0");
@@ -3513,7 +3513,7 @@ public class ConnectivityServiceTest {
         mCellNetworkAgent.connect(false);
         waitForIdle();
         verify(mNetworkManagementService, times(1)).setDnsConfigurationForNetwork(
-                anyInt(), mStringArrayCaptor.capture(), any());
+                anyInt(), mStringArrayCaptor.capture(), any(), any(), anyBoolean(), anyString());
         // CS tells netd about the empty DNS config for this network.
         assertEmpty(mStringArrayCaptor.getValue());
         reset(mNetworkManagementService);
@@ -3522,7 +3522,7 @@ public class ConnectivityServiceTest {
         mCellNetworkAgent.sendLinkProperties(cellLp);
         waitForIdle();
         verify(mNetworkManagementService, times(1)).setDnsConfigurationForNetwork(
-                anyInt(), mStringArrayCaptor.capture(), any());
+                anyInt(), mStringArrayCaptor.capture(), any(), any(), anyBoolean(), anyString());
         assertEquals(1, mStringArrayCaptor.getValue().length);
         assertTrue(ArrayUtils.contains(mStringArrayCaptor.getValue(), "2001:db8::1"));
         reset(mNetworkManagementService);
@@ -3531,7 +3531,7 @@ public class ConnectivityServiceTest {
         mCellNetworkAgent.sendLinkProperties(cellLp);
         waitForIdle();
         verify(mNetworkManagementService, times(1)).setDnsConfigurationForNetwork(
-                anyInt(), mStringArrayCaptor.capture(), any());
+                anyInt(), mStringArrayCaptor.capture(), any(), any(), anyBoolean(), anyString());
         assertEquals(2, mStringArrayCaptor.getValue().length);
         assertTrue(ArrayUtils.containsAll(mStringArrayCaptor.getValue(),
                 new String[]{"2001:db8::1", "192.0.2.1"}));