net.dns patch 1/2

diff --git a/service/src/com/android/server/ConnectivityService.java b/service/src/com/android/server/ConnectivityService.java
index 1ff6fc1ac..b8260346f 100644
--- a/service/src/com/android/server/ConnectivityService.java
+++ b/service/src/com/android/server/ConnectivityService.java
@@ -1470,7 +1470,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
                 mContext, mHandler, () -> updateAvoidBadWifi());
         mMultinetworkPolicyTracker.start();

-        mDnsManager = new DnsManager(mContext, mDnsResolver);
+        mDnsManager = new DnsManager(mContext, mDnsResolver, mSystemProperties);
         registerPrivateDnsSettingsCallbacks();

         // This NAI is a sentinel used to offer no service to apps that are on a multi-layer
@@ -7187,12 +7187,20 @@ public class ConnectivityService extends IConnectivityManager.Stub
             return;  // no updating necessary
         }

+        final NetworkAgentInfo defaultNai = getDefaultNetwork();
+        final boolean isDefaultNetwork = (defaultNai != null && defaultNai.network.netId == netId);
+
         if (DBG) {
             final Collection<InetAddress> dnses = newLp.getDnsServers();
             log("Setting DNS servers for network " + netId + " to " + dnses);
         }
         try {
             mDnsManager.noteDnsServersForNetwork(netId, newLp);
+            // 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) mDnsManager.setDefaultDnsSystemProperties(newLp.getDnsServers());
             mDnsManager.flushVmDnsCache();
         } catch (Exception e) {
             loge("Exception in setDnsConfigurationForNetwork: " + e);
diff --git a/service/src/com/android/server/connectivity/DnsManager.java b/service/src/com/android/server/connectivity/DnsManager.java
index 1493cae79..2aea01199 100644
--- a/service/src/com/android/server/connectivity/DnsManager.java
+++ b/service/src/com/android/server/connectivity/DnsManager.java
@@ -247,21 +247,24 @@ public class DnsManager {
     private final Context mContext;
     private final ContentResolver mContentResolver;
     private final IDnsResolver mDnsResolver;
+    private final MockableSystemProperties mSystemProperties;
     private final ConcurrentHashMap<Integer, PrivateDnsConfig> mPrivateDnsMap;
     // TODO: Replace the Map with SparseArrays.
     private final Map<Integer, PrivateDnsValidationStatuses> mPrivateDnsValidationMap;
     private final Map<Integer, LinkProperties> mLinkPropertiesMap;
     private final Map<Integer, int[]> mTransportsMap;

+    private int mNumDnsEntries;
     private int mSampleValidity;
     private int mSuccessThreshold;
     private int mMinSamples;
     private int mMaxSamples;

-    public DnsManager(Context ctx, IDnsResolver dnsResolver) {
+    public DnsManager(Context ctx, IDnsResolver dnsResolver, MockableSystemProperties sp) {
         mContext = ctx;
         mContentResolver = mContext.getContentResolver();
         mDnsResolver = dnsResolver;
+        mSystemProperties = sp;
         mPrivateDnsMap = new ConcurrentHashMap<>();
         mPrivateDnsValidationMap = new HashMap<>();
         mLinkPropertiesMap = new HashMap<>();
@@ -412,6 +415,18 @@ public class DnsManager {
         }
     }

+    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;
+    }
+
     /**
      * Flush DNS caches and events work before boot has completed.
      */
@@ -467,6 +482,16 @@ public class DnsManager {
         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) {
+            Log.e(TAG, "Error setting unsupported net.dns property: ", e);
+        }
+    }
+
     /**
      * Create a string array of host addresses from a collection of InetAddresses
      *
diff --git a/service/src/com/android/server/connectivity/MockableSystemProperties.java b/service/src/com/android/server/connectivity/MockableSystemProperties.java
index a25b89ac0..77b86d8e4 100644
--- a/service/src/com/android/server/connectivity/MockableSystemProperties.java
+++ b/service/src/com/android/server/connectivity/MockableSystemProperties.java
@@ -31,4 +31,8 @@ public class MockableSystemProperties {
     public boolean getBoolean(String key, boolean def) {
         return SystemProperties.getBoolean(key, def);
     }
+
+    public void set(String key, String value) {
+        SystemProperties.set(key, value);
+    }
 }
diff --git a/tests/unit/java/com/android/server/connectivity/DnsManagerTest.java b/tests/unit/java/com/android/server/connectivity/DnsManagerTest.java
index 24aecdb90..6ddef92b9 100644
--- a/tests/unit/java/com/android/server/connectivity/DnsManagerTest.java
+++ b/tests/unit/java/com/android/server/connectivity/DnsManagerTest.java
@@ -105,6 +105,7 @@ public class DnsManagerTest {

     @Mock Context mCtx;
     @Mock IDnsResolver mMockDnsResolver;
+    @Mock MockableSystemProperties mSystemProperties;

     private void assertResolverOptionsEquals(
             @Nullable ResolverOptionsParcel actual,
@@ -149,7 +150,7 @@ public class DnsManagerTest {
         mContentResolver.addProvider(Settings.AUTHORITY,
                 new FakeSettingsProvider());
         when(mCtx.getContentResolver()).thenReturn(mContentResolver);
-        mDnsManager = new DnsManager(mCtx, mMockDnsResolver);
+        mDnsManager = new DnsManager(mCtx, mMockDnsResolver, mSystemProperties);

         // Clear the private DNS settings
         Settings.Global.putString(mContentResolver, PRIVATE_DNS_DEFAULT_MODE, "");
@@ -171,6 +172,7 @@ public class DnsManagerTest {
         // Send a validation event that is tracked on the alternate netId
         mDnsManager.updateTransportsForNetwork(TEST_NETID, TEST_TRANSPORT_TYPES);
         mDnsManager.noteDnsServersForNetwork(TEST_NETID, lp);
+        mDnsManager.setDefaultDnsSystemProperties(lp.getDnsServers());
         mDnsManager.flushVmDnsCache();
         mDnsManager.updateTransportsForNetwork(TEST_NETID_ALTERNATE, TEST_TRANSPORT_TYPES);
         mDnsManager.noteDnsServersForNetwork(TEST_NETID_ALTERNATE, lp);
@@ -207,6 +209,7 @@ public class DnsManagerTest {
                     }));
         mDnsManager.updateTransportsForNetwork(TEST_NETID, TEST_TRANSPORT_TYPES);
         mDnsManager.noteDnsServersForNetwork(TEST_NETID, lp);
+        mDnsManager.setDefaultDnsSystemProperties(lp.getDnsServers());
         mDnsManager.flushVmDnsCache();
         fixedLp = new LinkProperties(lp);
         mDnsManager.updatePrivateDnsStatus(TEST_NETID, fixedLp);
@@ -244,6 +247,7 @@ public class DnsManagerTest {
         lp.addDnsServer(InetAddress.getByName("3.3.3.3"));
         mDnsManager.updateTransportsForNetwork(TEST_NETID, TEST_TRANSPORT_TYPES);
         mDnsManager.noteDnsServersForNetwork(TEST_NETID, lp);
+        mDnsManager.setDefaultDnsSystemProperties(lp.getDnsServers());
         mDnsManager.flushVmDnsCache();
         mDnsManager.updatePrivateDnsValidation(
                 new DnsManager.PrivateDnsValidationUpdate(TEST_NETID,
@@ -258,6 +262,7 @@ public class DnsManagerTest {
                 mDnsManager.getPrivateDnsConfig());
         mDnsManager.updateTransportsForNetwork(TEST_NETID, TEST_TRANSPORT_TYPES);
         mDnsManager.noteDnsServersForNetwork(TEST_NETID, lp);
+        mDnsManager.setDefaultDnsSystemProperties(lp.getDnsServers());
         mDnsManager.flushVmDnsCache();
         mDnsManager.updatePrivateDnsValidation(
                 new DnsManager.PrivateDnsValidationUpdate(TEST_NETID_UNTRACKED,
@@ -309,6 +314,7 @@ public class DnsManagerTest {
                 mDnsManager.getPrivateDnsConfig());
         mDnsManager.updateTransportsForNetwork(TEST_NETID, TEST_TRANSPORT_TYPES);
         mDnsManager.noteDnsServersForNetwork(TEST_NETID, lp);
+        mDnsManager.setDefaultDnsSystemProperties(lp.getDnsServers());
         mDnsManager.flushVmDnsCache();
         mDnsManager.updatePrivateDnsValidation(
                 new DnsManager.PrivateDnsValidationUpdate(TEST_NETID,
@@ -354,6 +360,7 @@ public class DnsManagerTest {
         lp.addDnsServer(InetAddress.getByName("4.4.4.4"));
         mDnsManager.updateTransportsForNetwork(TEST_NETID, TEST_TRANSPORT_TYPES);
         mDnsManager.noteDnsServersForNetwork(TEST_NETID, lp);
+        mDnsManager.setDefaultDnsSystemProperties(lp.getDnsServers());
         mDnsManager.flushVmDnsCache();

         final ArgumentCaptor<ResolverParamsParcel> resolverParamsParcelCaptor =