[MAC rand] Removing persistent storage

am: 84c9ba1c7c

Change-Id: Ic017c1b13886590e5f7b4da63e4d928d08a96673

2 files changed, 178 insertions, 32 deletions

diff --git a/service/java/com/android/server/wifi/WifiConfigManager.java b/service/java/com/android/server/wifi/WifiConfigManager.java
index b21893404..7aaeb4821 100644
--- a/service/java/com/android/server/wifi/WifiConfigManager.java
+++ b/service/java/com/android/server/wifi/WifiConfigManager.java
@@ -76,6 +76,8 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
+import javax.crypto.Mac;
+
 /**
  * This class provides the APIs to manage configured Wi-Fi networks.
  * It deals with the following:
@@ -228,6 +230,9 @@ public class WifiConfigManager {
     private static final int WIFI_PNO_FREQUENCY_CULLING_ENABLED_DEFAULT = 1; // 0 = disabled
     private static final int WIFI_PNO_RECENCY_SORTING_ENABLED_DEFAULT = 1; // 0 = disabled:
 
+    private static final MacAddress DEFAULT_MAC_ADDRESS =
+            MacAddress.fromString(WifiInfo.DEFAULT_MAC_ADDRESS);
+
     /**
      * Expiration timeout for deleted ephemeral ssids. (1 day)
      */
@@ -263,6 +268,7 @@ public class WifiConfigManager {
      */
     private final Context mContext;
     private final Clock mClock;
+    private final Mac mMac;
     private final UserManager mUserManager;
     private final BackupManagerProxy mBackupManagerProxy;
     private final TelephonyManager mTelephonyManager;
@@ -446,6 +452,11 @@ public class WifiConfigManager {
         } catch (PackageManager.NameNotFoundException e) {
             Log.e(TAG, "Unable to resolve SystemUI's UID.");
         }
+        mMac = WifiConfigurationUtil.obtainMacRandHashFunction(Process.WIFI_UID);
+        if (mMac == null) {
+            Log.wtf(TAG, "Failed to obtain secret for MAC randomization."
+                    + " All randomized MAC addresses are lost!");
+        }
     }
 
     /**
@@ -464,6 +475,59 @@ public class WifiConfigManager {
         return sb.toString();
     }
 
+    @VisibleForTesting
+    protected int getRandomizedMacAddressMappingSize() {
+        return mRandomizedMacAddressMapping.size();
+    }
+
+    /**
+     * The persistent randomized MAC address is locally generated for each SSID and does not
+     * change until factory reset of the device. In the initial Q release the per-SSID randomized
+     * MAC is saved on the device, but in an update the storing of randomized MAC is removed.
+     * Instead, the randomized MAC is calculated directly from the SSID and a on device secret.
+     * For backward compatibility, this method first checks the device storage for saved
+     * randomized MAC. If it is not found or the saved MAC is invalid then it will calculate the
+     * randomized MAC directly.
+     *
+     * In the future as devices launched on Q no longer get supported, this method should get
+     * simplified to return the calculated MAC address directly.
+     * @param config the WifiConfiguration to obtain MAC address for.
+     * @return persistent MAC address for this WifiConfiguration
+     */
+    private MacAddress getPersistentMacAddress(WifiConfiguration config) {
+        // mRandomizedMacAddressMapping had been the location to save randomized MAC addresses.
+        String persistentMacString = mRandomizedMacAddressMapping.get(
+                config.getSsidAndSecurityTypeString());
+        // Use the MAC address stored in the storage if it exists and is valid. Otherwise
+        // use the MAC address calculated from a hash function as the persistent MAC.
+        if (persistentMacString != null) {
+            try {
+                return MacAddress.fromString(persistentMacString);
+            } catch (IllegalArgumentException e) {
+                Log.e(TAG, "Error creating randomized MAC address from stored value.");
+                mRandomizedMacAddressMapping.remove(config.getSsidAndSecurityTypeString());
+            }
+        }
+        return WifiConfigurationUtil.calculatePersistentMacForConfiguration(config, mMac);
+    }
+
+    /**
+     * Obtain the persistent MAC address by first reading from an internal database. If non exists
+     * then calculate the persistent MAC using HMAC-SHA256.
+     * Finally set the randomized MAC of the configuration to the randomized MAC obtained.
+     * @param config the WifiConfiguration to make the update
+     * @return the persistent MacAddress or null if the operation is unsuccessful
+     */
+    private MacAddress setRandomizedMacToPersistentMac(WifiConfiguration config) {
+        MacAddress persistentMac = getPersistentMacAddress(config);
+        if (persistentMac == null || persistentMac.equals(config.getRandomizedMacAddress())) {
+            return persistentMac;
+        }
+        WifiConfiguration internalConfig = getInternalConfiguredNetwork(config.networkId);
+        internalConfig.setRandomizedMacAddress(persistentMac);
+        return persistentMac;
+    }
+
     /**
      * Enable/disable verbose logging in WifiConfigManager & its helper classes.
      */
@@ -520,8 +584,7 @@ public class WifiConfigManager {
      * @param configuration WifiConfiguration to hide the MAC address
      */
     private void maskRandomizedMacAddressInWifiConfiguration(WifiConfiguration configuration) {
-        MacAddress defaultMac = MacAddress.fromString(WifiInfo.DEFAULT_MAC_ADDRESS);
-        configuration.setRandomizedMacAddress(defaultMac);
+        configuration.setRandomizedMacAddress(DEFAULT_MAC_ADDRESS);
     }
 
     /**
@@ -1050,34 +1113,11 @@ public class WifiConfigManager {
                 packageName != null ? packageName : mContext.getPackageManager().getNameForUid(uid);
         newInternalConfig.creationTime = newInternalConfig.updateTime =
                 createDebugTimeStampString(mClock.getWallClockMillis());
-        updateRandomizedMacAddress(newInternalConfig);
-
-        return newInternalConfig;
-    }
-
-    /**
-     * Sets the randomized address for the given configuration from stored map if it exist.
-     * Otherwise generates a new randomized address and save to the stored map.
-     * @param config
-     */
-    private void updateRandomizedMacAddress(WifiConfiguration config) {
-        // Update randomized MAC address according to stored map
-        final String key = config.getSsidAndSecurityTypeString();
-        // If the key is not found in the current store, then it means this network has never been
-        // seen before. So add it to store.
-        if (!mRandomizedMacAddressMapping.containsKey(key)) {
-            mRandomizedMacAddressMapping.put(key,
-                    config.getOrCreateRandomizedMacAddress().toString());
-        } else { // Otherwise read from the store and set the WifiConfiguration
-            try {
-                config.setRandomizedMacAddress(
-                        MacAddress.fromString(mRandomizedMacAddressMapping.get(key)));
-            } catch (IllegalArgumentException e) {
-                Log.e(TAG, "Error creating randomized MAC address from stored value.");
-                mRandomizedMacAddressMapping.put(key,
-                        config.getOrCreateRandomizedMacAddress().toString());
-            }
+        MacAddress randomizedMac = getPersistentMacAddress(newInternalConfig);
+        if (randomizedMac != null) {
+            newInternalConfig.setRandomizedMacAddress(randomizedMac);
         }
+        return newInternalConfig;
     }
 
     /**
@@ -3033,12 +3073,16 @@ public class WifiConfigManager {
     }
 
     /**
-     * Generate randomized MAC addresses for configured networks and persist mapping to storage.
+     * Assign randomized MAC addresses for configured networks.
+     * This is needed to generate persistent randomized MAC address for existing networks when
+     * a device updates to Q+ for the first time since we are not calling addOrUpdateNetwork when
+     * we load configuration at boot.
      */
     private void generateRandomizedMacAddresses() {
         for (WifiConfiguration config : getInternalConfiguredNetworks()) {
-            mRandomizedMacAddressMapping.put(config.getSsidAndSecurityTypeString(),
-                    config.getOrCreateRandomizedMacAddress().toString());
+            if (DEFAULT_MAC_ADDRESS.equals(config.getRandomizedMacAddress())) {
+                setRandomizedMacToPersistentMac(config);
+            }
         }
     }
 
diff --git a/service/java/com/android/server/wifi/WifiConfigurationUtil.java b/service/java/com/android/server/wifi/WifiConfigurationUtil.java
index a99253463..c59d4faf7 100644
--- a/service/java/com/android/server/wifi/WifiConfigurationUtil.java
+++ b/service/java/com/android/server/wifi/WifiConfigurationUtil.java
@@ -28,6 +28,9 @@ import android.net.wifi.WifiNetworkSpecifier;
 import android.net.wifi.WifiScanner;
 import android.os.PatternMatcher;
 import android.os.UserHandle;
+import android.security.keystore.AndroidKeyStoreProvider;
+import android.security.keystore.KeyGenParameterSpec;
+import android.security.keystore.KeyProperties;
 import android.text.TextUtils;
 import android.util.Log;
 import android.util.Pair;
@@ -36,7 +39,17 @@ import com.android.internal.annotations.VisibleForTesting;
 import com.android.server.wifi.util.NativeUtil;
 import com.android.server.wifi.util.TelephonyUtil;
 
+import java.nio.ByteBuffer;
 import java.nio.charset.StandardCharsets;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+import java.security.Key;
+import java.security.KeyStore;
+import java.security.KeyStoreException;
+import java.security.NoSuchAlgorithmException;
+import java.security.NoSuchProviderException;
+import java.security.ProviderException;
+import java.security.UnrecoverableKeyException;
 import java.security.cert.X509Certificate;
 import java.util.Arrays;
 import java.util.BitSet;
@@ -44,6 +57,10 @@ import java.util.Comparator;
 import java.util.List;
 import java.util.Objects;
 
+import javax.crypto.KeyGenerator;
+import javax.crypto.Mac;
+import javax.crypto.SecretKey;
+
 /**
  * WifiConfiguration utility for any {@link android.net.wifi.WifiConfiguration} related operations.
  * Currently contains:
@@ -72,6 +89,10 @@ public class WifiConfigurationUtil {
             new Pair(MacAddress.BROADCAST_ADDRESS, MacAddress.BROADCAST_ADDRESS);
     private static final Pair<MacAddress, MacAddress> MATCH_ALL_BSSID_PATTERN =
             new Pair(MacAddress.ALL_ZEROS_ADDRESS, MacAddress.ALL_ZEROS_ADDRESS);
+    private static final String MAC_RANDOMIZATION_ALIAS = "MacRandSecret";
+    private static final long MAC_ADDRESS_VALID_LONG_MASK = (1L << 48) - 1;
+    private static final long MAC_ADDRESS_LOCALLY_ASSIGNED_MASK = 1L << 41;
+    private static final long MAC_ADDRESS_MULTICAST_MASK = 1L << 40;
 
     /**
      * Check whether a network configuration is visible to a user or any of its managed profiles.
@@ -227,6 +248,87 @@ public class WifiConfigurationUtil {
     }
 
     /**
+     * Computes the persistent randomized MAC of the given configuration using the given
+     * hash function.
+     * @param config the WifiConfiguration to compute MAC address for
+     * @param hashFunction the hash function that will perform the MAC address computation.
+     * @return The persistent randomized MAC address or null if inputs are invalid.
+     */
+    public static MacAddress calculatePersistentMacForConfiguration(WifiConfiguration config,
+            Mac hashFunction) {
+        if (config == null || hashFunction == null) {
+            return null;
+        }
+        byte[] hashedBytes = hashFunction.doFinal(
+                config.getSsidAndSecurityTypeString().getBytes(StandardCharsets.UTF_8));
+        ByteBuffer bf = ByteBuffer.wrap(hashedBytes);
+        long longFromSsid = bf.getLong();
+        /**
+         * Masks the generated long so that it represents a valid randomized MAC address.
+         * Specifically, this sets the locally assigned bit to 1, multicast bit to 0
+         */
+        longFromSsid &= MAC_ADDRESS_VALID_LONG_MASK;
+        longFromSsid |= MAC_ADDRESS_LOCALLY_ASSIGNED_MASK;
+        longFromSsid &= ~MAC_ADDRESS_MULTICAST_MASK;
+        bf.clear();
+        bf.putLong(0, longFromSsid);
+
+        // MacAddress.fromBytes requires input of length 6, which is obtained from the
+        // last 6 bytes from the generated long.
+        MacAddress macAddress = MacAddress.fromBytes(Arrays.copyOfRange(bf.array(), 2, 8));
+        return macAddress;
+    }
+
+    /**
+     * Retrieves a Hash function that could be used to calculate the persistent randomized MAC
+     * for a WifiConfiguration.
+     * @param uid the UID of the KeyStore to get the secret of the hash function from.
+     */
+    public static Mac obtainMacRandHashFunction(int uid) {
+        try {
+            KeyStore keyStore = AndroidKeyStoreProvider.getKeyStoreForUid(uid);
+            // tries to retrieve the secret, and generate a new one if it's unavailable.
+            Key key = keyStore.getKey(MAC_RANDOMIZATION_ALIAS, null);
+            if (key == null) {
+                key = generateAndPersistNewMacRandomizationSecret(uid);
+            }
+            if (key == null) {
+                Log.e(TAG, "Failed to generate secret for " + MAC_RANDOMIZATION_ALIAS);
+                return null;
+            }
+            Mac result = Mac.getInstance("HmacSHA256");
+            result.init(key);
+            return result;
+        } catch (KeyStoreException | NoSuchAlgorithmException | InvalidKeyException
+                | UnrecoverableKeyException | NoSuchProviderException e) {
+            Log.e(TAG, "Failure in obtainMacRandHashFunction", e);
+            return null;
+        }
+    }
+
+    /**
+     * Generates and returns a secret key to use for Mac randomization.
+     * Will also persist the generated secret inside KeyStore, accessible in the
+     * future with KeyGenerator#getKey.
+     */
+    private static SecretKey generateAndPersistNewMacRandomizationSecret(int uid) {
+        try {
+            KeyGenerator keyGenerator = KeyGenerator.getInstance(
+                    KeyProperties.KEY_ALGORITHM_HMAC_SHA256, "AndroidKeyStore");
+            keyGenerator.init(
+                    new KeyGenParameterSpec.Builder(MAC_RANDOMIZATION_ALIAS,
+                            KeyProperties.PURPOSE_SIGN)
+                            .setUid(uid)
+                            .build());
+            return keyGenerator.generateKey();
+        } catch (NoSuchAlgorithmException | InvalidAlgorithmParameterException
+                | NoSuchProviderException | ProviderException e) {
+            Log.e(TAG, "Failure in generateMacRandomizationSecret", e);
+            return null;
+        }
+    }
+
+    /**
      * Compare existing and new WifiEnterpriseConfig objects after a network update and return if
      * credential parameters have changed or not.
      *