cmhw: Add PersistentStorage API

 * This API is used for storing key-value pairs which persist across
   a factory reset.
 * The default implementation will attempt to use the /persist
   partition which is available on most QCOM based devices. If this
   is not applicable, a device should implement this HAL in a
   way which makes sense.

Change-Id: Ia8d0a1af5dc19ffbbfaefaf8b5ce87b08d41538a

1 files changed, 196 insertions, 0 deletions

diff --git a/src/org/cyanogenmod/hardware/PersistentStorage.java b/src/org/cyanogenmod/hardware/PersistentStorage.java
new file mode 100644
index 0000000..910f41b
--- /dev/null
+++ b/src/org/cyanogenmod/hardware/PersistentStorage.java
@@ -0,0 +1,196 @@
+/*
+ * Copyright (C) 2015 The CyanogenMod 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 org.cyanogenmod.hardware;
+
+import android.os.FileUtils;
+import android.util.Slog;
+
+import java.io.File;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.security.MessageDigest;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+/**
+ * Support for storage of key-value pairs which persists across device wipes /
+ * factory resets. This is used for various security related features. A
+ * reasonable implementation of this needs to store items on a partition which
+ * is unaffected by factory reset. The actual format of the storage is left up
+ * to the implementation. The implementation in this file is suitable for
+ * devices which have a /persist partition (recent QCOM devices fit this
+ * criteria).
+ */
+public class PersistentStorage {
+
+    public static final int MAX_KEY_LEN = 64;
+    public static final int MAX_VALUE_LEN = 4096;
+
+    private static final String TAG = "PersistentStorage";
+
+    private static final String PERSIST_DATA_PATH = "/persist/properties";
+
+    private static final boolean DEBUG = false;
+
+    private static final ReadWriteLock rwl = new ReentrantReadWriteLock();
+
+    /**
+     * Whether device supports persistent properties
+     *
+     * @return boolean Supported devices must return always true
+     */
+    public static boolean isSupported() {
+        final File file = new File(PERSIST_DATA_PATH);
+        return file.exists() && file.isDirectory() && file.canRead() && file.canWrite();
+    }
+
+    /**
+     * Gets an array of bytes from persistent storage.
+     *
+     * @param key
+     * @return previously stored byte array, null if not found
+     */
+    public static byte[] get(String key) {
+        if (!isSupported() || key.length() > MAX_KEY_LEN) {
+            return null;
+        }
+
+        final String encodedKey = encode(key);
+        if (encodedKey == null) {
+            return null;
+        }
+
+        FileInputStream fis = null;
+
+        try {
+            rwl.readLock().lock();
+
+            final File prop = new File(PERSIST_DATA_PATH + "/" + encodedKey);
+
+            if (!prop.exists()) {
+                if (DEBUG) {
+                    Slog.e(TAG, "Unable to read from " + prop.getAbsolutePath());
+                }
+                return null;
+            }
+
+            final byte[] buffer = new byte[MAX_VALUE_LEN];
+            fis = new FileInputStream(prop);
+            ByteArrayOutputStream bos = new ByteArrayOutputStream();
+            int len = fis.read(buffer);
+            bos.write(buffer, 0, len);
+            return bos.toByteArray();
+
+        } catch (Exception e) {
+            Slog.e(TAG, e.getMessage(), e);
+        } finally {
+            if (fis != null) {
+                try {
+                    fis.close();
+                } catch (IOException ex) {
+                    // skip it
+                }
+            }
+            rwl.readLock().unlock();
+        }
+
+        return null;
+    }
+
+    /**
+     * Writes a byte array to persistent storage.
+     *
+     * The storage of the data is implementation specific. In this implementation,
+     * we hash the key with SHA-256 and use the hex string as the stored key.
+     *
+     * Implementations should delete the key if a null buffer is passed.
+     *
+     * @param key
+     * @param buffer
+     * @return true if the operation succeeded
+     */
+    public static boolean set(String key, byte[] buffer) {
+        if (!isSupported() ||
+                key == null || key.length() > MAX_KEY_LEN ||
+                (buffer != null && buffer.length > MAX_VALUE_LEN)) {
+            return false;
+        }
+
+        final String encodedKey = encode(key);
+        if (encodedKey == null) {
+            return false;
+        }
+
+        try {
+            rwl.writeLock().lock();
+
+            final File prop = new File(PERSIST_DATA_PATH + "/" + encodedKey);
+
+            File tmp = null;
+            if (buffer != null) {
+                tmp = File.createTempFile(key, "tmp",
+                        new File(PERSIST_DATA_PATH));
+                if (!FileUtils.copyToFile(new ByteArrayInputStream(buffer), tmp)) {
+                    Slog.e(TAG, "Unable to create temporary file!");
+                    return false;
+                }
+            }
+
+            if (prop.exists()) {
+                prop.delete();
+            }
+
+            if (tmp != null) {
+                tmp.renameTo(prop);
+            }
+
+        } catch (Exception e) {
+            Slog.e(TAG, e.getMessage(), e);
+            return false;
+
+        } finally {
+            rwl.writeLock().unlock();
+        }
+        return true;
+    }
+
+    /**
+     * Used for encoding keys with SHA-256
+     *
+     * @param key
+     * @return
+     */
+    private static String encode(String key) {
+        try {
+            MessageDigest d = MessageDigest.getInstance("SHA-256");
+            byte[] hash = d.digest(key.getBytes("UTF-8"));
+            StringBuilder encoded = new StringBuilder();
+
+            for (byte b : hash) {
+                encoded.append(String.format("%02x", b & 0xff));
+            }
+
+            return encoded.toString();
+        } catch (Exception e) {
+            Slog.e(TAG, e.getMessage(), e);
+        }
+        return null;
+    }
+}