Merge "Make EntropyMixer mix in output of Hardware RNG into Linux RNG." (84742149) · Commits · e / os / android_frameworks_base

services/java/com/android/server/EntropyMixer.java

+34 −3

Original line number	Diff line number	Diff line
		@@ -36,7 +36,8 @@ import android.util.Slog;

		/**
		* A service designed to load and periodically save "randomness"
		* for the Linux kernel.
		* for the Linux kernel RNG and to mix in data from Hardware RNG (if present)
		* into the Linux RNG.
		*
		* <p>When a Linux system starts up, the entropy pool associated with
		* {@code /dev/random} may be in a fairly predictable state. Applications which
		@@ -45,6 +46,13 @@ import android.util.Slog;
		* this effect, it's helpful to carry the entropy pool information across
		* shutdowns and startups.
		*
		* <p>On systems with Hardware RNG (/dev/hw_random), a block of output from HW
		* RNG is mixed into the Linux RNG on EntropyMixer's startup and whenever
		* EntropyMixer periodically runs to save a block of output from Linux RNG on
		* disk. This mixing is done in a way that does not increase the Linux RNG's
		* entropy estimate is not increased. This is to avoid having to trust/verify
		* the quality and authenticity of the "randomness" of the HW RNG.
		*
		* <p>This class was modeled after the script in
		* <a href="http://www.kernel.org/doc/man-pages/online/pages/man4/random.4.html">man
		* 4 random</a>.
		@@ -57,6 +65,7 @@ public class EntropyMixer extends Binder {
		private static final long START_NANOTIME = System.nanoTime();

		private final String randomDevice;
		private final String hwRandomDevice;
		private final String entropyFile;

		/**
		@@ -69,6 +78,7 @@ public class EntropyMixer extends Binder {
		Slog.e(TAG, "Will not process invalid message");
		return;
		}
		addHwRandomEntropy();
		writeEntropy();
		scheduleEntropyWriter();
		}
		@@ -82,18 +92,25 @@ public class EntropyMixer extends Binder {
		};

		public EntropyMixer(Context context) {
		this(context, getSystemDir() + "/entropy.dat", "/dev/urandom");
		this(context, getSystemDir() + "/entropy.dat", "/dev/urandom", "/dev/hw_random");
		}

		/** Test only interface, not for public use */
		public EntropyMixer(Context context, String entropyFile, String randomDevice) {
		public EntropyMixer(
		Context context,
		String entropyFile,
		String randomDevice,
		String hwRandomDevice) {
		if (randomDevice == null) { throw new NullPointerException("randomDevice"); }
		if (hwRandomDevice == null) { throw new NullPointerException("hwRandomDevice"); }
		if (entropyFile == null) { throw new NullPointerException("entropyFile"); }

		this.randomDevice = randomDevice;
		this.hwRandomDevice = hwRandomDevice;
		this.entropyFile = entropyFile;
		loadInitialEntropy();
		addDeviceSpecificEntropy();
		addHwRandomEntropy();
		writeEntropy();
		scheduleEntropyWriter();
		IntentFilter broadcastFilter = new IntentFilter(Intent.ACTION_SHUTDOWN);
		@@ -168,6 +185,20 @@ public class EntropyMixer extends Binder {
		}
		}

		/**
		* Mixes in the output from HW RNG (if present) into the Linux RNG.
		*/
		private void addHwRandomEntropy() {
		try {
		RandomBlock.fromFile(hwRandomDevice).toFile(randomDevice, false);
		Slog.i(TAG, "Added HW RNG output to entropy pool");
		} catch (FileNotFoundException ignored) {
		// HW RNG not present/exposed -- ignore
		} catch (IOException e) {
		Slog.w(TAG, "Failed to add HW RNG output to entropy pool", e);
		}
		}

		private static String getSystemDir() {
		File dataDir = Environment.getDataDirectory();
		File systemDir = new File(dataDir, "system");

services/tests/servicestests/src/com/android/server/EntropyMixerTest.java

+1 −1

Original line number	Diff line number	Diff line
		@@ -34,7 +34,7 @@ public class EntropyMixerTest extends AndroidTestCase {
		assertEquals(0, FileUtils.readTextFile(file, 0, null).length());

		// The constructor has the side effect of writing to file
		new EntropyMixer(getContext(), "/dev/null", file.getCanonicalPath());
		new EntropyMixer(getContext(), "/dev/null", file.getCanonicalPath(), "/dev/null");

		assertTrue(FileUtils.readTextFile(file, 0, null).length() > 0);
		}