DO NOT MERGE Check fingerprint client against top activity in auth callback
Due to a race condition with activity task stack broadcasts, it's
currently possible for fingerprint authentication to succeed for a
non-top activity. This means, for example, that a malicious overlay
could be drawn in order to mislead the user about what they are
authenticating for.
This commit addresses the issue by adding a check to the biometric
authentication client interface that ensures the authenticating
activity is on top at the time of authentication. Otherwise, the
pending authentication will fail, as if an incorrect biometric had
been presented.
Test: Follow steps from b/159249069:
1. Install com.pro100svitlo.fingerprintauthdemo from the Play store.
2. Install the PoC attack app from b/159249069.
3. Start the PoC attack app and press the "Launch PoC attack" button.
4. Use fingerprint to authenticate while the overlay is showing.
Before: Authentication succeeds, and a new activity is launched.
After: Authentication fails, and no new activity is launched.
Bug: 159249069
Change-Id: Ie5a0f8c3e9b92d348a78678a6ed192d440c45ffc
Merged-In: I289d67e5c7055ed60f7a96725c523d07cd047b23
Merged-In: I3a810cd7e6b97333f648c978e44242662342ec57
(cherry picked from commit 09c1b8ebf9e58cd402ec6a7ae9b1948cf83982d1)
diff --git a/services/core/java/com/android/server/biometrics/AuthenticationClient.java b/services/core/java/com/android/server/biometrics/AuthenticationClient.java
index edc8f15..8ca37b81 100644
--- a/services/core/java/com/android/server/biometrics/AuthenticationClient.java
+++ b/services/core/java/com/android/server/biometrics/AuthenticationClient.java
@@ -16,16 +16,22 @@
package com.android.server.biometrics;
+import android.app.ActivityManager;
+import android.app.ActivityTaskManager;
+import android.content.ComponentName;
import android.content.Context;
+import android.content.pm.ApplicationInfo;
import android.hardware.biometrics.BiometricAuthenticator;
import android.hardware.biometrics.BiometricConstants;
import android.hardware.biometrics.BiometricsProtoEnums;
import android.os.IBinder;
import android.os.RemoteException;
import android.security.KeyStore;
+import android.util.EventLog;
import android.util.Slog;
import java.util.ArrayList;
+import java.util.List;
/**
* A class to keep track of the authentication state for a given client.
@@ -148,7 +154,54 @@
+ ", requireConfirmation: " + mRequireConfirmation
+ ", user: " + getTargetUserId());
+ // Ensure authentication only succeeds if the client activity is on top or is keyguard.
+ boolean isBackgroundAuth = false;
+ if (authenticated && !Utils.isKeyguard(getContext(), getOwnerString())) {
+ try {
+ final List<ActivityManager.RunningTaskInfo> tasks =
+ ActivityTaskManager.getService().getTasks(1);
+ if (tasks == null || tasks.isEmpty()) {
+ Slog.e(TAG, "No running tasks reported");
+ isBackgroundAuth = true;
+ } else {
+ final ComponentName topActivity = tasks.get(0).topActivity;
+ if (topActivity == null) {
+ Slog.e(TAG, "Unable to get top activity");
+ isBackgroundAuth = true;
+ } else {
+ final String topPackage = topActivity.getPackageName();
+ if (!topPackage.contentEquals(getOwnerString())) {
+ Slog.e(TAG, "Background authentication detected, top: " + topPackage
+ + ", client: " + this);
+ isBackgroundAuth = true;
+ }
+ }
+ }
+ } catch (RemoteException e) {
+ Slog.e(TAG, "Unable to get running tasks", e);
+ isBackgroundAuth = true;
+ }
+ }
+
+ // Fail authentication if we can't confirm the client activity is on top.
+ if (isBackgroundAuth) {
+ Slog.e(TAG, "Failing possible background authentication");
+ authenticated = false;
+
+ // SafetyNet logging for exploitation attempts of b/159249069.
+ final ApplicationInfo appInfo = getContext().getApplicationInfo();
+ EventLog.writeEvent(0x534e4554, "159249069", appInfo != null ? appInfo.uid : -1,
+ "Attempted background authentication");
+ }
+
if (authenticated) {
+ // SafetyNet logging for b/159249069 if constraint is violated.
+ if (isBackgroundAuth) {
+ final ApplicationInfo appInfo = getContext().getApplicationInfo();
+ EventLog.writeEvent(0x534e4554, "159249069", appInfo != null ? appInfo.uid : -1,
+ "Successful background authentication!");
+ }
+
mAlreadyDone = true;
if (listener != null) {
