Add SecurityPolicy factory method for apps signed with the platform certificate

binder/src/main/java/io/grpc/binder/SecurityPolicies.java

@@ -16,6 +16,8 @@
 
 package io.grpc.binder;
 
+import static com.google.common.base.Preconditions.checkState;
+
 import android.annotation.SuppressLint;
 import android.app.admin.DevicePolicyManager;
 import android.content.Context;
@@ -32,6 +34,8 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.hash.Hashing;
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.ListenableFuture;
 import com.google.errorprone.annotations.CheckReturnValue;
 import io.grpc.ExperimentalApi;
 import io.grpc.Status;
@@ -40,6 +44,7 @@
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.List;
+import java.util.concurrent.Executor;
 
 /** Static factory methods for creating standard security policies. */
 @CheckReturnValue
@@ -97,6 +102,42 @@ public static SecurityPolicy hasSignature(
         packageManager, packageName, ImmutableList.of(requiredSignature));
   }
 
+  /**
+   * Creates a {@link SecurityPolicy} which checks if the given package is signed with the same
+   * certificate that the current Android platform was signed with.
+   *
+   * @param packageName the package name of the allowed package.
+   * @param backgroundExecutor an executor suitable for blocking disk I/O.
+   * @throws NullPointerException if any of the inputs are {@code null}.
+   */
+  @ExperimentalApi("https://github.com/grpc/grpc-java/issues/11238")
+  public static AsyncSecurityPolicy hasSameSignatureAsPlatform(
+      PackageManager packageManager, String packageName, Executor backgroundExecutor) {
+    return new AsyncSecurityPolicy() {
+      @Override
+      public ListenableFuture<Status> checkAuthorizationAsync(int uid) {
+        return Futures.submit(
+            () -> {
+              PackageInfo platformPackageInfo;
+              try {
+                platformPackageInfo =
+                    packageManager.getPackageInfo(
+                        "android", packageManager.GET_SIGNING_CERTIFICATES);
+              } catch (PackageManager.NameNotFoundException e) {
+                throw new AssertionError(
+                    e); // impossible; the platform package is always available.
+              }
+              return oneOfSignatures(
+                      packageManager,
+                      packageName,
+                      ImmutableList.copyOf(platformPackageInfo.signatures))
+                  .checkAuthorization(uid);
+            },
+            backgroundExecutor);
+      }
+    };
+  }
+
   /**
    * Creates {@link SecurityPolicy} which checks if the SHA-256 hash of the package signature
    * matches {@code requiredSignatureSha256Hash}.

binder/src/test/java/io/grpc/binder/SecurityPoliciesTest.java

@@ -35,6 +35,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.hash.Hashing;
+import com.google.common.util.concurrent.MoreExecutors;
 import io.grpc.Status;
 import java.util.HashMap;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -84,6 +85,12 @@ private void installPackages(int uid, PackageInfo... packageInfo) {
     shadowOf(packageManager).setPackagesForUid(uid, packageNames);
   }
 
+  private void setupPlatformSignature(Signature... signatures) {
+    PackageInfo platformPackageInfo =
+        newBuilder().setPackageName("android").setSignatures(signatures).build();
+    installPackages(Process.SYSTEM_UID, platformPackageInfo);
+  }
+
   @Test
   public void testInternalOnly() throws Exception {
     policy = SecurityPolicies.internalOnly();
@@ -151,6 +158,64 @@ public void testHasSignature_failsIfSignatureDoesNotMatch() throws Exception {
         .isEqualTo(Status.PERMISSION_DENIED.getCode());
   }
 
+  @Test
+  public void testHasSameSignatureAsPlatform_succeedsIfSignaturesMatch() {
+    setupPlatformSignature(SIG2, SIG1);
+    PackageInfo info =
+        newBuilder().setPackageName(OTHER_UID_PACKAGE_NAME).setSignatures(SIG1).build();
+    installPackages(OTHER_UID, info);
+
+    policy =
+        SecurityPolicies.hasSameSignatureAsPlatform(
+            packageManager, OTHER_UID_PACKAGE_NAME, MoreExecutors.newDirectExecutorService());
+
+    assertThat(policy.checkAuthorization(OTHER_UID).getCode()).isEqualTo(Status.OK.getCode());
+  }
+
+  @Test
+  public void testHasSameSignatureAsPlatform_failsIfPackageNameDoesNotMatch() {
+    setupPlatformSignature(SIG1);
+    PackageInfo info =
+        newBuilder()
+            .setPackageName(OTHER_UID_SAME_SIGNATURE_PACKAGE_NAME)
+            .setSignatures(SIG1)
+            .build();
+    installPackages(OTHER_UID_SAME_SIGNATURE, info);
+
+    policy =
+        SecurityPolicies.hasSameSignatureAsPlatform(
+            packageManager, appContext.getPackageName(), MoreExecutors.newDirectExecutorService());
+
+    assertThat(policy.checkAuthorization(OTHER_UID_SAME_SIGNATURE).getCode())
+        .isEqualTo(Status.PERMISSION_DENIED.getCode());
+  }
+
+  @Test
+  public void testHasSameSignatureAsPlatform_failsIfSignatureDoesNotMatch() {
+    setupPlatformSignature(SIG1);
+    PackageInfo info =
+        newBuilder().setPackageName(OTHER_UID_PACKAGE_NAME).setSignatures(SIG2).build();
+    installPackages(OTHER_UID, info);
+
+    policy =
+        SecurityPolicies.hasSameSignatureAsPlatform(
+            packageManager, OTHER_UID_PACKAGE_NAME, MoreExecutors.newDirectExecutorService());
+
+    assertThat(policy.checkAuthorization(OTHER_UID).getCode())
+        .isEqualTo(Status.PERMISSION_DENIED.getCode());
+  }
+
+  @Test
+  public void testHasSameSignatureAsPlatform_failsIfUidUnknown() {
+    setupPlatformSignature(SIG1);
+    policy =
+        SecurityPolicies.hasSameSignatureAsPlatform(
+            packageManager, appContext.getPackageName(), MoreExecutors.newDirectExecutorService());
+
+    assertThat(policy.checkAuthorization(OTHER_UID_UNKNOWN).getCode())
+        .isEqualTo(Status.UNAUTHENTICATED.getCode());
+  }
+
   @Test
   public void testOneOfSignatures_succeedsIfPackageNameAndSignaturesMatch()
       throws Exception {