Sample DexPatcher framework patch to implement microG-style signature spoofing

PackageParser.java

/*
 * Copyright (C) 2014 Marvin W <https://github.com/mar-v-in>
 * Copyright (C) 2016 Lanchon <https://github.com/Lanchon>
 *
 * This is Marvin's work converted to a DexPatcher patch by Lanchon.
 *
 * https://gerrit.omnirom.org/#/c/8672/
 *
 * 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 android.content.pm;

import android.os.Bundle;
import android.util.Log;

import java.util.ArrayList;
import java.util.HashSet;

import lanchon.dexpatcher.annotation.*;

// Lets modify the PackageParser class.
@DexEdit(onlyEditMembers = true)
public class PackageParser {

    // We need to declare these framework symbols so that the compiler will find
    // them when building the patch.
    @DexIgnore
    public final static class Package {
        public final ArrayList<String> requestedPermissions = new ArrayList<String>();
        public Bundle mAppMetaData = null;
    }

    // Wrap the existing generatePackageInfo(...) method with this new method.
    // The new method calls the original, modifies its return value if needed,
    // and passes it back to the caller.
    @DexWrap
    public static PackageInfo generatePackageInfo(PackageParser.Package p,
            int gids[], int flags, long firstInstallTime, long lastUpdateTime,
            HashSet<String> grantedPermissions, PackageUserState state, int userId) {
        // This recursive call gets converted to an invocation of the original
        // method being wrapped.
        PackageInfo pi = generatePackageInfo(p, gids, flags, firstInstallTime,
            lastUpdateTime, grantedPermissions, state, userId);
        if (pi != null) {
            if ((flags & PackageManager.GET_SIGNATURES) != 0) {
                try {
                    if (p.requestedPermissions.contains("android.permission.FAKE_PACKAGE_SIGNATURE") &&
                            p.mAppMetaData != null) {
                        Object fakeSignatureMetaData = p.mAppMetaData.get("fake-signature");
                        if (fakeSignatureMetaData instanceof String) {
                            pi.signatures = new Signature[] { new Signature((String) fakeSignatureMetaData) };
                        }
                    }
                } catch (Throwable t) {
                    // We should never die because of any failures, this is system code!
                    // Eating up instances of Error might seem excessive, but they can be
                    // the result of improperly applied patches so we will handle them here.
                    Log.e("PackageParser_FakePackageSignature", "hook exception", t);
                }
            }
        }
        return pi;
    }

}