xref: /aosp14/frameworks/base/services/core/java/com/android/server/pm/ApkChecksums.java

/*
 * Copyright (C) 2020 The Android Open Source 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 com.android.server.pm;

import static android.content.pm.Checksum.TYPE_PARTIAL_MERKLE_ROOT_1M_SHA256;
import static android.content.pm.Checksum.TYPE_PARTIAL_MERKLE_ROOT_1M_SHA512;
import static android.content.pm.Checksum.TYPE_WHOLE_MD5;
import static android.content.pm.Checksum.TYPE_WHOLE_MERKLE_ROOT_4K_SHA256;
import static android.content.pm.Checksum.TYPE_WHOLE_SHA1;
import static android.content.pm.Checksum.TYPE_WHOLE_SHA256;
import static android.content.pm.Checksum.TYPE_WHOLE_SHA512;
import static android.content.pm.parsing.ApkLiteParseUtils.APK_FILE_EXTENSION;
import static android.util.apk.ApkSigningBlockUtils.CONTENT_DIGEST_CHUNKED_SHA256;
import static android.util.apk.ApkSigningBlockUtils.CONTENT_DIGEST_CHUNKED_SHA512;
import static android.util.apk.ApkSigningBlockUtils.CONTENT_DIGEST_VERITY_CHUNKED_SHA256;

import android.annotation.NonNull;
import android.annotation.Nullable;
import android.content.Context;
import android.content.pm.ApkChecksum;
import android.content.pm.Checksum;
import android.content.pm.IOnChecksumsReadyListener;
import android.content.pm.PackageManagerInternal;
import android.content.pm.Signature;
import android.content.pm.SigningDetails.SignatureSchemeVersion;
import android.content.pm.parsing.ApkLiteParseUtils;
import android.content.pm.parsing.result.ParseResult;
import android.content.pm.parsing.result.ParseTypeImpl;
import android.os.Environment;
import android.os.FileUtils;
import android.os.Handler;
import android.os.RemoteException;
import android.os.SystemClock;
import android.os.incremental.IncrementalManager;
import android.os.incremental.IncrementalStorage;
import android.util.ArrayMap;
import android.util.ArraySet;
import android.util.Pair;
import android.util.Slog;
import android.util.apk.ApkSignatureSchemeV2Verifier;
import android.util.apk.ApkSignatureSchemeV3Verifier;
import android.util.apk.ApkSignatureSchemeV4Verifier;
import android.util.apk.ApkSignatureVerifier;
import android.util.apk.ApkSigningBlockUtils;
import android.util.apk.ByteBufferFactory;
import android.util.apk.SignatureInfo;
import android.util.apk.SignatureNotFoundException;
import android.util.apk.VerityBuilder;

import com.android.internal.annotations.VisibleForTesting;
import com.android.internal.security.VerityUtils;
import com.android.server.pm.pkg.AndroidPackage;

import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.file.Files;
import java.security.DigestException;
import java.security.InvalidParameterException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SignatureException;
import java.security.cert.Certificate;
import java.security.cert.CertificateEncodingException;
import java.security.cert.X509Certificate;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Set;

import sun.security.pkcs.PKCS7;
import sun.security.pkcs.SignerInfo;

/**
 * Provides checksums for APK.
 */
public class ApkChecksums {
    static final String TAG = "ApkChecksums";

    private static final String DIGESTS_FILE_EXTENSION = ".digests";
    private static final String DIGESTS_SIGNATURE_FILE_EXTENSION = ".signature";

    // MessageDigest algorithms.
    static final String ALGO_MD5 = "MD5";
    static final String ALGO_SHA1 = "SHA1";
    static final String ALGO_SHA256 = "SHA256";
    static final String ALGO_SHA512 = "SHA512";

    private static final Certificate[] EMPTY_CERTIFICATE_ARRAY = {};

    /**
     * Check back in 1 second after we detected we needed to wait for the APK to be fully available.
     */
    private static final long PROCESS_REQUIRED_CHECKSUMS_DELAY_MILLIS = 1000;

    /**
     * 24 hours timeout to wait till all files are loaded.
     */
    private static final long PROCESS_REQUIRED_CHECKSUMS_TIMEOUT_MILLIS = 1000 * 3600 * 24;

    /**
     * Unit tests will instantiate, extend and/or mock to mock dependencies / behaviors.
     *
     * NOTE: All getters should return the same instance for every call.
     */
    @VisibleForTesting(visibility = VisibleForTesting.Visibility.PRIVATE)
    static class Injector {

        @VisibleForTesting(visibility = VisibleForTesting.Visibility.PRIVATE)
        interface Producer<T> {
            /** Produce an instance of type {@link T} */
            T produce();
        }

        private final Producer<Context> mContext;
        private final Producer<Handler> mHandlerProducer;
        private final Producer<IncrementalManager> mIncrementalManagerProducer;
        private final Producer<PackageManagerInternal> mPackageManagerInternalProducer;

        Injector(Producer<Context> context, Producer<Handler> handlerProducer,
                Producer<IncrementalManager> incrementalManagerProducer,
                Producer<PackageManagerInternal> packageManagerInternalProducer) {
            mContext = context;
            mHandlerProducer = handlerProducer;
            mIncrementalManagerProducer = incrementalManagerProducer;
            mPackageManagerInternalProducer = packageManagerInternalProducer;
        }

        public Context getContext() {
            return mContext.produce();
        }

        public Handler getHandler() {
            return mHandlerProducer.produce();
        }

        public IncrementalManager getIncrementalManager() {
            return mIncrementalManagerProducer.produce();
        }

        public PackageManagerInternal getPackageManagerInternal() {
            return mPackageManagerInternalProducer.produce();
        }
    }

    /**
     * Return the digests path associated with the given code path
     * (replaces '.apk' extension with '.digests')
     *
     * @throws IllegalArgumentException if the code path is not an .apk.
     */
    public static String buildDigestsPathForApk(String codePath) {
        if (!ApkLiteParseUtils.isApkPath(codePath)) {
            throw new IllegalStateException("Code path is not an apk " + codePath);
        }
        return codePath.substring(0, codePath.length() - APK_FILE_EXTENSION.length())
                + DIGESTS_FILE_EXTENSION;
    }

    /**
     * Return the signature path associated with the given digests path.
     * (appends '.signature' to the end)
     */
    public static String buildSignaturePathForDigests(String digestsPath) {
        return digestsPath + DIGESTS_SIGNATURE_FILE_EXTENSION;
    }

    /** Returns true if the given file looks like containing digests or digests' signature. */
    public static boolean isDigestOrDigestSignatureFile(File file) {
        final String name = file.getName();
        return name.endsWith(DIGESTS_FILE_EXTENSION) || name.endsWith(
                DIGESTS_SIGNATURE_FILE_EXTENSION);
    }

    /**
     * Search for the digests file associated with the given target file.
     * If it exists, the method returns the digests file; otherwise it returns null.
     */
    public static File findDigestsForFile(File targetFile) {
        String digestsPath = buildDigestsPathForApk(targetFile.getAbsolutePath());
        File digestsFile = new File(digestsPath);
        return digestsFile.exists() ? digestsFile : null;
    }

    /**
     * Search for the signature file associated with the given digests file.
     * If it exists, the method returns the signature file; otherwise it returns null.
     */
    public static File findSignatureForDigests(File digestsFile) {
        String signaturePath = buildSignaturePathForDigests(digestsFile.getAbsolutePath());
        File signatureFile = new File(signaturePath);
        return signatureFile.exists() ? signatureFile : null;
    }

    /**
     * Serialize checksums to the stream in binary format.
     */
    public static void writeChecksums(OutputStream os, Checksum[] checksums)
            throws IOException {
        try (DataOutputStream dos = new DataOutputStream(os)) {
            for (Checksum checksum : checksums) {
                Checksum.writeToStream(dos, checksum);
            }
        }
    }

    private static Checksum[] readChecksums(File file) throws IOException {
        try (InputStream is = new FileInputStream(file)) {
            return readChecksums(is);
        }
    }

    /**
     * Deserialize array of checksums previously stored in
     * {@link #writeChecksums(OutputStream, Checksum[])}.
     */
    public static Checksum[] readChecksums(InputStream is) throws IOException {
        try (DataInputStream dis = new DataInputStream(is)) {
            ArrayList<Checksum> checksums = new ArrayList<>();
            try {
                // 100 is an arbitrary very big number. We should stop at EOF.
                for (int i = 0; i < 100; ++i) {
                    checksums.add(Checksum.readFromStream(dis));
                }
            } catch (EOFException e) {
                // expected
            }
            return checksums.toArray(new Checksum[checksums.size()]);
        }
    }

    /**
     * Verifies signature over binary serialized checksums.
     * @param checksums array of checksums
     * @param signature detached PKCS7 signature in DER format
     * @return all certificates that passed verification
     * @throws SignatureException if verification fails
     */
    public static @NonNull Certificate[] verifySignature(Checksum[] checksums, byte[] signature)
            throws NoSuchAlgorithmException, IOException, SignatureException {
        final byte[] blob;
        try (ByteArrayOutputStream os = new ByteArrayOutputStream()) {
            writeChecksums(os, checksums);
            blob = os.toByteArray();
        }

        PKCS7 pkcs7 = new PKCS7(signature);

        final Certificate[] certs = pkcs7.getCertificates();
        if (certs == null || certs.length == 0) {
            throw new SignatureException("Signature missing certificates");
        }

        final SignerInfo[] signerInfos = pkcs7.verify(blob);
        if (signerInfos == null || signerInfos.length == 0) {
            throw new SignatureException("Verification failed");
        }

        ArrayList<Certificate> certificates = new ArrayList<>(signerInfos.length);
        for (SignerInfo signerInfo : signerInfos) {
            ArrayList<X509Certificate> chain = signerInfo.getCertificateChain(pkcs7);
            if (chain == null) {
                throw new SignatureException(
                        "Verification passed, but certification chain is empty.");
            }
            certificates.addAll(chain);
        }

        return certificates.toArray(new Certificate[certificates.size()]);
    }

    /**
     * Fetch or calculate checksums for the collection of files.
     *
     * @param filesToChecksum          split name, null for base and File to fetch checksums for
     * @param optional                 mask to fetch readily available checksums
     * @param required                 mask to forcefully calculate if not available
     * @param installerPackageName     package name of the installer of the packages
     * @param trustedInstallers        array of certificate to trust, two specific cases:
     *                                 null - trust anybody,
     *                                 [] - trust nobody.
     * @param onChecksumsReadyListener to receive the resulting checksums
     */
    public static void getChecksums(List<Pair<String, File>> filesToChecksum,
            @Checksum.TypeMask int optional,
            @Checksum.TypeMask int required,
            @Nullable String installerPackageName,
            @Nullable Certificate[] trustedInstallers,
            @NonNull IOnChecksumsReadyListener onChecksumsReadyListener,
            @NonNull Injector injector) {
        List<Map<Integer, ApkChecksum>> result = new ArrayList<>(filesToChecksum.size());
        for (int i = 0, size = filesToChecksum.size(); i < size; ++i) {
            final String split = filesToChecksum.get(i).first;
            final File file = filesToChecksum.get(i).second;
            Map<Integer, ApkChecksum> checksums = new ArrayMap<>();
            result.add(checksums);

            try {
                getAvailableApkChecksums(split, file, optional | required, installerPackageName,
                        trustedInstallers, checksums, injector);
            } catch (Throwable e) {
                Slog.e(TAG, "Preferred checksum calculation error", e);
            }
        }

        long startTime = SystemClock.uptimeMillis();
        processRequiredChecksums(filesToChecksum, result, required, onChecksumsReadyListener,
                injector, startTime);
    }

    private static void processRequiredChecksums(List<Pair<String, File>> filesToChecksum,
            List<Map<Integer, ApkChecksum>> result,
            @Checksum.TypeMask int required,
            @NonNull IOnChecksumsReadyListener onChecksumsReadyListener,
            @NonNull Injector injector,
            long startTime) {
        final boolean timeout =
                SystemClock.uptimeMillis() - startTime >= PROCESS_REQUIRED_CHECKSUMS_TIMEOUT_MILLIS;
        List<ApkChecksum> allChecksums = new ArrayList<>();
        for (int i = 0, size = filesToChecksum.size(); i < size; ++i) {
            final String split = filesToChecksum.get(i).first;
            final File file = filesToChecksum.get(i).second;
            Map<Integer, ApkChecksum> checksums = result.get(i);

            try {
                if (!timeout || required != 0) {
                    if (needToWait(file, required, checksums, injector)) {
                        // Not ready, come back later.
                        injector.getHandler().postDelayed(() -> {
                            processRequiredChecksums(filesToChecksum, result, required,
                                    onChecksumsReadyListener, injector, startTime);
                        }, PROCESS_REQUIRED_CHECKSUMS_DELAY_MILLIS);
                        return;
                    }

                    getRequiredApkChecksums(split, file, required, checksums);
                }
                allChecksums.addAll(checksums.values());
            } catch (Throwable e) {
                Slog.e(TAG, "Required checksum calculation error", e);
            }
        }

        try {
            onChecksumsReadyListener.onChecksumsReady(allChecksums);
        } catch (RemoteException e) {
            Slog.w(TAG, e);
        }
    }

    /**
     * Fetch readily available checksums - enforced by kernel or provided by Installer.
     *
     * @param split                 split name, null for base
     * @param file                  to fetch checksums for
     * @param types                 mask to fetch checksums
     * @param installerPackageName  package name of the installer of the packages
     * @param trustedInstallers     array of certificate to trust, two specific cases:
     *                              null - trust anybody,
     *                              [] - trust nobody.
     * @param checksums             resulting checksums
     */
    private static void getAvailableApkChecksums(String split, File file,
            @Checksum.TypeMask int types,
            @Nullable String installerPackageName,
            @Nullable Certificate[] trustedInstallers,
            Map<Integer, ApkChecksum> checksums,
            @NonNull Injector injector) {
        final String filePath = file.getAbsolutePath();

        // Always available: FSI or IncFs.
        if (isRequired(TYPE_WHOLE_MERKLE_ROOT_4K_SHA256, types, checksums)) {
            // Hashes in fs-verity and IncFS are always verified.
            ApkChecksum checksum = extractHashFromFS(split, filePath);
            if (checksum != null) {
                checksums.put(checksum.getType(), checksum);
            }
        }

        // System enforced: v2/v3.
        if (isRequired(TYPE_PARTIAL_MERKLE_ROOT_1M_SHA256, types, checksums) || isRequired(
                TYPE_PARTIAL_MERKLE_ROOT_1M_SHA512, types, checksums)) {
            Map<Integer, ApkChecksum> v2v3checksums = extractHashFromV2V3Signature(
                    split, filePath, types);
            if (v2v3checksums != null) {
                checksums.putAll(v2v3checksums);
            }
        }

        // Note: this compares installer and system digests internally and
        // has to be called right after all system digests are populated.
        getInstallerChecksums(split, file, types, installerPackageName, trustedInstallers,
                checksums, injector);
    }

    private static void getInstallerChecksums(String split, File file,
            @Checksum.TypeMask int types,
            @Nullable String installerPackageName,
            @Nullable Certificate[] trustedInstallers,
            Map<Integer, ApkChecksum> checksums,
            @NonNull Injector injector) {
        if (PackageManagerServiceUtils.isInstalledByAdb(installerPackageName)) {
            return;
        }
        if (trustedInstallers != null && trustedInstallers.length == 0) {
            return;
        }

        final File digestsFile = findDigestsForFile(file);
        if (digestsFile == null) {
            return;
        }
        final File signatureFile = findSignatureForDigests(digestsFile);

        try {
            final Checksum[] digests = readChecksums(digestsFile);
            final Signature[] certs;
            final Signature[] pastCerts;

            if (signatureFile != null) {
                final Certificate[] certificates = verifySignature(digests,
                        Files.readAllBytes(signatureFile.toPath()));
                if (certificates == null || certificates.length == 0) {
                    Slog.e(TAG, "Error validating signature");
                    return;
                }

                certs = new Signature[certificates.length];
                for (int i = 0, size = certificates.length; i < size; i++) {
                    certs[i] = new Signature(certificates[i].getEncoded());
                }

                pastCerts = null;
            } else {
                final AndroidPackage installer = injector.getPackageManagerInternal().getPackage(
                        installerPackageName);
                if (installer == null) {
                    Slog.e(TAG, "Installer package not found.");
                    return;
                }

                // Obtaining array of certificates used for signing the installer package.
                certs = installer.getSigningDetails().getSignatures();
                pastCerts = installer.getSigningDetails().getPastSigningCertificates();
            }
            if (certs == null || certs.length == 0 || certs[0] == null) {
                Slog.e(TAG, "Can't obtain certificates.");
                return;
            }

            // According to V2/V3 signing schema, the first certificate corresponds to the public
            // key in the signing block.
            byte[] trustedCertBytes = certs[0].toByteArray();

            final Set<Signature> trusted = convertToSet(trustedInstallers);

            if (trusted != null && !trusted.isEmpty()) {
                // Obtaining array of certificates used for signing the installer package.
                Signature trustedCert = isTrusted(certs, trusted);
                if (trustedCert == null) {
                    trustedCert = isTrusted(pastCerts, trusted);
                }
                if (trustedCert == null) {
                    return;
                }
                trustedCertBytes = trustedCert.toByteArray();
            }

            // Compare OS-enforced digests.
            for (Checksum digest : digests) {
                final ApkChecksum system = checksums.get(digest.getType());
                if (system != null && !Arrays.equals(system.getValue(), digest.getValue())) {
                    throw new InvalidParameterException("System digest " + digest.getType()
                            + " mismatch, can't bind installer-provided digests to the APK.");
                }
            }

            // Append missing digests.
            for (Checksum digest : digests) {
                if (isRequired(digest.getType(), types, checksums)) {
                    checksums.put(digest.getType(),
                            new ApkChecksum(split, digest, installerPackageName, trustedCertBytes));
                }
            }
        } catch (IOException e) {
            Slog.e(TAG, "Error reading .digests or .signature", e);
        } catch (NoSuchAlgorithmException | SignatureException | InvalidParameterException e) {
            Slog.e(TAG, "Error validating digests. Invalid digests will be removed", e);
            try {
                Files.deleteIfExists(digestsFile.toPath());
                if (signatureFile != null) {
                    Files.deleteIfExists(signatureFile.toPath());
                }
            } catch (IOException ignored) {
            }
        } catch (CertificateEncodingException e) {
            Slog.e(TAG, "Error encoding trustedInstallers", e);
        }
    }

    /**
     * Whether the file is available for checksumming or we need to wait.
     */
    private static boolean needToWait(File file,
            @Checksum.TypeMask int types,
            Map<Integer, ApkChecksum> checksums,
            @NonNull Injector injector) throws IOException {
        if (!isRequired(TYPE_WHOLE_MERKLE_ROOT_4K_SHA256, types, checksums)
                && !isRequired(TYPE_WHOLE_MD5, types, checksums)
                && !isRequired(TYPE_WHOLE_SHA1, types, checksums)
                && !isRequired(TYPE_WHOLE_SHA256, types, checksums)
                && !isRequired(TYPE_WHOLE_SHA512, types, checksums)
                && !isRequired(TYPE_PARTIAL_MERKLE_ROOT_1M_SHA256, types, checksums)
                && !isRequired(TYPE_PARTIAL_MERKLE_ROOT_1M_SHA512, types, checksums)) {
            return false;
        }

        final String filePath = file.getAbsolutePath();
        if (!IncrementalManager.isIncrementalPath(filePath)) {
            return false;
        }

        IncrementalManager manager = injector.getIncrementalManager();
        if (manager == null) {
            Slog.e(TAG, "IncrementalManager is missing.");
            return false;
        }
        IncrementalStorage storage = manager.openStorage(filePath);
        if (storage == null) {
            Slog.e(TAG, "IncrementalStorage is missing for a path on IncFs: " + filePath);
            return false;
        }

        return !storage.isFileFullyLoaded(filePath);
    }

    /**
     * Fetch or calculate checksums for the specific file.
     *
     * @param split     split name, null for base
     * @param file      to fetch checksums for
     * @param types     mask to forcefully calculate if not available
     * @param checksums resulting checksums
     */
    private static void getRequiredApkChecksums(String split, File file,
            @Checksum.TypeMask int types,
            Map<Integer, ApkChecksum> checksums) {
        final String filePath = file.getAbsolutePath();

        // Manually calculating required checksums if not readily available.
        if (isRequired(TYPE_WHOLE_MERKLE_ROOT_4K_SHA256, types, checksums)) {
            try {
                byte[] generatedRootHash = VerityBuilder.generateFsVerityRootHash(
                        filePath, /*salt=*/null,
                        new ByteBufferFactory() {
                            @Override
                            public ByteBuffer create(int capacity) {
                                return ByteBuffer.allocate(capacity);
                            }
                        });
                checksums.put(TYPE_WHOLE_MERKLE_ROOT_4K_SHA256,
                        new ApkChecksum(split, TYPE_WHOLE_MERKLE_ROOT_4K_SHA256,
                                verityHashForFile(file, generatedRootHash)));
            } catch (IOException | NoSuchAlgorithmException | DigestException e) {
                Slog.e(TAG, "Error calculating WHOLE_MERKLE_ROOT_4K_SHA256", e);
            }
        }

        calculateChecksumIfRequested(checksums, split, file, types, TYPE_WHOLE_MD5);
        calculateChecksumIfRequested(checksums, split, file, types, TYPE_WHOLE_SHA1);
        calculateChecksumIfRequested(checksums, split, file, types, TYPE_WHOLE_SHA256);
        calculateChecksumIfRequested(checksums, split, file, types, TYPE_WHOLE_SHA512);

        calculatePartialChecksumsIfRequested(checksums, split, file, types);
    }

    private static boolean isRequired(@Checksum.Type int type,
            @Checksum.TypeMask int types, Map<Integer, ApkChecksum> checksums) {
        if ((types & type) == 0) {
            return false;
        }
        if (checksums.containsKey(type)) {
            return false;
        }
        return true;
    }

    /**
     * Signature class provides a fast way to compare certificates using their hashes.
     * The hash is exactly the same as in X509/Certificate.
     */
    private static Set<Signature> convertToSet(@Nullable Certificate[] array) throws
            CertificateEncodingException {
        if (array == null) {
            return null;
        }
        final Set<Signature> set = new ArraySet<>(array.length);
        for (Certificate item : array) {
            set.add(new Signature(item.getEncoded()));
        }
        return set;
    }

    private static Signature isTrusted(Signature[] signatures, Set<Signature> trusted) {
        if (signatures == null) {
            return null;
        }
        for (Signature signature : signatures) {
            if (trusted.contains(signature)) {
                return signature;
            }
        }
        return null;
    }

    private static boolean containsFile(File dir, String filePath) {
        if (dir == null) {
            return false;
        }
        return FileUtils.contains(dir.getAbsolutePath(), filePath);
    }

    private static ApkChecksum extractHashFromFS(String split, String filePath) {
        // verity first
        // Skip /product folder.
        // TODO(b/231354111): remove this hack once we are allowed to change SELinux rules.
        if (!containsFile(Environment.getProductDirectory(), filePath)) {
            byte[] verityHash = VerityUtils.getFsverityDigest(filePath);
            if (verityHash != null) {
                return new ApkChecksum(split, TYPE_WHOLE_MERKLE_ROOT_4K_SHA256, verityHash);
            }
        }
        // v4 next
        try {
            ApkSignatureSchemeV4Verifier.VerifiedSigner signer =
                    ApkSignatureSchemeV4Verifier.extractCertificates(filePath);
            byte[] rootHash = signer.contentDigests.getOrDefault(
                    CONTENT_DIGEST_VERITY_CHUNKED_SHA256, null);
            if (rootHash != null) {
                return new ApkChecksum(split, TYPE_WHOLE_MERKLE_ROOT_4K_SHA256,
                        verityHashForFile(new File(filePath), rootHash));
            }
        } catch (SignatureNotFoundException e) {
            // Nothing
        } catch (SecurityException e) {
            Slog.e(TAG, "V4 signature error", e);
        }
        return null;
    }

    /**
     * Returns fs-verity digest as described in
     * https://www.kernel.org/doc/html/latest/filesystems/fsverity.html#fs-verity-descriptor
     * @param file the Merkle tree is built over
     * @param rootHash Merkle tree root hash
     */
    static byte[] verityHashForFile(File file, byte[] rootHash) {
        try {
            ByteBuffer buffer = ByteBuffer.allocate(256); // sizeof(fsverity_descriptor)
            buffer.order(ByteOrder.LITTLE_ENDIAN);
            buffer.put((byte) 1);               // __u8 version, must be 1
            buffer.put((byte) 1);               // __u8 hash_algorithm, FS_VERITY_HASH_ALG_SHA256
            buffer.put((byte) 12);              // __u8, FS_VERITY_LOG_BLOCKSIZE
            buffer.put((byte) 0);               // __u8, size of salt in bytes; 0 if none
            buffer.putInt(0);                   // __le32 __reserved_0x04, must be 0
            buffer.putLong(file.length());      // __le64 data_size
            buffer.put(rootHash);               // root_hash, first 32 bytes
            final int padding = 32 + 32 + 144;  // root_hash, last 32 bytes, we are using sha256.
            // salt, 32 bytes
            // reserved, 144 bytes
            for (int i = 0; i < padding; ++i) {
                buffer.put((byte) 0);
            }

            buffer.flip();

            final MessageDigest md = MessageDigest.getInstance(ALGO_SHA256);
            md.update(buffer);
            return md.digest();
        } catch (NoSuchAlgorithmException e) {
            Slog.e(TAG, "Device does not support MessageDigest algorithm", e);
            return null;
        }
    }

    private static Map<Integer, ApkChecksum> extractHashFromV2V3Signature(
            String split, String filePath, int types) {
        Map<Integer, byte[]> contentDigests = null;
        final ParseTypeImpl input = ParseTypeImpl.forDefaultParsing();
        final ParseResult<ApkSignatureVerifier.SigningDetailsWithDigests> result =
                ApkSignatureVerifier.verifySignaturesInternal(input, filePath,
                        SignatureSchemeVersion.SIGNING_BLOCK_V2, false /*verifyFull*/);
        if (result.isError()) {
            if (!(result.getException() instanceof SignatureNotFoundException)) {
                Slog.e(TAG, "Signature verification error", result.getException());
            }
        } else {
            contentDigests = result.getResult().contentDigests;
        }

        if (contentDigests == null) {
            return null;
        }

        Map<Integer, ApkChecksum> checksums = new ArrayMap<>();
        if ((types & TYPE_PARTIAL_MERKLE_ROOT_1M_SHA256) != 0) {
            byte[] hash = contentDigests.getOrDefault(CONTENT_DIGEST_CHUNKED_SHA256, null);
            if (hash != null) {
                checksums.put(TYPE_PARTIAL_MERKLE_ROOT_1M_SHA256,
                        new ApkChecksum(split, TYPE_PARTIAL_MERKLE_ROOT_1M_SHA256, hash));
            }
        }
        if ((types & TYPE_PARTIAL_MERKLE_ROOT_1M_SHA512) != 0) {
            byte[] hash = contentDigests.getOrDefault(CONTENT_DIGEST_CHUNKED_SHA512, null);
            if (hash != null) {
                checksums.put(TYPE_PARTIAL_MERKLE_ROOT_1M_SHA512,
                        new ApkChecksum(split, TYPE_PARTIAL_MERKLE_ROOT_1M_SHA512, hash));
            }
        }
        return checksums;
    }

    private static String getMessageDigestAlgoForChecksumKind(int type)
            throws NoSuchAlgorithmException {
        switch (type) {
            case TYPE_WHOLE_MD5:
                return ALGO_MD5;
            case TYPE_WHOLE_SHA1:
                return ALGO_SHA1;
            case TYPE_WHOLE_SHA256:
                return ALGO_SHA256;
            case TYPE_WHOLE_SHA512:
                return ALGO_SHA512;
            default:
                throw new NoSuchAlgorithmException("Invalid checksum type: " + type);
        }
    }

    private static void calculateChecksumIfRequested(Map<Integer, ApkChecksum> checksums,
            String split, File file, int required, int type) {
        if ((required & type) != 0 && !checksums.containsKey(type)) {
            final byte[] checksum = getApkChecksum(file, type);
            if (checksum != null) {
                checksums.put(type, new ApkChecksum(split, type, checksum));
            }
        }
    }

    static final int MIN_BUFFER_SIZE = 4 * 1024;
    static final int MAX_BUFFER_SIZE = 128 * 1024;

    private static byte[] getApkChecksum(File file, int type) {
        final int bufferSize = (int) Math.max(MIN_BUFFER_SIZE,
                Math.min(MAX_BUFFER_SIZE, file.length()));
        try (FileInputStream fis = new FileInputStream(file)) {
            final byte[] buffer = new byte[bufferSize];
            int nread = 0;

            final String algo = getMessageDigestAlgoForChecksumKind(type);
            MessageDigest md = MessageDigest.getInstance(algo);
            while ((nread = fis.read(buffer)) != -1) {
                md.update(buffer, 0, nread);
            }

            return md.digest();
        } catch (IOException e) {
            Slog.e(TAG, "Error reading " + file.getAbsolutePath() + " to compute hash.", e);
            return null;
        } catch (NoSuchAlgorithmException e) {
            Slog.e(TAG, "Device does not support MessageDigest algorithm", e);
            return null;
        }
    }

    private static int[] getContentDigestAlgos(boolean needSignatureSha256,
            boolean needSignatureSha512) {
        if (needSignatureSha256 && needSignatureSha512) {
            // Signature block present, but no digests???
            return new int[]{CONTENT_DIGEST_CHUNKED_SHA256, CONTENT_DIGEST_CHUNKED_SHA512};
        } else if (needSignatureSha256) {
            return new int[]{CONTENT_DIGEST_CHUNKED_SHA256};
        } else {
            return new int[]{CONTENT_DIGEST_CHUNKED_SHA512};
        }
    }

    private static int getChecksumKindForContentDigestAlgo(int contentDigestAlgo) {
        switch (contentDigestAlgo) {
            case CONTENT_DIGEST_CHUNKED_SHA256:
                return TYPE_PARTIAL_MERKLE_ROOT_1M_SHA256;
            case CONTENT_DIGEST_CHUNKED_SHA512:
                return TYPE_PARTIAL_MERKLE_ROOT_1M_SHA512;
            default:
                return -1;
        }
    }

    private static void calculatePartialChecksumsIfRequested(Map<Integer, ApkChecksum> checksums,
            String split, File file, int required) {
        boolean needSignatureSha256 =
                (required & TYPE_PARTIAL_MERKLE_ROOT_1M_SHA256) != 0 && !checksums.containsKey(
                        TYPE_PARTIAL_MERKLE_ROOT_1M_SHA256);
        boolean needSignatureSha512 =
                (required & TYPE_PARTIAL_MERKLE_ROOT_1M_SHA512) != 0 && !checksums.containsKey(
                        TYPE_PARTIAL_MERKLE_ROOT_1M_SHA512);
        if (!needSignatureSha256 && !needSignatureSha512) {
            return;
        }

        try (RandomAccessFile raf = new RandomAccessFile(file, "r")) {
            SignatureInfo signatureInfo = null;
            try {
                signatureInfo = ApkSignatureSchemeV3Verifier.findSignature(raf);
            } catch (SignatureNotFoundException e) {
                try {
                    signatureInfo = ApkSignatureSchemeV2Verifier.findSignature(raf);
                } catch (SignatureNotFoundException ee) {
                }
            }
            if (signatureInfo == null) {
                Slog.e(TAG, "V2/V3 signatures not found in " + file.getAbsolutePath());
                return;
            }

            final int[] digestAlgos = getContentDigestAlgos(needSignatureSha256,
                    needSignatureSha512);
            byte[][] digests = ApkSigningBlockUtils.computeContentDigestsPer1MbChunk(digestAlgos,
                    raf.getFD(), signatureInfo);
            for (int i = 0, size = digestAlgos.length; i < size; ++i) {
                int checksumKind = getChecksumKindForContentDigestAlgo(digestAlgos[i]);
                if (checksumKind != -1) {
                    checksums.put(checksumKind, new ApkChecksum(split, checksumKind, digests[i]));
                }
            }
        } catch (IOException | DigestException e) {
            Slog.e(TAG, "Error computing hash.", e);
        }
    }
}