apex/apexd/apex_file_repository.cpp

/*
 * Copyright (C) 2019 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.
 */

#include "apex_file_repository.h"

#include <ApexProperties.sysprop.h>
#include <android-base/file.h>
#include <android-base/properties.h>
#include <android-base/result.h>
#include <android-base/stringprintf.h>
#include <android-base/strings.h>
#include <microdroid/metadata.h>

#include <cstdint>
#include <filesystem>
#include <future>
#include <queue>
#include <unordered_map>

#include "apex_blocklist.h"
#include "apex_constants.h"
#include "apex_file.h"
#include "apexd_brand_new_verifier.h"
#include "apexd_utils.h"
#include "apexd_vendor_apex.h"
#include "apexd_verity.h"

using android::base::EndsWith;
using android::base::Error;
using android::base::GetProperty;
using android::base::Result;
using ::apex::proto::ApexBlocklist;

namespace android {
namespace apex {

std::string ConsumeApexPackageSuffix(const std::string& path) {
  std::string_view path_view(path);
  android::base::ConsumeSuffix(&path_view, kApexPackageSuffix);
  android::base::ConsumeSuffix(&path_view, kCompressedApexPackageSuffix);
  return std::string(path_view);
}

std::string GetApexSelectFilenameFromProp(
    const std::vector<std::string>& prefixes, const std::string& apex_name) {
  for (const std::string& prefix : prefixes) {
    const std::string& filename = GetProperty(prefix + apex_name, "");
    if (filename != "") {
      return ConsumeApexPackageSuffix(filename);
    }
  }
  return "";
}

void ApexFileRepository::StorePreInstalledApex(ApexFile&& apex_file,
                                               ApexPartition partition) {
  const std::string& name = apex_file.GetManifest().name();

  // Check if this APEX name is treated as a multi-install APEX.
  //
  // Note: apexd is a oneshot service which runs at boot, but can be
  // restarted when needed (such as staging an APEX update). If a
  // multi-install select property changes between boot and when apexd
  // restarts, the LOG messages below will report the version that will be
  // activated on next reboot, which may differ from the currently-active
  // version.
  std::string select_filename =
      GetApexSelectFilenameFromProp(multi_install_select_prop_prefixes_, name);
  if (!select_filename.empty()) {
    std::string path;
    if (!android::base::Realpath(apex_file.GetPath(), &path)) {
      LOG(ERROR) << "Unable to resolve realpath of APEX with path "
                 << apex_file.GetPath();
      return;
    }
    if (enforce_multi_install_partition_ &&
        partition != ApexPartition::Vendor && partition != ApexPartition::Odm) {
      LOG(ERROR) << "Multi-install APEX " << path
                 << " can only be preinstalled on /{odm,vendor}/apex/.";
      return;
    }

    auto& keys = multi_install_public_keys_[name];
    keys.insert(apex_file.GetBundledPublicKey());
    if (keys.size() > 1) {
      LOG(ERROR) << "Multi-install APEXes for " << name
                 << " have different public keys.";
      // If any versions of a multi-installed APEX differ in public key,
      // then no version should be installed.
      if (auto it = pre_installed_store_.find(name);
          it != pre_installed_store_.end()) {
        pre_installed_store_.erase(it);
        partition_store_.erase(name);
      }
      return;
    }

    if (ConsumeApexPackageSuffix(android::base::Basename(path)) ==
        select_filename) {
      LOG(INFO) << "Found APEX at path " << path << " for multi-install APEX "
                << name;
      // A copy is needed because apex_file is moved here
      const std::string apex_name = name;
      // Add the APEX file to the store if its filename matches the
      // property.
      pre_installed_store_.emplace(apex_name, std::move(apex_file));
      partition_store_.emplace(apex_name, partition);
    } else {
      LOG(INFO) << "Skipping APEX at path " << path
                << " because it does not match expected multi-install"
                << " APEX property for " << name;
    }

    return;
  }

  auto it = pre_installed_store_.find(name);
  if (it == pre_installed_store_.end()) {
    // A copy is needed because apex_file is moved here
    const std::string apex_name = name;
    pre_installed_store_.emplace(apex_name, std::move(apex_file));
    partition_store_.emplace(apex_name, partition);
  } else if (it->second.GetPath() != apex_file.GetPath()) {
    LOG(FATAL) << "Found two apex packages " << it->second.GetPath() << " and "
               << apex_file.GetPath() << " with the same module name " << name;
  } else if (it->second.GetBundledPublicKey() !=
             apex_file.GetBundledPublicKey()) {
    LOG(FATAL) << "Public key of apex package " << it->second.GetPath() << " ("
               << name << ") has unexpectedly changed";
  }
}

Result<std::vector<ApexPath>> ApexFileRepository::CollectPreInstalledApex(
    const std::unordered_map<ApexPartition, std::string>&
        partition_to_prebuilt_dirs) {
  std::vector<ApexPath> all_apex_paths;
  for (const auto& [partition, dir] : partition_to_prebuilt_dirs) {
    LOG(INFO) << "Scanning " << dir << " for pre-installed ApexFiles";
    if (access(dir.c_str(), F_OK) != 0 && errno == ENOENT) {
      LOG(WARNING) << dir << " does not exist. Skipping";
      continue;
    }

    std::vector<std::string> apex_paths = OR_RETURN(FindFilesBySuffix(
        dir, {kApexPackageSuffix, kCompressedApexPackageSuffix}));
    for (auto&& path : apex_paths) {
      LOG(INFO) << "Found pre-installed APEX " << path;
      all_apex_paths.emplace_back(std::move(path), partition);
    }
  }
  return all_apex_paths;
}

Result<std::vector<ApexFileAndPartition>> ApexFileRepository::OpenApexFiles(
    const std::vector<ApexPath>& apex_paths) {
  std::atomic_size_t shared_index{0};
  size_t apex_count = apex_paths.size();

  size_t worker_num =
      android::sysprop::ApexProperties::apex_file_open_threads().value_or(0);
  if (worker_num == 0) {
    worker_num = apex_count;
  } else {
    worker_num = std::min(apex_count, worker_num);
  }

  struct IndexedApexFile {
    ApexFileAndPartition apex_file;
    size_t index;
  };
  std::vector<std::future<Result<std::vector<IndexedApexFile>>>> futures;
  futures.reserve(worker_num);

  for (size_t i = 0; i < worker_num; i++) {
    futures.push_back(std::async(
        std::launch::async,
        [&shared_index, apex_paths,
         apex_count]() -> Result<std::vector<IndexedApexFile>> {
          std::vector<IndexedApexFile> ret;
          size_t current_index;
          while ((current_index = shared_index.fetch_add(
                      1, std::memory_order_relaxed)) < apex_count) {
            const ApexPath& apex_path = apex_paths[current_index];
            Result<ApexFile> apex_file = ApexFile::Open(apex_path.path);
            if (apex_file.ok()) {
              ret.emplace_back(ApexFileAndPartition(std::move(*apex_file),
                                                    apex_path.partition),
                               current_index);
            } else {
              return Error() << "Failed to open apex file " << apex_path.path
                             << " : " << apex_file.error();
            }
          }
          return {ret};
        }));
  }

  std::vector<std::optional<ApexFileAndPartition>> optional_apex_files;
  optional_apex_files.resize(apex_count);
  for (auto& future : futures) {
    auto res = OR_RETURN(future.get());
    for (auto&& indexed_apex_file : res) {
      optional_apex_files[indexed_apex_file.index] =
          std::move(indexed_apex_file.apex_file);
    }
  }

  std::vector<ApexFileAndPartition> apex_files;
  apex_files.reserve(apex_count);
  for (auto&& optional_apex_file : optional_apex_files) {
    if (optional_apex_file.has_value()) {
      apex_files.push_back(optional_apex_file.value());
    }
  }
  return apex_files;
}

ApexFileRepository& ApexFileRepository::GetInstance() {
  static ApexFileRepository instance;
  return instance;
}

android::base::Result<void> ApexFileRepository::AddPreInstalledApex(
    const std::unordered_map<ApexPartition, std::string>&
        partition_to_prebuilt_dirs) {
  auto all_apex_paths =
      OR_RETURN(CollectPreInstalledApex(partition_to_prebuilt_dirs));

  for (const auto& apex_path : all_apex_paths) {
    Result<ApexFile> apex_file = ApexFile::Open(apex_path.path);
    if (!apex_file.ok()) {
      return Error() << "Failed to open " << apex_path.path << " : "
                     << apex_file.error();
    }

    StorePreInstalledApex(std::move(*apex_file), apex_path.partition);
  }
  multi_install_public_keys_.clear();
  return {};
}

android::base::Result<void> ApexFileRepository::AddPreInstalledApexParallel(
    const std::unordered_map<ApexPartition, std::string>&
        partition_to_prebuilt_dirs) {
  auto all_apex_paths =
      OR_RETURN(CollectPreInstalledApex(partition_to_prebuilt_dirs));

  auto apex_file_and_partition = OR_RETURN(OpenApexFiles(all_apex_paths));

  for (auto&& [apex_file, partition] : apex_file_and_partition) {
    StorePreInstalledApex(std::move(apex_file), partition);
  }
  multi_install_public_keys_.clear();
  return {};
}

Result<int> ApexFileRepository::AddBlockApex(
    const std::string& metadata_partition) {
  CHECK(!block_disk_path_.has_value())
      << "AddBlockApex() can't be called twice.";

  auto metadata_ready = WaitForFile(metadata_partition, kBlockApexWaitTime);
  if (!metadata_ready.ok()) {
    LOG(ERROR) << "Error waiting for metadata_partition : "
               << metadata_ready.error();
    return {};
  }

  // TODO(b/185069443) consider moving the logic to find disk_path from
  // metadata_partition to its own library
  LOG(INFO) << "Scanning " << metadata_partition << " for host apexes";
  if (access(metadata_partition.c_str(), F_OK) != 0 && errno == ENOENT) {
    LOG(WARNING) << metadata_partition << " does not exist. Skipping";
    return {};
  }

  std::string metadata_realpath;
  if (!android::base::Realpath(metadata_partition, &metadata_realpath)) {
    LOG(WARNING) << "Can't get realpath of " << metadata_partition
                 << ". Skipping";
    return {};
  }

  std::string_view metadata_path_view(metadata_realpath);
  if (!android::base::ConsumeSuffix(&metadata_path_view, "1")) {
    LOG(WARNING) << metadata_realpath << " is not a first partition. Skipping";
    return {};
  }

  block_disk_path_ = std::string(metadata_path_view);

  // Read the payload metadata.
  // "metadata" can be overridden by microdroid_manager. To ensure that
  // "microdroid" is started with the same/unmodified set of host APEXes,
  // microdroid stores APEXes' pubkeys in its encrypted instance disk. Next
  // time, microdroid checks if there's pubkeys in the instance disk and use
  // them to activate APEXes. Microdroid_manager passes pubkeys in instance.img
  // via the following file.
  if (auto exists = PathExists("/apex/vm-payload-metadata");
      exists.ok() && *exists) {
    metadata_realpath = "/apex/vm-payload-metadata";
    LOG(INFO) << "Overriding metadata to " << metadata_realpath;
  }
  auto metadata = android::microdroid::ReadMetadata(metadata_realpath);
  if (!metadata.ok()) {
    LOG(WARNING) << "Failed to load metadata from " << metadata_realpath
                 << ". Skipping: " << metadata.error();
    return {};
  }

  int ret = 0;

  // subsequent partitions are APEX archives.
  static constexpr const int kFirstApexPartition = 2;
  for (int i = 0; i < metadata->apexes_size(); i++) {
    const auto& apex_config = metadata->apexes(i);

    const std::string apex_path =
        *block_disk_path_ + std::to_string(i + kFirstApexPartition);

    auto apex_ready = WaitForFile(apex_path, kBlockApexWaitTime);
    if (!apex_ready.ok()) {
      return Error() << "Error waiting for apex file : " << apex_ready.error();
    }

    auto apex_file = ApexFile::Open(apex_path);
    if (!apex_file.ok()) {
      return Error() << "Failed to open " << apex_path << " : "
                     << apex_file.error();
    }

    const std::string& name = apex_file->GetManifest().name();
    LOG(INFO) << "Found host apex " << name << " at " << apex_path;

    // When metadata specifies the public key of the apex, it should match the
    // bundled key. Otherwise we accept it.
    if (apex_config.public_key() != "" &&
        apex_config.public_key() != apex_file->GetBundledPublicKey()) {
      return Error() << "public key doesn't match: " << apex_path;
    }

    // When metadata specifies the manifest name and version of the apex, it
    // should match what we see in the manifest.
    if (apex_config.manifest_name() != "" &&
        apex_config.manifest_name() != name) {
      return Error() << "manifest name doesn't match: " << apex_path;
    }

    if (apex_config.manifest_version() != 0 &&
        apex_config.manifest_version() != apex_file->GetManifest().version()) {
      return Error() << "manifest version doesn't match: " << apex_path;
    }

    BlockApexOverride overrides;

    // A block device doesn't have an inherent timestamp, so it is carried in
    // the metadata.
    if (int64_t last_update_seconds = apex_config.last_update_seconds();
        last_update_seconds != 0) {
      overrides.last_update_seconds = last_update_seconds;
    }

    // When metadata specifies the root digest of the apex, it should be used
    // when activating the apex. So we need to keep it.
    if (auto root_digest = apex_config.root_digest(); root_digest != "") {
      overrides.block_apex_root_digest =
          BytesToHex(reinterpret_cast<const uint8_t*>(root_digest.data()),
                     root_digest.size());
    }

    if (overrides.last_update_seconds.has_value() ||
        overrides.block_apex_root_digest.has_value()) {
      block_apex_overrides_.emplace(apex_path, std::move(overrides));
    }

    // Depending on whether the APEX was a factory version in the host or not,
    // put it to different stores.
    auto& store = apex_config.is_factory() ? pre_installed_store_ : data_store_;
    // We want "uniqueness" in each store.
    if (auto it = store.find(name); it != store.end()) {
      return Error() << "duplicate of " << name << " found in "
                     << it->second.GetPath();
    }
    store.emplace(name, std::move(*apex_file));
    // NOTE: We consider block APEXes are SYSTEM. APEX Config should be extended
    //       to support non-system block APEXes.
    partition_store_.emplace(name, ApexPartition::System);

    ret++;
  }
  return {ret};
}

// TODO(b/179497746): AddDataApex should not concern with filtering out invalid
//   apex.
Result<void> ApexFileRepository::AddDataApex(const std::string& data_dir) {
  LOG(INFO) << "Scanning " << data_dir << " for data ApexFiles";
  if (access(data_dir.c_str(), F_OK) != 0 && errno == ENOENT) {
    LOG(WARNING) << data_dir << " does not exist. Skipping";
    return {};
  }

  Result<std::vector<std::string>> active_apex =
      FindFilesBySuffix(data_dir, {kApexPackageSuffix});
  if (!active_apex.ok()) {
    return active_apex.error();
  }

  // TODO(b/179248390): scan parallelly if possible
  for (const auto& file : *active_apex) {
    LOG(INFO) << "Found updated apex " << file;
    Result<ApexFile> apex_file = ApexFile::Open(file);
    if (!apex_file.ok()) {
      LOG(ERROR) << "Failed to open " << file << " : " << apex_file.error();
      continue;
    }

    const std::string& name = apex_file->GetManifest().name();
    auto preinstalled = pre_installed_store_.find(name);
    if (preinstalled != pre_installed_store_.end()) {
      if (preinstalled->second.GetBundledPublicKey() !=
          apex_file->GetBundledPublicKey()) {
        // Ignore data apex if public key doesn't match with pre-installed apex
        LOG(ERROR) << "Skipping " << file
                   << " : public key doesn't match pre-installed one";
        continue;
      }
    } else if (ApexFileRepository::IsBrandNewApexEnabled()) {
      auto verified_partition =
          VerifyBrandNewPackageAgainstPreinstalled(*apex_file);
      if (!verified_partition.ok()) {
        LOG(ERROR) << "Skipping " << file << " : "
                   << verified_partition.error();
        continue;
      }
      // Stores partition for already-verified brand-new APEX.
      partition_store_.emplace(name, *verified_partition);
    } else {
      LOG(ERROR) << "Skipping " << file << " : no preinstalled apex";
      // Ignore data apex without corresponding pre-installed apex
      continue;
    }

    std::string select_filename = GetApexSelectFilenameFromProp(
        multi_install_select_prop_prefixes_, name);
    if (!select_filename.empty()) {
      LOG(WARNING) << "APEX " << name << " is a multi-installed APEX."
                   << " Any updated version in /data will always overwrite"
                   << " the multi-installed preinstalled version, if possible.";
    }

    if (EndsWith(apex_file->GetPath(), kDecompressedApexPackageSuffix)) {
      LOG(WARNING) << "Skipping " << file
                   << " : Non-decompressed APEX should not have "
                   << kDecompressedApexPackageSuffix << " suffix";
      continue;
    }

    auto it = data_store_.find(name);
    if (it == data_store_.end()) {
      data_store_.emplace(name, std::move(*apex_file));
      continue;
    }

    const auto& existing_version = it->second.GetManifest().version();
    const auto new_version = apex_file->GetManifest().version();
    // If multiple data apexs are preset, select the one with highest version
    bool prioritize_higher_version = new_version > existing_version;
    // For same version, non-decompressed apex gets priority
    if (prioritize_higher_version) {
      it->second = std::move(*apex_file);
    }
  }
  return {};
}

Result<void> ApexFileRepository::AddBrandNewApexCredentialAndBlocklist(
    const std::unordered_map<ApexPartition, std::string>&
        partition_to_dir_map) {
  for (const auto& [partition, dir] : partition_to_dir_map) {
    LOG(INFO)
        << "Scanning " << dir
        << " for pre-installed public keys and blocklists of brand-new APEX";
    if (access(dir.c_str(), F_OK) != 0 && errno == ENOENT) {
      continue;
    }

    std::vector<std::string> all_credential_files =
        OR_RETURN(FindFilesBySuffix(dir, {kBrandNewApexPublicKeySuffix}));
    for (const std::string& credential_path : all_credential_files) {
      std::string content;
      CHECK(android::base::ReadFileToString(credential_path, &content));
      const auto& [it, inserted] =
          brand_new_apex_pubkeys_.emplace(content, partition);
      CHECK(inserted || it->second == partition)
          << "Duplicate public keys are found in different partitions.";
    }

    const std::string& blocklist_path =
        std::filesystem::path(dir) / kBrandNewApexBlocklistFileName;
    const auto blocklist_exists = OR_RETURN(PathExists(blocklist_path));
    if (!blocklist_exists) {
      continue;
    }

    std::unordered_map<std::string, int64_t> apex_name_to_version;
    ApexBlocklist blocklist = OR_RETURN(ReadBlocklist(blocklist_path));
    for (const auto& block_item : blocklist.blocked_apex()) {
      const auto& [it, inserted] =
          apex_name_to_version.emplace(block_item.name(), block_item.version());
      CHECK(inserted) << "Duplicate APEX names are found in blocklist.";
    }
    brand_new_apex_blocked_version_.emplace(partition, apex_name_to_version);
  }
  return {};
}

Result<ApexPartition> ApexFileRepository::GetPartition(
    const ApexFile& apex) const {
  const std::string& name = apex.GetManifest().name();
  auto it = partition_store_.find(name);
  if (it != partition_store_.end()) {
    return it->second;
  }

  // Supports staged but not-yet-activated brand-new APEX.
  if (!ApexFileRepository::IsBrandNewApexEnabled()) {
    return Error() << "No preinstalled data found for package " << name;
  }
  return VerifyBrandNewPackageAgainstPreinstalled(apex);
}

// TODO(b/179497746): remove this method when we add api for fetching ApexFile
//  by name
Result<const std::string> ApexFileRepository::GetPublicKey(
    const std::string& name) const {
  auto it = pre_installed_store_.find(name);
  if (it == pre_installed_store_.end()) {
    // Special casing for APEXes backed by block devices, i.e. APEXes in VM.
    // Inside a VM, we fall back to find the key from data_store_. This is
    // because an APEX is put to either pre_installed_store_ or data_store,
    // depending on whether it was a factory APEX or not in the host.
    it = data_store_.find(name);
    if (it != data_store_.end() && IsBlockApex(it->second)) {
      return it->second.GetBundledPublicKey();
    }
    return Error() << "No preinstalled apex found for package " << name;
  }
  return it->second.GetBundledPublicKey();
}

Result<const std::string> ApexFileRepository::GetPreinstalledPath(
    const std::string& name) const {
  auto it = pre_installed_store_.find(name);
  if (it == pre_installed_store_.end()) {
    return Error() << "No preinstalled data found for package " << name;
  }
  return it->second.GetPath();
}

std::optional<std::string> ApexFileRepository::GetBlockApexRootDigest(
    const std::string& path) const {
  auto it = block_apex_overrides_.find(path);
  if (it == block_apex_overrides_.end()) {
    return std::nullopt;
  }
  return it->second.block_apex_root_digest;
}

std::optional<int64_t> ApexFileRepository::GetBlockApexLastUpdateSeconds(
    const std::string& path) const {
  auto it = block_apex_overrides_.find(path);
  if (it == block_apex_overrides_.end()) {
    return std::nullopt;
  }
  return it->second.last_update_seconds;
}

bool ApexFileRepository::HasPreInstalledVersion(const std::string& name) const {
  return pre_installed_store_.find(name) != pre_installed_store_.end();
}

bool ApexFileRepository::HasDataVersion(const std::string& name) const {
  return data_store_.find(name) != data_store_.end();
}

// ApexFile is considered a decompressed APEX if it is located in decompression
// dir
bool ApexFileRepository::IsDecompressedApex(const ApexFile& apex) const {
  return apex.GetPath().starts_with(decompression_dir_);
}

bool ApexFileRepository::IsPreInstalledApex(const ApexFile& apex) const {
  auto it = pre_installed_store_.find(apex.GetManifest().name());
  if (it == pre_installed_store_.end()) {
    return false;
  }
  return it->second.GetPath() == apex.GetPath() || IsDecompressedApex(apex);
}

bool ApexFileRepository::IsBlockApex(const ApexFile& apex) const {
  return block_disk_path_.has_value() &&
         apex.GetPath().starts_with(*block_disk_path_);
}

std::vector<ApexFileRef> ApexFileRepository::GetPreInstalledApexFiles() const {
  std::vector<ApexFileRef> result;
  result.reserve(pre_installed_store_.size());
  for (const auto& it : pre_installed_store_) {
    result.emplace_back(std::cref(it.second));
  }
  return result;
}

std::vector<ApexFileRef> ApexFileRepository::GetDataApexFiles() const {
  std::vector<ApexFileRef> result;
  result.reserve(data_store_.size());
  for (const auto& it : data_store_) {
    result.emplace_back(std::cref(it.second));
  }
  return result;
}

std::optional<ApexPartition>
ApexFileRepository::GetBrandNewApexPublicKeyPartition(
    const std::string& public_key) const {
  auto it = brand_new_apex_pubkeys_.find(public_key);
  if (it == brand_new_apex_pubkeys_.end()) {
    return std::nullopt;
  }
  return it->second;
}

std::optional<int64_t> ApexFileRepository::GetBrandNewApexBlockedVersion(
    ApexPartition partition, const std::string& apex_name) const {
  auto it = brand_new_apex_blocked_version_.find(partition);
  if (it == brand_new_apex_blocked_version_.end()) {
    return std::nullopt;
  }
  const auto& apex_name_to_version = it->second;
  auto itt = apex_name_to_version.find(apex_name);
  if (itt == apex_name_to_version.end()) {
    return std::nullopt;
  }
  return itt->second;
}

// Group pre-installed APEX and data APEX by name
std::unordered_map<std::string, std::vector<ApexFileRef>>
ApexFileRepository::AllApexFilesByName() const {
  // Group them by name
  std::unordered_map<std::string, std::vector<ApexFileRef>> result;
  for (const auto* store : {&pre_installed_store_, &data_store_}) {
    for (const auto& [name, apex] : *store) {
      result[name].emplace_back(std::cref(apex));
    }
  }
  return result;
}

ApexFileRef ApexFileRepository::GetDataApex(const std::string& name) const {
  auto it = data_store_.find(name);
  CHECK(it != data_store_.end());
  return std::cref(it->second);
}

ApexFileRef ApexFileRepository::GetPreInstalledApex(
    const std::string& name) const {
  auto it = pre_installed_store_.find(name);
  CHECK(it != pre_installed_store_.end());
  return std::cref(it->second);
}

}  // namespace apex
}  // namespace android