imageloader/component.cc

// Copyright 2016 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "component.h"

#include <fcntl.h>

#include <algorithm>
#include <string>
#include <vector>

#include <base/files/file.h>
#include <base/files/file_path.h>
#include <base/files/file_util.h>
#include <base/files/scoped_file.h>
#include <base/json/json_string_value_serializer.h>
#include <base/logging.h>
#include <base/numerics/safe_conversions.h>
#include <base/strings/string_number_conversions.h>
#include <base/posix/eintr_wrapper.h>
#include <base/strings/string_util.h>
#include <crypto/secure_hash.h>
#include <crypto/sha2.h>
#include <crypto/signature_verifier.h>

namespace imageloader {

namespace {

// The name of the imageloader manifest file.
constexpr char kManifestName[] = "imageloader.json";
// The name of the fingerprint file.
constexpr char kFingerprintName[] = "manifest.fingerprint";
// The manifest signature.
constexpr char kManifestSignatureName[] = "imageloader.sig.1";
// The current version of the manifest file.
constexpr int kCurrentManifestVersion = 1;
// The name of the version field in the manifest.
constexpr char kManifestVersionField[] = "manifest-version";
// The name of the component version field in the manifest.
constexpr char kVersionField[] = "version";
// The name of the field containing the image hash.
constexpr char kImageHashField[] = "image-sha256-hash";
// The name of the image file.
constexpr char kImageFileName[] = "image.squash";
// The name of the field containing the table hash.
constexpr char kTableHashField[] = "table-sha256-hash";
// The name of the table file.
constexpr char kTableFileName[] = "table";
// The maximum size of any file to read into memory.
constexpr size_t kMaximumFilesize = 4096 * 10;

base::FilePath GetManifestPath(const base::FilePath& component_dir) {
  return component_dir.Append(kManifestName);
}

base::FilePath GetSignaturePath(const base::FilePath& component_dir) {
  return component_dir.Append(kManifestSignatureName);
}

base::FilePath GetFingerprintPath(const base::FilePath& component_dir) {
  return component_dir.Append(kFingerprintName);
}

base::FilePath GetTablePath(const base::FilePath& component_dir) {
  return component_dir.Append(kTableFileName);
}

base::FilePath GetImagePath(const base::FilePath& component_dir) {
  return component_dir.Append(kImageFileName);
}

bool WriteFileToDisk(const base::FilePath& path, const std::string& contents) {
  base::ScopedFD fd(HANDLE_EINTR(open(path.value().c_str(),
                                      O_CREAT | O_WRONLY | O_EXCL,
                                      kComponentFilePerms)));
  if (!fd.is_valid()) {
    PLOG(ERROR) << "Error creating file for " << path.value();
    return false;
  }

  base::File file(fd.release());
  int size = base::checked_cast<int>(contents.size());
  return file.Write(0, contents.data(), contents.size()) == size;
}

bool GetSHA256FromString(const std::string& hash_str,
                         std::vector<uint8_t>* bytes) {
  if (!base::HexStringToBytes(hash_str, bytes)) return false;
  return bytes->size() == crypto::kSHA256Length;
}

bool GetAndVerifyTable(const base::FilePath& path,
                       const std::vector<uint8_t>& hash,
                       std::string* out_table) {
  std::string table;
  if (!base::ReadFileToStringWithMaxSize(path, &table, kMaximumFilesize)) {
    return false;
  }

  std::vector<uint8_t> table_hash(crypto::kSHA256Length);
  crypto::SHA256HashString(table, table_hash.data(), table_hash.size());
  if (table_hash != hash) {
    LOG(ERROR) << "dm-verity table file has the wrong hash.";
    return false;
  }

  out_table->assign(table);
  return true;
}

}  // namespace

Component::Component(const base::FilePath& component_dir)
    : component_dir_(component_dir) {}

bool Component::Init(const std::vector<uint8_t>& public_key) {
  if (initialized_) {
    NOTREACHED() << "Component already initialized";
    return false;
  }
  initialized_ = LoadManifest(public_key);
  return initialized_;
}

const Component::Manifest& Component::manifest() {
  // If the manifest is accessed without initialization, crash.
  CHECK(initialized_);
  return manifest_;
}

bool Component::Mount(VerityMounter* mounter, const base::FilePath& dest_dir) {
  if (!initialized_) {
    NOTREACHED() << "Component not initialized";
    return false;
  }
  // Now read the table in and verify the hash.
  std::string table;
  if (!GetAndVerifyTable(GetTablePath(component_dir_), manifest_.table_sha256,
                         &table)) {
    LOG(ERROR) << "Could not read and verify dm-verity table.";
    return false;
  }

  base::FilePath image_path(GetImagePath(component_dir_));
  base::File image(image_path, base::File::FLAG_OPEN | base::File::FLAG_READ);
  if (!image.IsValid()) {
    LOG(ERROR) << "Could not open image file.";
    return false;
  }
  base::ScopedFD image_fd(image.TakePlatformFile());

  // The mount point is not yet taken, so go ahead.
  if (!mounter->Mount(image_fd, dest_dir, table)) {
    LOG(ERROR) << "Failed to mount image.";
    return false;
  }
  return true;
}

bool Component::ParseManifest() {
  // Now deserialize the manifest json and read out the rest of the component.
  int error_code;
  std::string error_message;
  JSONStringValueDeserializer deserializer(manifest_raw_);
  std::unique_ptr<base::Value> value =
      deserializer.Deserialize(&error_code, &error_message);

  if (!value) {
    LOG(ERROR) << "Could not deserialize the manifest file. Error "
               << error_code << ": " << error_message;
    return false;
  }

  base::DictionaryValue* manifest_dict = nullptr;
  if (!value->GetAsDictionary(&manifest_dict)) {
    LOG(ERROR) << "Could not parse manifest file as JSON.";
    return false;
  }

  // This will have to be changed if the manifest version is bumped.
  int version;
  if (!manifest_dict->GetInteger(kManifestVersionField, &version)) {
    LOG(ERROR) << "Could not parse manifest version field from manifest.";
    return false;
  }
  if (version != kCurrentManifestVersion) {
    LOG(ERROR) << "Unsupported version of the manifest.";
    return false;
  }
  manifest_.manifest_version = version;

  std::string image_hash_str;
  if (!manifest_dict->GetString(kImageHashField, &image_hash_str)) {
    LOG(ERROR) << "Could not parse image hash from manifest.";
    return false;
  }

  if (!GetSHA256FromString(image_hash_str, &(manifest_.image_sha256))) {
    LOG(ERROR) << "Could not convert image hash to bytes.";
    return false;
  }

  std::string table_hash_str;
  if (!manifest_dict->GetString(kTableHashField, &table_hash_str)) {
    LOG(ERROR) << "Could not parse table hash from manifest.";
    return false;
  }

  if (!GetSHA256FromString(table_hash_str, &(manifest_.table_sha256))) {
    LOG(ERROR) << "Could not convert table hash to bytes.";
    return false;
  }

  if (!manifest_dict->GetString(kVersionField, &(manifest_.version))) {
    LOG(ERROR) << "Could not parse component version from manifest.";
    return false;
  }

  return true;
}

bool Component::LoadManifest(const std::vector<uint8_t>& public_key) {
  if (!base::ReadFileToStringWithMaxSize(GetManifestPath(component_dir_),
                                         &manifest_raw_, kMaximumFilesize)) {
    LOG(ERROR) << "Could not read manifest file.";
    return false;
  }
  if (!base::ReadFileToStringWithMaxSize(GetSignaturePath(component_dir_),
                                         &manifest_sig_, kMaximumFilesize)) {
    LOG(ERROR) << "Could not read signature file.";
    return false;
  }

  crypto::SignatureVerifier verifier;

  if (!verifier.VerifyInit(
          crypto::SignatureVerifier::ECDSA_SHA256,
          reinterpret_cast<const uint8_t*>(manifest_sig_.data()),
          base::checked_cast<int>(manifest_sig_.size()), public_key.data(),
          base::checked_cast<int>(public_key.size()))) {
    LOG(ERROR) << "Failed to initialize signature verification.";
    return false;
  }

  verifier.VerifyUpdate(reinterpret_cast<const uint8_t*>(manifest_raw_.data()),
                        base::checked_cast<int>(manifest_raw_.size()));

  if (!verifier.VerifyFinal()) {
    LOG(ERROR) << "Manifest failed signature verification.";
    return false;
  }
  return ParseManifest();
}

bool Component::CopyTo(const base::FilePath& dest_dir) {
  if (!initialized_) {
    NOTREACHED() << "Component not initialized";
    return false;
  }

  if (!WriteFileToDisk(GetManifestPath(dest_dir), manifest_raw_) ||
      !WriteFileToDisk(GetSignaturePath(dest_dir), manifest_sig_)) {
    LOG(ERROR) << "Could not write manifest and signature to disk.";
    return false;
  }

  base::FilePath table_src(GetTablePath(component_dir_));
  base::FilePath table_dest(GetTablePath(dest_dir));
  if (!CopyComponentFile(table_src, table_dest, manifest_.table_sha256)) {
    LOG(ERROR) << "Could not copy table file.";
    return false;
  }

  base::FilePath image_src(GetImagePath(component_dir_));
  base::FilePath image_dest(GetImagePath(dest_dir));
  if (!CopyComponentFile(image_src, image_dest, manifest_.image_sha256)) {
    LOG(ERROR) << "Could not copy image file.";
    return false;
  }

  if (!CopyFingerprintFile(component_dir_, dest_dir)) {
    LOG(ERROR) << "Could not copy manifest.fingerprint file.";
    return false;
  }

  return true;
}

bool Component::CopyComponentFile(const base::FilePath& src,
                                const base::FilePath& dest_path,
                                const std::vector<uint8_t>& expected_hash) {
  base::File file(src, base::File::FLAG_OPEN | base::File::FLAG_READ);
  if (!file.IsValid()) return false;

  base::ScopedFD dest(
      HANDLE_EINTR(open(dest_path.value().c_str(), O_CREAT | O_WRONLY | O_EXCL,
                        kComponentFilePerms)));
  if (!dest.is_valid()) return false;

  base::File out_file(dest.release());
  std::unique_ptr<crypto::SecureHash> sha256(
      crypto::SecureHash::Create(crypto::SecureHash::SHA256));

  std::vector<uint8_t> file_hash(crypto::kSHA256Length);
  if (!ReadHashAndCopyFile(&file, &file_hash, &out_file)) {
    LOG(ERROR) << "Failed to read image file.";
    return false;
  }

  if (expected_hash != file_hash) {
    LOG(ERROR) << "Image is corrupt or modified.";
    return false;
  }
  return true;
}

bool Component::ReadHashAndCopyFile(base::File* file,
                                    std::vector<uint8_t>* file_hash,
                                    base::File* out_file) {
  std::unique_ptr<crypto::SecureHash> sha256(
      crypto::SecureHash::Create(crypto::SecureHash::SHA256));
  int size = file->GetLength();
  if (size <= 0) return false;

  int rv = 0, bytes_read = 0;
  char buf[4096];
  do {
    int remaining = size - bytes_read;
    int bytes_to_read =
        std::min(remaining, base::checked_cast<int>(sizeof(buf)));

    rv = file->ReadAtCurrentPos(buf, bytes_to_read);
    if (rv <= 0) break;

    bytes_read += rv;
    sha256->Update(buf, rv);
    if (out_file) {
      out_file->WriteAtCurrentPos(buf, rv);
    }
  } while (bytes_read <= size);

  sha256->Finish(file_hash->data(), file_hash->size());
  return bytes_read == size;
}

bool Component::CopyFingerprintFile(const base::FilePath& src,
                                    const base::FilePath& dest) {
  base::FilePath fingerprint_path(GetFingerprintPath(src));
  if (base::PathExists(fingerprint_path)) {
    std::string fingerprint_contents;
    if (!base::ReadFileToStringWithMaxSize(
            fingerprint_path, &fingerprint_contents, kMaximumFilesize)) {
      return false;
    }

    if (!IsValidFingerprintFile(fingerprint_contents)) return false;

    if (!WriteFileToDisk(GetFingerprintPath(dest), fingerprint_contents)) {
      return false;
    }
  }
  return true;
}

// The client inserts manifest.fingerprint into components after unpacking the
// CRX. The file is used for delta updates. Since Chrome OS doesn't rely on it
// for security of the disk image, we are fine with sanity checking the contents
// and then preserving the unsigned file.
bool Component::IsValidFingerprintFile(const std::string& contents) {
  return contents.size() <= 256 &&
         std::find_if_not(contents.begin(), contents.end(), [](char ch) {
           return base::IsAsciiAlpha(ch) || base::IsAsciiDigit(ch) || ch == '.';
         }) == contents.end();
}

}  // namespace imageloader