Refactor CRX verification in preparation to support CRX₃ files.

components/crx_file/crx_verifier.cc

Index: components/crx_file/crx_verifier.cc
diff --git a/components/crx_file/crx_verifier.cc b/components/crx_file/crx_verifier.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ec03ecbf1286832b669e4f5fbf153b42507d4bae
--- /dev/null
+++ b/components/crx_file/crx_verifier.cc
@@ -0,0 +1,171 @@
+// Copyright 2017 The Chromium 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 "components/crx_file/crx_verifier.h"
+
+#include <cstring>
+#include <memory>
+
+#include "base/base64.h"
+#include "base/files/file.h"
+#include "base/files/file_path.h"
+#include "base/memory/ptr_util.h"
+#include "components/crx_file/crx2_file.h"
+#include "components/crx_file/id_util.h"
+#include "crypto/secure_hash.h"
+#include "crypto/secure_util.h"
+#include "crypto/sha2.h"
+#include "crypto/signature_verifier.h"
+
+namespace crx_file {
+
+namespace {
+
+// The maximum size the crx2 parser will tolerate for a public key.
+constexpr uint32_t kMaxPublicKeySize = 1 << 16;
+
+// The maximum size the crx2 parser will tolerate for a signature.
+constexpr uint32_t kMaxSignatureSize = 1 << 16;
+
+int ReadAndHashBuffer(uint8_t* buffer,
+                      int length,
+                      base::File* file,
+                      crypto::SecureHash* hash) {
+  static_assert(sizeof(char) == sizeof(uint8_t), "Unsupported char size.");
+  int read = file->ReadAtCurrentPos(reinterpret_cast<char*>(buffer), length);
+  hash->Update(buffer, read);
+  return read;
+}
+
+// Returns UINT32_MAX in the case of an unexpected EOF or read error, else
+// returns the read uint32.
+uint32_t ReadAndHashLittleEndianUInt32(base::File* file,
+                                       crypto::SecureHash* hash) {
+  uint8_t buffer[4] = {};
+  if (ReadAndHashBuffer(buffer, 4, file, hash) != 4)
+    return UINT32_MAX;
+  return buffer[3] << 24 | buffer[2] << 16 | buffer[1] << 8 | buffer[0];
+}
+
+VerifierResult VerifyCrx3(
+    base::File* file,
+    crypto::SecureHash* hash,
+    const std::vector<std::vector<uint8_t>>& required_key_hashes,
+    std::string* public_key,
+    std::string* crx_id) {
+  // Crx3 files are not yet supported - treat this as a malformed header.
+  return VerifierResult::ERROR_HEADER_INVALID;
+}
+
+VerifierResult VerifyCrx2(
+    base::File* file,
+    crypto::SecureHash* hash,
+    const std::vector<std::vector<uint8_t>>& required_key_hashes,
+    std::string* public_key,
+    std::string* crx_id) {
+  const uint32_t key_size = ReadAndHashLittleEndianUInt32(file, hash);
+  if (key_size > kMaxPublicKeySize)
+    return VerifierResult::ERROR_HEADER_INVALID;
+  const uint32_t sig_size = ReadAndHashLittleEndianUInt32(file, hash);
+  if (sig_size > kMaxSignatureSize)
+    return VerifierResult::ERROR_HEADER_INVALID;
+  std::vector<uint8_t> key(key_size);
+  if (ReadAndHashBuffer(key.data(), key_size, file, hash) !=
+      static_cast<int>(key_size))
+    return VerifierResult::ERROR_HEADER_INVALID;
+  for (const auto& expected_hash : required_key_hashes) {
+    // In practice we expect zero or one key_hashes_ for CRX2 files.
+    std::vector<uint8_t> hash(crypto::kSHA256Length);
+    std::unique_ptr<crypto::SecureHash> sha256 =
+        crypto::SecureHash::Create(crypto::SecureHash::SHA256);
+    sha256->Update(key.data(), key.size());
+    sha256->Finish(hash.data(), hash.size());
+    if (hash != expected_hash)
+      return VerifierResult::ERROR_REQUIRED_PROOF_MISSING;
+  }
+
+  std::vector<uint8_t> sig(sig_size);
+  if (ReadAndHashBuffer(sig.data(), sig_size, file, hash) !=
+      static_cast<int>(sig_size))
+    return VerifierResult::ERROR_HEADER_INVALID;
+  crypto::SignatureVerifier verifier;
+  if (!verifier.VerifyInit(crypto::SignatureVerifier::RSA_PKCS1_SHA1,
+                           sig.data(), sig.size(), key.data(), key.size())) {
+    return VerifierResult::ERROR_SIGNATURE_INITIALIZATION_FAILED;
+  }
+
+  // Read the rest of the file.
+  uint8_t buffer[1 << 12] = {};
+  size_t len = 0;
+  while ((len = ReadAndHashBuffer(buffer, arraysize(buffer), file, hash)) > 0)
+    verifier.VerifyUpdate(buffer, len);
+  if (!verifier.VerifyFinal())
+    return VerifierResult::ERROR_SIGNATURE_VERIFICATION_FAILED;
+
+  const std::string public_key_bytes(key.begin(), key.end());
+  if (public_key)
+    base::Base64Encode(public_key_bytes, public_key);
+  if (crx_id)
+    *crx_id = id_util::GenerateId(public_key_bytes);
+  return VerifierResult::OK_FULL;
+}
+
+}  // namespace
+
+VerifierResult Verify(
+    const base::FilePath& crx_path,
+    const VerifierFormat& format,
+    const std::vector<std::vector<uint8_t>>& required_key_hashes,
+    const std::vector<uint8_t>& required_file_hash,
+    std::string* public_key,
+    std::string* crx_id) {
+  base::File file(crx_path, base::File::FLAG_OPEN | base::File::FLAG_READ);
+  if (!file.IsValid())
+    return VerifierResult::ERROR_FILE_NOT_READABLE;
+
+  std::unique_ptr<crypto::SecureHash> file_hash =
+      crypto::SecureHash::Create(crypto::SecureHash::SHA256);
+
+  // Magic number.
+  bool diff = false;
+  char buffer[kCrx2FileHeaderMagicSize] = {};
+  if (file.ReadAtCurrentPos(buffer, kCrx2FileHeaderMagicSize) !=
+      kCrx2FileHeaderMagicSize)
+    return VerifierResult::ERROR_HEADER_INVALID;
+  if (!strncmp(buffer, kCrxDiffFileHeaderMagic, kCrx2FileHeaderMagicSize))
+    diff = true;
+  else if (strncmp(buffer, kCrx2FileHeaderMagic, kCrx2FileHeaderMagicSize))
+    return VerifierResult::ERROR_HEADER_INVALID;
+  file_hash->Update(buffer, sizeof(buffer));
+
+  // Version number.
+  const uint32_t version =
+      ReadAndHashLittleEndianUInt32(&file, file_hash.get());
+  VerifierResult result;
+  if (format == VerifierFormat::CRX2_OR_CRX3 &&
+      (version == 2 || (diff && version == 0)))
+    result = VerifyCrx2(&file, file_hash.get(), required_key_hashes, public_key,
+                        crx_id);
+  else if (version == 3)
+    result = VerifyCrx3(&file, file_hash.get(), required_key_hashes, public_key,
+                        crx_id);
+  else
+    return VerifierResult::ERROR_HEADER_INVALID;

[Sorin Jianu, 2017/05/16 20:54:50]

we could say result = VerifierResult::ERROR_HEADER_INVALID;
then the code returns naturally due to the if statement below.

[waffles, 2017/05/16 22:34:52]

Done.

+  if (result != VerifierResult::OK_FULL)
+    return result;
+
+  // Finalize file hash.
+  uint8_t final_hash[crypto::kSHA256Length] = {};
+  file_hash->Finish(final_hash, sizeof(final_hash));
+  if (!required_file_hash.empty()) {
+    if (required_file_hash.size() != crypto::kSHA256Length)
+      return VerifierResult::ERROR_EXPECTED_HASH_INVALID;
+    if (!crypto::SecureMemEqual(final_hash, required_file_hash.data(),
+                                crypto::kSHA256Length))
+      return VerifierResult::ERROR_FILE_HASH_FAILED;
+  }
+  return diff ? VerifierResult::OK_DELTA : VerifierResult::OK_FULL;
+}
+
+}  // namespace crx_file