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// Copyright 2014 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_file.h"
#include "base/base64.h"
#include "base/files/file_path.h"
#include "base/files/file_util.h"
#include "base/files/scoped_file.h"
#include "base/memory/scoped_ptr.h"
#include "base/numerics/safe_math.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_util.h"
#include "components/crx_file/constants.h"
#include "components/crx_file/id_util.h"
#include "crypto/secure_hash.h"
#include "crypto/sha2.h"
#include "crypto/signature_verifier.h"
namespace crx_file {
namespace {
// The current version of the crx format.
static const uint32 kCurrentVersion = 2;
// The current version of the crx diff format.
static const uint32 kCurrentDiffVersion = 0;
// The maximum size the crx parser will tolerate for a public key.
static const uint32 kMaxPublicKeySize = 1 << 16;
// The maximum size the crx parser will tolerate for a signature.
static const uint32 kMaxSignatureSize = 1 << 16;
// Helper function to read bytes into a buffer while also updating a hash with
// those bytes. Returns the number of bytes read.
size_t ReadAndHash(void* ptr,
size_t size,
size_t nmemb,
FILE* stream,
crypto::SecureHash* hash) {
size_t item_count = fread(ptr, size, nmemb, stream);
base::CheckedNumeric<size_t> byte_count(item_count);
byte_count *= size;
if (!byte_count.IsValid())
return 0;
if (item_count > 0 && hash) {
hash->Update(ptr, byte_count.ValueOrDie());
}
return byte_count.ValueOrDie();
}
// Helper function to finish computing a hash and return an error if the
// result of the hash didn't meet an expected base64-encoded value.
CrxFile::ValidateError FinalizeHash(const std::string& extension_id,
crypto::SecureHash* hash,
const std::string& expected_hash) {
CHECK(hash != nullptr);
uint8 output[crypto::kSHA256Length] = {};
hash->Finish(output, sizeof(output));
std::string hash_base64 =
base::ToLowerASCII(base::HexEncode(output, sizeof(output)));
if (hash_base64 != expected_hash) {
LOG(ERROR) << "Hash check failed for extension: " << extension_id
<< ", expected " << expected_hash << ", got " << hash_base64;
return CrxFile::ValidateError::CRX_HASH_VERIFICATION_FAILED;
} else {
return CrxFile::ValidateError::NONE;
}
}
} // namespace
// The magic string embedded in the header.
const char kCrxFileHeaderMagic[] = "Cr24";
const char kCrxDiffFileHeaderMagic[] = "CrOD";
scoped_ptr<CrxFile> CrxFile::Parse(const CrxFile::Header& header,
CrxFile::Error* error) {
if (HeaderIsValid(header, error))
return scoped_ptr<CrxFile>(new CrxFile(header));
return scoped_ptr<CrxFile>();
}
scoped_ptr<CrxFile> CrxFile::Create(const uint32 key_size,
const uint32 signature_size,
CrxFile::Error* error) {
CrxFile::Header header;
memcpy(&header.magic, kCrxFileHeaderMagic, kCrxFileHeaderMagicSize);
header.version = kCurrentVersion;
header.key_size = key_size;
header.signature_size = signature_size;
if (HeaderIsValid(header, error))
return scoped_ptr<CrxFile>(new CrxFile(header));
return scoped_ptr<CrxFile>();
}
bool CrxFile::HeaderIsDelta(const CrxFile::Header& header) {
return !strncmp(kCrxDiffFileHeaderMagic, header.magic, sizeof(header.magic));
}
// static
CrxFile::ValidateError CrxFile::ValidateSignature(
const base::FilePath& crx_path,
const std::string& expected_hash,
std::string* public_key,
std::string* extension_id,
CrxFile::Header* header_out) {
base::ScopedFILE file(base::OpenFile(crx_path, "rb"));
scoped_ptr<crypto::SecureHash> hash;
if (!expected_hash.empty())
hash.reset(crypto::SecureHash::Create(crypto::SecureHash::SHA256));
if (!file.get())
return ValidateError::CRX_FILE_NOT_READABLE;
CrxFile::Header header;
size_t len = ReadAndHash(&header, sizeof(header), 1, file.get(), hash.get());
if (len != sizeof(header))
return ValidateError::CRX_HEADER_INVALID;
if (header_out)
*header_out = header;
CrxFile::Error error;
scoped_ptr<CrxFile> crx(CrxFile::Parse(header, &error));
if (!crx) {
switch (error) {
case CrxFile::kWrongMagic:
return ValidateError::CRX_MAGIC_NUMBER_INVALID;
case CrxFile::kInvalidVersion:
return ValidateError::CRX_VERSION_NUMBER_INVALID;
case CrxFile::kInvalidKeyTooLarge:
case CrxFile::kInvalidSignatureTooLarge:
return ValidateError::CRX_EXCESSIVELY_LARGE_KEY_OR_SIGNATURE;
case CrxFile::kInvalidKeyTooSmall:
return ValidateError::CRX_ZERO_KEY_LENGTH;
case CrxFile::kInvalidSignatureTooSmall:
return ValidateError::CRX_ZERO_SIGNATURE_LENGTH;
default:
return ValidateError::CRX_HEADER_INVALID;
}
}
std::vector<uint8> key(header.key_size);
len = ReadAndHash(&key.front(), sizeof(uint8), header.key_size, file.get(),
hash.get());
if (len != header.key_size)
return ValidateError::CRX_PUBLIC_KEY_INVALID;
std::vector<uint8> signature(header.signature_size);
len = ReadAndHash(&signature.front(), sizeof(uint8), header.signature_size,
file.get(), hash.get());
if (len < header.signature_size)
return ValidateError::CRX_SIGNATURE_INVALID;
crypto::SignatureVerifier verifier;
if (!verifier.VerifyInit(
crx_file::kSignatureAlgorithm, sizeof(crx_file::kSignatureAlgorithm),
&signature.front(), static_cast<int>(signature.size()), &key.front(),
static_cast<int>(key.size()))) {
// Signature verification initialization failed. This is most likely
// caused by a public key in the wrong format (should encode algorithm).
return ValidateError::CRX_SIGNATURE_VERIFICATION_INITIALIZATION_FAILED;
}
uint8 buf[1 << 12] = {};
while ((len = ReadAndHash(buf, sizeof(buf[0]), arraysize(buf), file.get(),
hash.get())) > 0)
verifier.VerifyUpdate(buf, static_cast<int>(len));
if (!verifier.VerifyFinal())
return ValidateError::CRX_SIGNATURE_VERIFICATION_FAILED;
std::string public_key_bytes =
std::string(reinterpret_cast<char*>(&key.front()), key.size());
if (public_key)
base::Base64Encode(public_key_bytes, public_key);
std::string id = id_util::GenerateId(public_key_bytes);
if (extension_id)
*extension_id = id;
if (!expected_hash.empty())
return FinalizeHash(id, hash.get(), expected_hash);
return ValidateError::NONE;
}
CrxFile::CrxFile(const Header& header) : header_(header) {}
bool CrxFile::HeaderIsValid(const CrxFile::Header& header,
CrxFile::Error* error) {
bool valid = false;
bool diffCrx = false;
if (!strncmp(kCrxDiffFileHeaderMagic, header.magic, sizeof(header.magic)))
diffCrx = true;
if (strncmp(kCrxFileHeaderMagic, header.magic, sizeof(header.magic)) &&
!diffCrx)
*error = kWrongMagic;
else if (header.version != kCurrentVersion
&& !(diffCrx && header.version == kCurrentDiffVersion))
*error = kInvalidVersion;
else if (header.key_size > kMaxPublicKeySize)
*error = kInvalidKeyTooLarge;
else if (header.key_size == 0)
*error = kInvalidKeyTooSmall;
else if (header.signature_size > kMaxSignatureSize)
*error = kInvalidSignatureTooLarge;
else if (header.signature_size == 0)
*error = kInvalidSignatureTooSmall;
else
valid = true;
return valid;
}
} // namespace crx_file
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