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platform_system_vold/KeyStorage.cpp
Pavel Grafov e2e2d308df Zero memory used for encryuption keys. 
std::vector with custom zeroing allocator is used instead of
std::string for data that can contain encryption keys.

Bug: 64201177
Test: manually created a managed profile, changed it's credentials
Test: manually upgraded a phone with profile from O to MR1.
Change-Id: Ic31877049f69eba9f8ea64fd99acaaca5a01d3dd
2017-08-10 17:31:03 +01:00

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21 KiB
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/*
* Copyright (C) 2016 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 "KeyStorage.h"
#include "Keymaster.h"
#include "ScryptParameters.h"
#include "Utils.h"
#include <vector>
#include <errno.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/sha.h>
#include <android-base/file.h>
#include <android-base/logging.h>
#include <cutils/properties.h>
#include <hardware/hw_auth_token.h>
#include <keystore/authorization_set.h>
#include <keystore/keystore_hidl_support.h>
extern "C" {
#include "crypto_scrypt.h"
}
namespace android {
namespace vold {
using namespace keystore;
const KeyAuthentication kEmptyAuthentication{"", ""};
static constexpr size_t AES_KEY_BYTES = 32;
static constexpr size_t GCM_NONCE_BYTES = 12;
static constexpr size_t GCM_MAC_BYTES = 16;
static constexpr size_t SALT_BYTES = 1 << 4;
static constexpr size_t SECDISCARDABLE_BYTES = 1 << 14;
static constexpr size_t STRETCHED_BYTES = 1 << 6;
static constexpr uint32_t AUTH_TIMEOUT = 30; // Seconds
static const char* kCurrentVersion = "1";
static const char* kRmPath = "/system/bin/rm";
static const char* kSecdiscardPath = "/system/bin/secdiscard";
static const char* kStretch_none = "none";
static const char* kStretch_nopassword = "nopassword";
static const std::string kStretchPrefix_scrypt = "scrypt ";
static const char* kHashPrefix_secdiscardable = "Android secdiscardable SHA512";
static const char* kHashPrefix_keygen = "Android key wrapping key generation SHA512";
static const char* kFn_encrypted_key = "encrypted_key";
static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
static const char* kFn_keymaster_key_blob_upgraded = "keymaster_key_blob_upgraded";
static const char* kFn_salt = "salt";
static const char* kFn_secdiscardable = "secdiscardable";
static const char* kFn_stretching = "stretching";
static const char* kFn_version = "version";
static bool checkSize(const std::string& kind, size_t actual, size_t expected) {
if (actual != expected) {
LOG(ERROR) << "Wrong number of bytes in " << kind << ", expected " << expected << " got "
<< actual;
return false;
}
return true;
}
static std::string hashWithPrefix(char const* prefix, const std::string& tohash) {
SHA512_CTX c;
SHA512_Init(&c);
// Personalise the hashing by introducing a fixed prefix.
// Hashing applications should use personalization except when there is a
// specific reason not to; see section 4.11 of https://www.schneier.com/skein1.3.pdf
std::string hashingPrefix = prefix;
hashingPrefix.resize(SHA512_CBLOCK);
SHA512_Update(&c, hashingPrefix.data(), hashingPrefix.size());
SHA512_Update(&c, tohash.data(), tohash.size());
std::string res(SHA512_DIGEST_LENGTH, '\0');
SHA512_Final(reinterpret_cast<uint8_t*>(&res[0]), &c);
return res;
}
static bool generateKeymasterKey(Keymaster& keymaster, const KeyAuthentication& auth,
const std::string& appId, std::string* key) {
auto paramBuilder = AuthorizationSetBuilder()
.AesEncryptionKey(AES_KEY_BYTES * 8)
.Authorization(TAG_BLOCK_MODE, BlockMode::GCM)
.Authorization(TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
.Authorization(TAG_PADDING, PaddingMode::NONE)
.Authorization(TAG_APPLICATION_ID, blob2hidlVec(appId));
if (auth.token.empty()) {
LOG(DEBUG) << "Creating key that doesn't need auth token";
paramBuilder.Authorization(TAG_NO_AUTH_REQUIRED);
} else {
LOG(DEBUG) << "Auth token required for key";
if (auth.token.size() != sizeof(hw_auth_token_t)) {
LOG(ERROR) << "Auth token should be " << sizeof(hw_auth_token_t) << " bytes, was "
<< auth.token.size() << " bytes";
return false;
}
const hw_auth_token_t* at = reinterpret_cast<const hw_auth_token_t*>(auth.token.data());
paramBuilder.Authorization(TAG_USER_SECURE_ID, at->user_id);
paramBuilder.Authorization(TAG_USER_AUTH_TYPE, HardwareAuthenticatorType::PASSWORD);
paramBuilder.Authorization(TAG_AUTH_TIMEOUT, AUTH_TIMEOUT);
}
return keymaster.generateKey(paramBuilder, key);
}
static AuthorizationSet beginParams(const KeyAuthentication& auth,
const std::string& appId) {
auto paramBuilder = AuthorizationSetBuilder()
.Authorization(TAG_BLOCK_MODE, BlockMode::GCM)
.Authorization(TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
.Authorization(TAG_PADDING, PaddingMode::NONE)
.Authorization(TAG_APPLICATION_ID, blob2hidlVec(appId));
if (!auth.token.empty()) {
LOG(DEBUG) << "Supplying auth token to Keymaster";
paramBuilder.Authorization(TAG_AUTH_TOKEN, blob2hidlVec(auth.token));
}
return paramBuilder;
}
static bool readFileToString(const std::string& filename, std::string* result) {
if (!android::base::ReadFileToString(filename, result)) {
PLOG(ERROR) << "Failed to read from " << filename;
return false;
}
return true;
}
static bool writeStringToFile(const std::string& payload, const std::string& filename) {
if (!android::base::WriteStringToFile(payload, filename)) {
PLOG(ERROR) << "Failed to write to " << filename;
return false;
}
return true;
}
static KeymasterOperation begin(Keymaster& keymaster, const std::string& dir,
KeyPurpose purpose,
const AuthorizationSet &keyParams,
const AuthorizationSet &opParams,
AuthorizationSet* outParams) {
auto kmKeyPath = dir + "/" + kFn_keymaster_key_blob;
std::string kmKey;
if (!readFileToString(kmKeyPath, &kmKey)) return KeymasterOperation();
AuthorizationSet inParams(keyParams);
inParams.append(opParams.begin(), opParams.end());
for (;;) {
auto opHandle = keymaster.begin(purpose, kmKey, inParams, outParams);
if (opHandle) {
return opHandle;
}
if (opHandle.errorCode() != ErrorCode::KEY_REQUIRES_UPGRADE) return opHandle;
LOG(DEBUG) << "Upgrading key: " << dir;
std::string newKey;
if (!keymaster.upgradeKey(kmKey, keyParams, &newKey)) return KeymasterOperation();
auto newKeyPath = dir + "/" + kFn_keymaster_key_blob_upgraded;
if (!writeStringToFile(newKey, newKeyPath)) return KeymasterOperation();
if (rename(newKeyPath.c_str(), kmKeyPath.c_str()) != 0) {
PLOG(ERROR) << "Unable to move upgraded key to location: " << kmKeyPath;
return KeymasterOperation();
}
if (!keymaster.deleteKey(kmKey)) {
LOG(ERROR) << "Key deletion failed during upgrade, continuing anyway: " << dir;
}
kmKey = newKey;
LOG(INFO) << "Key upgraded: " << dir;
}
}
static bool encryptWithKeymasterKey(Keymaster& keymaster, const std::string& dir,
const AuthorizationSet &keyParams,
const KeyBuffer& message, std::string* ciphertext) {
AuthorizationSet opParams;
AuthorizationSet outParams;
auto opHandle = begin(keymaster, dir, KeyPurpose::ENCRYPT, keyParams, opParams, &outParams);
if (!opHandle) return false;
auto nonceBlob = outParams.GetTagValue(TAG_NONCE);
if (!nonceBlob.isOk()) {
LOG(ERROR) << "GCM encryption but no nonce generated";
return false;
}
// nonceBlob here is just a pointer into existing data, must not be freed
std::string nonce(reinterpret_cast<const char*>(&nonceBlob.value()[0]), nonceBlob.value().size());
if (!checkSize("nonce", nonce.size(), GCM_NONCE_BYTES)) return false;
std::string body;
if (!opHandle.updateCompletely(message, &body)) return false;
std::string mac;
if (!opHandle.finish(&mac)) return false;
if (!checkSize("mac", mac.size(), GCM_MAC_BYTES)) return false;
*ciphertext = nonce + body + mac;
return true;
}
static bool decryptWithKeymasterKey(Keymaster& keymaster, const std::string& dir,
const AuthorizationSet &keyParams,
const std::string& ciphertext, KeyBuffer* message) {
auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
auto opParams = AuthorizationSetBuilder()
.Authorization(TAG_NONCE, blob2hidlVec(nonce));
auto opHandle = begin(keymaster, dir, KeyPurpose::DECRYPT, keyParams, opParams, nullptr);
if (!opHandle) return false;
if (!opHandle.updateCompletely(bodyAndMac, message)) return false;
if (!opHandle.finish(nullptr)) return false;
return true;
}
static std::string getStretching(const KeyAuthentication& auth) {
if (!auth.usesKeymaster()) {
return kStretch_none;
} else if (auth.secret.empty()) {
return kStretch_nopassword;
} else {
char paramstr[PROPERTY_VALUE_MAX];
property_get(SCRYPT_PROP, paramstr, SCRYPT_DEFAULTS);
return std::string() + kStretchPrefix_scrypt + paramstr;
}
}
static bool stretchingNeedsSalt(const std::string& stretching) {
return stretching != kStretch_nopassword && stretching != kStretch_none;
}
static bool stretchSecret(const std::string& stretching, const std::string& secret,
const std::string& salt, std::string* stretched) {
if (stretching == kStretch_nopassword) {
if (!secret.empty()) {
LOG(WARNING) << "Password present but stretching is nopassword";
// Continue anyway
}
stretched->clear();
} else if (stretching == kStretch_none) {
*stretched = secret;
} else if (std::equal(kStretchPrefix_scrypt.begin(), kStretchPrefix_scrypt.end(),
stretching.begin())) {
int Nf, rf, pf;
if (!parse_scrypt_parameters(stretching.substr(kStretchPrefix_scrypt.size()).c_str(), &Nf,
&rf, &pf)) {
LOG(ERROR) << "Unable to parse scrypt params in stretching: " << stretching;
return false;
}
stretched->assign(STRETCHED_BYTES, '\0');
if (crypto_scrypt(reinterpret_cast<const uint8_t*>(secret.data()), secret.size(),
reinterpret_cast<const uint8_t*>(salt.data()), salt.size(),
1 << Nf, 1 << rf, 1 << pf,
reinterpret_cast<uint8_t*>(&(*stretched)[0]), stretched->size()) != 0) {
LOG(ERROR) << "scrypt failed with params: " << stretching;
return false;
}
} else {
LOG(ERROR) << "Unknown stretching type: " << stretching;
return false;
}
return true;
}
static bool generateAppId(const KeyAuthentication& auth, const std::string& stretching,
const std::string& salt, const std::string& secdiscardable,
std::string* appId) {
std::string stretched;
if (!stretchSecret(stretching, auth.secret, salt, &stretched)) return false;
*appId = hashWithPrefix(kHashPrefix_secdiscardable, secdiscardable) + stretched;
return true;
}
static bool readRandomBytesOrLog(size_t count, std::string* out) {
auto status = ReadRandomBytes(count, *out);
if (status != OK) {
LOG(ERROR) << "Random read failed with status: " << status;
return false;
}
return true;
}
static void logOpensslError() {
LOG(ERROR) << "Openssl error: " << ERR_get_error();
}
static bool encryptWithoutKeymaster(const std::string& preKey,
const KeyBuffer& plaintext, std::string* ciphertext) {
auto key = hashWithPrefix(kHashPrefix_keygen, preKey);
key.resize(AES_KEY_BYTES);
if (!readRandomBytesOrLog(GCM_NONCE_BYTES, ciphertext)) return false;
auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free);
if (!ctx) {
logOpensslError();
return false;
}
if (1 != EVP_EncryptInit_ex(ctx.get(), EVP_aes_256_gcm(), NULL,
reinterpret_cast<const uint8_t*>(key.data()),
reinterpret_cast<const uint8_t*>(ciphertext->data()))) {
logOpensslError();
return false;
}
ciphertext->resize(GCM_NONCE_BYTES + plaintext.size() + GCM_MAC_BYTES);
int outlen;
if (1 != EVP_EncryptUpdate(ctx.get(),
reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES), &outlen,
reinterpret_cast<const uint8_t*>(plaintext.data()), plaintext.size())) {
logOpensslError();
return false;
}
if (outlen != static_cast<int>(plaintext.size())) {
LOG(ERROR) << "GCM ciphertext length should be " << plaintext.size() << " was " << outlen;
return false;
}
if (1 != EVP_EncryptFinal_ex(ctx.get(),
reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()), &outlen)) {
logOpensslError();
return false;
}
if (outlen != 0) {
LOG(ERROR) << "GCM EncryptFinal should be 0, was " << outlen;
return false;
}
if (1 != EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_GET_TAG, GCM_MAC_BYTES,
reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()))) {
logOpensslError();
return false;
}
return true;
}
static bool decryptWithoutKeymaster(const std::string& preKey,
const std::string& ciphertext, KeyBuffer* plaintext) {
if (ciphertext.size() < GCM_NONCE_BYTES + GCM_MAC_BYTES) {
LOG(ERROR) << "GCM ciphertext too small: " << ciphertext.size();
return false;
}
auto key = hashWithPrefix(kHashPrefix_keygen, preKey);
key.resize(AES_KEY_BYTES);
auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free);
if (!ctx) {
logOpensslError();
return false;
}
if (1 != EVP_DecryptInit_ex(ctx.get(), EVP_aes_256_gcm(), NULL,
reinterpret_cast<const uint8_t*>(key.data()),
reinterpret_cast<const uint8_t*>(ciphertext.data()))) {
logOpensslError();
return false;
}
*plaintext = KeyBuffer(ciphertext.size() - GCM_NONCE_BYTES - GCM_MAC_BYTES);
int outlen;
if (1 != EVP_DecryptUpdate(ctx.get(),
reinterpret_cast<uint8_t*>(&(*plaintext)[0]), &outlen,
reinterpret_cast<const uint8_t*>(ciphertext.data() + GCM_NONCE_BYTES), plaintext->size())) {
logOpensslError();
return false;
}
if (outlen != static_cast<int>(plaintext->size())) {
LOG(ERROR) << "GCM plaintext length should be " << plaintext->size() << " was " << outlen;
return false;
}
if (1 != EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_SET_TAG, GCM_MAC_BYTES,
const_cast<void *>(
reinterpret_cast<const void*>(ciphertext.data() + GCM_NONCE_BYTES + plaintext->size())))) {
logOpensslError();
return false;
}
if (1 != EVP_DecryptFinal_ex(ctx.get(),
reinterpret_cast<uint8_t*>(&(*plaintext)[0] + plaintext->size()), &outlen)) {
logOpensslError();
return false;
}
if (outlen != 0) {
LOG(ERROR) << "GCM EncryptFinal should be 0, was " << outlen;
return false;
}
return true;
}
bool pathExists(const std::string& path) {
return access(path.c_str(), F_OK) == 0;
}
bool storeKey(const std::string& dir, const KeyAuthentication& auth, const KeyBuffer& key) {
if (TEMP_FAILURE_RETRY(mkdir(dir.c_str(), 0700)) == -1) {
PLOG(ERROR) << "key mkdir " << dir;
return false;
}
if (!writeStringToFile(kCurrentVersion, dir + "/" + kFn_version)) return false;
std::string secdiscardable;
if (!readRandomBytesOrLog(SECDISCARDABLE_BYTES, &secdiscardable)) return false;
if (!writeStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) return false;
std::string stretching = getStretching(auth);
if (!writeStringToFile(stretching, dir + "/" + kFn_stretching)) return false;
std::string salt;
if (stretchingNeedsSalt(stretching)) {
if (ReadRandomBytes(SALT_BYTES, salt) != OK) {
LOG(ERROR) << "Random read failed";
return false;
}
if (!writeStringToFile(salt, dir + "/" + kFn_salt)) return false;
}
std::string appId;
if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
std::string encryptedKey;
if (auth.usesKeymaster()) {
Keymaster keymaster;
if (!keymaster) return false;
std::string kmKey;
if (!generateKeymasterKey(keymaster, auth, appId, &kmKey)) return false;
if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
auto keyParams = beginParams(auth, appId);
if (!encryptWithKeymasterKey(keymaster, dir, keyParams, key, &encryptedKey)) return false;
} else {
if (!encryptWithoutKeymaster(appId, key, &encryptedKey)) return false;
}
if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
return true;
}
bool storeKeyAtomically(const std::string& key_path, const std::string& tmp_path,
const KeyAuthentication& auth, const KeyBuffer& key) {
if (pathExists(key_path)) {
LOG(ERROR) << "Already exists, cannot create key at: " << key_path;
return false;
}
if (pathExists(tmp_path)) {
LOG(DEBUG) << "Already exists, destroying: " << tmp_path;
destroyKey(tmp_path); // May be partially created so ignore errors
}
if (!storeKey(tmp_path, auth, key)) return false;
if (rename(tmp_path.c_str(), key_path.c_str()) != 0) {
PLOG(ERROR) << "Unable to move new key to location: " << key_path;
return false;
}
LOG(DEBUG) << "Created key: " << key_path;
return true;
}
bool retrieveKey(const std::string& dir, const KeyAuthentication& auth, KeyBuffer* key) {
std::string version;
if (!readFileToString(dir + "/" + kFn_version, &version)) return false;
if (version != kCurrentVersion) {
LOG(ERROR) << "Version mismatch, expected " << kCurrentVersion << " got " << version;
return false;
}
std::string secdiscardable;
if (!readFileToString(dir + "/" + kFn_secdiscardable, &secdiscardable)) return false;
std::string stretching;
if (!readFileToString(dir + "/" + kFn_stretching, &stretching)) return false;
std::string salt;
if (stretchingNeedsSalt(stretching)) {
if (!readFileToString(dir + "/" + kFn_salt, &salt)) return false;
}
std::string appId;
if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
std::string encryptedMessage;
if (!readFileToString(dir + "/" + kFn_encrypted_key, &encryptedMessage)) return false;
if (auth.usesKeymaster()) {
Keymaster keymaster;
if (!keymaster) return false;
auto keyParams = beginParams(auth, appId);
if (!decryptWithKeymasterKey(keymaster, dir, keyParams, encryptedMessage, key)) return false;
} else {
if (!decryptWithoutKeymaster(appId, encryptedMessage, key)) return false;
}
return true;
}
static bool deleteKey(const std::string& dir) {
std::string kmKey;
if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, &kmKey)) return false;
Keymaster keymaster;
if (!keymaster) return false;
if (!keymaster.deleteKey(kmKey)) return false;
return true;
}
static bool runSecdiscard(const std::string& dir) {
if (ForkExecvp(
std::vector<std::string>{kSecdiscardPath, "--",
dir + "/" + kFn_encrypted_key,
dir + "/" + kFn_keymaster_key_blob,
dir + "/" + kFn_secdiscardable,
}) != 0) {
LOG(ERROR) << "secdiscard failed";
return false;
}
return true;
}
bool runSecdiscardSingle(const std::string& file) {
if (ForkExecvp(
std::vector<std::string>{kSecdiscardPath, "--",
file}) != 0) {
LOG(ERROR) << "secdiscard failed";
return false;
}
return true;
}
static bool recursiveDeleteKey(const std::string& dir) {
if (ForkExecvp(std::vector<std::string>{kRmPath, "-rf", dir}) != 0) {
LOG(ERROR) << "recursive delete failed";
return false;
}
return true;
}
bool destroyKey(const std::string& dir) {
bool success = true;
// Try each thing, even if previous things failed.
success &= deleteKey(dir);
success &= runSecdiscard(dir);
success &= recursiveDeleteKey(dir);
return success;
}
} // namespace vold
} // namespace android
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