gatekeeper.cpp - platform/system/gatekeeper - Git at Google

 /*
  * Copyright 2015 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 <gatekeeper/UniquePtr.h>
 #include <gatekeeper/gatekeeper.h>

 #include <endian.h>
 #include <stddef.h>

 #define DAY_IN_MS (1000 * 60 * 60 * 24)

 namespace gatekeeper {

 void GateKeeper::Enroll(const EnrollRequest &request, EnrollResponse *response) {
     if (response == nullptr) return;

     if (!request.provided_password) {
         response->error = ERROR_INVALID;
         return;
     }

     secure_id_t user_id = 0;// todo: rename to policy
     uint32_t uid = request.user_id;

     if (!request.password_handle) {
         // Password handle does not match what is stored, generate new SecureID
         GetRandom(&user_id, sizeof(secure_id_t));
     } else {
         const password_handle_t *pw_handle = request.password_handle.Data<password_handle_t>();

         if (!pw_handle || pw_handle->version > HANDLE_VERSION) {
             response->error = ERROR_INVALID;
             return;
         }

         user_id = pw_handle->user_id;

         uint64_t timestamp = GetMillisecondsSinceBoot();

         uint32_t timeout = 0;
         bool throttle = (pw_handle->version >= HANDLE_VERSION_THROTTLE);
         if (throttle) {
             bool throttle_secure = pw_handle->flags & HANDLE_FLAG_THROTTLE_SECURE;
             failure_record_t record;
             if (!GetFailureRecord(uid, user_id, &record, throttle_secure)) {
                 response->error = ERROR_UNKNOWN;
                 return;
             }

             if (ThrottleRequest(uid, timestamp, &record, throttle_secure, response)) return;

             if (!IncrementFailureRecord(uid, user_id, timestamp, &record, throttle_secure)) {
                 response->error = ERROR_UNKNOWN;
                 return;
             }

             timeout = ComputeRetryTimeout(&record);
         }

         if (!DoVerify(pw_handle, request.enrolled_password)) {
             // incorrect old password
             if (throttle && timeout > 0) {
                 response->SetRetryTimeout(timeout);
             } else {
                 response->error = ERROR_INVALID;
             }
             return;
         }
     }

     uint64_t flags = 0;
     if (ClearFailureRecord(uid, user_id, true)) {
         flags |= HANDLE_FLAG_THROTTLE_SECURE;
     } else {
         ClearFailureRecord(uid, user_id, false);
     }

     salt_t salt;
     GetRandom(&salt, sizeof(salt));

     SizedBuffer password_handle;
     if (!CreatePasswordHandle(&password_handle,
             salt, user_id, flags, HANDLE_VERSION, request.provided_password)) {
         response->error = ERROR_INVALID;
         return;
     }

     response->SetEnrolledPasswordHandle(move(password_handle));
 }

 void GateKeeper::Verify(const VerifyRequest &request, VerifyResponse *response) {
     if (response == nullptr) return;

     if (!request.provided_password || !request.password_handle) {
         response->error = ERROR_INVALID;
         return;
     }

     const password_handle_t *password_handle = request.password_handle.Data<password_handle_t>();

     if (!password_handle || password_handle->version > HANDLE_VERSION) {
         response->error = ERROR_INVALID;
         return;
     }

     secure_id_t user_id = password_handle->user_id;
     secure_id_t authenticator_id = 0;
     uint32_t uid = request.user_id;

     uint64_t timestamp = GetMillisecondsSinceBoot();

     uint32_t timeout = 0;
     bool throttle = (password_handle->version >= HANDLE_VERSION_THROTTLE);
     bool throttle_secure = password_handle->flags & HANDLE_FLAG_THROTTLE_SECURE;
     if (throttle) {
         failure_record_t record;
         if (!GetFailureRecord(uid, user_id, &record, throttle_secure)) {
             response->error = ERROR_UNKNOWN;
             return;
         }

         if (ThrottleRequest(uid, timestamp, &record, throttle_secure, response)) return;

         if (!IncrementFailureRecord(uid, user_id, timestamp, &record, throttle_secure)) {
             response->error = ERROR_UNKNOWN;
             return;
         }

         timeout = ComputeRetryTimeout(&record);
     } else {
         response->request_reenroll = true;
     }

     if (DoVerify(password_handle, request.provided_password)) {
         // Signature matches
         SizedBuffer auth_token;
         response->error = MintAuthToken(&auth_token, timestamp,
                 user_id, authenticator_id, request.challenge);

         if (response->error != ERROR_NONE) return;

         response->SetVerificationToken(move(auth_token));
         if (throttle) ClearFailureRecord(uid, user_id, throttle_secure);
     } else {
         // compute the new timeout given the incremented record
         if (throttle && timeout > 0) {
             response->SetRetryTimeout(timeout);
         } else {
             response->error = ERROR_INVALID;
         }
     }
 }

 bool GateKeeper::CreatePasswordHandle(SizedBuffer *password_handle_buffer, salt_t salt,
         secure_id_t user_id, uint64_t flags, uint8_t handle_version, const SizedBuffer & password) {
     if (password_handle_buffer == nullptr) return false;

     password_handle_t password_handle;

     password_handle.version = handle_version;
     password_handle.salt = salt;
     password_handle.user_id = user_id;
     password_handle.flags = flags;
     password_handle.hardware_backed = IsHardwareBacked();

     constexpr uint32_t metadata_length = sizeof(password_handle.version) +
                                          sizeof(password_handle.user_id) +
                                          sizeof(password_handle.flags);
     static_assert(offsetof(password_handle_t, salt) == metadata_length,
             "password_handle_t does not appear to be packed");

     const size_t to_sign_size = password.size() + metadata_length;

     UniquePtr<uint8_t[]> to_sign(new(std::nothrow) uint8_t[to_sign_size]);
     if (!to_sign) return false;

     memcpy(to_sign.get(), &password_handle, metadata_length);
     memcpy(to_sign.get() + metadata_length, password.Data<uint8_t>(), password.size());

     const uint8_t *password_key = nullptr;
     uint32_t password_key_length = 0;
     GetPasswordKey(&password_key, &password_key_length);

     if (!password_key || password_key_length == 0) {
         return false;
     }

     ComputePasswordSignature(password_handle.signature, sizeof(password_handle.signature),
             password_key, password_key_length, to_sign.get(), to_sign_size, salt);

     uint8_t *ph_buffer = new(std::nothrow) uint8_t[sizeof(password_handle_t)];
     if (ph_buffer == nullptr) return false;

     *password_handle_buffer = { ph_buffer, sizeof(password_handle_t) };
     memcpy(ph_buffer, &password_handle, sizeof(password_handle_t));

     return true;
 }

 bool GateKeeper::DoVerify(const password_handle_t *expected_handle, const SizedBuffer &password) {
     if (!password) return false;

     SizedBuffer provided_handle;
     if (!CreatePasswordHandle(&provided_handle, expected_handle->salt, expected_handle->user_id,
             expected_handle->flags, expected_handle->version, password)) {
         return false;
     }

     const password_handle_t *generated_handle = provided_handle.Data<password_handle_t>();
     return memcmp_s(generated_handle->signature, expected_handle->signature,
             sizeof(expected_handle->signature)) == 0;
 }

 gatekeeper_error_t GateKeeper::MintAuthToken(SizedBuffer *auth_token,
         uint64_t timestamp, secure_id_t user_id, secure_id_t authenticator_id,
         uint64_t challenge) {
     if (auth_token == nullptr) return ERROR_INVALID;

     hw_auth_token_t token;

     token.version = HW_AUTH_TOKEN_VERSION;
     token.challenge = challenge;
     token.user_id = user_id;
     token.authenticator_id = authenticator_id;
     token.authenticator_type = htobe32(HW_AUTH_PASSWORD);
     token.timestamp = htobe64(timestamp);

     constexpr uint32_t hashable_length = sizeof(token.version) +
                                          sizeof(token.challenge) +
                                          sizeof(token.user_id) +
                                          sizeof(token.authenticator_id) +
                                          sizeof(token.authenticator_type) +
                                          sizeof(token.timestamp);

     static_assert(offsetof(hw_auth_token_t, hmac) == hashable_length,
             "hw_auth_token_t does not appear to be packed");

     const uint8_t *auth_token_key = nullptr;
     uint32_t key_len = 0;
     if (GetAuthTokenKey(&auth_token_key, &key_len)) {
         ComputeSignature(token.hmac, sizeof(token.hmac), auth_token_key, key_len,
                 reinterpret_cast<uint8_t *>(&token), hashable_length);
     } else {
         memset(token.hmac, 0, sizeof(token.hmac));
     }

     uint8_t *token_buffer = new(std::nothrow) uint8_t[sizeof(hw_auth_token_t)];
     if (token_buffer == nullptr) return ERROR_MEMORY_ALLOCATION_FAILED;

     *reinterpret_cast<hw_auth_token_t*>(token_buffer) = token;

     *auth_token = { token_buffer, sizeof(hw_auth_token_t) };
     return ERROR_NONE;
 }

 /*
  * Calculates the timeout in milliseconds as a function of the failure
  * counter 'x' as follows:
  *
  * [0, 4] -> 0
  * 5 -> 30
  * [6, 10] -> 0
  * [11, 29] -> 30
  * [30, 139] -> 30 * (2^((x - 30)/10))
  * [140, inf) -> 1 day
  *
  */
 uint32_t GateKeeper::ComputeRetryTimeout(const failure_record_t *record) {
     static const int failure_timeout_ms = 30000;
     if (record->failure_counter == 0) return 0;

     if (record->failure_counter > 0 && record->failure_counter <= 10) {
         if (record->failure_counter % 5 == 0) {
             return failure_timeout_ms;
         }  else {
             return 0;
         }
     } else if (record->failure_counter < 30) {
         return failure_timeout_ms;
     } else if (record->failure_counter < 140) {
         return failure_timeout_ms << ((record->failure_counter - 30) / 10);
     }

     return DAY_IN_MS;
 }

 bool GateKeeper::ThrottleRequest(uint32_t uid, uint64_t timestamp,
         failure_record_t *record, bool secure, GateKeeperMessage *response) {

     uint64_t last_checked = record->last_checked_timestamp;
     uint32_t timeout = ComputeRetryTimeout(record);

     if (timeout > 0) {
         // we have a pending timeout
         if (timestamp < last_checked + timeout && timestamp > last_checked) {
             // attempt before timeout expired, return remaining time
             response->SetRetryTimeout(timeout - (timestamp - last_checked));
             return true;
         } else if (timestamp <= last_checked) {
             // device was rebooted or timer reset, don't count as new failure but
             // reset timeout
             record->last_checked_timestamp = timestamp;
             if (!WriteFailureRecord(uid, record, secure)) {
                 response->error = ERROR_UNKNOWN;
                 return true;
             }
             response->SetRetryTimeout(timeout);
             return true;
         }
     }

     return false;
 }

 bool GateKeeper::IncrementFailureRecord(uint32_t uid, secure_id_t user_id, uint64_t timestamp,
             failure_record_t *record, bool secure) {
     record->secure_user_id = user_id;
     record->failure_counter++;
     record->last_checked_timestamp = timestamp;

     return WriteFailureRecord(uid, record, secure);
 }
 } // namespace gatekeeper
	/*
	* Copyright 2015 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 <gatekeeper/UniquePtr.h>
	#include <gatekeeper/gatekeeper.h>

	#include <endian.h>
	#include <stddef.h>

	#define DAY_IN_MS (1000 * 60 * 60 * 24)

	namespace gatekeeper {

	void GateKeeper::Enroll(const EnrollRequest &request, EnrollResponse *response) {
	if (response == nullptr) return;

	if (!request.provided_password) {
	response->error = ERROR_INVALID;
	return;
	}

	secure_id_t user_id = 0;// todo: rename to policy
	uint32_t uid = request.user_id;

	if (!request.password_handle) {
	// Password handle does not match what is stored, generate new SecureID
	GetRandom(&user_id, sizeof(secure_id_t));
	} else {
	const password_handle_t *pw_handle = request.password_handle.Data<password_handle_t>();

	if (!pw_handle \|\| pw_handle->version > HANDLE_VERSION) {
	response->error = ERROR_INVALID;
	return;
	}

	user_id = pw_handle->user_id;

	uint64_t timestamp = GetMillisecondsSinceBoot();

	uint32_t timeout = 0;
	bool throttle = (pw_handle->version >= HANDLE_VERSION_THROTTLE);
	if (throttle) {
	bool throttle_secure = pw_handle->flags & HANDLE_FLAG_THROTTLE_SECURE;
	failure_record_t record;
	if (!GetFailureRecord(uid, user_id, &record, throttle_secure)) {
	response->error = ERROR_UNKNOWN;
	return;
	}

	if (ThrottleRequest(uid, timestamp, &record, throttle_secure, response)) return;

	if (!IncrementFailureRecord(uid, user_id, timestamp, &record, throttle_secure)) {
	response->error = ERROR_UNKNOWN;
	return;
	}

	timeout = ComputeRetryTimeout(&record);
	}

	if (!DoVerify(pw_handle, request.enrolled_password)) {
	// incorrect old password
	if (throttle && timeout > 0) {
	response->SetRetryTimeout(timeout);
	} else {
	response->error = ERROR_INVALID;
	}
	return;
	}
	}

	uint64_t flags = 0;
	if (ClearFailureRecord(uid, user_id, true)) {
	flags \|= HANDLE_FLAG_THROTTLE_SECURE;
	} else {
	ClearFailureRecord(uid, user_id, false);
	}

	salt_t salt;
	GetRandom(&salt, sizeof(salt));

	SizedBuffer password_handle;
	if (!CreatePasswordHandle(&password_handle,
	salt, user_id, flags, HANDLE_VERSION, request.provided_password)) {
	response->error = ERROR_INVALID;
	return;
	}

	response->SetEnrolledPasswordHandle(move(password_handle));
	}

	void GateKeeper::Verify(const VerifyRequest &request, VerifyResponse *response) {
	if (response == nullptr) return;

	if (!request.provided_password \|\| !request.password_handle) {
	response->error = ERROR_INVALID;
	return;
	}

	const password_handle_t *password_handle = request.password_handle.Data<password_handle_t>();

	if (!password_handle \|\| password_handle->version > HANDLE_VERSION) {
	response->error = ERROR_INVALID;
	return;
	}

	secure_id_t user_id = password_handle->user_id;
	secure_id_t authenticator_id = 0;
	uint32_t uid = request.user_id;

	uint64_t timestamp = GetMillisecondsSinceBoot();

	uint32_t timeout = 0;
	bool throttle = (password_handle->version >= HANDLE_VERSION_THROTTLE);
	bool throttle_secure = password_handle->flags & HANDLE_FLAG_THROTTLE_SECURE;
	if (throttle) {
	failure_record_t record;
	if (!GetFailureRecord(uid, user_id, &record, throttle_secure)) {
	response->error = ERROR_UNKNOWN;
	return;
	}

	if (ThrottleRequest(uid, timestamp, &record, throttle_secure, response)) return;

	if (!IncrementFailureRecord(uid, user_id, timestamp, &record, throttle_secure)) {
	response->error = ERROR_UNKNOWN;
	return;
	}

	timeout = ComputeRetryTimeout(&record);
	} else {
	response->request_reenroll = true;
	}

	if (DoVerify(password_handle, request.provided_password)) {
	// Signature matches
	SizedBuffer auth_token;
	response->error = MintAuthToken(&auth_token, timestamp,
	user_id, authenticator_id, request.challenge);

	if (response->error != ERROR_NONE) return;

	response->SetVerificationToken(move(auth_token));
	if (throttle) ClearFailureRecord(uid, user_id, throttle_secure);
	} else {
	// compute the new timeout given the incremented record
	if (throttle && timeout > 0) {
	response->SetRetryTimeout(timeout);
	} else {
	response->error = ERROR_INVALID;
	}
	}
	}

	bool GateKeeper::CreatePasswordHandle(SizedBuffer *password_handle_buffer, salt_t salt,
	secure_id_t user_id, uint64_t flags, uint8_t handle_version, const SizedBuffer & password) {
	if (password_handle_buffer == nullptr) return false;

	password_handle_t password_handle;

	password_handle.version = handle_version;
	password_handle.salt = salt;
	password_handle.user_id = user_id;
	password_handle.flags = flags;
	password_handle.hardware_backed = IsHardwareBacked();

	constexpr uint32_t metadata_length = sizeof(password_handle.version) +
	sizeof(password_handle.user_id) +
	sizeof(password_handle.flags);
	static_assert(offsetof(password_handle_t, salt) == metadata_length,
	"password_handle_t does not appear to be packed");

	const size_t to_sign_size = password.size() + metadata_length;

	UniquePtr<uint8_t[]> to_sign(new(std::nothrow) uint8_t[to_sign_size]);
	if (!to_sign) return false;

	memcpy(to_sign.get(), &password_handle, metadata_length);
	memcpy(to_sign.get() + metadata_length, password.Data<uint8_t>(), password.size());

	const uint8_t *password_key = nullptr;
	uint32_t password_key_length = 0;
	GetPasswordKey(&password_key, &password_key_length);

	if (!password_key \|\| password_key_length == 0) {
	return false;
	}

	ComputePasswordSignature(password_handle.signature, sizeof(password_handle.signature),
	password_key, password_key_length, to_sign.get(), to_sign_size, salt);

	uint8_t *ph_buffer = new(std::nothrow) uint8_t[sizeof(password_handle_t)];
	if (ph_buffer == nullptr) return false;

	*password_handle_buffer = { ph_buffer, sizeof(password_handle_t) };
	memcpy(ph_buffer, &password_handle, sizeof(password_handle_t));

	return true;
	}

	bool GateKeeper::DoVerify(const password_handle_t *expected_handle, const SizedBuffer &password) {
	if (!password) return false;

	SizedBuffer provided_handle;
	if (!CreatePasswordHandle(&provided_handle, expected_handle->salt, expected_handle->user_id,
	expected_handle->flags, expected_handle->version, password)) {
	return false;
	}

	const password_handle_t *generated_handle = provided_handle.Data<password_handle_t>();
	return memcmp_s(generated_handle->signature, expected_handle->signature,
	sizeof(expected_handle->signature)) == 0;
	}

	gatekeeper_error_t GateKeeper::MintAuthToken(SizedBuffer *auth_token,
	uint64_t timestamp, secure_id_t user_id, secure_id_t authenticator_id,
	uint64_t challenge) {
	if (auth_token == nullptr) return ERROR_INVALID;

	hw_auth_token_t token;

	token.version = HW_AUTH_TOKEN_VERSION;
	token.challenge = challenge;
	token.user_id = user_id;
	token.authenticator_id = authenticator_id;
	token.authenticator_type = htobe32(HW_AUTH_PASSWORD);
	token.timestamp = htobe64(timestamp);

	constexpr uint32_t hashable_length = sizeof(token.version) +
	sizeof(token.challenge) +
	sizeof(token.user_id) +
	sizeof(token.authenticator_id) +
	sizeof(token.authenticator_type) +
	sizeof(token.timestamp);

	static_assert(offsetof(hw_auth_token_t, hmac) == hashable_length,
	"hw_auth_token_t does not appear to be packed");

	const uint8_t *auth_token_key = nullptr;
	uint32_t key_len = 0;
	if (GetAuthTokenKey(&auth_token_key, &key_len)) {
	ComputeSignature(token.hmac, sizeof(token.hmac), auth_token_key, key_len,
	reinterpret_cast<uint8_t *>(&token), hashable_length);
	} else {
	memset(token.hmac, 0, sizeof(token.hmac));
	}

	uint8_t *token_buffer = new(std::nothrow) uint8_t[sizeof(hw_auth_token_t)];
	if (token_buffer == nullptr) return ERROR_MEMORY_ALLOCATION_FAILED;

	reinterpret_cast<hw_auth_token_t>(token_buffer) = token;

	*auth_token = { token_buffer, sizeof(hw_auth_token_t) };
	return ERROR_NONE;
	}

	/*
	* Calculates the timeout in milliseconds as a function of the failure
	* counter 'x' as follows:
	*
	* [0, 4] -> 0
	* 5 -> 30
	* [6, 10] -> 0
	* [11, 29] -> 30
	* [30, 139] -> 30 * (2^((x - 30)/10))
	* [140, inf) -> 1 day
	*
	*/
	uint32_t GateKeeper::ComputeRetryTimeout(const failure_record_t *record) {
	static const int failure_timeout_ms = 30000;
	if (record->failure_counter == 0) return 0;

	if (record->failure_counter > 0 && record->failure_counter <= 10) {
	if (record->failure_counter % 5 == 0) {
	return failure_timeout_ms;
	} else {
	return 0;
	}
	} else if (record->failure_counter < 30) {
	return failure_timeout_ms;
	} else if (record->failure_counter < 140) {
	return failure_timeout_ms << ((record->failure_counter - 30) / 10);
	}

	return DAY_IN_MS;
	}

	bool GateKeeper::ThrottleRequest(uint32_t uid, uint64_t timestamp,
	failure_record_t record, bool secure, GateKeeperMessage response) {

	uint64_t last_checked = record->last_checked_timestamp;
	uint32_t timeout = ComputeRetryTimeout(record);

	if (timeout > 0) {
	// we have a pending timeout
	if (timestamp < last_checked + timeout && timestamp > last_checked) {
	// attempt before timeout expired, return remaining time
	response->SetRetryTimeout(timeout - (timestamp - last_checked));
	return true;
	} else if (timestamp <= last_checked) {
	// device was rebooted or timer reset, don't count as new failure but
	// reset timeout
	record->last_checked_timestamp = timestamp;
	if (!WriteFailureRecord(uid, record, secure)) {
	response->error = ERROR_UNKNOWN;
	return true;
	}
	response->SetRetryTimeout(timeout);
	return true;
	}
	}

	return false;
	}

	bool GateKeeper::IncrementFailureRecord(uint32_t uid, secure_id_t user_id, uint64_t timestamp,
	failure_record_t *record, bool secure) {
	record->secure_user_id = user_id;
	record->failure_counter++;
	record->last_checked_timestamp = timestamp;

	return WriteFailureRecord(uid, record, secure);
	}
	} // namespace gatekeeper