1 /*
2 * Copyright 2015 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16 #include <UniquePtr.h>
17 #include <gatekeeper/gatekeeper.h>
18
19 #include <endian.h>
20
21 #define DAY_IN_MS (1000 * 60 * 60 * 24)
22
23 namespace gatekeeper {
24
Enroll(const EnrollRequest & request,EnrollResponse * response)25 void GateKeeper::Enroll(const EnrollRequest &request, EnrollResponse *response) {
26 if (response == NULL) return;
27
28 if (!request.provided_password.buffer.get()) {
29 response->error = ERROR_INVALID;
30 return;
31 }
32
33 secure_id_t user_id = 0;// todo: rename to policy
34 uint32_t uid = request.user_id;
35
36 if (request.password_handle.buffer.get() == NULL) {
37 // Password handle does not match what is stored, generate new SecureID
38 GetRandom(&user_id, sizeof(secure_id_t));
39 } else {
40 password_handle_t *pw_handle =
41 reinterpret_cast<password_handle_t *>(request.password_handle.buffer.get());
42
43 if (pw_handle->version > HANDLE_VERSION) {
44 response->error = ERROR_INVALID;
45 return;
46 }
47
48 user_id = pw_handle->user_id;
49
50 uint64_t timestamp = GetMillisecondsSinceBoot();
51
52 uint32_t timeout = 0;
53 bool throttle = (pw_handle->version >= HANDLE_VERSION_THROTTLE);
54 if (throttle) {
55 bool throttle_secure = pw_handle->flags & HANDLE_FLAG_THROTTLE_SECURE;
56 failure_record_t record;
57 if (!GetFailureRecord(uid, user_id, &record, throttle_secure)) {
58 response->error = ERROR_UNKNOWN;
59 return;
60 }
61
62 if (ThrottleRequest(uid, timestamp, &record, throttle_secure, response)) return;
63
64 if (!IncrementFailureRecord(uid, user_id, timestamp, &record, throttle_secure)) {
65 response->error = ERROR_UNKNOWN;
66 return;
67 }
68
69 timeout = ComputeRetryTimeout(&record);
70 }
71
72 if (!DoVerify(pw_handle, request.enrolled_password)) {
73 // incorrect old password
74 if (throttle && timeout > 0) {
75 response->SetRetryTimeout(timeout);
76 } else {
77 response->error = ERROR_INVALID;
78 }
79 return;
80 }
81 }
82
83 uint64_t flags = 0;
84 if (ClearFailureRecord(uid, user_id, true)) {
85 flags |= HANDLE_FLAG_THROTTLE_SECURE;
86 } else {
87 ClearFailureRecord(uid, user_id, false);
88 }
89
90 salt_t salt;
91 GetRandom(&salt, sizeof(salt));
92
93 SizedBuffer password_handle;
94 if (!CreatePasswordHandle(&password_handle,
95 salt, user_id, flags, HANDLE_VERSION, request.provided_password.buffer.get(),
96 request.provided_password.length)) {
97 response->error = ERROR_INVALID;
98 return;
99 }
100
101 response->SetEnrolledPasswordHandle(&password_handle);
102 }
103
Verify(const VerifyRequest & request,VerifyResponse * response)104 void GateKeeper::Verify(const VerifyRequest &request, VerifyResponse *response) {
105 if (response == NULL) return;
106
107 if (!request.provided_password.buffer.get() || !request.password_handle.buffer.get()) {
108 response->error = ERROR_INVALID;
109 return;
110 }
111
112 password_handle_t *password_handle = reinterpret_cast<password_handle_t *>(
113 request.password_handle.buffer.get());
114
115 if (password_handle->version > HANDLE_VERSION) {
116 response->error = ERROR_INVALID;
117 return;
118 }
119
120 secure_id_t user_id = password_handle->user_id;
121 secure_id_t authenticator_id = 0;
122 uint32_t uid = request.user_id;
123
124 uint64_t timestamp = GetMillisecondsSinceBoot();
125
126 uint32_t timeout = 0;
127 bool throttle = (password_handle->version >= HANDLE_VERSION_THROTTLE);
128 bool throttle_secure = password_handle->flags & HANDLE_FLAG_THROTTLE_SECURE;
129 if (throttle) {
130 failure_record_t record;
131 if (!GetFailureRecord(uid, user_id, &record, throttle_secure)) {
132 response->error = ERROR_UNKNOWN;
133 return;
134 }
135
136 if (ThrottleRequest(uid, timestamp, &record, throttle_secure, response)) return;
137
138 if (!IncrementFailureRecord(uid, user_id, timestamp, &record, throttle_secure)) {
139 response->error = ERROR_UNKNOWN;
140 return;
141 }
142
143 timeout = ComputeRetryTimeout(&record);
144 } else {
145 response->request_reenroll = true;
146 }
147
148 if (DoVerify(password_handle, request.provided_password)) {
149 // Signature matches
150 UniquePtr<uint8_t> auth_token_buffer;
151 uint32_t auth_token_len;
152 MintAuthToken(&auth_token_buffer, &auth_token_len, timestamp,
153 user_id, authenticator_id, request.challenge);
154
155 SizedBuffer auth_token(auth_token_len);
156 memcpy(auth_token.buffer.get(), auth_token_buffer.get(), auth_token_len);
157 response->SetVerificationToken(&auth_token);
158 if (throttle) ClearFailureRecord(uid, user_id, throttle_secure);
159 } else {
160 // compute the new timeout given the incremented record
161 if (throttle && timeout > 0) {
162 response->SetRetryTimeout(timeout);
163 } else {
164 response->error = ERROR_INVALID;
165 }
166 }
167 }
168
CreatePasswordHandle(SizedBuffer * password_handle_buffer,salt_t salt,secure_id_t user_id,uint64_t flags,uint8_t handle_version,const uint8_t * password,uint32_t password_length)169 bool GateKeeper::CreatePasswordHandle(SizedBuffer *password_handle_buffer, salt_t salt,
170 secure_id_t user_id, uint64_t flags, uint8_t handle_version, const uint8_t *password,
171 uint32_t password_length) {
172 password_handle_buffer->buffer.reset(new uint8_t[sizeof(password_handle_t)]);
173 password_handle_buffer->length = sizeof(password_handle_t);
174
175 password_handle_t *password_handle = reinterpret_cast<password_handle_t *>(
176 password_handle_buffer->buffer.get());
177 password_handle->version = handle_version;
178 password_handle->salt = salt;
179 password_handle->user_id = user_id;
180 password_handle->flags = flags;
181 password_handle->hardware_backed = IsHardwareBacked();
182
183 uint32_t metadata_length = sizeof(user_id) + sizeof(flags) + sizeof(HANDLE_VERSION);
184 const size_t to_sign_size = password_length + metadata_length;
185 UniquePtr<uint8_t> to_sign(new uint8_t[to_sign_size]);
186
187 if (to_sign.get() == nullptr) {
188 return false;
189 }
190
191 memcpy(to_sign.get(), password_handle, metadata_length);
192 memcpy(to_sign.get() + metadata_length, password, password_length);
193
194 const uint8_t *password_key = NULL;
195 uint32_t password_key_length = 0;
196 GetPasswordKey(&password_key, &password_key_length);
197
198 if (!password_key || password_key_length == 0) {
199 return false;
200 }
201
202 ComputePasswordSignature(password_handle->signature, sizeof(password_handle->signature),
203 password_key, password_key_length, to_sign.get(), to_sign_size, salt);
204 return true;
205 }
206
DoVerify(const password_handle_t * expected_handle,const SizedBuffer & password)207 bool GateKeeper::DoVerify(const password_handle_t *expected_handle, const SizedBuffer &password) {
208 if (!password.buffer.get()) return false;
209
210 SizedBuffer provided_handle;
211 if (!CreatePasswordHandle(&provided_handle, expected_handle->salt, expected_handle->user_id,
212 expected_handle->flags, expected_handle->version,
213 password.buffer.get(), password.length)) {
214 return false;
215 }
216
217 password_handle_t *generated_handle =
218 reinterpret_cast<password_handle_t *>(provided_handle.buffer.get());
219 return memcmp_s(generated_handle->signature, expected_handle->signature,
220 sizeof(expected_handle->signature)) == 0;
221 }
222
MintAuthToken(UniquePtr<uint8_t> * auth_token,uint32_t * length,uint64_t timestamp,secure_id_t user_id,secure_id_t authenticator_id,uint64_t challenge)223 void GateKeeper::MintAuthToken(UniquePtr<uint8_t> *auth_token, uint32_t *length,
224 uint64_t timestamp, secure_id_t user_id, secure_id_t authenticator_id,
225 uint64_t challenge) {
226 if (auth_token == NULL) return;
227
228 hw_auth_token_t *token = new hw_auth_token_t;
229 SizedBuffer serialized_auth_token;
230
231 token->version = HW_AUTH_TOKEN_VERSION;
232 token->challenge = challenge;
233 token->user_id = user_id;
234 token->authenticator_id = authenticator_id;
235 token->authenticator_type = htonl(HW_AUTH_PASSWORD);
236 token->timestamp = htobe64(timestamp);
237
238 const uint8_t *auth_token_key = NULL;
239 uint32_t key_len = 0;
240 if (GetAuthTokenKey(&auth_token_key, &key_len)) {
241 uint32_t hash_len = (uint32_t)((uint8_t *)&token->hmac - (uint8_t *)token);
242 ComputeSignature(token->hmac, sizeof(token->hmac), auth_token_key, key_len,
243 reinterpret_cast<uint8_t *>(token), hash_len);
244 delete[] auth_token_key;
245 } else {
246 memset(token->hmac, 0, sizeof(token->hmac));
247 }
248
249 if (length != NULL) *length = sizeof(*token);
250 auth_token->reset(reinterpret_cast<uint8_t *>(token));
251 }
252
253 /*
254 * Calculates the timeout in milliseconds as a function of the failure
255 * counter 'x' as follows:
256 *
257 * [0. 5) -> 0
258 * 5 -> 30
259 * [6, 10) -> 0
260 * [11, 30) -> 30
261 * [30, 140) -> 30 * (2^((x - 30)/10))
262 * [140, inf) -> 1 day
263 *
264 */
ComputeRetryTimeout(const failure_record_t * record)265 uint32_t GateKeeper::ComputeRetryTimeout(const failure_record_t *record) {
266 static const int failure_timeout_ms = 30000;
267 if (record->failure_counter == 0) return 0;
268
269 if (record->failure_counter > 0 && record->failure_counter <= 10) {
270 if (record->failure_counter % 5 == 0) {
271 return failure_timeout_ms;
272 } else {
273 return 0;
274 }
275 } else if (record->failure_counter < 30) {
276 return failure_timeout_ms;
277 } else if (record->failure_counter < 140) {
278 return failure_timeout_ms << ((record->failure_counter - 30) / 10);
279 }
280
281 return DAY_IN_MS;
282 }
283
ThrottleRequest(uint32_t uid,uint64_t timestamp,failure_record_t * record,bool secure,GateKeeperMessage * response)284 bool GateKeeper::ThrottleRequest(uint32_t uid, uint64_t timestamp,
285 failure_record_t *record, bool secure, GateKeeperMessage *response) {
286
287 uint64_t last_checked = record->last_checked_timestamp;
288 uint32_t timeout = ComputeRetryTimeout(record);
289
290 if (timeout > 0) {
291 // we have a pending timeout
292 if (timestamp < last_checked + timeout && timestamp > last_checked) {
293 // attempt before timeout expired, return remaining time
294 response->SetRetryTimeout(timeout - (timestamp - last_checked));
295 return true;
296 } else if (timestamp <= last_checked) {
297 // device was rebooted or timer reset, don't count as new failure but
298 // reset timeout
299 record->last_checked_timestamp = timestamp;
300 if (!WriteFailureRecord(uid, record, secure)) {
301 response->error = ERROR_UNKNOWN;
302 return true;
303 }
304 response->SetRetryTimeout(timeout);
305 return true;
306 }
307 }
308
309 return false;
310 }
311
IncrementFailureRecord(uint32_t uid,secure_id_t user_id,uint64_t timestamp,failure_record_t * record,bool secure)312 bool GateKeeper::IncrementFailureRecord(uint32_t uid, secure_id_t user_id, uint64_t timestamp,
313 failure_record_t *record, bool secure) {
314 record->secure_user_id = user_id;
315 record->failure_counter++;
316 record->last_checked_timestamp = timestamp;
317
318 return WriteFailureRecord(uid, record, secure);
319 }
320 } // namespace gatekeeper
321
322