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 <gatekeeper/UniquePtr.h>
17 #include <gatekeeper/gatekeeper.h>
18
19 #include <endian.h>
20 #include <stddef.h>
21
22 #define DAY_IN_MS (1000 * 60 * 60 * 24)
23
24 namespace gatekeeper {
25
Enroll(const EnrollRequest & request,EnrollResponse * response)26 void GateKeeper::Enroll(const EnrollRequest &request, EnrollResponse *response) {
27 if (response == nullptr) return;
28
29 if (!request.provided_password) {
30 response->error = ERROR_INVALID;
31 return;
32 }
33
34 secure_id_t user_id = 0;// todo: rename to policy
35 uint32_t uid = request.user_id;
36
37 if (!request.password_handle) {
38 // Password handle does not match what is stored, generate new SecureID
39 GetRandom(&user_id, sizeof(secure_id_t));
40 } else {
41 const password_handle_t *pw_handle = request.password_handle.Data<password_handle_t>();
42
43 if (!pw_handle || 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)) {
96 response->error = ERROR_INVALID;
97 return;
98 }
99
100 response->SetEnrolledPasswordHandle(move(password_handle));
101 }
102
Verify(const VerifyRequest & request,VerifyResponse * response)103 void GateKeeper::Verify(const VerifyRequest &request, VerifyResponse *response) {
104 if (response == nullptr) return;
105
106 if (!request.provided_password || !request.password_handle) {
107 response->error = ERROR_INVALID;
108 return;
109 }
110
111 const password_handle_t *password_handle = request.password_handle.Data<password_handle_t>();
112
113 if (!password_handle || password_handle->version > HANDLE_VERSION) {
114 response->error = ERROR_INVALID;
115 return;
116 }
117
118 secure_id_t user_id = password_handle->user_id;
119 secure_id_t authenticator_id = 0;
120 uint32_t uid = request.user_id;
121
122 uint64_t timestamp = GetMillisecondsSinceBoot();
123
124 uint32_t timeout = 0;
125 bool throttle = (password_handle->version >= HANDLE_VERSION_THROTTLE);
126 bool throttle_secure = password_handle->flags & HANDLE_FLAG_THROTTLE_SECURE;
127 if (throttle) {
128 failure_record_t record;
129 if (!GetFailureRecord(uid, user_id, &record, throttle_secure)) {
130 response->error = ERROR_UNKNOWN;
131 return;
132 }
133
134 if (ThrottleRequest(uid, timestamp, &record, throttle_secure, response)) return;
135
136 if (!IncrementFailureRecord(uid, user_id, timestamp, &record, throttle_secure)) {
137 response->error = ERROR_UNKNOWN;
138 return;
139 }
140
141 timeout = ComputeRetryTimeout(&record);
142 } else {
143 response->request_reenroll = true;
144 }
145
146 if (DoVerify(password_handle, request.provided_password)) {
147 // Signature matches
148 SizedBuffer auth_token;
149 response->error = MintAuthToken(&auth_token, timestamp,
150 user_id, authenticator_id, request.challenge);
151
152 if (response->error != ERROR_NONE) return;
153
154 response->SetVerificationToken(move(auth_token));
155 if (throttle) ClearFailureRecord(uid, user_id, throttle_secure);
156 } else {
157 // compute the new timeout given the incremented record
158 if (throttle && timeout > 0) {
159 response->SetRetryTimeout(timeout);
160 } else {
161 response->error = ERROR_INVALID;
162 }
163 }
164 }
165
CreatePasswordHandle(SizedBuffer * password_handle_buffer,salt_t salt,secure_id_t user_id,uint64_t flags,uint8_t handle_version,const SizedBuffer & password)166 bool GateKeeper::CreatePasswordHandle(SizedBuffer *password_handle_buffer, salt_t salt,
167 secure_id_t user_id, uint64_t flags, uint8_t handle_version, const SizedBuffer & password) {
168 if (password_handle_buffer == nullptr) return false;
169
170 password_handle_t password_handle;
171
172 password_handle.version = handle_version;
173 password_handle.salt = salt;
174 password_handle.user_id = user_id;
175 password_handle.flags = flags;
176 password_handle.hardware_backed = IsHardwareBacked();
177
178 constexpr uint32_t metadata_length = sizeof(password_handle.version) +
179 sizeof(password_handle.user_id) +
180 sizeof(password_handle.flags);
181 static_assert(offsetof(password_handle_t, salt) == metadata_length,
182 "password_handle_t does not appear to be packed");
183
184 const size_t to_sign_size = password.size() + metadata_length;
185
186 UniquePtr<uint8_t[]> to_sign(new(std::nothrow) uint8_t[to_sign_size]);
187 if (!to_sign) return false;
188
189 memcpy(to_sign.get(), &password_handle, metadata_length);
190 memcpy(to_sign.get() + metadata_length, password.Data<uint8_t>(), password.size());
191
192 const uint8_t *password_key = nullptr;
193 uint32_t password_key_length = 0;
194 GetPasswordKey(&password_key, &password_key_length);
195
196 if (!password_key || password_key_length == 0) {
197 return false;
198 }
199
200 ComputePasswordSignature(password_handle.signature, sizeof(password_handle.signature),
201 password_key, password_key_length, to_sign.get(), to_sign_size, salt);
202
203 uint8_t *ph_buffer = new(std::nothrow) uint8_t[sizeof(password_handle_t)];
204 if (ph_buffer == nullptr) return false;
205
206 *password_handle_buffer = { ph_buffer, sizeof(password_handle_t) };
207 memcpy(ph_buffer, &password_handle, sizeof(password_handle_t));
208
209 return true;
210 }
211
DoVerify(const password_handle_t * expected_handle,const SizedBuffer & password)212 bool GateKeeper::DoVerify(const password_handle_t *expected_handle, const SizedBuffer &password) {
213 if (!password) return false;
214
215 SizedBuffer provided_handle;
216 if (!CreatePasswordHandle(&provided_handle, expected_handle->salt, expected_handle->user_id,
217 expected_handle->flags, expected_handle->version, password)) {
218 return false;
219 }
220
221 const password_handle_t *generated_handle = provided_handle.Data<password_handle_t>();
222 return memcmp_s(generated_handle->signature, expected_handle->signature,
223 sizeof(expected_handle->signature)) == 0;
224 }
225
MintAuthToken(SizedBuffer * auth_token,uint64_t timestamp,secure_id_t user_id,secure_id_t authenticator_id,uint64_t challenge)226 gatekeeper_error_t GateKeeper::MintAuthToken(SizedBuffer *auth_token,
227 uint64_t timestamp, secure_id_t user_id, secure_id_t authenticator_id,
228 uint64_t challenge) {
229 if (auth_token == nullptr) return ERROR_INVALID;
230
231 hw_auth_token_t token;
232
233 token.version = HW_AUTH_TOKEN_VERSION;
234 token.challenge = challenge;
235 token.user_id = user_id;
236 token.authenticator_id = authenticator_id;
237 token.authenticator_type = htobe32(HW_AUTH_PASSWORD);
238 token.timestamp = htobe64(timestamp);
239
240 constexpr uint32_t hashable_length = sizeof(token.version) +
241 sizeof(token.challenge) +
242 sizeof(token.user_id) +
243 sizeof(token.authenticator_id) +
244 sizeof(token.authenticator_type) +
245 sizeof(token.timestamp);
246
247 static_assert(offsetof(hw_auth_token_t, hmac) == hashable_length,
248 "hw_auth_token_t does not appear to be packed");
249
250 const uint8_t *auth_token_key = nullptr;
251 uint32_t key_len = 0;
252 if (GetAuthTokenKey(&auth_token_key, &key_len)) {
253 ComputeSignature(token.hmac, sizeof(token.hmac), auth_token_key, key_len,
254 reinterpret_cast<uint8_t *>(&token), hashable_length);
255 } else {
256 memset(token.hmac, 0, sizeof(token.hmac));
257 }
258
259 uint8_t *token_buffer = new(std::nothrow) uint8_t[sizeof(hw_auth_token_t)];
260 if (token_buffer == nullptr) return ERROR_MEMORY_ALLOCATION_FAILED;
261
262 *reinterpret_cast<hw_auth_token_t*>(token_buffer) = token;
263
264 *auth_token = { token_buffer, sizeof(hw_auth_token_t) };
265 return ERROR_NONE;
266 }
267
268 /*
269 * Calculates the timeout in milliseconds as a function of the failure
270 * counter 'x' as follows:
271 *
272 * [0, 4] -> 0
273 * 5 -> 30
274 * [6, 10] -> 0
275 * [11, 29] -> 30
276 * [30, 139] -> 30 * (2^((x - 30)/10))
277 * [140, inf) -> 1 day
278 *
279 */
ComputeRetryTimeout(const failure_record_t * record)280 uint32_t GateKeeper::ComputeRetryTimeout(const failure_record_t *record) {
281 static const int failure_timeout_ms = 30000;
282 if (record->failure_counter == 0) return 0;
283
284 if (record->failure_counter > 0 && record->failure_counter <= 10) {
285 if (record->failure_counter % 5 == 0) {
286 return failure_timeout_ms;
287 } else {
288 return 0;
289 }
290 } else if (record->failure_counter < 30) {
291 return failure_timeout_ms;
292 } else if (record->failure_counter < 140) {
293 return failure_timeout_ms << ((record->failure_counter - 30) / 10);
294 }
295
296 return DAY_IN_MS;
297 }
298
ThrottleRequest(uint32_t uid,uint64_t timestamp,failure_record_t * record,bool secure,GateKeeperMessage * response)299 bool GateKeeper::ThrottleRequest(uint32_t uid, uint64_t timestamp,
300 failure_record_t *record, bool secure, GateKeeperMessage *response) {
301
302 uint64_t last_checked = record->last_checked_timestamp;
303 uint32_t timeout = ComputeRetryTimeout(record);
304
305 if (timeout > 0) {
306 // we have a pending timeout
307 if (timestamp < last_checked + timeout && timestamp > last_checked) {
308 // attempt before timeout expired, return remaining time
309 response->SetRetryTimeout(timeout - (timestamp - last_checked));
310 return true;
311 } else if (timestamp <= last_checked) {
312 // device was rebooted or timer reset, don't count as new failure but
313 // reset timeout
314 record->last_checked_timestamp = timestamp;
315 if (!WriteFailureRecord(uid, record, secure)) {
316 response->error = ERROR_UNKNOWN;
317 return true;
318 }
319 response->SetRetryTimeout(timeout);
320 return true;
321 }
322 }
323
324 return false;
325 }
326
IncrementFailureRecord(uint32_t uid,secure_id_t user_id,uint64_t timestamp,failure_record_t * record,bool secure)327 bool GateKeeper::IncrementFailureRecord(uint32_t uid, secure_id_t user_id, uint64_t timestamp,
328 failure_record_t *record, bool secure) {
329 record->secure_user_id = user_id;
330 record->failure_counter++;
331 record->last_checked_timestamp = timestamp;
332
333 return WriteFailureRecord(uid, record, secure);
334 }
335 } // namespace gatekeeper
336
337