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      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 
     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 
    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 
    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     uint8_t to_sign[password_length + metadata_length];
    185     memcpy(to_sign, password_handle, metadata_length);
    186     memcpy(to_sign + metadata_length, password, password_length);
    187 
    188     const uint8_t *password_key = NULL;
    189     uint32_t password_key_length = 0;
    190     GetPasswordKey(&password_key, &password_key_length);
    191 
    192     if (!password_key || password_key_length == 0) {
    193         return false;
    194     }
    195 
    196     ComputePasswordSignature(password_handle->signature, sizeof(password_handle->signature),
    197             password_key, password_key_length, to_sign, sizeof(to_sign), salt);
    198     return true;
    199 }
    200 
    201 bool GateKeeper::DoVerify(const password_handle_t *expected_handle, const SizedBuffer &password) {
    202     if (!password.buffer.get()) return false;
    203 
    204     SizedBuffer provided_handle;
    205     if (!CreatePasswordHandle(&provided_handle, expected_handle->salt, expected_handle->user_id,
    206             expected_handle->flags, expected_handle->version,
    207             password.buffer.get(), password.length)) {
    208         return false;
    209     }
    210 
    211     password_handle_t *generated_handle =
    212             reinterpret_cast<password_handle_t *>(provided_handle.buffer.get());
    213     return memcmp_s(generated_handle->signature, expected_handle->signature,
    214             sizeof(expected_handle->signature)) == 0;
    215 }
    216 
    217 void GateKeeper::MintAuthToken(UniquePtr<uint8_t> *auth_token, uint32_t *length,
    218         uint64_t timestamp, secure_id_t user_id, secure_id_t authenticator_id,
    219         uint64_t challenge) {
    220     if (auth_token == NULL) return;
    221 
    222     hw_auth_token_t *token = new hw_auth_token_t;
    223     SizedBuffer serialized_auth_token;
    224 
    225     token->version = HW_AUTH_TOKEN_VERSION;
    226     token->challenge = challenge;
    227     token->user_id = user_id;
    228     token->authenticator_id = authenticator_id;
    229     token->authenticator_type = htonl(HW_AUTH_PASSWORD);
    230     token->timestamp = htobe64(timestamp);
    231 
    232     const uint8_t *auth_token_key = NULL;
    233     uint32_t key_len = 0;
    234     if (GetAuthTokenKey(&auth_token_key, &key_len)) {
    235         uint32_t hash_len = (uint32_t)((uint8_t *)&token->hmac - (uint8_t *)token);
    236         ComputeSignature(token->hmac, sizeof(token->hmac), auth_token_key, key_len,
    237                 reinterpret_cast<uint8_t *>(token), hash_len);
    238         delete[] auth_token_key;
    239     } else {
    240         memset(token->hmac, 0, sizeof(token->hmac));
    241     }
    242 
    243     if (length != NULL) *length = sizeof(*token);
    244     auth_token->reset(reinterpret_cast<uint8_t *>(token));
    245 }
    246 
    247 /*
    248  * Calculates the timeout in milliseconds as a function of the failure
    249  * counter 'x' as follows:
    250  *
    251  * [0. 5) -> 0
    252  * 5 -> 30
    253  * [6, 10) -> 0
    254  * [11, 30) -> 30
    255  * [30, 140) -> 30 * (2^((x - 30)/10))
    256  * [140, inf) -> 1 day
    257  *
    258  */
    259 uint32_t GateKeeper::ComputeRetryTimeout(const failure_record_t *record) {
    260     static const int failure_timeout_ms = 30000;
    261     if (record->failure_counter == 0) return 0;
    262 
    263     if (record->failure_counter > 0 && record->failure_counter <= 10) {
    264         if (record->failure_counter % 5 == 0) {
    265             return failure_timeout_ms;
    266         }  else {
    267             return 0;
    268         }
    269     } else if (record->failure_counter < 30) {
    270         return failure_timeout_ms;
    271     } else if (record->failure_counter < 140) {
    272         return failure_timeout_ms << ((record->failure_counter - 30) / 10);
    273     }
    274 
    275     return DAY_IN_MS;
    276 }
    277 
    278 bool GateKeeper::ThrottleRequest(uint32_t uid, uint64_t timestamp,
    279         failure_record_t *record, bool secure, GateKeeperMessage *response) {
    280 
    281     uint64_t last_checked = record->last_checked_timestamp;
    282     uint32_t timeout = ComputeRetryTimeout(record);
    283 
    284     if (timeout > 0) {
    285         // we have a pending timeout
    286         if (timestamp < last_checked + timeout && timestamp > last_checked) {
    287             // attempt before timeout expired, return remaining time
    288             response->SetRetryTimeout(timeout - (timestamp - last_checked));
    289             return true;
    290         } else if (timestamp <= last_checked) {
    291             // device was rebooted or timer reset, don't count as new failure but
    292             // reset timeout
    293             record->last_checked_timestamp = timestamp;
    294             if (!WriteFailureRecord(uid, record, secure)) {
    295                 response->error = ERROR_UNKNOWN;
    296                 return true;
    297             }
    298             response->SetRetryTimeout(timeout);
    299             return true;
    300         }
    301     }
    302 
    303     return false;
    304 }
    305 
    306 bool GateKeeper::IncrementFailureRecord(uint32_t uid, secure_id_t user_id, uint64_t timestamp,
    307             failure_record_t *record, bool secure) {
    308     record->secure_user_id = user_id;
    309     record->failure_counter++;
    310     record->last_checked_timestamp = timestamp;
    311 
    312     return WriteFailureRecord(uid, record, secure);
    313 }
    314 } // namespace gatekeeper
    315 
    316