diff options
Diffstat (limited to 'server/src/leap/soledad/server/__init__.py')
| -rw-r--r-- | server/src/leap/soledad/server/__init__.py | 270 |
1 files changed, 259 insertions, 11 deletions
diff --git a/server/src/leap/soledad/server/__init__.py b/server/src/leap/soledad/server/__init__.py index b4b715e2..c80b4c68 100644 --- a/server/src/leap/soledad/server/__init__.py +++ b/server/src/leap/soledad/server/__init__.py @@ -19,6 +19,9 @@ """ A U1DB server that stores data using CouchDB as its persistence layer. +General information +=================== + This is written as a Twisted application and intended to be run using the twistd command. To start the soledad server, run: @@ -27,14 +30,69 @@ twistd command. To start the soledad server, run: An initscript is included and will be installed system wide to make it feasible to start and stop the Soledad server service using a standard interface. + +Server database organization +============================ + +Soledad Server works with one database per user and one shared database in +which user's encrypted secrets might be stored. + +User database +------------- + +Users' databases in the server are named 'user-<uuid>' and Soledad Client +may perform synchronization between its local replicas and the user's +database in the server. Authorization for creating, updating, deleting and +retrieving information about the user database as well as performing +synchronization is handled by the `leap.soledad.server.auth` module. + +Shared database +--------------- + +Each user may store password-encrypted recovery data in the shared database, +as well as obtain a lock on the shared database in order to prevent creation +of multiple secrets in parallel. + +Recovery documents are stored in the database without any information that +may identify the user. In order to achieve this, the doc_id of recovery +documents are obtained as a hash of the user's uid and the user's password. +User's must have a valid token to interact with recovery documents, but the +server does not perform further authentication because it has no way to know +which recovery document belongs to each user. + +This has some implications: + + * The security of the recovery document doc_id, and thus of access to the + recovery document (encrypted) content, as well as tampering with the + stored data, all rely on the difficulty of obtaining the user's password + (supposing the user's uid is somewhat public) and the security of the hash + function used to calculate the doc_id. + + * The security of the content of a recovery document relies on the + difficulty of obtaining the user's password. + + * If the user looses his/her password, he/she will not be able to obtain the + recovery document. + + * Because of the above, it is recommended that recovery documents expire + (not implemented yet) to prevent excess storage. + +Lock documents, on the other hand, may be more thoroughly protected by the +server. Their doc_id's are calculated from the SHARED_DB_LOCK_DOC_ID_PREFIX +and the user's uid. + +The authorization for creating, updating, deleting and retrieving recovery +and lock documents on the shared database is handled by +`leap.soledad.server.auth` module. """ import configparser - +import time +import hashlib +import os from u1db.remote import http_app - # Keep OpenSSL's tsafe before importing Twisted submodules so we can put # it back if Twisted==12.0.0 messes with it. from OpenSSL import tsafe @@ -42,6 +100,8 @@ old_tsafe = tsafe from twisted.web.wsgi import WSGIResource from twisted.internet import reactor +from twisted.internet.error import TimeoutError +from twisted.python.lockfile import FilesystemLock from twisted import version if version.base() == "12.0.0": # Put OpenSSL's tsafe back into place. This can probably be removed if we @@ -49,9 +109,17 @@ if version.base() == "12.0.0": import sys sys.modules['OpenSSL.tsafe'] = old_tsafe - from leap.soledad.server.auth import SoledadTokenAuthMiddleware +from leap.soledad.common import ( + SHARED_DB_NAME, + SHARED_DB_LOCK_DOC_ID_PREFIX, +) from leap.soledad.common.couch import CouchServerState +from leap.soledad.common.errors import ( + InvalidTokenError, + NotLockedError, + AlreadyLockedError, +) #----------------------------------------------------------------------------- @@ -63,16 +131,11 @@ class SoledadApp(http_app.HTTPApp): Soledad WSGI application """ - SHARED_DB_NAME = 'shared' + SHARED_DB_NAME = SHARED_DB_NAME """ The name of the shared database that holds user's encrypted secrets. """ - USER_DB_PREFIX = 'user-' - """ - The string prefix of users' databases. - """ - def __call__(self, environ, start_response): """ Handle a WSGI call to the Soledad application. @@ -91,6 +154,192 @@ class SoledadApp(http_app.HTTPApp): return http_app.HTTPApp.__call__(self, environ, start_response) +# +# LockResource: a lock based on a document in the shared database. +# + +@http_app.url_to_resource.register +class LockResource(object): + """ + Handle requests for locking documents. + + This class uses Twisted's Filesystem lock to manage a lock in the shared + database. + """ + + url_pattern = '/%s/lock/{uuid}' % SoledadApp.SHARED_DB_NAME + """ + """ + + TIMEOUT = 300 # XXX is 5 minutes reasonable? + """ + The timeout after which the lock expires. + """ + + # used for lock doc storage + TIMESTAMP_KEY = '_timestamp' + LOCK_TOKEN_KEY = '_token' + + FILESYSTEM_LOCK_TRIES = 5 + FILESYSTEM_LOCK_SLEEP_SECONDS = 1 + + + def __init__(self, uuid, state, responder): + """ + Initialize the lock resource. Parameters to this constructor are + automatically passed by u1db. + + :param uuid: The user unique id. + :type uuid: str + :param state: The backend database state. + :type state: u1db.remote.ServerState + :param responder: The infrastructure to send responses to client. + :type responder: u1db.remote.HTTPResponder + """ + self._shared_db = state.open_database(SoledadApp.SHARED_DB_NAME) + self._lock_doc_id = '%s%s' % (SHARED_DB_LOCK_DOC_ID_PREFIX, uuid) + self._lock = FilesystemLock( + hashlib.sha512(self._lock_doc_id).hexdigest()) + self._state = state + self._responder = responder + + @http_app.http_method(content=str) + def put(self, content=None): + """ + Handle a PUT request to the lock document. + + A lock is a document in the shared db with doc_id equal to + 'lock-<uuid>' and the timestamp of its creation as content. This + method obtains a threaded-lock and creates a lock document if it does + not exist or if it has expired. + + It returns '201 Created' and a pair containing a token to unlock and + the lock timeout, or '403 AlreadyLockedError' and the remaining amount + of seconds the lock will still be valid. + + :param content: The content of the PUT request. It is only here + because PUT requests with empty content are considered + invalid requests by u1db. + :type content: str + """ + # obtain filesystem lock + if not self._try_obtain_filesystem_lock(): + self._responder.send_response_json(408) # error: request timeout + return + + created_lock = False + now = time.time() + token = hashlib.sha256(os.urandom(10)).hexdigest() # for releasing + lock_doc = self._shared_db.get_doc(self._lock_doc_id) + remaining = self._remaining(lock_doc, now) + + # if there's no lock, create one + if lock_doc is None: + lock_doc = self._shared_db.create_doc( + { + self.TIMESTAMP_KEY: now, + self.LOCK_TOKEN_KEY: token, + }, + doc_id=self._lock_doc_id) + created_lock = True + else: + if remaining == 0: + # lock expired, create new one + lock_doc.content = { + self.TIMESTAMP_KEY: now, + self.LOCK_TOKEN_KEY: token, + } + self._shared_db.put_doc(lock_doc) + created_lock = True + + self._try_release_filesystem_lock() + + # send response to client + if created_lock is True: + self._responder.send_response_json( + 201, timeout=self.TIMEOUT, token=token) # success: created + else: + wire_descr = AlreadyLockedError.wire_description + self._responder.send_response_json( + AlreadyLockedError.status, # error: forbidden + error=AlreadyLockedError.wire_description, remaining=remaining) + + @http_app.http_method(token=str) + def delete(self, token=None): + """ + Delete the lock if the C{token} is valid. + + Delete the lock document in case C{token} is equal to the token stored + in the lock document. + + :param token: The token returned when locking. + :type token: str + + :raise NotLockedError: Raised in case the lock is not locked. + :raise InvalidTokenError: Raised in case the token is invalid for + unlocking. + """ + lock_doc = self._shared_db.get_doc(self._lock_doc_id) + if lock_doc is None or self._remaining(lock_doc, time.time()) == 0: + self._responder.send_response_json( + NotLockedError.status, # error: not found + error=NotLockedError.wire_description) + elif token != lock_doc.content[self.LOCK_TOKEN_KEY]: + self._responder.send_response_json( + InvalidTokenError.status, # error: unauthorized + error=InvalidTokenError.wire_description) + else: + self._shared_db.delete_doc(lock_doc) + self._responder.send_response_json(200) # success: should use 204 + # but u1db does not + # support it. + + def _remaining(self, lock_doc, now): + """ + Return the number of seconds the lock contained in C{lock_doc} is + still valid, when compared to C{now}. + + :param lock_doc: The document containing the lock. + :type lock_doc: u1db.Document + :param now: The time to which to compare the lock timestamp. + :type now: float + + :return: The amount of seconds the lock is still valid. + :rtype: float + """ + if lock_doc is not None: + lock_timestamp = lock_doc.content[self.TIMESTAMP_KEY] + remaining = lock_timestamp + self.TIMEOUT - now + return remaining if remaining > 0 else 0.0 + return 0.0 + + def _try_obtain_filesystem_lock(self): + """ + Try to obtain the file system lock. + + @return: Whether the lock was succesfully obtained. + @rtype: bool + """ + tries = self.FILESYSTEM_LOCK_TRIES + while tries > 0: + try: + return self._lock.lock() + except Exception as e: + tries -= 1 + time.sleep(self.FILESYSTEM_LOCK_SLEEP_SECONDS) + return False + + def _try_release_filesystem_lock(self): + """ + Release the filesystem lock. + """ + try: + self._lock.unlock() + return True + except Exception: + return False + + #----------------------------------------------------------------------------- # Auxiliary functions #----------------------------------------------------------------------------- @@ -128,8 +377,7 @@ def application(environ, start_response): state = CouchServerState( conf['couch_url'], SoledadApp.SHARED_DB_NAME, - SoledadTokenAuthMiddleware.TOKENS_DB, - SoledadApp.USER_DB_PREFIX) + SoledadTokenAuthMiddleware.TOKENS_DB) # WSGI application that may be used by `twistd -web` application = SoledadTokenAuthMiddleware(SoledadApp(state)) resource = WSGIResource(reactor, reactor.getThreadPool(), application) |