Enforce validity period on server_keys for fed requests. (#5321)

When handling incoming federation requests, make sure that we have an
up-to-date copy of the signing key.

We do not yet enforce the validity period for event signatures.

4 files changed, 119 insertions, 61 deletions

diff --git a/synapse/crypto/keyring.py b/synapse/crypto/keyring.py
index b2f4cea536..cdec06c88e 100644
--- a/synapse/crypto/keyring.py
+++ b/synapse/crypto/keyring.py
@@ -15,6 +15,7 @@
 # limitations under the License.
 
 import logging
+from collections import defaultdict
 
 import six
 from six import raise_from
@@ -70,6 +71,9 @@ class VerifyKeyRequest(object):
 
         json_object(dict): The JSON object to verify.
 
+        minimum_valid_until_ts (int): time at which we require the signing key to
+            be valid. (0 implies we don't care)
+
         deferred(Deferred[str, str, nacl.signing.VerifyKey]):
             A deferred (server_name, key_id, verify_key) tuple that resolves when
             a verify key has been fetched. The deferreds' callbacks are run with no
@@ -82,7 +86,8 @@ class VerifyKeyRequest(object):
     server_name = attr.ib()
     key_ids = attr.ib()
     json_object = attr.ib()
-    deferred = attr.ib()
+    minimum_valid_until_ts = attr.ib()
+    deferred = attr.ib(default=attr.Factory(defer.Deferred))
 
 
 class KeyLookupError(ValueError):
@@ -90,14 +95,16 @@ class KeyLookupError(ValueError):
 
 
 class Keyring(object):
-    def __init__(self, hs):
+    def __init__(self, hs, key_fetchers=None):
         self.clock = hs.get_clock()
 
-        self._key_fetchers = (
-            StoreKeyFetcher(hs),
-            PerspectivesKeyFetcher(hs),
-            ServerKeyFetcher(hs),
-        )
+        if key_fetchers is None:
+            key_fetchers = (
+                StoreKeyFetcher(hs),
+                PerspectivesKeyFetcher(hs),
+                ServerKeyFetcher(hs),
+            )
+        self._key_fetchers = key_fetchers
 
         # map from server name to Deferred. Has an entry for each server with
         # an ongoing key download; the Deferred completes once the download
@@ -106,9 +113,25 @@ class Keyring(object):
         # These are regular, logcontext-agnostic Deferreds.
         self.key_downloads = {}
 
-    def verify_json_for_server(self, server_name, json_object):
+    def verify_json_for_server(self, server_name, json_object, validity_time):
+        """Verify that a JSON object has been signed by a given server
+
+        Args:
+            server_name (str): name of the server which must have signed this object
+
+            json_object (dict): object to be checked
+
+            validity_time (int): timestamp at which we require the signing key to
+                be valid. (0 implies we don't care)
+
+        Returns:
+            Deferred[None]: completes if the the object was correctly signed, otherwise
+                errbacks with an error
+        """
+        req = server_name, json_object, validity_time
+
         return logcontext.make_deferred_yieldable(
-            self.verify_json_objects_for_server([(server_name, json_object)])[0]
+            self.verify_json_objects_for_server((req,))[0]
         )
 
     def verify_json_objects_for_server(self, server_and_json):
@@ -116,10 +139,12 @@ class Keyring(object):
         necessary.
 
         Args:
-            server_and_json (list): List of pairs of (server_name, json_object)
+            server_and_json (iterable[Tuple[str, dict, int]):
+                Iterable of triplets of (server_name, json_object, validity_time)
+                validity_time is a timestamp at which the signing key must be valid.
 
         Returns:
-            List<Deferred>: for each input pair, a deferred indicating success
+            List<Deferred[None]>: for each input triplet, a deferred indicating success
                 or failure to verify each json object's signature for the given
                 server_name. The deferreds run their callbacks in the sentinel
                 logcontext.
@@ -128,12 +153,12 @@ class Keyring(object):
         verify_requests = []
         handle = preserve_fn(_handle_key_deferred)
 
-        def process(server_name, json_object):
+        def process(server_name, json_object, validity_time):
             """Process an entry in the request list
 
-            Given a (server_name, json_object) pair from the request list,
-            adds a key request to verify_requests, and returns a deferred which will
-            complete or fail (in the sentinel context) when verification completes.
+            Given a (server_name, json_object, validity_time) triplet from the request
+            list, adds a key request to verify_requests, and returns a deferred which
+            will complete or fail (in the sentinel context) when verification completes.
             """
             key_ids = signature_ids(json_object, server_name)
 
@@ -148,7 +173,7 @@ class Keyring(object):
 
             # add the key request to the queue, but don't start it off yet.
             verify_request = VerifyKeyRequest(
-                server_name, key_ids, json_object, defer.Deferred()
+                server_name, key_ids, json_object, validity_time
             )
             verify_requests.append(verify_request)
 
@@ -160,8 +185,8 @@ class Keyring(object):
             return handle(verify_request)
 
         results = [
-            process(server_name, json_object)
-            for server_name, json_object in server_and_json
+            process(server_name, json_object, validity_time)
+            for server_name, json_object, validity_time in server_and_json
         ]
 
         if verify_requests:
@@ -298,8 +323,12 @@ class Keyring(object):
                         verify_request.deferred.errback(
                             SynapseError(
                                 401,
-                                "No key for %s with id %s"
-                                % (verify_request.server_name, verify_request.key_ids),
+                                "No key for %s with ids in %s (min_validity %i)"
+                                % (
+                                    verify_request.server_name,
+                                    verify_request.key_ids,
+                                    verify_request.minimum_valid_until_ts,
+                                ),
                                 Codes.UNAUTHORIZED,
                             )
                         )
@@ -323,18 +352,28 @@ class Keyring(object):
         Args:
             fetcher (KeyFetcher): fetcher to use to fetch the keys
             remaining_requests (set[VerifyKeyRequest]): outstanding key requests.
-                Any successfully-completed requests will be reomved from the list.
+                Any successfully-completed requests will be removed from the list.
         """
-        # dict[str, set(str)]: keys to fetch for each server
-        missing_keys = {}
+        # dict[str, dict[str, int]]: keys to fetch.
+        # server_name -> key_id -> min_valid_ts
+        missing_keys = defaultdict(dict)
+
         for verify_request in remaining_requests:
             # any completed requests should already have been removed
             assert not verify_request.deferred.called
-            missing_keys.setdefault(verify_request.server_name, set()).update(
-                verify_request.key_ids
-            )
+            keys_for_server = missing_keys[verify_request.server_name]
 
-        results = yield fetcher.get_keys(missing_keys.items())
+            for key_id in verify_request.key_ids:
+                # If we have several requests for the same key, then we only need to
+                # request that key once, but we should do so with the greatest
+                # min_valid_until_ts of the requests, so that we can satisfy all of
+                # the requests.
+                keys_for_server[key_id] = max(
+                    keys_for_server.get(key_id, -1),
+                    verify_request.minimum_valid_until_ts
+                )
+
+        results = yield fetcher.get_keys(missing_keys)
 
         completed = list()
         for verify_request in remaining_requests:
@@ -344,25 +383,34 @@ class Keyring(object):
             # complete this VerifyKeyRequest.
             result_keys = results.get(server_name, {})
             for key_id in verify_request.key_ids:
-                key = result_keys.get(key_id)
-                if key:
-                    with PreserveLoggingContext():
-                        verify_request.deferred.callback(
-                            (server_name, key_id, key.verify_key)
-                        )
-                    completed.append(verify_request)
-                    break
+                fetch_key_result = result_keys.get(key_id)
+                if not fetch_key_result:
+                    # we didn't get a result for this key
+                    continue
+
+                if (
+                    fetch_key_result.valid_until_ts
+                    < verify_request.minimum_valid_until_ts
+                ):
+                    # key was not valid at this point
+                    continue
+
+                with PreserveLoggingContext():
+                    verify_request.deferred.callback(
+                        (server_name, key_id, fetch_key_result.verify_key)
+                    )
+                completed.append(verify_request)
+                break
 
         remaining_requests.difference_update(completed)
 
 
 class KeyFetcher(object):
-    def get_keys(self, server_name_and_key_ids):
+    def get_keys(self, keys_to_fetch):
         """
         Args:
-            server_name_and_key_ids (iterable[Tuple[str, iterable[str]]]):
-                list of (server_name, iterable[key_id]) tuples to fetch keys for
-                Note that the iterables may be iterated more than once.
+            keys_to_fetch (dict[str, dict[str, int]]):
+                the keys to be fetched. server_name -> key_id -> min_valid_ts
 
         Returns:
             Deferred[dict[str, dict[str, synapse.storage.keys.FetchKeyResult|None]]]:
@@ -378,13 +426,15 @@ class StoreKeyFetcher(KeyFetcher):
         self.store = hs.get_datastore()
 
     @defer.inlineCallbacks
-    def get_keys(self, server_name_and_key_ids):
+    def get_keys(self, keys_to_fetch):
         """see KeyFetcher.get_keys"""
+
         keys_to_fetch = (
             (server_name, key_id)
-            for server_name, key_ids in server_name_and_key_ids
-            for key_id in key_ids
+            for server_name, keys_for_server in keys_to_fetch.items()
+            for key_id in keys_for_server.keys()
         )
+
         res = yield self.store.get_server_verify_keys(keys_to_fetch)
         keys = {}
         for (server_name, key_id), key in res.items():
@@ -508,14 +558,14 @@ class PerspectivesKeyFetcher(BaseV2KeyFetcher):
         self.perspective_servers = self.config.perspectives
 
     @defer.inlineCallbacks
-    def get_keys(self, server_name_and_key_ids):
+    def get_keys(self, keys_to_fetch):
         """see KeyFetcher.get_keys"""
 
         @defer.inlineCallbacks
         def get_key(perspective_name, perspective_keys):
             try:
                 result = yield self.get_server_verify_key_v2_indirect(
-                    server_name_and_key_ids, perspective_name, perspective_keys
+                    keys_to_fetch, perspective_name, perspective_keys
                 )
                 defer.returnValue(result)
             except KeyLookupError as e:
@@ -549,13 +599,15 @@ class PerspectivesKeyFetcher(BaseV2KeyFetcher):
 
     @defer.inlineCallbacks
     def get_server_verify_key_v2_indirect(
-        self, server_names_and_key_ids, perspective_name, perspective_keys
+        self, keys_to_fetch, perspective_name, perspective_keys
     ):
         """
         Args:
-            server_names_and_key_ids (iterable[Tuple[str, iterable[str]]]):
-                list of (server_name, iterable[key_id]) tuples to fetch keys for
+            keys_to_fetch (dict[str, dict[str, int]]):
+                the keys to be fetched. server_name -> key_id -> min_valid_ts
+
             perspective_name (str): name of the notary server to query for the keys
+
             perspective_keys (dict[str, VerifyKey]): map of key_id->key for the
                 notary server
 
@@ -569,12 +621,10 @@ class PerspectivesKeyFetcher(BaseV2KeyFetcher):
         """
         logger.info(
             "Requesting keys %s from notary server %s",
-            server_names_and_key_ids,
+            keys_to_fetch.items(),
             perspective_name,
         )
-        # TODO(mark): Set the minimum_valid_until_ts to that needed by
-        # the events being validated or the current time if validating
-        # an incoming request.
+
         try:
             query_response = yield self.client.post_json(
                 destination=perspective_name,
@@ -582,9 +632,10 @@ class PerspectivesKeyFetcher(BaseV2KeyFetcher):
                 data={
                     u"server_keys": {
                         server_name: {
-                            key_id: {u"minimum_valid_until_ts": 0} for key_id in key_ids
+                            key_id: {u"minimum_valid_until_ts": min_valid_ts}
+                            for key_id, min_valid_ts in server_keys.items()
                         }
-                        for server_name, key_ids in server_names_and_key_ids
+                        for server_name, server_keys in keys_to_fetch.items()
                     }
                 },
                 long_retries=True,
@@ -694,15 +745,18 @@ class ServerKeyFetcher(BaseV2KeyFetcher):
         self.client = hs.get_http_client()
 
     @defer.inlineCallbacks
-    def get_keys(self, server_name_and_key_ids):
+    def get_keys(self, keys_to_fetch):
         """see KeyFetcher.get_keys"""
+        # TODO make this more resilient
         results = yield logcontext.make_deferred_yieldable(
             defer.gatherResults(
                 [
                     run_in_background(
-                        self.get_server_verify_key_v2_direct, server_name, key_ids
+                        self.get_server_verify_key_v2_direct,
+                        server_name,
+                        server_keys.keys(),
                     )
-                    for server_name, key_ids in server_name_and_key_ids
+                    for server_name, server_keys in keys_to_fetch.items()
                 ],
                 consumeErrors=True,
             ).addErrback(unwrapFirstError)
@@ -721,6 +775,7 @@ class ServerKeyFetcher(BaseV2KeyFetcher):
         keys = {}  # type: dict[str, FetchKeyResult]
 
         for requested_key_id in key_ids:
+            # we may have found this key as a side-effect of asking for another.
             if requested_key_id in keys:
                 continue
 
diff --git a/synapse/federation/federation_base.py b/synapse/federation/federation_base.py
index cffa831d80..4b38f7c759 100644
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -265,7 +265,7 @@ def _check_sigs_on_pdus(keyring, room_version, pdus):
     ]
 
     more_deferreds = keyring.verify_json_objects_for_server([
-        (p.sender_domain, p.redacted_pdu_json)
+        (p.sender_domain, p.redacted_pdu_json, 0)
         for p in pdus_to_check_sender
     ])
 
@@ -298,7 +298,7 @@ def _check_sigs_on_pdus(keyring, room_version, pdus):
         ]
 
         more_deferreds = keyring.verify_json_objects_for_server([
-            (get_domain_from_id(p.pdu.event_id), p.redacted_pdu_json)
+            (get_domain_from_id(p.pdu.event_id), p.redacted_pdu_json, 0)
             for p in pdus_to_check_event_id
         ])
 
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index d0efc4e0d3..0db8858cf1 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -94,6 +94,7 @@ class NoAuthenticationError(AuthenticationError):
 
 class Authenticator(object):
     def __init__(self, hs):
+        self._clock = hs.get_clock()
         self.keyring = hs.get_keyring()
         self.server_name = hs.hostname
         self.store = hs.get_datastore()
@@ -102,6 +103,7 @@ class Authenticator(object):
     # A method just so we can pass 'self' as the authenticator to the Servlets
     @defer.inlineCallbacks
     def authenticate_request(self, request, content):
+        now = self._clock.time_msec()
         json_request = {
             "method": request.method.decode('ascii'),
             "uri": request.uri.decode('ascii'),
@@ -138,7 +140,7 @@ class Authenticator(object):
                 401, "Missing Authorization headers", Codes.UNAUTHORIZED,
             )
 
-        yield self.keyring.verify_json_for_server(origin, json_request)
+        yield self.keyring.verify_json_for_server(origin, json_request, now)
 
         logger.info("Request from %s", origin)
         request.authenticated_entity = origin
diff --git a/synapse/groups/attestations.py b/synapse/groups/attestations.py
index 786149be65..fa6b641ee1 100644
--- a/synapse/groups/attestations.py
+++ b/synapse/groups/attestations.py
@@ -97,10 +97,11 @@ class GroupAttestationSigning(object):
 
         # TODO: We also want to check that *new* attestations that people give
         # us to store are valid for at least a little while.
-        if valid_until_ms < self.clock.time_msec():
+        now = self.clock.time_msec()
+        if valid_until_ms < now:
             raise SynapseError(400, "Attestation expired")
 
-        yield self.keyring.verify_json_for_server(server_name, attestation)
+        yield self.keyring.verify_json_for_server(server_name, attestation, now)
 
     def create_attestation(self, group_id, user_id):
         """Create an attestation for the group_id and user_id with default