diff --git a/changelog.d/5251.bugfix b/changelog.d/5251.bugfix
new file mode 100644
index 0000000000..9a053204b6
--- /dev/null
+++ b/changelog.d/5251.bugfix
@@ -0,0 +1 @@
+Ensure that server_keys fetched via a notary server are correctly signed.
\ No newline at end of file
diff --git a/synapse/crypto/keyring.py b/synapse/crypto/keyring.py
index d6ad7f1772..c63f106cf3 100644
--- a/synapse/crypto/keyring.py
+++ b/synapse/crypto/keyring.py
@@ -17,6 +17,7 @@
import logging
from collections import namedtuple
+import six
from six import raise_from
from six.moves import urllib
@@ -346,6 +347,7 @@ class KeyFetcher(object):
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.
Returns:
Deferred[dict[str, dict[str, synapse.storage.keys.FetchKeyResult|None]]]:
@@ -391,8 +393,7 @@ class BaseV2KeyFetcher(object):
POST /_matrix/key/v2/query.
Checks that each signature in the response that claims to come from the origin
- server is valid. (Does not check that there actually is such a signature, for
- some reason.)
+ server is valid, and that there is at least one such signature.
Stores the json in server_keys_json so that it can be used for future responses
to /_matrix/key/v2/query.
@@ -427,16 +428,25 @@ class BaseV2KeyFetcher(object):
verify_key=verify_key, valid_until_ts=ts_valid_until_ms
)
- # TODO: improve this signature checking
server_name = response_json["server_name"]
+ verified = False
for key_id in response_json["signatures"].get(server_name, {}):
- if key_id not in verify_keys:
+ # each of the keys used for the signature must be present in the response
+ # json.
+ key = verify_keys.get(key_id)
+ if not key:
raise KeyLookupError(
- "Key response must include verification keys for all signatures"
+ "Key response is signed by key id %s:%s but that key is not "
+ "present in the response" % (server_name, key_id)
)
- verify_signed_json(
- response_json, server_name, verify_keys[key_id].verify_key
+ verify_signed_json(response_json, server_name, key.verify_key)
+ verified = True
+
+ if not verified:
+ raise KeyLookupError(
+ "Key response for %s is not signed by the origin server"
+ % (server_name,)
)
for key_id, key_data in response_json["old_verify_keys"].items():
@@ -546,7 +556,16 @@ class PerspectivesKeyFetcher(BaseV2KeyFetcher):
Returns:
Deferred[dict[str, dict[str, synapse.storage.keys.FetchKeyResult]]]: map
from server_name -> key_id -> FetchKeyResult
+
+ Raises:
+ KeyLookupError if there was an error processing the entire response from
+ the server
"""
+ logger.info(
+ "Requesting keys %s from notary server %s",
+ server_names_and_key_ids,
+ 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.
@@ -575,40 +594,31 @@ class PerspectivesKeyFetcher(BaseV2KeyFetcher):
time_now_ms = self.clock.time_msec()
for response in query_response["server_keys"]:
- if (
- u"signatures" not in response
- or perspective_name not in response[u"signatures"]
- ):
+ # do this first, so that we can give useful errors thereafter
+ server_name = response.get("server_name")
+ if not isinstance(server_name, six.string_types):
raise KeyLookupError(
- "Key response not signed by perspective server"
- " %r" % (perspective_name,)
+ "Malformed response from key notary server %s: invalid server_name"
+ % (perspective_name,)
)
- verified = False
- for key_id in response[u"signatures"][perspective_name]:
- if key_id in perspective_keys:
- verify_signed_json(
- response, perspective_name, perspective_keys[key_id]
- )
- verified = True
-
- if not verified:
- logging.info(
- "Response from perspective server %r not signed with a"
- " known key, signed with: %r, known keys: %r",
+ try:
+ processed_response = yield self._process_perspectives_response(
perspective_name,
- list(response[u"signatures"][perspective_name]),
- list(perspective_keys),
+ perspective_keys,
+ response,
+ time_added_ms=time_now_ms,
)
- raise KeyLookupError(
- "Response not signed with a known key for perspective"
- " server %r" % (perspective_name,)
+ except KeyLookupError as e:
+ logger.warning(
+ "Error processing response from key notary server %s for origin "
+ "server %s: %s",
+ perspective_name,
+ server_name,
+ e,
)
-
- processed_response = yield self.process_v2_response(
- perspective_name, response, time_added_ms=time_now_ms
- )
- server_name = response["server_name"]
+ # we continue to process the rest of the response
+ continue
added_keys.extend(
(server_name, key_id, key) for key_id, key in processed_response.items()
@@ -621,6 +631,53 @@ class PerspectivesKeyFetcher(BaseV2KeyFetcher):
defer.returnValue(keys)
+ def _process_perspectives_response(
+ self, perspective_name, perspective_keys, response, time_added_ms
+ ):
+ """Parse a 'Server Keys' structure from the result of a /key/query request
+
+ Checks that the entry is correctly signed by the perspectives server, and then
+ passes over to process_v2_response
+
+ Args:
+ perspective_name (str): the name of the notary server that produced this
+ result
+
+ perspective_keys (dict[str, VerifyKey]): map of key_id->key for the
+ notary server
+
+ response (dict): the json-decoded Server Keys response object
+
+ time_added_ms (int): the timestamp to record in server_keys_json
+
+ Returns:
+ Deferred[dict[str, FetchKeyResult]]: map from key_id to result object
+ """
+ if (
+ u"signatures" not in response
+ or perspective_name not in response[u"signatures"]
+ ):
+ raise KeyLookupError("Response not signed by the notary server")
+
+ verified = False
+ for key_id in response[u"signatures"][perspective_name]:
+ if key_id in perspective_keys:
+ verify_signed_json(response, perspective_name, perspective_keys[key_id])
+ verified = True
+
+ if not verified:
+ raise KeyLookupError(
+ "Response not signed with a known key: signed with: %r, known keys: %r"
+ % (
+ list(response[u"signatures"][perspective_name].keys()),
+ list(perspective_keys.keys()),
+ )
+ )
+
+ return self.process_v2_response(
+ perspective_name, response, time_added_ms=time_added_ms
+ )
+
class ServerKeyFetcher(BaseV2KeyFetcher):
"""KeyFetcher impl which fetches keys from the origin servers"""
@@ -674,12 +731,6 @@ class ServerKeyFetcher(BaseV2KeyFetcher):
except HttpResponseException as e:
raise_from(KeyLookupError("Remote server returned an error"), e)
- if (
- u"signatures" not in response
- or server_name not in response[u"signatures"]
- ):
- raise KeyLookupError("Key response not signed by remote server")
-
if response["server_name"] != server_name:
raise KeyLookupError(
"Expected a response for server %r not %r"
diff --git a/tests/crypto/test_keyring.py b/tests/crypto/test_keyring.py
index 4fba462d44..3933ad4347 100644
--- a/tests/crypto/test_keyring.py
+++ b/tests/crypto/test_keyring.py
@@ -55,11 +55,11 @@ class MockPerspectiveServer(object):
key_id: {"key": signedjson.key.encode_verify_key_base64(verify_key)}
},
}
- return self.get_signed_response(res)
+ self.sign_response(res)
+ return res
- def get_signed_response(self, res):
+ def sign_response(self, res):
signedjson.sign.sign_json(res, self.server_name, self.key)
- return res
class KeyringTestCase(unittest.HomeserverTestCase):
@@ -238,7 +238,7 @@ class ServerKeyFetcherTestCase(unittest.HomeserverTestCase):
testkey = signedjson.key.generate_signing_key("ver1")
testverifykey = signedjson.key.get_verify_key(testkey)
testverifykey_id = "ed25519:ver1"
- VALID_UNTIL_TS = 1000
+ VALID_UNTIL_TS = 200 * 1000
# valid response
response = {
@@ -326,9 +326,10 @@ class PerspectivesKeyFetcherTestCase(unittest.HomeserverTestCase):
},
}
- persp_resp = {
- "server_keys": [self.mock_perspective_server.get_signed_response(response)]
- }
+ # the response must be signed by both the origin server and the perspectives
+ # server.
+ signedjson.sign.sign_json(response, SERVER_NAME, testkey)
+ self.mock_perspective_server.sign_response(response)
def post_json(destination, path, data, **kwargs):
self.assertEqual(destination, self.mock_perspective_server.server_name)
@@ -337,7 +338,7 @@ class PerspectivesKeyFetcherTestCase(unittest.HomeserverTestCase):
# check that the request is for the expected key
q = data["server_keys"]
self.assertEqual(list(q[SERVER_NAME].keys()), ["key1"])
- return persp_resp
+ return {"server_keys": [response]}
self.http_client.post_json.side_effect = post_json
@@ -365,9 +366,74 @@ class PerspectivesKeyFetcherTestCase(unittest.HomeserverTestCase):
self.assertEqual(
bytes(res["key_json"]),
- canonicaljson.encode_canonical_json(persp_resp["server_keys"][0]),
+ canonicaljson.encode_canonical_json(response),
)
+ def test_invalid_perspectives_responses(self):
+ """Check that invalid responses from the perspectives server are rejected"""
+ # arbitrarily advance the clock a bit
+ self.reactor.advance(100)
+
+ SERVER_NAME = "server2"
+ testkey = signedjson.key.generate_signing_key("ver1")
+ testverifykey = signedjson.key.get_verify_key(testkey)
+ testverifykey_id = "ed25519:ver1"
+ VALID_UNTIL_TS = 200 * 1000
+
+ def build_response():
+ # valid response
+ response = {
+ "server_name": SERVER_NAME,
+ "old_verify_keys": {},
+ "valid_until_ts": VALID_UNTIL_TS,
+ "verify_keys": {
+ testverifykey_id: {
+ "key": signedjson.key.encode_verify_key_base64(testverifykey)
+ }
+ },
+ }
+
+ # the response must be signed by both the origin server and the perspectives
+ # server.
+ signedjson.sign.sign_json(response, SERVER_NAME, testkey)
+ self.mock_perspective_server.sign_response(response)
+ return response
+
+ def get_key_from_perspectives(response):
+ fetcher = PerspectivesKeyFetcher(self.hs)
+ server_name_and_key_ids = [(SERVER_NAME, ("key1",))]
+
+ def post_json(destination, path, data, **kwargs):
+ self.assertEqual(destination, self.mock_perspective_server.server_name)
+ self.assertEqual(path, "/_matrix/key/v2/query")
+ return {"server_keys": [response]}
+
+ self.http_client.post_json.side_effect = post_json
+
+ return self.get_success(
+ fetcher.get_keys(server_name_and_key_ids)
+ )
+
+ # start with a valid response so we can check we are testing the right thing
+ response = build_response()
+ keys = get_key_from_perspectives(response)
+ k = keys[SERVER_NAME][testverifykey_id]
+ self.assertEqual(k.verify_key, testverifykey)
+
+ # remove the perspectives server's signature
+ response = build_response()
+ del response["signatures"][self.mock_perspective_server.server_name]
+ self.http_client.post_json.return_value = {"server_keys": [response]}
+ keys = get_key_from_perspectives(response)
+ self.assertEqual(keys, {}, "Expected empty dict with missing persp server sig")
+
+ # remove the origin server's signature
+ response = build_response()
+ del response["signatures"][SERVER_NAME]
+ self.http_client.post_json.return_value = {"server_keys": [response]}
+ keys = get_key_from_perspectives(response)
+ self.assertEqual(keys, {}, "Expected empty dict with missing origin server sig")
+
@defer.inlineCallbacks
def run_in_context(f, *args, **kwargs):
|
