diff options
| -rw-r--r-- | changelog.d/5724.bugfix | 1 | ||||
| -rw-r--r-- | synapse/crypto/keyring.py | 92 | ||||
| -rw-r--r-- | tests/crypto/test_keyring.py | 29 |
3 files changed, 42 insertions, 80 deletions
diff --git a/changelog.d/5724.bugfix b/changelog.d/5724.bugfix new file mode 100644 index 0000000000..1b3683daf6 --- /dev/null +++ b/changelog.d/5724.bugfix @@ -0,0 +1 @@ +Fix stack overflow in server key lookup code. \ No newline at end of file diff --git a/synapse/crypto/keyring.py b/synapse/crypto/keyring.py index 341c863152..e8bb420ad1 100644 --- a/synapse/crypto/keyring.py +++ b/synapse/crypto/keyring.py @@ -238,27 +238,9 @@ class Keyring(object): """ try: - # create a deferred for each server we're going to look up the keys - # for; we'll resolve them once we have completed our lookups. - # These will be passed into wait_for_previous_lookups to block - # any other lookups until we have finished. - # The deferreds are called with no logcontext. - server_to_deferred = { - rq.server_name: defer.Deferred() for rq in verify_requests - } - - # We want to wait for any previous lookups to complete before - # proceeding. - yield self.wait_for_previous_lookups(server_to_deferred) + ctx = LoggingContext.current_context() - # Actually start fetching keys. - self._get_server_verify_keys(verify_requests) - - # When we've finished fetching all the keys for a given server_name, - # resolve the deferred passed to `wait_for_previous_lookups` so that - # any lookups waiting will proceed. - # - # map from server name to a set of request ids + # map from server name to a set of outstanding request ids server_to_request_ids = {} for verify_request in verify_requests: @@ -266,40 +248,61 @@ class Keyring(object): request_id = id(verify_request) server_to_request_ids.setdefault(server_name, set()).add(request_id) - def remove_deferreds(res, verify_request): + # Wait for any previous lookups to complete before proceeding. + yield self.wait_for_previous_lookups(server_to_request_ids.keys()) + + # take out a lock on each of the servers by sticking a Deferred in + # key_downloads + for server_name in server_to_request_ids.keys(): + self.key_downloads[server_name] = defer.Deferred() + logger.debug("Got key lookup lock on %s", server_name) + + # When we've finished fetching all the keys for a given server_name, + # drop the lock by resolving the deferred in key_downloads. + def drop_server_lock(server_name): + d = self.key_downloads.pop(server_name) + d.callback(None) + + def lookup_done(res, verify_request): server_name = verify_request.server_name - request_id = id(verify_request) - server_to_request_ids[server_name].discard(request_id) - if not server_to_request_ids[server_name]: - d = server_to_deferred.pop(server_name, None) - if d: - d.callback(None) + server_requests = server_to_request_ids[server_name] + server_requests.remove(id(verify_request)) + + # if there are no more requests for this server, we can drop the lock. + if not server_requests: + with PreserveLoggingContext(ctx): + logger.debug("Releasing key lookup lock on %s", server_name) + + # ... but not immediately, as that can cause stack explosions if + # we get a long queue of lookups. + self.clock.call_later(0, drop_server_lock, server_name) + return res for verify_request in verify_requests: - verify_request.key_ready.addBoth(remove_deferreds, verify_request) + verify_request.key_ready.addBoth(lookup_done, verify_request) + + # Actually start fetching keys. + self._get_server_verify_keys(verify_requests) except Exception: logger.exception("Error starting key lookups") @defer.inlineCallbacks - def wait_for_previous_lookups(self, server_to_deferred): + def wait_for_previous_lookups(self, server_names): """Waits for any previous key lookups for the given servers to finish. Args: - server_to_deferred (dict[str, Deferred]): server_name to deferred which gets - resolved once we've finished looking up keys for that server. - The Deferreds should be regular twisted ones which call their - callbacks with no logcontext. - - Returns: a Deferred which resolves once all key lookups for the given - servers have completed. Follows the synapse rules of logcontext - preservation. + server_names (Iterable[str]): list of servers which we want to look up + + Returns: + Deferred[None]: resolves once all key lookups for the given servers have + completed. Follows the synapse rules of logcontext preservation. """ loop_count = 1 while True: wait_on = [ (server_name, self.key_downloads[server_name]) - for server_name in server_to_deferred.keys() + for server_name in server_names if server_name in self.key_downloads ] if not wait_on: @@ -314,19 +317,6 @@ class Keyring(object): loop_count += 1 - ctx = LoggingContext.current_context() - - def rm(r, server_name_): - with PreserveLoggingContext(ctx): - logger.debug("Releasing key lookup lock on %s", server_name_) - self.key_downloads.pop(server_name_, None) - return r - - for server_name, deferred in server_to_deferred.items(): - logger.debug("Got key lookup lock on %s", server_name) - self.key_downloads[server_name] = deferred - deferred.addBoth(rm, server_name) - def _get_server_verify_keys(self, verify_requests): """Tries to find at least one key for each verify request diff --git a/tests/crypto/test_keyring.py b/tests/crypto/test_keyring.py index 795703967d..8d94a503d6 100644 --- a/tests/crypto/test_keyring.py +++ b/tests/crypto/test_keyring.py @@ -86,35 +86,6 @@ class KeyringTestCase(unittest.HomeserverTestCase): getattr(LoggingContext.current_context(), "request", None), expected ) - def test_wait_for_previous_lookups(self): - kr = keyring.Keyring(self.hs) - - lookup_1_deferred = defer.Deferred() - lookup_2_deferred = defer.Deferred() - - # we run the lookup in a logcontext so that the patched inlineCallbacks can check - # it is doing the right thing with logcontexts. - wait_1_deferred = run_in_context( - kr.wait_for_previous_lookups, {"server1": lookup_1_deferred} - ) - - # there were no previous lookups, so the deferred should be ready - self.successResultOf(wait_1_deferred) - - # set off another wait. It should block because the first lookup - # hasn't yet completed. - wait_2_deferred = run_in_context( - kr.wait_for_previous_lookups, {"server1": lookup_2_deferred} - ) - - self.assertFalse(wait_2_deferred.called) - - # let the first lookup complete (in the sentinel context) - lookup_1_deferred.callback(None) - - # now the second wait should complete. - self.successResultOf(wait_2_deferred) - def test_verify_json_objects_for_server_awaits_previous_requests(self): key1 = signedjson.key.generate_signing_key(1) |