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Rip out auth-event reconciliation code (#12943)

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There is a corner in `_check_event_auth` (long known as "the weird corner") where, if we get an event with auth_events which don't match those we were expecting, we attempt to resolve the diffence between our state and the remote's with a state resolution.

This isn't specced, and there's general agreement we shouldn't be doing it.

However, it turns out that the faster-joins code was relying on it, so we need to introduce something similar (but rather simpler) for that.
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Richard van der Hoff 2022-07-14 22:52:26 +01:00 • committed by GitHub
parent df55b377be
commit fe15a865a5
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6 changed files with 90 additions and 377 deletions
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281
synapse/handlers/federation_event.py
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@ -12,6 +12,7 @@
# See the License for the specific language governing permissions and
# limitations under the License.
import collections
import itertools
import logging
from http import HTTPStatus
@ -347,7 +348,7 @@ class FederationEventHandler:
event.internal_metadata.send_on_behalf_of = origin
context = await self._state_handler.compute_event_context(event)
context = await self._check_event_auth(origin, event, context)
await self._check_event_auth(origin, event, context)
if context.rejected:
raise SynapseError(
403, f"{event.membership} event was rejected", Codes.FORBIDDEN
@ -485,7 +486,7 @@ class FederationEventHandler:
partial_state=partial_state,
)
context = await self._check_event_auth(origin, event, context)
await self._check_event_auth(origin, event, context)
if context.rejected:
raise SynapseError(400, "Join event was rejected")
@ -1116,11 +1117,7 @@ class FederationEventHandler:
state_ids_before_event=state_ids,
)
try:
context = await self._check_event_auth(
origin,
event,
context,
)
await self._check_event_auth(origin, event, context)
except AuthError as e:
# This happens only if we couldn't find the auth events. We'll already have
# logged a warning, so now we just convert to a FederationError.
@ -1495,11 +1492,8 @@ class FederationEventHandler:
)
async def _check_event_auth(
self,
origin: str,
event: EventBase,
context: EventContext,
) -> EventContext:
self, origin: str, event: EventBase, context: EventContext
) -> None:
"""
Checks whether an event should be rejected (for failing auth checks).
@ -1509,9 +1503,6 @@ class FederationEventHandler:
context:
The event context.
Returns:
The updated context object.
Raises:
AuthError if we were unable to find copies of the event's auth events.
(Most other failures just cause us to set `context.rejected`.)
@ -1526,7 +1517,7 @@ class FederationEventHandler:
logger.warning("While validating received event %r: %s", event, e)
# TODO: use a different rejected reason here?
context.rejected = RejectedReason.AUTH_ERROR
return context
return
# next, check that we have all of the event's auth events.
#
@ -1538,6 +1529,9 @@ class FederationEventHandler:
)
# ... and check that the event passes auth at those auth events.
# https://spec.matrix.org/v1.3/server-server-api/#checks-performed-on-receipt-of-a-pdu:
# 4. Passes authorization rules based on the event’s auth events,
# otherwise it is rejected.
try:
await check_state_independent_auth_rules(self._store, event)
check_state_dependent_auth_rules(event, claimed_auth_events)
@ -1546,55 +1540,90 @@ class FederationEventHandler:
"While checking auth of %r against auth_events: %s", event, e
)
context.rejected = RejectedReason.AUTH_ERROR
return context
return
# now check auth against what we think the auth events *should* be.
event_types = event_auth.auth_types_for_event(event.room_version, event)
prev_state_ids = await context.get_prev_state_ids(
StateFilter.from_types(event_types)
)
# now check the auth rules pass against the room state before the event
# https://spec.matrix.org/v1.3/server-server-api/#checks-performed-on-receipt-of-a-pdu:
# 5. Passes authorization rules based on the state before the event,
# otherwise it is rejected.
#
# ... however, if we only have partial state for the room, then there is a good
# chance that we'll be missing some of the state needed to auth the new event.
# So, we state-resolve the auth events that we are given against the state that
# we know about, which ensures things like bans are applied. (Note that we'll
# already have checked we have all the auth events, in
# _load_or_fetch_auth_events_for_event above)
if context.partial_state:
room_version = await self._store.get_room_version_id(event.room_id)
auth_events_ids = self._event_auth_handler.compute_auth_events(
event, prev_state_ids, for_verification=True
)
auth_events_x = await self._store.get_events(auth_events_ids)
calculated_auth_event_map = {
(e.type, e.state_key): e for e in auth_events_x.values()
}
local_state_id_map = await context.get_prev_state_ids()
claimed_auth_events_id_map = {
(ev.type, ev.state_key): ev.event_id for ev in claimed_auth_events
}
try:
updated_auth_events = await self._update_auth_events_for_auth(
event,
calculated_auth_event_map=calculated_auth_event_map,
state_for_auth_id_map = (
await self._state_resolution_handler.resolve_events_with_store(
event.room_id,
room_version,
[local_state_id_map, claimed_auth_events_id_map],
event_map=None,
state_res_store=StateResolutionStore(self._store),
)
)
except Exception:
# We don't really mind if the above fails, so lets not fail
# processing if it does. However, it really shouldn't fail so
# let's still log as an exception since we'll still want to fix
# any bugs.
logger.exception(
"Failed to double check auth events for %s with remote. "
"Ignoring failure and continuing processing of event.",
event.event_id,
)
updated_auth_events = None
if updated_auth_events:
context = await self._update_context_for_auth_events(
event, context, updated_auth_events
)
auth_events_for_auth = updated_auth_events
else:
auth_events_for_auth = calculated_auth_event_map
event_types = event_auth.auth_types_for_event(event.room_version, event)
state_for_auth_id_map = await context.get_prev_state_ids(
StateFilter.from_types(event_types)
)
calculated_auth_event_ids = self._event_auth_handler.compute_auth_events(
event, state_for_auth_id_map, for_verification=True
)
# if those are the same, we're done here.
if collections.Counter(event.auth_event_ids()) == collections.Counter(
calculated_auth_event_ids
):
return
# otherwise, re-run the auth checks based on what we calculated.
calculated_auth_events = await self._store.get_events_as_list(
calculated_auth_event_ids
)
# log the differences
claimed_auth_event_map = {(e.type, e.state_key): e for e in claimed_auth_events}
calculated_auth_event_map = {
(e.type, e.state_key): e for e in calculated_auth_events
}
logger.info(
"event's auth_events are different to our calculated auth_events. "
"Claimed but not calculated: %s. Calculated but not claimed: %s",
[
ev
for k, ev in claimed_auth_event_map.items()
if k not in calculated_auth_event_map
or calculated_auth_event_map[k].event_id != ev.event_id
],
[
ev
for k, ev in calculated_auth_event_map.items()
if k not in claimed_auth_event_map
or claimed_auth_event_map[k].event_id != ev.event_id
],
)
try:
check_state_dependent_auth_rules(event, auth_events_for_auth.values())
check_state_dependent_auth_rules(event, calculated_auth_events)
except AuthError as e:
logger.warning("Failed auth resolution for %r because %s", event, e)
logger.warning(
"While checking auth of %r against room state before the event: %s",
event,
e,
)
context.rejected = RejectedReason.AUTH_ERROR
return context
async def _maybe_kick_guest_users(self, event: EventBase) -> None:
if event.type != EventTypes.GuestAccess:
return
@ -1704,93 +1733,6 @@ class FederationEventHandler:
soft_failed_event_counter.inc()
event.internal_metadata.soft_failed = True
async def _update_auth_events_for_auth(
self,
event: EventBase,
calculated_auth_event_map: StateMap[EventBase],
) -> Optional[StateMap[EventBase]]:
"""Helper for _check_event_auth. See there for docs.
Checks whether a given event has the expected auth events. If it
doesn't then we talk to the remote server to compare state to see if
we can come to a consensus (e.g. if one server missed some valid
state).
This attempts to resolve any potential divergence of state between
servers, but is not essential and so failures should not block further
processing of the event.
Args:
event:
calculated_auth_event_map:
Our calculated auth_events based on the state of the room
at the event's position in the DAG.
Returns:
updated auth event map, or None if no changes are needed.
"""
assert not event.internal_metadata.outlier
# check for events which are in the event's claimed auth_events, but not
# in our calculated event map.
event_auth_events = set(event.auth_event_ids())
different_auth = event_auth_events.difference(
e.event_id for e in calculated_auth_event_map.values()
)
if not different_auth:
return None
logger.info(
"auth_events refers to events which are not in our calculated auth "
"chain: %s",
different_auth,
)
# XXX: currently this checks for redactions but I'm not convinced that is
# necessary?
different_events = await self._store.get_events_as_list(different_auth)
# double-check they're all in the same room - we should already have checked
# this but it doesn't hurt to check again.
for d in different_events:
assert (
d.room_id == event.room_id
), f"Event {event.event_id} refers to auth_event {d.event_id} which is in a different room"
# now we state-resolve between our own idea of the auth events, and the remote's
# idea of them.
local_state = calculated_auth_event_map.values()
remote_auth_events = dict(calculated_auth_event_map)
remote_auth_events.update({(d.type, d.state_key): d for d in different_events})
remote_state = remote_auth_events.values()
room_version = await self._store.get_room_version_id(event.room_id)
new_state = await self._state_handler.resolve_events(
room_version, (local_state, remote_state), event
)
different_state = {
(d.type, d.state_key): d
for d in new_state.values()
if calculated_auth_event_map.get((d.type, d.state_key)) != d
}
if not different_state:
logger.info("State res returned no new state")
return None
logger.info(
"After state res: updating auth_events with new state %s",
different_state.values(),
)
# take a copy of calculated_auth_event_map before we modify it.
auth_events = dict(calculated_auth_event_map)
auth_events.update(different_state)
return auth_events
async def _load_or_fetch_auth_events_for_event(
self, destination: str, event: EventBase
) -> Collection[EventBase]:
@ -1888,61 +1830,6 @@ class FederationEventHandler:
await self._auth_and_persist_outliers(room_id, remote_auth_events)
async def _update_context_for_auth_events(
self, event: EventBase, context: EventContext, auth_events: StateMap[EventBase]
) -> EventContext:
"""Update the state_ids in an event context after auth event resolution,
storing the changes as a new state group.
Args:
event: The event we're handling the context for
context: initial event context
auth_events: Events to update in the event context.
Returns:
new event context
"""
# exclude the state key of the new event from the current_state in the context.
if event.is_state():
event_key: Optional[Tuple[str, str]] = (event.type, event.state_key)
else:
event_key = None
state_updates = {
k: a.event_id for k, a in auth_events.items() if k != event_key
}
current_state_ids = await context.get_current_state_ids()
current_state_ids = dict(current_state_ids) # type: ignore
current_state_ids.update(state_updates)
prev_state_ids = await context.get_prev_state_ids()
prev_state_ids = dict(prev_state_ids)
prev_state_ids.update({k: a.event_id for k, a in auth_events.items()})
# create a new state group as a delta from the existing one.
prev_group = context.state_group
state_group = await self._state_storage_controller.store_state_group(
event.event_id,
event.room_id,
prev_group=prev_group,
delta_ids=state_updates,
current_state_ids=current_state_ids,
)
return EventContext.with_state(
storage=self._storage_controllers,
state_group=state_group,
state_group_before_event=context.state_group_before_event,
state_delta_due_to_event=state_updates,
prev_group=prev_group,
delta_ids=state_updates,
partial_state=context.partial_state,
)
async def _run_push_actions_and_persist_event(
self, event: EventBase, context: EventContext, backfilled: bool = False
) -> None: