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Clean up _update_auth_events_and_context_for_auth #11122

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Oct 20, 2021
Merged

Clean up _update_auth_events_and_context_for_auth #11122

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4a8b5cc
remove redundant code in _update_auth_events_and_context_for_auth
richvdh Oct 19, 2021
53db7c2
_update_auth_events_and_context_for_auth: delay copy of auth_events
richvdh Oct 4, 2021
535aec7
`_update_auth_events_and_context_for_auth`: remove redundant `origin`…
richvdh Oct 4, 2021
5e971ee
replace room_id check with an assertion
richvdh Oct 19, 2021
d1389f0
`_update_auth_events_and_context_for_auth`: bail out earlier
richvdh Oct 19, 2021
6d17246
`_update_auth_events_and_context_for_auth`: just return auth map
richvdh Oct 4, 2021
f5674f7
changelog
richvdh Oct 19, 2021
bb07db5
drop redundant type hint
richvdh Oct 20, 2021
8b3dfd9
lint
richvdh Oct 20, 2021
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1 change: 1 addition & 0 deletions changelog.d/11122.misc
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Clean up some of the federation event authentication code for clarity.
150 changes: 37 additions & 113 deletions synapse/handlers/federation_event.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1417,13 +1417,8 @@ async def _check_event_auth(
}

try:
(
context,
auth_events_for_auth,
) = await self._update_auth_events_and_context_for_auth(
origin,
updated_auth_events = await self._update_auth_events_for_auth(
event,
context,
calculated_auth_event_map=calculated_auth_event_map,
)
except Exception:
Expand All @@ -1436,6 +1431,14 @@ async def _check_event_auth(
"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

try:
Expand Down Expand Up @@ -1560,13 +1563,11 @@ async def _check_for_soft_fail(
soft_failed_event_counter.inc()
event.internal_metadata.soft_failed = True

async def _update_auth_events_and_context_for_auth(
async def _update_auth_events_for_auth(
self,
origin: str,
event: EventBase,
context: EventContext,
calculated_auth_event_map: StateMap[EventBase],
) -> Tuple[EventContext, 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
Expand All @@ -1579,96 +1580,27 @@ async def _update_auth_events_and_context_for_auth(
processing of the event.

Args:
origin:
event:
context:

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 context, updated auth event map
updated auth event map, or None if no changes are needed.

"""
assert not event.internal_metadata.outlier

# take a copy of calculated_auth_event_map before we modify it.
auth_events: MutableStateMap[EventBase] = dict(calculated_auth_event_map)

# 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())

# missing_auth is the set of the event's auth_events which we don't yet have
# in auth_events.
missing_auth = event_auth_events.difference(
e.event_id for e in auth_events.values()
)

# if we have missing events, we need to fetch those events from somewhere.
#
# we start by checking if they are in the store, and then try calling /event_auth/.
#
# TODO: this code is now redundant, since it should be impossible for us to
# get here without already having the auth events.
if missing_auth:
have_events = await self._store.have_seen_events(
event.room_id, missing_auth
)
logger.debug("Events %s are in the store", have_events)
missing_auth.difference_update(have_events)
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@richvdh richvdh Oct 19, 2021 •
edited
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at this point, missing_auth must be an empty set, because we all of the events in event_auth_events must be in our database (otherwise we would have rejected the event sooner, thanks to the changes in #11001).

(I toyed with the idea of changing this to an assertion, but the have_seen_events lookup isn't entirely negligible and I figured it was better just to clear it out.)


# missing_auth is now the set of event_ids which:
# a. are listed in event.auth_events, *and*
# b. are *not* part of our calculated auth events based on room state, *and*
# c. are *not* yet in our database.

if missing_auth:
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... which means that this is never true.

# If we don't have all the auth events, we need to get them.
logger.info("auth_events contains unknown events: %s", missing_auth)
try:
await self._get_remote_auth_chain_for_event(
origin, event.room_id, event.event_id
)
except Exception:
logger.exception("Failed to get auth chain")
else:
# load any auth events we might have persisted from the database. This
# has the side-effect of correctly setting the rejected_reason on them.
auth_events.update(
{
(ae.type, ae.state_key): ae
for ae in await self._store.get_events_as_list(
missing_auth, allow_rejected=True
)
}
)

# auth_events now contains
# 1. our *calculated* auth events based on the room state, plus:
# 2. any events which:
# a. are listed in `event.auth_events`, *and*
# b. are not part of our calculated auth events, *and*
# c. were not in our database before the call to /event_auth
# d. have since been added to our database (most likely by /event_auth).

different_auth = event_auth_events.difference(
e.event_id for e in auth_events.values()
e.event_id for e in calculated_auth_event_map.values()
)

# different_auth is the set of events which *are* in `event.auth_events`, but
# which are *not* in `auth_events`. Comparing with (2.) above, this means
# exclusively the set of `event.auth_events` which we already had in our
# database before any call to /event_auth.
#
# I'm reasonably sure that the fact that events returned by /event_auth are
# blindly added to auth_events (and hence excluded from different_auth) is a bug
# - though it's a very long-standing one (see
# https://github.com/matrix-org/synapse/commit/78015948a7febb18e000651f72f8f58830a55b93#diff-0bc92da3d703202f5b9be2d3f845e375f5b1a6bc6ba61705a8af9be1121f5e42R786
# from Jan 2015 which seems to add it, though it actually just moves it from
# elsewhere (before that, it gets lost in a mess of huge "various bug fixes"
# PRs).

if not different_auth:
return context, auth_events
return None

logger.info(
"auth_events refers to events which are not in our calculated auth "
Expand All @@ -1680,51 +1612,43 @@ async def _update_auth_events_and_context_for_auth(
# 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:
if d.room_id != event.room_id:
logger.warning(
"Event %s refers to auth_event %s which is in a different room",
event.event_id,
d.event_id,
)

# don't attempt to resolve the claimed auth events against our own
# in this case: just use our own auth events.
#
# XXX: should we reject the event in this case? It feels like we should,
# but then shouldn't we also do so if we've failed to fetch any of the
# auth events?
return context, auth_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 = auth_events.values()
remote_auth_events = dict(auth_events)
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",
{
d
for d in new_state.values()
if auth_events.get((d.type, d.state_key)) != d
},
different_state.values(),
)

auth_events.update(new_state)

context = await self._update_context_for_auth_events(
event, context, auth_events
)

return context, auth_events
# take a copy of calculated_auth_event_map before we modify it.
auth_events = dict(calculated_auth_event_map)
auth_events.update(different_state)
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This is equivalent since different_state is new_state - calculated_auth_event_map, so including all of new_state is guaranteed to do some unnecessary updates?

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yes, exactly so. sorry, should have made that clear.

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Makes sense as a small optimization, just wasn't sure I was missing something!

return auth_events

async def _load_or_fetch_auth_events_for_event(
self, destination: str, event: EventBase
Expand Down