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Fix redaction authentication (#5700)

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Ensures that redactions are correctly authenticated for recent room versions.

There are a few things going on here:

 * `_fetch_event_rows` is updated to return a dict rather than a list of rows.

 * Rather than returning multiple copies of an event which was redacted
   multiple times, it returns the redactions as a list within the dict.

 * It also returns the actual rejection reason, rather than merely the fact
   that it was rejected, so that we don't have to query the table again in
   `_get_event_from_row`.

 * The redaction handling is factored out of `_get_event_from_row`, and now
   checks if any of the redactions are valid.
This commit is contained in:
Richard van der Hoff 2019-07-17 16:52:02 +01:00 committed by GitHub
parent 65c5592b8e
commit 375162b3c3
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2 changed files with 131 additions and 85 deletions
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2
changelog.d/5700.bugfix Normal file
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@ -0,0 +1,2 @@
Fix some problems with authenticating redactions in recent room versions.

214
synapse/storage/events_worker.py
View file

@ -37,6 +37,7 @@ from synapse.logging.context import (
)
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.types import get_domain_from_id
from synapse.util import batch_iter
from synapse.util.metrics import Measure
from ._base import SQLBaseStore
@ -240,27 +241,8 @@ class EventsWorkerStore(SQLBaseStore):
# instead.
if not allow_rejected and entry.event.type == EventTypes.Redaction:
if entry.event.internal_metadata.need_to_check_redaction():
# XXX: we need to avoid calling get_event here.
#
# The problem is that we end up at this point when an event
# which has been redacted is pulled out of the database by
# _enqueue_events, because _enqueue_events needs to check
# the redaction before it can cache the redacted event. So
# obviously, calling get_event to get the redacted event out
# of the database gives us an infinite loop.
#
# For now (quick hack to fix during 0.99 release cycle), we
# just go and fetch the relevant row from the db, but it
# would be nice to think about how we can cache this rather
# than hit the db every time we access a redaction event.
#
# One thought on how to do this:
# 1. split get_events_as_list up so that it is divided into
# (a) get the rawish event from the db/cache, (b) do the
# redaction/rejection filtering
# 2. have _get_event_from_row just call the first half of
# that
# XXX: we should probably use _get_events_from_cache_or_db here,
# so that we can benefit from caching.
orig_sender = yield self._simple_select_one_onecol(
table="events",
keyvalues={"event_id": entry.event.redacts},
@ -410,19 +392,16 @@ class EventsWorkerStore(SQLBaseStore):
The fetch requests. Each entry consists of a list of event
ids to be fetched, and a deferred to be completed once the
events have been fetched.
"""
with Measure(self._clock, "_fetch_event_list"):
try:
event_id_lists = list(zip(*event_list))[0]
event_ids = [item for sublist in event_id_lists for item in sublist]
rows = self._new_transaction(
row_dict = self._new_transaction(
conn, "do_fetch", [], [], self._fetch_event_rows, event_ids
)
row_dict = {r["event_id"]: r for r in rows}
# We only want to resolve deferreds from the main thread
def fire(lst, res):
for ids, d in lst:
@ -480,7 +459,7 @@ class EventsWorkerStore(SQLBaseStore):
logger.debug("Loaded %d events (%d rows)", len(events), len(rows))
if not allow_rejected:
rows[:] = [r for r in rows if not r["rejects"]]
rows[:] = [r for r in rows if r["rejected_reason"] is None]
res = yield make_deferred_yieldable(
defer.gatherResults(
@ -489,8 +468,8 @@ class EventsWorkerStore(SQLBaseStore):
self._get_event_from_row,
row["internal_metadata"],
row["json"],
row["redacts"],
rejected_reason=row["rejects"],
row["redactions"],
rejected_reason=row["rejected_reason"],
format_version=row["format_version"],
)
for row in rows
@ -501,49 +480,98 @@ class EventsWorkerStore(SQLBaseStore):
defer.returnValue({e.event.event_id: e for e in res if e})
def _fetch_event_rows(self, txn, events):
rows = []
N = 200
for i in range(1 + len(events) // N):
evs = events[i * N : (i + 1) * N]
if not evs:
break
def _fetch_event_rows(self, txn, event_ids):
"""Fetch event rows from the database
Events which are not found are omitted from the result.
The returned per-event dicts contain the following keys:
* event_id (str)
* json (str): json-encoded event structure
* internal_metadata (str): json-encoded internal metadata dict
* format_version (int|None): The format of the event. Hopefully one
of EventFormatVersions. 'None' means the event predates
EventFormatVersions (so the event is format V1).
* rejected_reason (str|None): if the event was rejected, the reason
why.
* redactions (List[str]): a list of event-ids which (claim to) redact
this event.
Args:
txn (twisted.enterprise.adbapi.Connection):
event_ids (Iterable[str]): event IDs to fetch
Returns:
Dict[str, Dict]: a map from event id to event info.
"""
event_dict = {}
for evs in batch_iter(event_ids, 200):
sql = (
"SELECT "
" e.event_id as event_id, "
" e.event_id, "
" e.internal_metadata,"
" e.json,"
" e.format_version, "
" r.redacts as redacts,"
" rej.event_id as rejects "
" rej.reason "
" FROM event_json as e"
" LEFT JOIN rejections as rej USING (event_id)"
" LEFT JOIN redactions as r ON e.event_id = r.redacts"
" WHERE e.event_id IN (%s)"
) % (",".join(["?"] * len(evs)),)
txn.execute(sql, evs)
rows.extend(self.cursor_to_dict(txn))
return rows
for row in txn:
event_id = row[0]
event_dict[event_id] = {
"event_id": event_id,
"internal_metadata": row[1],
"json": row[2],
"format_version": row[3],
"rejected_reason": row[4],
"redactions": [],
}
# check for redactions
redactions_sql = (
"SELECT event_id, redacts FROM redactions WHERE redacts IN (%s)"
) % (",".join(["?"] * len(evs)),)
txn.execute(redactions_sql, evs)
for (redacter, redacted) in txn:
d = event_dict.get(redacted)
if d:
d["redactions"].append(redacter)
return event_dict
@defer.inlineCallbacks
def _get_event_from_row(
self, internal_metadata, js, redacted, format_version, rejected_reason=None
self, internal_metadata, js, redactions, format_version, rejected_reason=None
):
"""Parse an event row which has been read from the database
Args:
internal_metadata (str): json-encoded internal_metadata column
js (str): json-encoded event body from event_json
redactions (list[str]): a list of the events which claim to have redacted
this event, from the redactions table
format_version: (str): the 'format_version' column
rejected_reason (str|None): the reason this event was rejected, if any
Returns:
_EventCacheEntry
"""
with Measure(self._clock, "_get_event_from_row"):
d = json.loads(js)
internal_metadata = json.loads(internal_metadata)
if rejected_reason:
rejected_reason = yield self._simple_select_one_onecol(
table="rejections",
keyvalues={"event_id": rejected_reason},
retcol="reason",
desc="_get_event_from_row_rejected_reason",
)
if format_version is None:
# This means that we stored the event before we had the concept
# of a event format version, so it must be a V1 event.
@ -555,41 +583,7 @@ class EventsWorkerStore(SQLBaseStore):
rejected_reason=rejected_reason,
)
redacted_event = None
if redacted:
redacted_event = prune_event(original_ev)
redaction_id = yield self._simple_select_one_onecol(
table="redactions",
keyvalues={"redacts": redacted_event.event_id},
retcol="event_id",
desc="_get_event_from_row_redactions",
)
redacted_event.unsigned["redacted_by"] = redaction_id
# Get the redaction event.
because = yield self.get_event(
redaction_id, check_redacted=False, allow_none=True
)
if because:
# It's fine to do add the event directly, since get_pdu_json
# will serialise this field correctly
redacted_event.unsigned["redacted_because"] = because
# Starting in room version v3, some redactions need to be
# rechecked if we didn't have the redacted event at the
# time, so we recheck on read instead.
if because.internal_metadata.need_to_check_redaction():
expected_domain = get_domain_from_id(original_ev.sender)
if get_domain_from_id(because.sender) == expected_domain:
# This redaction event is allowed. Mark as not needing a
# recheck.
because.internal_metadata.recheck_redaction = False
else:
# Senders don't match, so the event isn't actually redacted
redacted_event = None
redacted_event = yield self._maybe_redact_event_row(original_ev, redactions)
cache_entry = _EventCacheEntry(
event=original_ev, redacted_event=redacted_event
@ -599,6 +593,56 @@ class EventsWorkerStore(SQLBaseStore):
defer.returnValue(cache_entry)
@defer.inlineCallbacks
def _maybe_redact_event_row(self, original_ev, redactions):
"""Given an event object and a list of possible redacting event ids,
determine whether to honour any of those redactions and if so return a redacted
event.
Args:
original_ev (EventBase):
redactions (iterable[str]): list of event ids of potential redaction events
Returns:
Deferred[EventBase|None]: if the event should be redacted, a pruned
event object. Otherwise, None.
"""
redaction_map = yield self._get_events_from_cache_or_db(redactions)
for redaction_id in redactions:
redaction_entry = redaction_map.get(redaction_id)
if not redaction_entry:
# we don't have the redaction event, or the redaction event was not
# authorized.
continue
redaction_event = redaction_entry.event
# Starting in room version v3, some redactions need to be
# rechecked if we didn't have the redacted event at the
# time, so we recheck on read instead.
if redaction_event.internal_metadata.need_to_check_redaction():
expected_domain = get_domain_from_id(original_ev.sender)
if get_domain_from_id(redaction_event.sender) == expected_domain:
# This redaction event is allowed. Mark as not needing a recheck.
redaction_event.internal_metadata.recheck_redaction = False
else:
# Senders don't match, so the event isn't actually redacted
continue
# we found a good redaction event. Redact!
redacted_event = prune_event(original_ev)
redacted_event.unsigned["redacted_by"] = redaction_id
# It's fine to add the event directly, since get_pdu_json
# will serialise this field correctly
redacted_event.unsigned["redacted_because"] = redaction_event
return redacted_event
# no valid redaction found for this event
return None
@defer.inlineCallbacks
def have_events_in_timeline(self, event_ids):
"""Given a list of event ids, check if we have already processed and