forked-synapse/synapse/visibility.py
Matthew Hodgson 8e64c5a24c filter out m.room.aliases from the CS API until a better solution is specced (#6878)
We're in the middle of properly mitigating spam caused by malicious aliases being added to a room. However, until this work fully lands, we temporarily filter out all m.room.aliases events from /sync and /messages on the CS API, to remove abusive aliases. This is considered acceptable as m.room.aliases events were never a reliable record of the given alias->id mapping and were purely informational, and in their current state do more harm than good.
2020-02-10 09:36:23 +00:00

430 lines
16 KiB
Python

# -*- coding: utf-8 -*-
# Copyright 2014 - 2016 OpenMarket Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
import operator
from six import iteritems, itervalues
from six.moves import map
from twisted.internet import defer
from synapse.api.constants import EventTypes, Membership
from synapse.events.utils import prune_event
from synapse.storage import Storage
from synapse.storage.state import StateFilter
from synapse.types import get_domain_from_id
logger = logging.getLogger(__name__)
VISIBILITY_PRIORITY = ("world_readable", "shared", "invited", "joined")
MEMBERSHIP_PRIORITY = (
Membership.JOIN,
Membership.INVITE,
Membership.KNOCK,
Membership.LEAVE,
Membership.BAN,
)
@defer.inlineCallbacks
def filter_events_for_client(
storage: Storage,
user_id,
events,
is_peeking=False,
always_include_ids=frozenset(),
apply_retention_policies=True,
):
"""
Check which events a user is allowed to see. If the user can see the event but its
sender asked for their data to be erased, prune the content of the event.
Args:
storage
user_id(str): user id to be checked
events(list[synapse.events.EventBase]): sequence of events to be checked
is_peeking(bool): should be True if:
* the user is not currently a member of the room, and:
* the user has not been a member of the room since the given
events
always_include_ids (set(event_id)): set of event ids to specifically
include (unless sender is ignored)
apply_retention_policies (bool): Whether to filter out events that's older than
allowed by the room's retention policy. Useful when this function is called
to e.g. check whether a user should be allowed to see the state at a given
event rather than to know if it should send an event to a user's client(s).
Returns:
Deferred[list[synapse.events.EventBase]]
"""
# Filter out events that have been soft failed so that we don't relay them
# to clients.
events = list(e for e in events if not e.internal_metadata.is_soft_failed())
types = ((EventTypes.RoomHistoryVisibility, ""), (EventTypes.Member, user_id))
event_id_to_state = yield storage.state.get_state_for_events(
frozenset(e.event_id for e in events),
state_filter=StateFilter.from_types(types),
)
ignore_dict_content = yield storage.main.get_global_account_data_by_type_for_user(
"m.ignored_user_list", user_id
)
# FIXME: This will explode if people upload something incorrect.
ignore_list = frozenset(
ignore_dict_content.get("ignored_users", {}).keys()
if ignore_dict_content
else []
)
erased_senders = yield storage.main.are_users_erased((e.sender for e in events))
if apply_retention_policies:
room_ids = set(e.room_id for e in events)
retention_policies = {}
for room_id in room_ids:
retention_policies[
room_id
] = yield storage.main.get_retention_policy_for_room(room_id)
def allowed(event):
"""
Args:
event (synapse.events.EventBase): event to check
Returns:
None|EventBase:
None if the user cannot see this event at all
a redacted copy of the event if they can only see a redacted
version
the original event if they can see it as normal.
"""
if not event.is_state() and event.sender in ignore_list:
return None
# Until MSC2261 has landed we can't redact malicious alias events, so for
# now we temporarily filter out m.room.aliases entirely to mitigate
# abuse, while we spec a better solution to advertising aliases
# on rooms.
if event.type == EventTypes.Aliases:
return None
# Don't try to apply the room's retention policy if the event is a state event, as
# MSC1763 states that retention is only considered for non-state events.
if apply_retention_policies and not event.is_state():
retention_policy = retention_policies[event.room_id]
max_lifetime = retention_policy.get("max_lifetime")
if max_lifetime is not None:
oldest_allowed_ts = storage.main.clock.time_msec() - max_lifetime
if event.origin_server_ts < oldest_allowed_ts:
return None
if event.event_id in always_include_ids:
return event
state = event_id_to_state[event.event_id]
# get the room_visibility at the time of the event.
visibility_event = state.get((EventTypes.RoomHistoryVisibility, ""), None)
if visibility_event:
visibility = visibility_event.content.get("history_visibility", "shared")
else:
visibility = "shared"
if visibility not in VISIBILITY_PRIORITY:
visibility = "shared"
# Always allow history visibility events on boundaries. This is done
# by setting the effective visibility to the least restrictive
# of the old vs new.
if event.type == EventTypes.RoomHistoryVisibility:
prev_content = event.unsigned.get("prev_content", {})
prev_visibility = prev_content.get("history_visibility", None)
if prev_visibility not in VISIBILITY_PRIORITY:
prev_visibility = "shared"
new_priority = VISIBILITY_PRIORITY.index(visibility)
old_priority = VISIBILITY_PRIORITY.index(prev_visibility)
if old_priority < new_priority:
visibility = prev_visibility
# likewise, if the event is the user's own membership event, use
# the 'most joined' membership
membership = None
if event.type == EventTypes.Member and event.state_key == user_id:
membership = event.content.get("membership", None)
if membership not in MEMBERSHIP_PRIORITY:
membership = "leave"
prev_content = event.unsigned.get("prev_content", {})
prev_membership = prev_content.get("membership", None)
if prev_membership not in MEMBERSHIP_PRIORITY:
prev_membership = "leave"
# Always allow the user to see their own leave events, otherwise
# they won't see the room disappear if they reject the invite
if membership == "leave" and (
prev_membership == "join" or prev_membership == "invite"
):
return event
new_priority = MEMBERSHIP_PRIORITY.index(membership)
old_priority = MEMBERSHIP_PRIORITY.index(prev_membership)
if old_priority < new_priority:
membership = prev_membership
# otherwise, get the user's membership at the time of the event.
if membership is None:
membership_event = state.get((EventTypes.Member, user_id), None)
if membership_event:
membership = membership_event.membership
# if the user was a member of the room at the time of the event,
# they can see it.
if membership == Membership.JOIN:
return event
# otherwise, it depends on the room visibility.
if visibility == "joined":
# we weren't a member at the time of the event, so we can't
# see this event.
return None
elif visibility == "invited":
# user can also see the event if they were *invited* at the time
# of the event.
return event if membership == Membership.INVITE else None
elif visibility == "shared" and is_peeking:
# if the visibility is shared, users cannot see the event unless
# they have *subequently* joined the room (or were members at the
# time, of course)
#
# XXX: if the user has subsequently joined and then left again,
# ideally we would share history up to the point they left. But
# we don't know when they left. We just treat it as though they
# never joined, and restrict access.
return None
# the visibility is either shared or world_readable, and the user was
# not a member at the time. We allow it, provided the original sender
# has not requested their data to be erased, in which case, we return
# a redacted version.
if erased_senders[event.sender]:
return prune_event(event)
return event
# check each event: gives an iterable[None|EventBase]
filtered_events = map(allowed, events)
# remove the None entries
filtered_events = filter(operator.truth, filtered_events)
# we turn it into a list before returning it.
return list(filtered_events)
@defer.inlineCallbacks
def filter_events_for_server(
storage: Storage,
server_name,
events,
redact=True,
check_history_visibility_only=False,
):
"""Filter a list of events based on whether given server is allowed to
see them.
Args:
storage
server_name (str)
events (iterable[FrozenEvent])
redact (bool): Whether to return a redacted version of the event, or
to filter them out entirely.
check_history_visibility_only (bool): Whether to only check the
history visibility, rather than things like if the sender has been
erased. This is used e.g. during pagination to decide whether to
backfill or not.
Returns
Deferred[list[FrozenEvent]]
"""
def is_sender_erased(event, erased_senders):
if erased_senders and erased_senders[event.sender]:
logger.info("Sender of %s has been erased, redacting", event.event_id)
return True
return False
def check_event_is_visible(event, state):
history = state.get((EventTypes.RoomHistoryVisibility, ""), None)
if history:
visibility = history.content.get("history_visibility", "shared")
if visibility in ["invited", "joined"]:
# We now loop through all state events looking for
# membership states for the requesting server to determine
# if the server is either in the room or has been invited
# into the room.
for ev in itervalues(state):
if ev.type != EventTypes.Member:
continue
try:
domain = get_domain_from_id(ev.state_key)
except Exception:
continue
if domain != server_name:
continue
memtype = ev.membership
if memtype == Membership.JOIN:
return True
elif memtype == Membership.INVITE:
if visibility == "invited":
return True
else:
# server has no users in the room: redact
return False
return True
# Lets check to see if all the events have a history visibility
# of "shared" or "world_readable". If thats the case then we don't
# need to check membership (as we know the server is in the room).
event_to_state_ids = yield storage.state.get_state_ids_for_events(
frozenset(e.event_id for e in events),
state_filter=StateFilter.from_types(
types=((EventTypes.RoomHistoryVisibility, ""),)
),
)
visibility_ids = set()
for sids in itervalues(event_to_state_ids):
hist = sids.get((EventTypes.RoomHistoryVisibility, ""))
if hist:
visibility_ids.add(hist)
# If we failed to find any history visibility events then the default
# is "shared" visiblity.
if not visibility_ids:
all_open = True
else:
event_map = yield storage.main.get_events(visibility_ids)
all_open = all(
e.content.get("history_visibility") in (None, "shared", "world_readable")
for e in itervalues(event_map)
)
if not check_history_visibility_only:
erased_senders = yield storage.main.are_users_erased((e.sender for e in events))
else:
# We don't want to check whether users are erased, which is equivalent
# to no users having been erased.
erased_senders = {}
if all_open:
# all the history_visibility state affecting these events is open, so
# we don't need to filter by membership state. We *do* need to check
# for user erasure, though.
if erased_senders:
to_return = []
for e in events:
if not is_sender_erased(e, erased_senders):
to_return.append(e)
elif redact:
to_return.append(prune_event(e))
return to_return
# If there are no erased users then we can just return the given list
# of events without having to copy it.
return events
# Ok, so we're dealing with events that have non-trivial visibility
# rules, so we need to also get the memberships of the room.
# first, for each event we're wanting to return, get the event_ids
# of the history vis and membership state at those events.
event_to_state_ids = yield storage.state.get_state_ids_for_events(
frozenset(e.event_id for e in events),
state_filter=StateFilter.from_types(
types=((EventTypes.RoomHistoryVisibility, ""), (EventTypes.Member, None))
),
)
# We only want to pull out member events that correspond to the
# server's domain.
#
# event_to_state_ids contains lots of duplicates, so it turns out to be
# cheaper to build a complete event_id => (type, state_key) dict, and then
# filter out the ones we don't want
#
event_id_to_state_key = {
event_id: key
for key_to_eid in itervalues(event_to_state_ids)
for key, event_id in iteritems(key_to_eid)
}
def include(typ, state_key):
if typ != EventTypes.Member:
return True
# we avoid using get_domain_from_id here for efficiency.
idx = state_key.find(":")
if idx == -1:
return False
return state_key[idx + 1 :] == server_name
event_map = yield storage.main.get_events(
[
e_id
for e_id, key in iteritems(event_id_to_state_key)
if include(key[0], key[1])
]
)
event_to_state = {
e_id: {
key: event_map[inner_e_id]
for key, inner_e_id in iteritems(key_to_eid)
if inner_e_id in event_map
}
for e_id, key_to_eid in iteritems(event_to_state_ids)
}
to_return = []
for e in events:
erased = is_sender_erased(e, erased_senders)
visible = check_event_is_visible(e, event_to_state[e.event_id])
if visible and not erased:
to_return.append(e)
elif redact:
to_return.append(prune_event(e))
return to_return