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Add a filter_event_for_clients_with_state function (#13222)

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Erik Johnston 2022-07-11 14:14:09 +01:00 • committed by GitHub
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546
synapse/visibility.py
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@ -13,16 +13,21 @@
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
from enum import Enum, auto
from typing import Collection, Dict, FrozenSet, List, Optional, Tuple
import attr
from typing_extensions import Final
from synapse.api.constants import EventTypes, HistoryVisibility, Membership
from synapse.events import EventBase
from synapse.events.snapshot import EventContext
from synapse.events.utils import prune_event
from synapse.storage.controllers import StorageControllers
from synapse.storage.databases.main import DataStore
from synapse.storage.state import StateFilter
from synapse.types import RetentionPolicy, StateMap, get_domain_from_id
from synapse.util import Clock
logger = logging.getLogger(__name__)
@ -102,153 +107,18 @@ async def filter_events_for_client(
] = await storage.main.get_retention_policy_for_room(room_id)
def allowed(event: EventBase) -> Optional[EventBase]:
"""
Args:
event: event to check
Returns:
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.
"""
# Only run some checks if these events aren't about to be sent to clients. This is
# because, if this is not the case, we're probably only checking if the users can
# see events in the room at that point in the DAG, and that shouldn't be decided
# on those checks.
if filter_send_to_client:
if event.type == EventTypes.Dummy:
return None
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 not event.is_state():
retention_policy = retention_policies[event.room_id]
max_lifetime = retention_policy.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
# we need to handle outliers separately, since we don't have the room state.
if event.internal_metadata.outlier:
# Normally these can't be seen by clients, but we make an exception for
# for out-of-band membership events (eg, incoming invites, or rejections of
# said invite) for the user themselves.
if event.type == EventTypes.Member and event.state_key == user_id:
logger.debug("Returning out-of-band-membership event %s", event)
return event
return None
state = event_id_to_state[event.event_id]
# get the room_visibility at the time of the event.
visibility = get_effective_room_visibility_from_state(state)
# 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 = HistoryVisibility.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
#
# (Note this doesn't work for out-of-band invite rejections, which don't
# have prev_state populated. They are handled above in the outlier code.)
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 == HistoryVisibility.JOINED:
# we weren't a member at the time of the event, so we can't
# see this event.
return None
elif visibility == HistoryVisibility.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 == HistoryVisibility.SHARED and is_peeking:
# if the visibility is shared, users cannot see the event unless
# they have *subsequently* 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
return _check_client_allowed_to_see_event(
user_id=user_id,
event=event,
clock=storage.main.clock,
filter_send_to_client=filter_send_to_client,
sender_ignored=event.sender in ignore_list,
always_include_ids=always_include_ids,
retention_policy=retention_policies[room_id],
state=event_id_to_state.get(event.event_id),
is_peeking=is_peeking,
sender_erased=erased_senders.get(event.sender, False),
)
# Check each event: gives an iterable of None or (a potentially modified)
# EventBase.
@ -258,9 +128,389 @@ async def filter_events_for_client(
return [ev for ev in filtered_events if ev]
async def filter_event_for_clients_with_state(
store: DataStore,
user_ids: Collection[str],
event: EventBase,
context: EventContext,
is_peeking: bool = False,
filter_send_to_client: bool = True,
) -> Collection[str]:
"""
Checks to see if an event is visible to the users in the list at the time of
the event.
Note: This does *not* check if the sender of the event was erased.
Args:
store: databases
user_ids: user_ids to be checked
event: the event to be checked
context: EventContext for the event to be checked
is_peeking: Whether the users are peeking into the room, ie not
currently joined
filter_send_to_client: Whether we're checking an event that's going to be
sent to a client. This might not always be the case since this function can
also be called to check whether a user can see the state at a given point.
Returns:
Collection of user IDs for whom the event is visible
"""
# None of the users should see the event if it is soft_failed
if event.internal_metadata.is_soft_failed():
return []
# Make a set for all user IDs that haven't been filtered out by a check.
allowed_user_ids = set(user_ids)
# Only run some checks if these events aren't about to be sent to clients. This is
# because, if this is not the case, we're probably only checking if the users can
# see events in the room at that point in the DAG, and that shouldn't be decided
# on those checks.
if filter_send_to_client:
ignored_by = await store.ignored_by(event.sender)
retention_policy = await store.get_retention_policy_for_room(event.room_id)
for user_id in user_ids:
if (
_check_filter_send_to_client(
event,
store.clock,
retention_policy,
sender_ignored=user_id in ignored_by,
)
== _CheckFilter.DENIED
):
allowed_user_ids.discard(user_id)
if event.internal_metadata.outlier:
# Normally these can't be seen by clients, but we make an exception for
# for out-of-band membership events (eg, incoming invites, or rejections of
# said invite) for the user themselves.
if event.type == EventTypes.Member and event.state_key in allowed_user_ids:
logger.debug("Returning out-of-band-membership event %s", event)
return {event.state_key}
return set()
# First we get just the history visibility in case its shared/world-readable
# room.
visibility_state_map = await _get_state_map(
store, event, context, StateFilter.from_types([_HISTORY_VIS_KEY])
)
visibility = get_effective_room_visibility_from_state(visibility_state_map)
if (
_check_history_visibility(event, visibility, is_peeking=is_peeking)
== _CheckVisibility.ALLOWED
):
return allowed_user_ids
# The history visibility isn't lax, so we now need to fetch the membership
# events of all the users.
filter_list = []
for user_id in allowed_user_ids:
filter_list.append((EventTypes.Member, user_id))
filter_list.append((EventTypes.RoomHistoryVisibility, ""))
state_filter = StateFilter.from_types(filter_list)
state_map = await _get_state_map(store, event, context, state_filter)
# Now we check whether the membership allows each user to see the event.
return {
user_id
for user_id in allowed_user_ids
if _check_membership(user_id, event, visibility, state_map, is_peeking).allowed
}
async def _get_state_map(
store: DataStore, event: EventBase, context: EventContext, state_filter: StateFilter
) -> StateMap[EventBase]:
"""Helper function for getting a `StateMap[EventBase]` from an `EventContext`"""
state_map = await context.get_prev_state_ids(state_filter)
# Use events rather than event ids as content from the events are needed in
# _check_visibility
event_map = await store.get_events(state_map.values(), get_prev_content=False)
updated_state_map = {}
for state_key, event_id in state_map.items():
state_event = event_map.get(event_id)
if state_event:
updated_state_map[state_key] = state_event
if event.is_state():
current_state_key = (event.type, event.state_key)
# Add current event to updated_state_map, we need to do this here as it
# may not have been persisted to the db yet
updated_state_map[current_state_key] = event
return updated_state_map
def _check_client_allowed_to_see_event(
user_id: str,
event: EventBase,
clock: Clock,
filter_send_to_client: bool,
is_peeking: bool,
always_include_ids: FrozenSet[str],
sender_ignored: bool,
retention_policy: RetentionPolicy,
state: Optional[StateMap[EventBase]],
sender_erased: bool,
) -> Optional[EventBase]:
"""Check with the given user is allowed to see the given event
See `filter_events_for_client` for details about args
Args:
user_id
event
clock
filter_send_to_client
is_peeking
always_include_ids
sender_ignored: Whether the user is ignoring the event sender
retention_policy: The retention policy of the room
state: The state at the event, unless its an outlier
sender_erased: Whether the event sender has been marked as "erased"
Returns:
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.
"""
# Only run some checks if these events aren't about to be sent to clients. This is
# because, if this is not the case, we're probably only checking if the users can
# see events in the room at that point in the DAG, and that shouldn't be decided
# on those checks.
if filter_send_to_client:
if (
_check_filter_send_to_client(event, clock, retention_policy, sender_ignored)
== _CheckFilter.DENIED
):
return None
if event.event_id in always_include_ids:
return event
# we need to handle outliers separately, since we don't have the room state.
if event.internal_metadata.outlier:
# Normally these can't be seen by clients, but we make an exception for
# for out-of-band membership events (eg, incoming invites, or rejections of
# said invite) for the user themselves.
if event.type == EventTypes.Member and event.state_key == user_id:
logger.debug("Returning out-of-band-membership event %s", event)
return event
return None
if state is None:
raise Exception("Missing state for non-outlier event")
# get the room_visibility at the time of the event.
visibility = get_effective_room_visibility_from_state(state)
# Check if the room has lax history visibility, allowing us to skip
# membership checks.
#
# We can only do this check if the sender has *not* been erased, as if they
# have we need to check the user's membership.
if (
not sender_erased
and _check_history_visibility(event, visibility, is_peeking)
== _CheckVisibility.ALLOWED
):
return event
membership_result = _check_membership(user_id, event, visibility, state, is_peeking)
if not membership_result.allowed:
return None
# If the sender has been erased and the user was not joined at the time, we
# must only return the redacted form.
if sender_erased and not membership_result.joined:
event = prune_event(event)
return event
@attr.s(frozen=True, slots=True, auto_attribs=True)
class _CheckMembershipReturn:
"Return value of _check_membership"
allowed: bool
joined: bool
def _check_membership(
user_id: str,
event: EventBase,
visibility: str,
state: StateMap[EventBase],
is_peeking: bool,
) -> _CheckMembershipReturn:
"""Check whether the user can see the event due to their membership
Returns:
True if they can, False if they can't, plus the membership of the user
at the event.
"""
# 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
#
# (Note this doesn't work for out-of-band invite rejections, which don't
# have prev_state populated. They are handled above in the outlier code.)
if membership == "leave" and (
prev_membership == "join" or prev_membership == "invite"
):
return _CheckMembershipReturn(True, membership == Membership.JOIN)
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 _CheckMembershipReturn(True, True)
# otherwise, it depends on the room visibility.
if visibility == HistoryVisibility.JOINED:
# we weren't a member at the time of the event, so we can't
# see this event.
return _CheckMembershipReturn(False, False)
elif visibility == HistoryVisibility.INVITED:
# user can also see the event if they were *invited* at the time
# of the event.
return _CheckMembershipReturn(membership == Membership.INVITE, False)
elif visibility == HistoryVisibility.SHARED and is_peeking:
# if the visibility is shared, users cannot see the event unless
# they have *subsequently* 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 _CheckMembershipReturn(False, False)
# The visibility is either shared or world_readable, and the user was
# not a member at the time. We allow it.
return _CheckMembershipReturn(True, False)
class _CheckFilter(Enum):
MAYBE_ALLOWED = auto()
DENIED = auto()
def _check_filter_send_to_client(
event: EventBase,
clock: Clock,
retention_policy: RetentionPolicy,
sender_ignored: bool,
) -> _CheckFilter:
"""Apply checks for sending events to client
Returns:
True if might be allowed to be sent to clients, False if definitely not.
"""
if event.type == EventTypes.Dummy:
return _CheckFilter.DENIED
if not event.is_state() and sender_ignored:
return _CheckFilter.DENIED
# 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 _CheckFilter.DENIED
# 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 not event.is_state():
max_lifetime = retention_policy.max_lifetime
if max_lifetime is not None:
oldest_allowed_ts = clock.time_msec() - max_lifetime
if event.origin_server_ts < oldest_allowed_ts:
return _CheckFilter.DENIED
return _CheckFilter.MAYBE_ALLOWED
class _CheckVisibility(Enum):
ALLOWED = auto()
MAYBE_DENIED = auto()
def _check_history_visibility(
event: EventBase, visibility: str, is_peeking: bool
) -> _CheckVisibility:
"""Check if event is allowed to be seen due to lax history visibility.
Returns:
True if user can definitely see the event, False if maybe not.
"""
# 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 = HistoryVisibility.SHARED
new_priority = VISIBILITY_PRIORITY.index(visibility)
old_priority = VISIBILITY_PRIORITY.index(prev_visibility)
if old_priority < new_priority:
visibility = prev_visibility
if visibility == HistoryVisibility.SHARED and not is_peeking:
return _CheckVisibility.ALLOWED
elif visibility == HistoryVisibility.WORLD_READABLE:
return _CheckVisibility.ALLOWED
return _CheckVisibility.MAYBE_DENIED
def get_effective_room_visibility_from_state(state: StateMap[EventBase]) -> str:
"""Get the actual history vis, from a state map including the history_visibility event
Handles missing and invalid history visibility events.
"""
visibility_event = state.get(_HISTORY_VIS_KEY, None)