MatrixSynapse/synapse/handlers/event_auth.py

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# Copyright 2021 The Matrix.org Foundation C.I.C.
#
# 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
from typing import TYPE_CHECKING, Collection, List, Optional, Union
from synapse import event_auth
from synapse.api.constants import (
EventTypes,
JoinRules,
Membership,
RestrictedJoinRuleTypes,
)
from synapse.api.errors import AuthError, Codes, SynapseError
from synapse.api.room_versions import RoomVersion
from synapse.event_auth import (
check_state_dependent_auth_rules,
check_state_independent_auth_rules,
)
from synapse.events import EventBase
from synapse.events.builder import EventBuilder
from synapse.events.snapshot import EventContext
from synapse.types import StateMap, get_domain_from_id
from synapse.util.metrics import Measure
if TYPE_CHECKING:
from synapse.server import HomeServer
logger = logging.getLogger(__name__)
class EventAuthHandler:
"""
This class contains methods for authenticating events added to room graphs.
"""
def __init__(self, hs: "HomeServer"):
self._clock = hs.get_clock()
self._store = hs.get_datastores().main
self._server_name = hs.hostname
async def check_auth_rules_from_context(
self,
event: EventBase,
context: EventContext,
) -> None:
"""Check an event passes the auth rules at its own auth events"""
await check_state_independent_auth_rules(self._store, event)
auth_event_ids = event.auth_event_ids()
auth_events_by_id = await self._store.get_events(auth_event_ids)
check_state_dependent_auth_rules(event, auth_events_by_id.values())
def compute_auth_events(
self,
event: Union[EventBase, EventBuilder],
current_state_ids: StateMap[str],
for_verification: bool = False,
) -> List[str]:
"""Given an event and current state return the list of event IDs used
to auth an event.
If `for_verification` is False then only return auth events that
should be added to the event's `auth_events`.
Returns:
List of event IDs.
"""
if event.type == EventTypes.Create:
return []
# Currently we ignore the `for_verification` flag even though there are
# some situations where we can drop particular auth events when adding
# to the event's `auth_events` (e.g. joins pointing to previous joins
# when room is publicly joinable). Dropping event IDs has the
# advantage that the auth chain for the room grows slower, but we use
# the auth chain in state resolution v2 to order events, which means
# care must be taken if dropping events to ensure that it doesn't
# introduce undesirable "state reset" behaviour.
#
# All of which sounds a bit tricky so we don't bother for now.
auth_ids = []
for etype, state_key in event_auth.auth_types_for_event(
event.room_version, event
):
auth_ev_id = current_state_ids.get((etype, state_key))
if auth_ev_id:
auth_ids.append(auth_ev_id)
return auth_ids
async def get_user_which_could_invite(
self, room_id: str, current_state_ids: StateMap[str]
) -> str:
"""
Searches the room state for a local user who has the power level necessary
to invite other users.
Args:
room_id: The room ID under search.
current_state_ids: The current state of the room.
Returns:
The MXID of the user which could issue an invite.
Raises:
SynapseError if no appropriate user is found.
"""
power_level_event_id = current_state_ids.get((EventTypes.PowerLevels, ""))
invite_level = 0
users_default_level = 0
if power_level_event_id:
power_level_event = await self._store.get_event(power_level_event_id)
invite_level = power_level_event.content.get("invite", invite_level)
users_default_level = power_level_event.content.get(
"users_default", users_default_level
)
users = power_level_event.content.get("users", {})
else:
users = {}
# Find the user with the highest power level (only interested in local
# users).
local_users_in_room = await self._store.get_local_users_in_room(room_id)
chosen_user = max(
local_users_in_room,
key=lambda user: users.get(user, users_default_level),
default=None,
)
# Return the chosen if they can issue invites.
user_power_level = users.get(chosen_user, users_default_level)
if chosen_user and user_power_level >= invite_level:
logger.debug(
"Found a user who can issue invites %s with power level %d >= invite level %d",
chosen_user,
user_power_level,
invite_level,
)
return chosen_user
# No user was found.
raise SynapseError(
400,
"Unable to find a user which could issue an invite",
Codes.UNABLE_TO_GRANT_JOIN,
)
async def check_host_in_room(self, room_id: str, host: str) -> bool:
with Measure(self._clock, "check_host_in_room"):
return await self._store.is_host_joined(room_id, host)
async def check_restricted_join_rules(
self,
state_ids: StateMap[str],
room_version: RoomVersion,
user_id: str,
prev_member_event: Optional[EventBase],
) -> None:
"""
Check whether a user can join a room without an invite due to restricted join rules.
When joining a room with restricted joined rules (as defined in MSC3083),
the membership of rooms must be checked during a room join.
Args:
state_ids: The state of the room as it currently is.
room_version: The room version of the room being joined.
user_id: The user joining the room.
prev_member_event: The current membership event for this user.
Raises:
AuthError if the user cannot join the room.
"""
# If the member is invited or currently joined, then nothing to do.
if prev_member_event and (
prev_member_event.membership in (Membership.JOIN, Membership.INVITE)
):
return
# This is not a room with a restricted join rule, so we don't need to do the
# restricted room specific checks.
#
# Note: We'll be applying the standard join rule checks later, which will
# catch the cases of e.g. trying to join private rooms without an invite.
if not await self.has_restricted_join_rules(state_ids, room_version):
return
# Get the rooms which allow access to this room and check if the user is
# in any of them.
allowed_rooms = await self.get_rooms_that_allow_join(state_ids)
if not await self.is_user_in_rooms(allowed_rooms, user_id):
# If this is a remote request, the user might be in an allowed room
# that we do not know about.
if get_domain_from_id(user_id) != self._server_name:
for room_id in allowed_rooms:
if not await self._store.is_host_joined(room_id, self._server_name):
raise SynapseError(
400,
f"Unable to check if {user_id} is in allowed rooms.",
Codes.UNABLE_AUTHORISE_JOIN,
)
raise AuthError(
403,
"You do not belong to any of the required rooms/spaces to join this room.",
)
async def has_restricted_join_rules(
self, state_ids: StateMap[str], room_version: RoomVersion
) -> bool:
"""
Return if the room has the proper join rules set for access via rooms.
Args:
state_ids: The state of the room as it currently is.
room_version: The room version of the room to query.
Returns:
True if the proper room version and join rules are set for restricted access.
"""
# This only applies to room versions which support the new join rule.
if not room_version.msc3083_join_rules:
return False
# If there's no join rule, then it defaults to invite (so this doesn't apply).
join_rules_event_id = state_ids.get((EventTypes.JoinRules, ""), None)
if not join_rules_event_id:
return False
# If the join rule is not restricted, this doesn't apply.
join_rules_event = await self._store.get_event(join_rules_event_id)
content_join_rule = join_rules_event.content.get("join_rule")
if content_join_rule == JoinRules.RESTRICTED:
return True
# also check for MSC3787 behaviour
if room_version.msc3787_knock_restricted_join_rule:
return content_join_rule == JoinRules.KNOCK_RESTRICTED
return False
async def get_rooms_that_allow_join(
self, state_ids: StateMap[str]
) -> Collection[str]:
"""
Generate a list of rooms in which membership allows access to a room.
Args:
state_ids: The current state of the room the user wishes to join
Returns:
A collection of room IDs. Membership in any of the rooms in the list grants the ability to join the target room.
"""
# If there's no join rule, then it defaults to invite (so this doesn't apply).
join_rules_event_id = state_ids.get((EventTypes.JoinRules, ""), None)
if not join_rules_event_id:
return ()
# If the join rule is not restricted, this doesn't apply.
join_rules_event = await self._store.get_event(join_rules_event_id)
# If allowed is of the wrong form, then only allow invited users.
allow_list = join_rules_event.content.get("allow", [])
if not isinstance(allow_list, list):
return ()
# Pull out the other room IDs, invalid data gets filtered.
result = []
for allow in allow_list:
if not isinstance(allow, dict):
continue
# If the type is unexpected, skip it.
if allow.get("type") != RestrictedJoinRuleTypes.ROOM_MEMBERSHIP:
continue
room_id = allow.get("room_id")
if not isinstance(room_id, str):
continue
result.append(room_id)
return result
async def is_user_in_rooms(self, room_ids: Collection[str], user_id: str) -> bool:
"""
Check whether a user is a member of any of the provided rooms.
Args:
room_ids: The rooms to check for membership.
user_id: The user to check.
Returns:
True if the user is in any of the rooms, false otherwise.
"""
if not room_ids:
return False
# Get the list of joined rooms and see if there's an overlap.
joined_rooms = await self._store.get_rooms_for_user(user_id)
# Check each room and see if the user is in it.
for room_id in room_ids:
if room_id in joined_rooms:
return True
# The user was not in any of the rooms.
return False