anonymousland-synapse/synapse/handlers/event_auth.py
Richard van der Hoff 428174f902
Split event_auth.check into two parts (#10940)
Broadly, the existing `event_auth.check` function has two parts:
 * a validation section: checks that the event isn't too big, that it has the rught signatures, etc. 
   This bit is independent of the rest of the state in the room, and so need only be done once 
   for each event.
 * an auth section: ensures that the event is allowed, given the rest of the state in the room.
   This gets done multiple times, against various sets of room state, because it forms part of
   the state res algorithm.

Currently, this is implemented with `do_sig_check` and `do_size_check` parameters, but I think
that makes everything hard to follow. Instead, we split the function in two and call each part
separately where it is needed.
2021-09-29 18:59:15 +01:00

314 lines
12 KiB
Python

# 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_auth_rules_for_event
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_datastore()
self._server_name = hs.hostname
async def check_auth_rules_from_context(
self,
room_version_obj: RoomVersion,
event: EventBase,
context: EventContext,
) -> None:
"""Check an event passes the auth rules at its own auth events"""
auth_event_ids = event.auth_event_ids()
auth_events_by_id = await self._store.get_events(auth_event_ids)
auth_events = {(e.type, e.state_key): e for e in auth_events_by_id.values()}
check_auth_rules_for_event(room_version_obj, event, auth_events)
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.
users_in_room = await self._store.get_users_in_room(room_id)
# Only interested in local users.
local_users_in_room = [
u for u in users_in_room if get_domain_from_id(u) == self._server_name
]
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)
return join_rules_event.content.get("join_rule") == JoinRules.RESTRICTED
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