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Use state before join to determine if we _should_perform_remote_join (
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#13270)

Co-authored-by: Richard van der Hoff <[email protected]>
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David Robertson and richvdh authored Jul 15, 2022
1 parent d765ada commit 7281591
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Showing 4 changed files with 35 additions and 24 deletions.
1 change: 1 addition & 0 deletions changelog.d/13270.bugfix
Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix a bug introduced in Synapse 1.40 where a user invited to a restricted room would be briefly unable to join.
2 changes: 1 addition & 1 deletion synapse/events/builder.py
Original file line number Diff line number Diff line change
Expand Up @@ -120,7 +120,7 @@ async def build(
The signed and hashed event.
"""
if auth_event_ids is None:
state_ids = await self._state.get_current_state_ids(
state_ids = await self._state.compute_state_after_events(
self.room_id, prev_event_ids
)
auth_event_ids = self._event_auth_handler.compute_auth_events(
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35 changes: 20 additions & 15 deletions synapse/handlers/room_member.py
Original file line number Diff line number Diff line change
Expand Up @@ -755,14 +755,14 @@ async def update_membership_locked(

latest_event_ids = await self.store.get_prev_events_for_room(room_id)

current_state_ids = await self.state_handler.get_current_state_ids(
room_id, latest_event_ids=latest_event_ids
state_before_join = await self.state_handler.compute_state_after_events(
room_id, latest_event_ids
)

# TODO: Refactor into dictionary of explicitly allowed transitions
# between old and new state, with specific error messages for some
# transitions and generic otherwise
old_state_id = current_state_ids.get((EventTypes.Member, target.to_string()))
old_state_id = state_before_join.get((EventTypes.Member, target.to_string()))
if old_state_id:
old_state = await self.store.get_event(old_state_id, allow_none=True)
old_membership = old_state.content.get("membership") if old_state else None
Expand Down Expand Up @@ -813,11 +813,11 @@ async def update_membership_locked(
if action == "kick":
raise AuthError(403, "The target user is not in the room")

is_host_in_room = await self._is_host_in_room(current_state_ids)
is_host_in_room = await self._is_host_in_room(state_before_join)

if effective_membership_state == Membership.JOIN:
if requester.is_guest:
guest_can_join = await self._can_guest_join(current_state_ids)
guest_can_join = await self._can_guest_join(state_before_join)
if not guest_can_join:
# This should be an auth check, but guests are a local concept,
# so don't really fit into the general auth process.
Expand Down Expand Up @@ -855,7 +855,12 @@ async def update_membership_locked(

# Check if a remote join should be performed.
remote_join, remote_room_hosts = await self._should_perform_remote_join(
target.to_string(), room_id, remote_room_hosts, content, is_host_in_room
target.to_string(),
room_id,
remote_room_hosts,
content,
is_host_in_room,
state_before_join,
)
if remote_join:
if ratelimit:
Expand Down Expand Up @@ -995,6 +1000,7 @@ async def _should_perform_remote_join(
remote_room_hosts: List[str],
content: JsonDict,
is_host_in_room: bool,
state_before_join: StateMap[str],
) -> Tuple[bool, List[str]]:
"""
Check whether the server should do a remote join (as opposed to a local
Expand All @@ -1014,6 +1020,8 @@ async def _should_perform_remote_join(
content: The content to use as the event body of the join. This may
be modified.
is_host_in_room: True if the host is in the room.
state_before_join: The state before the join event (i.e. the resolution of
the states after its parent events).
Returns:
A tuple of:
Expand All @@ -1030,20 +1038,17 @@ async def _should_perform_remote_join(
# If the host is in the room, but not one of the authorised hosts
# for restricted join rules, a remote join must be used.
room_version = await self.store.get_room_version(room_id)
current_state_ids = await self._storage_controllers.state.get_current_state_ids(
room_id
)

# If restricted join rules are not being used, a local join can always
# be used.
if not await self.event_auth_handler.has_restricted_join_rules(
current_state_ids, room_version
state_before_join, room_version
):
return False, []

# If the user is invited to the room or already joined, the join
# event can always be issued locally.
prev_member_event_id = current_state_ids.get((EventTypes.Member, user_id), None)
prev_member_event_id = state_before_join.get((EventTypes.Member, user_id), None)
prev_member_event = None
if prev_member_event_id:
prev_member_event = await self.store.get_event(prev_member_event_id)
Expand All @@ -1058,10 +1063,10 @@ async def _should_perform_remote_join(
#
# If not, generate a new list of remote hosts based on which
# can issue invites.
event_map = await self.store.get_events(current_state_ids.values())
event_map = await self.store.get_events(state_before_join.values())
current_state = {
state_key: event_map[event_id]
for state_key, event_id in current_state_ids.items()
for state_key, event_id in state_before_join.items()
}
allowed_servers = get_servers_from_users(
get_users_which_can_issue_invite(current_state)
Expand All @@ -1075,7 +1080,7 @@ async def _should_perform_remote_join(

# Ensure the member should be allowed access via membership in a room.
await self.event_auth_handler.check_restricted_join_rules(
current_state_ids, room_version, user_id, prev_member_event
state_before_join, room_version, user_id, prev_member_event
)

# If this is going to be a local join, additional information must
Expand All @@ -1085,7 +1090,7 @@ async def _should_perform_remote_join(
EventContentFields.AUTHORISING_USER
] = await self.event_auth_handler.get_user_which_could_invite(
room_id,
current_state_ids,
state_before_join,
)

return False, []
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21 changes: 13 additions & 8 deletions synapse/state/__init__.py
Original file line number Diff line number Diff line change
Expand Up @@ -153,22 +153,27 @@ def __init__(self, hs: "HomeServer"):
ReplicationUpdateCurrentStateRestServlet.make_client(hs)
)

async def get_current_state_ids(
async def compute_state_after_events(
self,
room_id: str,
latest_event_ids: Collection[str],
event_ids: Collection[str],
) -> StateMap[str]:
"""Get the current state, or the state at a set of events, for a room
"""Fetch the state after each of the given event IDs. Resolve them and return.
This is typically used where `event_ids` is a collection of forward extremities
in a room, intended to become the `prev_events` of a new event E. If so, the
return value of this function represents the state before E.
Args:
room_id:
latest_event_ids: The forward extremities to resolve.
room_id: the room_id containing the given events.
event_ids: the events whose state should be fetched and resolved.
Returns:
the state dict, mapping from (event_type, state_key) -> event_id
the state dict (a mapping from (event_type, state_key) -> event_id) which
holds the resolution of the states after the given event IDs.
"""
logger.debug("calling resolve_state_groups from get_current_state_ids")
ret = await self.resolve_state_groups_for_events(room_id, latest_event_ids)
logger.debug("calling resolve_state_groups from compute_state_after_events")
ret = await self.resolve_state_groups_for_events(room_id, event_ids)
return await ret.get_state(self._state_storage_controller, StateFilter.all())

async def get_current_users_in_room(
Expand Down

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