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Improve validation for `send_{join,leave,knock}` (#10225)

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The idea here is to stop people sending things that aren't joins/leaves/knocks through these endpoints: previously you could send anything you liked through them. I wasn't able to find any security holes from doing so, but it doesn't sound like a good thing.
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Richard van der Hoff 3 years ago committed by GitHub
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  1. 1
      changelog.d/10225.feature
  2. 121
      synapse/federation/federation_server.py
  3. 12
      synapse/federation/transport/server.py
  4. 177
      synapse/handlers/federation.py
  5. 2
      tests/handlers/test_federation.py
  6. 2
      tests/replication/test_federation_sender_shard.py

1
changelog.d/10225.feature
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@ -0,0 +1 @@
Improve validation on federation `send_{join,leave,knock}` endpoints.

121
synapse/federation/federation_server.py
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@ -34,7 +34,7 @@ from twisted.internet import defer
from twisted.internet.abstract import isIPAddress from twisted.internet.abstract import isIPAddress
from twisted.python import failure from twisted.python import failure
from synapse.api.constants import EduTypes, EventTypes from synapse.api.constants import EduTypes, EventTypes, Membership
from synapse.api.errors import ( from synapse.api.errors import (
AuthError, AuthError,
Codes, Codes,
@ -46,6 +46,7 @@ from synapse.api.errors import (
) )
from synapse.api.room_versions import KNOWN_ROOM_VERSIONS from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
from synapse.events import EventBase from synapse.events import EventBase
from synapse.events.snapshot import EventContext
from synapse.federation.federation_base import FederationBase, event_from_pdu_json from synapse.federation.federation_base import FederationBase, event_from_pdu_json
from synapse.federation.persistence import TransactionActions from synapse.federation.persistence import TransactionActions
from synapse.federation.units import Edu, Transaction from synapse.federation.units import Edu, Transaction
@ -537,26 +538,21 @@ class FederationServer(FederationBase):
return {"event": ret_pdu.get_pdu_json(time_now)} return {"event": ret_pdu.get_pdu_json(time_now)}
async def on_send_join_request( async def on_send_join_request(
self, origin: str, content: JsonDict self, origin: str, content: JsonDict, room_id: str
) -> Dict[str, Any]: ) -> Dict[str, Any]:
logger.debug("on_send_join_request: content: %s", content) context = await self._on_send_membership_event(
origin, content, Membership.JOIN, room_id
assert_params_in_dict(content, ["room_id"]) )
room_version = await self.store.get_room_version(content["room_id"])
pdu = event_from_pdu_json(content, room_version)
origin_host, _ = parse_server_name(origin)
await self.check_server_matches_acl(origin_host, pdu.room_id)
logger.debug("on_send_join_request: pdu sigs: %s", pdu.signatures)
pdu = await self._check_sigs_and_hash(room_version, pdu) prev_state_ids = await context.get_prev_state_ids()
state_ids = list(prev_state_ids.values())
auth_chain = await self.store.get_auth_chain(room_id, state_ids)
state = await self.store.get_events(state_ids)
res_pdus = await self.handler.on_send_join_request(origin, pdu)
time_now = self._clock.time_msec() time_now = self._clock.time_msec()
return { return {
"state": [p.get_pdu_json(time_now) for p in res_pdus["state"]], "state": [p.get_pdu_json(time_now) for p in state.values()],
"auth_chain": [p.get_pdu_json(time_now) for p in res_pdus["auth_chain"]], "auth_chain": [p.get_pdu_json(time_now) for p in auth_chain],
} }
async def on_make_leave_request( async def on_make_leave_request(
@ -571,21 +567,11 @@ class FederationServer(FederationBase):
time_now = self._clock.time_msec() time_now = self._clock.time_msec()
return {"event": pdu.get_pdu_json(time_now), "room_version": room_version} return {"event": pdu.get_pdu_json(time_now), "room_version": room_version}
async def on_send_leave_request(self, origin: str, content: JsonDict) -> dict: async def on_send_leave_request(
self, origin: str, content: JsonDict, room_id: str
) -> dict:
logger.debug("on_send_leave_request: content: %s", content) logger.debug("on_send_leave_request: content: %s", content)
await self._on_send_membership_event(origin, content, Membership.LEAVE, room_id)
assert_params_in_dict(content, ["room_id"])
room_version = await self.store.get_room_version(content["room_id"])
pdu = event_from_pdu_json(content, room_version)
origin_host, _ = parse_server_name(origin)
await self.check_server_matches_acl(origin_host, pdu.room_id)
logger.debug("on_send_leave_request: pdu sigs: %s", pdu.signatures)
pdu = await self._check_sigs_and_hash(room_version, pdu)
await self.handler.on_send_leave_request(origin, pdu)
return {} return {}
async def on_make_knock_request( async def on_make_knock_request(
@ -651,39 +637,76 @@ class FederationServer(FederationBase):
Returns: Returns:
The stripped room state. The stripped room state.
""" """
logger.debug("on_send_knock_request: content: %s", content) event_context = await self._on_send_membership_event(
origin, content, Membership.KNOCK, room_id
)
# Retrieve stripped state events from the room and send them back to the remote
# server. This will allow the remote server's clients to display information
# related to the room while the knock request is pending.
stripped_room_state = (
await self.store.get_stripped_room_state_from_event_context(
event_context, self._room_prejoin_state_types
)
)
return {"knock_state_events": stripped_room_state}
async def _on_send_membership_event(
self, origin: str, content: JsonDict, membership_type: str, room_id: str
) -> EventContext:
"""Handle an on_send_{join,leave,knock} request
Does some preliminary validation before passing the request on to the
federation handler.
Args:
origin: The (authenticated) requesting server
content: The body of the send_* request - a complete membership event
membership_type: The expected membership type (join or leave, depending
on the endpoint)
room_id: The room_id from the request, to be validated against the room_id
in the event
Returns:
The context of the event after inserting it into the room graph.
Raises:
SynapseError if there is a problem with the request, including things like
the room_id not matching or the event not being authorized.
"""
assert_params_in_dict(content, ["room_id"])
if content["room_id"] != room_id:
raise SynapseError(
400,
"Room ID in body does not match that in request path",
Codes.BAD_JSON,
)
room_version = await self.store.get_room_version(room_id) room_version = await self.store.get_room_version(room_id)
# Check that this room supports knocking as defined by its room version if membership_type == Membership.KNOCK and not room_version.msc2403_knocking:
if not room_version.msc2403_knocking:
raise SynapseError( raise SynapseError(
403, 403,
"This room version does not support knocking", "This room version does not support knocking",
errcode=Codes.FORBIDDEN, errcode=Codes.FORBIDDEN,
) )
pdu = event_from_pdu_json(content, room_version) event = event_from_pdu_json(content, room_version)
origin_host, _ = parse_server_name(origin) if event.type != EventTypes.Member or not event.is_state():
await self.check_server_matches_acl(origin_host, pdu.room_id) raise SynapseError(400, "Not an m.room.member event", Codes.BAD_JSON)
logger.debug("on_send_knock_request: pdu sigs: %s", pdu.signatures) if event.content.get("membership") != membership_type:
raise SynapseError(400, "Not a %s event" % membership_type, Codes.BAD_JSON)
pdu = await self._check_sigs_and_hash(room_version, pdu) origin_host, _ = parse_server_name(origin)
await self.check_server_matches_acl(origin_host, event.room_id)
# Handle the event, and retrieve the EventContext logger.debug("_on_send_membership_event: pdu sigs: %s", event.signatures)
event_context = await self.handler.on_send_knock_request(origin, pdu)
# Retrieve stripped state events from the room and send them back to the remote event = await self._check_sigs_and_hash(room_version, event)
# server. This will allow the remote server's clients to display information
# related to the room while the knock request is pending. return await self.handler.on_send_membership_event(origin, event)
stripped_room_state = (
await self.store.get_stripped_room_state_from_event_context(
event_context, self._room_prejoin_state_types
)
)
return {"knock_state_events": stripped_room_state}
async def on_event_auth( async def on_event_auth(
self, origin: str, room_id: str, event_id: str self, origin: str, room_id: str, event_id: str

12
synapse/federation/transport/server.py
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@ -553,7 +553,7 @@ class FederationV1SendLeaveServlet(BaseFederationServerServlet):
PATH = "/send_leave/(?P<room_id>[^/]*)/(?P<event_id>[^/]*)" PATH = "/send_leave/(?P<room_id>[^/]*)/(?P<event_id>[^/]*)"
async def on_PUT(self, origin, content, query, room_id, event_id): async def on_PUT(self, origin, content, query, room_id, event_id):
content = await self.handler.on_send_leave_request(origin, content) content = await self.handler.on_send_leave_request(origin, content, room_id)
return 200, (200, content) return 200, (200, content)
@ -563,7 +563,7 @@ class FederationV2SendLeaveServlet(BaseFederationServerServlet):
PREFIX = FEDERATION_V2_PREFIX PREFIX = FEDERATION_V2_PREFIX
async def on_PUT(self, origin, content, query, room_id, event_id): async def on_PUT(self, origin, content, query, room_id, event_id):
content = await self.handler.on_send_leave_request(origin, content) content = await self.handler.on_send_leave_request(origin, content, room_id)
return 200, content return 200, content
@ -602,9 +602,9 @@ class FederationV1SendJoinServlet(BaseFederationServerServlet):
PATH = "/send_join/(?P<room_id>[^/]*)/(?P<event_id>[^/]*)" PATH = "/send_join/(?P<room_id>[^/]*)/(?P<event_id>[^/]*)"
async def on_PUT(self, origin, content, query, room_id, event_id): async def on_PUT(self, origin, content, query, room_id, event_id):
# TODO(paul): assert that room_id/event_id parsed from path actually # TODO(paul): assert that event_id parsed from path actually
# match those given in content # match those given in content
content = await self.handler.on_send_join_request(origin, content) content = await self.handler.on_send_join_request(origin, content, room_id)
return 200, (200, content) return 200, (200, content)
@ -614,9 +614,9 @@ class FederationV2SendJoinServlet(BaseFederationServerServlet):
PREFIX = FEDERATION_V2_PREFIX PREFIX = FEDERATION_V2_PREFIX
async def on_PUT(self, origin, content, query, room_id, event_id): async def on_PUT(self, origin, content, query, room_id, event_id):
# TODO(paul): assert that room_id/event_id parsed from path actually # TODO(paul): assert that event_id parsed from path actually
# match those given in content # match those given in content
content = await self.handler.on_send_join_request(origin, content) content = await self.handler.on_send_join_request(origin, content, room_id)
return 200, content return 200, content

177
synapse/handlers/federation.py
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@ -1711,80 +1711,6 @@ class FederationHandler(BaseHandler):
return event return event
async def on_send_join_request(self, origin: str, pdu: EventBase) -> JsonDict:
"""We have received a join event for a room. Fully process it and
respond with the current state and auth chains.
"""
event = pdu
logger.debug(
"on_send_join_request from %s: Got event: %s, signatures: %s",
origin,
event.event_id,
event.signatures,
)
if get_domain_from_id(event.sender) != origin:
logger.info(
"Got /send_join request for user %r from different origin %s",
event.sender,
origin,
)
raise SynapseError(403, "User not from origin", Codes.FORBIDDEN)
event.internal_metadata.outlier = False
# Send this event on behalf of the origin server.
#
# The reasons we have the destination server rather than the origin
# server send it are slightly mysterious: the origin server should have
# all the necessary state once it gets the response to the send_join,
# so it could send the event itself if it wanted to. It may be that
# doing it this way reduces failure modes, or avoids certain attacks
# where a new server selectively tells a subset of the federation that
# it has joined.
#
# The fact is that, as of the current writing, Synapse doesn't send out
# the join event over federation after joining, and changing it now
# would introduce the danger of backwards-compatibility problems.
event.internal_metadata.send_on_behalf_of = origin
# Calculate the event context.
context = await self.state_handler.compute_event_context(event)
# Get the state before the new event.
prev_state_ids = await context.get_prev_state_ids()
# Check if the user is already in the room or invited to the room.
user_id = event.state_key
prev_member_event_id = prev_state_ids.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)
# Check if the member should be allowed access via membership in a space.
await self._event_auth_handler.check_restricted_join_rules(
prev_state_ids,
event.room_version,
user_id,
prev_member_event,
)
# Persist the event.
await self._auth_and_persist_event(origin, event, context)
logger.debug(
"on_send_join_request: After _auth_and_persist_event: %s, sigs: %s",
event.event_id,
event.signatures,
)
state_ids = list(prev_state_ids.values())
auth_chain = await self.store.get_auth_chain(event.room_id, state_ids)
state = await self.store.get_events(list(prev_state_ids.values()))
return {"state": list(state.values()), "auth_chain": auth_chain}
async def on_invite_request( async def on_invite_request(
self, origin: str, event: EventBase, room_version: RoomVersion self, origin: str, event: EventBase, room_version: RoomVersion
) -> EventBase: ) -> EventBase:
@ -1960,44 +1886,6 @@ class FederationHandler(BaseHandler):
return event return event
async def on_send_leave_request(self, origin: str, pdu: EventBase) -> None:
"""We have received a leave event for a room. Fully process it."""
event = pdu
logger.debug(
"on_send_leave_request: Got event: %s, signatures: %s",
event.event_id,
event.signatures,
)
if get_domain_from_id(event.sender) != origin:
logger.info(
"Got /send_leave request for user %r from different origin %s",
event.sender,
origin,
)
raise SynapseError(403, "User not from origin", Codes.FORBIDDEN)
event.internal_metadata.outlier = False
# Send this event on behalf of the other server.
#
# The remote server isn't a full participant in the room at this point, so
# may not have an up-to-date list of the other homeservers participating in
# the room, so we send it on their behalf.
event.internal_metadata.send_on_behalf_of = origin
context = await self.state_handler.compute_event_context(event)
await self._auth_and_persist_event(origin, event, context)
logger.debug(
"on_send_leave_request: After _auth_and_persist_event: %s, sigs: %s",
event.event_id,
event.signatures,
)
return None
@log_function @log_function
async def on_make_knock_request( async def on_make_knock_request(
self, origin: str, room_id: str, user_id: str self, origin: str, room_id: str, user_id: str
@ -2061,34 +1949,38 @@ class FederationHandler(BaseHandler):
return event return event
@log_function @log_function
async def on_send_knock_request( async def on_send_membership_event(
self, origin: str, event: EventBase self, origin: str, event: EventBase
) -> EventContext: ) -> EventContext:
""" """
We have received a knock event for a room. Verify that event and send it into the room We have received a join/leave/knock event for a room.
on the knocking homeserver's behalf.
Verify that event and send it into the room on the remote homeserver's behalf.
Args: Args:
origin: The remote homeserver of the knocking user. origin: The homeserver of the remote (joining/invited/knocking) user.
event: The knocking member event that has been signed by the remote homeserver. event: The member event that has been signed by the remote homeserver.
Returns: Returns:
The context of the event after inserting it into the room graph. The context of the event after inserting it into the room graph.
""" """
logger.debug( logger.debug(
"on_send_knock_request: Got event: %s, signatures: %s", "on_send_membership_event: Got event: %s, signatures: %s",
event.event_id, event.event_id,
event.signatures, event.signatures,
) )
if get_domain_from_id(event.sender) != origin: if get_domain_from_id(event.sender) != origin:
logger.info( logger.info(
"Got /send_knock request for user %r from different origin %s", "Got send_membership request for user %r from different origin %s",
event.sender, event.sender,
origin, origin,
) )
raise SynapseError(403, "User not from origin", Codes.FORBIDDEN) raise SynapseError(403, "User not from origin", Codes.FORBIDDEN)
if event.sender != event.state_key:
raise SynapseError(400, "state_key and sender must match", Codes.BAD_JSON)
event.internal_metadata.outlier = False event.internal_metadata.outlier = False
# Send this event on behalf of the other server. # Send this event on behalf of the other server.
@ -2100,19 +1992,52 @@ class FederationHandler(BaseHandler):
context = await self.state_handler.compute_event_context(event) context = await self.state_handler.compute_event_context(event)
event_allowed = await self.third_party_event_rules.check_event_allowed( # for joins, we need to check the restrictions of restricted rooms
event, context if event.membership == Membership.JOIN:
) await self._check_join_restrictions(context, event)
if not event_allowed:
logger.info("Sending of knock %s forbidden by third-party rules", event) # for knock events, we run the third-party event rules. It's not entirely clear
raise SynapseError( # why we don't do this for other sorts of membership events.
403, "This event is not allowed in this context", Codes.FORBIDDEN if event.membership == Membership.KNOCK:
event_allowed = await self.third_party_event_rules.check_event_allowed(
event, context
) )
if not event_allowed:
logger.info("Sending of knock %s forbidden by third-party rules", event)
raise SynapseError(
403, "This event is not allowed in this context", Codes.FORBIDDEN
)
await self._auth_and_persist_event(origin, event, context) await self._auth_and_persist_event(origin, event, context)
return context return context
async def _check_join_restrictions(
self, context: EventContext, event: EventBase
) -> None:
"""Check that restrictions in restricted join rules are matched
Called when we receive a join event via send_join.
Raises an auth error if the restrictions are not matched.
"""
prev_state_ids = await context.get_prev_state_ids()
# Check if the user is already in the room or invited to the room.
user_id = event.state_key
prev_member_event_id = prev_state_ids.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)
# Check if the member should be allowed access via membership in a space.
await self._event_auth_handler.check_restricted_join_rules(
prev_state_ids,
event.room_version,
user_id,
prev_member_event,
)
async def get_state_for_pdu(self, room_id: str, event_id: str) -> List[EventBase]: async def get_state_for_pdu(self, room_id: str, event_id: str) -> List[EventBase]:
"""Returns the state at the event. i.e. not including said event.""" """Returns the state at the event. i.e. not including said event."""

2
tests/handlers/test_federation.py
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@ -251,7 +251,7 @@ class FederationTestCase(unittest.HomeserverTestCase):
join_event.signatures[other_server] = {"x": "y"} join_event.signatures[other_server] = {"x": "y"}
with LoggingContext("send_join"): with LoggingContext("send_join"):
d = run_in_background( d = run_in_background(
self.handler.on_send_join_request, other_server, join_event self.handler.on_send_membership_event, other_server, join_event
) )
self.get_success(d) self.get_success(d)

2
tests/replication/test_federation_sender_shard.py
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@ -228,7 +228,7 @@ class FederationSenderTestCase(BaseMultiWorkerStreamTestCase):
builder.build(prev_event_ids=prev_event_ids, auth_event_ids=None) builder.build(prev_event_ids=prev_event_ids, auth_event_ids=None)
) )
self.get_success(federation.on_send_join_request(remote_server, join_event)) self.get_success(federation.on_send_membership_event(remote_server, join_event))
self.replicate() self.replicate()
return room return room

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