add options to require an access_token to GET /profile and /publicRooms on CS API (#5083)

This commit adds two config options:

* `restrict_public_rooms_to_local_users`

Requires auth to fetch the public rooms directory through the CS API and disables fetching it through the federation API.

* `require_auth_for_profile_requests`

When set to `true`, requires that requests to `/profile` over the CS API are authenticated, and only returns the user's profile if the requester shares a room with the profile's owner, as per MSC1301.

MSC1301 also specifies a behaviour for federation (only returning the profile if the server asking for it shares a room with the profile's owner), but that's currently really non-trivial to do in a not too expensive way. Next step is writing down a MSC that allows a HS to specify which user sent the profile query. In this implementation, Synapse won't send a profile query over federation if it doesn't believe it already shares a room with the profile's owner, though.

Groups have been intentionally omitted from this commit.

5 files changed, 114 insertions, 12 deletions

diff --git a/synapse/config/server.py b/synapse/config/server.py
index 147a976485..8dce75c56a 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -72,6 +72,19 @@ class ServerConfig(Config):
         # master, potentially causing inconsistency.
         self.enable_media_repo = config.get("enable_media_repo", True)
 
+        # Whether to require authentication to retrieve profile data (avatars,
+        # display names) of other users through the client API.
+        self.require_auth_for_profile_requests = config.get(
+            "require_auth_for_profile_requests", False,
+        )
+
+        # If set to 'True', requires authentication to access the server's
+        # public rooms directory through the client API, and forbids any other
+        # homeserver to fetch it via federation.
+        self.restrict_public_rooms_to_local_users = config.get(
+            "restrict_public_rooms_to_local_users", False,
+        )
+
         # whether to enable search. If disabled, new entries will not be inserted
         # into the search tables and they will not be indexed. Users will receive
         # errors when attempting to search for messages.
@@ -327,6 +340,20 @@ class ServerConfig(Config):
         #
         #use_presence: false
 
+        # Whether to require authentication to retrieve profile data (avatars,
+        # display names) of other users through the client API. Defaults to
+        # 'false'. Note that profile data is also available via the federation
+        # API, so this setting is of limited value if federation is enabled on
+        # the server.
+        #
+        #require_auth_for_profile_requests: true
+
+        # If set to 'true', requires authentication to access the server's
+        # public rooms directory through the client API, and forbids any other
+        # homeserver to fetch it via federation. Defaults to 'false'.
+        #
+        #restrict_public_rooms_to_local_users: true
+
         # The GC threshold parameters to pass to `gc.set_threshold`, if defined
         #
         #gc_thresholds: [700, 10, 10]
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index 452599e1a1..9030eb18c5 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -716,8 +716,17 @@ class PublicRoomList(BaseFederationServlet):
 
     PATH = "/publicRooms"
 
+    def __init__(self, handler, authenticator, ratelimiter, server_name, deny_access):
+        super(PublicRoomList, self).__init__(
+            handler, authenticator, ratelimiter, server_name,
+        )
+        self.deny_access = deny_access
+
     @defer.inlineCallbacks
     def on_GET(self, origin, content, query):
+        if self.deny_access:
+            raise FederationDeniedError(origin)
+
         limit = parse_integer_from_args(query, "limit", 0)
         since_token = parse_string_from_args(query, "since", None)
         include_all_networks = parse_boolean_from_args(
@@ -1417,6 +1426,7 @@ def register_servlets(hs, resource, authenticator, ratelimiter, servlet_groups=N
                 authenticator=authenticator,
                 ratelimiter=ratelimiter,
                 server_name=hs.hostname,
+                deny_access=hs.config.restrict_public_rooms_to_local_users,
             ).register(resource)
 
     if "group_server" in servlet_groups:
diff --git a/synapse/handlers/profile.py b/synapse/handlers/profile.py
index a65c98ff5c..91fc718ff8 100644
--- a/synapse/handlers/profile.py
+++ b/synapse/handlers/profile.py
@@ -53,6 +53,7 @@ class BaseProfileHandler(BaseHandler):
     @defer.inlineCallbacks
     def get_profile(self, user_id):
         target_user = UserID.from_string(user_id)
+
         if self.hs.is_mine(target_user):
             try:
                 displayname = yield self.store.get_profile_displayname(
@@ -283,6 +284,48 @@ class BaseProfileHandler(BaseHandler):
                     room_id, str(e)
                 )
 
+    @defer.inlineCallbacks
+    def check_profile_query_allowed(self, target_user, requester=None):
+        """Checks whether a profile query is allowed. If the
+        'require_auth_for_profile_requests' config flag is set to True and a
+        'requester' is provided, the query is only allowed if the two users
+        share a room.
+
+        Args:
+            target_user (UserID): The owner of the queried profile.
+            requester (None|UserID): The user querying for the profile.
+
+        Raises:
+            SynapseError(403): The two users share no room, or ne user couldn't
+                be found to be in any room the server is in, and therefore the query
+                is denied.
+        """
+        # Implementation of MSC1301: don't allow looking up profiles if the
+        # requester isn't in the same room as the target. We expect requester to
+        # be None when this function is called outside of a profile query, e.g.
+        # when building a membership event. In this case, we must allow the
+        # lookup.
+        if not self.hs.config.require_auth_for_profile_requests or not requester:
+            return
+
+        try:
+            requester_rooms = yield self.store.get_rooms_for_user(
+                requester.to_string()
+            )
+            target_user_rooms = yield self.store.get_rooms_for_user(
+                target_user.to_string(),
+            )
+
+            # Check if the room lists have no elements in common.
+            if requester_rooms.isdisjoint(target_user_rooms):
+                raise SynapseError(403, "Profile isn't available", Codes.FORBIDDEN)
+        except StoreError as e:
+            if e.code == 404:
+                # This likely means that one of the users doesn't exist,
+                # so we act as if we couldn't find the profile.
+                raise SynapseError(403, "Profile isn't available", Codes.FORBIDDEN)
+            raise
+
 
 class MasterProfileHandler(BaseProfileHandler):
     PROFILE_UPDATE_MS = 60 * 1000
diff --git a/synapse/rest/client/v1/profile.py b/synapse/rest/client/v1/profile.py
index a23edd8fe5..eac1966c5e 100644
--- a/synapse/rest/client/v1/profile.py
+++ b/synapse/rest/client/v1/profile.py
@@ -31,11 +31,17 @@ class ProfileDisplaynameRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
+        requester_user = None
+
+        if self.hs.config.require_auth_for_profile_requests:
+            requester = yield self.auth.get_user_by_req(request)
+            requester_user = requester.user
+
         user = UserID.from_string(user_id)
 
-        displayname = yield self.profile_handler.get_displayname(
-            user,
-        )
+        yield self.profile_handler.check_profile_query_allowed(user, requester_user)
+
+        displayname = yield self.profile_handler.get_displayname(user)
 
         ret = {}
         if displayname is not None:
@@ -74,11 +80,17 @@ class ProfileAvatarURLRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
+        requester_user = None
+
+        if self.hs.config.require_auth_for_profile_requests:
+            requester = yield self.auth.get_user_by_req(request)
+            requester_user = requester.user
+
         user = UserID.from_string(user_id)
 
-        avatar_url = yield self.profile_handler.get_avatar_url(
-            user,
-        )
+        yield self.profile_handler.check_profile_query_allowed(user, requester_user)
+
+        avatar_url = yield self.profile_handler.get_avatar_url(user)
 
         ret = {}
         if avatar_url is not None:
@@ -116,14 +128,18 @@ class ProfileRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
+        requester_user = None
+
+        if self.hs.config.require_auth_for_profile_requests:
+            requester = yield self.auth.get_user_by_req(request)
+            requester_user = requester.user
+
         user = UserID.from_string(user_id)
 
-        displayname = yield self.profile_handler.get_displayname(
-            user,
-        )
-        avatar_url = yield self.profile_handler.get_avatar_url(
-            user,
-        )
+        yield self.profile_handler.check_profile_query_allowed(user, requester_user)
+
+        displayname = yield self.profile_handler.get_displayname(user)
+        avatar_url = yield self.profile_handler.get_avatar_url(user)
 
         ret = {}
         if displayname is not None:
diff --git a/synapse/rest/client/v1/room.py b/synapse/rest/client/v1/room.py
index 48da4d557f..fab04965cb 100644
--- a/synapse/rest/client/v1/room.py
+++ b/synapse/rest/client/v1/room.py
@@ -301,6 +301,12 @@ class PublicRoomListRestServlet(ClientV1RestServlet):
         try:
             yield self.auth.get_user_by_req(request, allow_guest=True)
         except AuthError as e:
+            # Option to allow servers to require auth when accessing
+            # /publicRooms via CS API. This is especially helpful in private
+            # federations.
+            if self.hs.config.restrict_public_rooms_to_local_users:
+                raise
+
             # We allow people to not be authed if they're just looking at our
             # room list, but require auth when we proxy the request.
             # In both cases we call the auth function, as that has the side