Allow server admin to get admin bit in rooms where local user is an admin (#8756)

This adds an admin API that allows a server admin to get power in a room if a local user has power in a room. Will also invite the user if they're not in the room and its a private room. Can specify another user (rather than the admin user) to be granted power.

Co-authored-by: Matthew Hodgson <matthew@matrix.org>

5 files changed, 294 insertions, 3 deletions

diff --git a/changelog.d/8756.feature b/changelog.d/8756.feature
new file mode 100644
index 0000000000..03eb79fb0a
--- /dev/null
+++ b/changelog.d/8756.feature
@@ -0,0 +1 @@
+Add admin API that lets server admins get power in rooms in which local users have power.
diff --git a/docs/admin_api/rooms.md b/docs/admin_api/rooms.md
index d7b1740fe3..9e560003a9 100644
--- a/docs/admin_api/rooms.md
+++ b/docs/admin_api/rooms.md
@@ -8,6 +8,7 @@
   * [Parameters](#parameters-1)
   * [Response](#response)
   * [Undoing room shutdowns](#undoing-room-shutdowns)
+- [Make Room Admin API](#make-room-admin-api)
 
 # List Room API
 
@@ -467,6 +468,7 @@ The following fields are returned in the JSON response body:
                     the old room to the new.
 * `new_room_id` - A string representing the room ID of the new room.
 
+
 ## Undoing room shutdowns
 
 *Note*: This guide may be outdated by the time you read it. By nature of room shutdowns being performed at the database level,
@@ -492,4 +494,20 @@ You will have to manually handle, if you so choose, the following:
 
 * Aliases that would have been redirected to the Content Violation room.
 * Users that would have been booted from the room (and will have been force-joined to the Content Violation room).
-* Removal of the Content Violation room if desired.
\ No newline at end of file
+* Removal of the Content Violation room if desired.
+
+
+# Make Room Admin API
+
+Grants another user the highest power available to a local user who is in the room.
+If the user is not in the room, and it is not publicly joinable, then invite the user.
+
+By default the server admin (the caller) is granted power, but another user can
+optionally be specified, e.g.:
+
+```
+    POST /_synapse/admin/v1/rooms/<room_id_or_alias>/make_room_admin
+    {
+        "user_id": "@foo:example.com"
+    }
+```
diff --git a/synapse/rest/admin/__init__.py b/synapse/rest/admin/__init__.py
index 55ddebb4fe..6f7dc06503 100644
--- a/synapse/rest/admin/__init__.py
+++ b/synapse/rest/admin/__init__.py
@@ -38,6 +38,7 @@ from synapse.rest.admin.rooms import (
     DeleteRoomRestServlet,
     JoinRoomAliasServlet,
     ListRoomRestServlet,
+    MakeRoomAdminRestServlet,
     RoomMembersRestServlet,
     RoomRestServlet,
     ShutdownRoomRestServlet,
@@ -228,6 +229,7 @@ def register_servlets(hs, http_server):
     EventReportDetailRestServlet(hs).register(http_server)
     EventReportsRestServlet(hs).register(http_server)
     PushersRestServlet(hs).register(http_server)
+    MakeRoomAdminRestServlet(hs).register(http_server)
 
 
 def register_servlets_for_client_rest_resource(hs, http_server):
diff --git a/synapse/rest/admin/rooms.py b/synapse/rest/admin/rooms.py
index b902af8028..ab7cc9102a 100644
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -16,8 +16,8 @@ import logging
 from http import HTTPStatus
 from typing import TYPE_CHECKING, List, Optional, Tuple
 
-from synapse.api.constants import EventTypes, JoinRules
-from synapse.api.errors import Codes, NotFoundError, SynapseError
+from synapse.api.constants import EventTypes, JoinRules, Membership
+from synapse.api.errors import AuthError, Codes, NotFoundError, SynapseError
 from synapse.http.servlet import (
     RestServlet,
     assert_params_in_dict,
@@ -37,6 +37,7 @@ from synapse.types import JsonDict, RoomAlias, RoomID, UserID, create_requester
 if TYPE_CHECKING:
     from synapse.server import HomeServer
 
+
 logger = logging.getLogger(__name__)
 
 
@@ -367,3 +368,134 @@ class JoinRoomAliasServlet(RestServlet):
         )
 
         return 200, {"room_id": room_id}
+
+
+class MakeRoomAdminRestServlet(RestServlet):
+    """Allows a server admin to get power in a room if a local user has power in
+    a room. Will also invite the user if they're not in the room and it's a
+    private room. Can specify another user (rather than the admin user) to be
+    granted power, e.g.:
+
+        POST/_synapse/admin/v1/rooms/<room_id_or_alias>/make_room_admin
+        {
+            "user_id": "@foo:example.com"
+        }
+    """
+
+    PATTERNS = admin_patterns("/rooms/(?P<room_identifier>[^/]*)/make_room_admin")
+
+    def __init__(self, hs: "HomeServer"):
+        self.hs = hs
+        self.auth = hs.get_auth()
+        self.room_member_handler = hs.get_room_member_handler()
+        self.event_creation_handler = hs.get_event_creation_handler()
+        self.state_handler = hs.get_state_handler()
+        self.is_mine_id = hs.is_mine_id
+
+    async def on_POST(self, request, room_identifier):
+        requester = await self.auth.get_user_by_req(request)
+        await assert_user_is_admin(self.auth, requester.user)
+        content = parse_json_object_from_request(request, allow_empty_body=True)
+
+        # Resolve to a room ID, if necessary.
+        if RoomID.is_valid(room_identifier):
+            room_id = room_identifier
+        elif RoomAlias.is_valid(room_identifier):
+            room_alias = RoomAlias.from_string(room_identifier)
+            room_id, _ = await self.room_member_handler.lookup_room_alias(room_alias)
+            room_id = room_id.to_string()
+        else:
+            raise SynapseError(
+                400, "%s was not legal room ID or room alias" % (room_identifier,)
+            )
+
+        # Which user to grant room admin rights to.
+        user_to_add = content.get("user_id", requester.user.to_string())
+
+        # Figure out which local users currently have power in the room, if any.
+        room_state = await self.state_handler.get_current_state(room_id)
+        if not room_state:
+            raise SynapseError(400, "Server not in room")
+
+        create_event = room_state[(EventTypes.Create, "")]
+        power_levels = room_state.get((EventTypes.PowerLevels, ""))
+
+        if power_levels is not None:
+            # We pick the local user with the highest power.
+            user_power = power_levels.content.get("users", {})
+            admin_users = [
+                user_id for user_id in user_power if self.is_mine_id(user_id)
+            ]
+            admin_users.sort(key=lambda user: user_power[user])
+
+            if not admin_users:
+                raise SynapseError(400, "No local admin user in room")
+
+            admin_user_id = admin_users[-1]
+
+            pl_content = power_levels.content
+        else:
+            # If there is no power level events then the creator has rights.
+            pl_content = {}
+            admin_user_id = create_event.sender
+            if not self.is_mine_id(admin_user_id):
+                raise SynapseError(
+                    400, "No local admin user in room",
+                )
+
+        # Grant the user power equal to the room admin by attempting to send an
+        # updated power level event.
+        new_pl_content = dict(pl_content)
+        new_pl_content["users"] = dict(pl_content.get("users", {}))
+        new_pl_content["users"][user_to_add] = new_pl_content["users"][admin_user_id]
+
+        fake_requester = create_requester(
+            admin_user_id, authenticated_entity=requester.authenticated_entity,
+        )
+
+        try:
+            await self.event_creation_handler.create_and_send_nonmember_event(
+                fake_requester,
+                event_dict={
+                    "content": new_pl_content,
+                    "sender": admin_user_id,
+                    "type": EventTypes.PowerLevels,
+                    "state_key": "",
+                    "room_id": room_id,
+                },
+            )
+        except AuthError:
+            # The admin user we found turned out not to have enough power.
+            raise SynapseError(
+                400, "No local admin user in room with power to update power levels."
+            )
+
+        # Now we check if the user we're granting admin rights to is already in
+        # the room. If not and it's not a public room we invite them.
+        member_event = room_state.get((EventTypes.Member, user_to_add))
+        is_joined = False
+        if member_event:
+            is_joined = member_event.content["membership"] in (
+                Membership.JOIN,
+                Membership.INVITE,
+            )
+
+        if is_joined:
+            return 200, {}
+
+        join_rules = room_state.get((EventTypes.JoinRules, ""))
+        is_public = False
+        if join_rules:
+            is_public = join_rules.content.get("join_rule") == JoinRules.PUBLIC
+
+        if is_public:
+            return 200, {}
+
+        await self.room_member_handler.update_membership(
+            fake_requester,
+            target=UserID.from_string(user_to_add),
+            room_id=room_id,
+            action=Membership.INVITE,
+        )
+
+        return 200, {}
diff --git a/tests/rest/admin/test_room.py b/tests/rest/admin/test_room.py
index 014c30287a..60a5fcecf7 100644
--- a/tests/rest/admin/test_room.py
+++ b/tests/rest/admin/test_room.py
@@ -20,6 +20,7 @@ from typing import List, Optional
 from mock import Mock
 
 import synapse.rest.admin
+from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import Codes
 from synapse.rest.client.v1 import directory, events, login, room
 
@@ -1432,6 +1433,143 @@ class JoinAliasRoomTestCase(unittest.HomeserverTestCase):
         self.assertEqual(private_room_id, channel.json_body["joined_rooms"][0])
 
 
+class MakeRoomAdminTestCase(unittest.HomeserverTestCase):
+    servlets = [
+        synapse.rest.admin.register_servlets,
+        room.register_servlets,
+        login.register_servlets,
+    ]
+
+    def prepare(self, reactor, clock, homeserver):
+        self.admin_user = self.register_user("admin", "pass", admin=True)
+        self.admin_user_tok = self.login("admin", "pass")
+
+        self.creator = self.register_user("creator", "test")
+        self.creator_tok = self.login("creator", "test")
+
+        self.second_user_id = self.register_user("second", "test")
+        self.second_tok = self.login("second", "test")
+
+        self.public_room_id = self.helper.create_room_as(
+            self.creator, tok=self.creator_tok, is_public=True
+        )
+        self.url = "/_synapse/admin/v1/rooms/{}/make_room_admin".format(
+            self.public_room_id
+        )
+
+    def test_public_room(self):
+        """Test that getting admin in a public room works.
+        """
+        room_id = self.helper.create_room_as(
+            self.creator, tok=self.creator_tok, is_public=True
+        )
+
+        channel = self.make_request(
+            "POST",
+            "/_synapse/admin/v1/rooms/{}/make_room_admin".format(room_id),
+            content={},
+            access_token=self.admin_user_tok,
+        )
+
+        self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+
+        # Now we test that we can join the room and ban a user.
+        self.helper.join(room_id, self.admin_user, tok=self.admin_user_tok)
+        self.helper.change_membership(
+            room_id,
+            self.admin_user,
+            "@test:test",
+            Membership.BAN,
+            tok=self.admin_user_tok,
+        )
+
+    def test_private_room(self):
+        """Test that getting admin in a private room works and we get invited.
+        """
+        room_id = self.helper.create_room_as(
+            self.creator, tok=self.creator_tok, is_public=False,
+        )
+
+        channel = self.make_request(
+            "POST",
+            "/_synapse/admin/v1/rooms/{}/make_room_admin".format(room_id),
+            content={},
+            access_token=self.admin_user_tok,
+        )
+
+        self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+
+        # Now we test that we can join the room (we should have received an
+        # invite) and can ban a user.
+        self.helper.join(room_id, self.admin_user, tok=self.admin_user_tok)
+        self.helper.change_membership(
+            room_id,
+            self.admin_user,
+            "@test:test",
+            Membership.BAN,
+            tok=self.admin_user_tok,
+        )
+
+    def test_other_user(self):
+        """Test that giving admin in a public room works to a non-admin user works.
+        """
+        room_id = self.helper.create_room_as(
+            self.creator, tok=self.creator_tok, is_public=True
+        )
+
+        channel = self.make_request(
+            "POST",
+            "/_synapse/admin/v1/rooms/{}/make_room_admin".format(room_id),
+            content={"user_id": self.second_user_id},
+            access_token=self.admin_user_tok,
+        )
+
+        self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
+
+        # Now we test that we can join the room and ban a user.
+        self.helper.join(room_id, self.second_user_id, tok=self.second_tok)
+        self.helper.change_membership(
+            room_id,
+            self.second_user_id,
+            "@test:test",
+            Membership.BAN,
+            tok=self.second_tok,
+        )
+
+    def test_not_enough_power(self):
+        """Test that we get a sensible error if there are no local room admins.
+        """
+        room_id = self.helper.create_room_as(
+            self.creator, tok=self.creator_tok, is_public=True
+        )
+
+        # The creator drops admin rights in the room.
+        pl = self.helper.get_state(
+            room_id, EventTypes.PowerLevels, tok=self.creator_tok
+        )
+        pl["users"][self.creator] = 0
+        self.helper.send_state(
+            room_id, EventTypes.PowerLevels, body=pl, tok=self.creator_tok
+        )
+
+        channel = self.make_request(
+            "POST",
+            "/_synapse/admin/v1/rooms/{}/make_room_admin".format(room_id),
+            content={},
+            access_token=self.admin_user_tok,
+        )
+
+        # We expect this to fail with a 400 as there are no room admins.
+        #
+        # (Note we assert the error message to ensure that it's not denied for
+        # some other reason)
+        self.assertEqual(400, int(channel.result["code"]), msg=channel.result["body"])
+        self.assertEqual(
+            channel.json_body["error"],
+            "No local admin user in room with power to update power levels.",
+        )
+
+
 PURGE_TABLES = [
     "current_state_events",
     "event_backward_extremities",