Implement cancellation support/protection for module callbacks (#12568)

There's no guarantee that module callbacks will handle cancellation
appropriately. Protect module callbacks with read semantics from
cancellation and avoid swallowing `CancelledError`s that arise.

Other module callbacks, such as the `on_*` callbacks, are presumed to
live on code paths that involve writes and aren't cancellation-friendly.
These module callbacks have been left alone.

Signed-off-by: Sean Quah <seanq@element.io>

1 files changed, 25 insertions, 11 deletions

diff --git a/synapse/events/spamcheck.py b/synapse/events/spamcheck.py
index cd80fcf9d1..3b6795d40f 100644
--- a/synapse/events/spamcheck.py
+++ b/synapse/events/spamcheck.py
@@ -31,7 +31,7 @@ from synapse.rest.media.v1._base import FileInfo
 from synapse.rest.media.v1.media_storage import ReadableFileWrapper
 from synapse.spam_checker_api import RegistrationBehaviour
 from synapse.types import RoomAlias, UserProfile
-from synapse.util.async_helpers import maybe_awaitable
+from synapse.util.async_helpers import delay_cancellation, maybe_awaitable
 
 if TYPE_CHECKING:
     import synapse.events
@@ -255,7 +255,7 @@ class SpamChecker:
             will be used as the error message returned to the user.
         """
         for callback in self._check_event_for_spam_callbacks:
-            res: Union[bool, str] = await callback(event)
+            res: Union[bool, str] = await delay_cancellation(callback(event))
             if res:
                 return res
 
@@ -276,7 +276,10 @@ class SpamChecker:
             Whether the user may join the room
         """
         for callback in self._user_may_join_room_callbacks:
-            if await callback(user_id, room_id, is_invited) is False:
+            may_join_room = await delay_cancellation(
+                callback(user_id, room_id, is_invited)
+            )
+            if may_join_room is False:
                 return False
 
         return True
@@ -297,7 +300,10 @@ class SpamChecker:
             True if the user may send an invite, otherwise False
         """
         for callback in self._user_may_invite_callbacks:
-            if await callback(inviter_userid, invitee_userid, room_id) is False:
+            may_invite = await delay_cancellation(
+                callback(inviter_userid, invitee_userid, room_id)
+            )
+            if may_invite is False:
                 return False
 
         return True
@@ -322,7 +328,10 @@ class SpamChecker:
             True if the user may send the invite, otherwise False
         """
         for callback in self._user_may_send_3pid_invite_callbacks:
-            if await callback(inviter_userid, medium, address, room_id) is False:
+            may_send_3pid_invite = await delay_cancellation(
+                callback(inviter_userid, medium, address, room_id)
+            )
+            if may_send_3pid_invite is False:
                 return False
 
         return True
@@ -339,7 +348,8 @@ class SpamChecker:
             True if the user may create a room, otherwise False
         """
         for callback in self._user_may_create_room_callbacks:
-            if await callback(userid) is False:
+            may_create_room = await delay_cancellation(callback(userid))
+            if may_create_room is False:
                 return False
 
         return True
@@ -359,7 +369,10 @@ class SpamChecker:
             True if the user may create a room alias, otherwise False
         """
         for callback in self._user_may_create_room_alias_callbacks:
-            if await callback(userid, room_alias) is False:
+            may_create_room_alias = await delay_cancellation(
+                callback(userid, room_alias)
+            )
+            if may_create_room_alias is False:
                 return False
 
         return True
@@ -377,7 +390,8 @@ class SpamChecker:
             True if the user may publish the room, otherwise False
         """
         for callback in self._user_may_publish_room_callbacks:
-            if await callback(userid, room_id) is False:
+            may_publish_room = await delay_cancellation(callback(userid, room_id))
+            if may_publish_room is False:
                 return False
 
         return True
@@ -400,7 +414,7 @@ class SpamChecker:
         for callback in self._check_username_for_spam_callbacks:
             # Make a copy of the user profile object to ensure the spam checker cannot
             # modify it.
-            if await callback(user_profile.copy()):
+            if await delay_cancellation(callback(user_profile.copy())):
                 return True
 
         return False
@@ -428,7 +442,7 @@ class SpamChecker:
         """
 
         for callback in self._check_registration_for_spam_callbacks:
-            behaviour = await (
+            behaviour = await delay_cancellation(
                 callback(email_threepid, username, request_info, auth_provider_id)
             )
             assert isinstance(behaviour, RegistrationBehaviour)
@@ -472,7 +486,7 @@ class SpamChecker:
         """
 
         for callback in self._check_media_file_for_spam_callbacks:
-            spam = await callback(file_wrapper, file_info)
+            spam = await delay_cancellation(callback(file_wrapper, file_info))
             if spam:
                 return True