Add config option to prevent media downloads from listed domains. (#15197)

This stops media (and thumbnails) from being accessed from the
listed domains. It does not delete any already locally cached media,
but will prevent accessing it.

Note that admin APIs are unaffected by this change.

1 files changed, 9 insertions, 0 deletions

diff --git a/synapse/rest/media/thumbnail_resource.py b/synapse/rest/media/thumbnail_resource.py
index a6396fb05a..661e604b85 100644
--- a/synapse/rest/media/thumbnail_resource.py
+++ b/synapse/rest/media/thumbnail_resource.py
@@ -60,6 +60,7 @@ class ThumbnailResource(DirectServeJsonResource):
         self.media_storage = media_storage
         self.dynamic_thumbnails = hs.config.media.dynamic_thumbnails
         self._is_mine_server_name = hs.is_mine_server_name
+        self.prevent_media_downloads_from = hs.config.media.prevent_media_downloads_from
 
     async def _async_render_GET(self, request: SynapseRequest) -> None:
         set_cors_headers(request)
@@ -82,6 +83,14 @@ class ThumbnailResource(DirectServeJsonResource):
                 )
             self.media_repo.mark_recently_accessed(None, media_id)
         else:
+            # Don't let users download media from configured domains, even if it
+            # is already downloaded. This is Trust & Safety tooling to make some
+            # media inaccessible to local users.
+            # See `prevent_media_downloads_from` config docs for more info.
+            if server_name in self.prevent_media_downloads_from:
+                respond_404(request)
+                return
+
             if self.dynamic_thumbnails:
                 await self._select_or_generate_remote_thumbnail(
                     request, server_name, media_id, width, height, method, m_type