Prepare for authenticated media freeze (#17433)

As part of the rollout of
[MSC3916](https://github.com/matrix-org/matrix-spec-proposals/blob/main/proposals/3916-authentication-for-media.md)
this PR adds support for designating authenticated media and ensuring
that authenticated media is not served over unauthenticated endpoints.

2 files changed, 81 insertions, 6 deletions

diff --git a/synapse/media/media_repository.py b/synapse/media/media_repository.py
index 87c929eb20..8bc92305fe 100644
--- a/synapse/media/media_repository.py
+++ b/synapse/media/media_repository.py
@@ -430,6 +430,7 @@ class MediaRepository:
         media_id: str,
         name: Optional[str],
         max_timeout_ms: int,
+        allow_authenticated: bool = True,
         federation: bool = False,
     ) -> None:
         """Responds to requests for local media, if exists, or returns 404.
@@ -442,6 +443,7 @@ class MediaRepository:
                 the filename in the Content-Disposition header of the response.
             max_timeout_ms: the maximum number of milliseconds to wait for the
                 media to be uploaded.
+            allow_authenticated: whether media marked as authenticated may be served to this request
             federation: whether the local media being fetched is for a federation request
 
         Returns:
@@ -451,6 +453,10 @@ class MediaRepository:
         if not media_info:
             return
 
+        if self.hs.config.media.enable_authenticated_media and not allow_authenticated:
+            if media_info.authenticated:
+                raise NotFoundError()
+
         self.mark_recently_accessed(None, media_id)
 
         media_type = media_info.media_type
@@ -481,6 +487,7 @@ class MediaRepository:
         max_timeout_ms: int,
         ip_address: str,
         use_federation_endpoint: bool,
+        allow_authenticated: bool = True,
     ) -> None:
         """Respond to requests for remote media.
 
@@ -495,6 +502,8 @@ class MediaRepository:
             ip_address: the IP address of the requester
             use_federation_endpoint: whether to request the remote media over the new
                 federation `/download` endpoint
+            allow_authenticated: whether media marked as authenticated may be served to this
+                request
 
         Returns:
             Resolves once a response has successfully been written to request
@@ -526,6 +535,7 @@ class MediaRepository:
                 self.download_ratelimiter,
                 ip_address,
                 use_federation_endpoint,
+                allow_authenticated,
             )
 
         # We deliberately stream the file outside the lock
@@ -548,6 +558,7 @@ class MediaRepository:
         max_timeout_ms: int,
         ip_address: str,
         use_federation: bool,
+        allow_authenticated: bool,
     ) -> RemoteMedia:
         """Gets the media info associated with the remote file, downloading
         if necessary.
@@ -560,6 +571,8 @@ class MediaRepository:
             ip_address: IP address of the requester
             use_federation: if a download is necessary, whether to request the remote file
                 over the federation `/download` endpoint
+            allow_authenticated: whether media marked as authenticated may be served to this
+                request
 
         Returns:
             The media info of the file
@@ -581,6 +594,7 @@ class MediaRepository:
                 self.download_ratelimiter,
                 ip_address,
                 use_federation,
+                allow_authenticated,
             )
 
         # Ensure we actually use the responder so that it releases resources
@@ -598,6 +612,7 @@ class MediaRepository:
         download_ratelimiter: Ratelimiter,
         ip_address: str,
         use_federation_endpoint: bool,
+        allow_authenticated: bool,
     ) -> Tuple[Optional[Responder], RemoteMedia]:
         """Looks for media in local cache, if not there then attempt to
         download from remote server.
@@ -619,6 +634,11 @@ class MediaRepository:
         """
         media_info = await self.store.get_cached_remote_media(server_name, media_id)
 
+        if self.hs.config.media.enable_authenticated_media and not allow_authenticated:
+            # if it isn't cached then don't fetch it or if it's authenticated then don't serve it
+            if not media_info or media_info.authenticated:
+                raise NotFoundError()
+
         # file_id is the ID we use to track the file locally. If we've already
         # seen the file then reuse the existing ID, otherwise generate a new
         # one.
@@ -792,6 +812,11 @@ class MediaRepository:
 
         logger.info("Stored remote media in file %r", fname)
 
+        if self.hs.config.media.enable_authenticated_media:
+            authenticated = True
+        else:
+            authenticated = False
+
         return RemoteMedia(
             media_origin=server_name,
             media_id=media_id,
@@ -802,6 +827,7 @@ class MediaRepository:
             filesystem_id=file_id,
             last_access_ts=time_now_ms,
             quarantined_by=None,
+            authenticated=authenticated,
         )
 
     async def _federation_download_remote_file(
@@ -915,6 +941,11 @@ class MediaRepository:
 
         logger.debug("Stored remote media in file %r", fname)
 
+        if self.hs.config.media.enable_authenticated_media:
+            authenticated = True
+        else:
+            authenticated = False
+
         return RemoteMedia(
             media_origin=server_name,
             media_id=media_id,
@@ -925,6 +956,7 @@ class MediaRepository:
             filesystem_id=file_id,
             last_access_ts=time_now_ms,
             quarantined_by=None,
+            authenticated=authenticated,
         )
 
     def _get_thumbnail_requirements(
@@ -1030,7 +1062,12 @@ class MediaRepository:
             t_len = os.path.getsize(output_path)
 
             await self.store.store_local_thumbnail(
-                media_id, t_width, t_height, t_type, t_method, t_len
+                media_id,
+                t_width,
+                t_height,
+                t_type,
+                t_method,
+                t_len,
             )
 
             return output_path
diff --git a/synapse/media/thumbnailer.py b/synapse/media/thumbnailer.py
index 413a720e40..ef6aa8ccf5 100644
--- a/synapse/media/thumbnailer.py
+++ b/synapse/media/thumbnailer.py
@@ -26,7 +26,7 @@ from typing import TYPE_CHECKING, List, Optional, Tuple, Type
 
 from PIL import Image
 
-from synapse.api.errors import Codes, SynapseError, cs_error
+from synapse.api.errors import Codes, NotFoundError, SynapseError, cs_error
 from synapse.config.repository import THUMBNAIL_SUPPORTED_MEDIA_FORMAT_MAP
 from synapse.http.server import respond_with_json
 from synapse.http.site import SynapseRequest
@@ -274,6 +274,7 @@ class ThumbnailProvider:
         m_type: str,
         max_timeout_ms: int,
         for_federation: bool,
+        allow_authenticated: bool = True,
     ) -> None:
         media_info = await self.media_repo.get_local_media_info(
             request, media_id, max_timeout_ms
@@ -281,6 +282,12 @@ class ThumbnailProvider:
         if not media_info:
             return
 
+        # if the media the thumbnail is generated from is authenticated, don't serve the
+        # thumbnail over an unauthenticated endpoint
+        if self.hs.config.media.enable_authenticated_media and not allow_authenticated:
+            if media_info.authenticated:
+                raise NotFoundError()
+
         thumbnail_infos = await self.store.get_local_media_thumbnails(media_id)
         await self._select_and_respond_with_thumbnail(
             request,
@@ -307,14 +314,20 @@ class ThumbnailProvider:
         desired_type: str,
         max_timeout_ms: int,
         for_federation: bool,
+        allow_authenticated: bool = True,
     ) -> None:
         media_info = await self.media_repo.get_local_media_info(
             request, media_id, max_timeout_ms
         )
-
         if not media_info:
             return
 
+        # if the media the thumbnail is generated from is authenticated, don't serve the
+        # thumbnail over an unauthenticated endpoint
+        if self.hs.config.media.enable_authenticated_media and not allow_authenticated:
+            if media_info.authenticated:
+                raise NotFoundError()
+
         thumbnail_infos = await self.store.get_local_media_thumbnails(media_id)
         for info in thumbnail_infos:
             t_w = info.width == desired_width
@@ -381,14 +394,27 @@ class ThumbnailProvider:
         max_timeout_ms: int,
         ip_address: str,
         use_federation: bool,
+        allow_authenticated: bool = True,
     ) -> None:
         media_info = await self.media_repo.get_remote_media_info(
-            server_name, media_id, max_timeout_ms, ip_address, use_federation
+            server_name,
+            media_id,
+            max_timeout_ms,
+            ip_address,
+            use_federation,
+            allow_authenticated,
         )
         if not media_info:
             respond_404(request)
             return
 
+        # if the media the thumbnail is generated from is authenticated, don't serve the
+        # thumbnail over an unauthenticated endpoint
+        if self.hs.config.media.enable_authenticated_media and not allow_authenticated:
+            if media_info.authenticated:
+                respond_404(request)
+                return
+
         thumbnail_infos = await self.store.get_remote_media_thumbnails(
             server_name, media_id
         )
@@ -446,16 +472,28 @@ class ThumbnailProvider:
         max_timeout_ms: int,
         ip_address: str,
         use_federation: bool,
+        allow_authenticated: bool = True,
     ) -> None:
         # TODO: Don't download the whole remote file
         # We should proxy the thumbnail from the remote server instead of
         # downloading the remote file and generating our own thumbnails.
         media_info = await self.media_repo.get_remote_media_info(
-            server_name, media_id, max_timeout_ms, ip_address, use_federation
+            server_name,
+            media_id,
+            max_timeout_ms,
+            ip_address,
+            use_federation,
+            allow_authenticated,
         )
         if not media_info:
             return
 
+        # if the media the thumbnail is generated from is authenticated, don't serve the
+        # thumbnail over an unauthenticated endpoint
+        if self.hs.config.media.enable_authenticated_media and not allow_authenticated:
+            if media_info.authenticated:
+                raise NotFoundError()
+
         thumbnail_infos = await self.store.get_remote_media_thumbnails(
             server_name, media_id
         )
@@ -485,8 +523,8 @@ class ThumbnailProvider:
         file_id: str,
         url_cache: bool,
         for_federation: bool,
-        server_name: Optional[str] = None,
         media_info: Optional[LocalMedia] = None,
+        server_name: Optional[str] = None,
     ) -> None:
         """
         Respond to a request with an appropriate thumbnail from the previously generated thumbnails.