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, 139 insertions, 0 deletions

diff --git a/tests/rest/media/test_domain_blocking.py b/tests/rest/media/test_domain_blocking.py
new file mode 100644
index 0000000000..9beeeab843
--- /dev/null
+++ b/tests/rest/media/test_domain_blocking.py
@@ -0,0 +1,139 @@
+# Copyright 2023 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from typing import Dict
+
+from twisted.test.proto_helpers import MemoryReactor
+from twisted.web.resource import Resource
+
+from synapse.media._base import FileInfo
+from synapse.server import HomeServer
+from synapse.util import Clock
+
+from tests import unittest
+from tests.test_utils import SMALL_PNG
+from tests.unittest import override_config
+
+
+class MediaDomainBlockingTests(unittest.HomeserverTestCase):
+    remote_media_id = "doesnotmatter"
+    remote_server_name = "evil.com"
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.store = hs.get_datastores().main
+
+        # Inject a piece of media. We'll use this to ensure we're returning a sane
+        # response when we're not supposed to block it, distinguishing a media block
+        # from a regular 404.
+        file_id = "abcdefg12345"
+        file_info = FileInfo(server_name=self.remote_server_name, file_id=file_id)
+        with hs.get_media_repository().media_storage.store_into_file(file_info) as (
+            f,
+            fname,
+            finish,
+        ):
+            f.write(SMALL_PNG)
+            self.get_success(finish())
+
+        self.get_success(
+            self.store.store_cached_remote_media(
+                origin=self.remote_server_name,
+                media_id=self.remote_media_id,
+                media_type="image/png",
+                media_length=1,
+                time_now_ms=clock.time_msec(),
+                upload_name="test.png",
+                filesystem_id=file_id,
+            )
+        )
+
+    def create_resource_dict(self) -> Dict[str, Resource]:
+        # We need to manually set the resource tree to include media, the
+        # default only does `/_matrix/client` APIs.
+        return {"/_matrix/media": self.hs.get_media_repository_resource()}
+
+    @override_config(
+        {
+            # Disable downloads from the domain we'll be trying to download from.
+            # Should result in a 404.
+            "prevent_media_downloads_from": ["evil.com"]
+        }
+    )
+    def test_cannot_download_blocked_media(self) -> None:
+        """
+        Tests to ensure that remote media which is blocked cannot be downloaded.
+        """
+        response = self.make_request(
+            "GET",
+            f"/_matrix/media/v3/download/evil.com/{self.remote_media_id}",
+            shorthand=False,
+        )
+        self.assertEqual(response.code, 404)
+
+    @override_config(
+        {
+            # Disable downloads from a domain we won't be requesting downloads from.
+            # This proves we haven't broken anything.
+            "prevent_media_downloads_from": ["not-listed.com"]
+        }
+    )
+    def test_remote_media_normally_unblocked(self) -> None:
+        """
+        Tests to ensure that remote media is normally able to be downloaded
+        when no domain block is in place.
+        """
+        response = self.make_request(
+            "GET",
+            f"/_matrix/media/v3/download/evil.com/{self.remote_media_id}",
+            shorthand=False,
+        )
+        self.assertEqual(response.code, 200)
+
+    @override_config(
+        {
+            # Disable downloads from the domain we'll be trying to download from.
+            # Should result in a 404.
+            "prevent_media_downloads_from": ["evil.com"],
+            "dynamic_thumbnails": True,
+        }
+    )
+    def test_cannot_download_blocked_media_thumbnail(self) -> None:
+        """
+        Same test as test_cannot_download_blocked_media but for thumbnails.
+        """
+        response = self.make_request(
+            "GET",
+            f"/_matrix/media/v3/thumbnail/evil.com/{self.remote_media_id}?width=100&height=100",
+            shorthand=False,
+            content={"width": 100, "height": 100},
+        )
+        self.assertEqual(response.code, 404)
+
+    @override_config(
+        {
+            # Disable downloads from a domain we won't be requesting downloads from.
+            # This proves we haven't broken anything.
+            "prevent_media_downloads_from": ["not-listed.com"],
+            "dynamic_thumbnails": True,
+        }
+    )
+    def test_remote_media_thumbnail_normally_unblocked(self) -> None:
+        """
+        Same test as test_remote_media_normally_unblocked but for thumbnails.
+        """
+        response = self.make_request(
+            "GET",
+            f"/_matrix/media/v3/thumbnail/evil.com/{self.remote_media_id}?width=100&height=100",
+            shorthand=False,
+        )
+        self.assertEqual(response.code, 200)