Add ability to un-shadow-ban via the admin API. (#11347)

5 files changed, 53 insertions, 12 deletions

diff --git a/changelog.d/11347.feature b/changelog.d/11347.feature
new file mode 100644
index 0000000000..b0cb5345a0
--- /dev/null
+++ b/changelog.d/11347.feature
@@ -0,0 +1 @@
+Add admin API to un-shadow-ban a user.
diff --git a/docs/admin_api/user_admin_api.md b/docs/admin_api/user_admin_api.md
index 16ec33b3c1..ba574d795f 100644
--- a/docs/admin_api/user_admin_api.md
+++ b/docs/admin_api/user_admin_api.md
@@ -948,7 +948,7 @@ The following fields are returned in the JSON response body:
 See also the
 [Client-Server API Spec on pushers](https://matrix.org/docs/spec/client_server/latest#get-matrix-client-r0-pushers).
 
-## Shadow-banning users
+## Controlling whether a user is shadow-banned
 
 Shadow-banning is a useful tool for moderating malicious or egregiously abusive users.
 A shadow-banned users receives successful responses to their client-server API requests,
@@ -961,16 +961,22 @@ or broken behaviour for the client. A shadow-banned user will not receive any
 notification and it is generally more appropriate to ban or kick abusive users.
 A shadow-banned user will be unable to contact anyone on the server.
 
-The API is:
+To shadow-ban a user the API is:
 
 ```
 POST /_synapse/admin/v1/users/<user_id>/shadow_ban
 ```
 
+To un-shadow-ban a user the API is:
+
+```
+DELETE /_synapse/admin/v1/users/<user_id>/shadow_ban
+```
+
 To use it, you will need to authenticate by providing an `access_token` for a
 server admin: [Admin API](../usage/administration/admin_api)
 
-An empty JSON dict is returned.
+An empty JSON dict is returned in both cases.
 
 **Parameters**
 
diff --git a/synapse/rest/admin/users.py b/synapse/rest/admin/users.py
index d14fafbbc9..23a8bf1fdb 100644
--- a/synapse/rest/admin/users.py
+++ b/synapse/rest/admin/users.py
@@ -909,7 +909,7 @@ class UserTokenRestServlet(RestServlet):
 
 
 class ShadowBanRestServlet(RestServlet):
-    """An admin API for shadow-banning a user.
+    """An admin API for controlling whether a user is shadow-banned.
 
     A shadow-banned users receives successful responses to their client-server
     API requests, but the events are not propagated into rooms.
@@ -917,13 +917,21 @@ class ShadowBanRestServlet(RestServlet):
     Shadow-banning a user should be used as a tool of last resort and may lead
     to confusing or broken behaviour for the client.
 
-    Example:
+    Example of shadow-banning a user:
 
         POST /_synapse/admin/v1/users/@test:example.com/shadow_ban
         {}
 
         200 OK
         {}
+
+    Example of removing a user from being shadow-banned:
+
+        DELETE /_synapse/admin/v1/users/@test:example.com/shadow_ban
+        {}
+
+        200 OK
+        {}
     """
 
     PATTERNS = admin_patterns("/users/(?P<user_id>[^/]*)/shadow_ban")
@@ -945,6 +953,18 @@ class ShadowBanRestServlet(RestServlet):
 
         return 200, {}
 
+    async def on_DELETE(
+        self, request: SynapseRequest, user_id: str
+    ) -> Tuple[int, JsonDict]:
+        await assert_requester_is_admin(self.auth, request)
+
+        if not self.hs.is_mine_id(user_id):
+            raise SynapseError(400, "Only local users can be shadow-banned")
+
+        await self.store.set_shadow_banned(UserID.from_string(user_id), False)
+
+        return 200, {}
+
 
 class RateLimitRestServlet(RestServlet):
     """An admin API to override ratelimiting for an user.
diff --git a/synapse/storage/databases/main/registration.py b/synapse/storage/databases/main/registration.py
index 6c7d6ba508..5e55440570 100644
--- a/synapse/storage/databases/main/registration.py
+++ b/synapse/storage/databases/main/registration.py
@@ -476,7 +476,7 @@ class RegistrationWorkerStore(CacheInvalidationWorkerStore):
             shadow_banned: true iff the user is to be shadow-banned, false otherwise.
         """
 
-        def set_shadow_banned_txn(txn):
+        def set_shadow_banned_txn(txn: LoggingTransaction) -> None:
             user_id = user.to_string()
             self.db_pool.simple_update_one_txn(
                 txn,
diff --git a/tests/rest/admin/test_user.py b/tests/rest/admin/test_user.py
index 25e8d6cf27..c9fe0f06c2 100644
--- a/tests/rest/admin/test_user.py
+++ b/tests/rest/admin/test_user.py
@@ -3592,31 +3592,34 @@ class ShadowBanRestTestCase(unittest.HomeserverTestCase):
             self.other_user
         )
 
-    def test_no_auth(self):
+    @parameterized.expand(["POST", "DELETE"])
+    def test_no_auth(self, method: str):
         """
         Try to get information of an user without authentication.
         """
-        channel = self.make_request("POST", self.url)
+        channel = self.make_request(method, self.url)
         self.assertEqual(401, channel.code, msg=channel.json_body)
         self.assertEqual(Codes.MISSING_TOKEN, channel.json_body["errcode"])
 
-    def test_requester_is_not_admin(self):
+    @parameterized.expand(["POST", "DELETE"])
+    def test_requester_is_not_admin(self, method: str):
         """
         If the user is not a server admin, an error is returned.
         """
         other_user_token = self.login("user", "pass")
 
-        channel = self.make_request("POST", self.url, access_token=other_user_token)
+        channel = self.make_request(method, self.url, access_token=other_user_token)
         self.assertEqual(403, channel.code, msg=channel.json_body)
         self.assertEqual(Codes.FORBIDDEN, channel.json_body["errcode"])
 
-    def test_user_is_not_local(self):
+    @parameterized.expand(["POST", "DELETE"])
+    def test_user_is_not_local(self, method: str):
         """
         Tests that shadow-banning for a user that is not a local returns a 400
         """
         url = "/_synapse/admin/v1/whois/@unknown_person:unknown_domain"
 
-        channel = self.make_request("POST", url, access_token=self.admin_user_tok)
+        channel = self.make_request(method, url, access_token=self.admin_user_tok)
         self.assertEqual(400, channel.code, msg=channel.json_body)
 
     def test_success(self):
@@ -3636,6 +3639,17 @@ class ShadowBanRestTestCase(unittest.HomeserverTestCase):
         result = self.get_success(self.store.get_user_by_access_token(other_user_token))
         self.assertTrue(result.shadow_banned)
 
+        # Un-shadow-ban the user.
+        channel = self.make_request(
+            "DELETE", self.url, access_token=self.admin_user_tok
+        )
+        self.assertEqual(200, channel.code, msg=channel.json_body)
+        self.assertEqual({}, channel.json_body)
+
+        # Ensure the user is no longer shadow-banned (and the cache was cleared).
+        result = self.get_success(self.store.get_user_by_access_token(other_user_token))
+        self.assertFalse(result.shadow_banned)
+
 
 class RateLimitTestCase(unittest.HomeserverTestCase):