Only do `rc_login` ratelimiting on succesful login.

We were doing this in a number of places which meant that some login
code paths incremented the counter multiple times.

It was also applying ratelimiting to UIA endpoints, which was probably
not intentional.

In particular, some custom auth modules were calling
`check_user_exists`, which incremented the counters, meaning that people
would fail to login sometimes.

1 files changed, 93 insertions, 18 deletions

diff --git a/synapse/rest/client/v1/login.py b/synapse/rest/client/v1/login.py
index 24a0ce74f2..abc210da57 100644
--- a/synapse/rest/client/v1/login.py
+++ b/synapse/rest/client/v1/login.py
@@ -92,8 +92,11 @@ class LoginRestServlet(RestServlet):
         self.auth_handler = self.hs.get_auth_handler()
         self.registration_handler = hs.get_registration_handler()
         self.handlers = hs.get_handlers()
+        self._clock = hs.get_clock()
         self._well_known_builder = WellKnownBuilder(hs)
         self._address_ratelimiter = Ratelimiter()
+        self._account_ratelimiter = Ratelimiter()
+        self._failed_attempts_ratelimiter = Ratelimiter()
 
     def on_GET(self, request):
         flows = []
@@ -202,6 +205,16 @@ class LoginRestServlet(RestServlet):
                 # (See add_threepid in synapse/handlers/auth.py)
                 address = address.lower()
 
+            # We also apply account rate limiting using the 3PID as a key, as
+            # otherwise using 3PID bypasses the ratelimiting based on user ID.
+            self._failed_attempts_ratelimiter.ratelimit(
+                (medium, address),
+                time_now_s=self._clock.time(),
+                rate_hz=self.hs.config.rc_login_failed_attempts.per_second,
+                burst_count=self.hs.config.rc_login_failed_attempts.burst_count,
+                update=False,
+            )
+
             # Check for login providers that support 3pid login types
             (
                 canonical_user_id,
@@ -211,7 +224,8 @@ class LoginRestServlet(RestServlet):
             )
             if canonical_user_id:
                 # Authentication through password provider and 3pid succeeded
-                result = yield self._register_device_with_callback(
+
+                result = yield self._complete_login(
                     canonical_user_id, login_submission, callback_3pid
                 )
                 return result
@@ -225,6 +239,21 @@ class LoginRestServlet(RestServlet):
                 logger.warning(
                     "unknown 3pid identifier medium %s, address %r", medium, address
                 )
+                # We mark that we've failed to log in here, as
+                # `check_password_provider_3pid` might have returned `None` due
+                # to an incorrect password, rather than the account not
+                # existing.
+                #
+                # If it returned None but the 3PID was bound then we won't hit
+                # this code path, which is fine as then the per-user ratelimit
+                # will kick in below.
+                self._failed_attempts_ratelimiter.can_do_action(
+                    (medium, address),
+                    time_now_s=self._clock.time(),
+                    rate_hz=self.hs.config.rc_login_failed_attempts.per_second,
+                    burst_count=self.hs.config.rc_login_failed_attempts.burst_count,
+                    update=True,
+                )
                 raise LoginError(403, "", errcode=Codes.FORBIDDEN)
 
             identifier = {"type": "m.id.user", "user": user_id}
@@ -236,29 +265,84 @@ class LoginRestServlet(RestServlet):
         if "user" not in identifier:
             raise SynapseError(400, "User identifier is missing 'user' key")
 
-        canonical_user_id, callback = yield self.auth_handler.validate_login(
-            identifier["user"], login_submission
+        if identifier["user"].startswith("@"):
+            qualified_user_id = identifier["user"]
+        else:
+            qualified_user_id = UserID(identifier["user"], self.hs.hostname).to_string()
+
+        # Check if we've hit the failed ratelimit (but don't update it)
+        self._failed_attempts_ratelimiter.ratelimit(
+            qualified_user_id.lower(),
+            time_now_s=self._clock.time(),
+            rate_hz=self.hs.config.rc_login_failed_attempts.per_second,
+            burst_count=self.hs.config.rc_login_failed_attempts.burst_count,
+            update=False,
         )
 
-        result = yield self._register_device_with_callback(
+        try:
+            canonical_user_id, callback = yield self.auth_handler.validate_login(
+                identifier["user"], login_submission
+            )
+        except LoginError:
+            # The user has failed to log in, so we need to update the rate
+            # limiter. Using `can_do_action` avoids us raising a ratelimit
+            # exception and masking the LoginError. The actual ratelimiting
+            # should have happened above.
+            self._failed_attempts_ratelimiter.can_do_action(
+                qualified_user_id.lower(),
+                time_now_s=self._clock.time(),
+                rate_hz=self.hs.config.rc_login_failed_attempts.per_second,
+                burst_count=self.hs.config.rc_login_failed_attempts.burst_count,
+                update=True,
+            )
+            raise
+
+        result = yield self._complete_login(
             canonical_user_id, login_submission, callback
         )
         return result
 
     @defer.inlineCallbacks
-    def _register_device_with_callback(self, user_id, login_submission, callback=None):
-        """ Registers a device with a given user_id. Optionally run a callback
-        function after registration has completed.
+    def _complete_login(
+        self, user_id, login_submission, callback=None, create_non_existant_users=False
+    ):
+        """Called when we've successfully authed the user and now need to
+        actually login them in (e.g. create devices). This gets called on
+        all succesful logins.
+
+        Applies the ratelimiting for succesful login attempts against an
+        account.
 
         Args:
             user_id (str): ID of the user to register.
             login_submission (dict): Dictionary of login information.
             callback (func|None): Callback function to run after registration.
+            create_non_existant_users (bool): Whether to create the user if
+                they don't exist. Defaults to False.
 
         Returns:
             result (Dict[str,str]): Dictionary of account information after
                 successful registration.
         """
+
+        # Before we actually log them in we check if they've already logged in
+        # too often. This happens here rather than before as we don't
+        # necessarily know the user before now.
+        self._account_ratelimiter.ratelimit(
+            user_id.lower(),
+            time_now_s=self._clock.time(),
+            rate_hz=self.hs.config.rc_login_account.per_second,
+            burst_count=self.hs.config.rc_login_account.burst_count,
+            update=True,
+        )
+
+        if create_non_existant_users:
+            user_id = yield self.auth_handler.check_user_exists(user_id)
+            if not user_id:
+                user_id = yield self.registration_handler.register_user(
+                    localpart=UserID.from_string(user_id).localpart
+                )
+
         device_id = login_submission.get("device_id")
         initial_display_name = login_submission.get("initial_device_display_name")
         device_id, access_token = yield self.registration_handler.register_device(
@@ -285,7 +369,7 @@ class LoginRestServlet(RestServlet):
             token
         )
 
-        result = yield self._register_device_with_callback(user_id, login_submission)
+        result = yield self._complete_login(user_id, login_submission)
         return result
 
     @defer.inlineCallbacks
@@ -313,16 +397,7 @@ class LoginRestServlet(RestServlet):
             raise LoginError(401, "Invalid JWT", errcode=Codes.UNAUTHORIZED)
 
         user_id = UserID(user, self.hs.hostname).to_string()
-
-        registered_user_id = yield self.auth_handler.check_user_exists(user_id)
-        if not registered_user_id:
-            registered_user_id = yield self.registration_handler.register_user(
-                localpart=user
-            )
-
-        result = yield self._register_device_with_callback(
-            registered_user_id, login_submission
-        )
+        result = yield self._complete_login(user_id, login_submission)
         return result