rate_limit: Merge two IP rate limits domains that send emails.

Both `create_realm_by_ip` and `find_account_by_ip` send emails to
arbitrary email addresses, and as such can be used to spam users.
Lump their IP rate limits into the same bucket; most legitimate users
will likely not be using both of these endpoints at similar times.

The rate is set at 5 in 30 minutes, the more quickly-restrictive of
the two previous rates.

zerver/tests/test_external.py

@@ -203,7 +203,7 @@ class RateLimitTests(ZulipTestCase):
         resp = self.send_unauthed_api_request(REMOTE_ADDR="127.0.0.2")
         self.assertNotEqual(resp.status_code, 429)
 
-    @rate_limit_rule(1, 5, domain="create_realm_by_ip")
+    @rate_limit_rule(1, 5, domain="sends_email_by_ip")
     def test_create_realm_rate_limiting(self) -> None:
         with self.settings(OPEN_REALM_CREATION=True):
             self.do_test_hit_ratelimits(
@@ -211,7 +211,7 @@ class RateLimitTests(ZulipTestCase):
                 is_json=False,
             )
 
-    @rate_limit_rule(1, 5, domain="find_account_by_ip")
+    @rate_limit_rule(1, 5, domain="sends_email_by_ip")
     def test_find_account_rate_limiting(self) -> None:
         self.do_test_hit_ratelimits(
             lambda: self.client_post("/accounts/find/", {"emails": "new@zulip.com"}),
@@ -221,13 +221,28 @@ class RateLimitTests(ZulipTestCase):
     # Test whether submitting multiple emails is handled correctly.
     # The limit is set to 10 per second, so 5 requests with 2 emails
     # submitted in each should be allowed.
-    @rate_limit_rule(1, 10, domain="find_account_by_ip")
+    @rate_limit_rule(1, 10, domain="sends_email_by_ip")
     def test_find_account_rate_limiting_multiple(self) -> None:
         self.do_test_hit_ratelimits(
             lambda: self.client_post("/accounts/find/", {"emails": "new@zulip.com,new2@zulip.com"}),
             is_json=False,
         )
 
+    @rate_limit_rule(1, 5, domain="sends_email_by_ip")
+    def test_combined_ip_limits(self) -> None:
+        # Alternate requests to /new/ and /accounts/find/
+        request_count = 0
+
+        def alternate_requests() -> HttpResponse:
+            nonlocal request_count
+            request_count += 1
+            if request_count % 2 == 1:
+                return self.client_post("/new/", {"email": "new@zulip.com"})
+            else:
+                return self.client_post("/accounts/find/", {"emails": "new@zulip.com"})
+
+        self.do_test_hit_ratelimits(alternate_requests, is_json=False)
+
     @skipUnless(settings.ZILENCER_ENABLED, "requires zilencer")
     @rate_limit_rule(1, 5, domain="api_by_remote_server")
     def test_hit_ratelimits_as_remote_server(self) -> None:

zerver/views/registration.py

@@ -605,7 +605,7 @@ def create_realm(request: HttpRequest, creation_key: Optional[str] = None) -> Ht
         form = RealmCreationForm(request.POST)
         if form.is_valid():
             try:
-                rate_limit_request_by_ip(request, domain="create_realm_by_ip")
+                rate_limit_request_by_ip(request, domain="sends_email_by_ip")
             except RateLimited as e:
                 assert e.secs_to_freedom is not None
                 return render(
@@ -725,7 +725,7 @@ def find_account(
             emails = form.cleaned_data["emails"]
             for i in range(len(emails)):
                 try:
-                    rate_limit_request_by_ip(request, domain="find_account_by_ip")
+                    rate_limit_request_by_ip(request, domain="sends_email_by_ip")
                 except RateLimited as e:
                     assert e.secs_to_freedom is not None
                     return render(

zproject/computed_settings.py

@@ -385,16 +385,13 @@ RATE_LIMITING_RULES = {
     "authenticate_by_username": [
         (1800, 5),  # 5 login attempts within 30 minutes
     ],
-    "create_realm_by_ip": [
-        (1800, 5),
-    ],
-    "find_account_by_ip": [
-        (3600, 10),
-    ],
     "password_reset_form_by_email": [
         (3600, 2),  # 2 reset emails per hour
         (86400, 5),  # 5 per day
     ],
+    "sends_email_by_ip": [
+        (1800, 5),
+    ],
 }
 
 # List of domains that, when applied to a request in a Tornado process,

zproject/test_extra_settings.py

@@ -266,8 +266,7 @@ RATE_LIMITING_RULES: Dict[str, List[Tuple[int, int]]] = {
     "api_by_ip": [],
     "api_by_remote_server": [],
     "authenticate_by_username": [],
-    "create_realm_by_ip": [],
-    "find_account_by_ip": [],
+    "sends_email_by_ip": [],
     "password_reset_form_by_email": [],
 }