Rate limiting for the "Log In" emails

CHANGELOG.md

@@ -9,7 +9,7 @@ All notable changes to this project will be documented in this file.
 - Upgrade to Django 2.2
 - Can configure the email integration to only report the "down" events (#231)
 - Add "Test!" function in the Integrations page (#207)
-
+- Rate limiting for the "Log In" emails
 
 ## 1.6.0 - 2019-04-01
 

hc/accounts/tests/test_login.py

@@ -1,6 +1,7 @@
 from django.conf import settings
 from django.core import mail
-from hc.api.models import Check
+from django.test.utils import override_settings
+from hc.api.models import Check, TokenBucket
 from hc.test import BaseTestCase
 
 
@@ -32,6 +33,36 @@ class LoginTestCase(BaseTestCase):
         body = mail.outbox[0].body
         self.assertTrue("/?next=/integrations/add_slack/" in body)
 
+    @override_settings(SECRET_KEY="test-secret")
+    def test_it_rate_limits_emails(self):
+        # "d60d..." is sha1("alice@example.orgtest-secret")
+        obj = TokenBucket(value="em-d60db3b2343e713a4de3e92d4eb417e4f05f06ab")
+        obj.tokens = 0
+        obj.save()
+
+        form = {"identity": "alice@example.org"}
+
+        r = self.client.post("/accounts/login/", form)
+        self.assertContains(r, "Too Many Requests")
+
+        # No email should have been sent
+        self.assertEqual(len(mail.outbox), 0)
+
+    @override_settings(SECRET_KEY="test-secret")
+    def test_it_rate_limits_ips(self):
+        # 4b84.... is sha1("127.0.0.1test-secret")
+        obj = TokenBucket(value="ip-4b84b15bff6ee5796152495a230e45e3d7e947d9")
+        obj.tokens = 0
+        obj.save()
+
+        form = {"identity": "alice@example.org"}
+
+        r = self.client.post("/accounts/login/", form)
+        self.assertContains(r, "Too Many Requests")
+
+        # No email should have been sent
+        self.assertEqual(len(mail.outbox), 0)
+
     def test_it_pops_bad_link_from_session(self):
         self.client.session["bad_link"] = True
         self.client.get("/accounts/login/")

hc/accounts/views.py

@@ -22,7 +22,7 @@ from hc.accounts.forms import (ChangeEmailForm, EmailPasswordForm,
                                ProjectNameForm, AvailableEmailForm,
                                ExistingEmailForm)
 from hc.accounts.models import Profile, Project, Member
-from hc.api.models import Channel, Check
+from hc.api.models import Channel, Check, TokenBucket
 from hc.payments.models import Subscription
 
 NEXT_WHITELIST = ("hc-checks",
@@ -102,14 +102,18 @@ def login(request):
         else:
             magic_form = ExistingEmailForm(request.POST)
             if magic_form.is_valid():
-                profile = Profile.objects.for_user(magic_form.user)
+                user = magic_form.user
+                if not TokenBucket.authorize_login_email(user.email):
+                    return render(request, "try_later.html")
+                if not TokenBucket.authorize_login_ip(request):
+                    return render(request, "try_later.html")
 
                 redirect_url = request.GET.get("next")
-                if _is_whitelisted(redirect_url):
-                    profile.send_instant_login_link(redirect_url=redirect_url)
-                else:
-                    profile.send_instant_login_link()
+                if not _is_whitelisted(redirect_url):
+                    redirect_url = None
 
+                profile = Profile.objects.for_user(user)
+                profile.send_instant_login_link(redirect_url=redirect_url)
                 return redirect("hc-login-link-sent")
 
     bad_link = request.session.pop("bad_link", None)

hc/api/migrations/0060_tokenbucket.py

@@ -0,0 +1,22 @@
+# Generated by Django 2.2 on 2019-04-25 12:46
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0059_auto_20190314_1744'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='TokenBucket',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('value', models.CharField(max_length=80, unique=True)),
+                ('tokens', models.FloatField(default=1.0)),
+                ('updated', models.DateTimeField(auto_now_add=True)),
+            ],
+        ),
+    ]

hc/api/models.py

@@ -591,3 +591,56 @@ class Flip(models.Model):
                 errors.append((channel, error))
 
         return errors
+
+
+class TokenBucket(models.Model):
+    value = models.CharField(max_length=80, unique=True)
+    tokens = models.FloatField(default=1.0)
+    updated = models.DateTimeField(default=timezone.now)
+
+    @staticmethod
+    def authorize(value, capacity, refill_time_secs):
+        now = timezone.now()
+        obj, created = TokenBucket.objects.get_or_create(value=value)
+
+        if not created:
+            # Top up the bucket:
+            delta_secs = (now - obj.updated).total_seconds()
+            obj.tokens = min(1.0, obj.tokens + delta_secs / refill_time_secs)
+
+        obj.tokens -= 1.0 / capacity
+        if obj.tokens < 0:
+            # Not enough tokens
+            return False
+
+        # Race condition: two concurrent authorize calls can overwrite each
+        # other's changes. It's OK to be a little inexact here for the sake
+        # of simplicity.
+        obj.updated = now
+        obj.save()
+
+        return True
+
+    @staticmethod
+    def authorize_login_email(email):
+        # remove dots and alias:
+        mailbox, domain = email.split("@")
+        mailbox = mailbox.replace(".", "")
+        mailbox = mailbox.split("+")[0]
+        email = mailbox + "@" + domain
+
+        b = (email + settings.SECRET_KEY).encode()
+        value = "em-%s" % hashlib.sha1(b).hexdigest()
+
+        # 20 emails per 3600 seconds (1 hour):
+        return TokenBucket.authorize(value, 20, 3600)
+
+    @staticmethod
+    def authorize_login_ip(request):
+        headers = request.META
+        ip = headers.get("HTTP_X_FORWARDED_FOR", headers["REMOTE_ADDR"])
+        ip = ip.split(",")[0]
+        value = "ip-%s" % hashlib.sha1(ip.encode()).hexdigest()
+
+        # 20 login attempts from a single IP per 3600 seconds (1 hour):
+        return TokenBucket.authorize(value, 20, 3600)

hc/api/tests/test_tokenbucket.py

@@ -0,0 +1,47 @@
+from datetime import timedelta as td
+
+from django.test.utils import override_settings
+from django.utils.timezone import now
+from hc.api.models import TokenBucket
+from hc.test import BaseTestCase
+
+# This is sha1("alice@example.org" + "test-secred")
+ALICE_HASH = "d60db3b2343e713a4de3e92d4eb417e4f05f06ab"
+
+
+@override_settings(SECRET_KEY="test-secret")
+class TokenBucketTestCase(BaseTestCase):
+
+    def test_it_works(self):
+        r = TokenBucket.authorize_login_email("alice@example.org")
+        self.assertTrue(r)
+
+        obj = TokenBucket.objects.get()
+        self.assertEqual(obj.tokens, 0.95)
+        self.assertEqual(obj.value, "em-" + ALICE_HASH)
+
+    def test_it_handles_insufficient_tokens(self):
+        TokenBucket.objects.create(value="em-" + ALICE_HASH, tokens=0.04)
+
+        r = TokenBucket.authorize_login_email("alice@example.org")
+        self.assertFalse(r)
+
+    def test_it_tops_up(self):
+        obj = TokenBucket(value="em-" + ALICE_HASH)
+        obj.tokens = 0
+        obj.updated = now() - td(minutes=30)
+        obj.save()
+
+        r = TokenBucket.authorize_login_email("alice@example.org")
+        self.assertTrue(r)
+
+        obj.refresh_from_db()
+        self.assertAlmostEqual(obj.tokens, 0.45, places=5)
+
+    def test_it_normalizes_email(self):
+        emails = ("alice+alias@example.org", "a.li.ce@example.org")
+
+        for email in emails:
+            TokenBucket.authorize_login_email(email)
+
+        self.assertEqual(TokenBucket.objects.count(), 1)

templates/try_later.html

@@ -0,0 +1,14 @@
+{% extends "base.html" %}
+
+{% block content %}
+<div class="row">
+    <div class="col-sm-6 col-sm-offset-3">
+        <div class="hc-dialog text-center">
+            <h1>Too Many Requests</h1>
+            <div class="dialog-body">
+                <p>Please try again later.</p>
+            </div>
+        </div>
+    </div>
+</div>
+{% endblock %}