Add canonical e-mail blocks for suspended accounts (#16049)

Prevent new accounts from being created using the same underlying
e-mail as a suspended account using extensions and period
permutations. Stores e-mails as a SHA256 hash

app/helpers/email_helper.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module EmailHelper
+  def self.included(base)
+    base.extend(self)
+  end
+
+  def email_to_canonical_email(str)
+    username, domain = str.downcase.split('@', 2)
+    username, = username.gsub('.', '').split('+', 2)
+
+    "#{username}@#{domain}"
+  end
+
+  def email_to_canonical_email_hash(str)
+    Digest::SHA2.new(256).hexdigest(email_to_canonical_email(str))
+  end
+end

app/models/account.rb

@@ -235,6 +235,7 @@ class Account < ApplicationRecord
     transaction do
       create_deletion_request!
       update!(suspended_at: date, suspension_origin: origin)
+      create_canonical_email_block!
     end
   end
 
@@ -242,6 +243,7 @@ class Account < ApplicationRecord
     transaction do
       deletion_request&.destroy!
       update!(suspended_at: nil, suspension_origin: nil)
+      destroy_canonical_email_block!
     end
   end
 
@@ -569,4 +571,16 @@ class Account < ApplicationRecord
   def clean_feed_manager
     FeedManager.instance.clean_feeds!(:home, [id])
   end
+
+  def create_canonical_email_block!
+    return unless local? && user_email.present?
+
+    CanonicalEmailBlock.create(reference_account: self, email: user_email)
+  end
+
+  def destroy_canonical_email_block!
+    return unless local?
+
+    CanonicalEmailBlock.where(reference_account: self).delete_all
+  end
 end

app/models/canonical_email_block.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+# == Schema Information
+#
+# Table name: canonical_email_blocks
+#
+#  id                   :bigint(8)        not null, primary key
+#  canonical_email_hash :string           default(""), not null
+#  reference_account_id :bigint(8)        not null
+#  created_at           :datetime         not null
+#  updated_at           :datetime         not null
+#
+
+class CanonicalEmailBlock < ApplicationRecord
+  include EmailHelper
+
+  belongs_to :reference_account, class_name: 'Account'
+
+  validates :canonical_email_hash, presence: true
+
+  def email=(email)
+    self.canonical_email_hash = email_to_canonical_email_hash(email)
+  end
+
+  def self.block?(email)
+    where(canonical_email_hash: email_to_canonical_email_hash(email)).exists?
+  end
+end

app/validators/blacklisted_email_validator.rb

@@ -6,26 +6,25 @@ class BlacklistedEmailValidator < ActiveModel::Validator
 
     @email = user.email
 
-    user.errors.add(:email, :blocked) if blocked_email?
+    user.errors.add(:email, :blocked) if blocked_email_provider?
+    user.errors.add(:email, :taken) if blocked_canonical_email?
   end
 
   private
 
-  def blocked_email?
-    on_blacklist? || not_on_whitelist?
+  def blocked_email_provider?
+    disallowed_through_email_domain_block? || disallowed_through_configuration? || not_allowed_through_configuration?
   end
 
-  def on_blacklist?
-    return true  if EmailDomainBlock.block?(@email)
-    return false if Rails.configuration.x.email_domains_blacklist.blank?
-
-    domains = Rails.configuration.x.email_domains_blacklist.gsub('.', '\.')
-    regexp  = Regexp.new("@(.+\\.)?(#{domains})", true)
-
-    regexp.match?(@email)
+  def blocked_canonical_email?
+    CanonicalEmailBlock.block?(@email)
   end
 
-  def not_on_whitelist?
+  def disallowed_through_email_domain_block?
+    EmailDomainBlock.block?(@email)
+  end
+
+  def not_allowed_through_configuration?
     return false if Rails.configuration.x.email_domains_whitelist.blank?
 
     domains = Rails.configuration.x.email_domains_whitelist.gsub('.', '\.')
@@ -33,4 +32,13 @@ class BlacklistedEmailValidator < ActiveModel::Validator
 
     @email !~ regexp
   end
+
+  def disallowed_through_configuration?
+    return false if Rails.configuration.x.email_domains_blacklist.blank?
+
+    domains = Rails.configuration.x.email_domains_blacklist.gsub('.', '\.')
+    regexp  = Regexp.new("@(.+\\.)?(#{domains})", true)
+
+    regexp.match?(@email)
+  end
 end

db/migrate/20210416200740_create_canonical_email_blocks.rb

@@ -0,0 +1,10 @@
+class CreateCanonicalEmailBlocks < ActiveRecord::Migration[6.1]
+  def change
+    create_table :canonical_email_blocks do |t|
+      t.string :canonical_email_hash, null: false, default: '', index: { unique: true }
+      t.belongs_to :reference_account, null: false, foreign_key: { on_cascade: :delete, to_table: 'accounts' }
+
+      t.timestamps
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2021_03_24_171613) do
+ActiveRecord::Schema.define(version: 2021_04_16_200740) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -280,6 +280,15 @@ ActiveRecord::Schema.define(version: 2021_03_24_171613) do
     t.index ["status_id"], name: "index_bookmarks_on_status_id"
   end
 
+  create_table "canonical_email_blocks", force: :cascade do |t|
+    t.string "canonical_email_hash", default: "", null: false
+    t.bigint "reference_account_id", null: false
+    t.datetime "created_at", precision: 6, null: false
+    t.datetime "updated_at", precision: 6, null: false
+    t.index ["canonical_email_hash"], name: "index_canonical_email_blocks_on_canonical_email_hash", unique: true
+    t.index ["reference_account_id"], name: "index_canonical_email_blocks_on_reference_account_id"
+  end
+
   create_table "conversation_mutes", force: :cascade do |t|
     t.bigint "conversation_id", null: false
     t.bigint "account_id", null: false
@@ -991,6 +1000,7 @@ ActiveRecord::Schema.define(version: 2021_03_24_171613) do
   add_foreign_key "blocks", "accounts", name: "fk_4269e03e65", on_delete: :cascade
   add_foreign_key "bookmarks", "accounts", on_delete: :cascade
   add_foreign_key "bookmarks", "statuses", on_delete: :cascade
+  add_foreign_key "canonical_email_blocks", "accounts", column: "reference_account_id"
   add_foreign_key "conversation_mutes", "accounts", name: "fk_225b4212bb", on_delete: :cascade
   add_foreign_key "conversation_mutes", "conversations", on_delete: :cascade
   add_foreign_key "custom_filters", "accounts", on_delete: :cascade

spec/fabricators/canonical_email_block_fabricator.rb

@@ -0,0 +1,4 @@
+Fabricator(:canonical_email_block) do
+  email "test@example.com"
+  reference_account { Fabricate(:account) }
+end

spec/models/canonical_email_block_spec.rb

@@ -0,0 +1,47 @@
+require 'rails_helper'
+
+RSpec.describe CanonicalEmailBlock, type: :model do
+  describe '#email=' do
+    let(:target_hash) { '973dfe463ec85785f5f95af5ba3906eedb2d931c24e69824a89ea65dba4e813b' }
+
+    it 'sets canonical_email_hash' do
+      subject.email = 'test@example.com'
+      expect(subject.canonical_email_hash).to eq target_hash
+    end
+
+    it 'sets the same hash even with dot permutations' do
+      subject.email = 't.e.s.t@example.com'
+      expect(subject.canonical_email_hash).to eq target_hash
+    end
+
+    it 'sets the same hash even with extensions' do
+      subject.email = 'test+mastodon1@example.com'
+      expect(subject.canonical_email_hash).to eq target_hash
+    end
+
+    it 'sets the same hash with different casing' do
+      subject.email = 'Test@EXAMPLE.com'
+      expect(subject.canonical_email_hash).to eq target_hash
+    end
+  end
+
+  describe '.block?' do
+    let!(:canonical_email_block) { Fabricate(:canonical_email_block, email: 'foo@bar.com') }
+
+    it 'returns true for the same email' do
+      expect(described_class.block?('foo@bar.com')).to be true
+    end
+
+    it 'returns true for the same email with dots' do
+      expect(described_class.block?('f.oo@bar.com')).to be true
+    end
+
+    it 'returns true for the same email with extensions' do
+      expect(described_class.block?('foo+spam@bar.com')).to be true
+    end
+
+    it 'returns false for different email' do
+      expect(described_class.block?('hoge@bar.com')).to be false
+    end
+  end
+end

spec/validators/blacklisted_email_validator_spec.rb

@@ -9,23 +9,36 @@ RSpec.describe BlacklistedEmailValidator, type: :validator do
 
     before do
       allow(user).to receive(:valid_invitation?) { false }
-      allow_any_instance_of(described_class).to receive(:blocked_email?) { blocked_email }
-      described_class.new.validate(user)
+      allow_any_instance_of(described_class).to receive(:blocked_email_provider?) { blocked_email }
     end
 
-    context 'blocked_email?' do
+    subject { described_class.new.validate(user); errors }
+
+    context 'when e-mail provider is blocked' do
       let(:blocked_email) { true }
 
-      it 'calls errors.add' do
-        expect(errors).to have_received(:add).with(:email, :blocked)
+      it 'adds error' do
+        expect(subject).to have_received(:add).with(:email, :blocked)
       end
     end
 
-    context '!blocked_email?' do
+    context 'when e-mail provider is not blocked' do
       let(:blocked_email) { false }
 
-      it 'not calls errors.add' do
-        expect(errors).not_to have_received(:add).with(:email, :blocked)
+      it 'does not add errors' do
+        expect(subject).not_to have_received(:add).with(:email, :blocked)
+      end
+
+      context 'when canonical e-mail is blocked' do
+        let(:other_user) { Fabricate(:user, email: 'i.n.f.o@mail.com') }
+
+        before do
+          other_user.account.suspend!
+        end
+
+        it 'adds error' do
+          expect(subject).to have_received(:add).with(:email, :taken)
+        end
       end
     end
   end