blacklist system logins for aliases and logins

We blacklist based on three things:
* blacklist in APP_CONFIG[:handle_blacklist]
* emails in RFC 2142
* usernames in /etc/passwd

The latter two can be allowed by explicitly whitelisting them in APP_CONFIG[:handle_whitelist].

We stick to blocking names that have been configured as both blacklisted and whitelisted - better be save than sorry.

2 files changed, 64 insertions, 0 deletions

diff --git a/users/app/models/local_email.rb b/users/app/models/local_email.rb
index 6303bb6..2b4c65e 100644
--- a/users/app/models/local_email.rb
+++ b/users/app/models/local_email.rb
@@ -1,5 +1,10 @@
 class LocalEmail < Email
 
+  BLACKLIST_FROM_RFC2142 = [
+    'postmaster', 'hostmaster', 'domainadmin', 'webmaster', 'www',
+    'abuse', 'noc', 'security', 'usenet', 'news', 'uucp',
+    'ftp', 'sales', 'marketing', 'support', 'info'
+  ]
 
   def self.domain
     APP_CONFIG[:domain]
@@ -11,6 +16,8 @@ class LocalEmail < Email
       :message => "needs to end in @#{domain}"
     }
 
+  validate :handle_allowed
+
   def initialize(s)
     super
     append_domain_if_needed
@@ -32,4 +39,30 @@ class LocalEmail < Email
     end
   end
 
+  def handle_allowed
+    errors.add(:handle, "is reserved.") if handle_reserved?
+  end
+
+  def handle_reserved?
+    # *ARRAY in a case statement tests if ARRAY includes the handle.
+    case handle
+    when *APP_CONFIG[:handle_blacklist]
+      true
+    when *APP_CONFIG[:handle_whitelist]
+      false
+    when *BLACKLIST_FROM_RFC2142
+      true
+    else
+      handle_in_passwd?
+    end
+  end
+
+  def handle_in_passwd?
+    begin
+      !!Etc.getpwnam(handle)
+    rescue ArgumentError
+      # handle was not found
+      return false
+    end
+  end
 end
diff --git a/users/test/unit/local_email_test.rb b/users/test/unit/local_email_test.rb
index b25f46f..20ee7f1 100644
--- a/users/test/unit/local_email_test.rb
+++ b/users/test/unit/local_email_test.rb
@@ -24,6 +24,37 @@ class LocalEmailTest < ActiveSupport::TestCase
     assert_equal ["needs to end in @#{LocalEmail.domain}"], local.errors[:email]
   end
 
+  test "blacklists rfc2142" do
+    black_listed = LocalEmail.new('hostmaster')
+    assert !black_listed.valid?
+  end
+
+  test "blacklists etc passwd" do
+    black_listed = LocalEmail.new('nobody')
+    assert !black_listed.valid?
+  end
+
+  test "whitelist overwrites automatic blacklists" do
+    with_config handle_whitelist: ['nobody', 'hostmaster'] do
+      white_listed = LocalEmail.new('nobody')
+      assert white_listed.valid?
+      white_listed = LocalEmail.new('hostmaster')
+      assert white_listed.valid?
+    end
+  end
+
+  test "blacklists from config" do
+    black_listed = LocalEmail.new('www-data')
+    assert !black_listed.valid?
+  end
+
+  test "blacklist from config overwrites whitelist" do
+    with_config handle_whitelist: ['www-data'] do
+      black_listed = LocalEmail.new('www-data')
+      assert !black_listed.valid?
+    end
+  end
+
   def handle
     @handle ||= Faker::Internet.user_name
   end