Protect community from confusable homoglyphs

liberapay/models/community.py

@@ -5,6 +5,7 @@
 from psycopg2 import IntegrityError
 
 from liberapay.exceptions import CommunityAlreadyExists, InvalidCommunityName
+from liberapay.utils.unconfusable import unconfusable_string
 
 
 name_maxlength = 40
@@ -38,8 +39,18 @@ def create(cls, name, creator_id, lang='mul'):
         name = unicodedata.normalize('NFKC', name)
         if name_re.match(name) is None:
             raise InvalidCommunityName(name)
+
         try:
             with cls.db.get_cursor() as cursor:
+                unconfusable_name = unconfusable_string(name)
+                all_names = cursor.all("""
+                    SELECT name
+                    FROM communities
+                    """)
+                for existing_name in all_names:
+                    if unconfusable_name == unconfusable_string(existing_name):
+                        raise CommunityAlreadyExists
+
                 p_id = cursor.one("""
                     INSERT INTO participants
                                 (kind, status, join_time)

liberapay/utils/unconfusable.py

@@ -0,0 +1,13 @@
+from confusable_homoglyphs import confusables
+
+# Convert an Unicode string to its equivalent replacing all confusable homoglyphs
+# to its common/latin equivalent
+def unconfusable_string(s):
+    unconfusable_string = ''
+    for c in s:
+        confusable = confusables.is_confusable(c, preferred_aliases=['COMMON', 'LATIN'])
+        if confusable:
+            # if the character is confusable we replace it with the first prefered alias
+            c = confusable[0]['homoglyphs'][0]['c']
+        unconfusable_string += c
+    return unconfusable_string

requirements_base.txt

@@ -243,3 +243,7 @@ cryptography==2.4.2 \
     asn1crypto==0.24.0 \
         --hash=sha256:2f1adbb7546ed199e3c90ef23ec95c5cf3585bac7d11fb7eb562a3fe89c64e87 \
         --hash=sha256:9d5c20441baf0cb60a4ac34cc447c6c189024b6b4c6cd7877034f4965c464e49
+
+confusable_homoglyphs==3.2.0 \
+    --hash=sha256:3b4a0d9fa510669498820c91a0bfc0c327568cecec90648cf3819d4a6fc6a751 \
+    --hash=sha256:e3ce611028d882b74a5faa69e3cbb5bd4dcd9f69936da6e73d33eda42c917944

tests/py/test_communities.py

@@ -1,6 +1,6 @@
 import json
 
-from liberapay.exceptions import AuthRequired
+from liberapay.exceptions import AuthRequired, CommunityAlreadyExists
 from liberapay.models.community import Community
 from liberapay.testing import Harness
 
@@ -101,6 +101,22 @@ def test_join_and_leave(self):
         communities = self.bob.get_communities()
         assert len(communities) == 0
 
+    def test_create_community_already_taken(self):
+        with self.assertRaises(CommunityAlreadyExists):
+            Community.create('test', self.alice.id)
+
+    def test_create_community_already_taken_is_case_insensitive(self):
+        with self.assertRaises(CommunityAlreadyExists):
+            Community.create('TeSt', self.alice.id)
+
+    def test_create_community_already_taken_with_confusable_homoglyphs(self):
+        latin_string = 'AlaskaJazz'
+        mixed_string = 'ΑlaskaJazz'
+
+        Community.create(latin_string, self.bob.id)
+        with self.assertRaises(CommunityAlreadyExists):
+            Community.create(mixed_string, self.alice.id)
+
 
 class TestCommunityEdit(Harness):
 

tests/py/test_utils.py

@@ -7,7 +7,7 @@
 from liberapay import utils
 from liberapay.i18n.currencies import Money, MoneyBasket
 from liberapay.testing import Harness
-from liberapay.utils import markdown, b64encode_s, b64decode_s, cbor
+from liberapay.utils import markdown, b64encode_s, b64decode_s, cbor, unconfusable
 from liberapay.wireup import CSP
 
 
@@ -244,3 +244,14 @@ def test_csp_handles_valueless_directives_correctly(self):
         csp2 = CSP(csp)
         assert csp == csp2
         assert csp2.directives[b'upgrade-insecure-requests'] == b''
+
+    # Unconfusable
+    # ============
+
+    def test_unconfusable_string(self):
+        self.assertEqual('user2', unconfusable.unconfusable_string('user2'))
+        self.assertEqual('alice', unconfusable.unconfusable_string('alice'))
+        latin_string = 'AlaskaJazz'
+        mixed_string = 'ΑlaskaJazz'
+        self.assertNotEqual(latin_string, mixed_string)
+        self.assertEqual(latin_string, unconfusable.unconfusable_string(mixed_string))