Allow custom domain labels

Original validator checked for domain labels as defined by RFC1034, however real
internet deals with other domains as well - starting with digits or symbols.
This change allows modifying the pattern to allow custom / relaxed rules.

Validation has been removed from adding a domain to a new extension, since it's
only used in fixups and the domain should be already validated. (or not, if not
configured)

Closes-bug: 1592489

Change-Id: Ib453054ba5f554bab28cff392c539e713fa28918

anchor/X509/extension.py

@@ -24,7 +24,6 @@ from pyasn1.type import tag as asn1_tag
 from pyasn1.type import univ as asn1_univ
 
 from anchor.asn1 import rfc5280
-from anchor import util as a_utils
 from anchor.X509 import errors
 from anchor.X509 import utils
 
@@ -331,11 +330,6 @@ class X509ExtensionSubjectAltName(X509Extension):
 
     @modifies_ext_value
     def add_dns_id(self, dns_id, validate=True, ext_value=None):
-        if validate:
-            try:
-                a_utils.verify_domain(dns_id, allow_wildcards=True)
-            except ValueError as e:
-                raise errors.X509Error("invalid domain provided: %s" % str(e))
         new_pos = len(ext_value)
         ext_value[new_pos] = None
         ext_value[new_pos]['dNSName'] = dns_id

anchor/util.py

@@ -15,18 +15,12 @@ from __future__ import absolute_import
 
 import base64
 import os
-import re
 import stat
 
 from anchor import errors
 
 
-# RFC1034 allows a simple " " too, but it's not allowed in certificates, so it
-# will not match
-RE_DOMAIN_LABEL = re.compile("^[a-z](?:[-a-z0-9]*[a-z0-9])?$", re.IGNORECASE)
-
-
-def verify_domain(domain, allow_wildcards=False):
+def verify_domain(domain, label_re_comp, allow_wildcards=False):
     labels = domain.split('.')
     if labels[-1] == "":
         # single trailing . is ok, ignore
@@ -44,7 +38,7 @@ def verify_domain(domain, allow_wildcards=False):
                     "domain <%s> has wildcard that's not in the "
                     "left-most label (RFC6125/6.4.3)" % (domain,))
         else:
-            if RE_DOMAIN_LABEL.match(label) is None:
+            if label_re_comp.match(label) is None:
                 raise ValueError(
                     "domain <%s> contains invalid characters "
                     "(RFC1034/3.5)" % (domain,))

anchor/validators/standards.py

@@ -28,12 +28,22 @@ from anchor.validators import errors
 from anchor.X509 import errors as x509_errors
 from anchor.X509 import extension
 
+import re
 
-def standards_compliance(csr=None, **kwargs):
+
+# RFC1034 allows a simple " " too, but it's not allowed in certificates, so it
+# will not match
+#
+# This pattern is RFC1034 compatible otherwise, but since newer RFCs actually
+# allow any binary value as the domain label, some operators may want to relax
+# the pattern in the configuration, for example to allow leading digits or
+# hyphens.
+def standards_compliance(csr=None, label_re="^[a-z](?:[-a-z0-9]*[a-z0-9])?$",
+                         **kwargs):
     """Collection of separate cases of standards validation."""
     _no_extension_duplicates(csr)
     _critical_flags(csr)
-    _valid_domains(csr)
+    _valid_domains(csr, label_re)
     _csr_signature(csr)
     # TODO(stan): validate srv/uri, distinct DNs, email format, identity keys
 
@@ -67,7 +77,7 @@ def _critical_flags(csr):
                     "(RFC5280/4.1.2.9)")
 
 
-def _valid_domains(csr):
+def _valid_domains(csr, label_re="^[a-z](?:[-a-z0-9]*[a-z0-9])?$"):
     """Format of the domin names
 
     See RFC5280 section 4.2.1.6 / RFC6125 / RFC1034
@@ -76,10 +86,12 @@ def _valid_domains(csr):
     if not sans:
         return
 
+    label_re_comp = re.compile(label_re, re.IGNORECASE)
+
     ext = sans[0]
     for domain in ext.get_dns_ids():
         try:
-            util.verify_domain(domain, allow_wildcards=True)
+            util.verify_domain(domain, label_re_comp, allow_wildcards=True)
         except ValueError as e:
             raise errors.ValidationError(str(e))
 

config.json

@@ -21,7 +21,9 @@
       "authentication": "method_1",
       "signing_ca": "local",
       "validators": {
-        "standards_compliance": {},
+        "standards_compliance": {
+		  "label_re": "^[a-z](?:[-a-z0-9]*[a-z0-9])?$"
+		},
         "source_cidrs": {
           "cidrs": ["127.0.0.0/8"]
         }

doc/source/validators.rst

@@ -21,6 +21,10 @@ The following validators are implemented at the moment:
     Any requests produced using standard tooling that fail this check should be
     reported as Anchor issues.
 
+    Parameters:
+
+    - ``label_re``: pattern for acceptable domain label format
+
 ``whitelist_names``
     Verifies: CSR. Parameters:
 

tests/X509/test_extension.py

@@ -146,11 +146,6 @@ class TestSubjectAltName(unittest.TestCase):
         self.ext.add_ip(self.ip)
         self.assertEqual([self.domain], self.ext.get_dns_ids())
 
-    def test_add_dns_id_validation(self):
-        self.ext.add_dns_id("good.exapmle.com")
-        with self.assertRaises(errors.X509Error):
-            self.ext.add_dns_id("-blah")
-
     def test_ips(self):
         self.ext.add_dns_id(self.domain)
         self.ext.add_ip(self.ip)

tests/validators/test_standards_validator.py

@@ -163,6 +163,11 @@ class TestValidDomains(unittest.TestCase):
         with self.assertRaises(errors.ValidationError):
             standards._valid_domains(csr)
 
+    def test_custom_re(self):
+        csr = self._create_csr_with_domain_san('123.example.com.')
+        with self.assertRaises(errors.ValidationError):
+            standards._valid_domains(csr, "^\s\+$")
+
 
 class TestCsrSignature(tests.DefaultRequestMixin, unittest.TestCase):
     def test_csr_signature(self):