x509: fix handling of multiple URIs in Certificate#crl_uris

The implementation of OpenSSL::X509::Certificate#crl_uris makes the
assumption that each DistributionPoint in the CRL distribution points
extension contains a single general name of type URI. This is not
guaranteed by RFC 5280. A DistributionPoint may only contains something
other than a URI, or more than one URI.

Let's include all URIs seen in the extension. If only non-URI pointers
are found, return an empty array.

Fixes: #775

lib/openssl/x509.rb

@@ -135,14 +135,14 @@ def crl_uris
             raise ASN1::ASN1Error, "invalid extension"
           end
 
-          crl_uris = cdp_asn1.map do |crl_distribution_point|
+          crl_uris = cdp_asn1.flat_map do |crl_distribution_point|
             distribution_point = crl_distribution_point.value.find do |v|
               v.tag_class == :CONTEXT_SPECIFIC && v.tag == 0
             end
             full_name = distribution_point&.value&.find do |v|
               v.tag_class == :CONTEXT_SPECIFIC && v.tag == 0
             end
-            full_name&.value&.find do |v|
+            full_name&.value&.select do |v|
               v.tag_class == :CONTEXT_SPECIFIC && v.tag == 6 # uniformResourceIdentifier
             end
           end

test/openssl/test_x509cert.rb

@@ -151,6 +151,39 @@ def test_crl_uris
     )
   end
 
+  def test_crl_uris_multiple_general_names
+    # Single DistributionPoint contains multiple general names of type URI
+    ef = OpenSSL::X509::ExtensionFactory.new
+    ef.config = OpenSSL::Config.parse(<<~_cnf_)
+      [crlDistPts_section]
+      fullname = URI:http://www.example.com/crl, URI:ldap://ldap.example.com/cn=ca?certificateRevocationList;binary
+    _cnf_
+    cdp_cert = generate_cert(@ee1, @rsa2048, 3, nil)
+    ef.subject_certificate = cdp_cert
+    cdp_cert.add_extension(ef.create_extension("crlDistributionPoints", "crlDistPts_section"))
+    cdp_cert.sign(@rsa2048, "sha256")
+    assert_equal(
+      ["http://www.example.com/crl", "ldap://ldap.example.com/cn=ca?certificateRevocationList;binary"],
+      cdp_cert.crl_uris
+    )
+  end
+
+  def test_crl_uris_no_uris
+    # The only DistributionPointName is a directoryName
+    ef = OpenSSL::X509::ExtensionFactory.new
+    ef.config = OpenSSL::Config.parse(<<~_cnf_)
+      [crlDistPts_section]
+      fullname = dirName:dirname_section
+      [dirname_section]
+      CN = dirname
+    _cnf_
+    cdp_cert = generate_cert(@ee1, @rsa2048, 3, nil)
+    ef.subject_certificate = cdp_cert
+    cdp_cert.add_extension(ef.create_extension("crlDistributionPoints", "crlDistPts_section"))
+    cdp_cert.sign(@rsa2048, "sha256")
+    assert_equal([], cdp_cert.crl_uris)
+  end
+
   def test_aia_missing
     cert = issue_cert(@ee1, @rsa2048, 1, [], nil, nil)
     assert_nil(cert.ca_issuer_uris)