Prevent installation with single label domains

Adds validation to prevent user to install ipa with single label
domain.

https://pagure.io/freeipa/issue/7207

Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>

ipalib/install/service.py

@@ -129,6 +129,10 @@ class ServiceInstallInterface(common.Installable,
         cli_names='--realm',
     )
 
+    @realm_name.validator
+    def realm_name(self, value):
+        validate_domain_name(value, entity="realm")
+
     host_name = knob(
         str, None,
         description="The hostname of this machine (FQDN). If specified, the "

ipalib/util.py

@@ -388,12 +388,19 @@ def validate_dns_label(dns_label, allow_underscore=False, allow_slash=False):
                            % dict(chars=chars, chars2=chars2))
 
 
-def validate_domain_name(domain_name, allow_underscore=False, allow_slash=False):
+def validate_domain_name(
+    domain_name, allow_underscore=False,
+    allow_slash=False, entity='domain'
+):
     if domain_name.endswith('.'):
         domain_name = domain_name[:-1]
 
     domain_name = domain_name.split(".")
 
+    if len(domain_name) < 2:
+        raise ValueError(_(
+            'single label {}s are not supported'.format(entity)))
+
     # apply DNS name validator to every name part
     for label in domain_name:
         validate_dns_label(label, allow_underscore, allow_slash)