validate_principal: Don't try to verify that the realm is known

The actual value is less important than whether it matches the
regular expression. A number of legal but difficult to know in
context realms could be passed in here (trust for example).

This fixes CVE-2024-1481

Fixes: https://pagure.io/freeipa/issue/9541

Signed-off-by: Rob Crittenden <rcritten@redhat.com>
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>

ipalib/install/kinit.py

@@ -15,7 +15,6 @@
 from ipapython.ipautil import run
 from ipalib.constants import PATTERN_GROUPUSER_NAME
 from ipalib.util import validate_hostname
-from ipalib import api
 
 logger = logging.getLogger(__name__)
 
@@ -39,7 +38,9 @@ def validate_principal(principal):
     if ('/' in principal) and (' ' in principal):
         raise RuntimeError('Invalid principal: bad spacing')
     else:
-        realm = None
+        # For a user match in the regex
+        # username = match[1]
+        # realm = match[2]
         match = user_pattern.match(principal)
         if match is None:
             match = service_pattern.match(principal)
@@ -48,16 +49,11 @@ def validate_principal(principal):
             else:
                 # service = match[1]
                 hostname = match[2]
-                realm = match[3]
+                # realm = match[3]
                 try:
                     validate_hostname(hostname)
                 except ValueError as e:
                     raise RuntimeError(str(e))
-        else:  # user match, validate realm
-            # username = match[1]
-            realm = match[2]
-        if realm and 'realm' in api.env and realm != api.env.realm:
-            raise RuntimeError('Invalid principal: realm mismatch')
 
 
 def kinit_keytab(principal, keytab, ccache_name, config=None, attempts=1):

ipatests/test_ipalib_install/test_kinit.py

@@ -17,13 +17,16 @@
     ('test/ipa.example.test@EXAMPLE.TEST', None),
     ('test/ipa@EXAMPLE.TEST', RuntimeError),
     ('test/-ipa.example.test@EXAMPLE.TEST', RuntimeError),
-    ('test/ipa.1example.test@EXAMPLE.TEST', RuntimeError),
+    ('test/ipa.1example.test@EXAMPLE.TEST', None),
     ('test /ipa.example,test', RuntimeError),
-    ('testuser@OTHER.TEST', RuntimeError),
-    ('test/ipa.example.test@OTHER.TEST', RuntimeError),
+    ('testuser@OTHER.TEST', None),
+    ('test/ipa.example.test@OTHER.TEST', None)
 ])
 def test_validate_principal(principal, exception):
     try:
         validate_principal(principal)
     except Exception as e:
         assert e.__class__ == exception
+    else:
+        if exception is not None:
+            raise RuntimeError('Test should have failed')