From 6c2375adcfd9d87ce6dbd4ef7ce44c457a630040 Mon Sep 17 00:00:00 2001
From: Sam Hartman <hartmans@mit.edu>
Date: Mon, 12 Jan 2009 19:59:16 +0000
Subject: [PATCH] Patch from Luke Howard: Previously when using the kdb keytab,
 there was a check to confirm that the server was supported as a server and
 that attackers could not force an enctype downgrade. Add these to
 kdc_get_server_key

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@21727 dc483132-0cff-0310-8789-dd5450dbe970
---
 src/kdc/do_tgs_req.c |  1 +
 src/kdc/kdc_util.c   | 35 ++++++++++++++++++++++++++++-------
 src/kdc/kdc_util.h   |  1 +
 3 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/src/kdc/do_tgs_req.c b/src/kdc/do_tgs_req.c
index 381269880..17c7f1534 100644
--- a/src/kdc/do_tgs_req.c
+++ b/src/kdc/do_tgs_req.c
@@ -282,6 +282,7 @@ tgt_again:
 	 */
 	if ((errcode = kdc_get_server_key(request->second_ticket[st_idx],
 					  c_flags,
+					  TRUE, /* match_enctype */
 					  &st_client,
 					  &st_nprincs,
 					  &st_sealing_key,
diff --git a/src/kdc/kdc_util.c b/src/kdc/kdc_util.c
index 987c61cac..549fb9758 100644
--- a/src/kdc/kdc_util.c
+++ b/src/kdc/kdc_util.c
@@ -292,7 +292,8 @@ kdc_process_tgs_req(krb5_kdc_req *request, const krb5_fulladdr *from,
 	goto cleanup_auth_context;
 #endif
 
-    if ((retval = kdc_get_server_key(apreq->ticket, 0, krbtgt, nprincs, &key, &kvno)))
+    if ((retval = kdc_get_server_key(apreq->ticket, 0, foreign_server,
+				     krbtgt, nprincs, &key, &kvno)))
 	goto cleanup_auth_context;
     /*
      * We do not use the KDB keytab because other parts of the TGS need the TGT key.
@@ -408,11 +409,11 @@ cleanup:
  */
 krb5_error_code
 kdc_get_server_key(krb5_ticket *ticket, unsigned int flags,
-		   krb5_db_entry *server,
+		   krb5_boolean match_enctype, krb5_db_entry *server,
 		   int *nprincs, krb5_keyblock **key, krb5_kvno *kvno)
 {
     krb5_error_code 	  retval;
-    krb5_boolean 	  more;
+    krb5_boolean 	  more, similar;
     krb5_key_data	* server_key;
 
     *nprincs = 1;
@@ -438,23 +439,43 @@ kdc_get_server_key(krb5_ticket *ticket, unsigned int flags,
 	}
 	return(KRB5KDC_ERR_S_PRINCIPAL_UNKNOWN);
     }
+    if (server->attributes & KRB5_KDB_DISALLOW_SVR ||
+	server->attributes & KRB5_KDB_DISALLOW_ALL_TIX) {
+	retval = KRB5KDC_ERR_S_PRINCIPAL_UNKNOWN;
+	goto errout;
+    }
     retval = krb5_dbe_find_enctype(kdc_context, server,
-				   ticket->enc_part.enctype, -1,
-				   (krb5_int32)ticket->enc_part.kvno, &server_key);
+				   match_enctype ? ticket->enc_part.enctype : -1,
+				   -1, (krb5_int32)ticket->enc_part.kvno,
+				   &server_key);
     if (retval)
 	goto errout;
     if (!server_key) {
 	retval = KRB5KDC_ERR_S_PRINCIPAL_UNKNOWN;
 	goto errout;
     }
-    *kvno = server_key->key_data_kvno;
     if ((*key = (krb5_keyblock *)malloc(sizeof **key))) {
 	retval = krb5_dbekd_decrypt_key_data(kdc_context, &master_keyblock,
 					     server_key,
 					     *key, NULL);
     } else
 	retval = ENOMEM;
+    retval = krb5_c_enctype_compare(kdc_context, ticket->enc_part.enctype,
+				    (*key)->enctype, &similar);
+    if (retval)
+	goto errout;
+    if (!similar) {
+	retval = KRB5_KDB_NO_PERMITTED_KEY;
+	goto errout;
+    }
+    (*key)->enctype = ticket->enc_part.enctype;
+    *kvno = server_key->key_data_kvno;
 errout:
+    if (retval != 0) {
+	krb5_db_free_principal(kdc_context, server, *nprincs);
+	*nprincs = 0;
+    }
+
     return retval;
 }
 
@@ -1985,7 +2006,7 @@ check_allowed_to_delegate_to(krb5_context context,
 
     /* Must be in same realm */
     if (!krb5_realm_compare(context, server->princ, proxy)) {
-	return KRB5_IN_TKT_REALM_MISMATCH; /* XXX */
+	return KRB5KDC_ERR_BADOPTION;
     }
 
     req.server = server;
diff --git a/src/kdc/kdc_util.h b/src/kdc/kdc_util.h
index 0d8e36bfd..d17b0b7f8 100644
--- a/src/kdc/kdc_util.h
+++ b/src/kdc/kdc_util.h
@@ -69,6 +69,7 @@ krb5_error_code kdc_process_tgs_req
 	           krb5_keyblock **);
 
 krb5_error_code kdc_get_server_key (krb5_ticket *, unsigned int,
+				    krb5_boolean match_enctype,
 				    krb5_db_entry *, int *,
 				    krb5_keyblock **, krb5_kvno *);
 
-- 
2.26.2