Ignore password attributes for S4U2Self requests

For consistency with Windows KDCs, allow protocol transition to work
even if the password has expired or needs changing.

Also, when looking up an enterprise principal with an AS request,
treat ERR_KEY_EXP as confirmation that the client is present in the
realm.

[ghudson@mit.edu: added comment in kdc_process_s4u2self_req(); edited
commit message]

ticket: 8763 (new)
tags: pullup
target_version: 1.17

src/kdc/kdc_util.c

@@ -1607,6 +1607,11 @@ kdc_process_s4u2self_req(kdc_realm_t *kdc_active_realm,
 
         memset(&no_server, 0, sizeof(no_server));
 
+        /* Ignore password expiration and needchange attributes (as Windows
+         * does), since S4U2Self is not password authentication. */
+        princ->pw_expiration = 0;
+        clear(princ->attributes, KRB5_KDB_REQUIRES_PWCHANGE);
+
         code = validate_as_request(kdc_active_realm, request, *princ,
                                    no_server, kdc_time, status, &e_data);
         if (code) {

src/lib/krb5/krb/s4u_creds.c

@@ -116,7 +116,7 @@ s4u_identify_user(krb5_context context,
     code = k5_get_init_creds(context, &creds, &client, NULL, NULL, 0, NULL,
                              opts, krb5_get_as_key_noop, &userid, &use_master,
                              NULL);
-    if (code == 0 || code == KRB5_PREAUTH_FAILED) {
+    if (!code || code == KRB5_PREAUTH_FAILED || code == KRB5KDC_ERR_KEY_EXP) {
         *canon_user = userid.user;
         userid.user = NULL;
         code = 0;

src/tests/gssapi/t_s4u.py

@@ -19,6 +19,14 @@
 # Get forwardable creds for service1 in the default cache.
 realm.kinit(service1, None, ['-f', '-k'])
 
+# Try S4U2Self for user with a restricted password.
+realm.run([kadminl, 'modprinc', '+needchange', realm.user_princ])
+realm.run(['./t_s4u', 'e:user', '-'])
+realm.run([kadminl, 'modprinc', '-needchange',
+          '-pwexpire', '1/1/2000', realm.user_princ])
+realm.run(['./t_s4u', 'e:user', '-'])
+realm.run([kadminl, 'modprinc', '-pwexpire', 'never', realm.user_princ])
+
 # Try krb5 -> S4U2Proxy with forwardable user creds.  This should fail
 # at the S4U2Proxy step since the DB2 back end currently has no
 # support for allowing it.