From 5e6d1796106df8ba6bc1973ee0917c170d929086 Mon Sep 17 00:00:00 2001
From: Isaac Boukris <iboukris@gmail.com>
Date: Mon, 3 Dec 2018 02:33:07 +0200
Subject: [PATCH] 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           | 5 +++++
 src/lib/krb5/krb/s4u_creds.c | 2 +-
 src/tests/gssapi/t_s4u.py    | 8 ++++++++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/kdc/kdc_util.c b/src/kdc/kdc_util.c
index 6d53173fb0..6517a213cd 100644
--- a/src/kdc/kdc_util.c
+++ b/src/kdc/kdc_util.c
@@ -1574,6 +1574,11 @@ 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) {
diff --git a/src/lib/krb5/krb/s4u_creds.c b/src/lib/krb5/krb/s4u_creds.c
index d2fdcb3f16..614ed41908 100644
--- a/src/lib/krb5/krb/s4u_creds.c
+++ b/src/lib/krb5/krb/s4u_creds.c
@@ -117,7 +117,7 @@ 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;
diff --git a/src/tests/gssapi/t_s4u.py b/src/tests/gssapi/t_s4u.py
index fd29e1a270..84f3fbd752 100755
--- a/src/tests/gssapi/t_s4u.py
+++ b/src/tests/gssapi/t_s4u.py
@@ -20,6 +20,14 @@
 # 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.