KRB5: Do not attempt to get a TGT after a password change using OTP

https://fedorahosted.org/sssd/ticket/2271

The current krb5_child code attempts to get a TGT for the convenience of
the user using the new password after a password change operation.
However, an OTP should never be used twice, which means we can't perform
the kinit operation after chpass is finished. Instead, we only print a
PAM information instructing the user to log out and back in manually.

Reviewed-by: Alexander Bokovoy <abokovoy@redhat.com>

src/providers/krb5/krb5_auth.c

@@ -815,6 +815,7 @@ static void krb5_auth_done(struct tevent_req *subreq)
     char *renew_interval_str;
     time_t renew_interval_time = 0;
     bool use_enterprise_principal;
+    uint32_t user_info_type;
 
     ret = handle_child_recv(subreq, pd, &buf, &len);
     talloc_zfree(subreq);
@@ -1062,9 +1063,23 @@ static void krb5_auth_done(struct tevent_req *subreq)
 
     ret = sss_krb5_check_ccache_princ(kr->uid, kr->gid, kr->ccname, kr->upn);
     if (ret) {
-        DEBUG(SSSDBG_CRIT_FAILURE,
-                ("No ccache for %s in %s?\n", kr->upn, kr->ccname));
-        goto done;
+        if (res->otp == true && pd->cmd == SSS_PAM_CHAUTHTOK) {
+            DEBUG(SSSDBG_IMPORTANT_INFO,
+                  ("Password change succeeded but currently "
+                   "post-chpass kinit is not implemented\n"));
+
+            user_info_type = SSS_PAM_USER_INFO_OTP_CHPASS;
+            ret = pam_add_response(pd, SSS_PAM_USER_INFO, sizeof(uint32_t),
+                                   (const uint8_t *) &user_info_type);
+            if (ret != EOK) {
+                DEBUG(SSSDBG_CRIT_FAILURE, ("pam_add_response failed.\n"));
+                /* Not fatal */
+            }
+        } else {
+            DEBUG(SSSDBG_CRIT_FAILURE,
+                  ("No ccache for %s in %s?\n", kr->upn, kr->ccname));
+            goto done;
+        }
     }
 
     if (kr->old_ccname) {

src/providers/krb5/krb5_child.c

@@ -45,6 +45,7 @@ struct krb5_req {
     krb5_principal princ;
     char* name;
     krb5_creds *creds;
+    bool otp;
     krb5_get_init_creds_opt *options;
 
     struct pam_data *pd;
@@ -370,6 +371,8 @@ static krb5_error_code answer_otp(krb5_context ctx,
         goto done;
     }
 
+    kr->otp = true;
+
     /* Validate our assumptions about the contents of authtok. */
     ret = sss_authtok_get_password(kr->pd->authtok, &pwd, &len);
     if (ret != EOK)
@@ -694,6 +697,8 @@ static errno_t k5c_send_data(struct krb5_req *kr, int fd, errno_t error)
     size_t len;
     int ret;
 
+    DEBUG(SSSDBG_FUNC_DATA, ("Received error code %d\n", error));
+
     ret = pack_response_packet(kr, error, kr->pd->resp_list, &buf, &len);
     if (ret != EOK) {
         DEBUG(1, ("pack_response_packet failed.\n"));
@@ -1110,6 +1115,8 @@ static errno_t changepw_child(struct krb5_req *kr, bool prelim)
                                         prompter, kr, 0,
                                         SSSD_KRB5_CHANGEPW_PRINCIPAL,
                                         kr->options);
+    DEBUG(SSSDBG_TRACE_INTERNAL,
+          ("chpass is%s using OTP\n", kr->otp ? "" : " not"));
     if (kerr != 0) {
         ret = pack_user_info_chpass_error(kr->pd, "Old password not accepted.",
                                           &msg_len, &msg);
@@ -1205,6 +1212,11 @@ static errno_t changepw_child(struct krb5_req *kr, bool prelim)
 
     krb5_free_cred_contents(kr->ctx, kr->creds);
 
+    if (kr->otp == true) {
+        sss_authtok_set_empty(kr->pd->newauthtok);
+        return map_krb5_error(kerr);
+    }
+
     /* We changed some of the gic options for the password change, now we have
      * to change them back to get a fresh TGT. */
     revert_changepw_options(kr->options);

src/sss_client/pam_sss.c

@@ -771,6 +771,22 @@ static int user_info_offline_chpass(pam_handle_t *pamh)
     return PAM_SUCCESS;
 }
 
+static int user_info_otp_chpass(pam_handle_t *pamh)
+{
+    int ret;
+
+    ret = do_pam_conversation(pamh, PAM_TEXT_INFO,
+                              _("After changing the OTP password, you need to "
+                                "log out and back in order to acquire a ticket"),
+                              NULL, NULL);
+    if (ret != PAM_SUCCESS) {
+        D(("do_pam_conversation failed."));
+        return PAM_SYSTEM_ERR;
+    }
+
+    return PAM_SUCCESS;
+}
+
 static int user_info_chpass_error(pam_handle_t *pamh, size_t buflen,
                                   uint8_t *buf)
 {
@@ -856,6 +872,9 @@ static int eval_user_info_response(pam_handle_t *pamh, size_t buflen,
         case SSS_PAM_USER_INFO_OFFLINE_CHPASS:
             ret = user_info_offline_chpass(pamh);
             break;
+        case SSS_PAM_USER_INFO_OTP_CHPASS:
+            ret = user_info_otp_chpass(pamh);
+            break;
         case SSS_PAM_USER_INFO_CHPASS_ERROR:
             ret = user_info_chpass_error(pamh, buflen, buf);
             break;

src/sss_client/sss_cli.h

@@ -451,6 +451,9 @@ enum user_info_type {
                                        * possible to change the password while
                                        * the system is offline. This message
                                        * is generated by the PAM responder. */
+    SSS_PAM_USER_INFO_OTP_CHPASS,   /**< Tell the user that he needs to kinit
+                                      * or login and logout to get a TGT after
+                                      * an OTP password change */
     SSS_PAM_USER_INFO_CHPASS_ERROR, /**< Tell the user that a password change
                                      * failed and optionally give a reason.
                                      * @param Size of the message as unsigned