Commit message: Fix KDC null deref on TGS inner body null server

After the KDC decodes a FAST inner body, it does not check for a null
server.  Prior to commit 39548a5b17bbda9eeb63625a201cfd19b9de1c5b this
would typically result in an error from krb5_unparse_name(), but with
the addition of get_local_tgt() it results in a null dereference.  Add
a null check.

Reported by Joseph Sutton of Catalyst.

CVE-2021-37750:

In MIT krb5 releases 1.14 and later, an authenticated attacker can
cause a null dereference in the KDC by sending a FAST TGS request with
no server field.

ticket: 9008 (new)
tags: pullup
target_version: 1.19-next
target_version: 1.18-next
CVE: CVE-2021-37750
CWE: CWE-476
Vulnerability description: The Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) before 1.18.5 and 1.19.x before 1.19.3 has a NULL pointer dereference in kdc/do_tgs_req.c via a FAST inner body that lacks a server field.

Project: krb5
File: do_tgs_req.c

process_tgs_req(krb5_kdc_req *request, krb5_data *pkt,
                const krb5_fulladdr *from, kdc_realm_t *kdc_active_realm,
                krb5_data **response)
{
    krb5_keyblock * subkey = 0;
    krb5_keyblock *header_key = NULL;
    krb5_keyblock *stkt_server_key = NULL;
    krb5_keyblock *subject_key;
    krb5_db_entry *server = NULL;
    krb5_db_entry *stkt_server = NULL;
    krb5_db_entry *subject_server;
    krb5_kdc_rep reply;
    krb5_enc_kdc_rep_part reply_encpart;
    krb5_ticket ticket_reply, *header_ticket = 0;
    const krb5_ticket *stkt = NULL;
    krb5_enc_tkt_part enc_tkt_reply;
    int newtransited = 0;
    krb5_error_code retval = 0;
    krb5_keyblock server_keyblock, *encrypting_key;
    krb5_timestamp kdc_time, authtime = 0;
    krb5_keyblock session_key, local_tgt_key;
    krb5_keyblock *reply_key = NULL;
    krb5_principal cprinc = NULL, sprinc = NULL, altcprinc = NULL;
    krb5_const_principal authdata_client;
    krb5_principal stkt_authdata_client = NULL;
    krb5_last_req_entry *nolrarray[2], nolrentry;
    int errcode;
    const char        *status = 0;
    krb5_enc_tkt_part *header_enc_tkt = NULL; /* TGT */
    krb5_enc_tkt_part *subject_tkt = NULL; /* TGT or evidence ticket */
    krb5_db_entry *client = NULL, *header_server = NULL;
    krb5_db_entry *local_tgt, *local_tgt_storage = NULL;
    krb5_pa_s4u_x509_user *s4u_x509_user = NULL; /* protocol transition request */
    krb5_authdata **kdc_issued_auth_data = NULL; /* auth data issued by KDC */
    unsigned int c_flags = 0, s_flags = 0;       /* client/server KDB flags */
    krb5_boolean is_referral, is_crossrealm;
    const char *emsg = NULL;
    krb5_kvno ticket_kvno = 0;
    struct kdc_request_state *state = NULL;
    krb5_pa_data *pa_tgs_req; /*points into request*/
    krb5_data scratch;
    krb5_pa_data **e_data = NULL;
    krb5_audit_state *au_state = NULL;
    krb5_data **auth_indicators = NULL;
    void *ad_info = NULL, *stkt_ad_info = NULL;

    memset(&reply, 0, sizeof(reply));
    memset(&reply_encpart, 0, sizeof(reply_encpart));
    memset(&ticket_reply, 0, sizeof(ticket_reply));
    memset(&enc_tkt_reply, 0, sizeof(enc_tkt_reply));
    memset(&server_keyblock, 0, sizeof(server_keyblock));
    memset(&local_tgt_key, 0, sizeof(local_tgt_key));
    session_key.contents = NULL;

    /* Save pointer to client-requested service principal, in case of
     * errors before a successful call to search_sprinc(). */
    sprinc = request->server;

    if (request->msg_type != KRB5_TGS_REQ) {
        krb5_free_kdc_req(kdc_context, request);
        return KRB5_BADMSGTYPE;
    }

    errcode = kdc_make_rstate(kdc_active_realm, &state);
    if (errcode != 0)
        goto cleanup;

    /* Initialize audit state. */
    errcode = kau_init_kdc_req(kdc_context, request, from, &au_state);
    if (errcode)
        goto cleanup;

    /* Seed the audit trail with the request ID and basic information. */
    kau_tgs_req(kdc_context, TRUE, au_state);

    errcode = kdc_process_tgs_req(kdc_active_realm,
                                  request, from, pkt, &header_ticket,
                                  &header_server, &header_key, &subkey,
                                  &pa_tgs_req);
    if (header_ticket && header_ticket->enc_part2)
        cprinc = header_ticket->enc_part2->client;

    if (errcode) {
        status = "PROCESS_TGS";
        goto cleanup;
    }

    if (!header_ticket) {
        errcode = KRB5_NO_TKT_SUPPLIED;        /* XXX? */
        goto cleanup;
    }
    errcode = kau_make_tkt_id(kdc_context, header_ticket,
                              &au_state->tkt_in_id);
    if (errcode)
        goto cleanup;

    scratch.length = pa_tgs_req->length;
    scratch.data = (char *) pa_tgs_req->contents;
    errcode = kdc_find_fast(&request, &scratch, subkey,
                            header_ticket->enc_part2->session, state, NULL);
    /* Reset sprinc because kdc_find_fast() can replace request. */
    sprinc = request->server;
    if (errcode !=0) {
        status = "FIND_FAST";
        goto cleanup;
    }

    errcode = get_local_tgt(kdc_context, &sprinc->realm, header_server,
                            &local_tgt, &local_tgt_storage, &local_tgt_key);
    if (errcode) {
        status = "GET_LOCAL_TGT";
        goto cleanup;
    }

    /* Ignore (for now) the request modification due to FAST processing. */
    au_state->request = request;

    /*
     * Pointer to the encrypted part of the header ticket, which may be
     * replaced to point to the encrypted part of the evidence ticket
     * if constrained delegation is used. This simplifies the number of
     * special cases for constrained delegation.
     */
    header_enc_tkt = header_ticket->enc_part2;

    /*
     * We've already dealt with the AP_REQ authentication, so we can
     * use header_ticket freely.  The encrypted part (if any) has been
     * decrypted with the session key.
     */

    au_state->stage = SRVC_PRINC;

    /* XXX make sure server here has the proper realm...taken from AP_REQ
       header? */

    if (isflagset(request->kdc_options, KDC_OPT_CANONICALIZE)) {
        setflag(c_flags, KRB5_KDB_FLAG_CANONICALIZE);
        setflag(s_flags, KRB5_KDB_FLAG_CANONICALIZE);
    }

    errcode = search_sprinc(kdc_active_realm, request, s_flags, &server,
                            &status);
    if (errcode != 0)
        goto cleanup;
    sprinc = server->princ;

    /* If we got a cross-realm TGS which is not the requested server, we are
     * issuing a referral (or alternate TGT, which we treat similarly). */
    is_referral = is_cross_tgs_principal(server->princ) &&
        !krb5_principal_compare(kdc_context, request->server, server->princ);

    au_state->stage = VALIDATE_POL;

    if ((errcode = krb5_timeofday(kdc_context, &kdc_time)))
        goto cleanup;

    is_crossrealm = !data_eq(header_server->princ->realm, sprinc->realm);
    if (is_crossrealm)
        setflag(c_flags, KRB5_KDB_FLAG_CROSS_REALM);
    if (is_referral)
        setflag(c_flags, KRB5_KDB_FLAG_ISSUING_REFERRAL);

    /* Check for protocol transition */
    errcode = kdc_process_s4u2self_req(kdc_active_realm, request, server,
                                       subkey, header_enc_tkt->session,
                                       &s4u_x509_user, &client, &status);
    if (s4u_x509_user != NULL || errcode != 0) {
        if (s4u_x509_user != NULL)
            au_state->s4u2self_user = s4u_x509_user->user_id.user;
        au_state->status = status;
        kau_s4u2self(kdc_context, errcode ? FALSE : TRUE, au_state);
        au_state->s4u2self_user = NULL;
    }

    /* For user-to-user and S4U2Proxy requests, decrypt the second ticket. */
    errcode = decrypt_2ndtkt(kdc_active_realm, request, c_flags,
                             &stkt, &stkt_server, &stkt_server_key, &status);
    if (errcode)
        goto cleanup;

    retval = validate_tgs_request(kdc_active_realm, request, server,
                                  header_ticket, stkt, stkt_server, kdc_time,
                                  s4u_x509_user, client, is_crossrealm,
                                  is_referral, &status, &e_data);
    if (retval) {
        if (retval == KDC_ERR_POLICY || retval == KDC_ERR_BADOPTION)
            au_state->violation = PROT_CONSTRAINT;
        errcode = retval + ERROR_TABLE_BASE_krb5;
        goto cleanup;
    }

    if (errcode)
        goto cleanup;

    if (s4u_x509_user != NULL && client == NULL) {
        /*
         * For an S4U2Self referral request (the requesting service is
         * following a referral back to its own realm), the authdata in the
         * header ticket should be for the requested client.
         */
        setflag(c_flags, KRB5_KDB_FLAG_PROTOCOL_TRANSITION);
        authdata_client = s4u_x509_user->user_id.user;
    } else {
        /* Otherwise (including for initial S4U2Self requests), the authdata
         * should be for the header ticket client. */
        authdata_client = header_enc_tkt->client;
    }
    errcode = krb5_db_get_authdata_info(kdc_context, c_flags,
                                        header_enc_tkt->authorization_data,
                                        authdata_client, request->server,
                                        header_key, &local_tgt_key, local_tgt,
                                        header_enc_tkt->times.authtime,
                                        &ad_info, NULL);
    if (errcode && errcode != KRB5_PLUGIN_OP_NOTSUPP)
        goto cleanup;

    /* Flag all S4U2Self requests now that we have checked the authdata. */
    if (s4u_x509_user != NULL)
        setflag(c_flags, KRB5_KDB_FLAG_PROTOCOL_TRANSITION);

    if (isflagset(request->kdc_options, KDC_OPT_CNAME_IN_ADDL_TKT)) {
        /* Do constrained delegation protocol and authorization checks. */
        setflag(c_flags, KRB5_KDB_FLAG_CONSTRAINED_DELEGATION);

        errcode = kdc_process_s4u2proxy_req(kdc_active_realm, c_flags, request,
                                            stkt->enc_part2, local_tgt,
                                            &local_tgt_key, stkt_server,
                                            stkt_server_key,
                                            header_ticket->enc_part2->client,
                                            server, request->server, ad_info,
                                            &stkt_ad_info,
                                            &stkt_authdata_client,
                                            &status);
        if (errcode == KDC_ERR_POLICY || errcode == KDC_ERR_BADOPTION)
            au_state->violation = PROT_CONSTRAINT;
        else if (errcode)
            au_state->violation = LOCAL_POLICY;
        au_state->status = status;
        retval = kau_make_tkt_id(kdc_context, stkt, &au_state->evid_tkt_id);
        if (retval) {
            errcode = retval;
            goto cleanup;
        }
        kau_s4u2proxy(kdc_context, errcode ? FALSE : TRUE, au_state);
        if (errcode)
            goto cleanup;

        assert(krb5_is_tgs_principal(header_ticket->server));

        /* Use the parsed authdata from the second ticket during authdata
         * handling. */
        krb5_db_free_authdata_info(kdc_context, ad_info);
        ad_info = stkt_ad_info;
        stkt_ad_info = NULL;
    }

    au_state->stage = ISSUE_TKT;

    errcode = gen_session_key(kdc_active_realm, request, server, &session_key,
                              &status);
    if (errcode)
        goto cleanup;

    /*
     * subject_tkt will refer to the evidence ticket (for constrained
     * delegation) or the TGT. The distinction from header_enc_tkt is
     * necessary because the TGS signature only protects some fields:
     * the others could be forged by a malicious server.
     */

    if (isflagset(c_flags, KRB5_KDB_FLAG_CONSTRAINED_DELEGATION)) {
        subject_tkt = stkt->enc_part2;
        subject_server = stkt_server;
        subject_key = stkt_server_key;
    } else {
        subject_tkt = header_enc_tkt;
        subject_server = header_server;
        subject_key = header_key;
    }
    authtime = subject_tkt->times.authtime;

    /* Extract and check auth indicators from the subject ticket, except for
     * S4U2Self requests (where the client didn't authenticate). */
    if (s4u_x509_user == NULL) {
        errcode = get_auth_indicators(kdc_context, subject_tkt, local_tgt,
                                      &local_tgt_key, &auth_indicators);
        if (errcode) {
            status = "GET_AUTH_INDICATORS";
            goto cleanup;
        }

        errcode = check_indicators(kdc_context, server, auth_indicators);
        if (errcode) {
            status = "HIGHER_AUTHENTICATION_REQUIRED";
            goto cleanup;
        }
    }

    if (is_referral)
        ticket_reply.server = server->princ;
    else
        ticket_reply.server = request->server; /* XXX careful for realm... */

    enc_tkt_reply.flags = get_ticket_flags(request->kdc_options, client,
                                           server, header_enc_tkt);
    enc_tkt_reply.times.starttime = 0;

    /* OK_TO_AUTH_AS_DELEGATE must be set on the service requesting S4U2Self
     * for forwardable tickets to be issued. */
    if (isflagset(c_flags, KRB5_KDB_FLAG_PROTOCOL_TRANSITION) &&
        !is_referral &&
        !isflagset(server->attributes, KRB5_KDB_OK_TO_AUTH_AS_DELEGATE))
        clear(enc_tkt_reply.flags, TKT_FLG_FORWARDABLE);

    /* don't use new addresses unless forwarded, see below */

    enc_tkt_reply.caddrs = header_enc_tkt->caddrs;
    /* noaddrarray[0] = 0; */
    reply_encpart.caddrs = 0;/* optional...don't put it in */
    reply_encpart.enc_padata = NULL;

    /*
     * It should be noted that local policy may affect the
     * processing of any of these flags.  For example, some
     * realms may refuse to issue renewable tickets
     */

    if (isflagset(request->kdc_options, KDC_OPT_FORWARDED) ||
        isflagset(request->kdc_options, KDC_OPT_PROXY)) {

        /* include new addresses in ticket & reply */

        enc_tkt_reply.caddrs = request->addresses;
        reply_encpart.caddrs = request->addresses;
    }

    if (isflagset(request->kdc_options, KDC_OPT_POSTDATED))
        enc_tkt_reply.times.starttime = request->from;
    else
        enc_tkt_reply.times.starttime = kdc_time;

    if (isflagset(request->kdc_options, KDC_OPT_VALIDATE)) {
        assert(isflagset(c_flags, KRB5_KDB_FLAGS_S4U) == 0);
        /* BEWARE of allocation hanging off of ticket & enc_part2, it belongs
           to the caller */
        ticket_reply = *(header_ticket);
        enc_tkt_reply = *(header_ticket->enc_part2);
        enc_tkt_reply.authorization_data = NULL;
        clear(enc_tkt_reply.flags, TKT_FLG_INVALID);
    }

    if (isflagset(request->kdc_options, KDC_OPT_RENEW)) {
        krb5_timestamp old_starttime;
        krb5_deltat old_life;

        assert(isflagset(c_flags, KRB5_KDB_FLAGS_S4U) == 0);
        /* BEWARE of allocation hanging off of ticket & enc_part2, it belongs
           to the caller */
        ticket_reply = *(header_ticket);
        enc_tkt_reply = *(header_ticket->enc_part2);
        enc_tkt_reply.authorization_data = NULL;

        old_starttime = enc_tkt_reply.times.starttime ?
            enc_tkt_reply.times.starttime : enc_tkt_reply.times.authtime;
        old_life = ts_delta(enc_tkt_reply.times.endtime, old_starttime);

        enc_tkt_reply.times.starttime = kdc_time;
        enc_tkt_reply.times.endtime =
            ts_min(header_ticket->enc_part2->times.renew_till,
                   ts_incr(kdc_time, old_life));
    } else {
        /* not a renew request */
        enc_tkt_reply.times.starttime = kdc_time;

        kdc_get_ticket_endtime(kdc_active_realm, enc_tkt_reply.times.starttime,
                               header_enc_tkt->times.endtime, request->till,
                               client, server, &enc_tkt_reply.times.endtime);
    }

    kdc_get_ticket_renewtime(kdc_active_realm, request, header_enc_tkt, client,
                             server, &enc_tkt_reply);

    errcode = check_kdcpolicy_tgs(kdc_context, request, server, header_ticket,
                                  auth_indicators, kdc_time,
                                  &enc_tkt_reply.times, &status);
    if (errcode)
        goto cleanup;

    /*
     * Set authtime to be the same as header or evidence ticket's
     */
    enc_tkt_reply.times.authtime = authtime;

    /* starttime is optional, and treated as authtime if not present.
       so we can nuke it if it matches */
    if (enc_tkt_reply.times.starttime == enc_tkt_reply.times.authtime)
        enc_tkt_reply.times.starttime = 0;

    if (isflagset(c_flags, KRB5_KDB_FLAG_PROTOCOL_TRANSITION)) {
        altcprinc = s4u_x509_user->user_id.user;
    } else if (isflagset(c_flags, KRB5_KDB_FLAG_CONSTRAINED_DELEGATION)) {
        /* kdc_process_s4u2proxy_req() only allows cross-realm requests if
         * stkt_authdata_client is set. */
        altcprinc = is_crossrealm ? stkt_authdata_client : subject_tkt->client;
    } else {
        altcprinc = NULL;
    }
    if (isflagset(request->kdc_options, KDC_OPT_ENC_TKT_IN_SKEY)) {
        encrypting_key = stkt->enc_part2->session;
    } else {
        errcode = get_first_current_key(kdc_context, server, &server_keyblock);
        if (errcode) {
            status = "FINDING_SERVER_KEY";
            goto cleanup;
        }
        encrypting_key = &server_keyblock;
    }

    if (isflagset(c_flags, KRB5_KDB_FLAG_CONSTRAINED_DELEGATION)) {
        /*
         * Don't allow authorization data to be disabled if constrained
         * delegation is requested. We don't want to deny the server
         * the ability to validate that delegation was used.
         */
        clear(server->attributes, KRB5_KDB_NO_AUTH_DATA_REQUIRED);
    }
    if (isflagset(server->attributes, KRB5_KDB_NO_AUTH_DATA_REQUIRED) == 0) {
        /* If we are not doing protocol transition, try to look up the subject
         * principal so that KDB modules can add additional authdata. */
        if (!isflagset(c_flags, KRB5_KDB_FLAG_PROTOCOL_TRANSITION)) {
            /* Generate authorization data so we can include it in ticket */
            setflag(c_flags, KRB5_KDB_FLAG_INCLUDE_PAC);
            /* Map principals from foreign (possibly non-AD) realms */
            setflag(c_flags, KRB5_KDB_FLAG_MAP_PRINCIPALS);

            assert(client == NULL); /* should not have been set already */

            errcode = krb5_db_get_principal(kdc_context, subject_tkt->client,
                                            c_flags, &client);
        }
    }

    if (isflagset(c_flags, KRB5_KDB_FLAGS_S4U) && !is_referral)
        enc_tkt_reply.client = altcprinc;
    else
        enc_tkt_reply.client = header_enc_tkt->client;

    enc_tkt_reply.session = &session_key;
    enc_tkt_reply.transited.tr_type = KRB5_DOMAIN_X500_COMPRESS;
    enc_tkt_reply.transited.tr_contents = empty_string; /* equivalent of "" */

    /*
     * Only add the realm of the presented tgt to the transited list if
     * it is different than the server realm (cross-realm) and it is different
     * than the realm of the client (since the realm of the client is already
     * implicitly part of the transited list and should not be explicitly
     * listed).
     */
    if (!is_crossrealm ||
        krb5_realm_compare(kdc_context, header_ticket->server,
                           enc_tkt_reply.client)) {
        /* tgt issued by local realm or issued by realm of client */
        enc_tkt_reply.transited = header_enc_tkt->transited;
    } else {
        /* tgt issued by some other realm and not the realm of the client */
        /* assemble new transited field into allocated storage */
        if (header_enc_tkt->transited.tr_type !=
            KRB5_DOMAIN_X500_COMPRESS) {
            status = "VALIDATE_TRANSIT_TYPE";
            errcode = KRB5KDC_ERR_TRTYPE_NOSUPP;
            goto cleanup;
        }
        memset(&enc_tkt_reply.transited, 0, sizeof(enc_tkt_reply.transited));
        enc_tkt_reply.transited.tr_type = KRB5_DOMAIN_X500_COMPRESS;
        if ((errcode =
             add_to_transited(&header_enc_tkt->transited.tr_contents,
                              &enc_tkt_reply.transited.tr_contents,
                              header_ticket->server,
                              enc_tkt_reply.client,
                              request->server))) {
            status = "ADD_TO_TRANSITED_LIST";
            goto cleanup;
        }
        newtransited = 1;
    }
    if (!isflagset (request->kdc_options, KDC_OPT_DISABLE_TRANSITED_CHECK)) {
        errcode = kdc_check_transited_list (kdc_active_realm,
                                            &enc_tkt_reply.transited.tr_contents,
                                            krb5_princ_realm (kdc_context, header_enc_tkt->client),
                                            krb5_princ_realm (kdc_context, request->server));
        if (errcode == 0) {
            setflag (enc_tkt_reply.flags, TKT_FLG_TRANSIT_POLICY_CHECKED);
        } else {
            log_tgs_badtrans(kdc_context, cprinc, sprinc,
                             &enc_tkt_reply.transited.tr_contents, errcode);
        }
    } else
        krb5_klog_syslog(LOG_INFO, _("not checking transit path"));
    if (kdc_active_realm->realm_reject_bad_transit &&
        !isflagset(enc_tkt_reply.flags, TKT_FLG_TRANSIT_POLICY_CHECKED)) {
        errcode = KRB5KDC_ERR_POLICY;
        status = "BAD_TRANSIT";
        au_state->violation = LOCAL_POLICY;
        goto cleanup;
    }

    errcode = handle_authdata(kdc_context, c_flags, client, server,
                              subject_server, local_tgt, &local_tgt_key,
                              subkey != NULL ? subkey :
                              header_ticket->enc_part2->session,
                              encrypting_key, subject_key, pkt, request,
                              altcprinc, ad_info, subject_tkt,
                              &auth_indicators, &enc_tkt_reply);
    if (errcode) {
        krb5_klog_syslog(LOG_INFO, _("TGS_REQ : handle_authdata (%d)"),
                         errcode);
        status = "HANDLE_AUTHDATA";
        goto cleanup;
    }

    ticket_reply.enc_part2 = &enc_tkt_reply;

    /* If we are doing user-to-user authentication, encrypt the ticket using
     * the session key of the second ticket. */
    if (isflagset(request->kdc_options, KDC_OPT_ENC_TKT_IN_SKEY)) {
        ticket_kvno = 0;
        ticket_reply.enc_part.enctype = stkt->enc_part2->session->enctype;
        kau_u2u(kdc_context, TRUE, au_state);
    } else {
        ticket_kvno = current_kvno(server);
    }

    errcode = krb5_encrypt_tkt_part(kdc_context, encrypting_key,
                                    &ticket_reply);
    if (errcode)
        goto cleanup;
    ticket_reply.enc_part.kvno = ticket_kvno;
    /* Start assembling the response */
    au_state->stage = ENCR_REP;
    reply.msg_type = KRB5_TGS_REP;
    if (isflagset(c_flags, KRB5_KDB_FLAG_PROTOCOL_TRANSITION) &&
        krb5int_find_pa_data(kdc_context, request->padata,
                             KRB5_PADATA_S4U_X509_USER) != NULL) {
        errcode = kdc_make_s4u2self_rep(kdc_context,
                                        subkey,
                                        header_ticket->enc_part2->session,
                                        s4u_x509_user,
                                        &reply,
                                        &reply_encpart);
        if (errcode)
            au_state->status = status;
        kau_s4u2self(kdc_context, errcode ? FALSE : TRUE, au_state);
        if (errcode)
            goto cleanup;
    }

    reply.client = enc_tkt_reply.client;
    reply.enc_part.kvno = 0;/* We are using the session key */
    reply.ticket = &ticket_reply;

    reply_encpart.session = &session_key;
    reply_encpart.nonce = request->nonce;

    /* copy the time fields */
    reply_encpart.times = enc_tkt_reply.times;

    nolrentry.lr_type = KRB5_LRQ_NONE;
    nolrentry.value = 0;
    nolrentry.magic = 0;
    nolrarray[0] = &nolrentry;
    nolrarray[1] = 0;
    reply_encpart.last_req = nolrarray;        /* not available for TGS reqs */
    reply_encpart.key_exp = 0;/* ditto */
    reply_encpart.flags = enc_tkt_reply.flags;
    reply_encpart.server = ticket_reply.server;

    /* use the session key in the ticket, unless there's a subsession key
       in the AP_REQ */
    reply.enc_part.enctype = subkey ? subkey->enctype :
        header_ticket->enc_part2->session->enctype;
    errcode  = kdc_fast_response_handle_padata(state, request, &reply,
                                               subkey ? subkey->enctype : header_ticket->enc_part2->session->enctype);
    if (errcode)
        goto cleanup;
    errcode =kdc_fast_handle_reply_key(state,
                                       subkey?subkey:header_ticket->enc_part2->session, &reply_key);
    if (errcode)
        goto cleanup;
    errcode = return_enc_padata(kdc_context, pkt, request,
                                reply_key, server, &reply_encpart,
                                is_referral &&
                                isflagset(s_flags,
                                          KRB5_KDB_FLAG_CANONICALIZE));
    if (errcode) {
        status = "KDC_RETURN_ENC_PADATA";
        goto cleanup;
    }

    errcode = kau_make_tkt_id(kdc_context, &ticket_reply, &au_state->tkt_out_id);
    if (errcode)
        goto cleanup;

    if (kdc_fast_hide_client(state))
        reply.client = (krb5_principal)krb5_anonymous_principal();
    errcode = krb5_encode_kdc_rep(kdc_context, KRB5_TGS_REP, &reply_encpart,
                                  subkey ? 1 : 0,
                                  reply_key,
                                  &reply, response);
    if (!errcode)
        status = "ISSUE";

    memset(ticket_reply.enc_part.ciphertext.data, 0,
           ticket_reply.enc_part.ciphertext.length);
    free(ticket_reply.enc_part.ciphertext.data);
    /* these parts are left on as a courtesy from krb5_encode_kdc_rep so we
       can use them in raw form if needed.  But, we don't... */
    memset(reply.enc_part.ciphertext.data, 0,
           reply.enc_part.ciphertext.length);
    free(reply.enc_part.ciphertext.data);

cleanup:
    if (status == NULL)
        status = "UNKNOWN_REASON";
    krb5_free_keyblock_contents(kdc_context, &server_keyblock);
    if (reply_key)
        krb5_free_keyblock(kdc_context, reply_key);
    if (stkt_server_key)
        krb5_free_keyblock(kdc_context, stkt_server_key);
    if (errcode)
        emsg = krb5_get_error_message (kdc_context, errcode);

    if (au_state != NULL) {
        au_state->status = status;
        if (!errcode)
            au_state->reply = &reply;
        kau_tgs_req(kdc_context, errcode ? FALSE : TRUE, au_state);
        kau_free_kdc_req(au_state);
    }

    log_tgs_req(kdc_context, from, request, &reply, cprinc,
                sprinc, altcprinc, authtime,
                c_flags, status, errcode, emsg);
    if (errcode) {
        krb5_free_error_message (kdc_context, emsg);
        emsg = NULL;
    }

    if (errcode && state != NULL) {
        int got_err = 0;
        if (status == 0) {
            status = krb5_get_error_message (kdc_context, errcode);
            got_err = 1;
        }
        errcode -= ERROR_TABLE_BASE_krb5;
        if (errcode < 0 || errcode > KRB_ERR_MAX)
            errcode = KRB_ERR_GENERIC;

        retval = prepare_error_tgs(state, request, header_ticket, errcode,
                                   (server != NULL) ? server->princ : NULL,
                                   response, status, e_data);
        if (got_err) {
            krb5_free_error_message (kdc_context, status);
            status = 0;
        }
    }

    if (header_ticket != NULL)
        krb5_free_ticket(kdc_context, header_ticket);
    if (request != NULL)
        krb5_free_kdc_req(kdc_context, request);
    if (state)
        kdc_free_rstate(state);
    krb5_db_free_principal(kdc_context, server);
    krb5_db_free_principal(kdc_context, stkt_server);
    krb5_db_free_principal(kdc_context, header_server);
    krb5_db_free_principal(kdc_context, client);
    krb5_db_free_principal(kdc_context, local_tgt_storage);
    if (local_tgt_key.contents != NULL)
        krb5_free_keyblock_contents(kdc_context, &local_tgt_key);
    if (session_key.contents != NULL)
        krb5_free_keyblock_contents(kdc_context, &session_key);
    if (newtransited)
        free(enc_tkt_reply.transited.tr_contents.data);
    if (s4u_x509_user != NULL)
        krb5_free_pa_s4u_x509_user(kdc_context, s4u_x509_user);
    if (kdc_issued_auth_data != NULL)
        krb5_free_authdata(kdc_context, kdc_issued_auth_data);
    if (subkey != NULL)
        krb5_free_keyblock(kdc_context, subkey);
    if (header_key != NULL)
        krb5_free_keyblock(kdc_context, header_key);
    if (reply.padata)
        krb5_free_pa_data(kdc_context, reply.padata);
    if (reply_encpart.enc_padata)
        krb5_free_pa_data(kdc_context, reply_encpart.enc_padata);
    if (enc_tkt_reply.authorization_data != NULL)
        krb5_free_authdata(kdc_context, enc_tkt_reply.authorization_data);
    krb5_free_pa_data(kdc_context, e_data);
    k5_free_data_ptr_list(auth_indicators);
    krb5_db_free_authdata_info(kdc_context, ad_info);
    krb5_db_free_authdata_info(kdc_context, stkt_ad_info);
    krb5_free_principal(kdc_context, stkt_authdata_client);

    return retval;
}