lib/util: add debug_set_forced_log_priority()

[Samba.git] / source3 / libads / kerberos.c

/*
   Unix SMB/CIFS implementation.
   kerberos utility library
   Copyright (C) Andrew Tridgell 2001
   Copyright (C) Remus Koos 2001
   Copyright (C) Nalin Dahyabhai <nalin@redhat.com> 2004.
   Copyright (C) Jeremy Allison 2004.
   Copyright (C) Gerald Carter 2006.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "libsmb/namequery.h"
#include "system/filesys.h"
#include "smb_krb5.h"
#include "../librpc/gen_ndr/ndr_misc.h"
#include "libads/kerberos_proto.h"
#include "libads/cldap.h"
#include "secrets.h"
#include "../lib/tsocket/tsocket.h"
#include "lib/util/asn1.h"

#ifdef HAVE_KRB5

#define LIBADS_CCACHE_NAME "MEMORY:libads"

/*
  we use a prompter to avoid a crash bug in the kerberos libs when
  dealing with empty passwords
  this prompter is just a string copy ...
*/
static krb5_error_code
kerb_prompter(krb5_context ctx, void *data,
               const char *name,
               const char *banner,
               int num_prompts,
               krb5_prompt prompts[])
{
        if (num_prompts == 0) return 0;
        if (num_prompts == 2) {
                /*
                 * only heimdal has a prompt type and we need to deal with it here to
                 * avoid loops.
                 *
                 * removing the prompter completely is not an option as at least these
                 * versions would crash: heimdal-1.0.2 and heimdal-1.1. Later heimdal
                 * version have looping detection and return with a proper error code.
                 */

#if defined(HAVE_KRB5_PROMPT_TYPE) /* Heimdal */
                 if (prompts[0].type == KRB5_PROMPT_TYPE_NEW_PASSWORD &&
                     prompts[1].type == KRB5_PROMPT_TYPE_NEW_PASSWORD_AGAIN) {
                        /*
                         * We don't want to change passwords here. We're
                         * called from heimal when the KDC returns
                         * KRB5KDC_ERR_KEY_EXPIRED, but at this point we don't
                         * have the chance to ask the user for a new
                         * password. If we return 0 (i.e. success), we will be
                         * spinning in the endless for-loop in
                         * change_password() in
                         * source4/heimdal/lib/krb5/init_creds_pw.c:526ff
                         */
                        return KRB5KDC_ERR_KEY_EXPIRED;
                }
#elif defined(HAVE_KRB5_GET_PROMPT_TYPES) /* MIT */
                krb5_prompt_type *prompt_types = NULL;

                prompt_types = krb5_get_prompt_types(ctx);
                if (prompt_types != NULL) {
                        if (prompt_types[0] == KRB5_PROMPT_TYPE_NEW_PASSWORD &&
                            prompt_types[1] == KRB5_PROMPT_TYPE_NEW_PASSWORD_AGAIN) {
                                return KRB5KDC_ERR_KEY_EXP;
                        }
                }
#endif
        }

        memset(prompts[0].reply->data, '\0', prompts[0].reply->length);
        if (prompts[0].reply->length > 0) {
                if (data) {
                        strncpy((char *)prompts[0].reply->data, (const char *)data,
                                prompts[0].reply->length-1);
                        prompts[0].reply->length = strlen((const char *)prompts[0].reply->data);
                } else {
                        prompts[0].reply->length = 0;
                }
        }
        return 0;
}

/*
  simulate a kinit, putting the tgt in the given cache location. If cache_name == NULL
  place in default cache location.
  remus@snapserver.com
*/
int kerberos_kinit_password_ext(const char *given_principal,
                                const char *password,
                                int time_offset,
                                time_t *expire_time,
                                time_t *renew_till_time,
                                const char *cache_name,
                                bool request_pac,
                                bool add_netbios_addr,
                                time_t renewable_time,
                                TALLOC_CTX *mem_ctx,
                                char **_canon_principal,
                                char **_canon_realm,
                                NTSTATUS *ntstatus)
{
        TALLOC_CTX *frame = talloc_stackframe();
        krb5_context ctx = NULL;
        krb5_error_code code = 0;
        krb5_ccache cc = NULL;
        krb5_principal me = NULL;
        krb5_principal canon_princ = NULL;
        krb5_creds my_creds;
        krb5_get_init_creds_opt *opt = NULL;
        smb_krb5_addresses *addr = NULL;
        char *canon_principal = NULL;
        char *canon_realm = NULL;

        ZERO_STRUCT(my_creds);

        code = smb_krb5_init_context_common(&ctx);
        if (code != 0) {
                DBG_ERR("kerberos init context failed (%s)\n",
                        error_message(code));
                TALLOC_FREE(frame);
                return code;
        }

        if (time_offset != 0) {
                krb5_set_real_time(ctx, time(NULL) + time_offset, 0);
        }

        DBG_DEBUG("as %s using [%s] as ccache and config [%s]\n",
                  given_principal,
                  cache_name ? cache_name: krb5_cc_default_name(ctx),
                  getenv("KRB5_CONFIG"));

        if ((code = krb5_cc_resolve(ctx, cache_name ? cache_name : krb5_cc_default_name(ctx), &cc))) {
                goto out;
        }

        if ((code = smb_krb5_parse_name(ctx, given_principal, &me))) {
                goto out;
        }

        if ((code = krb5_get_init_creds_opt_alloc(ctx, &opt))) {
                goto out;
        }

        krb5_get_init_creds_opt_set_renew_life(opt, renewable_time);
        krb5_get_init_creds_opt_set_forwardable(opt, True);

        /* Turn on canonicalization for lower case realm support */
#ifdef SAMBA4_USES_HEIMDAL
        krb5_get_init_creds_opt_set_win2k(ctx, opt, true);
        krb5_get_init_creds_opt_set_canonicalize(ctx, opt, true);
#else /* MIT */
        krb5_get_init_creds_opt_set_canonicalize(opt, true);
#endif /* MIT */
#if 0
        /* insane testing */
        krb5_get_init_creds_opt_set_tkt_life(opt, 60);
#endif

#ifdef HAVE_KRB5_GET_INIT_CREDS_OPT_SET_PAC_REQUEST
        if (request_pac) {
                if ((code = krb5_get_init_creds_opt_set_pac_request(ctx, opt, (krb5_boolean)request_pac))) {
                        goto out;
                }
        }
#endif
        if (add_netbios_addr) {
                if ((code = smb_krb5_gen_netbios_krb5_address(&addr,
                                                        lp_netbios_name()))) {
                        goto out;
                }
                krb5_get_init_creds_opt_set_address_list(opt, addr->addrs);
        }

        if ((code = krb5_get_init_creds_password(ctx, &my_creds, me, discard_const_p(char,password),
                                                 kerb_prompter, discard_const_p(char, password),
                                                 0, NULL, opt))) {
                goto out;
        }

        canon_princ = my_creds.client;

        code = smb_krb5_unparse_name(frame,
                                     ctx,
                                     canon_princ,
                                     &canon_principal);
        if (code != 0) {
                goto out;
        }

        DBG_DEBUG("%s mapped to %s\n", given_principal, canon_principal);

        canon_realm = smb_krb5_principal_get_realm(frame, ctx, canon_princ);
        if (canon_realm == NULL) {
                code = ENOMEM;
                goto out;
        }

        if ((code = krb5_cc_initialize(ctx, cc, canon_princ))) {
                goto out;
        }

        if ((code = krb5_cc_store_cred(ctx, cc, &my_creds))) {
                goto out;
        }

        if (expire_time) {
                *expire_time = (time_t) my_creds.times.endtime;
        }

        if (renew_till_time) {
                *renew_till_time = (time_t) my_creds.times.renew_till;
        }

        if (_canon_principal != NULL) {
                *_canon_principal = talloc_move(mem_ctx, &canon_principal);
        }
        if (_canon_realm != NULL) {
                *_canon_realm = talloc_move(mem_ctx, &canon_realm);
        }
 out:
        if (ntstatus) {
                /* fast path */
                if (code == 0) {
                        *ntstatus = NT_STATUS_OK;
                        goto cleanup;
                }

                /* fall back to self-made-mapping */
                *ntstatus = krb5_to_nt_status(code);
        }

 cleanup:
        krb5_free_cred_contents(ctx, &my_creds);
        if (me) {
                krb5_free_principal(ctx, me);
        }
        if (addr) {
                smb_krb5_free_addresses(ctx, addr);
        }
        if (opt) {
                krb5_get_init_creds_opt_free(ctx, opt);
        }
        if (cc) {
                krb5_cc_close(ctx, cc);
        }
        if (ctx) {
                krb5_free_context(ctx);
        }
        TALLOC_FREE(frame);
        return code;
}

int ads_kdestroy(const char *cc_name)
{
        krb5_error_code code;
        krb5_context ctx = NULL;
        krb5_ccache cc = NULL;

        code = smb_krb5_init_context_common(&ctx);
        if (code != 0) {
                DBG_ERR("kerberos init context failed (%s)\n",
                        error_message(code));
                return code;
        }

        if (!cc_name) {
                if ((code = krb5_cc_default(ctx, &cc))) {
                        krb5_free_context(ctx);
                        return code;
                }
        } else {
                if ((code = krb5_cc_resolve(ctx, cc_name, &cc))) {
                        DEBUG(3, ("ads_kdestroy: krb5_cc_resolve failed: %s\n",
                                  error_message(code)));
                        krb5_free_context(ctx);
                        return code;
                }
        }

        if ((code = krb5_cc_destroy (ctx, cc))) {
                DEBUG(3, ("ads_kdestroy: krb5_cc_destroy failed: %s\n",
                        error_message(code)));
        }

        krb5_free_context (ctx);
        return code;
}

int create_kerberos_key_from_string(krb5_context context,
                                        krb5_principal host_princ,
                                        krb5_principal salt_princ,
                                        krb5_data *password,
                                        krb5_keyblock *key,
                                        krb5_enctype enctype,
                                        bool no_salt)
{
        int ret;
        /*
         * Check if we've determined that the KDC is salting keys for this
         * principal/enctype in a non-obvious way.  If it is, try to match
         * its behavior.
         */
        if (no_salt) {
                KRB5_KEY_DATA(key) = (KRB5_KEY_DATA_CAST *)SMB_MALLOC(password->length);
                if (!KRB5_KEY_DATA(key)) {
                        return ENOMEM;
                }
                memcpy(KRB5_KEY_DATA(key), password->data, password->length);
                KRB5_KEY_LENGTH(key) = password->length;
                KRB5_KEY_TYPE(key) = enctype;
                return 0;
        }
        ret = smb_krb5_create_key_from_string(context,
                                              salt_princ ? salt_princ : host_princ,
                                              NULL,
                                              password,
                                              enctype,
                                              key);
        return ret;
}

/************************************************************************
************************************************************************/

int kerberos_kinit_password(const char *principal,
                            const char *password,
                            int time_offset,
                            const char *cache_name)
{
        return kerberos_kinit_password_ext(principal,
                                           password,
                                           time_offset,
                                           0,
                                           0,
                                           cache_name,
                                           False,
                                           False,
                                           0,
                                           NULL,
                                           NULL,
                                           NULL,
                                           NULL);
}

/************************************************************************
************************************************************************/

/************************************************************************
 Create a string list of available kdc's, possibly searching by sitename.
 Does DNS queries.

 If "sitename" is given, the DC's in that site are listed first.

************************************************************************/

static void add_sockaddr_unique(struct sockaddr_storage *addrs, size_t *num_addrs,
                                const struct sockaddr_storage *addr)
{
        size_t i;

        for (i=0; i<*num_addrs; i++) {
                if (sockaddr_equal((const struct sockaddr *)&addrs[i],
                                   (const struct sockaddr *)addr)) {
                        return;
                }
        }
        addrs[i] = *addr;
        *num_addrs += 1;
}

/* print_canonical_sockaddr prints an ipv6 addr in the form of
* [ipv6.addr]. This string, when put in a generated krb5.conf file is not
* always properly dealt with by some older krb5 libraries. Adding the hard-coded
* portnumber workarounds the issue. - gd */

static char *print_canonical_sockaddr_with_port(TALLOC_CTX *mem_ctx,
                                                const struct sockaddr_storage *pss)
{
        char *str = NULL;

        str = print_canonical_sockaddr(mem_ctx, pss);
        if (str == NULL) {
                return NULL;
        }

        if (pss->ss_family != AF_INET6) {
                return str;
        }

#if defined(HAVE_IPV6)
        str = talloc_asprintf_append(str, ":88");
#endif
        return str;
}

static char *get_kdc_ip_string(char *mem_ctx,
                const char *realm,
                const char *sitename,
                const struct sockaddr_storage *pss)
{
        TALLOC_CTX *frame = talloc_stackframe();
        size_t i;
        struct samba_sockaddr *ip_sa_site = NULL;
        struct samba_sockaddr *ip_sa_nonsite = NULL;
        struct samba_sockaddr sa = {0};
        size_t count_site = 0;
        size_t count_nonsite;
        size_t num_dcs;
        struct sockaddr_storage *dc_addrs = NULL;
        struct tsocket_address **dc_addrs2 = NULL;
        const struct tsocket_address * const *dc_addrs3 = NULL;
        char *result = NULL;
        struct netlogon_samlogon_response **responses = NULL;
        NTSTATUS status;
        bool ok;
        char *kdc_str = NULL;
        char *canon_sockaddr = NULL;

        SMB_ASSERT(pss != NULL);

        canon_sockaddr = print_canonical_sockaddr_with_port(frame, pss);
        if (canon_sockaddr == NULL) {
                goto out;
        }

        kdc_str = talloc_asprintf(frame,
                                  "\t\tkdc = %s\n",
                                  canon_sockaddr);
        if (kdc_str == NULL) {
                goto out;
        }

        ok = sockaddr_storage_to_samba_sockaddr(&sa, pss);
        if (!ok) {
                goto out;
        }

        /*
         * First get the KDC's only in this site, the rest will be
         * appended later
         */

        if (sitename) {
                status = get_kdc_list(frame,
                                        realm,
                                        sitename,
                                        &ip_sa_site,
                                        &count_site);
                if (!NT_STATUS_IS_OK(status)) {
                        DBG_ERR("get_kdc_list fail %s\n",
                                nt_errstr(status));
                        goto out;
                }
                DBG_DEBUG("got %zu addresses from site %s search\n",
                        count_site,
                        sitename);
        }

        /* Get all KDC's. */

        status = get_kdc_list(frame,
                                        realm,
                                        NULL,
                                        &ip_sa_nonsite,
                                        &count_nonsite);
        if (!NT_STATUS_IS_OK(status)) {
                DBG_ERR("get_kdc_list (site-less) fail %s\n",
                        nt_errstr(status));
                goto out;
        }
        DBG_DEBUG("got %zu addresses from site-less search\n", count_nonsite);

        if (count_site + count_nonsite < count_site) {
                /* Wrap check. */
                DBG_ERR("get_kdc_list_talloc (site-less) fail wrap error\n");
                goto out;
        }


        dc_addrs = talloc_array(talloc_tos(), struct sockaddr_storage,
                                count_site + count_nonsite);
        if (dc_addrs == NULL) {
                goto out;
        }

        num_dcs = 0;

        for (i = 0; i < count_site; i++) {
                if (!sockaddr_equal(&sa.u.sa, &ip_sa_site[i].u.sa)) {
                        add_sockaddr_unique(dc_addrs, &num_dcs,
                                            &ip_sa_site[i].u.ss);
                }
        }

        for (i = 0; i < count_nonsite; i++) {
                if (!sockaddr_equal(&sa.u.sa, &ip_sa_nonsite[i].u.sa)) {
                        add_sockaddr_unique(dc_addrs, &num_dcs,
                                            &ip_sa_nonsite[i].u.ss);
                }
        }

        DBG_DEBUG("%zu additional KDCs to test\n", num_dcs);
        if (num_dcs == 0) {
                /*
                 * We do not have additional KDCs, but we have the one passed
                 * in via `pss`. So just use that one and leave.
                 */
                result = talloc_move(mem_ctx, &kdc_str);
                goto out;
        }

        dc_addrs2 = talloc_zero_array(talloc_tos(),
                                      struct tsocket_address *,
                                      num_dcs);
        if (dc_addrs2 == NULL) {
                goto out;
        }

        for (i=0; i<num_dcs; i++) {
                char addr[INET6_ADDRSTRLEN];
                int ret;

                print_sockaddr(addr, sizeof(addr), &dc_addrs[i]);

                ret = tsocket_address_inet_from_strings(dc_addrs2, "ip",
                                                        addr, LDAP_PORT,
                                                        &dc_addrs2[i]);
                if (ret != 0) {
                        status = map_nt_error_from_unix(errno);
                        DEBUG(2,("Failed to create tsocket_address for %s - %s\n",
                                 addr, nt_errstr(status)));
                        goto out;
                }
        }

        dc_addrs3 = (const struct tsocket_address * const *)dc_addrs2;

        status = cldap_multi_netlogon(talloc_tos(),
                        dc_addrs3, num_dcs,
                        realm, lp_netbios_name(),
                        NETLOGON_NT_VERSION_5 | NETLOGON_NT_VERSION_5EX,
                        MIN(num_dcs, 3), timeval_current_ofs(3, 0), &responses);
        TALLOC_FREE(dc_addrs2);
        dc_addrs3 = NULL;

        if (!NT_STATUS_IS_OK(status)) {
                DEBUG(10,("get_kdc_ip_string: cldap_multi_netlogon failed: "
                          "%s\n", nt_errstr(status)));
                goto out;
        }

        for (i=0; i<num_dcs; i++) {
                char *new_kdc_str;

                if (responses[i] == NULL) {
                        continue;
                }

                /* Append to the string - inefficient but not done often. */
                new_kdc_str = talloc_asprintf_append(
                                kdc_str,
                                "\t\tkdc = %s\n",
                                print_canonical_sockaddr_with_port(
                                        mem_ctx, &dc_addrs[i]));
                if (new_kdc_str == NULL) {
                        goto out;
                }
                kdc_str = new_kdc_str;
        }

        result = talloc_move(mem_ctx, &kdc_str);
out:
        if (result != NULL) {
                DBG_DEBUG("Returning\n%s\n", result);
        } else {
                DBG_NOTICE("Failed to get KDC ip address\n");
        }

        TALLOC_FREE(frame);
        return result;
}

/************************************************************************
 Create  a specific krb5.conf file in the private directory pointing
 at a specific kdc for a realm. Keyed off domain name. Sets
 KRB5_CONFIG environment variable to point to this file. Must be
 run as root or will fail (which is a good thing :-).
************************************************************************/

#if !defined(SAMBA4_USES_HEIMDAL) /* MIT version */
static char *get_enctypes(TALLOC_CTX *mem_ctx)
{
        char *aes_enctypes = NULL;
        const char *legacy_enctypes = "";
        char *enctypes = NULL;

        aes_enctypes = talloc_strdup(mem_ctx, "");
        if (aes_enctypes == NULL) {
                goto done;
        }

        if (lp_kerberos_encryption_types() == KERBEROS_ETYPES_ALL ||
            lp_kerberos_encryption_types() == KERBEROS_ETYPES_STRONG) {
                aes_enctypes = talloc_asprintf_append(
                    aes_enctypes, "%s", "aes256-cts-hmac-sha1-96 ");
                if (aes_enctypes == NULL) {
                        goto done;
                }
                aes_enctypes = talloc_asprintf_append(
                    aes_enctypes, "%s", "aes128-cts-hmac-sha1-96");
                if (aes_enctypes == NULL) {
                        goto done;
                }
        }

        if (lp_weak_crypto() == SAMBA_WEAK_CRYPTO_ALLOWED &&
            (lp_kerberos_encryption_types() == KERBEROS_ETYPES_ALL ||
             lp_kerberos_encryption_types() == KERBEROS_ETYPES_LEGACY)) {
                legacy_enctypes = "RC4-HMAC";
        }

        enctypes =
            talloc_asprintf(mem_ctx, "\tdefault_tgs_enctypes = %s %s\n"
                                     "\tdefault_tkt_enctypes = %s %s\n"
                                     "\tpreferred_enctypes = %s %s\n",
                            aes_enctypes, legacy_enctypes, aes_enctypes,
                            legacy_enctypes, aes_enctypes, legacy_enctypes);
done:
        TALLOC_FREE(aes_enctypes);
        return enctypes;
}
#else /* Heimdal version */
static char *get_enctypes(TALLOC_CTX *mem_ctx)
{
        const char *aes_enctypes = "";
        const char *legacy_enctypes = "";
        char *enctypes = NULL;

        if (lp_kerberos_encryption_types() == KERBEROS_ETYPES_ALL ||
            lp_kerberos_encryption_types() == KERBEROS_ETYPES_STRONG) {
                aes_enctypes =
                    "aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96";
        }

        if (lp_kerberos_encryption_types() == KERBEROS_ETYPES_ALL ||
            lp_kerberos_encryption_types() == KERBEROS_ETYPES_LEGACY) {
                legacy_enctypes = "arcfour-hmac-md5";
        }

        enctypes = talloc_asprintf(mem_ctx, "\tdefault_etypes = %s %s\n",
                                   aes_enctypes, legacy_enctypes);

        return enctypes;
}
#endif

bool create_local_private_krb5_conf_for_domain(const char *realm,
                                                const char *domain,
                                                const char *sitename,
                                                const struct sockaddr_storage *pss)
{
        char *dname;
        char *tmpname = NULL;
        char *fname = NULL;
        char *file_contents = NULL;
        char *kdc_ip_string = NULL;
        size_t flen = 0;
        ssize_t ret;
        int fd;
        char *realm_upper = NULL;
        bool result = false;
        char *enctypes = NULL;
        const char *include_system_krb5 = "";
        mode_t mask;

        if (!lp_create_krb5_conf()) {
                return false;
        }

        if (realm == NULL) {
                DEBUG(0, ("No realm has been specified! Do you really want to "
                          "join an Active Directory server?\n"));
                return false;
        }

        if (domain == NULL || pss == NULL) {
                return false;
        }

        dname = lock_path(talloc_tos(), "smb_krb5");
        if (!dname) {
                return false;
        }
        if ((mkdir(dname, 0755)==-1) && (errno != EEXIST)) {
                DEBUG(0,("create_local_private_krb5_conf_for_domain: "
                        "failed to create directory %s. Error was %s\n",
                        dname, strerror(errno) ));
                goto done;
        }

        tmpname = lock_path(talloc_tos(), "smb_tmp_krb5.XXXXXX");
        if (!tmpname) {
                goto done;
        }

        fname = talloc_asprintf(dname, "%s/krb5.conf.%s", dname, domain);
        if (!fname) {
                goto done;
        }

        DEBUG(10,("create_local_private_krb5_conf_for_domain: fname = %s, realm = %s, domain = %s\n",
                fname, realm, domain ));

        realm_upper = talloc_strdup(fname, realm);
        if (!strupper_m(realm_upper)) {
                goto done;
        }

        kdc_ip_string = get_kdc_ip_string(dname, realm, sitename, pss);
        if (!kdc_ip_string) {
                goto done;
        }

        enctypes = get_enctypes(fname);
        if (enctypes == NULL) {
                goto done;
        }

#if !defined(SAMBA4_USES_HEIMDAL)
        if (lp_include_system_krb5_conf()) {
                include_system_krb5 = "include /etc/krb5.conf";
        }
#endif

        /*
         * We are setting 'dns_lookup_kdc' to true, because we want to lookup
         * KDCs which are not configured via DNS SRV records, eg. if we do:
         *
         *     net ads join -Uadmin@otherdomain
         */
        file_contents =
            talloc_asprintf(fname,
                            "[libdefaults]\n"
                            "\tdefault_realm = %s\n"
                            "%s"
                            "\tdns_lookup_realm = false\n"
                            "\tdns_lookup_kdc = true\n\n"
                            "[realms]\n\t%s = {\n"
                            "%s\t}\n"
                            "\t%s = {\n"
                            "%s\t}\n"
                            "%s\n",
                            realm_upper,
                            enctypes,
                            realm_upper,
                            kdc_ip_string,
                            domain,
                            kdc_ip_string,
                            include_system_krb5);

        if (!file_contents) {
                goto done;
        }

        flen = strlen(file_contents);

        mask = umask(S_IRWXO | S_IRWXG);
        fd = mkstemp(tmpname);
        umask(mask);
        if (fd == -1) {
                DBG_ERR("mkstemp failed, for file %s. Errno %s\n",
                        tmpname,
                        strerror(errno));
                goto done;
        }

        if (fchmod(fd, 0644)==-1) {
                DEBUG(0,("create_local_private_krb5_conf_for_domain: fchmod failed for %s."
                        " Errno %s\n",
                        tmpname, strerror(errno) ));
                unlink(tmpname);
                close(fd);
                goto done;
        }

        ret = write(fd, file_contents, flen);
        if (flen != ret) {
                DEBUG(0,("create_local_private_krb5_conf_for_domain: write failed,"
                        " returned %d (should be %u). Errno %s\n",
                        (int)ret, (unsigned int)flen, strerror(errno) ));
                unlink(tmpname);
                close(fd);
                goto done;
        }
        if (close(fd)==-1) {
                DEBUG(0,("create_local_private_krb5_conf_for_domain: close failed."
                        " Errno %s\n", strerror(errno) ));
                unlink(tmpname);
                goto done;
        }

        if (rename(tmpname, fname) == -1) {
                DEBUG(0,("create_local_private_krb5_conf_for_domain: rename "
                        "of %s to %s failed. Errno %s\n",
                        tmpname, fname, strerror(errno) ));
                unlink(tmpname);
                goto done;
        }

        DBG_INFO("wrote file %s with realm %s KDC list:\n%s\n",
                 fname, realm_upper, kdc_ip_string);

        /* Set the environment variable to this file. */
        setenv("KRB5_CONFIG", fname, 1);

        result = true;

#if defined(OVERWRITE_SYSTEM_KRB5_CONF)

#define SYSTEM_KRB5_CONF_PATH "/etc/krb5.conf"
        /* Insanity, sheer insanity..... */

        if (strequal(realm, lp_realm())) {
                SMB_STRUCT_STAT sbuf;

                if (sys_lstat(SYSTEM_KRB5_CONF_PATH, &sbuf, false) == 0) {
                        if (S_ISLNK(sbuf.st_ex_mode) && sbuf.st_ex_size) {
                                int lret;
                                size_t alloc_size = sbuf.st_ex_size + 1;
                                char *linkpath = talloc_array(talloc_tos(), char,
                                                alloc_size);
                                if (!linkpath) {
                                        goto done;
                                }
                                lret = readlink(SYSTEM_KRB5_CONF_PATH, linkpath,
                                                alloc_size - 1);
                                if (lret == -1) {
                                        TALLOC_FREE(linkpath);
                                        goto done;
                                }
                                linkpath[lret] = '\0';

                                if (strcmp(linkpath, fname) == 0) {
                                        /* Symlink already exists. */
                                        TALLOC_FREE(linkpath);
                                        goto done;
                                }
                                TALLOC_FREE(linkpath);
                        }
                }

                /* Try and replace with a symlink. */
                if (symlink(fname, SYSTEM_KRB5_CONF_PATH) == -1) {
                        const char *newpath = SYSTEM_KRB5_CONF_PATH ".saved";
                        if (errno != EEXIST) {
                                DEBUG(0,("create_local_private_krb5_conf_for_domain: symlink "
                                        "of %s to %s failed. Errno %s\n",
                                        fname, SYSTEM_KRB5_CONF_PATH, strerror(errno) ));
                                goto done; /* Not a fatal error. */
                        }

                        /* Yes, this is a race condition... too bad. */
                        if (rename(SYSTEM_KRB5_CONF_PATH, newpath) == -1) {
                                DEBUG(0,("create_local_private_krb5_conf_for_domain: rename "
                                        "of %s to %s failed. Errno %s\n",
                                        SYSTEM_KRB5_CONF_PATH, newpath,
                                        strerror(errno) ));
                                goto done; /* Not a fatal error. */
                        }

                        if (symlink(fname, SYSTEM_KRB5_CONF_PATH) == -1) {
                                DEBUG(0,("create_local_private_krb5_conf_for_domain: "
                                        "forced symlink of %s to /etc/krb5.conf failed. Errno %s\n",
                                        fname, strerror(errno) ));
                                goto done; /* Not a fatal error. */
                        }
                }
        }
#endif

done:
        TALLOC_FREE(tmpname);
        TALLOC_FREE(dname);

        return result;
}
#endif