samba-mirror/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 "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 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 *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,
				NTSTATUS *ntstatus)
{
	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;

	ZERO_STRUCT(my_creds);

	initialize_krb5_error_table();
	if ((code = krb5_init_context(&ctx)))
		goto out;

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

	DEBUG(10,("kerberos_kinit_password: as %s using [%s] as ccache and config [%s]\n",
			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, 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 */
#ifndef SAMBA4_USES_HEIMDAL /* 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 = me;
#ifndef SAMBA4_USES_HEIMDAL /* MIT */
	canon_princ = my_creds.client;
#endif /* MIT */

	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;
	}
 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);
	}
	return code;
}

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

	initialize_krb5_error_table();
	if ((code = krb5_init_context (&ctx))) {
		DEBUG(3, ("ads_kdestroy: kdb5_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;
}

/************************************************************************
 Routine to fetch the salting principal for a service.  Active
 Directory may use a non-obvious principal name to generate the salt
 when it determines the key to use for encrypting tickets for a service,
 and hopefully we detected that when we joined the domain.
 ************************************************************************/

static char *kerberos_secrets_fetch_salting_principal(const char *service, int enctype)
{
	char *key = NULL;
	char *ret = NULL;

	if (asprintf(&key, "%s/%s/enctype=%d",
		     SECRETS_SALTING_PRINCIPAL, service, enctype) == -1) {
		return NULL;
	}
	ret = (char *)secrets_fetch(key, NULL);
	SAFE_FREE(key);
	return ret;
}

/************************************************************************
 Return the standard DES salt key
************************************************************************/

char* kerberos_standard_des_salt( void )
{
	fstring salt;

	fstr_sprintf( salt, "host/%s.%s@", lp_netbios_name(), lp_realm() );
	(void)strlower_m( salt );
	fstrcat( salt, lp_realm() );

	return SMB_STRDUP( salt );
}

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

static char* des_salt_key( void )
{
	char *key;

	if (asprintf(&key, "%s/DES/%s", SECRETS_SALTING_PRINCIPAL,
		     lp_realm()) == -1) {
		return NULL;
	}

	return key;
}

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

bool kerberos_secrets_store_des_salt( const char* salt )
{
	char* key;
	bool ret;

	if ( (key = des_salt_key()) == NULL ) {
		DEBUG(0,("kerberos_secrets_store_des_salt: failed to generate key!\n"));
		return False;
	}

	if ( !salt ) {
		DEBUG(8,("kerberos_secrets_store_des_salt: deleting salt\n"));
		secrets_delete( key );
		return True;
	}

	DEBUG(3,("kerberos_secrets_store_des_salt: Storing salt \"%s\"\n", salt));

	ret = secrets_store( key, salt, strlen(salt)+1 );

	SAFE_FREE( key );

	return ret;
}

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

static
char* kerberos_secrets_fetch_des_salt( void )
{
	char *salt, *key;

	if ( (key = des_salt_key()) == NULL ) {
		DEBUG(0,("kerberos_secrets_fetch_des_salt: failed to generate key!\n"));
		return NULL;
	}

	salt = (char*)secrets_fetch( key, NULL );

	SAFE_FREE( key );

	return salt;
}

/************************************************************************
 Routine to get the salting principal for this service.  This is 
 maintained for backwards compatibilty with releases prior to 3.0.24.
 Since we store the salting principal string only at join, we may have 
 to look for the older tdb keys.  Caller must free if return is not null.
 ************************************************************************/

char *kerberos_fetch_salt_princ_for_host_princ(krb5_context context,
					       const char *host_princ_s,
					       int enctype)
{
	char *salt_princ_s;
	/* lookup new key first */

	salt_princ_s = kerberos_secrets_fetch_des_salt();
	if (salt_princ_s == NULL) {

		/* look under the old key.  If this fails, just use the standard key */
		salt_princ_s = kerberos_secrets_fetch_salting_principal(host_princ_s,
									enctype);
		if (salt_princ_s == NULL) {
			/* fall back to host/machine.realm@REALM */
			salt_princ_s = kerberos_standard_des_salt();
		}
	}

	return salt_princ_s;
}

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);
}

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

/************************************************************************
 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, int *num_addrs,
				const struct sockaddr_storage *addr)
{
	int 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();
	int i;
	struct ip_service *ip_srv_site = NULL;
	struct ip_service *ip_srv_nonsite = NULL;
	int count_site = 0;
	int count_nonsite;
	int num_dcs;
	struct sockaddr_storage *dc_addrs;
	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;
	char *kdc_str = talloc_asprintf(mem_ctx, "%s\t\tkdc = %s\n", "",
					print_canonical_sockaddr_with_port(mem_ctx, pss));

	if (kdc_str == NULL) {
		TALLOC_FREE(frame);
		return NULL;
	}

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

	if (sitename) {
		get_kdc_list(realm, sitename, &ip_srv_site, &count_site);
		DEBUG(10, ("got %d addresses from site %s search\n", count_site,
			   sitename));
	}

	/* Get all KDC's. */

	get_kdc_list(realm, NULL, &ip_srv_nonsite, &count_nonsite);
	DEBUG(10, ("got %d addresses from site-less search\n", count_nonsite));

	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(
			(const struct sockaddr *)pss,
			(const struct sockaddr *)&ip_srv_site[i].ss)) {
			add_sockaddr_unique(dc_addrs, &num_dcs,
					    &ip_srv_site[i].ss);
		}
	}

	for (i = 0; i < count_nonsite; i++) {
		if (!sockaddr_equal(
			(const struct sockaddr *)pss,
			(const struct sockaddr *)&ip_srv_nonsite[i].ss)) {
			add_sockaddr_unique(dc_addrs, &num_dcs,
					    &ip_srv_nonsite[i].ss);
		}
	}

	dc_addrs2 = talloc_zero_array(talloc_tos(),
				      struct tsocket_address *,
				      num_dcs);

	DEBUG(10, ("%d additional KDCs to test\n", num_dcs));
	if (num_dcs == 0) {
		goto out;
	}
	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(mem_ctx, "%s\t\tkdc = %s\n",
					      kdc_str,
					      print_canonical_sockaddr_with_port(mem_ctx, &dc_addrs[i]));
		if (new_kdc_str == NULL) {
			goto out;
		}
		TALLOC_FREE(kdc_str);
		kdc_str = new_kdc_str;
	}

out:
	DEBUG(10, ("get_kdc_ip_string: Returning %s\n", kdc_str));

	result = kdc_str;
	SAFE_FREE(ip_srv_site);
	SAFE_FREE(ip_srv_nonsite);
	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) {
#ifdef HAVE_ENCTYPE_AES256_CTS_HMAC_SHA1_96
		aes_enctypes = talloc_asprintf_append(
		    aes_enctypes, "%s", "aes256-cts-hmac-sha1-96 ");
		if (aes_enctypes == NULL) {
			goto done;
		}
#endif
#ifdef HAVE_ENCTYPE_AES128_CTS_HMAC_SHA1_96
		aes_enctypes = talloc_asprintf_append(
		    aes_enctypes, "%s", "aes128-cts-hmac-sha1-96");
		if (aes_enctypes == NULL) {
			goto done;
		}
#endif
	}

	if (lp_kerberos_encryption_types() == KERBEROS_ETYPES_ALL ||
	    lp_kerberos_encryption_types() == KERBEROS_ETYPES_LEGACY) {
		legacy_enctypes = "RC4-HMAC DES-CBC-CRC DES-CBC-MD5";
	}

	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 des-cbc-crc des-cbc-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("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("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

	file_contents =
	    talloc_asprintf(fname,
			    "[libdefaults]\n\tdefault_realm = %s\n"
			    "%s"
			    "\tdns_lookup_realm = false\n\n"
			    "[realms]\n\t%s = {\n"
			    "%s\t}\n"
			    "%s\n",
			    realm_upper,
			    enctypes,
			    realm_upper,
			    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) {
		DEBUG(0,("create_local_private_krb5_conf_for_domain: smb_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;
	}

	DEBUG(5,("create_local_private_krb5_conf_for_domain: wrote "
		"file %s with realm %s KDC list = %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 conditon... 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