path: root/source3/librpc/crypto/gse_krb5.c

/*
 *  GSSAPI Security Extensions
 *  Krb5 helpers
 *  Copyright (C) Simo Sorce 2010.
 *
 *  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 "smb_krb5.h"
#include "secrets.h"
#include "gse_krb5.h"

#ifdef HAVE_KRB5

static krb5_error_code flush_keytab(krb5_context krbctx, krb5_keytab keytab)
{
	krb5_error_code ret;
	krb5_kt_cursor kt_cursor;
	krb5_keytab_entry kt_entry;

	ZERO_STRUCT(kt_entry);

	ret = krb5_kt_start_seq_get(krbctx, keytab, &kt_cursor);
	if (ret == KRB5_KT_END || ret == ENOENT ) {
		/* no entries */
		return 0;
	}

	ret = krb5_kt_next_entry(krbctx, keytab, &kt_entry, &kt_cursor);
	while (ret == 0) {

		/* we need to close and reopen enumeration because we modify
		 * the keytab */
		ret = krb5_kt_end_seq_get(krbctx, keytab, &kt_cursor);
		if (ret) {
			DEBUG(1, (__location__ ": krb5_kt_end_seq_get() "
				  "failed (%s)\n", error_message(ret)));
			goto out;
		}

		/* remove the entry */
		ret = krb5_kt_remove_entry(krbctx, keytab, &kt_entry);
		if (ret) {
			DEBUG(1, (__location__ ": krb5_kt_remove_entry() "
				  "failed (%s)\n", error_message(ret)));
			goto out;
		}
		ret = smb_krb5_kt_free_entry(krbctx, &kt_entry);
		ZERO_STRUCT(kt_entry);

		/* now reopen */
		ret = krb5_kt_start_seq_get(krbctx, keytab, &kt_cursor);
		if (ret) {
			DEBUG(1, (__location__ ": krb5_kt_start_seq() failed "
				  "(%s)\n", error_message(ret)));
			goto out;
		}

		ret = krb5_kt_next_entry(krbctx, keytab,
					 &kt_entry, &kt_cursor);
	}

	if (ret != KRB5_KT_END && ret != ENOENT) {
		DEBUG(1, (__location__ ": flushing keytab we got [%s]!\n",
			  error_message(ret)));
	}

	ret = 0;

out:
	return ret;
}

static krb5_error_code get_host_principal(krb5_context krbctx,
					  krb5_principal *host_princ)
{
	krb5_error_code ret;
	char *host_princ_s = NULL;
	int err;

	err = asprintf(&host_princ_s, "%s$@%s", global_myname(), lp_realm());
	if (err == -1) {
		return -1;
	}

	strlower_m(host_princ_s);
	ret = smb_krb5_parse_name(krbctx, host_princ_s, host_princ);
	if (ret) {
		DEBUG(1, (__location__ ": smb_krb5_parse_name(%s) "
			  "failed (%s)\n",
			  host_princ_s, error_message(ret)));
	}

	SAFE_FREE(host_princ_s);
	return ret;
}

static krb5_error_code fill_keytab_from_password(krb5_context krbctx,
						 krb5_keytab keytab,
						 krb5_principal princ,
						 krb5_kvno vno,
						 krb5_data *password)
{
	krb5_error_code ret;
	krb5_enctype *enctypes;
	krb5_keytab_entry kt_entry;
	unsigned int i;

	ret = get_kerberos_allowed_etypes(krbctx, &enctypes);
	if (ret) {
		DEBUG(1, (__location__
			  ": Can't determine permitted enctypes!\n"));
		return ret;
	}

	for (i = 0; enctypes[i]; i++) {
		krb5_keyblock *key = NULL;

		if (!(key = SMB_MALLOC_P(krb5_keyblock))) {
			ret = ENOMEM;
			goto out;
		}

		if (create_kerberos_key_from_string(krbctx, princ,
						    password, key,
						    enctypes[i], false)) {
			DEBUG(10, ("Failed to create key for enctype %d "
				   "(error: %s)\n",
				   enctypes[i], error_message(ret)));
			SAFE_FREE(key);
			continue;
		}

		kt_entry.principal = princ;
		kt_entry.vno = vno;
		*(KRB5_KT_KEY(&kt_entry)) = *key;

		ret = krb5_kt_add_entry(krbctx, keytab, &kt_entry);
		if (ret) {
			DEBUG(1, (__location__ ": Failed to add entry to "
				  "keytab for enctype %d (error: %s)\n",
				   enctypes[i], error_message(ret)));
			krb5_free_keyblock(krbctx, key);
			goto out;
		}

		krb5_free_keyblock(krbctx, key);
	}

	ret = 0;

out:
	SAFE_FREE(enctypes);
	return ret;
}

#define SRV_MEM_KEYTAB_NAME "MEMORY:cifs_srv_keytab"
#define CLEARTEXT_PRIV_ENCTYPE -99

static krb5_error_code get_mem_keytab_from_secrets(krb5_context krbctx,
						   krb5_keytab *keytab)
{
	krb5_error_code ret;
	char *pwd = NULL;
	size_t pwd_len;
	krb5_kt_cursor kt_cursor;
	krb5_keytab_entry kt_entry;
	krb5_data password;
	krb5_principal princ = NULL;
	krb5_kvno kvno = 0; /* FIXME: fetch current vno from KDC ? */
	char *pwd_old = NULL;

	if (!secrets_init()) {
		DEBUG(1, (__location__ ": secrets_init failed\n"));
		return KRB5_CONFIG_CANTOPEN;
	}

	pwd = secrets_fetch_machine_password(lp_workgroup(), NULL, NULL);
	if (!pwd) {
		DEBUG(2, (__location__ ": failed to fetch machine password\n"));
		return KRB5_LIBOS_CANTREADPWD;
	}
	pwd_len = strlen(pwd);

	if (*keytab == NULL) {
		/* create memory keytab */
		ret = krb5_kt_resolve(krbctx, SRV_MEM_KEYTAB_NAME, keytab);
		if (ret) {
			DEBUG(1, (__location__ ": Failed to get memory "
				  "keytab!\n"));
			return ret;
		}
	}

	ZERO_STRUCT(kt_entry);
	ZERO_STRUCT(kt_cursor);

	/* check if the keytab already has any entry */
	ret = krb5_kt_start_seq_get(krbctx, *keytab, &kt_cursor);
	if (ret != KRB5_KT_END && ret != ENOENT ) {
		/* check if we have our special enctype used to hold
		 * the clear text password. If so, check it out so that
		 * we can verify if the keytab needs to be upgraded */
		while ((ret = krb5_kt_next_entry(krbctx, *keytab,
					   &kt_entry, &kt_cursor)) == 0) {
			if (smb_get_enctype_from_kt_entry(&kt_entry) == CLEARTEXT_PRIV_ENCTYPE) {
				break;
			}
			smb_krb5_kt_free_entry(krbctx, &kt_entry);
			ZERO_STRUCT(kt_entry);
		}

		if (ret != 0 && ret != KRB5_KT_END && ret != ENOENT ) {
			/* Error parsing keytab */
			DEBUG(1, (__location__ ": Failed to parse memory "
				  "keytab!\n"));
			goto out;
		}

		if (ret == 0) {
			/* found private entry,
			 * check if keytab is up to date */

			if ((pwd_len == KRB5_KEY_LENGTH(KRB5_KT_KEY(&kt_entry))) &&
			    (memcmp(KRB5_KEY_DATA(KRB5_KT_KEY(&kt_entry)),
						pwd, pwd_len) == 0)) {
				/* keytab is already up to date, return */
				smb_krb5_kt_free_entry(krbctx, &kt_entry);
				goto out;
			}

			smb_krb5_kt_free_entry(krbctx, &kt_entry);
			ZERO_STRUCT(kt_entry);


			/* flush keytab, we need to regen it */
			ret = flush_keytab(krbctx, *keytab);
			if (ret) {
				DEBUG(1, (__location__ ": Failed to flush "
					  "memory keytab!\n"));
				goto out;
			}
		}
	}

	{
		krb5_kt_cursor zero_csr;
		ZERO_STRUCT(zero_csr);
		if ((memcmp(&kt_cursor, &zero_csr, sizeof(krb5_kt_cursor)) != 0) && *keytab) {
			krb5_kt_end_seq_get(krbctx, *keytab, &kt_cursor);
		}
        }

	/* keytab is not up to date, fill it up */

	ret = get_host_principal(krbctx, &princ);
	if (ret) {
		DEBUG(1, (__location__ ": Failed to get host principal!\n"));
		goto out;
	}

	password.data = pwd;
	password.length = pwd_len;
	ret = fill_keytab_from_password(krbctx, *keytab,
					princ, kvno, &password);
	if (ret) {
		DEBUG(1, (__location__ ": Failed to fill memory keytab!\n"));
		goto out;
	}

	pwd_old = secrets_fetch_prev_machine_password(lp_workgroup());
	if (!pwd_old) {
		DEBUG(10, (__location__ ": no prev machine password\n"));
	} else {
		password.data = pwd_old;
		password.length = strlen(pwd_old);
		ret = fill_keytab_from_password(krbctx, *keytab,
						princ, kvno -1, &password);
		if (ret) {
			DEBUG(1, (__location__
				  ": Failed to fill memory keytab!\n"));
			goto out;
		}
	}

	/* add our private enctype + cleartext password so that we can
	 * update the keytab if secrets change later on */
	ZERO_STRUCT(kt_entry);
	kt_entry.principal = princ;
	kt_entry.vno = 0;

	KRB5_KEY_TYPE(KRB5_KT_KEY(&kt_entry)) = CLEARTEXT_PRIV_ENCTYPE;
	KRB5_KEY_LENGTH(KRB5_KT_KEY(&kt_entry)) = pwd_len;
	KRB5_KEY_DATA(KRB5_KT_KEY(&kt_entry)) = (uint8_t *)pwd;

	ret = krb5_kt_add_entry(krbctx, *keytab, &kt_entry);
	if (ret) {
		DEBUG(1, (__location__ ": Failed to add entry to "
			  "keytab for private enctype (%d) (error: %s)\n",
			   CLEARTEXT_PRIV_ENCTYPE, error_message(ret)));
		goto out;
	}

	ret = 0;

out:
	SAFE_FREE(pwd);
	SAFE_FREE(pwd_old);

	{
		krb5_kt_cursor zero_csr;
		ZERO_STRUCT(zero_csr);
		if ((memcmp(&kt_cursor, &zero_csr, sizeof(krb5_kt_cursor)) != 0) && *keytab) {
			krb5_kt_end_seq_get(krbctx, *keytab, &kt_cursor);
		}
        }

	if (princ) {
		krb5_free_principal(krbctx, princ);
	}

	if (ret) {
		if (*keytab) {
			krb5_kt_close(krbctx, *keytab);
			*keytab = NULL;
		}
	}

	return ret;
}

static krb5_error_code get_mem_keytab_from_system_keytab(krb5_context krbctx,
							 krb5_keytab *keytab,
							 bool verify)
{
	return KRB5_KT_NOTFOUND;
}

krb5_error_code gse_krb5_get_server_keytab(krb5_context krbctx,
					   krb5_keytab *keytab)
{
	krb5_error_code ret;

	*keytab = NULL;

	switch (lp_kerberos_method()) {
	default:
	case KERBEROS_VERIFY_SECRETS:
		ret = get_mem_keytab_from_secrets(krbctx, keytab);
		break;
	case KERBEROS_VERIFY_SYSTEM_KEYTAB:
		ret = get_mem_keytab_from_system_keytab(krbctx, keytab, true);
		break;
	case KERBEROS_VERIFY_DEDICATED_KEYTAB:
		/* just use whatever keytab is configured */
		ret = get_mem_keytab_from_system_keytab(krbctx, keytab, false);
		break;
	case KERBEROS_VERIFY_SECRETS_AND_KEYTAB:
		ret = get_mem_keytab_from_secrets(krbctx, keytab);
		if (ret) {
			DEBUG(3, (__location__ ": Warning! Unable to set mem "
				  "keytab from secrets!\n"));
		}
		/* Now append system keytab keys too */
		ret = get_mem_keytab_from_system_keytab(krbctx, keytab, true);
		if (ret) {
			DEBUG(3, (__location__ ": Warning! Unable to set mem "
				  "keytab from secrets!\n"));
		}
		break;
	}

	return ret;
}

#endif /* HAVE_KRB5 */