path: root/utils/gssd/krb5_util.c

/*
 *  Adapted in part from MIT Kerberos 5-1.2.1 slave/kprop.c and from
 *  http://docs.sun.com/?p=/doc/816-1331/6m7oo9sms&a=view
 *
 *  Copyright (c) 2002-2004 The Regents of the University of Michigan.
 *  All rights reserved.
 *
 *  Andy Adamson <andros@umich.edu>
 *  J. Bruce Fields <bfields@umich.edu>
 *  Marius Aamodt Eriksen <marius@umich.edu>
 *  Kevin Coffman <kwc@umich.edu>
 */

/*
 * slave/kprop.c
 *
 * Copyright 1990,1991 by the Massachusetts Institute of Technology.
 * All Rights Reserved.
 *
 * Export of this software from the United States of America may
 *   require a specific license from the United States Government.
 *   It is the responsibility of any person or organization contemplating
 *   export to obtain such a license before exporting.
 *
 * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
 * distribute this software and its documentation for any purpose and
 * without fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright notice and
 * this permission notice appear in supporting documentation, and that
 * the name of M.I.T. not be used in advertising or publicity pertaining
 * to distribution of the software without specific, written prior
 * permission.  Furthermore if you modify this software you must label
 * your software as modified software and not distribute it in such a
 * fashion that it might be confused with the original M.I.T. software.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is" without express
 * or implied warranty.
 */

/*
 * Copyright 1994 by OpenVision Technologies, Inc.
 *
 * Permission to use, copy, modify, distribute, and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appears in all copies and
 * that both that copyright notice and this permission notice appear in
 * supporting documentation, and that the name of OpenVision not be used
 * in advertising or publicity pertaining to distribution of the software
 * without specific, written prior permission. OpenVision makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 * OPENVISION DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
 * EVENT SHALL OPENVISION BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
 * USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
 * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */
/*
  krb5_util.c

  Copyright (c) 2004 The Regents of the University of Michigan.
  All rights reserved.

  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions
  are met:

  1. Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.
  2. Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in the
     documentation and/or other materials provided with the distribution.
  3. Neither the name of the University nor the names of its
     contributors may be used to endorse or promote products derived
     from this software without specific prior written permission.

  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
  BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

*/

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include "config.h"
#include <sys/param.h>
#include <rpc/rpc.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <errno.h>
#include <time.h>
#include <gssapi/gssapi.h>
#ifdef USE_PRIVATE_KRB5_FUNCTIONS
#include <gssapi/gssapi_krb5.h>
#endif
#include <krb5.h>
#include <rpc/auth_gss.h>

#include "gssd.h"
#include "err_util.h"
#include "gss_util.h"
#include "gss_oids.h"
#include "krb5_util.h"

/* Global list of principals/cache file names for machine credentials */
struct gssd_k5_kt_princ *gssd_k5_kt_princ_list = NULL;

/*==========================*/
/*===  Internal routines ===*/
/*==========================*/

static int select_krb5_ccache(const struct dirent *d);
static int gssd_find_existing_krb5_ccache(uid_t uid, struct dirent **d);
static int gssd_get_single_krb5_cred(krb5_context context,
		krb5_keytab kt, struct gssd_k5_kt_princ *ple);
static int gssd_have_realm_ple(krb5_data *realm);
static int gssd_process_krb5_keytab(krb5_context context, krb5_keytab kt,
		char *kt_name);

/*
 * Called from the scandir function to weed out potential krb5
 * credentials cache files
 *
 * Returns:
 *	0 => don't select this one
 *	1 => select this one
 */
static int
select_krb5_ccache(const struct dirent *d)
{
	/* Don't consider anything but regular files. (No symlinks, etc.) */
	if (d->d_type != DT_REG)
		return 0;

	if (strstr(d->d_name, GSSD_DEFAULT_CRED_PREFIX))
		return 1;
	else
		return 0;
}

/*
 * Look in the GSSD_DEFAULT_CRED_DIR for files that look like they
 * are Kerberos Credential Cache files for a given UID.  Return
 * non-zero and the dirent pointer for the entry most likely to be
 * what we want. Otherwise, return zero and no dirent pointer.
 * The caller is responsible for freeing the dirent if one is returned.
 *
 * Returns:
 *	0 => could not find an existing entry
 *	1 => found an existing entry
 */
static int
gssd_find_existing_krb5_ccache(uid_t uid, struct dirent **d)
{
	struct dirent **namelist;
	int n;
	int i;
	int found = 0;
	struct dirent *best_match_dir = NULL;
	struct stat best_match_stat, tmp_stat;

	*d = NULL;
	n = scandir(GSSD_DEFAULT_CRED_DIR, &namelist, select_krb5_ccache, 0);
	if (n < 0) {
		perror("scandir looking for krb5 credentials caches");
	}
	else if (n > 0) {
		char substring[128];
		char statname[1024];
		snprintf(substring, sizeof(substring), "_%d", uid);
		for (i = 0; i < n; i++) {
			printerr(3, "CC file '%s' being considered\n",
				 namelist[i]->d_name);
			if (strstr(namelist[i]->d_name, substring)) {
				snprintf(statname, sizeof(statname),
					 "%s/%s", GSSD_DEFAULT_CRED_DIR,
					 namelist[i]->d_name);
				if (stat(statname, &tmp_stat)) {
					printerr(0, "Error doing stat "
						    "on file '%s'\n",
						 statname);
					continue;
				}
				printerr(3, "CC file '%s' matches "
					    "name check and has "
					    "mtime of %u\n",
					 namelist[i]->d_name,
					 tmp_stat.st_mtime);
				/* if more than one match is found,
				 * return the most recent (the one
				 * with the latest mtime),
				 * and don't free the dirent */
				if (!found) {
					best_match_dir = namelist[i];
					best_match_stat = tmp_stat;
					found++;
				}
				else {
					/*
					 * If the current match has
					 * an mtime later than the
					 * one we are looking at,
					 * then use the current match.
					 * Otherwise, we still have
					 * the best match.
					 */
					if (tmp_stat.st_mtime >
						    best_match_stat.st_mtime) {
						free(best_match_dir);
						best_match_dir = namelist[i];
						best_match_stat = tmp_stat;
					}
					else {
						free(namelist[i]);
					}
					printerr(3, "CC file '%s' is our "
						    "current best match "
						    "with mtime of %u\n",
						 best_match_dir->d_name,
						 best_match_stat.st_mtime);
				}
			}
			else
				free(namelist[i]);
		}
		free(namelist);
	}
	if (found)
	{
		*d = best_match_dir;
	}
	return found;
}


#ifdef HAVE_SET_ALLOWABLE_ENCTYPES
/*
 * this routine obtains a credentials handle via gss_acquire_cred()
 * then calls gss_krb5_set_allowable_enctypes() to limit the encryption
 * types negotiated.
 *
 * XXX Should call some function to determine the enctypes supported
 * by the kernel. (Only need to do that once!)
 *
 * Returns:
 *	0 => all went well
 *     -1 => there was an error
 */

int
limit_krb5_enctypes(struct rpc_gss_sec *sec, uid_t uid)
{
	u_int maj_stat, min_stat;
	gss_cred_id_t credh;
/*	krb5_enctype enctypes[] = {ENCTYPE_DES3_CBC_SHA1};
				   ENCTYPE_ARCFOUR_HMAC, */
	krb5_enctype enctypes[] = {ENCTYPE_DES3_CBC_SHA1,
				   ENCTYPE_DES_CBC_MD5,
				   ENCTYPE_DES_CBC_CRC};
	int num_enctypes = sizeof(enctypes) / sizeof(enctypes[0]);

	maj_stat = gss_acquire_cred(&min_stat, NULL, 0,
				    GSS_C_NULL_OID_SET, GSS_C_INITIATE,
				    &credh, NULL, NULL);

	if (maj_stat != GSS_S_COMPLETE) {
		printerr(0, "WARNING: error from gss_acquire_cred "
			"for user with uid %d (%s)\n",
			uid, error_message(min_stat));
		return -1;
	}

	maj_stat = gss_set_allowable_enctypes(&min_stat, credh, &krb5oid,
					     num_enctypes, &enctypes);
	if (maj_stat != GSS_S_COMPLETE) {
		printerr(0, "WARNING: error from gss_set_allowable_enctypes "
			"for user with uid %d (%s)\n",
			uid, error_message(min_stat));
		return -1;
	}
	sec->cred = credh;

	return 0;
}
#endif	/* HAVE_SET_ALLOWABLE_ENCTYPES */

/*
 * Obtain credentials via a key in the keytab given
 * a keytab handle and a gssd_k5_kt_princ structure.
 * Checks to see if current credentials are expired,
 * if not, uses the keytab to obtain new credentials.
 *
 * Returns:
 *	0 => success (or credentials have not expired)
 *	nonzero => error
 */
static int
gssd_get_single_krb5_cred(krb5_context context,
			  krb5_keytab kt,
			  struct gssd_k5_kt_princ *ple)
{
	krb5_get_init_creds_opt options;
	krb5_creds my_creds;
	krb5_ccache ccache = NULL;
	char kt_name[BUFSIZ];
	char cc_name[BUFSIZ];
	int code;
	time_t now = time(0);

	memset(&my_creds, 0, sizeof(my_creds));

	if (ple->ccname && ple->endtime > now) {
		printerr(2, "INFO: Credentials in CC '%s' are good until %d\n",
			 ple->ccname, ple->endtime);
		code = 0;
		goto out;
	}

	if ((code = krb5_kt_get_name(context, kt, kt_name, BUFSIZ))) {
		printerr(0, "ERROR: Unable to get keytab name in "
			    "gssd_get_single_krb5_cred\n");
		goto out;
	}

	krb5_get_init_creds_opt_init(&options);
	krb5_get_init_creds_opt_set_address_list(&options, NULL);

#ifdef TEST_SHORT_LIFETIME
	/* set a short lifetime (for debugging only!) */
	printerr(0, "WARNING: Using (debug) short machine cred lifetime!\n");
	krb5_get_init_creds_opt_set_tkt_life(&options, 5*60);
#endif
        if ((code = krb5_get_init_creds_keytab(context, &my_creds, ple->princ,
	                                  kt, 0, 0, &options))) {
		char *pname;
		if ((krb5_unparse_name(context, ple->princ, &pname))) {
			pname = NULL;
		}
		printerr(0, "WARNING: %s while getting initial ticket for "
			    "principal '%s' from keytab '%s'\n",
			 error_message(code),
			 pname ? pname : "<unparsable>", kt_name);
		if (pname) krb5_free_unparsed_name(context, pname);
		goto out;
	}

	/*
	 * Initialize cache file which we're going to be using
	 */

	snprintf(cc_name, sizeof(cc_name), "FILE:%s/%s%s_%s",
		GSSD_DEFAULT_CRED_DIR, GSSD_DEFAULT_CRED_PREFIX,
		GSSD_DEFAULT_MACHINE_CRED_SUFFIX, ple->realm);
	ple->endtime = my_creds.times.endtime;
	ple->ccname = strdup(cc_name);
	if (ple->ccname == NULL) {
		printerr(0, "ERROR: no storage to duplicate credentials "
			    "cache name\n");
		code = ENOMEM;
		goto out;
	}
	if ((code = krb5_cc_resolve(context, cc_name, &ccache))) {
		printerr(0, "ERROR: %s while opening credential cache '%s'\n",
			 error_message(code), cc_name);
		goto out;
	}
	if ((code = krb5_cc_initialize(context, ccache, ple->princ))) {
		printerr(0, "ERROR: %s while initializing credential "
			 "cache '%s'\n", error_message(code), cc_name);
		goto out;
	}
	if ((code = krb5_cc_store_cred(context, ccache, &my_creds))) {
		printerr(0, "ERROR: %s while storing credentials in '%s'\n",
			 error_message(code), cc_name);
		goto out;
	}

	code = 0;
	printerr(1, "Using (machine) credentials cache: '%s'\n", cc_name);
  out:
	if (ccache)
		krb5_cc_close(context, ccache);
	krb5_free_cred_contents(context, &my_creds);
	return (code);
}

/*
 * Determine if we already have a ple for the given realm
 *
 * Returns:
 *	0 => no ple found for given realm
 *	1 => found ple for given realm
 */
static int
gssd_have_realm_ple(krb5_data *realm)
{
	struct gssd_k5_kt_princ *ple;

	for (ple = gssd_k5_kt_princ_list; ple; ple = ple->next) {
		if ((realm->length == strlen(ple->realm)) &&
		    (strncmp(realm->data, ple->realm, realm->length) == 0)) {
		    return 1;
		}
	}
	return 0;
}

/*
 * Process the given keytab file and create a list of principals we
 * might use to perform mount operations.
 *
 * Returns:
 *	0 => Sucess
 *	nonzero => Error
 */
static int
gssd_process_krb5_keytab(krb5_context context, krb5_keytab kt, char *kt_name)
{
	krb5_kt_cursor cursor;
	krb5_keytab_entry kte;
	krb5_error_code code;
	struct gssd_k5_kt_princ *ple;
	int retval = -1;

	/*
	 * Look through each entry in the keytab file and determine
	 * if we might want to use it later to do a mount.  If so,
	 * save info in the global principal list
	 * (gssd_k5_kt_princ_list).
	 * Note: (ple == principal list entry)
	 */
	if ((code = krb5_kt_start_seq_get(context, kt, &cursor))) {
		printerr(0, "ERROR: %s while beginning keytab scan "
			    "for keytab '%s'\n",
			error_message(code), kt_name);
		retval = code;
		goto out;
	}

	while ((code = krb5_kt_next_entry(context, kt, &kte, &cursor)) == 0) {
		char *pname;
		if ((code = krb5_unparse_name(context, kte.principal,
					      &pname))) {
			printerr(0, "WARNING: Skipping keytab entry because "
				    "we failed to unparse principal name: %s\n",
				 error_message(code));
			continue;
		}
		printerr(2, "Processing keytab entry for principal '%s'\n",
			 pname);
		if ( (kte.principal->data[0].length == GSSD_SERVICE_NAME_LEN) &&
		     (strncmp(kte.principal->data[0].data, GSSD_SERVICE_NAME,
			      GSSD_SERVICE_NAME_LEN) == 0) &&
		     (!gssd_have_realm_ple(&kte.principal->realm)) ) {
			printerr(2, "We will use this entry (%s)\n", pname);
			ple = malloc(sizeof(struct gssd_k5_kt_princ));
			if (ple == NULL) {
				printerr(0, "ERROR: could not allocate storage "
					    "for principal list entry\n");
				krb5_free_unparsed_name(context, pname);
				retval = ENOMEM;
				goto out;
			}
			/* These will be filled in later */
			ple->next = NULL;
			ple->ccname = NULL;
			ple->endtime = 0;
			if ((ple->realm =
				strndup(kte.principal->realm.data,
					kte.principal->realm.length))
					== NULL) {
				printerr(0, "ERROR: %s while copying realm to "
					    "principal list entry\n",
					 "not enough memory");
				krb5_free_unparsed_name(context, pname);
				retval = ENOMEM;
				goto out;
			}
			if ((code = krb5_copy_principal(context,
					kte.principal, &ple->princ))) {
				printerr(0, "ERROR: %s while copying principal "
					    "to principal list entry\n",
					error_message(code));
				krb5_free_unparsed_name(context, pname);
				retval = code;
				goto out;
			}
			if (gssd_k5_kt_princ_list == NULL)
				gssd_k5_kt_princ_list = ple;
			else {
				ple->next = gssd_k5_kt_princ_list;
				gssd_k5_kt_princ_list = ple;
			}
		}
		else {
			printerr(2, "We will NOT use this entry (%s)\n",
				pname);
		}
		krb5_free_unparsed_name(context, pname);
	}

	if ((code = krb5_kt_end_seq_get(context, kt, &cursor))) {
		printerr(0, "WARNING: %s while ending keytab scan for "
			    "keytab '%s'\n",
			 error_message(code), kt_name);
	}

	retval = 0;
  out:
	return retval;
}


/*==========================*/
/*===  External routines ===*/
/*==========================*/

/*
 * Attempt to find the best match for a credentials cache file
 * given only a UID.  We really need more information, but we
 * do the best we can.
 *
 * Returns:
 *	void
 */
void
gssd_setup_krb5_user_gss_ccache(uid_t uid, char *servername)
{
	char			buf[MAX_NETOBJ_SZ];
#ifdef HAVE_GSS_KRB5_CCACHE_NAME
	u_int			min_stat;
#endif
	struct dirent		*d;

	printerr(2, "getting credentials for client with uid %u for "
		    "server %s\n", uid, servername);
	memset(buf, 0, sizeof(buf));
	if (gssd_find_existing_krb5_ccache(uid, &d)) {
		snprintf(buf, sizeof(buf), "FILE:%s/%s",
			GSSD_DEFAULT_CRED_DIR, d->d_name);
		free(d);
	}
	else
		snprintf(buf, sizeof(buf), "FILE:%s/%s%u",
			GSSD_DEFAULT_CRED_DIR,
			GSSD_DEFAULT_CRED_PREFIX, uid);
	printerr(2, "using %s as credentials cache for client with "
		    "uid %u for server %s\n", buf, uid, servername);
#ifdef HAVE_GSS_KRB5_CCACHE_NAME
	gss_krb5_ccache_name(&min_stat, buf, NULL);
#else
	/*
	 * Set the KRB5CCNAME environment variable to tell the krb5 code
	 * which credentials cache to use.  (Instead of using the private
	 * function above for which there is no generic gssapi
	 * equivalent.)
	 */
	 setenv("KRB5CCNAME", buf, 1);
#endif
}

/*
 * Let the gss code know where to find the machine credentials ccache.
 *
 * Returns:
 *	void
 */
void
gssd_setup_krb5_machine_gss_ccache(char *ccname)
{
#ifdef HAVE_GSS_KRB5_CCACHE_NAME
	u_int			min_stat;
#endif
	printerr(2, "using %s as credentials cache for machine creds\n",
		 ccname);
#ifdef HAVE_GSS_KRB5_CCACHE_NAME
	gss_krb5_ccache_name(&min_stat, ccname, NULL);
#else
	/*
	 * Set the KRB5CCNAME environment variable to tell the krb5 code
	 * which credentials cache to use.  (Instead of using the private
	 * function above for which there is no generic gssapi
	 * equivalent.)
	 */
	 setenv("KRB5CCNAME", ccname, 1);
#endif
}

/*
 * The first time through this routine, go through the keytab and
 * determine which keys we will try to use as machine credentials.
 * Every time through this routine, try to obtain credentials using
 * the keytab entries selected the first time through.
 *
 * Returns:
 *	0 => obtained one or more credentials
 *	nonzero => error
 *
 */

int
gssd_refresh_krb5_machine_creds(void)
{
	krb5_context context = NULL;
	krb5_keytab kt = NULL;;
	krb5_error_code code;
	int retval = -1;
	struct gssd_k5_kt_princ *ple;
	int gotone = 0;
	static int processed_keytab = 0;


	code = krb5_init_context(&context);
	if (code) {
		printerr(0, "ERROR: %s while initializing krb5 in "
			    "gssd_refresh_krb5_machine_creds\n",
			 error_message(code));
		retval = code;
		goto out;
	}

	printerr(1, "Using keytab file '%s'\n", keytabfile);

	if ((code = krb5_kt_resolve(context, keytabfile, &kt))) {
		printerr(0, "ERROR: %s while resolving keytab '%s'\n",
			 error_message(code), keytabfile);
		goto out;
	}

	/* Only go through the keytab file once.  Only print messages once. */
	if (gssd_k5_kt_princ_list == NULL && !processed_keytab) {
		processed_keytab = 1;
		gssd_process_krb5_keytab(context, kt, keytabfile);
		if (gssd_k5_kt_princ_list == NULL) {
			printerr(0, "ERROR: No usable keytab entries found in "
				    "keytab '%s'\n", keytabfile);
			printerr(0, "Do you have a valid keytab entry for "
				    "%s/<your.host>@<YOUR.REALM> in "
				    "keytab file %s ?\n",
				    GSSD_SERVICE_NAME, keytabfile);
			printerr(0, "Continuing without (machine) credentials "
				    "- nfs4 mounts with Kerberos will fail\n");
		}
	}

	/*
	 * If we don't have any keytab entries we liked, then we have a problem
	 */
	if (gssd_k5_kt_princ_list == NULL) {
		retval = ENOENT;
		goto out;
	}

	/*
	 * Now go through the list of saved entries and get initial
	 * credentials for them (We can't do this while making the
	 * list because it messes up the keytab iteration cursor
	 * when we use the keytab to get credentials.)
	 */
	for (ple = gssd_k5_kt_princ_list; ple; ple = ple->next) {
		if ((gssd_get_single_krb5_cred(context, kt, ple)) == 0) {
			gotone++;
		}
	}
	if (!gotone) {
		printerr(0, "ERROR: No usable machine credentials obtained\n");
		goto out;
	}

	retval = 0;
  out:
  	if (kt) krb5_kt_close(context, kt);
	krb5_free_context(context);

	return retval;
}


/*
 * Return an array of pointers to names of credential cache files
 * which can be used to try to create gss contexts with a server.
 *
 * Returns:
 *	0 => list is attached
 *	nonzero => error
 */
int
gssd_get_krb5_machine_cred_list(char ***list)
{
	char **l;
	int listinc = 10;
	int listsize = listinc;
	int i = 0;
	int retval;
	struct gssd_k5_kt_princ *ple;

	/* Assume failure */
	retval = -1;
	*list = (char **) NULL;

	/* Refresh machine credentials */
	if ((retval = gssd_refresh_krb5_machine_creds())) {
		goto out;
	}

	if ((l = (char **) malloc(listsize * sizeof(char *))) == NULL) {
		retval = ENOMEM;
		goto out;
	}

	for (ple = gssd_k5_kt_princ_list; ple; ple = ple->next) {
		if (ple->ccname) {
			if (i + 1 > listsize) {
				listsize += listinc;
				l = (char **)
					realloc(l, listsize * sizeof(char *));
				if (l == NULL) {
					retval = ENOMEM;
					goto out;
				}
			}
			if ((l[i++] = strdup(ple->ccname)) == NULL) {
				retval = ENOMEM;
				goto out;
			}
		}
	}
	if (i > 0) {
		l[i] = NULL;
		*list = l;
		retval = 0;
		goto out;
	}
  out:
	return retval;
}

/*
 * Frees the list of names returned in get_krb5_machine_cred_list()
 */
void
gssd_free_krb5_machine_cred_list(char **list)
{
	char **n;

	if (list == NULL)
		return;
	for (n = list; n && *n; n++) {
		free(*n);
	}
	free(list);
}

/*
 * Called upon exit.  Destroys machine credentials.
 */
void
gssd_destroy_krb5_machine_creds(void)
{
	krb5_context context;
	krb5_error_code code = 0;
	krb5_ccache ccache;
	struct gssd_k5_kt_princ *ple;

	code = krb5_init_context(&context);
	if (code) {
		printerr(0, "ERROR: %s while initializing krb5\n",
			 error_message(code));
		goto out;
	}

	for (ple = gssd_k5_kt_princ_list; ple; ple = ple->next) {
		if (!ple->ccname)
			continue;
		if ((code = krb5_cc_resolve(context, ple->ccname, &ccache))) {
			printerr(0, "WARNING: %s while resolving credential "
				    "cache '%s' for destruction\n",
				 error_message(code), ple->ccname);
			continue;
		}

		if ((code = krb5_cc_destroy(context, ccache))) {
			printerr(0, "WARNING: %s while destroying credential "
				    "cache '%s'\n",
				 error_message(code), ple->ccname);
		}
	}
  out:
	krb5_free_context(context);
}