xref: /src/usr.bin/login/k5login.c

/*	$NetBSD: k5login.c,v 1.29 2012/04/23 15:07:02 christos Exp $	*/

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * 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 BY THE REGENTS AND CONTRIBUTORS ``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.
 */

/*
 * Copyright (c) 1980, 1987, 1988 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

#include <sys/cdefs.h>
#ifndef lint
#if 0
static char sccsid[] = "@(#)klogin.c	5.11 (Berkeley) 7/12/92";
#endif
__RCSID("$NetBSD: k5login.c,v 1.29 2012/04/23 15:07:02 christos Exp $");
#endif /* not lint */

#ifdef KERBEROS5
#include <sys/param.h>
#include <sys/syslog.h>
#include <krb5/krb5.h>
#include <pwd.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>

#define KRB5_DEFAULT_OPTIONS 0
#define KRB5_DEFAULT_LIFE 60*60*10 /* 10 hours */

krb5_context kcontext;

int notickets;
int krb5_configured;
char *krb5tkfile_env;
extern char *tty;
extern int login_krb5_forwardable_tgt;
extern int has_ccache;

static char tkt_location[MAXPATHLEN];
static krb5_creds forw_creds;
int have_forward;
static krb5_principal me, server;

int k5_read_creds(char *);
int k5_write_creds(void);
int k5_verify_creds(krb5_context, krb5_ccache);
int k5login(struct passwd *, char *, char *, char *);
void k5destroy(void);

static void __printflike(3, 4)
k5_log(krb5_context context, krb5_error_code kerror, const char *fmt, ...)
{
	const char *msg = krb5_get_error_message(context, kerror);
	char *str;
	va_list ap;

	va_start(ap, fmt);
	if (vasprintf(&str, fmt, ap) == -1) {
		va_end(ap);
		syslog(LOG_NOTICE, "Cannot allocate memory for error %s: %s",
		    fmt, msg);
		return;
	}
	va_end(ap);

	syslog(LOG_NOTICE, "warning: %s: %s", str, msg);
	krb5_free_error_message(kcontext, msg);
	free(str);
}

/*
 * Verify the Kerberos ticket-granting ticket just retrieved for the
 * user.  If the Kerberos server doesn't respond, assume the user is
 * trying to fake us out (since we DID just get a TGT from what is
 * supposedly our KDC).  If the host/<host> service is unknown (i.e.,
 * the local keytab doesn't have it), let her in.
 *
 * Returns 1 for confirmation, -1 for failure, 0 for uncertainty.
 */
int
k5_verify_creds(krb5_context c, krb5_ccache ccache)
{
	char phost[MAXHOSTNAMELEN];
	int retval, have_keys;
	krb5_principal princ;
	krb5_keyblock *kb = 0;
	krb5_error_code kerror;
	krb5_data packet;
	krb5_auth_context auth_context = NULL;
	krb5_ticket *ticket = NULL;

	kerror = krb5_sname_to_principal(c, 0, 0, KRB5_NT_SRV_HST, &princ);
	if (kerror) {
		krb5_warn(kcontext, kerror, "constructing local service name");
		return (-1);
	}

	/* Do we have host/<host> keys? */
	/* (use default keytab, kvno IGNORE_VNO to get the first match,
	 * and default enctype.) */
	kerror = krb5_kt_read_service_key(c, NULL, princ, 0, 0, &kb);
	if (kb)
		krb5_free_keyblock(c, kb);
	/* any failure means we don't have keys at all. */
	have_keys = kerror ? 0 : 1;

	/* XXX there should be a krb5 function like mk_req, but taking a full
	 * principal, instead of a service/hostname.  (Did I miss one?) */
	gethostname(phost, sizeof(phost));
	phost[sizeof(phost) - 1] = '\0';

	/* talk to the kdc and construct the ticket */
	kerror = krb5_mk_req(c, &auth_context, 0, "host", phost,
	                     0, ccache, &packet);
	/* wipe the auth context for rd_req */
	if (auth_context) {
		krb5_auth_con_free(c, auth_context);
		auth_context = NULL;
	}
	if (kerror == KRB5KDC_ERR_S_PRINCIPAL_UNKNOWN) {
		/* we have a service key, so something should be
		 * in the database, therefore this error packet could
		 * have come from an attacker. */
		if (have_keys) {
			retval = -1;
			goto EGRESS;
		}
		/* but if it is unknown and we've got no key, we don't
		 * have any security anyhow, so it is ok. */
		else {
			retval = 0;
			goto EGRESS;
		}
	}
	else if (kerror) {
		krb5_warn(kcontext, kerror,
			  "Unable to verify Kerberos V5 TGT: %s", phost);
		k5_log(kcontext, kerror, "Kerberos V5 TGT bad");
		retval = -1;
		goto EGRESS;
	}
	/* got ticket, try to use it */
	kerror = krb5_rd_req(c, &auth_context, &packet,
	                     princ, NULL, NULL, &ticket);
	if (kerror) {
		if (!have_keys) {
			/* The krb5 errors aren't specified well, but I think
			 * these values cover the cases we expect. */
			switch (kerror) {
			case ENOENT:	/* no keytab */
			case KRB5_KT_NOTFOUND:
				retval = 0;
				break;
			default:
				/* unexpected error: fail */
				retval = -1;
				break;
			}
		}
		else {
			/* we have keys, so if we got any error, we could be
			 * under attack. */
			retval = -1;
		}
		krb5_warn(kcontext, kerror, "Unable to verify host ticket");
		k5_log(kcontext, kerror, "can't verify v5 ticket (%s)",
		    retval ? "keytab found, assuming failure" :
		    "no keytab found, assuming success");
		goto EGRESS;
	}
	/*
	 * The host/<host> ticket has been received _and_ verified.
	 */
	retval = 1;

	/* do cleanup and return */
EGRESS:
	if (auth_context)
		krb5_auth_con_free(c, auth_context);
	krb5_free_principal(c, princ);
	/* possibly ticket and packet need freeing here as well */
	return (retval);
}

/*
 * Attempt to read forwarded kerberos creds
 *
 * return 0 on success (forwarded creds in memory)
 *        1 if no forwarded creds.
 */
int
k5_read_creds(char *username)
{
	krb5_error_code kerror;
	krb5_creds mcreds;
	krb5_ccache ccache;

	have_forward = 0;
	memset((char*) &mcreds, 0, sizeof(forw_creds));
	memset((char*) &forw_creds, 0, sizeof(forw_creds));

	kerror = krb5_cc_default(kcontext, &ccache);
	if (kerror) {
		krb5_warn(kcontext, kerror, "while getting default ccache");
		return(1);
	}

	kerror = krb5_parse_name(kcontext, username, &me);
	if (kerror) {
		krb5_warn(kcontext, kerror, "when parsing name %s", username);
		return(1);
	}

	mcreds.client = me;
	const char *realm = krb5_principal_get_realm(kcontext, me);
	size_t rlen = strlen(realm);
	kerror = krb5_build_principal_ext(kcontext, &mcreds.server,
			rlen, realm,
			KRB5_TGS_NAME_SIZE,
			KRB5_TGS_NAME,
			rlen, realm,
			0);
	if (kerror) {
		krb5_warn(kcontext, kerror, "while building server name");
		goto nuke_ccache;
	}

	kerror = krb5_cc_retrieve_cred(kcontext, ccache, 0,
				       &mcreds, &forw_creds);
	if (kerror) {
		krb5_warn(kcontext, kerror,
			  "while retrieving V5 initial ticket for copy");
		goto nuke_ccache;
	}

	have_forward = 1;

	strlcpy(tkt_location, getenv("KRB5CCNAME"), sizeof(tkt_location));
	krb5tkfile_env = tkt_location;
	has_ccache = 1;
	notickets = 0;

nuke_ccache:
	krb5_cc_destroy(kcontext, ccache);
	return(!have_forward);
}

int
k5_write_creds(void)
{
	krb5_error_code kerror;
	krb5_ccache ccache;

	if (!have_forward)
		return (1);

	kerror = krb5_cc_default(kcontext, &ccache);
	if (kerror) {
		krb5_warn(kcontext, kerror, "while getting default ccache");
		return (1);
	}

	kerror = krb5_cc_initialize(kcontext, ccache, me);
	if (kerror) {
		krb5_warn(kcontext, kerror,
			  "while re-initializing V5 ccache as user");
		goto nuke_ccache_contents;
	}

	kerror = krb5_cc_store_cred(kcontext, ccache, &forw_creds);
	if (kerror) {
		krb5_warn(kcontext, kerror,
			  "while re-storing V5 ccache as user");
		goto nuke_ccache_contents;
	}

nuke_ccache_contents:
	krb5_free_cred_contents(kcontext, &forw_creds);
	return (kerror != 0);
}

/*
 * Attempt to log the user in using Kerberos authentication
 *
 * return 0 on success (will be logged in)
 *	  1 if Kerberos failed (try local password in login)
 */
int
k5login(struct passwd *pw, char *instance, char *localhost, char *password)
{
        krb5_error_code kerror;
	krb5_creds my_creds;
	krb5_timestamp now;
	krb5_ccache ccache = NULL;
	long lifetime = KRB5_DEFAULT_LIFE;
	int options = KRB5_DEFAULT_OPTIONS;
	char *realm, *client_name;
	char *principal;

	krb5_configured = 1;

	if (login_krb5_forwardable_tgt)
		options |= KDC_OPT_FORWARDABLE;

	/*
	 * Root logins don't use Kerberos.
	 * If we have a realm, try getting a ticket-granting ticket
	 * and using it to authenticate.  Otherwise, return
	 * failure so that we can try the normal passwd file
	 * for a password.  If that's ok, log the user in
	 * without issuing any tickets.
	 */
	if (strcmp(pw->pw_name, "root") == 0 ||
	    krb5_get_default_realm(kcontext, &realm)) {
		krb5_configured = 0;
		return (1);
	}

	/*
	 * get TGT for local realm
	 * tickets are stored in a file named TKT_ROOT plus uid
	 * except for user.root tickets.
	 */

	if (strcmp(instance, "root") != 0)
		(void)snprintf(tkt_location, sizeof tkt_location,
				"FILE:/tmp/krb5cc_%d.%s", pw->pw_uid, tty);
	else
		(void)snprintf(tkt_location, sizeof tkt_location,
				"FILE:/tmp/krb5cc_root_%d.%s", pw->pw_uid, tty);
	krb5tkfile_env = tkt_location;
	has_ccache = 1;

	if (strlen(instance))
		asprintf(&principal, "%s/%s", pw->pw_name, instance);
	else
		principal = strdup(pw->pw_name);
	if (!principal) {
		syslog(LOG_NOTICE, "fatal: %s", strerror(errno));
		return (1);
	}

	if ((kerror = krb5_cc_resolve(kcontext, tkt_location, &ccache)) != 0) {
		k5_log(kcontext, kerror, "while getting default ccache");
		return (1);
	}

	if ((kerror = krb5_parse_name(kcontext, principal, &me)) != 0) {
		k5_log(kcontext, kerror, "when parsing name %s", principal);
		return (1);
	}

	if ((kerror = krb5_unparse_name(kcontext, me, &client_name)) != 0) {
		k5_log(kcontext, kerror, "when unparsing name %s", principal);
		return (1);
	}

	kerror = krb5_cc_initialize(kcontext, ccache, me);
	if (kerror != 0) {
		k5_log(kcontext, kerror, "when initializing cache %s",
		    tkt_location);
		return (1);
	}

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

	my_creds.client = me;

	const char *xrealm = krb5_principal_get_realm(kcontext, me);
	size_t rlen = strlen(xrealm);
	if ((kerror = krb5_build_principal_ext(kcontext,
			&server,
			rlen, xrealm,
			KRB5_TGS_NAME_SIZE,
			KRB5_TGS_NAME,
			rlen, xrealm,
			0)) != 0) {
		k5_log(kcontext, kerror, "while building server name");
		return (1);
	}

	my_creds.server = server;

	if ((kerror = krb5_timeofday(kcontext, &now)) != 0) {
		k5_log(kcontext, kerror, "while getting time of day");
		return (1);
	}

	my_creds.times.starttime = 0;	/* start timer when request
					   gets to KDC */
	my_creds.times.endtime = now + lifetime;
	my_creds.times.renew_till = 0;

	kerror = krb5_get_in_tkt_with_password(kcontext, options,
	    NULL, NULL, NULL, password, ccache, &my_creds, 0);

	if (my_creds.server != NULL)
		krb5_free_principal(kcontext, my_creds.server);

	if (chown(&tkt_location[5], pw->pw_uid, pw->pw_gid) < 0)
		syslog(LOG_ERR, "chown tkfile (%s): %m", &tkt_location[5]);

	if (kerror) {
		if (kerror == KRB5KRB_AP_ERR_BAD_INTEGRITY)
			printf("%s: Kerberos Password incorrect\n", principal);
		else
			krb5_warn(kcontext, kerror,
				  "while getting initial credentials");

		return (1);
	}

	if (k5_verify_creds(kcontext, ccache) < 0)
		return (1);

	/* Success */
	notickets = 0;
	return (0);
}

/*
 * Remove any credentials
 */
void
k5destroy(void)
{
        krb5_error_code kerror;
	krb5_ccache ccache = NULL;

	if (krb5tkfile_env == NULL)
		return;

	kerror = krb5_cc_resolve(kcontext, krb5tkfile_env, &ccache);
	if (kerror == 0)
		(void)krb5_cc_destroy(kcontext, ccache);
}
#endif /* KERBEROS5 */