auth/kerberos/kerberos_util.c

/*
   Unix SMB/CIFS implementation.

   Kerberos utility functions for GENSEC

   Copyright (C) Andrew Bartlett <abartlet@samba.org> 2004-2005

   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 2 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, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#include "includes.h"
#include "system/kerberos.h"
#include "auth/kerberos/kerberos.h"
#include "auth/credentials/credentials.h"
#include "auth/credentials/credentials_krb5.h"

struct principal_container {
	struct smb_krb5_context *smb_krb5_context;
	krb5_principal principal;
};

static int free_principal(struct principal_container *pc)
{
	/* current heimdal - 0.6.3, which we need anyway, fixes segfaults here */
	krb5_free_principal(pc->smb_krb5_context->krb5_context, pc->principal);

	return 0;
}

static krb5_error_code salt_principal_from_credentials(TALLOC_CTX *parent_ctx,
						       struct cli_credentials *machine_account,
						       struct smb_krb5_context *smb_krb5_context,
						       krb5_principal *salt_princ)
{
	krb5_error_code ret;
	char *machine_username;
	char *salt_body;
	char *lower_realm;
	const char *salt_principal;
	struct principal_container *mem_ctx = talloc(parent_ctx, struct principal_container);
	if (!mem_ctx) {
		return ENOMEM;
	}

	salt_principal = cli_credentials_get_salt_principal(machine_account);
	if (salt_principal) {
		ret = krb5_parse_name(smb_krb5_context->krb5_context, salt_principal, salt_princ);
	} else {
		machine_username = talloc_strdup(mem_ctx, cli_credentials_get_username(machine_account));

		if (!machine_username) {
			talloc_free(mem_ctx);
			return ENOMEM;
		}

		if (machine_username[strlen(machine_username)-1] == '$') {
			machine_username[strlen(machine_username)-1] = '\0';
		}
		lower_realm = strlower_talloc(mem_ctx, cli_credentials_get_realm(machine_account));
		if (!lower_realm) {
			talloc_free(mem_ctx);
			return ENOMEM;
		}

		salt_body = talloc_asprintf(mem_ctx, "%s.%s", machine_username,
					    lower_realm);
		if (!salt_body) {
			talloc_free(mem_ctx);
		return ENOMEM;
		}

		ret = krb5_make_principal(smb_krb5_context->krb5_context, salt_princ,
					  cli_credentials_get_realm(machine_account),
					  "host", salt_body, NULL);
	}

	if (ret == 0) {
		/* This song-and-dance effectivly puts the principal
		 * into talloc, so we can't loose it. */
		mem_ctx->smb_krb5_context = talloc_reference(mem_ctx, smb_krb5_context);
		mem_ctx->principal = *salt_princ;
		talloc_set_destructor(mem_ctx, free_principal);
	}
	return ret;
}

/* Obtain the principal set on this context.  Requires a
 * smb_krb5_context because we are doing krb5 principal parsing with
 * the library routines.  The returned princ is placed in the talloc
 * system by means of a destructor (do *not* free). */

krb5_error_code principal_from_credentials(TALLOC_CTX *parent_ctx,
					   struct cli_credentials *credentials,
					   struct smb_krb5_context *smb_krb5_context,
					   krb5_principal *princ)
{
	krb5_error_code ret;
	const char *princ_string;
	struct principal_container *mem_ctx = talloc(parent_ctx, struct principal_container);
	if (!mem_ctx) {
		return ENOMEM;
	}

	princ_string = cli_credentials_get_principal(credentials, mem_ctx);

	/* A NULL here has meaning, as the gssapi server case will
	 * then use the principal from the client */
	if (!princ_string) {
		talloc_free(mem_ctx);
		princ = NULL;
		return 0;
	}

	ret = krb5_parse_name(smb_krb5_context->krb5_context,
			      princ_string, princ);

	if (ret == 0) {
		/* This song-and-dance effectivly puts the principal
		 * into talloc, so we can't loose it. */
		mem_ctx->smb_krb5_context = talloc_reference(mem_ctx, smb_krb5_context);
		mem_ctx->principal = *princ;
		talloc_set_destructor(mem_ctx, free_principal);
	}
	return ret;
}

/**
 * Return a freshly allocated ccache (destroyed by destructor on child
 * of parent_ctx), for a given set of client credentials
 */

 krb5_error_code kinit_to_ccache(TALLOC_CTX *parent_ctx,
				 struct cli_credentials *credentials,
				 struct smb_krb5_context *smb_krb5_context,
				 krb5_ccache ccache)
{
	krb5_error_code ret;
	const char *password;
	time_t kdc_time = 0;
	krb5_principal princ;
	int tries;
	TALLOC_CTX *mem_ctx = talloc_new(parent_ctx);

	if (!mem_ctx) {
		return ENOMEM;
	}

	ret = principal_from_credentials(mem_ctx, credentials, smb_krb5_context, &princ);
	if (ret) {
		talloc_free(mem_ctx);
		return ret;
	}

	password = cli_credentials_get_password(credentials);

	tries = 2;
	while (tries--) {
		if (password) {
			ret = kerberos_kinit_password_cc(smb_krb5_context->krb5_context, ccache,
							 princ,
							 password, NULL, &kdc_time);
		} else {
			/* No password available, try to use a keyblock instead */

			krb5_keyblock keyblock;
			const struct samr_Password *mach_pwd;
			mach_pwd = cli_credentials_get_nt_hash(credentials, mem_ctx);
			if (!mach_pwd) {
				talloc_free(mem_ctx);
				DEBUG(1, ("kinit_to_ccache: No password available for kinit\n"));
				return EINVAL;
			}
			ret = krb5_keyblock_init(smb_krb5_context->krb5_context,
						 ETYPE_ARCFOUR_HMAC_MD5,
						 mach_pwd->hash, sizeof(mach_pwd->hash),
						 &keyblock);

			if (ret == 0) {
				ret = kerberos_kinit_keyblock_cc(smb_krb5_context->krb5_context, ccache,
								 princ,
								 &keyblock, NULL, &kdc_time);
				krb5_free_keyblock_contents(smb_krb5_context->krb5_context, &keyblock);
			}
		}

		if (ret == KRB5KRB_AP_ERR_SKEW || ret == KRB5_KDCREP_SKEW) {
			/* Perhaps we have been given an invalid skew, so try again without it */
			time_t t = time(NULL);
			krb5_set_real_time(smb_krb5_context->krb5_context, t, 0);
		} else {
			/* not a skew problem */
			break;
		}
	}

	if (ret == KRB5KRB_AP_ERR_SKEW || ret == KRB5_KDCREP_SKEW) {
		DEBUG(1,("kinit for %s failed (%s)\n",
			 cli_credentials_get_principal(credentials, mem_ctx),
			 smb_get_krb5_error_message(smb_krb5_context->krb5_context,
						    ret, mem_ctx)));
		talloc_free(mem_ctx);
		return ret;
	}

	/* cope with ticket being in the future due to clock skew */
	if ((unsigned)kdc_time > time(NULL)) {
		time_t t = time(NULL);
		int time_offset =(unsigned)kdc_time-t;
		DEBUG(4,("Advancing clock by %d seconds to cope with clock skew\n", time_offset));
		krb5_set_real_time(smb_krb5_context->krb5_context, t + time_offset + 1, 0);
	}

	if (ret == KRB5KDC_ERR_PREAUTH_FAILED && cli_credentials_wrong_password(credentials)) {
		ret = kinit_to_ccache(parent_ctx,
				      credentials,
				      smb_krb5_context,
				      ccache);
	}
	if (ret) {
		DEBUG(1,("kinit for %s failed (%s)\n",
			 cli_credentials_get_principal(credentials, mem_ctx),
			 smb_get_krb5_error_message(smb_krb5_context->krb5_context,
						    ret, mem_ctx)));
		talloc_free(mem_ctx);
		return ret;
	}
	return 0;
}

static int free_keytab(struct keytab_container *ktc)
{
	krb5_kt_close(ktc->smb_krb5_context->krb5_context, ktc->keytab);

	return 0;
}

int smb_krb5_open_keytab(TALLOC_CTX *mem_ctx,
			 struct smb_krb5_context *smb_krb5_context,
			 const char *keytab_name, struct keytab_container **ktc)
{
	krb5_keytab keytab;
	int ret;
	ret = krb5_kt_resolve(smb_krb5_context->krb5_context, keytab_name, &keytab);
	if (ret) {
		DEBUG(1,("failed to open krb5 keytab: %s\n",
			 smb_get_krb5_error_message(smb_krb5_context->krb5_context,
						    ret, mem_ctx)));
		return ret;
	}

	*ktc = talloc(mem_ctx, struct keytab_container);
	if (!*ktc) {
		return ENOMEM;
	}

	(*ktc)->smb_krb5_context = talloc_reference(*ktc, smb_krb5_context);
	(*ktc)->keytab = keytab;
	talloc_set_destructor(*ktc, free_keytab);

	return 0;
}

struct enctypes_container {
	struct smb_krb5_context *smb_krb5_context;
	krb5_enctype *enctypes;
};

static int free_enctypes(struct enctypes_container *etc)
{
	free_kerberos_etypes(etc->smb_krb5_context->krb5_context, etc->enctypes);
	return 0;
}

static krb5_error_code keytab_add_keys(TALLOC_CTX *parent_ctx,
				       const char *princ_string,
				       krb5_principal princ,
				       krb5_principal salt_princ,
				       int kvno,
				       const char *password_s,
				       struct smb_krb5_context *smb_krb5_context,
				       krb5_keytab keytab)
{
	int i;
	krb5_error_code ret;
	krb5_enctype *enctypes;
	char *enctype_string;
	struct enctypes_container *etc;
	krb5_data password;
	TALLOC_CTX *mem_ctx = talloc_new(parent_ctx);
	if (!mem_ctx) {
		return ENOMEM;
	}

	etc = talloc(mem_ctx, struct enctypes_container);
	if (!etc) {
		talloc_free(mem_ctx);
		return ENOMEM;
	}
	ret = get_kerberos_allowed_etypes(smb_krb5_context->krb5_context,
					  &enctypes);
	if (ret != 0) {
		DEBUG(1,("keytab_add_keys: getting encrption types failed (%s)\n",
			 error_message(ret)));
		talloc_free(mem_ctx);
		return ret;
	}

	etc->smb_krb5_context = talloc_reference(etc, smb_krb5_context);
	etc->enctypes = enctypes;

	talloc_set_destructor(etc, free_enctypes);

	password.data = discard_const_p(char *, password_s);
	password.length = strlen(password_s);

	for (i=0; enctypes[i]; i++) {
		krb5_keytab_entry entry;
		ret = create_kerberos_key_from_string(smb_krb5_context->krb5_context,
						      salt_princ, &password, &entry.keyblock, enctypes[i]);
		if (ret != 0) {
			talloc_free(mem_ctx);
			return ret;
		}

                entry.principal = princ;
                entry.vno       = kvno;
		ret = krb5_kt_add_entry(smb_krb5_context->krb5_context, keytab, &entry);
		enctype_string = NULL;
		krb5_enctype_to_string(smb_krb5_context->krb5_context, enctypes[i], &enctype_string);
		if (ret != 0) {
			DEBUG(1, ("Failed to add %s entry for %s(kvno %d) to keytab: %s\n",
				  enctype_string,
				  princ_string,
				  kvno,
				  smb_get_krb5_error_message(smb_krb5_context->krb5_context,
							     ret, mem_ctx)));
			talloc_free(mem_ctx);
			free(enctype_string);
			krb5_free_keyblock_contents(smb_krb5_context->krb5_context, &entry.keyblock);
			return ret;
		}

		DEBUG(5, ("Added %s(kvno %d) to keytab (%s)\n",
			  princ_string, kvno,
			  enctype_string));
		free(enctype_string);

		krb5_free_keyblock_contents(smb_krb5_context->krb5_context, &entry.keyblock);
	}
	talloc_free(mem_ctx);
	return 0;
}

static int create_keytab(TALLOC_CTX *parent_ctx,
			 struct cli_credentials *machine_account,
			 struct smb_krb5_context *smb_krb5_context,
			 krb5_keytab keytab,
			 BOOL add_old)
{
	krb5_error_code ret;
	const char *password_s;
	char *enctype_string;
	const char *old_secret;
	int kvno;
	krb5_principal salt_princ;
	krb5_principal princ;
	const char *princ_string;

	TALLOC_CTX *mem_ctx = talloc_new(parent_ctx);
	if (!mem_ctx) {
		return ENOMEM;
	}

	princ_string = cli_credentials_get_principal(machine_account, mem_ctx);
	/* Get the principal we will store the new keytab entries under */
	ret = principal_from_credentials(mem_ctx, machine_account, smb_krb5_context, &princ);
	if (ret) {
		DEBUG(1,("create_keytab: makeing krb5 principal failed (%s)\n",
			 smb_get_krb5_error_message(smb_krb5_context->krb5_context,
						    ret, mem_ctx)));
		talloc_free(mem_ctx);
		return ret;
	}

	/* The salt used to generate these entries may be different however, fetch that */
	ret = salt_principal_from_credentials(mem_ctx, machine_account,
					      smb_krb5_context,
					      &salt_princ);
	if (ret) {
		DEBUG(1,("create_keytab: makeing salt principal failed (%s)\n",
			 smb_get_krb5_error_message(smb_krb5_context->krb5_context,
						    ret, mem_ctx)));
		talloc_free(mem_ctx);
		return ret;
	}

	/* Finally, do the dance to get the password to put in the entry */
	password_s = cli_credentials_get_password(machine_account);
	if (!password_s) {
		/* If we don't have the plaintext password, try for
		 * the MD4 password hash */

		krb5_keytab_entry entry;
		const struct samr_Password *mach_pwd;
		mach_pwd = cli_credentials_get_nt_hash(machine_account, mem_ctx);
		if (!mach_pwd) {
			DEBUG(1, ("create_keytab: Domain trust informaton for account %s not available\n",
				  cli_credentials_get_principal(machine_account, mem_ctx)));
			talloc_free(mem_ctx);
			return EINVAL;
		}
		ret = krb5_keyblock_init(smb_krb5_context->krb5_context,
					 ETYPE_ARCFOUR_HMAC_MD5,
					 mach_pwd->hash, sizeof(mach_pwd->hash),
					 &entry.keyblock);
		if (ret) {
			DEBUG(1, ("create_keytab: krb5_keyblock_init failed: %s\n",
				  smb_get_krb5_error_message(smb_krb5_context->krb5_context,
							     ret, mem_ctx)));
			talloc_free(mem_ctx);
			return ret;
		}

		entry.principal = princ;
		entry.vno       = cli_credentials_get_kvno(machine_account);
		ret = krb5_kt_add_entry(smb_krb5_context->krb5_context, keytab, &entry);
		if (ret) {
			DEBUG(1, ("Failed to add ARCFOUR_HMAC (only) entry for %s to keytab: %s",
				  cli_credentials_get_principal(machine_account, mem_ctx),
				  smb_get_krb5_error_message(smb_krb5_context->krb5_context,
							     ret, mem_ctx)));
			talloc_free(mem_ctx);
			krb5_free_keyblock_contents(smb_krb5_context->krb5_context, &entry.keyblock);
			return ret;
		}

		krb5_enctype_to_string(smb_krb5_context->krb5_context,
				       ETYPE_ARCFOUR_HMAC_MD5,
				       &enctype_string);
		DEBUG(5, ("Added %s(kvno %d) to keytab (%s)\n",
			  cli_credentials_get_principal(machine_account, mem_ctx),
			  cli_credentials_get_kvno(machine_account),
			  enctype_string));
		free(enctype_string);

		krb5_free_keyblock_contents(smb_krb5_context->krb5_context, &entry.keyblock);

		/* Can't go any further, we only have this one key */
		talloc_free(mem_ctx);
		return 0;
	}

	kvno = cli_credentials_get_kvno(machine_account);
	/* good, we actually have the real plaintext */
	ret = keytab_add_keys(mem_ctx, princ_string, princ, salt_princ,
			      kvno, password_s, smb_krb5_context, keytab);
	if (!ret) {
		talloc_free(mem_ctx);
		return ret;
	}

	if (!add_old || kvno == 0) {
		talloc_free(mem_ctx);
		return 0;
	}

	old_secret = cli_credentials_get_old_password(machine_account);
	if (!old_secret) {
		talloc_free(mem_ctx);
		return 0;
	}

	ret = keytab_add_keys(mem_ctx, princ_string, princ, salt_princ,
			      kvno - 1, old_secret, smb_krb5_context, keytab);
	if (!ret) {
		talloc_free(mem_ctx);
		return ret;
	}

	talloc_free(mem_ctx);
	return 0;
}


/*
 * Walk the keytab, looking for entries of this principal name, with KVNO other than current kvno -1.
 *
 * These entries are now stale, we only keep the current, and previous entries around.
 *
 * Inspired by the code in Samba3 for 'use kerberos keytab'.
 *
 */

static krb5_error_code remove_old_entries(TALLOC_CTX *parent_ctx,
					  struct cli_credentials *machine_account,
					  struct smb_krb5_context *smb_krb5_context,
					  krb5_keytab keytab, BOOL *found_previous)
{
	krb5_error_code ret, ret2;
	krb5_kt_cursor cursor;
	krb5_principal princ;
	int kvno;
	TALLOC_CTX *mem_ctx = talloc_new(parent_ctx);
	const char *princ_string;
	if (!mem_ctx) {
		return ENOMEM;
	}

	*found_previous = False;
	princ_string = cli_credentials_get_principal(machine_account, mem_ctx);

	/* Get the principal we will store the new keytab entries under */
	ret = principal_from_credentials(mem_ctx, machine_account, smb_krb5_context, &princ);
	if (ret) {
		DEBUG(1,("update_keytab: makeing krb5 principal failed (%s)\n",
			 smb_get_krb5_error_message(smb_krb5_context->krb5_context,
						    ret, mem_ctx)));
		talloc_free(mem_ctx);
		return ret;
	}

	kvno = cli_credentials_get_kvno(machine_account);

	/* for each entry in the keytab */
	ret = krb5_kt_start_seq_get(smb_krb5_context->krb5_context, keytab, &cursor);
	switch (ret) {
	case 0:
		break;
	case HEIM_ERR_OPNOTSUPP:
	case ENOENT:
	case KRB5_KT_END:
		/* no point enumerating if there isn't anything here */
		talloc_free(mem_ctx);
		return 0;
	default:
		DEBUG(1,("failed to open keytab for read of old entries: %s\n",
			 smb_get_krb5_error_message(smb_krb5_context->krb5_context,
						    ret, mem_ctx)));
		talloc_free(mem_ctx);
		return ret;
	}

	while (!ret) {
		krb5_keytab_entry entry;
		ret = krb5_kt_next_entry(smb_krb5_context->krb5_context, keytab, &entry, &cursor);
		if (ret) {
			break;
		}
		/* if it matches our principal */
		if (!krb5_kt_compare(smb_krb5_context->krb5_context, &entry, princ, 0, 0)) {
			/* Free the entry, it wasn't the one we were looking for anyway */
			krb5_kt_free_entry(smb_krb5_context->krb5_context, &entry);
			continue;
		}

		/* delete it, if it is not kvno -1 */
		if (entry.vno != (kvno - 1 )) {
			/* Release the enumeration.  We are going to
			 * have to start this from the top again,
			 * because deletes during enumeration may not
			 * always be consistant.
			 *
			 * Also, the enumeration locks a FILE: keytab
			 */

			krb5_kt_end_seq_get(smb_krb5_context->krb5_context, keytab, &cursor);

			ret = krb5_kt_remove_entry(smb_krb5_context->krb5_context, keytab, &entry);
			krb5_kt_free_entry(smb_krb5_context->krb5_context, &entry);

			/* Deleted: Restart from the top */
			ret2 = krb5_kt_start_seq_get(smb_krb5_context->krb5_context, keytab, &cursor);
			if (ret2) {
				krb5_kt_free_entry(smb_krb5_context->krb5_context, &entry);
				DEBUG(1,("failed to restart enumeration of keytab: %s\n",
					 smb_get_krb5_error_message(smb_krb5_context->krb5_context,
								    ret, mem_ctx)));

				talloc_free(mem_ctx);
				return ret2;
			}

			if (ret) {
				break;
			}

		} else {
			*found_previous = True;
		}

		/* Free the entry, we don't need it any more */
		krb5_kt_free_entry(smb_krb5_context->krb5_context, &entry);


	}
	krb5_kt_end_seq_get(smb_krb5_context->krb5_context, keytab, &cursor);

	switch (ret) {
	case 0:
		break;
	case ENOENT:
	case KRB5_KT_END:
		ret = 0;
		break;
	default:
		DEBUG(1,("failed in deleting old entries for principal: %s: %s\n",
			 princ_string,
			 smb_get_krb5_error_message(smb_krb5_context->krb5_context,
						    ret, mem_ctx)));
	}
	talloc_free(mem_ctx);
	return ret;
}

int smb_krb5_update_keytab(TALLOC_CTX *parent_ctx,
			   struct cli_credentials *machine_account,
			   struct smb_krb5_context *smb_krb5_context,
			   struct keytab_container *keytab_container)
{
	krb5_error_code ret;
	BOOL found_previous;
	TALLOC_CTX *mem_ctx = talloc_new(parent_ctx);
	if (!mem_ctx) {
		return ENOMEM;
	}

	ret = remove_old_entries(mem_ctx, machine_account,
				 smb_krb5_context, keytab_container->keytab, &found_previous);
	if (ret != 0) {
		talloc_free(mem_ctx);
		return ret;
	}

	/* Create a new keytab.  If during the cleanout we found
	 * entires for kvno -1, then don't try and duplicate them.
	 * Otherwise, add kvno, and kvno -1 */

	ret = create_keytab(mem_ctx, machine_account, smb_krb5_context,
			    keytab_container->keytab,
			    found_previous ? False : True);
	talloc_free(mem_ctx);
	return ret;
}

_PUBLIC_ int smb_krb5_create_memory_keytab(TALLOC_CTX *parent_ctx,
				  struct cli_credentials *machine_account,
				  struct smb_krb5_context *smb_krb5_context,
				  struct keytab_container **keytab_container)
{
	krb5_error_code ret;
	TALLOC_CTX *mem_ctx = talloc_new(parent_ctx);
	const char *rand_string;
	const char *keytab_name;
	if (!mem_ctx) {
		return ENOMEM;
	}

	*keytab_container = talloc(mem_ctx, struct keytab_container);

	rand_string = generate_random_str(mem_ctx, 16);
	if (!rand_string) {
		talloc_free(mem_ctx);
		return ENOMEM;
	}

	keytab_name = talloc_asprintf(mem_ctx, "MEMORY:%s",
				      rand_string);
	if (!keytab_name) {
		talloc_free(mem_ctx);
		return ENOMEM;
	}

	ret = smb_krb5_open_keytab(mem_ctx, smb_krb5_context, keytab_name, keytab_container);
	if (ret) {
		return ret;
	}

	ret = smb_krb5_update_keytab(mem_ctx, machine_account, smb_krb5_context, *keytab_container);
	if (ret == 0) {
		talloc_steal(parent_ctx, *keytab_container);
	} else {
		*keytab_container = NULL;
	}
	talloc_free(mem_ctx);
	return ret;
}