heimdal/kdc/digest.c

/*
 * Copyright (c) 2006 Kungliga Tekniska Högskolan
 * (Royal Institute of Technology, Stockholm, Sweden). 
 * 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 Institute 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 INSTITUTE 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 INSTITUTE 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. 
 */

#include "kdc_locl.h"
#include <digest_asn1.h>
#include <hex.h>

RCSID("$Id$");

krb5_error_code
_kdc_do_digest(krb5_context context, 
	       krb5_kdc_configuration *config,
	       const DigestREQ *req, krb5_data *reply,
	       const char *from, struct sockaddr *addr)
{
    krb5_error_code ret = 0;
    krb5_ticket *ticket = NULL;
    krb5_auth_context ac = NULL;
    krb5_keytab id = NULL;
    krb5_crypto crypto = NULL;
    DigestReqInner ireq;
    DigestRepInner r;
    DigestREP rep;
    krb5_flags ap_req_options;
    krb5_data buf;
    size_t size;
    krb5_storage *sp = NULL;
    Checksum res;
    hdb_entry_ex *server = NULL, *user = NULL;
    char *password = NULL;
    krb5_data serverNonce;

    if(!config->enable_digest) {
	kdc_log(context, config, 0, "Rejected digest request from %s", from);
	return KRB5KDC_ERR_POLICY;
    }

    krb5_data_zero(&buf);
    krb5_data_zero(reply);
    krb5_data_zero(&serverNonce);
    memset(&ireq, 0, sizeof(ireq));
    memset(&r, 0, sizeof(r));
    memset(&rep, 0, sizeof(rep));

    kdc_log(context, config, 0, "Digest request from %s", from);

    ret = krb5_kt_resolve(context, "HDB:", &id);
    if (ret) {
	kdc_log(context, config, 0, "Can't open database for digest");
	goto out;
    }

    ret = krb5_rd_req(context, 
		      &ac,
		      &req->apReq,
		      NULL,
		      id,
		      &ap_req_options,
		      &ticket);
    if (ret)
	goto out;

    /* check the server principal in the ticket matches digest/R@R */
    {
	krb5_principal principal = NULL;
	const char *p, *r;

	ret = krb5_ticket_get_server(context, ticket, &principal);
	if (ret)
	    goto out;

	ret = EINVAL;
	krb5_clear_error_string(context);
	p = krb5_principal_get_comp_string(context, principal, 0);

	if (p == NULL) {
	    krb5_free_principal(context, principal);
	    goto out;
	}
	if (strcmp(p, KRB5_DIGEST_NAME) != 0) {
	    krb5_free_principal(context, principal);
	    goto out;
	}

	p = krb5_principal_get_comp_string(context, principal, 1);
	if (p == NULL) {
	    krb5_free_principal(context, principal);
	    goto out;
	}
	r = krb5_principal_get_realm(context, principal);
	if (r == NULL) {
	    krb5_free_principal(context, principal);
	    goto out;
	}
	if (strcmp(p, r) != 0) {
	    krb5_free_principal(context, principal);
	    goto out;
	}

	ret = _kdc_db_fetch(context, config, principal,
			    HDB_F_GET_SERVER, NULL, &server);
	if (ret)
	    goto out;

	krb5_free_principal(context, principal);
    }

    /* check the client is allowed to do digest auth */
    {
	krb5_principal principal = NULL;
	hdb_entry_ex *client;

	ret = krb5_ticket_get_client(context, ticket, &principal);
	if (ret)
	    goto out;

	ret = _kdc_db_fetch(context, config, principal,
			    HDB_F_GET_CLIENT, NULL, &client);
	krb5_free_principal(context, principal);
	if (ret)
	    goto out;

	if (client->entry.flags.allow_digest == 0) {
	    krb5_set_error_string(context, 
				  "server is not permitted to use digest");
	    ret = KRB5KDC_ERR_POLICY;
	    _kdc_free_ent (context, client);
	    goto out;
	}
	_kdc_free_ent (context, client);
    }

    /* unpack request */
    {
	krb5_keyblock *key;

	ret = krb5_auth_con_getremotesubkey(context, ac, &key);
	if (ret)
	    goto out;

	ret = krb5_crypto_init(context, key, 0, &crypto);
	krb5_free_keyblock (context, key);
	if (ret)
	    goto out;
    }

    ret = krb5_decrypt_EncryptedData(context, crypto, KRB5_KU_DIGEST_ENCRYPT,
				     &req->innerReq, &buf);
    krb5_crypto_destroy(context, crypto);
    crypto = NULL;
    if (ret)
	goto out;
	   
    ret = decode_DigestReqInner(buf.data, buf.length, &ireq, NULL);
    krb5_data_free(&buf);
    if (ret)
	goto out;

    /*
     * Process the inner request
     */

    switch (ireq.element) {
    case choice_DigestReqInner_init: {
	unsigned char server_nonce[16];
	char identifier;

	RAND_pseudo_bytes(&identifier, sizeof(identifier));
	RAND_pseudo_bytes(&server_nonce, sizeof(server_nonce));

	server_nonce[0] = kdc_time & 0xff;
	server_nonce[1] = (kdc_time >> 8) & 0xff;
	server_nonce[2] = (kdc_time >> 16) & 0xff;
	server_nonce[3] = (kdc_time >> 24) & 0xff;

	r.element = choice_DigestRepInner_initReply;

	hex_encode(server_nonce, sizeof(server_nonce), &r.u.initReply.nonce);
	if (r.u.initReply.nonce == NULL) {
	    krb5_set_error_string(context, "Failed to decode server nonce");
	    ret = ENOMEM;
	    goto out;
	}

	sp = krb5_storage_emem();
	if (sp == NULL) {
	    ret = ENOMEM;
	    krb5_set_error_string(context, "out of memory");
	    goto out;
	}
	ret = krb5_store_stringz(sp, ireq.u.init.type);
	if (ret) {
	    krb5_clear_error_string(context);
	    goto out;
	}

	if (ireq.u.init.channel) {
	    char *s;

	    asprintf(&s, "%s-%s:%s", r.u.initReply.nonce,
		     ireq.u.init.channel->cb_type,
		     ireq.u.init.channel->cb_binding);
	    if (s == NULL) {
		krb5_set_error_string(context, "Failed to allocate "
				      "channel binding");
		ret = ENOMEM;
		goto out;
	    }
	    free(r.u.initReply.nonce);
	    r.u.initReply.nonce = s;
	}
	
	ret = krb5_store_stringz(sp, r.u.initReply.nonce);
	if (ret) {
	    krb5_clear_error_string(context);
	    goto out;
	}

	if (strcasecmp(ireq.u.init.type, "CHAP") == 0) {
	    r.u.initReply.identifier = 
		malloc(sizeof(*r.u.initReply.identifier));
	    if (r.u.initReply.identifier == NULL) {
		krb5_set_error_string(context, "out of memory");
		ret = ENOMEM;
		goto out;
	    }

	    asprintf(r.u.initReply.identifier, "%02X", identifier & 0xff);
	    if (*r.u.initReply.identifier == NULL) {
		krb5_set_error_string(context, "out of memory");
		ret = ENOMEM;
		goto out;
	    }

	    ret = krb5_store_stringz(sp, *r.u.initReply.identifier);
	    if (ret) {
		krb5_clear_error_string(context);
		goto out;
	    }
	} else
	    r.u.initReply.identifier = NULL;

	if (ireq.u.init.hostname) {
	    ret = krb5_store_stringz(sp, *ireq.u.init.hostname);
	    if (ret) {
		krb5_clear_error_string(context);
		goto out;
	    }
	}

	ret = krb5_storage_to_data(sp, &buf);
	if (ret) {
	    krb5_clear_error_string(context);
	    goto out;
	}

	{
	    Key *key;
	    krb5_enctype enctype;

	    ret = _kdc_get_preferred_key(context,
					 config,
					 server,
					 "digest-service",
					 &enctype,
					 &key);
	    if (ret)
		goto out;
	    ret = krb5_crypto_init(context, &key->key, 0, &crypto);
	    if (ret)
		goto out;
	}

	ret = krb5_create_checksum(context,
				   crypto,
				   KRB5_KU_DIGEST_OPAQUE,
				   0,
				   buf.data,
				   buf.length,
				   &res);
	krb5_crypto_destroy(context, crypto);
	crypto = NULL;
	krb5_data_free(&buf);
	if (ret)
	    goto out;
	
	ASN1_MALLOC_ENCODE(Checksum, buf.data, buf.length, &res, &size, ret);
	free_Checksum(&res);
	if (ret) {
	    krb5_set_error_string(context, "Failed to encode "
				  "checksum in digest request");
	    goto out;
	}
	if (size != buf.length)
	    krb5_abortx(context, "ASN1 internal error");

	hex_encode(buf.data, buf.length, &r.u.initReply.opaque);
	if (r.u.initReply.opaque == NULL) {
	    krb5_clear_error_string(context);
	    ret = ENOMEM;
	    goto out;
	}

	break;
    }
    case choice_DigestReqInner_digestRequest: {
	krb5_principal clientprincipal;
	HDB *db;

	sp = krb5_storage_emem();
	if (sp == NULL) {
	    ret = ENOMEM;
	    krb5_set_error_string(context, "out of memory");
	    goto out;
	}
	krb5_store_stringz(sp, ireq.u.digestRequest.type);

	krb5_store_stringz(sp, ireq.u.digestRequest.serverNonce);
	if (ireq.u.digestRequest.identifier) {
	    ret = krb5_store_stringz(sp, *ireq.u.digestRequest.identifier);
	    if (ret) {
		krb5_clear_error_string(context);
		goto out;
	    }
	}
	if (ireq.u.digestRequest.hostname) {
	    ret = krb5_store_stringz(sp, *ireq.u.digestRequest.hostname);
	    if (ret) {
		krb5_clear_error_string(context);
		goto out;
	    }
	}

	buf.length = strlen(ireq.u.digestRequest.opaque);
	buf.data = malloc(buf.length);
	if (buf.data == NULL) {
	    krb5_set_error_string(context, "out of memory");
	    ret = ENOMEM;
	    goto out;
	}

	ret = hex_decode(ireq.u.digestRequest.opaque, buf.data, buf.length);
	if (ret <= 0) {
	    krb5_set_error_string(context, "Failed to decode opaque");
	    ret = ENOMEM;
	    goto out;
	}
	buf.length = ret;

	ret = decode_Checksum(buf.data, buf.length, &res, NULL);
	free(buf.data);
	if (ret) {
	    krb5_set_error_string(context, "Failed to decode digest Checksum");
	    goto out;
	}
	
	ret = krb5_storage_to_data(sp, &buf);
	if (ret) {
	    krb5_clear_error_string(context);
	    goto out;
	}

	serverNonce.length = strlen(ireq.u.digestRequest.serverNonce);
	serverNonce.data = malloc(serverNonce.length);
	if (serverNonce.data == NULL) {
	    krb5_set_error_string(context, "out of memory");
	    ret = ENOMEM;
	    goto out;
	}
	    
	/*
	 * CHAP does the checksum of the raw nonce, but do it for all
	 * types, since we need to check the timestamp.
	 */
	{
	    ssize_t ssize;
	    
	    ssize = hex_decode(ireq.u.digestRequest.serverNonce, 
			       serverNonce.data, serverNonce.length);
	    if (ssize <= 0) {
		krb5_set_error_string(context, "Failed to decode serverNonce");
		ret = ENOMEM;
		goto out;
	    }
	    serverNonce.length = ssize;
	}

	{
	    Key *key;
	    krb5_enctype enctype;

	    ret = _kdc_get_preferred_key(context,
					 config,
					 server,
					 "digest-service",
					 &enctype,
					 &key);
	    if (ret)
		goto out;
	    ret = krb5_crypto_init(context, &key->key, 0, &crypto);
	    if (ret)
		goto out;
	}

	ret = krb5_verify_checksum(context, crypto, 
				   KRB5_KU_DIGEST_OPAQUE,
				   buf.data, buf.length, &res);
	krb5_crypto_destroy(context, crypto);
	crypto = NULL;
	if (ret)
	    goto out;

	/* verify time */
	{
	    unsigned char *p = serverNonce.data;
	    uint32_t t;
	    
	    if (serverNonce.length < 4) {
		krb5_set_error_string(context, "server nonce too short");
		ret = EINVAL;
		goto out;
	    }
	    t = p[0] | (p[1] << 8) | (p[2] << 16) | (p[3] << 24);

	    if (abs((kdc_time & 0xffffffff) - t) > context->max_skew) {
		krb5_set_error_string(context, "time screw in server nonce ");
		ret = EINVAL;
		goto out;
	    }
	}

	/* get username */
	ret = krb5_parse_name(context,
			      ireq.u.digestRequest.username,
			      &clientprincipal);
	if (ret)
	    goto out;

	ret = _kdc_db_fetch(context, config, clientprincipal,
			    HDB_F_GET_CLIENT, &db, &user);

	if (ret)
	    goto out;

	ret = hdb_entry_get_password(context, db, &user->entry, &password);
	if (ret || password == NULL) {
	    if (ret == 0) {
		ret = EINVAL;
		krb5_set_error_string(context, "password missing");
	    }
	    goto out;
	}

	/* just support CHAP for now */
	if (strcasecmp(ireq.u.digestRequest.type, "CHAP") == 0) {
	    MD5_CTX ctx;
	    char md[MD5_DIGEST_LENGTH];
	    char id;

	    if (ireq.u.digestRequest.identifier == NULL) {
		krb5_set_error_string(context, "Identifier missing "
				      "from CHAP request");
		ret = EINVAL;
		goto out;
	    }
	    
	    if (hex_decode(*ireq.u.digestRequest.identifier, &id, 1) != 1) {
		krb5_set_error_string(context, "failed to decode identifier");
		ret = EINVAL;
		goto out;
	    }
	    
	    MD5_Init(&ctx);
	    MD5_Update(&ctx, &id, 1);
	    MD5_Update(&ctx, password, strlen(password));
	    MD5_Update(&ctx, serverNonce.data, serverNonce.length);
	    MD5_Final(md, &ctx);

	    r.element = choice_DigestRepInner_response;
	    hex_encode(md, sizeof(md), &r.u.response.responseData);
	    if (r.u.response.responseData == NULL) {
		krb5_clear_error_string(context);
		ret = ENOMEM;
		goto out;
	    }
	} else {
	    r.element = choice_DigestRepInner_error;
	    asprintf(&r.u.error.reason, "unsupported digest type %s", 
		     ireq.u.digestRequest.type);
	    if (r.u.error.reason == NULL) {
		krb5_set_error_string(context, "out of memory");
		ret = ENOMEM;
		goto out;
	    }
	    r.u.error.code = EINVAL;
	}

	break;
    }
    default:
	r.element = choice_DigestRepInner_error;
	r.u.error.reason = strdup("unknown operation");
	if (r.u.error.reason == NULL) {
	    krb5_set_error_string(context, "out of memory");
	    ret = ENOMEM;
	    goto out;
	}
	r.u.error.code = EINVAL;
	break;
    }

    ASN1_MALLOC_ENCODE(DigestRepInner, buf.data, buf.length, &r, &size, ret);
    if (ret) {
	krb5_set_error_string(context, "Failed to encode inner digest reply");
	goto out;
    }
    if (size != buf.length)
	krb5_abortx(context, "ASN1 internal error");

    krb5_auth_con_addflags(context, ac, KRB5_AUTH_CONTEXT_USE_SUBKEY, NULL);

    ret = krb5_mk_rep (context, ac, &rep.apRep);
    if (ret)
	goto out;

    {
	krb5_keyblock *key;

	ret = krb5_auth_con_getlocalsubkey(context, ac, &key);
	if (ret)
	    goto out;

	ret = krb5_crypto_init(context, key, 0, &crypto);
	krb5_free_keyblock (context, key);
	if (ret)
	    goto out;
    }

    ret = krb5_encrypt_EncryptedData(context, crypto, KRB5_KU_DIGEST_ENCRYPT, 
				     buf.data, buf.length, 0,
				     &rep.innerRep);
    
    ASN1_MALLOC_ENCODE(DigestREP, reply->data, reply->length, &rep, &size, ret);
    if (ret) {
	krb5_set_error_string(context, "Failed to encode digest reply");
	goto out;
    }
    if (size != reply->length)
	krb5_abortx(context, "ASN1 internal error");

    
out:
    if (ret)
	krb5_warn(context, ret, "Digest request from %s failed", from);
    if (ticket)
	krb5_free_ticket(context, ticket);
    if (id)
	krb5_kt_close(context, id);
    if (crypto)
	krb5_crypto_destroy(context, crypto);
    if (sp)
	krb5_storage_free(sp);
    if (user)
	_kdc_free_ent (context, user);
    if (server)
	_kdc_free_ent (context, server);
    if (password) {
	memset(password, 0, strlen(password));
	free (password);
    }
    krb5_data_free(&buf);
    krb5_data_free(&serverNonce);
    free_DigestREP(&rep);
    free_DigestRepInner(&r);
    free_DigestReqInner(&ireq);

    return ret;
}