/*

 * Copyright (c) 2001-2009 Simon Wilkinson. 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.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `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 AUTHOR 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.

 */

/*

 * May 22, 2015

 * In version 6.8 a new packet interface has been introduced to OpenSSH,

 * while the old packet API has been provided in opacket.c.

 * At this moment we are not rewritting GSS-API key exchange code to the new

 * API, just adjusting it to still work with new struct ssh.

 * Rewritting to the new API can be considered in the future.

 */

#include "includes.h"

#ifdef GSSAPI

#include "includes.h"

#include <openssl/crypto.h>

#include <openssl/bn.h>

#include <signal.h>	/* for sig_atomic_t in kex.h */

#include <string.h>

#include "xmalloc.h"

#include "buffer.h"

#include "ssh2.h"

#include "key.h"

#include "cipher.h"

#include "digest.h"

#include "kex.h"

#include "log.h"

#include "packet.h"

#include "dh.h"

#include "ssh-gss.h"

int

kexgss_client(struct ssh *ssh) {

	gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;

	gss_buffer_desc recv_tok, gssbuf, msg_tok, *token_ptr;

	Gssctxt *ctxt;

	OM_uint32 maj_status, min_status, ret_flags;

	uint_t klen, kout, slen = 0, strlen;

	BIGNUM *dh_server_pub = NULL;

	BIGNUM *shared_secret = NULL;

	BIGNUM *p = NULL;

	BIGNUM *g = NULL;

	uchar_t *kbuf;

	uchar_t *serverhostkey = NULL;

	uchar_t *empty = "";

	char *msg;

	char *lang;

	int type = 0;

	int first = 1;

	int nbits = 0, min = DH_GRP_MIN, max = DH_GRP_MAX;

	struct kex *kex = ssh->kex;

	int r;

	uchar_t hash[SSH_DIGEST_MAX_LENGTH];

	size_t hashlen;

	/* Initialise our GSSAPI world */

	ssh_gssapi_build_ctx(&ctxt);

	if (ssh_gssapi_id_kex(ctxt, kex->name, kex->kex_type)

	    == GSS_C_NO_OID)

		fatal("Couldn't identify host exchange");

	if (ssh_gssapi_import_name(ctxt, kex->gss_host))

		fatal("Couldn't import hostname");

	switch (kex->kex_type) {

	case KEX_GSS_GRP1_SHA1:

		kex->dh = dh_new_group1();

		break;

	case KEX_GSS_GRP14_SHA1:

		kex->dh = dh_new_group14();

		break;

	case KEX_GSS_GEX_SHA1:

		debug("Doing group exchange\n");

		nbits = dh_estimate(kex->we_need * 8);

		packet_start(SSH2_MSG_KEXGSS_GROUPREQ);

		packet_put_int(min);

		packet_put_int(nbits);

		packet_put_int(max);

		packet_send();

		packet_read_expect(SSH2_MSG_KEXGSS_GROUP);

		if ((p = BN_new()) == NULL)

			fatal("BN_new() failed");

		packet_get_bignum2(p);

		if ((g = BN_new()) == NULL)

			fatal("BN_new() failed");

		packet_get_bignum2(g);

		packet_check_eom();

		if (BN_num_bits(p) < min || BN_num_bits(p) > max)

			fatal("GSSGRP_GEX group out of range: %d !< %d !< %d",

			    min, BN_num_bits(p), max);

		kex->dh = dh_new_group(g, p);

		break;

	default:

		fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);

	}

	/* Step 1 - e is dh->pub_key */

	dh_gen_key(kex->dh, kex->we_need * 8);

	/* This is f, we initialise it now to make life easier */

	dh_server_pub = BN_new();

	if (dh_server_pub == NULL)

		fatal("dh_server_pub == NULL");

	token_ptr = GSS_C_NO_BUFFER;

	do {

		debug("Calling gss_init_sec_context");

		maj_status = ssh_gssapi_init_ctx(ctxt,

		    kex->gss_deleg_creds, token_ptr, &send_tok,

		    &ret_flags);

		if (GSS_ERROR(maj_status)) {

			if (send_tok.length != 0) {

				packet_start(SSH2_MSG_KEXGSS_CONTINUE);

				packet_put_string(send_tok.value,

				    send_tok.length);

			}

			fatal("gss_init_context failed");

		}

		/* If we've got an old receive buffer get rid of it */

		if (token_ptr != GSS_C_NO_BUFFER)

			free(recv_tok.value);

		if (maj_status == GSS_S_COMPLETE) {

			/* If mutual state flag is not true, kex fails */

			if (!(ret_flags & GSS_C_MUTUAL_FLAG))

				fatal("Mutual authentication failed");

			/* If integ avail flag is not true kex fails */

			if (!(ret_flags & GSS_C_INTEG_FLAG))

				fatal("Integrity check failed");

		}

		/*

		 * If we have data to send, then the last message that we

		 * received cannot have been a 'complete'.

		 */

		if (send_tok.length != 0) {

			if (first) {

				packet_start(SSH2_MSG_KEXGSS_INIT);

				packet_put_string(send_tok.value,

				    send_tok.length);

				packet_put_bignum2(kex->dh->pub_key);

				first = 0;

			} else {

				packet_start(SSH2_MSG_KEXGSS_CONTINUE);

				packet_put_string(send_tok.value,

				    send_tok.length);

			}

			packet_send();

			gss_release_buffer(&min_status, &send_tok);

			/* If we've sent them data, they should reply */

			do {

				type = packet_read();

				if (type == SSH2_MSG_KEXGSS_HOSTKEY) {

					debug("Received KEXGSS_HOSTKEY");

					if (serverhostkey)

						fatal("Server host key received"

						    "more than once");

					serverhostkey =

					    packet_get_string(&slen);

				}

			} while (type == SSH2_MSG_KEXGSS_HOSTKEY);

			switch (type) {

			case SSH2_MSG_KEXGSS_CONTINUE:

				debug("Received GSSAPI_CONTINUE");

				if (maj_status == GSS_S_COMPLETE)

					fatal("GSSAPI Continue received from"

					    "server when complete");

				recv_tok.value = packet_get_string(&strlen);

				recv_tok.length = strlen;

				break;

			case SSH2_MSG_KEXGSS_COMPLETE:

				debug("Received GSSAPI_COMPLETE");

				packet_get_bignum2(dh_server_pub);

				msg_tok.value =  packet_get_string(&strlen);

				msg_tok.length = strlen;

				/* Is there a token included? */

				if (packet_get_char()) {

					recv_tok.value=

					    packet_get_string(&strlen);

					recv_tok.length = strlen;

					/* If complete - protocol error */

					if (maj_status == GSS_S_COMPLETE)

						packet_disconnect("Protocol"

						    " error: received token"

						    " when complete");

				} else {

					/* No token included */

					if (maj_status != GSS_S_COMPLETE)

						packet_disconnect("Protocol"

						    " error: did not receive"

						    " final token");

				}

				break;

			case SSH2_MSG_KEXGSS_ERROR:

				debug("Received Error");

				maj_status = packet_get_int();

				min_status = packet_get_int();

				msg = packet_get_string(NULL);

				lang = packet_get_string(NULL);

				fatal("GSSAPI Error: \n%.400s", msg);

			default:

				packet_disconnect("Protocol error: didn't"

				    " expect packet type %d", type);

			}

			token_ptr = &recv_tok;

		} else {

			/* No data, and not complete */

			if (maj_status != GSS_S_COMPLETE)

				fatal("Not complete, and no token output");

		}

	} while (maj_status & GSS_S_CONTINUE_NEEDED);

	/*

	 * We _must_ have received a COMPLETE message in reply from the

	 * server, which will have set dh_server_pub and msg_tok

	 */

	if (type != SSH2_MSG_KEXGSS_COMPLETE)

		fatal("Didn't receive SSH2_MSG_KEXGSS_COMPLETE when expected");

	/* Check f in range [1, p-1] */

	if (!dh_pub_is_valid(kex->dh, dh_server_pub))

		packet_disconnect("bad server public DH value");

	/* compute K=f^x mod p */

	klen = DH_size(kex->dh);

	kbuf = xmalloc(klen);

	kout = DH_compute_key(kbuf, dh_server_pub, kex->dh);

	if (kout < 0)

		fatal("DH_compute_key: failed");

	shared_secret = BN_new();

	if (shared_secret == NULL)

		fatal("kexgss_client: BN_new failed");

	if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)

		fatal("kexdh_client: BN_bin2bn failed");

	memset(kbuf, 0, klen);

	free(kbuf);

	hashlen = sizeof (hash);

	switch (kex->kex_type) {

	case KEX_GSS_GRP1_SHA1:

	case KEX_GSS_GRP14_SHA1:

		    kex->server_version_string,

		    buffer_ptr(kex->my), buffer_len(kex->my),

		    buffer_ptr(kex->peer), buffer_len(kex->peer),

		    (serverhostkey ? serverhostkey : empty), slen,

		    kex->dh->pub_key,	/* e */

		    dh_server_pub,	/* f */

		    shared_secret,	/* K */

		    hash, &hashlen);

		break;

	case KEX_GSS_GEX_SHA1:

		kexgex_hash(

		    kex->hash_alg,

		    kex->client_version_string,

		    kex->server_version_string,

		    buffer_ptr(kex->my), buffer_len(kex->my),

		    buffer_ptr(kex->peer), buffer_len(kex->peer),

		    (serverhostkey ? serverhostkey : empty), slen,

		    min, nbits, max,

		    kex->dh->p, kex->dh->g,

		    kex->dh->pub_key,

		    dh_server_pub,

		    shared_secret,

		    hash, &hashlen);

		break;

	default:

		fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);

	}

	gssbuf.value = hash;

	gssbuf.length = hashlen;

	/* Verify that the hash matches the MIC we just got. */

	if (GSS_ERROR(ssh_gssapi_checkmic(ctxt, &gssbuf, &msg_tok)))

		packet_disconnect("Hash's MIC didn't verify");

	free(msg_tok.value);

	DH_free(kex->dh);

	if (serverhostkey)

		free(serverhostkey);

	BN_clear_free(dh_server_pub);

	/* save session id */

	if (kex->session_id == NULL) {

		kex->session_id_len = hashlen;

		kex->session_id = xmalloc(kex->session_id_len);

		memcpy(kex->session_id, hash, kex->session_id_len);

	}

	if (gss_kex_context == NULL)

		gss_kex_context = ctxt;

	else

		ssh_gssapi_delete_ctx(&ctxt);

	if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)

		r = kex_send_newkeys(ssh);

	return (r);

}

#endif /* GSSAPI */