/*

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

#include <string.h>

#include <openssl/crypto.h>

#include <openssl/bn.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"

#include "monitor_wrap.h"

int

kexgss_server(struct ssh *ssh)

{

	OM_uint32 maj_status, min_status;

	/*

	 * Some GSSAPI implementations use the input value of ret_flags (an

	 * output variable) as a means of triggering mechanism specific

	 * features. Initializing it to zero avoids inadvertently

	 * activating this non-standard behaviour.

	 */

	OM_uint32 ret_flags = 0;

	gss_buffer_desc gssbuf, recv_tok, msg_tok;

	gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;

	Gssctxt *ctxt = NULL;

	uint_t slen, klen, kout;

	uchar_t *kbuf;

	DH *dh;

	int min = -1, max = -1, nbits = -1;

	BIGNUM *shared_secret = NULL;

	BIGNUM *dh_client_pub = NULL;

	int type = 0;

	gss_OID oid;

	char *mechs;

	struct kex *kex = ssh->kex;

	int r;

	uchar_t hash[SSH_DIGEST_MAX_LENGTH];

	size_t hashlen;

	/* Initialise GSSAPI */

	/*

	 * If we're rekeying, privsep means that some of the private structures

	 * in the GSSAPI code are no longer available. This kludges them back

	 * into life

	 */

	if (!ssh_gssapi_oid_table_ok())

		if ((mechs = ssh_gssapi_server_mechanisms()))

			free(mechs);

	debug2("%s: Identifying %s", __func__, kex->name);

	oid = ssh_gssapi_id_kex(NULL, kex->name, kex->kex_type);

	if (oid == GSS_C_NO_OID)

		fatal("Unknown gssapi mechanism");

	debug2("%s: Acquiring credentials", __func__);

	if (GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctxt, oid))))

		fatal("Unable to acquire credentials for the server");

	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");

		packet_read_expect(SSH2_MSG_KEXGSS_GROUPREQ);

		min = packet_get_int();

		nbits = packet_get_int();

		max = packet_get_int();

		min = MAX(DH_GRP_MIN, min);

		max = MIN(DH_GRP_MAX, max);

		packet_check_eom();

		if (max < min || nbits < min || max < nbits)

			fatal("GSS_GEX, bad parameters: %d !< %d !< %d",

			    min, nbits, max);

		kex->dh = PRIVSEP(choose_dh(min, nbits, max));

		if (kex->dh == NULL)

			packet_disconnect("Protocol error:"

			    " no matching group found");

		packet_start(SSH2_MSG_KEXGSS_GROUP);

		packet_put_bignum2(kex->dh->p);

		packet_put_bignum2(kex->dh->g);

		packet_send();

		packet_write_wait();

		break;

	default:

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

	}

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

	do {

		debug("Wait SSH2_MSG_GSSAPI_INIT");

		type = packet_read();

		switch (type) {

		case SSH2_MSG_KEXGSS_INIT:

			if (dh_client_pub != NULL)

				fatal("Received KEXGSS_INIT after"

				    " initialising");

			recv_tok.value = packet_get_string(&slen);

			recv_tok.length = slen;

			if ((dh_client_pub = BN_new()) == NULL)

				fatal("dh_client_pub == NULL");

			packet_get_bignum2(dh_client_pub);

			/* Send SSH_MSG_KEXGSS_HOSTKEY here, if we want */

			break;

		case SSH2_MSG_KEXGSS_CONTINUE:

			recv_tok.value = packet_get_string(&slen);

			recv_tok.length = slen;

			break;

		default:

			packet_disconnect(

			    "Protocol error: didn't expect packet type %d",

			    type);

		}

		maj_status = PRIVSEP(ssh_gssapi_accept_ctx(ctxt, &recv_tok,

		    &send_tok, &ret_flags));

		free(recv_tok.value);

		if (maj_status != GSS_S_COMPLETE && send_tok.length == 0)

			fatal("Zero length token output when incomplete");

		if (dh_client_pub == NULL)

			fatal("No client public key");

		if (maj_status & GSS_S_CONTINUE_NEEDED) {

			debug("Sending GSSAPI_CONTINUE");

			packet_start(SSH2_MSG_KEXGSS_CONTINUE);

			packet_put_string(send_tok.value, send_tok.length);

			packet_send();

			gss_release_buffer(&min_status, &send_tok);

		}

	} while (maj_status & GSS_S_CONTINUE_NEEDED);

	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);

			packet_send();

		}

		fatal("accept_ctx died");

	}

	if (!(ret_flags & GSS_C_MUTUAL_FLAG))

		fatal("Mutual Authentication flag wasn't set");

	if (!(ret_flags & GSS_C_INTEG_FLAG))

		fatal("Integrity flag wasn't set");

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

		packet_disconnect("bad client public DH value");

	klen = DH_size(kex->dh);

	kbuf = xmalloc(klen);

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

	if (kout < 0)

		fatal("DH_compute_key: failed");

	shared_secret = BN_new();

	if (shared_secret == NULL)

		fatal("kexgss_server: BN_new failed");

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

		fatal("kexgss_server: 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_dh_hash(

		    kex->client_version_string, kex->server_version_string,

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

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

		    NULL, 0, /* Change this if we start sending host keys */

		    dh_client_pub, kex->dh->pub_key, shared_secret,

		    hash, &hashlen);

		break;

	case KEX_GSS_GEX_SHA1:

		kexgex_hash(

		    kex->hash_alg,

		    kex->client_version_string, kex->server_version_string,

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

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

		    NULL, 0,

		    min, nbits, max,

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

		    dh_client_pub,

		    kex->dh->pub_key,

		    shared_secret,

		    hash, &hashlen);

		break;

	default:

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

	}

	BN_clear_free(dh_client_pub);

	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);

	}

	gssbuf.value = hash;

	gssbuf.length = hashlen;

	if (GSS_ERROR(PRIVSEP(ssh_gssapi_sign(ctxt, &gssbuf, &msg_tok))))

		fatal("Couldn't get MIC");

	packet_start(SSH2_MSG_KEXGSS_COMPLETE);

	packet_put_bignum2(kex->dh->pub_key);

	packet_put_string(msg_tok.value, msg_tok.length);

	if (send_tok.length != 0) {

		packet_put_char(1); /* true */

		packet_put_string(send_tok.value, send_tok.length);

	} else {

		packet_put_char(0); /* false */

	}

	packet_send();

	gss_release_buffer(&min_status, &send_tok);

	gss_release_buffer(&min_status, &msg_tok);

	if (gss_kex_context == NULL)

		gss_kex_context = ctxt;

	else

		ssh_gssapi_delete_ctx(&ctxt);

	DH_free(kex->dh);

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

		r = kex_send_newkeys(ssh);

	return (r);

}

#endif /* GSSAPI */