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Add new structure for signature options

This is populated during signature verification with additional fields
that are present in and covered by the signature. At the moment, it is
only used to record security key-specific options, especially the flags
field.

with and ok markus@

/* $OpenBSD: kexgexc.c,v 1.35 2019/11/25 00:51:37 djm Exp $ */
/*
 * Copyright (c) 2000 Niels Provos.  All rights reserved.
 * Copyright (c) 2001 Markus Friedl.  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.
 */

#include <sys/types.h>

#include <openssl/dh.h>

#include <stdio.h>
#include <string.h>
#include <signal.h>

#include "sshkey.h"
#include "cipher.h"
#include "digest.h"
#include "kex.h"
#include "log.h"
#include "packet.h"
#include "dh.h"
#include "ssh2.h"
#include "compat.h"
#include "dispatch.h"
#include "ssherr.h"
#include "sshbuf.h"
#include "misc.h"

static int input_kex_dh_gex_group(int, u_int32_t, struct ssh *);
static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *);

int
kexgex_client(struct ssh *ssh)
{
	struct kex *kex = ssh->kex;
	int r;
	u_int nbits;

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

	kex->min = DH_GRP_MIN;
	kex->max = DH_GRP_MAX;
	kex->nbits = nbits;
	if (datafellows & SSH_BUG_DHGEX_LARGE)
		kex->nbits = MINIMUM(kex->nbits, 4096);
	/* New GEX request */
	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 ||
	    (r = sshpkt_put_u32(ssh, kex->min)) != 0 ||
	    (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 ||
	    (r = sshpkt_put_u32(ssh, kex->max)) != 0 ||
	    (r = sshpkt_send(ssh)) != 0)
		goto out;
	debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
	    kex->min, kex->nbits, kex->max);
#ifdef DEBUG_KEXDH
	fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
	    kex->min, kex->nbits, kex->max);
#endif
	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP,
	    &input_kex_dh_gex_group);
	r = 0;
 out:
	return r;
}

static int
input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh)
{
	struct kex *kex = ssh->kex;
	BIGNUM *p = NULL, *g = NULL;
	const BIGNUM *pub_key;
	int r, bits;

	debug("got SSH2_MSG_KEX_DH_GEX_GROUP");

	if ((r = sshpkt_get_bignum2(ssh, &p)) != 0 ||
	    (r = sshpkt_get_bignum2(ssh, &g)) != 0 ||
	    (r = sshpkt_get_end(ssh)) != 0)
		goto out;
	if ((bits = BN_num_bits(p)) < 0 ||
	    (u_int)bits < kex->min || (u_int)bits > kex->max) {
		r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
		goto out;
	}
	if ((kex->dh = dh_new_group(g, p)) == NULL) {
		r = SSH_ERR_ALLOC_FAIL;
		goto out;
	}
	p = g = NULL; /* belong to kex->dh now */

	/* generate and send 'e', client DH public key */
	if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
		goto out;
	DH_get0_key(kex->dh, &pub_key, NULL);
	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 ||
	    (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||
	    (r = sshpkt_send(ssh)) != 0)
		goto out;
	debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
#ifdef DEBUG_KEXDH
	DHparams_print_fp(stderr, kex->dh);
	fprintf(stderr, "pub= ");
	BN_print_fp(stderr, pub_key);
	fprintf(stderr, "\n");
#endif
	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, NULL);
	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply);
	r = 0;
out:
	BN_clear_free(p);
	BN_clear_free(g);
	return r;
}

static int
input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh)
{
	struct kex *kex = ssh->kex;
	BIGNUM *dh_server_pub = NULL;
	const BIGNUM *pub_key, *dh_p, *dh_g;
	struct sshbuf *shared_secret = NULL;
	struct sshbuf *tmp = NULL, *server_host_key_blob = NULL;
	struct sshkey *server_host_key = NULL;
	u_char *signature = NULL;
	u_char hash[SSH_DIGEST_MAX_LENGTH];
	size_t slen, hashlen;
	int r;

	debug("got SSH2_MSG_KEX_DH_GEX_REPLY");
	/* key, cert */
	if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0)
		goto out;
	/* sshkey_fromb() consumes its buffer, so make a copy */
	if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) {
		r = SSH_ERR_ALLOC_FAIL;
		goto out;
	}
	if ((r = sshkey_fromb(tmp, &server_host_key)) != 0 ||
	    (r = kex_verify_host_key(ssh, server_host_key)) != 0)
		goto out;
	/* DH parameter f, server public DH key, signed H */
	if ((r = sshpkt_get_bignum2(ssh, &dh_server_pub)) != 0 ||
	    (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
	    (r = sshpkt_get_end(ssh)) != 0)
		goto out;
	if ((shared_secret = sshbuf_new()) == NULL) {
		r = SSH_ERR_ALLOC_FAIL;
		goto out;
	}
	if ((r = kex_dh_compute_key(kex, dh_server_pub, shared_secret)) != 0)
		goto out;
	if (ssh->compat & SSH_OLD_DHGEX)
		kex->min = kex->max = -1;

	/* calc and verify H */
	DH_get0_key(kex->dh, &pub_key, NULL);
	DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
	hashlen = sizeof(hash);
	if ((r = kexgex_hash(
	    kex->hash_alg,
	    kex->client_version,
	    kex->server_version,
	    kex->my,
	    kex->peer,
	    server_host_key_blob,
	    kex->min, kex->nbits, kex->max,
	    dh_p, dh_g,
	    pub_key,
	    dh_server_pub,
	    sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
	    hash, &hashlen)) != 0)
		goto out;

	if ((r = sshkey_verify(server_host_key, signature, slen, hash,
	    hashlen, kex->hostkey_alg, ssh->compat, NULL)) != 0)
		goto out;

	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
		r = kex_send_newkeys(ssh);
 out:
	explicit_bzero(hash, sizeof(hash));
	DH_free(kex->dh);
	kex->dh = NULL;
	BN_clear_free(dh_server_pub);
	sshbuf_free(shared_secret);
	sshkey_free(server_host_key);
	sshbuf_free(tmp);
	sshbuf_free(server_host_key_blob);
	free(signature);
	return r;
}