/*
* 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 */