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openssh/kexgsss.c

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/*
* 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.
*/
#include "includes.h"
#if defined(GSSAPI) && defined(WITH_OPENSSL)
#include <string.h>
#include <openssl/crypto.h>
#include <openssl/bn.h>
#include "xmalloc.h"
#include "sshbuf.h"
#include "ssh2.h"
#include "sshkey.h"
#include "cipher.h"
#include "kex.h"
#include "log.h"
#include "packet.h"
#include "dh.h"
#include "ssh-gss.h"
#include "monitor_wrap.h"
#include "misc.h" /* servconf.h needs misc.h for struct ForwardOptions */
#include "servconf.h"
#include "ssh-gss.h"
#include "digest.h"
#include "ssherr.h"
extern ServerOptions options;
int
kexgss_server(struct ssh *ssh)
{
struct kex *kex = ssh->kex;
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;
struct sshbuf *shared_secret = NULL;
struct sshbuf *client_pubkey = NULL;
struct sshbuf *server_pubkey = NULL;
struct sshbuf *empty = sshbuf_new();
int type = 0;
gss_OID oid;
char *mechs;
u_char hash[SSH_DIGEST_MAX_LENGTH];
size_t hashlen;
int r;
/* 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()) {
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");
do {
debug("Wait SSH2_MSG_KEXGSS_INIT");
type = ssh_packet_read(ssh);
switch(type) {
case SSH2_MSG_KEXGSS_INIT:
if (client_pubkey != NULL)
fatal("Received KEXGSS_INIT after initialising");
if ((r = ssh_gssapi_sshpkt_get_buffer_desc(ssh,
&recv_tok)) != 0 ||
(r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 ||
(r = sshpkt_get_end(ssh)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
switch (kex->kex_type) {
case KEX_GSS_GRP1_SHA1:
case KEX_GSS_GRP14_SHA1:
case KEX_GSS_GRP14_SHA256:
case KEX_GSS_GRP16_SHA512:
r = kex_dh_enc(kex, client_pubkey, &server_pubkey,
&shared_secret);
break;
case KEX_GSS_NISTP256_SHA256:
r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey,
&shared_secret);
break;
case KEX_GSS_C25519_SHA256:
r = kex_c25519_enc(kex, client_pubkey, &server_pubkey,
&shared_secret);
break;
default:
fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
}
if (r != 0)
goto out;
/* Send SSH_MSG_KEXGSS_HOSTKEY here, if we want */
break;
case SSH2_MSG_KEXGSS_CONTINUE:
if ((r = ssh_gssapi_sshpkt_get_buffer_desc(ssh,
&recv_tok)) != 0 ||
(r = sshpkt_get_end(ssh)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
break;
default:
sshpkt_disconnect(ssh,
"Protocol error: didn't expect packet type %d",
type);
}
maj_status = PRIVSEP(ssh_gssapi_accept_ctx(ctxt, &recv_tok,
&send_tok, &ret_flags));
gss_release_buffer(&min_status, &recv_tok);
if (maj_status != GSS_S_COMPLETE && send_tok.length == 0)
fatal("Zero length token output when incomplete");
if (client_pubkey == NULL)
fatal("No client public key");
if (maj_status & GSS_S_CONTINUE_NEEDED) {
debug("Sending GSSAPI_CONTINUE");
if ((r = sshpkt_start(ssh, SSH2_MSG_KEXGSS_CONTINUE)) != 0 ||
(r = sshpkt_put_string(ssh, send_tok.value, send_tok.length)) != 0 ||
(r = sshpkt_send(ssh)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
gss_release_buffer(&min_status, &send_tok);
}
} while (maj_status & GSS_S_CONTINUE_NEEDED);
if (GSS_ERROR(maj_status)) {
if (send_tok.length > 0) {
if ((r = sshpkt_start(ssh, SSH2_MSG_KEXGSS_CONTINUE)) != 0 ||
(r = sshpkt_put_string(ssh, send_tok.value, send_tok.length)) != 0 ||
(r = sshpkt_send(ssh)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
}
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");
hashlen = sizeof(hash);
if ((r = kex_gen_hash(
kex->hash_alg,
kex->client_version,
kex->server_version,
kex->peer,
kex->my,
empty,
client_pubkey,
server_pubkey,
shared_secret,
hash, &hashlen)) != 0)
goto out;
gssbuf.value = hash;
gssbuf.length = hashlen;
if (GSS_ERROR(PRIVSEP(ssh_gssapi_sign(ctxt, &gssbuf, &msg_tok))))
fatal("Couldn't get MIC");
if ((r = sshpkt_start(ssh, SSH2_MSG_KEXGSS_COMPLETE)) != 0 ||
(r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 ||
(r = sshpkt_put_string(ssh, msg_tok.value, msg_tok.length)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
if (send_tok.length != 0) {
if ((r = sshpkt_put_u8(ssh, 1)) != 0 || /* true */
(r = sshpkt_put_string(ssh, send_tok.value, send_tok.length)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
} else {
if ((r = sshpkt_put_u8(ssh, 0)) != 0) /* false */
fatal("sshpkt failed: %s", ssh_err(r));
}
if ((r = sshpkt_send(ssh)) != 0)
fatal("sshpkt_send failed: %s", ssh_err(r));
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);
if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
r = kex_send_newkeys(ssh);
/* If this was a rekey, then save out any delegated credentials we
* just exchanged. */
if (options.gss_store_rekey)
ssh_gssapi_rekey_creds();
out:
sshbuf_free(empty);
explicit_bzero(hash, sizeof(hash));
sshbuf_free(shared_secret);
sshbuf_free(client_pubkey);
sshbuf_free(server_pubkey);
return r;
}
int
kexgssgex_server(struct ssh *ssh)
{
struct kex *kex = ssh->kex;
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;
struct sshbuf *shared_secret = NULL;
int type = 0;
gss_OID oid;
char *mechs;
u_char hash[SSH_DIGEST_MAX_LENGTH];
size_t hashlen;
BIGNUM *dh_client_pub = NULL;
const BIGNUM *pub_key, *dh_p, *dh_g;
int min = -1, max = -1, nbits = -1;
int cmin = -1, cmax = -1; /* client proposal */
struct sshbuf *empty = sshbuf_new();
int r;
/* 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");
/* 5. S generates an ephemeral key pair (do the allocations early) */
debug("Doing group exchange");
ssh_packet_read_expect(ssh, SSH2_MSG_KEXGSS_GROUPREQ);
/* store client proposal to provide valid signature */
if ((r = sshpkt_get_u32(ssh, &cmin)) != 0 ||
(r = sshpkt_get_u32(ssh, &nbits)) != 0 ||
(r = sshpkt_get_u32(ssh, &cmax)) != 0 ||
(r = sshpkt_get_end(ssh)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
kex->nbits = nbits;
kex->min = cmin;
kex->max = cmax;
min = MAX(DH_GRP_MIN, cmin);
max = MIN(DH_GRP_MAX, cmax);
nbits = MAXIMUM(DH_GRP_MIN, nbits);
nbits = MINIMUM(DH_GRP_MAX, nbits);
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) {
sshpkt_disconnect(ssh, "Protocol error: no matching group found");
fatal("Protocol error: no matching group found");
}
DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
if ((r = sshpkt_start(ssh, SSH2_MSG_KEXGSS_GROUP)) != 0 ||
(r = sshpkt_put_bignum2(ssh, dh_p)) != 0 ||
(r = sshpkt_put_bignum2(ssh, dh_g)) != 0 ||
(r = sshpkt_send(ssh)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
if ((r = ssh_packet_write_wait(ssh)) != 0)
fatal("ssh_packet_write_wait: %s", ssh_err(r));
/* Compute our exchange value in parallel with the client */
if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
goto out;
do {
debug("Wait SSH2_MSG_GSSAPI_INIT");
type = ssh_packet_read(ssh);
switch(type) {
case SSH2_MSG_KEXGSS_INIT:
if (dh_client_pub != NULL)
fatal("Received KEXGSS_INIT after initialising");
if ((r = ssh_gssapi_sshpkt_get_buffer_desc(ssh,
&recv_tok)) != 0 ||
(r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 ||
(r = sshpkt_get_end(ssh)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
/* Send SSH_MSG_KEXGSS_HOSTKEY here, if we want */
break;
case SSH2_MSG_KEXGSS_CONTINUE:
if ((r = ssh_gssapi_sshpkt_get_buffer_desc(ssh,
&recv_tok)) != 0 ||
(r = sshpkt_get_end(ssh)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
break;
default:
sshpkt_disconnect(ssh,
"Protocol error: didn't expect packet type %d",
type);
}
maj_status = PRIVSEP(ssh_gssapi_accept_ctx(ctxt, &recv_tok,
&send_tok, &ret_flags));
gss_release_buffer(&min_status, &recv_tok);
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");
if ((r = sshpkt_start(ssh, SSH2_MSG_KEXGSS_CONTINUE)) != 0 ||
(r = sshpkt_put_string(ssh, send_tok.value, send_tok.length)) != 0 ||
(r = sshpkt_send(ssh)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
gss_release_buffer(&min_status, &send_tok);
}
} while (maj_status & GSS_S_CONTINUE_NEEDED);
if (GSS_ERROR(maj_status)) {
if (send_tok.length > 0) {
if ((r = sshpkt_start(ssh, SSH2_MSG_KEXGSS_CONTINUE)) != 0 ||
(r = sshpkt_put_string(ssh, send_tok.value, send_tok.length)) != 0 ||
(r = sshpkt_send(ssh)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
}
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");
/* calculate shared secret */
if ((shared_secret = sshbuf_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0)
goto out;
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->peer,
kex->my,
empty,
cmin, nbits, cmax,
dh_p, dh_g,
dh_client_pub,
pub_key,
sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
hash, &hashlen)) != 0)
fatal("kexgex_hash failed: %s", ssh_err(r));
gssbuf.value = hash;
gssbuf.length = hashlen;
if (GSS_ERROR(PRIVSEP(ssh_gssapi_sign(ctxt, &gssbuf, &msg_tok))))
fatal("Couldn't get MIC");
if ((r = sshpkt_start(ssh, SSH2_MSG_KEXGSS_COMPLETE)) != 0 ||
(r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||
(r = sshpkt_put_string(ssh, msg_tok.value, msg_tok.length)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
if (send_tok.length != 0) {
if ((r = sshpkt_put_u8(ssh, 1)) != 0 || /* true */
(r = sshpkt_put_string(ssh, send_tok.value, send_tok.length)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
} else {
if ((r = sshpkt_put_u8(ssh, 0)) != 0) /* false */
fatal("sshpkt failed: %s", ssh_err(r));
}
if ((r = sshpkt_send(ssh)) != 0)
fatal("sshpkt failed: %s", ssh_err(r));
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);
/* Finally derive the keys and send them */
if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
r = kex_send_newkeys(ssh);
/* If this was a rekey, then save out any delegated credentials we
* just exchanged. */
if (options.gss_store_rekey)
ssh_gssapi_rekey_creds();
out:
sshbuf_free(empty);
explicit_bzero(hash, sizeof(hash));
DH_free(kex->dh);
kex->dh = NULL;
BN_clear_free(dh_client_pub);
sshbuf_free(shared_secret);
return r;
}
#endif /* defined(GSSAPI) && defined(WITH_OPENSSL) */
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