kexgssc.c

   1 /*
   2  * Copyright (c) 2001-2009 Simon Wilkinson. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  23  */
  24
  25 #include "includes.h"
  26
  27 #ifdef GSSAPI
  28
  29 #include "includes.h"
  30
  31 #include <openssl/crypto.h>
  32 #include <openssl/bn.h>
  33
  34 #include <string.h>
  35
  36 #include "xmalloc.h"
  37 #include "buffer.h"
  38 #include "ssh2.h"
  39 #include "key.h"
  40 #include "cipher.h"
  41 #include "kex.h"
  42 #include "log.h"
  43 #include "packet.h"
  44 #include "dh.h"
  45
  46 #include "ssh-gss.h"
  47
  48 void
  49 kexgss_client(Kex *kex) {
  50         gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
  51         gss_buffer_desc recv_tok, gssbuf, msg_tok, *token_ptr;
  52         Gssctxt *ctxt;
  53         OM_uint32 maj_status, min_status, ret_flags;
  54         u_int klen, kout, slen = 0, hashlen, strlen;
  55         DH *dh;
  56         BIGNUM *dh_server_pub = NULL;
  57         BIGNUM *shared_secret = NULL;
  58         BIGNUM *p = NULL;
  59         BIGNUM *g = NULL;
  60         u_char *kbuf, *hash;
  61         u_char *serverhostkey = NULL;
  62         u_char *empty = "";
  63         char *msg;
  64         char *lang;
  65         int type = 0;
  66         int first = 1;
  67         int nbits = 0, min = DH_GRP_MIN, max = DH_GRP_MAX;
  68
  69         /* Initialise our GSSAPI world */
  70         ssh_gssapi_build_ctx(&ctxt);
  71         if (ssh_gssapi_id_kex(ctxt, kex->name, kex->kex_type)
  72             == GSS_C_NO_OID)
  73                 fatal("Couldn't identify host exchange");
  74
  75         if (ssh_gssapi_import_name(ctxt, kex->gss_host))
  76                 fatal("Couldn't import hostname");
  77
  78         if (kex->gss_client &&
  79             ssh_gssapi_client_identity(ctxt, kex->gss_client))
  80                 fatal("Couldn't acquire client credentials");
  81
  82         switch (kex->kex_type) {
  83         case KEX_GSS_GRP1_SHA1:
  84                 dh = dh_new_group1();
  85                 break;
  86         case KEX_GSS_GRP14_SHA1:
  87                 dh = dh_new_group14();
  88                 break;
  89         case KEX_GSS_GEX_SHA1:
  90                 debug("Doing group exchange\n");
  91                 nbits = dh_estimate(kex->we_need * 8);
  92                 packet_start(SSH2_MSG_KEXGSS_GROUPREQ);
  93                 packet_put_int(min);
  94                 packet_put_int(nbits);
  95                 packet_put_int(max);
  96
  97                 packet_send();
  98
  99                 packet_read_expect(SSH2_MSG_KEXGSS_GROUP);
 100
 101                 if ((p = BN_new()) == NULL)
 102                         fatal("BN_new() failed");
 103                 packet_get_bignum2(p);
 104                 if ((g = BN_new()) == NULL)
 105                         fatal("BN_new() failed");
 106                 packet_get_bignum2(g);
 107                 packet_check_eom();
 108
 109                 if (BN_num_bits(p) < min || BN_num_bits(p) > max)
 110                         fatal("GSSGRP_GEX group out of range: %d !< %d !< %d",
 111                             min, BN_num_bits(p), max);
 112
 113                 dh = dh_new_group(g, p);
 114                 break;
 115         default:
 116                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
 117         }
 118
 119         /* Step 1 - e is dh->pub_key */
 120         dh_gen_key(dh, kex->we_need * 8);
 121
 122         /* This is f, we initialise it now to make life easier */
 123         dh_server_pub = BN_new();
 124         if (dh_server_pub == NULL)
 125                 fatal("dh_server_pub == NULL");
 126
 127         token_ptr = GSS_C_NO_BUFFER;
 128
 129         do {
 130                 debug("Calling gss_init_sec_context");
 131
 132                 maj_status = ssh_gssapi_init_ctx(ctxt,
 133                     kex->gss_deleg_creds, token_ptr, &send_tok,
 134                     &ret_flags);
 135
 136                 if (GSS_ERROR(maj_status)) {
 137                         if (send_tok.length != 0) {
 138                                 packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 139                                 packet_put_string(send_tok.value,
 140                                     send_tok.length);
 141                         }
 142                         fatal("gss_init_context failed");
 143                 }
 144
 145                 /* If we've got an old receive buffer get rid of it */
 146                 if (token_ptr != GSS_C_NO_BUFFER)
 147                         xfree(recv_tok.value);
 148
 149                 if (maj_status == GSS_S_COMPLETE) {
 150                         /* If mutual state flag is not true, kex fails */
 151                         if (!(ret_flags & GSS_C_MUTUAL_FLAG))
 152                                 fatal("Mutual authentication failed");
 153
 154                         /* If integ avail flag is not true kex fails */
 155                         if (!(ret_flags & GSS_C_INTEG_FLAG))
 156                                 fatal("Integrity check failed");
 157                 }
 158
 159                 /*
 160                  * If we have data to send, then the last message that we
 161                  * received cannot have been a 'complete'.
 162                  */
 163                 if (send_tok.length != 0) {
 164                         if (first) {
 165                                 packet_start(SSH2_MSG_KEXGSS_INIT);
 166                                 packet_put_string(send_tok.value,
 167                                     send_tok.length);
 168                                 packet_put_bignum2(dh->pub_key);
 169                                 first = 0;
 170                         } else {
 171                                 packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 172                                 packet_put_string(send_tok.value,
 173                                     send_tok.length);
 174                         }
 175                         packet_send();
 176                         gss_release_buffer(&min_status, &send_tok);
 177
 178                         /* If we've sent them data, they should reply */
 179                         do {
 180                                 type = packet_read();
 181                                 if (type == SSH2_MSG_KEXGSS_HOSTKEY) {
 182                                         debug("Received KEXGSS_HOSTKEY");
 183                                         if (serverhostkey)
 184                                                 fatal("Server host key received more than once");
 185                                         serverhostkey =
 186                                             packet_get_string(&slen);
 187                                 }
 188                         } while (type == SSH2_MSG_KEXGSS_HOSTKEY);
 189
 190                         switch (type) {
 191                         case SSH2_MSG_KEXGSS_CONTINUE:
 192                                 debug("Received GSSAPI_CONTINUE");
 193                                 if (maj_status == GSS_S_COMPLETE)
 194                                         fatal("GSSAPI Continue received from server when complete");
 195                                 recv_tok.value = packet_get_string(&strlen);
 196                                 recv_tok.length = strlen;
 197                                 break;
 198                         case SSH2_MSG_KEXGSS_COMPLETE:
 199                                 debug("Received GSSAPI_COMPLETE");
 200                                 packet_get_bignum2(dh_server_pub);
 201                                 msg_tok.value =  packet_get_string(&strlen);
 202                                 msg_tok.length = strlen;
 203
 204                                 /* Is there a token included? */
 205                                 if (packet_get_char()) {
 206                                         recv_tok.value=
 207                                             packet_get_string(&strlen);
 208                                         recv_tok.length = strlen;
 209                                         /* If we're already complete - protocol error */
 210                                         if (maj_status == GSS_S_COMPLETE)
 211                                                 packet_disconnect("Protocol error: received token when complete");
 212                                         } else {
 213                                                 /* No token included */
 214                                                 if (maj_status != GSS_S_COMPLETE)
 215                                                         packet_disconnect("Protocol error: did not receive final token");
 216                                 }
 217                                 break;
 218                         case SSH2_MSG_KEXGSS_ERROR:
 219                                 debug("Received Error");
 220                                 maj_status = packet_get_int();
 221                                 min_status = packet_get_int();
 222                                 msg = packet_get_string(NULL);
 223                                 lang = packet_get_string(NULL);
 224                                 fatal("GSSAPI Error: \n%.400s",msg);
 225                         default:
 226                                 packet_disconnect("Protocol error: didn't expect packet type %d",
 227                                 type);
 228                         }
 229                         token_ptr = &recv_tok;
 230                 } else {
 231                         /* No data, and not complete */
 232                         if (maj_status != GSS_S_COMPLETE)
 233                                 fatal("Not complete, and no token output");
 234                 }
 235         } while (maj_status & GSS_S_CONTINUE_NEEDED);
 236
 237         /*
 238          * We _must_ have received a COMPLETE message in reply from the
 239          * server, which will have set dh_server_pub and msg_tok
 240          */
 241
 242         if (type != SSH2_MSG_KEXGSS_COMPLETE)
 243                 fatal("Didn't receive a SSH2_MSG_KEXGSS_COMPLETE when I expected it");
 244
 245         /* Check f in range [1, p-1] */
 246         if (!dh_pub_is_valid(dh, dh_server_pub))
 247                 packet_disconnect("bad server public DH value");
 248
 249         /* compute K=f^x mod p */
 250         klen = DH_size(dh);
 251         kbuf = xmalloc(klen);
 252         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 253         if (kout < 0)
 254                 fatal("DH_compute_key: failed");
 255
 256         shared_secret = BN_new();
 257         if (shared_secret == NULL)
 258                 fatal("kexgss_client: BN_new failed");
 259
 260         if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
 261                 fatal("kexdh_client: BN_bin2bn failed");
 262
 263         memset(kbuf, 0, klen);
 264         xfree(kbuf);
 265
 266         switch (kex->kex_type) {
 267         case KEX_GSS_GRP1_SHA1:
 268         case KEX_GSS_GRP14_SHA1:
 269                 kex_dh_hash( kex->client_version_string,
 270                     kex->server_version_string,
 271                     buffer_ptr(&kex->my), buffer_len(&kex->my),
 272                     buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 273                     (serverhostkey ? serverhostkey : empty), slen,
 274                     dh->pub_key,        /* e */
 275                     dh_server_pub,      /* f */
 276                     shared_secret,      /* K */
 277                     &hash, &hashlen
 278                 );
 279                 break;
 280         case KEX_GSS_GEX_SHA1:
 281                 kexgex_hash(
 282                     kex->evp_md,
 283                     kex->client_version_string,
 284                     kex->server_version_string,
 285                     buffer_ptr(&kex->my), buffer_len(&kex->my),
 286                     buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 287                     (serverhostkey ? serverhostkey : empty), slen,
 288                     min, nbits, max,
 289                     dh->p, dh->g,
 290                     dh->pub_key,
 291                     dh_server_pub,
 292                     shared_secret,
 293                     &hash, &hashlen
 294                 );
 295                 break;
 296         default:
 297                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
 298         }
 299
 300         gssbuf.value = hash;
 301         gssbuf.length = hashlen;
 302
 303         /* Verify that the hash matches the MIC we just got. */
 304         if (GSS_ERROR(ssh_gssapi_checkmic(ctxt, &gssbuf, &msg_tok)))
 305                 packet_disconnect("Hash's MIC didn't verify");
 306
 307         xfree(msg_tok.value);
 308
 309         DH_free(dh);
 310         if (serverhostkey)
 311                 xfree(serverhostkey);
 312         BN_clear_free(dh_server_pub);
 313
 314         /* save session id */
 315         if (kex->session_id == NULL) {
 316                 kex->session_id_len = hashlen;
 317                 kex->session_id = xmalloc(kex->session_id_len);
 318                 memcpy(kex->session_id, hash, kex->session_id_len);
 319         }
 320
 321         if (kex->gss_deleg_creds)
 322                 ssh_gssapi_credentials_updated(ctxt);
 323
 324         if (gss_kex_context == NULL)
 325                 gss_kex_context = ctxt;
 326         else
 327                 ssh_gssapi_delete_ctx(&ctxt);
 328
 329         kex_derive_keys(kex, hash, hashlen, shared_secret);
 330         BN_clear_free(shared_secret);
 331         kex_finish(kex);
 332 }
 333
 334 #endif /* GSSAPI */