openssh/kexgssc.c

   1 /*
   2  * Copyright (c) 2001-2006 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 <openssl/crypto.h>
  30 #include <openssl/bn.h>
  31
  32 #include <string.h>
  33
  34 #include "xmalloc.h"
  35 #include "buffer.h"
  36 #include "ssh2.h"
  37 #include "key.h"
  38 #include "cipher.h"
  39 #include "kex.h"
  40 #include "log.h"
  41 #include "packet.h"
  42 #include "dh.h"
  43
  44 #include "ssh-gss.h"
  45
  46 void
  47 kexgss_client(Kex *kex) {
  48         gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
  49         gss_buffer_desc recv_tok, gssbuf, msg_tok, *token_ptr;
  50         Gssctxt *ctxt;
  51         OM_uint32 maj_status, min_status, ret_flags;
  52         u_int klen, kout, slen = 0, hashlen, strlen;
  53         DH *dh;
  54         BIGNUM *dh_server_pub = NULL;
  55         BIGNUM *shared_secret = NULL;
  56         BIGNUM *p = NULL;
  57         BIGNUM *g = NULL;
  58         u_char *kbuf, *hash;
  59         u_char *serverhostkey = NULL;
  60         char *msg;
  61         char *lang;
  62         int type = 0;
  63         int first = 1;
  64         int nbits = 0, min = DH_GRP_MIN, max = DH_GRP_MAX;
  65
  66         /* Initialise our GSSAPI world */
  67         ssh_gssapi_build_ctx(&ctxt);
  68         if (ssh_gssapi_id_kex(ctxt, kex->name, kex->kex_type)
  69             == GSS_C_NO_OID)
  70                 fatal("Couldn't identify host exchange");
  71
  72         if (ssh_gssapi_import_name(ctxt, kex->gss_host))
  73                 fatal("Couldn't import hostname");
  74
  75         switch (kex->kex_type) {
  76         case KEX_GSS_GRP1_SHA1:
  77                 dh = dh_new_group1();
  78                 break;
  79         case KEX_GSS_GRP14_SHA1:
  80                 dh = dh_new_group14();
  81                 break;
  82         case KEX_GSS_GEX_SHA1:
  83                 debug("Doing group exchange\n");
  84                 nbits = dh_estimate(kex->we_need * 8);
  85                 packet_start(SSH2_MSG_KEXGSS_GROUPREQ);
  86                 packet_put_int(min);
  87                 packet_put_int(nbits);
  88                 packet_put_int(max);
  89
  90                 packet_send();
  91
  92                 packet_read_expect(SSH2_MSG_KEXGSS_GROUP);
  93
  94                 if ((p = BN_new()) == NULL)
  95                         fatal("BN_new() failed");
  96                 packet_get_bignum2(p);
  97                 if ((g = BN_new()) == NULL)
  98                         fatal("BN_new() failed");
  99                 packet_get_bignum2(g);
 100                 packet_check_eom();
 101
 102                 if (BN_num_bits(p) < min || BN_num_bits(p) > max)
 103                         fatal("GSSGRP_GEX group out of range: %d !< %d !< %d",
 104                             min, BN_num_bits(p), max);
 105
 106                 dh = dh_new_group(g, p);
 107                 break;
 108         default:
 109                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
 110         }
 111
 112         /* Step 1 - e is dh->pub_key */
 113         dh_gen_key(dh, kex->we_need * 8);
 114
 115         /* This is f, we initialise it now to make life easier */
 116         dh_server_pub = BN_new();
 117         if (dh_server_pub == NULL)
 118                 fatal("dh_server_pub == NULL");
 119
 120         token_ptr = GSS_C_NO_BUFFER;
 121
 122         do {
 123                 debug("Calling gss_init_sec_context");
 124
 125                 maj_status = ssh_gssapi_init_ctx(ctxt,
 126                     kex->gss_deleg_creds, token_ptr, &send_tok,
 127                     &ret_flags);
 128
 129                 if (GSS_ERROR(maj_status)) {
 130                         if (send_tok.length != 0) {
 131                                 packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 132                                 packet_put_string(send_tok.value,
 133                                     send_tok.length);
 134                         }
 135                         fatal("gss_init_context failed");
 136                 }
 137
 138                 /* If we've got an old receive buffer get rid of it */
 139                 if (token_ptr != GSS_C_NO_BUFFER)
 140                         xfree(recv_tok.value);
 141
 142                 if (maj_status == GSS_S_COMPLETE) {
 143                         /* If mutual state flag is not true, kex fails */
 144                         if (!(ret_flags & GSS_C_MUTUAL_FLAG))
 145                                 fatal("Mutual authentication failed");
 146
 147                         /* If integ avail flag is not true kex fails */
 148                         if (!(ret_flags & GSS_C_INTEG_FLAG))
 149                                 fatal("Integrity check failed");
 150                 }
 151
 152                 /*
 153                  * If we have data to send, then the last message that we
 154                  * received cannot have been a 'complete'.
 155                  */
 156                 if (send_tok.length != 0) {
 157                         if (first) {
 158                                 packet_start(SSH2_MSG_KEXGSS_INIT);
 159                                 packet_put_string(send_tok.value,
 160                                     send_tok.length);
 161                                 packet_put_bignum2(dh->pub_key);
 162                                 first = 0;
 163                         } else {
 164                                 packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 165                                 packet_put_string(send_tok.value,
 166                                     send_tok.length);
 167                         }
 168                         packet_send();
 169                         gss_release_buffer(&min_status, &send_tok);
 170
 171                         /* If we've sent them data, they should reply */
 172                         do {
 173                                 type = packet_read();
 174                                 if (type == SSH2_MSG_KEXGSS_HOSTKEY) {
 175                                         debug("Received KEXGSS_HOSTKEY");
 176                                         if (serverhostkey)
 177                                                 fatal("Server host key received more than once");
 178                                         serverhostkey =
 179                                             packet_get_string(&slen);
 180                                 }
 181                         } while (type == SSH2_MSG_KEXGSS_HOSTKEY);
 182
 183                         switch (type) {
 184                         case SSH2_MSG_KEXGSS_CONTINUE:
 185                                 debug("Received GSSAPI_CONTINUE");
 186                                 if (maj_status == GSS_S_COMPLETE)
 187                                         fatal("GSSAPI Continue received from server when complete");
 188                                 recv_tok.value = packet_get_string(&strlen);
 189                                 recv_tok.length = strlen;
 190                                 break;
 191                         case SSH2_MSG_KEXGSS_COMPLETE:
 192                                 debug("Received GSSAPI_COMPLETE");
 193                                 packet_get_bignum2(dh_server_pub);
 194                                 msg_tok.value =  packet_get_string(&strlen);
 195                                 msg_tok.length = strlen;
 196
 197                                 /* Is there a token included? */
 198                                 if (packet_get_char()) {
 199                                         recv_tok.value=
 200                                             packet_get_string(&strlen);
 201                                         recv_tok.length = strlen;
 202                                         /* If we're already complete - protocol error */
 203                                         if (maj_status == GSS_S_COMPLETE)
 204                                                 packet_disconnect("Protocol error: received token when complete");
 205                                         } else {
 206                                                 /* No token included */
 207                                                 if (maj_status != GSS_S_COMPLETE)
 208                                                         packet_disconnect("Protocol error: did not receive final token");
 209                                 }
 210                                 break;
 211                         case SSH2_MSG_KEXGSS_ERROR:
 212                                 debug("Received Error");
 213                                 maj_status = packet_get_int();
 214                                 min_status = packet_get_int();
 215                                 msg = packet_get_string(NULL);
 216                                 lang = packet_get_string(NULL);
 217                                 fatal("GSSAPI Error: \n%.400s",msg);
 218                         default:
 219                                 packet_disconnect("Protocol error: didn't expect packet type %d",
 220                                 type);
 221                         }
 222                         token_ptr = &recv_tok;
 223                 } else {
 224                         /* No data, and not complete */
 225                         if (maj_status != GSS_S_COMPLETE)
 226                                 fatal("Not complete, and no token output");
 227                 }
 228         } while (maj_status & GSS_S_CONTINUE_NEEDED);
 229
 230         /*
 231          * We _must_ have received a COMPLETE message in reply from the
 232          * server, which will have set dh_server_pub and msg_tok
 233          */
 234
 235         if (type != SSH2_MSG_KEXGSS_COMPLETE)
 236                 fatal("Didn't receive a SSH2_MSG_KEXGSS_COMPLETE when I expected it");
 237
 238         /* Check f in range [1, p-1] */
 239         if (!dh_pub_is_valid(dh, dh_server_pub))
 240                 packet_disconnect("bad server public DH value");
 241
 242         /* compute K=f^x mod p */
 243         klen = DH_size(dh);
 244         kbuf = xmalloc(klen);
 245         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 246
 247         shared_secret = BN_new();
 248         BN_bin2bn(kbuf,kout, shared_secret);
 249         memset(kbuf, 0, klen);
 250         xfree(kbuf);
 251
 252         switch (kex->kex_type) {
 253         case KEX_GSS_GRP1_SHA1:
 254         case KEX_GSS_GRP14_SHA1:
 255                 kex_dh_hash( kex->client_version_string,
 256                     kex->server_version_string,
 257                     buffer_ptr(&kex->my), buffer_len(&kex->my),
 258                     buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 259                     serverhostkey, slen, /* server host key */
 260                     dh->pub_key,        /* e */
 261                     dh_server_pub,      /* f */
 262                     shared_secret,      /* K */
 263                     &hash, &hashlen
 264                 );
 265                 break;
 266         case KEX_GSS_GEX_SHA1:
 267                 kexgex_hash(
 268                     kex->evp_md,
 269                     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, slen,
 274                     min, nbits, max,
 275                     dh->p, dh->g,
 276                     dh->pub_key,
 277                     dh_server_pub,
 278                     shared_secret,
 279                     &hash, &hashlen
 280                 );
 281                 break;
 282         default:
 283                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
 284         }
 285
 286         gssbuf.value = hash;
 287         gssbuf.length = hashlen;
 288
 289         /* Verify that the hash matches the MIC we just got. */
 290         if (GSS_ERROR(ssh_gssapi_checkmic(ctxt, &gssbuf, &msg_tok)))
 291                 packet_disconnect("Hash's MIC didn't verify");
 292
 293         xfree(msg_tok.value);
 294
 295         DH_free(dh);
 296         if (serverhostkey)
 297                 xfree(serverhostkey);
 298         BN_clear_free(dh_server_pub);
 299
 300         /* save session id */
 301         if (kex->session_id == NULL) {
 302                 kex->session_id_len = hashlen;
 303                 kex->session_id = xmalloc(kex->session_id_len);
 304                 memcpy(kex->session_id, hash, kex->session_id_len);
 305         }
 306
 307         if (gss_kex_context == NULL)
 308                 gss_kex_context = ctxt;
 309         else
 310                 ssh_gssapi_delete_ctx(&ctxt);
 311
 312         kex_derive_keys(kex, hash, hashlen, shared_secret);
 313         BN_clear_free(shared_secret);
 314         kex_finish(kex);
 315 }
 316
 317 #endif /* GSSAPI */