openssh/kexgssc.c

   1 /*
   2  * Copyright (c) 2001-2005 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 "xmalloc.h"
  33 #include "buffer.h"
  34 #include "bufaux.h"
  35 #include "cipher.h"
  36 #include "key.h"
  37 #include "kex.h"
  38 #include "log.h"
  39 #include "packet.h"
  40 #include "dh.h"
  41 #include "canohost.h"
  42 #include "ssh2.h"
  43 #include "ssh-gss.h"
  44
  45 void
  46 kexgss_client(Kex *kex) {
  47         gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
  48         gss_buffer_desc recv_tok, gssbuf, msg_tok, *token_ptr;
  49         Gssctxt *ctxt;
  50         OM_uint32 maj_status, min_status, ret_flags;
  51         u_int klen, kout, slen = 0, hashlen, strlen;
  52         DH *dh;
  53         BIGNUM *dh_server_pub = NULL;
  54         BIGNUM *shared_secret = NULL;
  55         BIGNUM *p = NULL;
  56         BIGNUM *g = NULL;
  57         u_char *kbuf, *hash;
  58         u_char *serverhostkey = NULL;
  59         char *msg;
  60         char *lang;
  61         int type = 0;
  62         int first = 1;
  63         int gex = 0;
  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, &gex) == NULL)
  69                 fatal("Couldn't identify host exchange");
  70
  71         if (ssh_gssapi_import_name(ctxt, kex->gss_host))
  72                 fatal("Couldn't import hostname");
  73
  74         if (gex) {
  75                 debug("Doing group exchange\n");
  76                 nbits = dh_estimate(kex->we_need * 8);
  77                 packet_start(SSH2_MSG_KEXGSS_GROUPREQ);
  78                 packet_put_int(min);
  79                 packet_put_int(nbits);
  80                 packet_put_int(max);
  81
  82                 packet_send();
  83
  84                 packet_read_expect(SSH2_MSG_KEXGSS_GROUP);
  85
  86                 if ((p = BN_new()) == NULL)
  87                         fatal("BN_new() failed");
  88                 packet_get_bignum2(p);
  89                 if ((g = BN_new()) == NULL)
  90                         fatal("BN_new() failed");
  91                 packet_get_bignum2(g);
  92                 packet_check_eom();
  93
  94                 if (BN_num_bits(p) < min || BN_num_bits(p) > max)
  95                         fatal("GSSGRP_GEX group out of range: %d !< %d !< %d",
  96                             min, BN_num_bits(p), max);
  97
  98                 dh = dh_new_group(g, p);
  99         } else {
 100                 dh = dh_new_group1();
 101         }
 102
 103         /* Step 1 - e is dh->pub_key */
 104         dh_gen_key(dh, kex->we_need * 8);
 105
 106         /* This is f, we initialise it now to make life easier */
 107         dh_server_pub = BN_new();
 108         if (dh_server_pub == NULL)
 109                 fatal("dh_server_pub == NULL");
 110
 111         token_ptr = GSS_C_NO_BUFFER;
 112
 113         do {
 114                 debug("Calling gss_init_sec_context");
 115
 116                 maj_status = ssh_gssapi_init_ctx(ctxt,
 117                     kex->gss_deleg_creds, token_ptr, &send_tok,
 118                     &ret_flags);
 119
 120                 if (GSS_ERROR(maj_status)) {
 121                         if (send_tok.length != 0) {
 122                                 packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 123                                 packet_put_string(send_tok.value,
 124                                     send_tok.length);
 125                         }
 126                         fatal("gss_init_context failed");
 127                 }
 128
 129                 /* If we've got an old receive buffer get rid of it */
 130                 if (token_ptr != GSS_C_NO_BUFFER)
 131                         xfree(recv_tok.value);
 132
 133                 if (maj_status == GSS_S_COMPLETE) {
 134                         /* If mutual state flag is not true, kex fails */
 135                         if (!(ret_flags & GSS_C_MUTUAL_FLAG))
 136                                 fatal("Mutual authentication failed");
 137
 138                         /* If integ avail flag is not true kex fails */
 139                         if (!(ret_flags & GSS_C_INTEG_FLAG))
 140                                 fatal("Integrity check failed");
 141                 }
 142
 143                 /*
 144                  * If we have data to send, then the last message that we
 145                  * received cannot have been a 'complete'.
 146                  */
 147                 if (send_tok.length != 0) {
 148                         if (first) {
 149                                 packet_start(SSH2_MSG_KEXGSS_INIT);
 150                                 packet_put_string(send_tok.value,
 151                                     send_tok.length);
 152                                 packet_put_bignum2(dh->pub_key);
 153                                 first = 0;
 154                         } else {
 155                                 packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 156                                 packet_put_string(send_tok.value,
 157                                     send_tok.length);
 158                         }
 159                         packet_send();
 160                         gss_release_buffer(&min_status, &send_tok);
 161
 162                         /* If we've sent them data, they should reply */
 163                         do {
 164                                 type = packet_read();
 165                                 if (type == SSH2_MSG_KEXGSS_HOSTKEY) {
 166                                         debug("Received KEXGSS_HOSTKEY");
 167                                         if (serverhostkey)
 168                                                 fatal("Server host key received more than once");
 169                                         serverhostkey =
 170                                             packet_get_string(&slen);
 171                                 }
 172                         } while (type == SSH2_MSG_KEXGSS_HOSTKEY);
 173
 174                         switch (type) {
 175                         case SSH2_MSG_KEXGSS_CONTINUE:
 176                                 debug("Received GSSAPI_CONTINUE");
 177                                 if (maj_status == GSS_S_COMPLETE)
 178                                         fatal("GSSAPI Continue received from server when complete");
 179                                 recv_tok.value = packet_get_string(&strlen);
 180                                 recv_tok.length = strlen;
 181                                 break;
 182                         case SSH2_MSG_KEXGSS_COMPLETE:
 183                                 debug("Received GSSAPI_COMPLETE");
 184                                 packet_get_bignum2(dh_server_pub);
 185                                 msg_tok.value =  packet_get_string(&strlen);
 186                                 msg_tok.length = strlen;
 187
 188                                 /* Is there a token included? */
 189                                 if (packet_get_char()) {
 190                                         recv_tok.value=
 191                                             packet_get_string(&strlen);
 192                                         recv_tok.length = strlen;
 193                                         /* If we're already complete - protocol error */
 194                                         if (maj_status == GSS_S_COMPLETE)
 195                                                 packet_disconnect("Protocol error: received token when complete");
 196                                         } else {
 197                                                 /* No token included */
 198                                                 if (maj_status != GSS_S_COMPLETE)
 199                                                         packet_disconnect("Protocol error: did not receive final token");
 200                                 }
 201                                 break;
 202                         case SSH2_MSG_KEXGSS_ERROR:
 203                                 debug("Received Error");
 204                                 maj_status = packet_get_int();
 205                                 min_status = packet_get_int();
 206                                 msg = packet_get_string(NULL);
 207                                 lang = packet_get_string(NULL);
 208                                 fatal("GSSAPI Key Exchange Error: \n%s",msg);
 209                         default:
 210                                 packet_disconnect("Protocol error: didn't expect packet type %d",
 211                                 type);
 212                         }
 213                         token_ptr = &recv_tok;
 214                 } else {
 215                         /* No data, and not complete */
 216                         if (maj_status != GSS_S_COMPLETE)
 217                                 fatal("Not complete, and no token output");
 218                 }
 219         } while (maj_status & GSS_S_CONTINUE_NEEDED);
 220
 221         /*
 222          * We _must_ have received a COMPLETE message in reply from the
 223          * server, which will have set dh_server_pub and msg_tok
 224          */
 225
 226         if (type != SSH2_MSG_KEXGSS_COMPLETE)
 227                 fatal("Didn't receive a SSH2_MSG_KEXGSS_COMPLETE when I expected it");
 228
 229         /* Check f in range [1, p-1] */
 230         if (!dh_pub_is_valid(dh, dh_server_pub))
 231                 packet_disconnect("bad server public DH value");
 232
 233         /* compute K=f^x mod p */
 234         klen = DH_size(dh);
 235         kbuf = xmalloc(klen);
 236         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 237
 238         shared_secret = BN_new();
 239         BN_bin2bn(kbuf,kout, shared_secret);
 240         memset(kbuf, 0, klen);
 241         xfree(kbuf);
 242
 243         if (gex) {
 244                 kexgex_hash(
 245                     kex->evp_md,
 246                     kex->client_version_string,
 247                     kex->server_version_string,
 248                     buffer_ptr(&kex->my), buffer_len(&kex->my),
 249                     buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 250                     serverhostkey, slen,
 251                     min, nbits, max,
 252                     dh->p, dh->g,
 253                     dh->pub_key,
 254                     dh_server_pub,
 255                     shared_secret,
 256                     &hash, &hashlen
 257                 );
 258         } else {
 259                 /* The GSS hash is identical to the DH one */
 260                 kex_dh_hash( kex->client_version_string,
 261                     kex->server_version_string,
 262                     buffer_ptr(&kex->my), buffer_len(&kex->my),
 263                     buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 264                     serverhostkey, slen, /* server host key */
 265                     dh->pub_key,        /* e */
 266                     dh_server_pub,      /* f */
 267                     shared_secret,      /* K */
 268                     &hash, &hashlen
 269                 );
 270         }
 271
 272         gssbuf.value = hash;
 273         gssbuf.length = hashlen;
 274
 275         /* Verify that the hash matches the MIC we just got. */
 276         if (GSS_ERROR(ssh_gssapi_checkmic(ctxt, &gssbuf, &msg_tok)))
 277                 packet_disconnect("Hash's MIC didn't verify");
 278
 279         xfree(msg_tok.value);
 280
 281         DH_free(dh);
 282         if (serverhostkey)
 283                 xfree(serverhostkey);
 284         BN_clear_free(dh_server_pub);
 285
 286         /* save session id */
 287         if (kex->session_id == NULL) {
 288                 kex->session_id_len = hashlen;
 289                 kex->session_id = xmalloc(kex->session_id_len);
 290                 memcpy(kex->session_id, hash, kex->session_id_len);
 291         }
 292
 293         if (gss_kex_context == NULL)
 294                 gss_kex_context = ctxt;
 295         else
 296                 ssh_gssapi_delete_ctx(&ctxt);
 297
 298         kex_derive_keys(kex, hash, hashlen, shared_secret);
 299         BN_clear_free(shared_secret);
 300         kex_finish(kex);
 301 }
 302
 303 #endif /* GSSAPI */