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 "kex.h"
  36 #include "log.h"
  37 #include "packet.h"
  38 #include "dh.h"
  39 #include "canohost.h"
  40 #include "ssh2.h"
  41 #include "ssh-gss.h"
  42
  43 void
  44 kexgss_client(Kex *kex) {
  45         gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
  46         gss_buffer_desc recv_tok, gssbuf, msg_tok, *token_ptr;
  47         Gssctxt *ctxt;
  48         OM_uint32 maj_status, min_status, ret_flags;
  49         unsigned int klen, kout;
  50         DH *dh;
  51         BIGNUM *dh_server_pub = NULL;
  52         BIGNUM *shared_secret = NULL;
  53         BIGNUM *p = NULL;
  54         BIGNUM *g = NULL;
  55         unsigned char *kbuf;
  56         unsigned char *hash;
  57         unsigned int hashlen;
  58         unsigned char *serverhostkey = NULL;
  59         char *msg;
  60         char *lang;
  61         int type = 0;
  62         int first = 1;
  63         unsigned int slen = 0;
  64         int gex = 0;
  65         int nbits = -1, min = -1, max = -1;
  66         u_int strlen;
  67
  68         /* Initialise our GSSAPI world */
  69         ssh_gssapi_build_ctx(&ctxt);
  70         if (ssh_gssapi_id_kex(ctxt, kex->name, &gex) == NULL)
  71                 fatal("Couldn't identify host exchange");
  72
  73         if (ssh_gssapi_import_name(ctxt, kex->gss_host))
  74                 fatal("Couldn't import hostname");
  75
  76         if (gex) {
  77                 debug("Doing group exchange\n");
  78                 nbits = dh_estimate(kex->we_need * 8);
  79                 min = DH_GRP_MIN;
  80                 max = DH_GRP_MAX;
  81                 packet_start(SSH2_MSG_KEXGSS_GROUPREQ);
  82                 packet_put_int(min);
  83                 packet_put_int(nbits);
  84                 packet_put_int(max);
  85
  86                 packet_send();
  87
  88                 packet_read_expect(SSH2_MSG_KEXGSS_GROUP);
  89
  90                 if ((p = BN_new()) == NULL)
  91                         fatal("BN_new() failed");
  92                 packet_get_bignum2(p);
  93                 if ((g = BN_new()) == NULL)
  94                         fatal("BN_new() failed");
  95                 packet_get_bignum2(g);
  96                 packet_check_eom();
  97
  98                 if (BN_num_bits(p) < min || BN_num_bits(p) > max)
  99                         fatal("GSSGRP_GEX group out of range: %d !< %d !< %d",
 100                             min, BN_num_bits(p), max);
 101
 102                 dh = dh_new_group(g, p);
 103         } else {
 104                 dh = dh_new_group1();
 105         }
 106
 107         /* Step 1 - e is dh->pub_key */
 108         dh_gen_key(dh, kex->we_need * 8);
 109
 110         /* This is f, we initialise it now to make life easier */
 111         dh_server_pub = BN_new();
 112         if (dh_server_pub == NULL)
 113                 fatal("dh_server_pub == NULL");
 114
 115         token_ptr = GSS_C_NO_BUFFER;
 116
 117         do {
 118                 debug("Calling gss_init_sec_context");
 119
 120                 maj_status = ssh_gssapi_init_ctx(ctxt,
 121                     kex->gss_deleg_creds, token_ptr, &send_tok,
 122                     &ret_flags);
 123
 124                 if (GSS_ERROR(maj_status)) {
 125                         if (send_tok.length != 0) {
 126                                 packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 127                                 packet_put_string(send_tok.value,
 128                                     send_tok.length);
 129                         }
 130                         fatal("gss_init_context failed");
 131                 }
 132
 133                 /* If we've got an old receive buffer get rid of it */
 134                 if (token_ptr != GSS_C_NO_BUFFER)
 135                         xfree(recv_tok.value);
 136
 137                 if (maj_status == GSS_S_COMPLETE) {
 138                         /* If mutual state flag is not true, kex fails */
 139                         if (!(ret_flags & GSS_C_MUTUAL_FLAG))
 140                                 fatal("Mutual authentication failed");
 141
 142                         /* If integ avail flag is not true kex fails */
 143                         if (!(ret_flags & GSS_C_INTEG_FLAG))
 144                                 fatal("Integrity check failed");
 145                 }
 146
 147                 /*
 148                  * If we have data to send, then the last message that we
 149                  * received cannot have been a 'complete'.
 150                  */
 151                 if (send_tok.length != 0) {
 152                         if (first) {
 153                                 packet_start(SSH2_MSG_KEXGSS_INIT);
 154                                 packet_put_string(send_tok.value,
 155                                     send_tok.length);
 156                                 packet_put_bignum2(dh->pub_key);
 157                                 first = 0;
 158                         } else {
 159                                 packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 160                                 packet_put_string(send_tok.value,
 161                                     send_tok.length);
 162                         }
 163                         packet_send();
 164                         gss_release_buffer(&min_status, &send_tok);
 165
 166                         /* If we've sent them data, they should reply */
 167                         do {
 168                                 type = packet_read();
 169                                 if (type == SSH2_MSG_KEXGSS_HOSTKEY) {
 170                                         debug("Received KEXGSS_HOSTKEY");
 171                                         if (serverhostkey)
 172                                                 fatal("Server host key received more than once");
 173                                         serverhostkey =
 174                                             packet_get_string(&slen);
 175                                 }
 176                         } while (type == SSH2_MSG_KEXGSS_HOSTKEY);
 177
 178                         switch (type) {
 179                         case SSH2_MSG_KEXGSS_CONTINUE:
 180                                 debug("Received GSSAPI_CONTINUE");
 181                                 if (maj_status == GSS_S_COMPLETE)
 182                                         fatal("GSSAPI Continue received from server when complete");
 183                                 recv_tok.value = packet_get_string(&strlen);
 184                                 recv_tok.length = strlen;
 185                                 break;
 186                         case SSH2_MSG_KEXGSS_COMPLETE:
 187                                 debug("Received GSSAPI_COMPLETE");
 188                                 packet_get_bignum2(dh_server_pub);
 189                                 msg_tok.value =  packet_get_string(&strlen);
 190                                 msg_tok.length = strlen;
 191
 192                                 /* Is there a token included? */
 193                                 if (packet_get_char()) {
 194                                         recv_tok.value=
 195                                             packet_get_string(&strlen);
 196                                         recv_tok.length = strlen;
 197                                         /* If we're already complete - protocol error */
 198                                         if (maj_status == GSS_S_COMPLETE)
 199                                                 packet_disconnect("Protocol error: received token when complete");
 200                                         } else {
 201                                                 /* No token included */
 202                                                 if (maj_status != GSS_S_COMPLETE)
 203                                                         packet_disconnect("Protocol error: did not receive final token");
 204                                 }
 205                                 break;
 206                         case SSH2_MSG_KEXGSS_ERROR:
 207                                 debug("Received Error");
 208                                 maj_status = packet_get_int();
 209                                 min_status = packet_get_int();
 210                                 msg = packet_get_string(NULL);
 211                                 lang = packet_get_string(NULL);
 212                                 fatal("GSSAPI Key Exchange Error: \n%s",msg);
 213                         default:
 214                                 packet_disconnect("Protocol error: didn't expect packet type %d",
 215                                 type);
 216                         }
 217                         token_ptr = &recv_tok;
 218                 } else {
 219                         /* No data, and not complete */
 220                         if (maj_status != GSS_S_COMPLETE)
 221                                 fatal("Not complete, and no token output");
 222                 }
 223         } while (maj_status & GSS_S_CONTINUE_NEEDED);
 224
 225         /*
 226          * We _must_ have received a COMPLETE message in reply from the
 227          * server, which will have set dh_server_pub and msg_tok
 228          */
 229
 230         if (type != SSH2_MSG_KEXGSS_COMPLETE)
 231                 fatal("Didn't receive a SSH2_MSG_KEXGSS_COMPLETE when I expected it");
 232
 233         /* Check f in range [1, p-1] */
 234         if (!dh_pub_is_valid(dh, dh_server_pub))
 235                 packet_disconnect("bad server public DH value");
 236
 237         /* compute K=f^x mod p */
 238         klen = DH_size(dh);
 239         kbuf = xmalloc(klen);
 240         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 241
 242         shared_secret = BN_new();
 243         BN_bin2bn(kbuf,kout, shared_secret);
 244         memset(kbuf, 0, klen);
 245         xfree(kbuf);
 246
 247         if (gex) {
 248                 kexgex_hash(
 249                     kex->evp_md,
 250                     kex->client_version_string,
 251                     kex->server_version_string,
 252                     buffer_ptr(&kex->my), buffer_len(&kex->my),
 253                     buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 254                     serverhostkey, slen,
 255                     min, nbits, max,
 256                     dh->p, dh->g,
 257                     dh->pub_key,
 258                     dh_server_pub,
 259                     shared_secret,
 260                     &hash, &hashlen
 261                 );
 262         } else {
 263                 /* The GSS hash is identical to the DH one */
 264                 kex_dh_hash( kex->client_version_string,
 265                     kex->server_version_string,
 266                     buffer_ptr(&kex->my), buffer_len(&kex->my),
 267                     buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 268                     serverhostkey, slen, /* server host key */
 269                     dh->pub_key,        /* e */
 270                     dh_server_pub,      /* f */
 271                     shared_secret,      /* K */
 272                     &hash, &hashlen
 273                 );
 274         }
 275
 276         gssbuf.value = hash;
 277         gssbuf.length = 20;
 278
 279         /* Verify that the hash matches the MIC we just got. */
 280         if (GSS_ERROR(ssh_gssapi_checkmic(ctxt, &gssbuf, &msg_tok)))
 281                 packet_disconnect("Hash's MIC didn't verify");
 282
 283         xfree(msg_tok.value);
 284
 285         DH_free(dh);
 286         if (serverhostkey)
 287                 xfree(serverhostkey);
 288         BN_clear_free(dh_server_pub);
 289
 290         /* save session id */
 291         if (kex->session_id == NULL) {
 292                 kex->session_id_len = 20;
 293                 kex->session_id = xmalloc(kex->session_id_len);
 294                 memcpy(kex->session_id, hash, kex->session_id_len);
 295         }
 296
 297         if (gss_kex_context == NULL)
 298                 gss_kex_context = ctxt;
 299         else
 300                 ssh_gssapi_delete_ctx(&ctxt);
 301
 302         kex_derive_keys(kex, hash, hashlen, shared_secret);
 303         BN_clear_free(shared_secret);
 304         kex_finish(kex);
 305 }
 306
 307 #endif /* GSSAPI */