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