openssh/kexgssc.c

   1 /*
   2  * Copyright (c) 2001-2003 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 "ssh2.h"
  40 #include "ssh-gss.h"
  41
  42 void
  43 kexgss_client(Kex *kex)
  44 {
  45         gss_buffer_desc gssbuf,send_tok,recv_tok, msg_tok, *token_ptr;
  46         Gssctxt *ctxt;
  47         OM_uint32 maj_status, min_status, ret_flags;
  48         unsigned int klen, kout;
  49         DH *dh;
  50         BIGNUM *dh_server_pub = 0;
  51         BIGNUM *shared_secret = 0;
  52         unsigned char *kbuf;
  53         unsigned char *hash;
  54         unsigned char *serverhostkey;
  55         char *msg;
  56         char *lang;
  57         int type = 0;
  58         int first = 1;
  59         int slen = 0;
  60
  61         /* Initialise our GSSAPI world */
  62         ssh_gssapi_build_ctx(&ctxt);
  63         if (ssh_gssapi_client_id_kex(ctxt,kex->name)==NULL) {
  64                 fatal("Couldn't identify host exchange");
  65         }
  66
  67         if (ssh_gssapi_import_name(ctxt,kex->host)) {
  68                 fatal("Couldn't import hostname ");
  69         }
  70
  71         /* This code should match that in ssh_dh1_client */
  72
  73         /* Step 1 - e is dh->pub_key */
  74         dh = dh_new_group1();
  75         dh_gen_key(dh, kex->we_need * 8);
  76
  77         /* This is f, we initialise it now to make life easier */
  78         dh_server_pub = BN_new();
  79         if (dh_server_pub == NULL) {
  80                 fatal("dh_server_pub == NULL");
  81         }
  82
  83         token_ptr = GSS_C_NO_BUFFER;
  84
  85         do {
  86                 debug("Calling gss_init_sec_context");
  87
  88                 maj_status=ssh_gssapi_init_ctx(ctxt,
  89                                                kex->options.gss_deleg_creds,
  90                                                token_ptr,&send_tok,
  91                                                &ret_flags);
  92
  93                 if (GSS_ERROR(maj_status)) {
  94                         if (send_tok.length!=0) {
  95                                 /* Hmmm - not sure about this */
  96                                 packet_start(SSH2_MSG_KEXGSS_CONTINUE);
  97                                 packet_put_string(send_tok.value,
  98                                                   send_tok.length);
  99                         }
 100                         fatal("gss_init_context failed");
 101                 }
 102
 103                 /* If we've got an old receive buffer get rid of it */
 104                 if (token_ptr != GSS_C_NO_BUFFER)
 105                         (void) gss_release_buffer(&min_status, &recv_tok);
 106
 107
 108                 if (maj_status == GSS_S_COMPLETE) {
 109                         /* If mutual state flag is not true, kex fails */
 110                         if (!(ret_flags & GSS_C_MUTUAL_FLAG)) {
 111                                 fatal("Mutual authentication failed");
 112                         }
 113                         /* If integ avail flag is not true kex fails */
 114                         if (!(ret_flags & GSS_C_INTEG_FLAG)) {
 115                                 fatal("Integrity check failed");
 116                         }
 117                 }
 118
 119                 /* If we have data to send, then the last message that we
 120                  * received cannot have been a 'complete'. */
 121                 if (send_tok.length !=0) {
 122                         if (first) {
 123                                 packet_start(SSH2_MSG_KEXGSS_INIT);
 124                                 packet_put_string(send_tok.value,
 125                                                   send_tok.length);
 126                                 packet_put_bignum2(dh->pub_key);
 127                                 first=0;
 128                         } else {
 129                                 packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 130                                 packet_put_string(send_tok.value,
 131                                                   send_tok.length);
 132                         }
 133                         packet_send();
 134                         packet_write_wait();
 135
 136
 137                         /* If we've sent them data, they'd better be polite
 138                          * and reply. */
 139
 140                         type = packet_read();
 141                         switch (type) {
 142                         case SSH2_MSG_KEXGSS_HOSTKEY:
 143                                 debug("Received KEXGSS_HOSTKEY");
 144                                 serverhostkey=packet_get_string(&slen);
 145                                 break;
 146                         case SSH2_MSG_KEXGSS_CONTINUE:
 147                                 debug("Received GSSAPI_CONTINUE");
 148                                 if (maj_status == GSS_S_COMPLETE)
 149                                         fatal("GSSAPI Continue received from server when complete");
 150                                 recv_tok.value=packet_get_string(&recv_tok.length);
 151                                 break;
 152                         case SSH2_MSG_KEXGSS_COMPLETE:
 153                                 debug("Received GSSAPI_COMPLETE");
 154                                 packet_get_bignum2(dh_server_pub);
 155                                 msg_tok.value=
 156                                     packet_get_string(&msg_tok.length);
 157
 158                                 /* Is there a token included? */
 159                                 if (packet_get_char()) {
 160                                         recv_tok.value=
 161                                             packet_get_string(&recv_tok.length);
 162                                         /* If we're already complete - protocol error */
 163                                         if (maj_status == GSS_S_COMPLETE)
 164                                                 packet_disconnect("Protocol error: received token when complete");
 165                                 } else {
 166                                         /* No token included */
 167                                         if (maj_status != GSS_S_COMPLETE)
 168                                                 packet_disconnect("Protocol error: did not receive final token");
 169                                 }
 170                                 break;
 171                         case SSH2_MSG_KEXGSS_ERROR:
 172                                 debug("Received Error");
 173                                 maj_status=packet_get_int();
 174                                 min_status=packet_get_int();
 175                                 msg=packet_get_string(NULL);
 176                                 lang=packet_get_string(NULL);
 177                                 fprintf(stderr,"GSSAPI Error: \n%s",msg);
 178                         default:
 179                                 packet_disconnect("Protocol error: didn't expect packet type %d",
 180                                 type);
 181                         }
 182                         token_ptr=&recv_tok;
 183                 } else {
 184                         /* No data, and not complete */
 185                         if (maj_status!=GSS_S_COMPLETE) {
 186                                 fatal("Not complete, and no token output");
 187                         }
 188                 }
 189         } while (maj_status & GSS_S_CONTINUE_NEEDED);
 190
 191         /* We _must_ have received a COMPLETE message in reply from the
 192          * server, which will have set dh_server_pub and msg_tok */
 193
 194         if (type!=SSH2_MSG_KEXGSS_COMPLETE)
 195            fatal("Didn't receive a SSH2_MSG_KEXGSS_COMPLETE when I expected it");
 196
 197         /* Check f in range [1, p-1] */
 198         if (!dh_pub_is_valid(dh, dh_server_pub))
 199                         packet_disconnect("bad server public DH value");
 200
 201         /* compute K=f^x mod p */
 202         klen = DH_size(dh);
 203         kbuf = xmalloc(klen);
 204         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 205
 206         shared_secret = BN_new();
 207         BN_bin2bn(kbuf,kout, shared_secret);
 208         memset(kbuf, 0, klen);
 209         xfree(kbuf);
 210
 211         /* The GSS hash is identical to the DH one */
 212         hash = kex_dh_hash(
 213             kex->client_version_string,
 214             kex->server_version_string,
 215             buffer_ptr(&kex->my), buffer_len(&kex->my),
 216             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 217             serverhostkey, slen, /* server host key */
 218             dh->pub_key,        /* e */
 219             dh_server_pub,      /* f */
 220             shared_secret       /* K */
 221         );
 222
 223         gssbuf.value=hash;
 224         gssbuf.length=20;
 225
 226         /* Verify that H matches the token we just got. */
 227                 if ((maj_status = gss_verify_mic(&min_status,
 228                                          ctxt->context,
 229                                          &gssbuf,
 230                                          &msg_tok,
 231                                          NULL))) {
 232
 233                 packet_disconnect("Hash's MIC didn't verify");
 234         }
 235
 236         DH_free(dh);
 237         ssh_gssapi_delete_ctx(&ctxt);
 238         /* save session id */
 239         if (kex->session_id == NULL) {
 240                 kex->session_id_len = 20;
 241                 kex->session_id = xmalloc(kex->session_id_len);
 242                 memcpy(kex->session_id, hash, kex->session_id_len);
 243         }
 244
 245         kex_derive_keys(kex, hash, shared_secret);
 246         BN_clear_free(shared_secret);
 247         kex_finish(kex);
 248 }
 249
 250 #endif /* GSSAPI */