openssh/kexgsss.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 <string.h>
  30
  31 #include <openssl/crypto.h>
  32 #include <openssl/bn.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 #include "ssh-gss.h"
  44 #include "monitor_wrap.h"
  45
  46 static void kex_gss_send_error(Gssctxt *ctxt);
  47
  48 void
  49 kexgss_server(Kex *kex)
  50 {
  51         OM_uint32 maj_status, min_status;
  52
  53         /*
  54          * Some GSSAPI implementations use the input value of ret_flags (an
  55          * output variable) as a means of triggering mechanism specific
  56          * features. Initializing it to zero avoids inadvertently
  57          * activating this non-standard behaviour.
  58          */
  59
  60         OM_uint32 ret_flags = 0;
  61         gss_buffer_desc gssbuf, recv_tok, msg_tok;
  62         gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
  63         Gssctxt *ctxt = NULL;
  64         u_int slen, klen, kout, hashlen;
  65         u_char *kbuf, *hash;
  66         DH *dh;
  67         int min = -1, max = -1, nbits = -1;
  68         BIGNUM *shared_secret = NULL;
  69         BIGNUM *dh_client_pub = NULL;
  70         int type = 0;
  71         gss_OID oid;
  72
  73         /* Initialise GSSAPI */
  74
  75         /* If we're rekeying, privsep means that some of the private structures
  76          * in the GSSAPI code are no longer available. This kludges them back
  77          * into life
  78          */
  79         if (!ssh_gssapi_oid_table_ok())
  80                 ssh_gssapi_server_mechanisms();
  81
  82         debug2("%s: Identifying %s", __func__, kex->name);
  83         oid = ssh_gssapi_id_kex(NULL, kex->name, kex->kex_type);
  84         if (oid == GSS_C_NO_OID)
  85            fatal("Unknown gssapi mechanism");
  86
  87         debug2("%s: Acquiring credentials", __func__);
  88
  89         if (GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctxt, oid)))) {
  90                 kex_gss_send_error(ctxt);
  91                 fatal("Unable to acquire credentials for the server");
  92     }
  93
  94         switch (kex->kex_type) {
  95         case KEX_GSS_GRP1_SHA1:
  96                 dh = dh_new_group1();
  97                 break;
  98         case KEX_GSS_GRP14_SHA1:
  99                 dh = dh_new_group14();
 100                 break;
 101         case KEX_GSS_GEX_SHA1:
 102                 debug("Doing group exchange");
 103                 packet_read_expect(SSH2_MSG_KEXGSS_GROUPREQ);
 104                 min = packet_get_int();
 105                 nbits = packet_get_int();
 106                 max = packet_get_int();
 107                 min = MAX(DH_GRP_MIN, min);
 108                 max = MIN(DH_GRP_MAX, max);
 109                 packet_check_eom();
 110                 if (max < min || nbits < min || max < nbits)
 111                         fatal("GSS_GEX, bad parameters: %d !< %d !< %d",
 112                             min, nbits, max);
 113                 dh = PRIVSEP(choose_dh(min, nbits, max));
 114                 if (dh == NULL)
 115                         packet_disconnect("Protocol error: no matching group found");
 116
 117                 packet_start(SSH2_MSG_KEXGSS_GROUP);
 118                 packet_put_bignum2(dh->p);
 119                 packet_put_bignum2(dh->g);
 120                 packet_send();
 121
 122                 packet_write_wait();
 123                 break;
 124         default:
 125                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
 126         }
 127
 128         dh_gen_key(dh, kex->we_need * 8);
 129
 130         do {
 131                 debug("Wait SSH2_MSG_GSSAPI_INIT");
 132                 type = packet_read();
 133                 switch(type) {
 134                 case SSH2_MSG_KEXGSS_INIT:
 135                         if (dh_client_pub != NULL)
 136                                 fatal("Received KEXGSS_INIT after initialising");
 137                         recv_tok.value = packet_get_string(&slen);
 138                         recv_tok.length = slen;
 139
 140                         if ((dh_client_pub = BN_new()) == NULL)
 141                                 fatal("dh_client_pub == NULL");
 142
 143                         packet_get_bignum2(dh_client_pub);
 144
 145                         /* Send SSH_MSG_KEXGSS_HOSTKEY here, if we want */
 146                         break;
 147                 case SSH2_MSG_KEXGSS_CONTINUE:
 148                         recv_tok.value = packet_get_string(&slen);
 149                         recv_tok.length = slen;
 150                         break;
 151                 default:
 152                         packet_disconnect(
 153                             "Protocol error: didn't expect packet type %d",
 154                             type);
 155                 }
 156
 157                 maj_status = PRIVSEP(ssh_gssapi_accept_ctx(ctxt, &recv_tok,
 158                     &send_tok, &ret_flags));
 159
 160                 xfree(recv_tok.value);
 161
 162                 if (maj_status != GSS_S_COMPLETE && send_tok.length == 0)
 163                         fatal("Zero length token output when incomplete");
 164
 165                 if (dh_client_pub == NULL)
 166                         fatal("No client public key");
 167
 168                 if (maj_status & GSS_S_CONTINUE_NEEDED) {
 169                         debug("Sending GSSAPI_CONTINUE");
 170                         packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 171                         packet_put_string(send_tok.value, send_tok.length);
 172                         packet_send();
 173                         gss_release_buffer(&min_status, &send_tok);
 174                 }
 175         } while (maj_status & GSS_S_CONTINUE_NEEDED);
 176
 177         if (GSS_ERROR(maj_status)) {
 178                 kex_gss_send_error(ctxt);
 179                 if (send_tok.length > 0) {
 180                         packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 181                         packet_put_string(send_tok.value, send_tok.length);
 182                         packet_send();
 183                 }
 184                 packet_disconnect("GSSAPI Key Exchange handshake failed");
 185         }
 186
 187         if (!(ret_flags & GSS_C_MUTUAL_FLAG))
 188                 fatal("Mutual Authentication flag wasn't set");
 189
 190         if (!(ret_flags & GSS_C_INTEG_FLAG))
 191                 fatal("Integrity flag wasn't set");
 192
 193         if (!dh_pub_is_valid(dh, dh_client_pub))
 194                 packet_disconnect("bad client public DH value");
 195
 196         klen = DH_size(dh);
 197         kbuf = xmalloc(klen);
 198         kout = DH_compute_key(kbuf, dh_client_pub, dh);
 199
 200         shared_secret = BN_new();
 201         BN_bin2bn(kbuf, kout, shared_secret);
 202         memset(kbuf, 0, klen);
 203         xfree(kbuf);
 204
 205         switch (kex->kex_type) {
 206         case KEX_GSS_GRP1_SHA1:
 207         case KEX_GSS_GRP14_SHA1:
 208                 kex_dh_hash(
 209                     kex->client_version_string, kex->server_version_string,
 210                     buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 211                     buffer_ptr(&kex->my), buffer_len(&kex->my),
 212                     NULL, 0, /* Change this if we start sending host keys */
 213                     dh_client_pub, dh->pub_key, shared_secret,
 214                     &hash, &hashlen
 215                 );
 216                 break;
 217         case KEX_GSS_GEX_SHA1:
 218                 kexgex_hash(
 219                     kex->evp_md,
 220                     kex->client_version_string, kex->server_version_string,
 221                     buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 222                     buffer_ptr(&kex->my), buffer_len(&kex->my),
 223                     NULL, 0,
 224                     min, nbits, max,
 225                     dh->p, dh->g,
 226                     dh_client_pub,
 227                     dh->pub_key,
 228                     shared_secret,
 229                     &hash, &hashlen
 230                 );
 231                 break;
 232         default:
 233                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
 234         }
 235
 236         BN_free(dh_client_pub);
 237
 238         if (kex->session_id == NULL) {
 239                 kex->session_id_len = hashlen;
 240                 kex->session_id = xmalloc(kex->session_id_len);
 241                 memcpy(kex->session_id, hash, kex->session_id_len);
 242         }
 243
 244         gssbuf.value = hash;
 245         gssbuf.length = hashlen;
 246
 247         if (GSS_ERROR(PRIVSEP(ssh_gssapi_sign(ctxt,&gssbuf,&msg_tok))))
 248                 fatal("Couldn't get MIC");
 249
 250         packet_start(SSH2_MSG_KEXGSS_COMPLETE);
 251         packet_put_bignum2(dh->pub_key);
 252         packet_put_string((char *)msg_tok.value,msg_tok.length);
 253
 254         if (send_tok.length != 0) {
 255                 packet_put_char(1); /* true */
 256                 packet_put_string((char *)send_tok.value, send_tok.length);
 257         } else {
 258                 packet_put_char(0); /* false */
 259         }
 260         packet_send();
 261
 262         gss_release_buffer(&min_status, &send_tok);
 263         gss_release_buffer(&min_status, &msg_tok);
 264
 265         if (gss_kex_context == NULL)
 266                 gss_kex_context = ctxt;
 267         else
 268                 ssh_gssapi_delete_ctx(&ctxt);
 269
 270         DH_free(dh);
 271
 272         kex_derive_keys(kex, hash, hashlen, shared_secret);
 273         BN_clear_free(shared_secret);
 274         kex_finish(kex);
 275 }
 276
 277 static void
 278 kex_gss_send_error(Gssctxt *ctxt) {
 279         char *errstr;
 280         OM_uint32 maj,min;
 281
 282         errstr=PRIVSEP(ssh_gssapi_last_error(ctxt,&maj,&min));
 283         if (errstr) {
 284                 packet_start(SSH2_MSG_KEXGSS_ERROR);
 285                 packet_put_int(maj);
 286                 packet_put_int(min);
 287                 packet_put_cstring(errstr);
 288                 packet_put_cstring("");
 289                 packet_send();
 290                 packet_write_wait();
 291                 /* XXX - We should probably log the error locally here */
 292                 xfree(errstr);
 293         }
 294 }
 295 #endif /* GSSAPI */