openssh/kexgsss.c

   1 /*
   2  * Copyright (c) 2001-2009 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 #include "servconf.h"
  46
  47 static void kex_gss_send_error(Gssctxt *ctxt);
  48 extern ServerOptions options;
  49
  50 void
  51 kexgss_server(Kex *kex)
  52 {
  53         OM_uint32 maj_status, min_status;
  54
  55         /*
  56          * Some GSSAPI implementations use the input value of ret_flags (an
  57          * output variable) as a means of triggering mechanism specific
  58          * features. Initializing it to zero avoids inadvertently
  59          * activating this non-standard behaviour.
  60          */
  61
  62         OM_uint32 ret_flags = 0;
  63         gss_buffer_desc gssbuf, recv_tok, msg_tok;
  64         gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
  65         Gssctxt *ctxt = NULL;
  66         u_int slen, klen, kout, hashlen;
  67         u_char *kbuf, *hash;
  68         DH *dh;
  69         int min = -1, max = -1, nbits = -1;
  70         BIGNUM *shared_secret = NULL;
  71         BIGNUM *dh_client_pub = NULL;
  72         int type = 0;
  73         gss_OID oid;
  74         char *mechs;
  75
  76         /* Initialise GSSAPI */
  77
  78         /* If we're rekeying, privsep means that some of the private structures
  79          * in the GSSAPI code are no longer available. This kludges them back
  80          * into life
  81          */
  82         if (!ssh_gssapi_oid_table_ok())
  83                 if ((mechs = ssh_gssapi_server_mechanisms()))
  84                         xfree(mechs);
  85
  86         debug2("%s: Identifying %s", __func__, kex->name);
  87         oid = ssh_gssapi_id_kex(NULL, kex->name, kex->kex_type);
  88         if (oid == GSS_C_NO_OID)
  89            fatal("Unknown gssapi mechanism");
  90
  91         debug2("%s: Acquiring credentials", __func__);
  92
  93         if (GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctxt, oid)))) {
  94                 kex_gss_send_error(ctxt);
  95                 fatal("Unable to acquire credentials for the server");
  96     }
  97
  98         switch (kex->kex_type) {
  99         case KEX_GSS_GRP1_SHA1:
 100                 dh = dh_new_group1();
 101                 break;
 102         case KEX_GSS_GRP14_SHA1:
 103                 dh = dh_new_group14();
 104                 break;
 105         case KEX_GSS_GEX_SHA1:
 106                 debug("Doing group exchange");
 107                 packet_read_expect(SSH2_MSG_KEXGSS_GROUPREQ);
 108                 min = packet_get_int();
 109                 nbits = packet_get_int();
 110                 max = packet_get_int();
 111                 min = MAX(DH_GRP_MIN, min);
 112                 max = MIN(DH_GRP_MAX, max);
 113                 packet_check_eom();
 114                 if (max < min || nbits < min || max < nbits)
 115                         fatal("GSS_GEX, bad parameters: %d !< %d !< %d",
 116                             min, nbits, max);
 117                 dh = PRIVSEP(choose_dh(min, nbits, max));
 118                 if (dh == NULL)
 119                         packet_disconnect("Protocol error: no matching group found");
 120
 121                 packet_start(SSH2_MSG_KEXGSS_GROUP);
 122                 packet_put_bignum2(dh->p);
 123                 packet_put_bignum2(dh->g);
 124                 packet_send();
 125
 126                 packet_write_wait();
 127                 break;
 128         default:
 129                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
 130         }
 131
 132         dh_gen_key(dh, kex->we_need * 8);
 133
 134         do {
 135                 debug("Wait SSH2_MSG_GSSAPI_INIT");
 136                 type = packet_read();
 137                 switch(type) {
 138                 case SSH2_MSG_KEXGSS_INIT:
 139                         if (dh_client_pub != NULL)
 140                                 fatal("Received KEXGSS_INIT after initialising");
 141                         recv_tok.value = packet_get_string(&slen);
 142                         recv_tok.length = slen;
 143
 144                         if ((dh_client_pub = BN_new()) == NULL)
 145                                 fatal("dh_client_pub == NULL");
 146
 147                         packet_get_bignum2(dh_client_pub);
 148
 149                         /* Send SSH_MSG_KEXGSS_HOSTKEY here, if we want */
 150                         break;
 151                 case SSH2_MSG_KEXGSS_CONTINUE:
 152                         recv_tok.value = packet_get_string(&slen);
 153                         recv_tok.length = slen;
 154                         break;
 155                 default:
 156                         packet_disconnect(
 157                             "Protocol error: didn't expect packet type %d",
 158                             type);
 159                 }
 160
 161                 maj_status = PRIVSEP(ssh_gssapi_accept_ctx(ctxt, &recv_tok,
 162                     &send_tok, &ret_flags));
 163
 164                 xfree(recv_tok.value);
 165
 166                 if (maj_status != GSS_S_COMPLETE && send_tok.length == 0)
 167                         fatal("Zero length token output when incomplete");
 168
 169                 if (dh_client_pub == NULL)
 170                         fatal("No client public key");
 171
 172                 if (maj_status & GSS_S_CONTINUE_NEEDED) {
 173                         debug("Sending GSSAPI_CONTINUE");
 174                         packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 175                         packet_put_string((char *)send_tok.value, send_tok.length);
 176                         packet_send();
 177                         gss_release_buffer(&min_status, &send_tok);
 178                 }
 179         } while (maj_status & GSS_S_CONTINUE_NEEDED);
 180
 181         if (GSS_ERROR(maj_status)) {
 182                 kex_gss_send_error(ctxt);
 183                 if (send_tok.length > 0) {
 184                         packet_start(SSH2_MSG_KEXGSS_CONTINUE);
 185                         packet_put_string((char *)send_tok.value, send_tok.length);
 186                         packet_send();
 187                 }
 188                 packet_disconnect("GSSAPI Key Exchange handshake failed");
 189         }
 190
 191         if (!(ret_flags & GSS_C_MUTUAL_FLAG))
 192                 fatal("Mutual Authentication flag wasn't set");
 193
 194         if (!(ret_flags & GSS_C_INTEG_FLAG))
 195                 fatal("Integrity flag wasn't set");
 196
 197         if (!dh_pub_is_valid(dh, dh_client_pub))
 198                 packet_disconnect("bad client public DH value");
 199
 200         klen = DH_size(dh);
 201         kbuf = xmalloc(klen);
 202         kout = DH_compute_key(kbuf, dh_client_pub, dh);
 203         if (kout < 0)
 204                 fatal("DH_compute_key: failed");
 205
 206         shared_secret = BN_new();
 207         if (shared_secret == NULL)
 208                 fatal("kexgss_server: BN_new failed");
 209
 210         if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
 211                 fatal("kexgss_server: BN_bin2bn failed");
 212
 213         memset(kbuf, 0, klen);
 214         xfree(kbuf);
 215
 216         switch (kex->kex_type) {
 217         case KEX_GSS_GRP1_SHA1:
 218         case KEX_GSS_GRP14_SHA1:
 219                 kex_dh_hash(
 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, /* Change this if we start sending host keys */
 224                     dh_client_pub, dh->pub_key, shared_secret,
 225                     &hash, &hashlen
 226                 );
 227                 break;
 228         case KEX_GSS_GEX_SHA1:
 229                 kexgex_hash(
 230                     kex->evp_md,
 231                     kex->client_version_string, kex->server_version_string,
 232                     buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 233                     buffer_ptr(&kex->my), buffer_len(&kex->my),
 234                     NULL, 0,
 235                     min, nbits, max,
 236                     dh->p, dh->g,
 237                     dh_client_pub,
 238                     dh->pub_key,
 239                     shared_secret,
 240                     &hash, &hashlen
 241                 );
 242                 break;
 243         default:
 244                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
 245         }
 246
 247         BN_clear_free(dh_client_pub);
 248
 249         if (kex->session_id == NULL) {
 250                 kex->session_id_len = hashlen;
 251                 kex->session_id = xmalloc(kex->session_id_len);
 252                 memcpy(kex->session_id, hash, kex->session_id_len);
 253         }
 254
 255         gssbuf.value = hash;
 256         gssbuf.length = hashlen;
 257
 258         if (GSS_ERROR(PRIVSEP(ssh_gssapi_sign(ctxt,&gssbuf,&msg_tok))))
 259                 fatal("Couldn't get MIC");
 260
 261         packet_start(SSH2_MSG_KEXGSS_COMPLETE);
 262         packet_put_bignum2(dh->pub_key);
 263         packet_put_string((char *)msg_tok.value,msg_tok.length);
 264
 265         if (send_tok.length != 0) {
 266                 packet_put_char(1); /* true */
 267                 packet_put_string((char *)send_tok.value, send_tok.length);
 268         } else {
 269                 packet_put_char(0); /* false */
 270         }
 271         packet_send();
 272
 273         gss_release_buffer(&min_status, &send_tok);
 274         gss_release_buffer(&min_status, &msg_tok);
 275
 276         if (gss_kex_context == NULL)
 277                 gss_kex_context = ctxt;
 278         else
 279                 ssh_gssapi_delete_ctx(&ctxt);
 280
 281         DH_free(dh);
 282
 283         kex_derive_keys(kex, hash, hashlen, shared_secret);
 284         BN_clear_free(shared_secret);
 285         kex_finish(kex);
 286
 287         /* If this was a rekey, then save out any delegated credentials we
 288          * just exchanged.  */
 289         if (options.gss_store_rekey)
 290                 ssh_gssapi_rekey_creds();
 291 }
 292
 293 static void
 294 kex_gss_send_error(Gssctxt *ctxt) {
 295         char *errstr;
 296         OM_uint32 maj,min;
 297
 298         errstr=PRIVSEP(ssh_gssapi_last_error(ctxt,&maj,&min));
 299         if (errstr) {
 300                 packet_start(SSH2_MSG_KEXGSS_ERROR);
 301                 packet_put_int(maj);
 302                 packet_put_int(min);
 303                 packet_put_cstring(errstr);
 304                 packet_put_cstring("");
 305                 packet_send();
 306                 packet_write_wait();
 307                 /* XXX - We should probably log the error locally here */
 308                 xfree(errstr);
 309         }
 310 }
 311 #endif /* GSSAPI */