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