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