source4/dns_server/dns_crypto.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3
   4    DNS server handler for signed packets
   5
   6    Copyright (C) 2012 Kai Blin  <kai@samba.org>
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  20 */
  21
  22 #include "includes.h"
  23 #include "system/network.h"
  24 #include "librpc/ndr/libndr.h"
  25 #include "librpc/gen_ndr/ndr_dns.h"
  26 #include "dns_server/dns_server.h"
  27 #include "libcli/util/ntstatus.h"
  28 #include "auth/auth.h"
  29 #include "auth/gensec/gensec.h"
  30 #include "lib/util/bytearray.h"
  31
  32 #undef DBGC_CLASS
  33 #define DBGC_CLASS DBGC_DNS
  34
  35 static WERROR dns_copy_tsig(TALLOC_CTX *mem_ctx,
  36                             struct dns_res_rec *old,
  37                             struct dns_res_rec *new_rec)
  38 {
  39         new_rec->name = talloc_strdup(mem_ctx, old->name);
  40         W_ERROR_HAVE_NO_MEMORY(new_rec->name);
  41
  42         new_rec->rr_type = old->rr_type;
  43         new_rec->rr_class = old->rr_class;
  44         new_rec->ttl = old->ttl;
  45         new_rec->length = old->length;
  46         new_rec->rdata.tsig_record.algorithm_name = talloc_strdup(mem_ctx,
  47                                 old->rdata.tsig_record.algorithm_name);
  48         W_ERROR_HAVE_NO_MEMORY(new_rec->rdata.tsig_record.algorithm_name);
  49
  50         new_rec->rdata.tsig_record.time_prefix = old->rdata.tsig_record.time_prefix;
  51         new_rec->rdata.tsig_record.time = old->rdata.tsig_record.time;
  52         new_rec->rdata.tsig_record.fudge = old->rdata.tsig_record.fudge;
  53         new_rec->rdata.tsig_record.mac_size = old->rdata.tsig_record.mac_size;
  54         new_rec->rdata.tsig_record.mac = talloc_memdup(mem_ctx,
  55                                         old->rdata.tsig_record.mac,
  56                                         old->rdata.tsig_record.mac_size);
  57         W_ERROR_HAVE_NO_MEMORY(new_rec->rdata.tsig_record.mac);
  58
  59         new_rec->rdata.tsig_record.original_id = old->rdata.tsig_record.original_id;
  60         new_rec->rdata.tsig_record.error = old->rdata.tsig_record.error;
  61         new_rec->rdata.tsig_record.other_size = old->rdata.tsig_record.other_size;
  62         new_rec->rdata.tsig_record.other_data = talloc_memdup(mem_ctx,
  63                                         old->rdata.tsig_record.other_data,
  64                                         old->rdata.tsig_record.other_size);
  65         W_ERROR_HAVE_NO_MEMORY(new_rec->rdata.tsig_record.other_data);
  66
  67         return WERR_OK;
  68 }
  69
  70 struct dns_server_tkey *dns_find_tkey(struct dns_server_tkey_store *store,
  71                                       const char *name)
  72 {
  73         struct dns_server_tkey *tkey = NULL;
  74         uint16_t i = 0;
  75
  76         do {
  77                 struct dns_server_tkey *tmp_key = store->tkeys[i];
  78
  79                 i++;
  80                 i %= TKEY_BUFFER_SIZE;
  81
  82                 if (tmp_key == NULL) {
  83                         continue;
  84                 }
  85                 if (samba_dns_name_equal(name, tmp_key->name)) {
  86                         tkey = tmp_key;
  87                         break;
  88                 }
  89         } while (i != 0);
  90
  91         return tkey;
  92 }
  93
  94 WERROR dns_verify_tsig(struct dns_server *dns,
  95                        TALLOC_CTX *mem_ctx,
  96                        struct dns_request_state *state,
  97                        struct dns_name_packet *packet,
  98                        DATA_BLOB *in)
  99 {
 100         WERROR werror;
 101         NTSTATUS status;
 102         enum ndr_err_code ndr_err;
 103         uint16_t i, arcount = 0;
 104         DATA_BLOB tsig_blob, fake_tsig_blob, sig;
 105         uint8_t *buffer = NULL;
 106         size_t buffer_len = 0, packet_len = 0;
 107         struct dns_server_tkey *tkey = NULL;
 108         struct dns_fake_tsig_rec *check_rec = talloc_zero(mem_ctx,
 109                         struct dns_fake_tsig_rec);
 110         const char *algorithm = NULL;
 111
 112         /* Find the first TSIG record in the additional records */
 113         for (i=0; i < packet->arcount; i++) {
 114                 if (packet->additional[i].rr_type == DNS_QTYPE_TSIG) {
 115                         break;
 116                 }
 117         }
 118
 119         if (i == packet->arcount) {
 120                 /* no TSIG around */
 121                 return WERR_OK;
 122         }
 123
 124         /* The TSIG record needs to be the last additional record */
 125         if (i + 1 != packet->arcount) {
 126                 DEBUG(1, ("TSIG record not the last additional record!\n"));
 127                 return DNS_ERR(FORMAT_ERROR);
 128         }
 129
 130         /* We got a TSIG, so we need to sign our reply */
 131         state->sign = true;
 132         DBG_DEBUG("Got TSIG\n");
 133
 134         state->tsig = talloc_zero(state->mem_ctx, struct dns_res_rec);
 135         if (state->tsig == NULL) {
 136                 return WERR_NOT_ENOUGH_MEMORY;
 137         }
 138
 139         werror = dns_copy_tsig(state->tsig, &packet->additional[i],
 140                                state->tsig);
 141         if (!W_ERROR_IS_OK(werror)) {
 142                 return werror;
 143         }
 144
 145         packet->arcount--;
 146
 147         tkey = dns_find_tkey(dns->tkeys, state->tsig->name);
 148         if (tkey == NULL) {
 149                 DBG_DEBUG("dns_find_tkey() => REFUSED / DNS_RCODE_BADKEY\n");
 150                 /*
 151                  * We must save the name for use in the TSIG error
 152                  * response and have no choice here but to save the
 153                  * keyname from the TSIG request.
 154                  */
 155                 state->key_name = talloc_strdup(state->mem_ctx,
 156                                                 state->tsig->name);
 157                 if (state->key_name == NULL) {
 158                         return WERR_NOT_ENOUGH_MEMORY;
 159                 }
 160                 state->tsig_error = DNS_RCODE_BADKEY;
 161                 return DNS_ERR(REFUSED);
 162         }
 163         DBG_DEBUG("dns_find_tkey() => found\n");
 164
 165         algorithm = state->tsig->rdata.tsig_record.algorithm_name;
 166         if (strcmp(algorithm, "gss-tsig") == 0) {
 167                 /* ok */
 168         } else if (strcmp(algorithm, "gss.microsoft.com") == 0) {
 169                 /* ok */
 170         } else {
 171                 state->tsig_error = DNS_RCODE_BADKEY;
 172                 return DNS_ERR(REFUSED);
 173         }
 174
 175         /*
 176          * Remember the keyname that found an existing tkey, used
 177          * later to fetch the key with dns_find_tkey() when signing
 178          * and adding a TSIG record with MAC.
 179          */
 180         state->key_name = talloc_strdup(state->mem_ctx, tkey->name);
 181         if (state->key_name == NULL) {
 182                 return WERR_NOT_ENOUGH_MEMORY;
 183         }
 184
 185         /* FIXME: check TSIG here */
 186         if (check_rec == NULL) {
 187                 return WERR_NOT_ENOUGH_MEMORY;
 188         }
 189
 190         /* first build and verify check packet */
 191         check_rec->name = talloc_strdup(check_rec, tkey->name);
 192         if (check_rec->name == NULL) {
 193                 return WERR_NOT_ENOUGH_MEMORY;
 194         }
 195         check_rec->rr_class = DNS_QCLASS_ANY;
 196         check_rec->ttl = 0;
 197         check_rec->algorithm_name = talloc_strdup(check_rec, algorithm);
 198         if (check_rec->algorithm_name == NULL) {
 199                 return WERR_NOT_ENOUGH_MEMORY;
 200         }
 201         check_rec->time_prefix = 0;
 202         check_rec->time = state->tsig->rdata.tsig_record.time;
 203         check_rec->fudge = state->tsig->rdata.tsig_record.fudge;
 204         check_rec->error = 0;
 205         check_rec->other_size = 0;
 206         check_rec->other_data = NULL;
 207
 208         ndr_err = ndr_push_struct_blob(&tsig_blob, mem_ctx, state->tsig,
 209                 (ndr_push_flags_fn_t)ndr_push_dns_res_rec);
 210         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 211                 DEBUG(1, ("Failed to push packet: %s!\n",
 212                           ndr_errstr(ndr_err)));
 213                 return DNS_ERR(SERVER_FAILURE);
 214         }
 215
 216         ndr_err = ndr_push_struct_blob(&fake_tsig_blob, mem_ctx, check_rec,
 217                 (ndr_push_flags_fn_t)ndr_push_dns_fake_tsig_rec);
 218         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 219                 DEBUG(1, ("Failed to push packet: %s!\n",
 220                           ndr_errstr(ndr_err)));
 221                 return DNS_ERR(SERVER_FAILURE);
 222         }
 223
 224         /* we need to work some magic here. we need to keep the input packet
 225          * exactly like we got it, but we need to cut off the tsig record */
 226         packet_len = in->length - tsig_blob.length;
 227         buffer_len = packet_len + fake_tsig_blob.length;
 228         buffer = talloc_zero_array(mem_ctx, uint8_t, buffer_len);
 229         if (buffer == NULL) {
 230                 return WERR_NOT_ENOUGH_MEMORY;
 231         }
 232
 233         memcpy(buffer, in->data, packet_len);
 234         memcpy(buffer + packet_len, fake_tsig_blob.data, fake_tsig_blob.length);
 235
 236         sig.length = state->tsig->rdata.tsig_record.mac_size;
 237         sig.data = talloc_memdup(mem_ctx, state->tsig->rdata.tsig_record.mac, sig.length);
 238         if (sig.data == NULL) {
 239                 return WERR_NOT_ENOUGH_MEMORY;
 240         }
 241
 242         /* Now we also need to count down the additional record counter */
 243         arcount = RSVAL(buffer, 10);
 244         RSSVAL(buffer, 10, arcount-1);
 245
 246         status = gensec_check_packet(tkey->gensec, buffer, buffer_len,
 247                                     buffer, buffer_len, &sig);
 248         if (NT_STATUS_EQUAL(NT_STATUS_ACCESS_DENIED, status)) {
 249                 dump_data_dbgc(DBGC_DNS, 8, sig.data, sig.length);
 250                 dump_data_dbgc(DBGC_DNS, 8, buffer, buffer_len);
 251                 DBG_NOTICE("Verifying tsig failed: %s\n", nt_errstr(status));
 252                 state->tsig_error = DNS_RCODE_BADSIG;
 253                 return DNS_ERR(REFUSED);
 254         }
 255
 256         if (!NT_STATUS_IS_OK(status)) {
 257                 dump_data_dbgc(DBGC_DNS, 8, sig.data, sig.length);
 258                 dump_data_dbgc(DBGC_DNS, 8, buffer, buffer_len);
 259                 DEBUG(1, ("Verifying tsig failed: %s\n", nt_errstr(status)));
 260                 return ntstatus_to_werror(status);
 261         }
 262
 263         state->authenticated = true;
 264
 265         DBG_DEBUG("AUTHENTICATED\n");
 266         return WERR_OK;
 267 }
 268
 269 static WERROR dns_tsig_compute_mac(TALLOC_CTX *mem_ctx,
 270                                    struct dns_request_state *state,
 271                                    struct dns_name_packet *packet,
 272                                    struct dns_server_tkey *tkey,
 273                                    time_t current_time,
 274                                    DATA_BLOB *_psig)
 275 {
 276         NTSTATUS status;
 277         enum ndr_err_code ndr_err;
 278         DATA_BLOB packet_blob, tsig_blob, sig;
 279         uint8_t *buffer = NULL;
 280         uint8_t *p = NULL;
 281         size_t buffer_len = 0;
 282         struct dns_fake_tsig_rec *check_rec = talloc_zero(mem_ctx,
 283                         struct dns_fake_tsig_rec);
 284         size_t mac_size = 0;
 285         bool gss_tsig;
 286
 287         if (check_rec == NULL) {
 288                 return WERR_NOT_ENOUGH_MEMORY;
 289         }
 290
 291         if (strcmp(tkey->algorithm, "gss-tsig") == 0) {
 292                 gss_tsig = true;
 293         } else {
 294                 /* gss.microsoft.com */
 295                 gss_tsig = false;
 296         }
 297
 298         /* first build and verify check packet */
 299         check_rec->name = talloc_strdup(check_rec, tkey->name);
 300         if (check_rec->name == NULL) {
 301                 return WERR_NOT_ENOUGH_MEMORY;
 302         }
 303         check_rec->rr_class = DNS_QCLASS_ANY;
 304         check_rec->ttl = 0;
 305         check_rec->algorithm_name = talloc_strdup(check_rec, tkey->algorithm);
 306         if (check_rec->algorithm_name == NULL) {
 307                 return WERR_NOT_ENOUGH_MEMORY;
 308         }
 309         check_rec->time_prefix = 0;
 310         check_rec->time = current_time;
 311         check_rec->fudge = 300;
 312         check_rec->error = state->tsig_error;
 313         check_rec->other_size = 0;
 314         check_rec->other_data = NULL;
 315
 316         ndr_err = ndr_push_struct_blob(&packet_blob, mem_ctx, packet,
 317                 (ndr_push_flags_fn_t)ndr_push_dns_name_packet);
 318         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 319                 DEBUG(1, ("Failed to push packet: %s!\n",
 320                           ndr_errstr(ndr_err)));
 321                 return DNS_ERR(SERVER_FAILURE);
 322         }
 323
 324         ndr_err = ndr_push_struct_blob(&tsig_blob, mem_ctx, check_rec,
 325                 (ndr_push_flags_fn_t)ndr_push_dns_fake_tsig_rec);
 326         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 327                 DEBUG(1, ("Failed to push packet: %s!\n",
 328                           ndr_errstr(ndr_err)));
 329                 return DNS_ERR(SERVER_FAILURE);
 330         }
 331
 332         if (state->tsig != NULL) {
 333                 mac_size = state->tsig->rdata.tsig_record.mac_size;
 334         }
 335
 336         buffer_len = mac_size;
 337         if (gss_tsig && mac_size > 0) {
 338                 buffer_len += 2;
 339         }
 340
 341         buffer_len += packet_blob.length;
 342         if (buffer_len < packet_blob.length) {
 343                 return WERR_INVALID_PARAMETER;
 344         }
 345         buffer_len += tsig_blob.length;
 346         if (buffer_len < tsig_blob.length) {
 347                 return WERR_INVALID_PARAMETER;
 348         }
 349
 350         buffer = talloc_zero_array(mem_ctx, uint8_t, buffer_len);
 351         if (buffer == NULL) {
 352                 return WERR_NOT_ENOUGH_MEMORY;
 353         }
 354
 355         p = buffer;
 356
 357         /*
 358          * RFC 2845 "4.2 TSIG on Answers", how to lay out the buffer
 359          * that we're going to sign:
 360          * 1. if MAC of request is present
 361          *    - 16bit big endian length of MAC of request
 362          *    - MAC of request
 363          * 2. Outgoing packet
 364          * 3. TSIG record
 365          */
 366         if (mac_size > 0) {
 367                 if (gss_tsig) {
 368                         /*
 369                          * only gss-tsig not with
 370                          * gss.microsoft.com
 371                          */
 372                         PUSH_BE_U16(p, 0, mac_size);
 373                         p += 2;
 374                 }
 375                 memcpy(p, state->tsig->rdata.tsig_record.mac, mac_size);
 376                 p += mac_size;
 377         }
 378
 379         memcpy(p, packet_blob.data, packet_blob.length);
 380         p += packet_blob.length;
 381
 382         memcpy(p, tsig_blob.data, tsig_blob.length);
 383
 384         status = gensec_sign_packet(tkey->gensec, mem_ctx, buffer, buffer_len,
 385                                     buffer, buffer_len, &sig);
 386         if (!NT_STATUS_IS_OK(status)) {
 387                 return ntstatus_to_werror(status);
 388         }
 389
 390         *_psig = sig;
 391         return WERR_OK;
 392 }
 393
 394 WERROR dns_sign_tsig(struct dns_server *dns,
 395                      TALLOC_CTX *mem_ctx,
 396                      struct dns_request_state *state,
 397                      struct dns_name_packet *packet,
 398                      uint16_t error)
 399 {
 400         WERROR werror;
 401         time_t current_time = time(NULL);
 402         struct dns_res_rec *tsig = NULL;
 403         DATA_BLOB sig = (DATA_BLOB) {
 404                 .data = NULL,
 405                 .length = 0
 406         };
 407         const char *algorithm = "gss-tsig";
 408
 409         tsig = talloc_zero(mem_ctx, struct dns_res_rec);
 410         if (tsig == NULL) {
 411                 return WERR_NOT_ENOUGH_MEMORY;
 412         }
 413
 414         if (state->tsig_error == DNS_RCODE_OK) {
 415                 struct dns_server_tkey *tkey = dns_find_tkey(
 416                         dns->tkeys, state->key_name);
 417                 if (tkey == NULL) {
 418                         DBG_WARNING("dns_find_tkey() => NULL)\n");
 419                         return DNS_ERR(SERVER_FAILURE);
 420                 }
 421
 422                 werror = dns_tsig_compute_mac(mem_ctx, state, packet,
 423                                               tkey, current_time, &sig);
 424                 DBG_DEBUG("dns_tsig_compute_mac() => %s\n", win_errstr(werror));
 425                 if (!W_ERROR_IS_OK(werror)) {
 426                         return werror;
 427                 }
 428
 429                 algorithm = tkey->algorithm;
 430         }
 431
 432         tsig->name = talloc_strdup(tsig, state->key_name);
 433         if (tsig->name == NULL) {
 434                 return WERR_NOT_ENOUGH_MEMORY;
 435         }
 436         tsig->rr_class = DNS_QCLASS_ANY;
 437         tsig->rr_type = DNS_QTYPE_TSIG;
 438         tsig->ttl = 0;
 439         tsig->length = UINT16_MAX;
 440         tsig->rdata.tsig_record.algorithm_name = talloc_strdup(tsig, algorithm);
 441         if (tsig->rdata.tsig_record.algorithm_name == NULL) {
 442                 return WERR_NOT_ENOUGH_MEMORY;
 443         }
 444         tsig->rdata.tsig_record.time_prefix = 0;
 445         tsig->rdata.tsig_record.time = current_time;
 446         tsig->rdata.tsig_record.fudge = 300;
 447         tsig->rdata.tsig_record.error = state->tsig_error;
 448         tsig->rdata.tsig_record.original_id = packet->id;
 449         tsig->rdata.tsig_record.other_size = 0;
 450         tsig->rdata.tsig_record.other_data = NULL;
 451         if (sig.length > 0) {
 452                 tsig->rdata.tsig_record.mac_size = sig.length;
 453                 tsig->rdata.tsig_record.mac = talloc_memdup(tsig, sig.data, sig.length);
 454                 if (tsig->rdata.tsig_record.mac == NULL) {
 455                         return WERR_NOT_ENOUGH_MEMORY;
 456                 }
 457         }
 458
 459         DBG_DEBUG("sig.length=%zu\n", sig.length);
 460
 461         if (packet->arcount == 0) {
 462                 packet->additional = talloc_zero(mem_ctx, struct dns_res_rec);
 463                 if (packet->additional == NULL) {
 464                         return WERR_NOT_ENOUGH_MEMORY;
 465                 }
 466         }
 467         packet->additional = talloc_realloc(mem_ctx, packet->additional,
 468                                             struct dns_res_rec,
 469                                             packet->arcount + 1);
 470         if (packet->additional == NULL) {
 471                 return WERR_NOT_ENOUGH_MEMORY;
 472         }
 473
 474         werror = dns_copy_tsig(mem_ctx, tsig,
 475                                &packet->additional[packet->arcount]);
 476         DBG_DEBUG("dns_copy_tsig() => %s\n", win_errstr(werror));
 477         if (!W_ERROR_IS_OK(werror)) {
 478                 return werror;
 479         }
 480         packet->arcount++;
 481
 482         return WERR_OK;
 483 }