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 "lib/crypto/hmacmd5.h"
  24 #include "system/network.h"
  25 #include "librpc/ndr/libndr.h"
  26 #include "librpc/gen_ndr/ndr_dns.h"
  27 #include "dns_server/dns_server.h"
  28 #include "libcli/util/ntstatus.h"
  29 #include "auth/auth.h"
  30 #include "auth/gensec/gensec.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 (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
 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
 133         state->tsig = talloc_zero(state->mem_ctx, struct dns_res_rec);
 134         if (state->tsig == NULL) {
 135                 return WERR_NOT_ENOUGH_MEMORY;
 136         }
 137
 138         werror = dns_copy_tsig(state->tsig, &packet->additional[i],
 139                                state->tsig);
 140         if (!W_ERROR_IS_OK(werror)) {
 141                 return werror;
 142         }
 143
 144         packet->arcount--;
 145
 146         tkey = dns_find_tkey(dns->tkeys, state->tsig->name);
 147         if (tkey == NULL) {
 148                 /*
 149                  * We must save the name for use in the TSIG error
 150                  * response and have no choice here but to save the
 151                  * keyname from the TSIG request.
 152                  */
 153                 state->key_name = talloc_strdup(state->mem_ctx,
 154                                                 state->tsig->name);
 155                 if (state->key_name == NULL) {
 156                         return WERR_NOT_ENOUGH_MEMORY;
 157                 }
 158                 state->tsig_error = DNS_RCODE_BADKEY;
 159                 return DNS_ERR(NOTAUTH);
 160         }
 161
 162         /*
 163          * Remember the keyname that found an existing tkey, used
 164          * later to fetch the key with dns_find_tkey() when signing
 165          * and adding a TSIG record with MAC.
 166          */
 167         state->key_name = talloc_strdup(state->mem_ctx, tkey->name);
 168         if (state->key_name == NULL) {
 169                 return WERR_NOT_ENOUGH_MEMORY;
 170         }
 171
 172         /* FIXME: check TSIG here */
 173         if (check_rec == NULL) {
 174                 return WERR_NOT_ENOUGH_MEMORY;
 175         }
 176
 177         /* first build and verify check packet */
 178         check_rec->name = talloc_strdup(check_rec, tkey->name);
 179         if (check_rec->name == NULL) {
 180                 return WERR_NOT_ENOUGH_MEMORY;
 181         }
 182         check_rec->rr_class = DNS_QCLASS_ANY;
 183         check_rec->ttl = 0;
 184         check_rec->algorithm_name = talloc_strdup(check_rec, tkey->algorithm);
 185         if (check_rec->algorithm_name == NULL) {
 186                 return WERR_NOT_ENOUGH_MEMORY;
 187         }
 188         check_rec->time_prefix = 0;
 189         check_rec->time = state->tsig->rdata.tsig_record.time;
 190         check_rec->fudge = state->tsig->rdata.tsig_record.fudge;
 191         check_rec->error = 0;
 192         check_rec->other_size = 0;
 193         check_rec->other_data = NULL;
 194
 195         ndr_err = ndr_push_struct_blob(&tsig_blob, mem_ctx, state->tsig,
 196                 (ndr_push_flags_fn_t)ndr_push_dns_res_rec);
 197         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 198                 DEBUG(1, ("Failed to push packet: %s!\n",
 199                           ndr_errstr(ndr_err)));
 200                 return DNS_ERR(SERVER_FAILURE);
 201         }
 202
 203         ndr_err = ndr_push_struct_blob(&fake_tsig_blob, mem_ctx, check_rec,
 204                 (ndr_push_flags_fn_t)ndr_push_dns_fake_tsig_rec);
 205         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 206                 DEBUG(1, ("Failed to push packet: %s!\n",
 207                           ndr_errstr(ndr_err)));
 208                 return DNS_ERR(SERVER_FAILURE);
 209         }
 210
 211         /* we need to work some magic here. we need to keep the input packet
 212          * exactly like we got it, but we need to cut off the tsig record */
 213         packet_len = in->length - tsig_blob.length;
 214         buffer_len = packet_len + fake_tsig_blob.length;
 215         buffer = talloc_zero_array(mem_ctx, uint8_t, buffer_len);
 216         if (buffer == NULL) {
 217                 return WERR_NOT_ENOUGH_MEMORY;
 218         }
 219
 220         memcpy(buffer, in->data, packet_len);
 221         memcpy(buffer + packet_len, fake_tsig_blob.data, fake_tsig_blob.length);
 222
 223         sig.length = state->tsig->rdata.tsig_record.mac_size;
 224         sig.data = talloc_memdup(mem_ctx, state->tsig->rdata.tsig_record.mac, sig.length);
 225         if (sig.data == NULL) {
 226                 return WERR_NOT_ENOUGH_MEMORY;
 227         }
 228
 229         /* Now we also need to count down the additional record counter */
 230         arcount = RSVAL(buffer, 10);
 231         RSSVAL(buffer, 10, arcount-1);
 232
 233         status = gensec_check_packet(tkey->gensec, buffer, buffer_len,
 234                                     buffer, buffer_len, &sig);
 235         if (NT_STATUS_EQUAL(NT_STATUS_ACCESS_DENIED, status)) {
 236                 state->tsig_error = DNS_RCODE_BADSIG;
 237                 return DNS_ERR(NOTAUTH);
 238         }
 239
 240         if (!NT_STATUS_IS_OK(status)) {
 241                 DEBUG(1, ("Verifying tsig failed: %s\n", nt_errstr(status)));
 242                 return ntstatus_to_werror(status);
 243         }
 244
 245         state->authenticated = true;
 246
 247         return WERR_OK;
 248 }
 249
 250 static WERROR dns_tsig_compute_mac(TALLOC_CTX *mem_ctx,
 251                                    struct dns_request_state *state,
 252                                    struct dns_name_packet *packet,
 253                                    struct dns_server_tkey *tkey,
 254                                    time_t current_time,
 255                                    DATA_BLOB *_psig)
 256 {
 257         NTSTATUS status;
 258         enum ndr_err_code ndr_err;
 259         DATA_BLOB packet_blob, tsig_blob, sig;
 260         uint8_t *buffer = NULL;
 261         uint8_t *p = NULL;
 262         size_t buffer_len = 0;
 263         struct dns_fake_tsig_rec *check_rec = talloc_zero(mem_ctx,
 264                         struct dns_fake_tsig_rec);
 265         size_t mac_size = 0;
 266
 267         if (check_rec == NULL) {
 268                 return WERR_NOT_ENOUGH_MEMORY;
 269         }
 270
 271         /* first build and verify check packet */
 272         check_rec->name = talloc_strdup(check_rec, tkey->name);
 273         if (check_rec->name == NULL) {
 274                 return WERR_NOT_ENOUGH_MEMORY;
 275         }
 276         check_rec->rr_class = DNS_QCLASS_ANY;
 277         check_rec->ttl = 0;
 278         check_rec->algorithm_name = talloc_strdup(check_rec, tkey->algorithm);
 279         if (check_rec->algorithm_name == NULL) {
 280                 return WERR_NOT_ENOUGH_MEMORY;
 281         }
 282         check_rec->time_prefix = 0;
 283         check_rec->time = current_time;
 284         check_rec->fudge = 300;
 285         check_rec->error = state->tsig_error;
 286         check_rec->other_size = 0;
 287         check_rec->other_data = NULL;
 288
 289         ndr_err = ndr_push_struct_blob(&packet_blob, mem_ctx, packet,
 290                 (ndr_push_flags_fn_t)ndr_push_dns_name_packet);
 291         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 292                 DEBUG(1, ("Failed to push packet: %s!\n",
 293                           ndr_errstr(ndr_err)));
 294                 return DNS_ERR(SERVER_FAILURE);
 295         }
 296
 297         ndr_err = ndr_push_struct_blob(&tsig_blob, mem_ctx, check_rec,
 298                 (ndr_push_flags_fn_t)ndr_push_dns_fake_tsig_rec);
 299         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 300                 DEBUG(1, ("Failed to push packet: %s!\n",
 301                           ndr_errstr(ndr_err)));
 302                 return DNS_ERR(SERVER_FAILURE);
 303         }
 304
 305         if (state->tsig != NULL) {
 306                 mac_size = state->tsig->rdata.tsig_record.mac_size;
 307         }
 308
 309         buffer_len = mac_size;
 310
 311         buffer_len += packet_blob.length;
 312         if (buffer_len < packet_blob.length) {
 313                 return WERR_INVALID_PARAMETER;
 314         }
 315         buffer_len += tsig_blob.length;
 316         if (buffer_len < tsig_blob.length) {
 317                 return WERR_INVALID_PARAMETER;
 318         }
 319
 320         buffer = talloc_zero_array(mem_ctx, uint8_t, buffer_len);
 321         if (buffer == NULL) {
 322                 return WERR_NOT_ENOUGH_MEMORY;
 323         }
 324
 325         p = buffer;
 326
 327         /*
 328          * RFC 2845 "4.2 TSIG on Answers", how to lay out the buffer
 329          * that we're going to sign:
 330          * 1. MAC of request (if present)
 331          * 2. Outgoing packet
 332          * 3. TSIG record
 333          */
 334         if (mac_size > 0) {
 335                 memcpy(p, state->tsig->rdata.tsig_record.mac, mac_size);
 336                 p += mac_size;
 337         }
 338
 339         memcpy(p, packet_blob.data, packet_blob.length);
 340         p += packet_blob.length;
 341
 342         memcpy(p, tsig_blob.data, tsig_blob.length);
 343
 344         status = gensec_sign_packet(tkey->gensec, mem_ctx, buffer, buffer_len,
 345                                     buffer, buffer_len, &sig);
 346         if (!NT_STATUS_IS_OK(status)) {
 347                 return ntstatus_to_werror(status);
 348         }
 349
 350         *_psig = sig;
 351         return WERR_OK;
 352 }
 353
 354 WERROR dns_sign_tsig(struct dns_server *dns,
 355                      TALLOC_CTX *mem_ctx,
 356                      struct dns_request_state *state,
 357                      struct dns_name_packet *packet,
 358                      uint16_t error)
 359 {
 360         WERROR werror;
 361         time_t current_time = time(NULL);
 362         struct dns_res_rec *tsig = NULL;
 363         DATA_BLOB sig = (DATA_BLOB) {
 364                 .data = NULL,
 365                 .length = 0
 366         };
 367
 368         tsig = talloc_zero(mem_ctx, struct dns_res_rec);
 369         if (tsig == NULL) {
 370                 return WERR_NOT_ENOUGH_MEMORY;
 371         }
 372
 373         if (state->tsig_error == DNS_RCODE_OK) {
 374                 struct dns_server_tkey *tkey = dns_find_tkey(
 375                         dns->tkeys, state->key_name);
 376                 if (tkey == NULL) {
 377                         return DNS_ERR(SERVER_FAILURE);
 378                 }
 379
 380                 werror = dns_tsig_compute_mac(mem_ctx, state, packet,
 381                                               tkey, current_time, &sig);
 382                 if (!W_ERROR_IS_OK(werror)) {
 383                         return werror;
 384                 }
 385         }
 386
 387         tsig->name = talloc_strdup(tsig, state->key_name);
 388         if (tsig->name == NULL) {
 389                 return WERR_NOT_ENOUGH_MEMORY;
 390         }
 391         tsig->rr_class = DNS_QCLASS_ANY;
 392         tsig->rr_type = DNS_QTYPE_TSIG;
 393         tsig->ttl = 0;
 394         tsig->length = UINT16_MAX;
 395         tsig->rdata.tsig_record.algorithm_name = talloc_strdup(tsig, "gss-tsig");
 396         if (tsig->rdata.tsig_record.algorithm_name == NULL) {
 397                 return WERR_NOT_ENOUGH_MEMORY;
 398         }
 399         tsig->rdata.tsig_record.time_prefix = 0;
 400         tsig->rdata.tsig_record.time = current_time;
 401         tsig->rdata.tsig_record.fudge = 300;
 402         tsig->rdata.tsig_record.error = state->tsig_error;
 403         tsig->rdata.tsig_record.original_id = packet->id;
 404         tsig->rdata.tsig_record.other_size = 0;
 405         tsig->rdata.tsig_record.other_data = NULL;
 406         if (sig.length > 0) {
 407                 tsig->rdata.tsig_record.mac_size = sig.length;
 408                 tsig->rdata.tsig_record.mac = talloc_memdup(tsig, sig.data, sig.length);
 409                 if (tsig->rdata.tsig_record.mac == NULL) {
 410                         return WERR_NOT_ENOUGH_MEMORY;
 411                 }
 412         }
 413
 414         if (packet->arcount == 0) {
 415                 packet->additional = talloc_zero(mem_ctx, struct dns_res_rec);
 416                 if (packet->additional == NULL) {
 417                         return WERR_NOT_ENOUGH_MEMORY;
 418                 }
 419         }
 420         packet->additional = talloc_realloc(mem_ctx, packet->additional,
 421                                             struct dns_res_rec,
 422                                             packet->arcount + 1);
 423         if (packet->additional == NULL) {
 424                 return WERR_NOT_ENOUGH_MEMORY;
 425         }
 426
 427         werror = dns_copy_tsig(mem_ctx, tsig,
 428                                &packet->additional[packet->arcount]);
 429         if (!W_ERROR_IS_OK(werror)) {
 430                 return werror;
 431         }
 432         packet->arcount++;
 433
 434         return WERR_OK;
 435 }