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
  31 #undef DBGC_CLASS
  32 #define DBGC_CLASS DBGC_DNS
  33
  34 static WERROR dns_copy_tsig(TALLOC_CTX *mem_ctx,
  35                             struct dns_res_rec *old,
  36                             struct dns_res_rec *new_rec)
  37 {
  38         new_rec->name = talloc_strdup(mem_ctx, old->name);
  39         W_ERROR_HAVE_NO_MEMORY(new_rec->name);
  40
  41         new_rec->rr_type = old->rr_type;
  42         new_rec->rr_class = old->rr_class;
  43         new_rec->ttl = old->ttl;
  44         new_rec->length = old->length;
  45         new_rec->rdata.tsig_record.algorithm_name = talloc_strdup(mem_ctx,
  46                                 old->rdata.tsig_record.algorithm_name);
  47         W_ERROR_HAVE_NO_MEMORY(new_rec->rdata.tsig_record.algorithm_name);
  48
  49         new_rec->rdata.tsig_record.time_prefix = old->rdata.tsig_record.time_prefix;
  50         new_rec->rdata.tsig_record.time = old->rdata.tsig_record.time;
  51         new_rec->rdata.tsig_record.fudge = old->rdata.tsig_record.fudge;
  52         new_rec->rdata.tsig_record.mac_size = old->rdata.tsig_record.mac_size;
  53         new_rec->rdata.tsig_record.mac = talloc_memdup(mem_ctx,
  54                                         old->rdata.tsig_record.mac,
  55                                         old->rdata.tsig_record.mac_size);
  56         W_ERROR_HAVE_NO_MEMORY(new_rec->rdata.tsig_record.mac);
  57
  58         new_rec->rdata.tsig_record.original_id = old->rdata.tsig_record.original_id;
  59         new_rec->rdata.tsig_record.error = old->rdata.tsig_record.error;
  60         new_rec->rdata.tsig_record.other_size = old->rdata.tsig_record.other_size;
  61         new_rec->rdata.tsig_record.other_data = talloc_memdup(mem_ctx,
  62                                         old->rdata.tsig_record.other_data,
  63                                         old->rdata.tsig_record.other_size);
  64         W_ERROR_HAVE_NO_MEMORY(new_rec->rdata.tsig_record.other_data);
  65
  66         return WERR_OK;
  67 }
  68
  69 struct dns_server_tkey *dns_find_tkey(struct dns_server_tkey_store *store,
  70                                       const char *name)
  71 {
  72         struct dns_server_tkey *tkey = NULL;
  73         uint16_t i = 0;
  74
  75         do {
  76                 struct dns_server_tkey *tmp_key = store->tkeys[i];
  77
  78                 i++;
  79                 i %= TKEY_BUFFER_SIZE;
  80
  81                 if (tmp_key == NULL) {
  82                         continue;
  83                 }
  84                 if (samba_dns_name_equal(name, tmp_key->name)) {
  85                         tkey = tmp_key;
  86                         break;
  87                 }
  88         } while (i != 0);
  89
  90         return tkey;
  91 }
  92
  93 WERROR dns_verify_tsig(struct dns_server *dns,
  94                        TALLOC_CTX *mem_ctx,
  95                        struct dns_request_state *state,
  96                        struct dns_name_packet *packet,
  97                        DATA_BLOB *in)
  98 {
  99         WERROR werror;
 100         NTSTATUS status;
 101         enum ndr_err_code ndr_err;
 102         uint16_t i, arcount = 0;
 103         DATA_BLOB tsig_blob, fake_tsig_blob, sig;
 104         uint8_t *buffer = NULL;
 105         size_t buffer_len = 0, packet_len = 0;
 106         struct dns_server_tkey *tkey = NULL;
 107         struct dns_fake_tsig_rec *check_rec = talloc_zero(mem_ctx,
 108                         struct dns_fake_tsig_rec);
 109
 110
 111         /* Find the first TSIG record in the additional records */
 112         for (i=0; i < packet->arcount; i++) {
 113                 if (packet->additional[i].rr_type == DNS_QTYPE_TSIG) {
 114                         break;
 115                 }
 116         }
 117
 118         if (i == packet->arcount) {
 119                 /* no TSIG around */
 120                 return WERR_OK;
 121         }
 122
 123         /* The TSIG record needs to be the last additional record */
 124         if (i + 1 != packet->arcount) {
 125                 DEBUG(1, ("TSIG record not the last additional record!\n"));
 126                 return DNS_ERR(FORMAT_ERROR);
 127         }
 128
 129         /* We got a TSIG, so we need to sign our reply */
 130         state->sign = true;
 131
 132         state->tsig = talloc_zero(state->mem_ctx, struct dns_res_rec);
 133         if (state->tsig == NULL) {
 134                 return WERR_NOT_ENOUGH_MEMORY;
 135         }
 136
 137         werror = dns_copy_tsig(state->tsig, &packet->additional[i],
 138                                state->tsig);
 139         if (!W_ERROR_IS_OK(werror)) {
 140                 return werror;
 141         }
 142
 143         packet->arcount--;
 144
 145         tkey = dns_find_tkey(dns->tkeys, state->tsig->name);
 146         if (tkey == NULL) {
 147                 /*
 148                  * We must save the name for use in the TSIG error
 149                  * response and have no choice here but to save the
 150                  * keyname from the TSIG request.
 151                  */
 152                 state->key_name = talloc_strdup(state->mem_ctx,
 153                                                 state->tsig->name);
 154                 if (state->key_name == NULL) {
 155                         return WERR_NOT_ENOUGH_MEMORY;
 156                 }
 157                 state->tsig_error = DNS_RCODE_BADKEY;
 158                 return DNS_ERR(NOTAUTH);
 159         }
 160
 161         /*
 162          * Remember the keyname that found an existing tkey, used
 163          * later to fetch the key with dns_find_tkey() when signing
 164          * and adding a TSIG record with MAC.
 165          */
 166         state->key_name = talloc_strdup(state->mem_ctx, tkey->name);
 167         if (state->key_name == NULL) {
 168                 return WERR_NOT_ENOUGH_MEMORY;
 169         }
 170
 171         /* FIXME: check TSIG here */
 172         if (check_rec == NULL) {
 173                 return WERR_NOT_ENOUGH_MEMORY;
 174         }
 175
 176         /* first build and verify check packet */
 177         check_rec->name = talloc_strdup(check_rec, tkey->name);
 178         if (check_rec->name == NULL) {
 179                 return WERR_NOT_ENOUGH_MEMORY;
 180         }
 181         check_rec->rr_class = DNS_QCLASS_ANY;
 182         check_rec->ttl = 0;
 183         check_rec->algorithm_name = talloc_strdup(check_rec, tkey->algorithm);
 184         if (check_rec->algorithm_name == NULL) {
 185                 return WERR_NOT_ENOUGH_MEMORY;
 186         }
 187         check_rec->time_prefix = 0;
 188         check_rec->time = state->tsig->rdata.tsig_record.time;
 189         check_rec->fudge = state->tsig->rdata.tsig_record.fudge;
 190         check_rec->error = 0;
 191         check_rec->other_size = 0;
 192         check_rec->other_data = NULL;
 193
 194         ndr_err = ndr_push_struct_blob(&tsig_blob, mem_ctx, state->tsig,
 195                 (ndr_push_flags_fn_t)ndr_push_dns_res_rec);
 196         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 197                 DEBUG(1, ("Failed to push packet: %s!\n",
 198                           ndr_errstr(ndr_err)));
 199                 return DNS_ERR(SERVER_FAILURE);
 200         }
 201
 202         ndr_err = ndr_push_struct_blob(&fake_tsig_blob, mem_ctx, check_rec,
 203                 (ndr_push_flags_fn_t)ndr_push_dns_fake_tsig_rec);
 204         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 205                 DEBUG(1, ("Failed to push packet: %s!\n",
 206                           ndr_errstr(ndr_err)));
 207                 return DNS_ERR(SERVER_FAILURE);
 208         }
 209
 210         /* we need to work some magic here. we need to keep the input packet
 211          * exactly like we got it, but we need to cut off the tsig record */
 212         packet_len = in->length - tsig_blob.length;
 213         buffer_len = packet_len + fake_tsig_blob.length;
 214         buffer = talloc_zero_array(mem_ctx, uint8_t, buffer_len);
 215         if (buffer == NULL) {
 216                 return WERR_NOT_ENOUGH_MEMORY;
 217         }
 218
 219         memcpy(buffer, in->data, packet_len);
 220         memcpy(buffer + packet_len, fake_tsig_blob.data, fake_tsig_blob.length);
 221
 222         sig.length = state->tsig->rdata.tsig_record.mac_size;
 223         sig.data = talloc_memdup(mem_ctx, state->tsig->rdata.tsig_record.mac, sig.length);
 224         if (sig.data == NULL) {
 225                 return WERR_NOT_ENOUGH_MEMORY;
 226         }
 227
 228         /* Now we also need to count down the additional record counter */
 229         arcount = RSVAL(buffer, 10);
 230         RSSVAL(buffer, 10, arcount-1);
 231
 232         status = gensec_check_packet(tkey->gensec, buffer, buffer_len,
 233                                     buffer, buffer_len, &sig);
 234         if (NT_STATUS_EQUAL(NT_STATUS_ACCESS_DENIED, status)) {
 235                 state->tsig_error = DNS_RCODE_BADSIG;
 236                 return DNS_ERR(NOTAUTH);
 237         }
 238
 239         if (!NT_STATUS_IS_OK(status)) {
 240                 DEBUG(1, ("Verifying tsig failed: %s\n", nt_errstr(status)));
 241                 return ntstatus_to_werror(status);
 242         }
 243
 244         state->authenticated = true;
 245
 246         return WERR_OK;
 247 }
 248
 249 static WERROR dns_tsig_compute_mac(TALLOC_CTX *mem_ctx,
 250                                    struct dns_request_state *state,
 251                                    struct dns_name_packet *packet,
 252                                    struct dns_server_tkey *tkey,
 253                                    time_t current_time,
 254                                    DATA_BLOB *_psig)
 255 {
 256         NTSTATUS status;
 257         enum ndr_err_code ndr_err;
 258         DATA_BLOB packet_blob, tsig_blob, sig;
 259         uint8_t *buffer = NULL;
 260         uint8_t *p = NULL;
 261         size_t buffer_len = 0;
 262         struct dns_fake_tsig_rec *check_rec = talloc_zero(mem_ctx,
 263                         struct dns_fake_tsig_rec);
 264         size_t mac_size = 0;
 265
 266         if (check_rec == NULL) {
 267                 return WERR_NOT_ENOUGH_MEMORY;
 268         }
 269
 270         /* first build and verify check packet */
 271         check_rec->name = talloc_strdup(check_rec, tkey->name);
 272         if (check_rec->name == NULL) {
 273                 return WERR_NOT_ENOUGH_MEMORY;
 274         }
 275         check_rec->rr_class = DNS_QCLASS_ANY;
 276         check_rec->ttl = 0;
 277         check_rec->algorithm_name = talloc_strdup(check_rec, tkey->algorithm);
 278         if (check_rec->algorithm_name == NULL) {
 279                 return WERR_NOT_ENOUGH_MEMORY;
 280         }
 281         check_rec->time_prefix = 0;
 282         check_rec->time = current_time;
 283         check_rec->fudge = 300;
 284         check_rec->error = state->tsig_error;
 285         check_rec->other_size = 0;
 286         check_rec->other_data = NULL;
 287
 288         ndr_err = ndr_push_struct_blob(&packet_blob, mem_ctx, packet,
 289                 (ndr_push_flags_fn_t)ndr_push_dns_name_packet);
 290         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 291                 DEBUG(1, ("Failed to push packet: %s!\n",
 292                           ndr_errstr(ndr_err)));
 293                 return DNS_ERR(SERVER_FAILURE);
 294         }
 295
 296         ndr_err = ndr_push_struct_blob(&tsig_blob, mem_ctx, check_rec,
 297                 (ndr_push_flags_fn_t)ndr_push_dns_fake_tsig_rec);
 298         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 299                 DEBUG(1, ("Failed to push packet: %s!\n",
 300                           ndr_errstr(ndr_err)));
 301                 return DNS_ERR(SERVER_FAILURE);
 302         }
 303
 304         if (state->tsig != NULL) {
 305                 mac_size = state->tsig->rdata.tsig_record.mac_size;
 306         }
 307
 308         buffer_len = mac_size;
 309
 310         buffer_len += packet_blob.length;
 311         if (buffer_len < packet_blob.length) {
 312                 return WERR_INVALID_PARAMETER;
 313         }
 314         buffer_len += tsig_blob.length;
 315         if (buffer_len < tsig_blob.length) {
 316                 return WERR_INVALID_PARAMETER;
 317         }
 318
 319         buffer = talloc_zero_array(mem_ctx, uint8_t, buffer_len);
 320         if (buffer == NULL) {
 321                 return WERR_NOT_ENOUGH_MEMORY;
 322         }
 323
 324         p = buffer;
 325
 326         /*
 327          * RFC 2845 "4.2 TSIG on Answers", how to lay out the buffer
 328          * that we're going to sign:
 329          * 1. MAC of request (if present)
 330          * 2. Outgoing packet
 331          * 3. TSIG record
 332          */
 333         if (mac_size > 0) {
 334                 memcpy(p, state->tsig->rdata.tsig_record.mac, mac_size);
 335                 p += mac_size;
 336         }
 337
 338         memcpy(p, packet_blob.data, packet_blob.length);
 339         p += packet_blob.length;
 340
 341         memcpy(p, tsig_blob.data, tsig_blob.length);
 342
 343         status = gensec_sign_packet(tkey->gensec, mem_ctx, buffer, buffer_len,
 344                                     buffer, buffer_len, &sig);
 345         if (!NT_STATUS_IS_OK(status)) {
 346                 return ntstatus_to_werror(status);
 347         }
 348
 349         *_psig = sig;
 350         return WERR_OK;
 351 }
 352
 353 WERROR dns_sign_tsig(struct dns_server *dns,
 354                      TALLOC_CTX *mem_ctx,
 355                      struct dns_request_state *state,
 356                      struct dns_name_packet *packet,
 357                      uint16_t error)
 358 {
 359         WERROR werror;
 360         time_t current_time = time(NULL);
 361         struct dns_res_rec *tsig = NULL;
 362         DATA_BLOB sig = (DATA_BLOB) {
 363                 .data = NULL,
 364                 .length = 0
 365         };
 366
 367         tsig = talloc_zero(mem_ctx, struct dns_res_rec);
 368         if (tsig == NULL) {
 369                 return WERR_NOT_ENOUGH_MEMORY;
 370         }
 371
 372         if (state->tsig_error == DNS_RCODE_OK) {
 373                 struct dns_server_tkey *tkey = dns_find_tkey(
 374                         dns->tkeys, state->key_name);
 375                 if (tkey == NULL) {
 376                         return DNS_ERR(SERVER_FAILURE);
 377                 }
 378
 379                 werror = dns_tsig_compute_mac(mem_ctx, state, packet,
 380                                               tkey, current_time, &sig);
 381                 if (!W_ERROR_IS_OK(werror)) {
 382                         return werror;
 383                 }
 384         }
 385
 386         tsig->name = talloc_strdup(tsig, state->key_name);
 387         if (tsig->name == NULL) {
 388                 return WERR_NOT_ENOUGH_MEMORY;
 389         }
 390         tsig->rr_class = DNS_QCLASS_ANY;
 391         tsig->rr_type = DNS_QTYPE_TSIG;
 392         tsig->ttl = 0;
 393         tsig->length = UINT16_MAX;
 394         tsig->rdata.tsig_record.algorithm_name = talloc_strdup(tsig, "gss-tsig");
 395         if (tsig->rdata.tsig_record.algorithm_name == NULL) {
 396                 return WERR_NOT_ENOUGH_MEMORY;
 397         }
 398         tsig->rdata.tsig_record.time_prefix = 0;
 399         tsig->rdata.tsig_record.time = current_time;
 400         tsig->rdata.tsig_record.fudge = 300;
 401         tsig->rdata.tsig_record.error = state->tsig_error;
 402         tsig->rdata.tsig_record.original_id = packet->id;
 403         tsig->rdata.tsig_record.other_size = 0;
 404         tsig->rdata.tsig_record.other_data = NULL;
 405         if (sig.length > 0) {
 406                 tsig->rdata.tsig_record.mac_size = sig.length;
 407                 tsig->rdata.tsig_record.mac = talloc_memdup(tsig, sig.data, sig.length);
 408                 if (tsig->rdata.tsig_record.mac == NULL) {
 409                         return WERR_NOT_ENOUGH_MEMORY;
 410                 }
 411         }
 412
 413         if (packet->arcount == 0) {
 414                 packet->additional = talloc_zero(mem_ctx, struct dns_res_rec);
 415                 if (packet->additional == NULL) {
 416                         return WERR_NOT_ENOUGH_MEMORY;
 417                 }
 418         }
 419         packet->additional = talloc_realloc(mem_ctx, packet->additional,
 420                                             struct dns_res_rec,
 421                                             packet->arcount + 1);
 422         if (packet->additional == NULL) {
 423                 return WERR_NOT_ENOUGH_MEMORY;
 424         }
 425
 426         werror = dns_copy_tsig(mem_ctx, tsig,
 427                                &packet->additional[packet->arcount]);
 428         if (!W_ERROR_IS_OK(werror)) {
 429                 return werror;
 430         }
 431         packet->arcount++;
 432
 433         return WERR_OK;
 434 }