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         bool found_tsig = false;
 104         uint16_t i, arcount = 0;
 105         DATA_BLOB tsig_blob, fake_tsig_blob, sig;
 106         uint8_t *buffer = NULL;
 107         size_t buffer_len = 0, packet_len = 0;
 108         struct dns_server_tkey *tkey = NULL;
 109         struct dns_fake_tsig_rec *check_rec = talloc_zero(mem_ctx,
 110                         struct dns_fake_tsig_rec);
 111
 112
 113         /* Find the first TSIG record in the additional records */
 114         for (i=0; i < packet->arcount; i++) {
 115                 if (packet->additional[i].rr_type == DNS_QTYPE_TSIG) {
 116                         found_tsig = true;
 117                         break;
 118                 }
 119         }
 120
 121         if (!found_tsig) {
 122                 return WERR_OK;
 123         }
 124
 125         /* The TSIG record needs to be the last additional record */
 126         if (found_tsig && i + 1 != packet->arcount) {
 127                 DEBUG(1, ("TSIG record not the last additional record!\n"));
 128                 return DNS_ERR(FORMAT_ERROR);
 129         }
 130
 131         /* We got a TSIG, so we need to sign our reply */
 132         state->sign = true;
 133
 134         state->tsig = talloc_zero(state->mem_ctx, struct dns_res_rec);
 135         if (state->tsig == NULL) {
 136                 return WERR_NOMEM;
 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                 state->tsig_error = DNS_RCODE_BADKEY;
 150                 return DNS_ERR(NOTAUTH);
 151         }
 152
 153         /* FIXME: check TSIG here */
 154         if (check_rec == NULL) {
 155                 return WERR_NOMEM;
 156         }
 157
 158         /* first build and verify check packet */
 159         check_rec->name = talloc_strdup(check_rec, tkey->name);
 160         if (check_rec->name == NULL) {
 161                 return WERR_NOMEM;
 162         }
 163         check_rec->rr_class = DNS_QCLASS_ANY;
 164         check_rec->ttl = 0;
 165         check_rec->algorithm_name = talloc_strdup(check_rec, tkey->algorithm);
 166         if (check_rec->algorithm_name == NULL) {
 167                 return WERR_NOMEM;
 168         }
 169         check_rec->time_prefix = 0;
 170         check_rec->time = state->tsig->rdata.tsig_record.time;
 171         check_rec->fudge = state->tsig->rdata.tsig_record.fudge;
 172         check_rec->error = 0;
 173         check_rec->other_size = 0;
 174         check_rec->other_data = NULL;
 175
 176         ndr_err = ndr_push_struct_blob(&tsig_blob, mem_ctx, state->tsig,
 177                 (ndr_push_flags_fn_t)ndr_push_dns_res_rec);
 178         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 179                 DEBUG(1, ("Failed to push packet: %s!\n",
 180                           ndr_errstr(ndr_err)));
 181                 return DNS_ERR(SERVER_FAILURE);
 182         }
 183
 184         ndr_err = ndr_push_struct_blob(&fake_tsig_blob, mem_ctx, check_rec,
 185                 (ndr_push_flags_fn_t)ndr_push_dns_fake_tsig_rec);
 186         if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
 187                 DEBUG(1, ("Failed to push packet: %s!\n",
 188                           ndr_errstr(ndr_err)));
 189                 return DNS_ERR(SERVER_FAILURE);
 190         }
 191
 192         /* we need to work some magic here. we need to keep the input packet
 193          * exactly like we got it, but we need to cut off the tsig record */
 194         packet_len = in->length - tsig_blob.length;
 195         buffer_len = packet_len + fake_tsig_blob.length;
 196         buffer = talloc_zero_array(mem_ctx, uint8_t, buffer_len);
 197         if (buffer == NULL) {
 198                 return WERR_NOMEM;
 199         }
 200
 201         memcpy(buffer, in->data, packet_len);
 202         memcpy(buffer + packet_len, fake_tsig_blob.data, fake_tsig_blob.length);
 203
 204         sig.length = state->tsig->rdata.tsig_record.mac_size;
 205         sig.data = talloc_memdup(mem_ctx, state->tsig->rdata.tsig_record.mac, sig.length);
 206         if (sig.data == NULL) {
 207                 return WERR_NOMEM;
 208         }
 209
 210         /*FIXME: Why is there too much padding? */
 211         buffer_len -= 2;
 212
 213         /* Now we also need to count down the additional record counter */
 214         arcount = RSVAL(buffer, 10);
 215         RSSVAL(buffer, 10, arcount-1);
 216
 217         status = gensec_check_packet(tkey->gensec, buffer, buffer_len,
 218                                     buffer, buffer_len, &sig);
 219         if (NT_STATUS_EQUAL(NT_STATUS_ACCESS_DENIED, status)) {
 220                 return DNS_ERR(BADKEY);
 221         }
 222
 223         if (!NT_STATUS_IS_OK(status)) {
 224                 DEBUG(1, ("Verifying tsig failed: %s\n", nt_errstr(status)));
 225                 return ntstatus_to_werror(status);
 226         }
 227
 228         state->authenticated = true;
 229         state->key_name = talloc_strdup(state->mem_ctx, tkey->name);
 230         if (state->key_name == NULL) {
 231                 return WERR_NOMEM;
 232         }
 233
 234         return WERR_OK;
 235 }
 236
 237 WERROR dns_sign_tsig(struct dns_server *dns,
 238                      TALLOC_CTX *mem_ctx,
 239                      struct dns_request_state *state,
 240                      struct dns_name_packet *packet,
 241                      uint16_t error)
 242 {
 243         WERROR werror;
 244         NTSTATUS status;
 245         enum ndr_err_code ndr_err;
 246         time_t current_time = time(NULL);
 247         DATA_BLOB packet_blob, tsig_blob, sig;
 248         uint8_t *buffer = NULL;
 249         size_t buffer_len = 0;
 250         struct dns_server_tkey * tkey = NULL;
 251         struct dns_res_rec *tsig = talloc_zero(mem_ctx, struct dns_res_rec);
 252
 253         struct dns_fake_tsig_rec *check_rec = talloc_zero(mem_ctx,
 254                         struct dns_fake_tsig_rec);
 255
 256         if (tsig == NULL) {
 257                 return WERR_NOMEM;
 258         }
 259
 260         if (check_rec == NULL) {
 261                 return WERR_NOMEM;
 262         }
 263
 264         tkey = dns_find_tkey(dns->tkeys, state->key_name);
 265         if (tkey == NULL) {
 266                 /* FIXME: read up on what to do when we can't find a key */
 267                 return WERR_OK;
 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_NOMEM;
 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_NOMEM;
 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         buffer_len = packet_blob.length + tsig_blob.length;
 305         buffer = talloc_zero_array(mem_ctx, uint8_t, buffer_len);
 306         if (buffer == NULL) {
 307                 return WERR_NOMEM;
 308         }
 309
 310         memcpy(buffer, packet_blob.data, packet_blob.length);
 311         memcpy(buffer+packet_blob.length, tsig_blob.data, tsig_blob.length);
 312
 313
 314         status = gensec_sign_packet(tkey->gensec, mem_ctx, buffer, buffer_len,
 315                                     buffer, buffer_len, &sig);
 316         if (!NT_STATUS_IS_OK(status)) {
 317                 return ntstatus_to_werror(status);
 318         }
 319
 320         tsig->name = talloc_strdup(tsig, check_rec->name);
 321         if (tsig->name == NULL) {
 322                 return WERR_NOMEM;
 323         }
 324         tsig->rr_class = check_rec->rr_class;
 325         tsig->rr_type = DNS_QTYPE_TSIG;
 326         tsig->ttl = 0;
 327         tsig->length = UINT16_MAX;
 328         tsig->rdata.tsig_record.algorithm_name = talloc_strdup(tsig,
 329                         check_rec->algorithm_name);
 330         tsig->rdata.tsig_record.time_prefix = check_rec->time_prefix;
 331         tsig->rdata.tsig_record.time = check_rec->time;
 332         tsig->rdata.tsig_record.fudge = check_rec->fudge;
 333         tsig->rdata.tsig_record.error = state->tsig_error;
 334         tsig->rdata.tsig_record.original_id = packet->id;
 335         tsig->rdata.tsig_record.other_size = 0;
 336         tsig->rdata.tsig_record.other_data = NULL;
 337         tsig->rdata.tsig_record.mac_size = sig.length;
 338         tsig->rdata.tsig_record.mac = talloc_memdup(tsig, sig.data, sig.length);
 339
 340
 341         if (packet->arcount == 0) {
 342                 packet->additional = talloc_zero(mem_ctx, struct dns_res_rec);
 343                 if (packet->additional == NULL) {
 344                         return WERR_NOMEM;
 345                 }
 346         }
 347         packet->additional = talloc_realloc(mem_ctx, packet->additional,
 348                                             struct dns_res_rec,
 349                                             packet->arcount + 1);
 350         if (packet->additional == NULL) {
 351                 return WERR_NOMEM;
 352         }
 353
 354         werror = dns_copy_tsig(mem_ctx, tsig,
 355                                &packet->additional[packet->arcount]);
 356         if (!W_ERROR_IS_OK(werror)) {
 357                 return werror;
 358         }
 359         packet->arcount++;
 360
 361         return WERR_OK;
 362 }