lib/ldb/common/ldb_match.c

   1 /*
   2    ldb database library
   3
   4    Copyright (C) Andrew Tridgell  2004-2005
   5    Copyright (C) Simo Sorce            2005
   6
   7      ** NOTE! The following LGPL license applies to the ldb
   8      ** library. This does NOT imply that all of Samba is released
   9      ** under the LGPL
  10
  11    This library is free software; you can redistribute it and/or
  12    modify it under the terms of the GNU Lesser General Public
  13    License as published by the Free Software Foundation; either
  14    version 3 of the License, or (at your option) any later version.
  15
  16    This library is distributed in the hope that it will be useful,
  17    but WITHOUT ANY WARRANTY; without even the implied warranty of
  18    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19    Lesser General Public License for more details.
  20
  21    You should have received a copy of the GNU Lesser General Public
  22    License along with this library; if not, see <http://www.gnu.org/licenses/>.
  23 */
  24
  25 /*
  26  *  Name: ldb
  27  *
  28  *  Component: ldb expression matching
  29  *
  30  *  Description: ldb expression matching
  31  *
  32  *  Author: Andrew Tridgell
  33  */
  34
  35 #include "ldb_private.h"
  36 #include "dlinklist.h"
  37
  38 /*
  39   check if the scope matches in a search result
  40 */
  41 static int ldb_match_scope(struct ldb_context *ldb,
  42                            struct ldb_dn *base,
  43                            struct ldb_dn *dn,
  44                            enum ldb_scope scope)
  45 {
  46         int ret = 0;
  47
  48         if (base == NULL || dn == NULL) {
  49                 return 1;
  50         }
  51
  52         switch (scope) {
  53         case LDB_SCOPE_BASE:
  54                 if (ldb_dn_compare(base, dn) == 0) {
  55                         ret = 1;
  56                 }
  57                 break;
  58
  59         case LDB_SCOPE_ONELEVEL:
  60                 if (ldb_dn_get_comp_num(dn) == (ldb_dn_get_comp_num(base) + 1)) {
  61                         if (ldb_dn_compare_base(base, dn) == 0) {
  62                                 ret = 1;
  63                         }
  64                 }
  65                 break;
  66
  67         case LDB_SCOPE_SUBTREE:
  68         default:
  69                 if (ldb_dn_compare_base(base, dn) == 0) {
  70                         ret = 1;
  71                 }
  72                 break;
  73         }
  74
  75         return ret;
  76 }
  77
  78
  79 /*
  80   match if node is present
  81 */
  82 static int ldb_match_present(struct ldb_context *ldb,
  83                              const struct ldb_message *msg,
  84                              const struct ldb_parse_tree *tree,
  85                              enum ldb_scope scope, bool *matched)
  86 {
  87         const struct ldb_schema_attribute *a;
  88         struct ldb_message_element *el;
  89
  90         if (ldb_attr_dn(tree->u.present.attr) == 0) {
  91                 *matched = true;
  92                 return LDB_SUCCESS;
  93         }
  94
  95         el = ldb_msg_find_element(msg, tree->u.present.attr);
  96         if (el == NULL) {
  97                 *matched = false;
  98                 return LDB_SUCCESS;
  99         }
 100
 101         a = ldb_schema_attribute_by_name(ldb, el->name);
 102         if (!a) {
 103                 return LDB_ERR_INVALID_ATTRIBUTE_SYNTAX;
 104         }
 105
 106         if (a->syntax->operator_fn) {
 107                 unsigned int i;
 108                 for (i = 0; i < el->num_values; i++) {
 109                         int ret = a->syntax->operator_fn(ldb, LDB_OP_PRESENT, a, &el->values[i], NULL, matched);
 110                         if (ret != LDB_SUCCESS) return ret;
 111                         if (*matched) return LDB_SUCCESS;
 112                 }
 113                 *matched = false;
 114                 return LDB_SUCCESS;
 115         }
 116
 117         *matched = true;
 118         return LDB_SUCCESS;
 119 }
 120
 121 static int ldb_match_comparison(struct ldb_context *ldb,
 122                                 const struct ldb_message *msg,
 123                                 const struct ldb_parse_tree *tree,
 124                                 enum ldb_scope scope,
 125                                 enum ldb_parse_op comp_op, bool *matched)
 126 {
 127         unsigned int i;
 128         struct ldb_message_element *el;
 129         const struct ldb_schema_attribute *a;
 130
 131         /* FIXME: APPROX comparison not handled yet */
 132         if (comp_op == LDB_OP_APPROX) {
 133                 return LDB_ERR_INAPPROPRIATE_MATCHING;
 134         }
 135
 136         el = ldb_msg_find_element(msg, tree->u.comparison.attr);
 137         if (el == NULL) {
 138                 *matched = false;
 139                 return LDB_SUCCESS;
 140         }
 141
 142         a = ldb_schema_attribute_by_name(ldb, el->name);
 143         if (!a) {
 144                 return LDB_ERR_INVALID_ATTRIBUTE_SYNTAX;
 145         }
 146
 147         for (i = 0; i < el->num_values; i++) {
 148                 if (a->syntax->operator_fn) {
 149                         int ret;
 150                         ret = a->syntax->operator_fn(ldb, comp_op, a, &el->values[i], &tree->u.comparison.value, matched);
 151                         if (ret != LDB_SUCCESS) return ret;
 152                         if (*matched) return LDB_SUCCESS;
 153                 } else {
 154                         int ret = a->syntax->comparison_fn(ldb, ldb, &el->values[i], &tree->u.comparison.value);
 155
 156                         if (ret == 0) {
 157                                 *matched = true;
 158                                 return LDB_SUCCESS;
 159                         }
 160                         if (ret > 0 && comp_op == LDB_OP_GREATER) {
 161                                 *matched = true;
 162                                 return LDB_SUCCESS;
 163                         }
 164                         if (ret < 0 && comp_op == LDB_OP_LESS) {
 165                                 *matched = true;
 166                                 return LDB_SUCCESS;
 167                         }
 168                 }
 169         }
 170
 171         *matched = false;
 172         return LDB_SUCCESS;
 173 }
 174
 175 /*
 176   match a simple leaf node
 177 */
 178 static int ldb_match_equality(struct ldb_context *ldb,
 179                               const struct ldb_message *msg,
 180                               const struct ldb_parse_tree *tree,
 181                               enum ldb_scope scope,
 182                               bool *matched)
 183 {
 184         unsigned int i;
 185         struct ldb_message_element *el;
 186         const struct ldb_schema_attribute *a;
 187         struct ldb_dn *valuedn;
 188         int ret;
 189
 190         if (ldb_attr_dn(tree->u.equality.attr) == 0) {
 191                 valuedn = ldb_dn_from_ldb_val(ldb, ldb, &tree->u.equality.value);
 192                 if (valuedn == NULL) {
 193                         return LDB_ERR_INVALID_DN_SYNTAX;
 194                 }
 195
 196                 ret = ldb_dn_compare(msg->dn, valuedn);
 197
 198                 talloc_free(valuedn);
 199
 200                 *matched = (ret == 0);
 201                 return LDB_SUCCESS;
 202         }
 203
 204         /* TODO: handle the "*" case derived from an extended search
 205            operation without the attibute type defined */
 206         el = ldb_msg_find_element(msg, tree->u.equality.attr);
 207         if (el == NULL) {
 208                 *matched = false;
 209                 return LDB_SUCCESS;
 210         }
 211
 212         a = ldb_schema_attribute_by_name(ldb, el->name);
 213         if (a == NULL) {
 214                 return LDB_ERR_INVALID_ATTRIBUTE_SYNTAX;
 215         }
 216
 217         for (i=0;i<el->num_values;i++) {
 218                 if (a->syntax->operator_fn) {
 219                         ret = a->syntax->operator_fn(ldb, LDB_OP_EQUALITY, a,
 220                                                      &tree->u.equality.value, &el->values[i], matched);
 221                         if (ret != LDB_SUCCESS) return ret;
 222                         if (*matched) return LDB_SUCCESS;
 223                 } else {
 224                         if (a->syntax->comparison_fn(ldb, ldb, &tree->u.equality.value,
 225                                                      &el->values[i]) == 0) {
 226                                 *matched = true;
 227                                 return LDB_SUCCESS;
 228                         }
 229                 }
 230         }
 231
 232         *matched = false;
 233         return LDB_SUCCESS;
 234 }
 235
 236 static int ldb_wildcard_compare(struct ldb_context *ldb,
 237                                 const struct ldb_parse_tree *tree,
 238                                 const struct ldb_val value, bool *matched)
 239 {
 240         const struct ldb_schema_attribute *a;
 241         struct ldb_val val;
 242         struct ldb_val cnk;
 243         struct ldb_val *chunk;
 244         char *p, *g;
 245         uint8_t *save_p = NULL;
 246         unsigned int c = 0;
 247
 248         a = ldb_schema_attribute_by_name(ldb, tree->u.substring.attr);
 249         if (!a) {
 250                 return LDB_ERR_INVALID_ATTRIBUTE_SYNTAX;
 251         }
 252
 253         if (tree->u.substring.chunks == NULL) {
 254                 *matched = false;
 255                 return LDB_SUCCESS;
 256         }
 257
 258         if (a->syntax->canonicalise_fn(ldb, ldb, &value, &val) != 0) {
 259                 return LDB_ERR_INVALID_ATTRIBUTE_SYNTAX;
 260         }
 261
 262         save_p = val.data;
 263         cnk.data = NULL;
 264
 265         if ( ! tree->u.substring.start_with_wildcard ) {
 266
 267                 chunk = tree->u.substring.chunks[c];
 268                 if (a->syntax->canonicalise_fn(ldb, ldb, chunk, &cnk) != 0) goto mismatch;
 269
 270                 /* This deals with wildcard prefix searches on binary attributes (eg objectGUID) */
 271                 if (cnk.length > val.length) {
 272                         goto mismatch;
 273                 }
 274                 if (memcmp((char *)val.data, (char *)cnk.data, cnk.length) != 0) goto mismatch;
 275                 val.length -= cnk.length;
 276                 val.data += cnk.length;
 277                 c++;
 278                 talloc_free(cnk.data);
 279                 cnk.data = NULL;
 280         }
 281
 282         while (tree->u.substring.chunks[c]) {
 283
 284                 chunk = tree->u.substring.chunks[c];
 285                 if(a->syntax->canonicalise_fn(ldb, ldb, chunk, &cnk) != 0) goto mismatch;
 286
 287                 /* FIXME: case of embedded nulls */
 288                 p = strstr((char *)val.data, (char *)cnk.data);
 289                 if (p == NULL) goto mismatch;
 290                 if ( (! tree->u.substring.chunks[c + 1]) && (! tree->u.substring.end_with_wildcard) ) {
 291                         do { /* greedy */
 292                                 g = strstr((char *)p + cnk.length, (char *)cnk.data);
 293                                 if (g) p = g;
 294                         } while(g);
 295                 }
 296                 val.length = val.length - (p - (char *)(val.data)) - cnk.length;
 297                 val.data = (uint8_t *)(p + cnk.length);
 298                 c++;
 299                 talloc_free(cnk.data);
 300                 cnk.data = NULL;
 301         }
 302
 303         /* last chunk may not have reached end of string */
 304         if ( (! tree->u.substring.end_with_wildcard) && (*(val.data) != 0) ) goto mismatch;
 305         talloc_free(save_p);
 306         *matched = true;
 307         return LDB_SUCCESS;
 308
 309 mismatch:
 310         *matched = false;
 311         talloc_free(save_p);
 312         talloc_free(cnk.data);
 313         return LDB_SUCCESS;
 314 }
 315
 316 /*
 317   match a simple leaf node
 318 */
 319 static int ldb_match_substring(struct ldb_context *ldb,
 320                                const struct ldb_message *msg,
 321                                const struct ldb_parse_tree *tree,
 322                                enum ldb_scope scope, bool *matched)
 323 {
 324         unsigned int i;
 325         struct ldb_message_element *el;
 326
 327         el = ldb_msg_find_element(msg, tree->u.substring.attr);
 328         if (el == NULL) {
 329                 *matched = false;
 330                 return LDB_SUCCESS;
 331         }
 332
 333         for (i = 0; i < el->num_values; i++) {
 334                 int ret;
 335                 ret = ldb_wildcard_compare(ldb, tree, el->values[i], matched);
 336                 if (ret != LDB_SUCCESS) return ret;
 337                 if (*matched) return LDB_SUCCESS;
 338         }
 339
 340         *matched = false;
 341         return LDB_SUCCESS;
 342 }
 343
 344
 345 /*
 346   bitwise and/or comparator depending on oid
 347 */
 348 static int ldb_comparator_bitmask(const char *oid, const struct ldb_val *v1, const struct ldb_val *v2,
 349                                   bool *matched)
 350 {
 351         uint64_t i1, i2;
 352         char ibuf[100];
 353         char *endptr = NULL;
 354
 355         if (v1->length >= sizeof(ibuf)-1) {
 356                 return LDB_ERR_INVALID_ATTRIBUTE_SYNTAX;
 357         }
 358         memcpy(ibuf, (char *)v1->data, v1->length);
 359         ibuf[v1->length] = 0;
 360         i1 = strtoull(ibuf, &endptr, 0);
 361         if (endptr != NULL) {
 362                 if (endptr == ibuf || *endptr != 0) {
 363                         return LDB_ERR_INVALID_ATTRIBUTE_SYNTAX;
 364                 }
 365         }
 366
 367         if (v2->length >= sizeof(ibuf)-1) {
 368                 return LDB_ERR_INVALID_ATTRIBUTE_SYNTAX;
 369         }
 370         endptr = NULL;
 371         memcpy(ibuf, (char *)v2->data, v2->length);
 372         ibuf[v2->length] = 0;
 373         i2 = strtoull(ibuf, &endptr, 0);
 374         if (endptr != NULL) {
 375                 if (endptr == ibuf || *endptr != 0) {
 376                         return LDB_ERR_INVALID_ATTRIBUTE_SYNTAX;
 377                 }
 378         }
 379         if (strcmp(LDB_OID_COMPARATOR_AND, oid) == 0) {
 380                 *matched = ((i1 & i2) == i2);
 381         } else if (strcmp(LDB_OID_COMPARATOR_OR, oid) == 0) {
 382                 *matched = ((i1 & i2) != 0);
 383         } else {
 384                 return LDB_ERR_INAPPROPRIATE_MATCHING;
 385         }
 386         return LDB_SUCCESS;
 387 }
 388
 389 static int ldb_match_bitmask(struct ldb_context *ldb,
 390                              const char *oid,
 391                              const struct ldb_message *msg,
 392                              const char *attribute_to_match,
 393                              const struct ldb_val *value_to_match,
 394                              bool *matched)
 395 {
 396         unsigned int i;
 397         struct ldb_message_element *el;
 398
 399         /* find the message element */
 400         el = ldb_msg_find_element(msg, attribute_to_match);
 401         if (el == NULL) {
 402                 *matched = false;
 403                 return LDB_SUCCESS;
 404         }
 405
 406         for (i=0;i<el->num_values;i++) {
 407                 int ret;
 408                 struct ldb_val *v = &el->values[i];
 409
 410                 ret = ldb_comparator_bitmask(oid, v, value_to_match, matched);
 411                 if (ret != LDB_SUCCESS) {
 412                         return ret;
 413                 }
 414                 if (*matched) {
 415                         return LDB_SUCCESS;
 416                 }
 417         }
 418
 419         *matched = false;
 420         return LDB_SUCCESS;
 421 }
 422
 423 /*
 424   always return false
 425 */
 426 static int ldb_comparator_false(struct ldb_context *ldb,
 427                                 const char *oid,
 428                                 const struct ldb_message *msg,
 429                                 const char *attribute_to_match,
 430                                 const struct ldb_val *value_to_match,
 431                                 bool *matched)
 432 {
 433         *matched = false;
 434         return LDB_SUCCESS;
 435 }
 436
 437
 438 static const struct ldb_extended_match_rule *ldb_find_extended_match_rule(struct ldb_context *ldb,
 439                                                                           const char *oid)
 440 {
 441         struct ldb_extended_match_entry *extended_match_rule;
 442
 443         for (extended_match_rule = ldb->extended_match_rules;
 444              extended_match_rule;
 445              extended_match_rule = extended_match_rule->next) {
 446                 if (strcmp(extended_match_rule->rule->oid, oid) == 0) {
 447                         return extended_match_rule->rule;
 448                 }
 449         }
 450
 451         return NULL;
 452 }
 453
 454
 455 /*
 456   extended match, handles things like bitops
 457 */
 458 static int ldb_match_extended(struct ldb_context *ldb,
 459                               const struct ldb_message *msg,
 460                               const struct ldb_parse_tree *tree,
 461                               enum ldb_scope scope, bool *matched)
 462 {
 463         const struct ldb_extended_match_rule *rule;
 464
 465         if (tree->u.extended.dnAttributes) {
 466                 /* FIXME: We really need to find out what this ":dn" part in
 467                  * an extended match means and how to handle it. For now print
 468                  * only a warning to have s3 winbind and other tools working
 469                  * against us. - Matthias */
 470                 ldb_debug(ldb, LDB_DEBUG_WARNING, "ldb: dnAttributes extended match not supported yet");
 471         }
 472         if (tree->u.extended.rule_id == NULL) {
 473                 ldb_debug(ldb, LDB_DEBUG_ERROR, "ldb: no-rule extended matches not supported yet");
 474                 return LDB_ERR_INAPPROPRIATE_MATCHING;
 475         }
 476         if (tree->u.extended.attr == NULL) {
 477                 ldb_debug(ldb, LDB_DEBUG_ERROR, "ldb: no-attribute extended matches not supported yet");
 478                 return LDB_ERR_INAPPROPRIATE_MATCHING;
 479         }
 480
 481         rule = ldb_find_extended_match_rule(ldb, tree->u.extended.rule_id);
 482         if (rule == NULL) {
 483                 ldb_debug(ldb, LDB_DEBUG_ERROR, "ldb: unknown extended rule_id %s",
 484                           tree->u.extended.rule_id);
 485                 return LDB_ERR_INAPPROPRIATE_MATCHING;
 486         }
 487
 488         return rule->callback(ldb, rule->oid, msg,
 489                               tree->u.extended.attr,
 490                               &tree->u.extended.value, matched);
 491 }
 492
 493 /*
 494   return 0 if the given parse tree matches the given message. Assumes
 495   the message is in sorted order
 496
 497   return 1 if it matches, and 0 if it doesn't match
 498
 499   this is a recursive function, and does short-circuit evaluation
 500  */
 501 static int ldb_match_message(struct ldb_context *ldb,
 502                              const struct ldb_message *msg,
 503                              const struct ldb_parse_tree *tree,
 504                              enum ldb_scope scope, bool *matched)
 505 {
 506         unsigned int i;
 507         int ret;
 508
 509         *matched = false;
 510
 511         if (scope != LDB_SCOPE_BASE && ldb_dn_is_special(msg->dn)) {
 512                 /* don't match special records except on base searches */
 513                 return LDB_SUCCESS;
 514         }
 515
 516         switch (tree->operation) {
 517         case LDB_OP_AND:
 518                 for (i=0;i<tree->u.list.num_elements;i++) {
 519                         ret = ldb_match_message(ldb, msg, tree->u.list.elements[i], scope, matched);
 520                         if (ret != LDB_SUCCESS) return ret;
 521                         if (!*matched) return LDB_SUCCESS;
 522                 }
 523                 *matched = true;
 524                 return LDB_SUCCESS;
 525
 526         case LDB_OP_OR:
 527                 for (i=0;i<tree->u.list.num_elements;i++) {
 528                         ret = ldb_match_message(ldb, msg, tree->u.list.elements[i], scope, matched);
 529                         if (ret != LDB_SUCCESS) return ret;
 530                         if (*matched) return LDB_SUCCESS;
 531                 }
 532                 *matched = false;
 533                 return LDB_SUCCESS;
 534
 535         case LDB_OP_NOT:
 536                 ret = ldb_match_message(ldb, msg, tree->u.isnot.child, scope, matched);
 537                 if (ret != LDB_SUCCESS) return ret;
 538                 *matched = ! *matched;
 539                 return LDB_SUCCESS;
 540
 541         case LDB_OP_EQUALITY:
 542                 return ldb_match_equality(ldb, msg, tree, scope, matched);
 543
 544         case LDB_OP_SUBSTRING:
 545                 return ldb_match_substring(ldb, msg, tree, scope, matched);
 546
 547         case LDB_OP_GREATER:
 548                 return ldb_match_comparison(ldb, msg, tree, scope, LDB_OP_GREATER, matched);
 549
 550         case LDB_OP_LESS:
 551                 return ldb_match_comparison(ldb, msg, tree, scope, LDB_OP_LESS, matched);
 552
 553         case LDB_OP_PRESENT:
 554                 return ldb_match_present(ldb, msg, tree, scope, matched);
 555
 556         case LDB_OP_APPROX:
 557                 return ldb_match_comparison(ldb, msg, tree, scope, LDB_OP_APPROX, matched);
 558
 559         case LDB_OP_EXTENDED:
 560                 return ldb_match_extended(ldb, msg, tree, scope, matched);
 561         }
 562
 563         return LDB_ERR_INAPPROPRIATE_MATCHING;
 564 }
 565
 566 int ldb_match_msg(struct ldb_context *ldb,
 567                   const struct ldb_message *msg,
 568                   const struct ldb_parse_tree *tree,
 569                   struct ldb_dn *base,
 570                   enum ldb_scope scope)
 571 {
 572         bool matched;
 573         int ret;
 574
 575         if ( ! ldb_match_scope(ldb, base, msg->dn, scope) ) {
 576                 return 0;
 577         }
 578
 579         ret = ldb_match_message(ldb, msg, tree, scope, &matched);
 580         if (ret != LDB_SUCCESS) {
 581                 /* to match the old API, we need to consider this a
 582                    failure to match */
 583                 return 0;
 584         }
 585         return matched?1:0;
 586 }
 587
 588 int ldb_match_msg_error(struct ldb_context *ldb,
 589                         const struct ldb_message *msg,
 590                         const struct ldb_parse_tree *tree,
 591                         struct ldb_dn *base,
 592                         enum ldb_scope scope,
 593                         bool *matched)
 594 {
 595         if ( ! ldb_match_scope(ldb, base, msg->dn, scope) ) {
 596                 *matched = false;
 597                 return LDB_SUCCESS;
 598         }
 599
 600         return ldb_match_message(ldb, msg, tree, scope, matched);
 601 }
 602
 603 int ldb_match_msg_objectclass(const struct ldb_message *msg,
 604                               const char *objectclass)
 605 {
 606         unsigned int i;
 607         struct ldb_message_element *el = ldb_msg_find_element(msg, "objectClass");
 608         if (!el) {
 609                 return 0;
 610         }
 611         for (i=0; i < el->num_values; i++) {
 612                 if (ldb_attr_cmp((const char *)el->values[i].data, objectclass) == 0) {
 613                         return 1;
 614                 }
 615         }
 616         return 0;
 617 }
 618
 619 _PRIVATE_ int ldb_register_extended_match_rules(struct ldb_context *ldb)
 620 {
 621         struct ldb_extended_match_rule *bitmask_and;
 622         struct ldb_extended_match_rule *bitmask_or;
 623         struct ldb_extended_match_rule *always_false;
 624         int ret;
 625
 626         /* Register bitmask-and match */
 627         bitmask_and = talloc_zero(ldb, struct ldb_extended_match_rule);
 628         if (bitmask_and == NULL) {
 629                 return LDB_ERR_OPERATIONS_ERROR;
 630         }
 631
 632         bitmask_and->oid = LDB_OID_COMPARATOR_AND;
 633         bitmask_and->callback = ldb_match_bitmask;
 634
 635         ret = ldb_register_extended_match_rule(ldb, bitmask_and);
 636         if (ret != LDB_SUCCESS) {
 637                 return ret;
 638         }
 639
 640         /* Register bitmask-or match */
 641         bitmask_or = talloc_zero(ldb, struct ldb_extended_match_rule);
 642         if (bitmask_or == NULL) {
 643                 return LDB_ERR_OPERATIONS_ERROR;
 644         }
 645
 646         bitmask_or->oid = LDB_OID_COMPARATOR_OR;
 647         bitmask_or->callback = ldb_match_bitmask;
 648
 649         ret = ldb_register_extended_match_rule(ldb, bitmask_or);
 650         if (ret != LDB_SUCCESS) {
 651                 return ret;
 652         }
 653
 654         /* Register always-false match */
 655         always_false = talloc_zero(ldb, struct ldb_extended_match_rule);
 656         if (always_false == NULL) {
 657                 return LDB_ERR_OPERATIONS_ERROR;
 658         }
 659
 660         always_false->oid = SAMBA_LDAP_MATCH_ALWAYS_FALSE;
 661         always_false->callback = ldb_comparator_false;
 662
 663         ret = ldb_register_extended_match_rule(ldb, always_false);
 664         if (ret != LDB_SUCCESS) {
 665                 return ret;
 666         }
 667
 668         return LDB_SUCCESS;
 669 }
 670
 671 /*
 672   register a new ldb backend
 673
 674   if override is true, then override any existing backend for this prefix
 675 */
 676 int ldb_register_extended_match_rule(struct ldb_context *ldb,
 677                                      const struct ldb_extended_match_rule *rule)
 678 {
 679         const struct ldb_extended_match_rule *lookup_rule;
 680         struct ldb_extended_match_entry *entry;
 681
 682         lookup_rule = ldb_find_extended_match_rule(ldb, rule->oid);
 683         if (lookup_rule) {
 684                 return LDB_ERR_ENTRY_ALREADY_EXISTS;
 685         }
 686
 687         entry = talloc_zero(ldb, struct ldb_extended_match_entry);
 688         if (!entry) {
 689                 return LDB_ERR_OPERATIONS_ERROR;
 690         }
 691         entry->rule = rule;
 692         DLIST_ADD_END(ldb->extended_match_rules, entry, struct ldb_extended_match_entry);
 693
 694         return LDB_SUCCESS;
 695 }
 696