1 /* 2 * validator/val_nsec.c - validator NSEC denial of existance functions. 3 * 4 * Copyright (c) 2007, NLnet Labs. All rights reserved. 5 * 6 * This software is open source. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 12 * Redistributions of source code must retain the above copyright notice, 13 * this list of conditions and the following disclaimer. 14 * 15 * Redistributions in binary form must reproduce the above copyright notice, 16 * this list of conditions and the following disclaimer in the documentation 17 * and/or other materials provided with the distribution. 18 * 19 * Neither the name of the NLNET LABS nor the names of its contributors may 20 * be used to endorse or promote products derived from this software without 21 * specific prior written permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 24 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 25 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 26 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 27 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 28 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED 29 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 30 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 31 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 32 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 33 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 34 */ 35 36 /** 37 * \file 38 * 39 * This file contains helper functions for the validator module. 40 * The functions help with NSEC checking, the different NSEC proofs 41 * for denial of existance, and proofs for presence of types. 42 */ 43 #include "config.h" 44 #include "validator/val_nsec.h" 45 #include "validator/val_utils.h" 46 #include "util/data/msgreply.h" 47 #include "util/data/dname.h" 48 #include "util/net_help.h" 49 #include "util/module.h" 50 #include "services/cache/rrset.h" 51 52 /** get ttl of rrset */ 53 static uint32_t 54 rrset_get_ttl(struct ub_packed_rrset_key* k) 55 { 56 struct packed_rrset_data* d = (struct packed_rrset_data*)k->entry.data; 57 return d->ttl; 58 } 59 60 int 61 nsecbitmap_has_type_rdata(uint8_t* bitmap, size_t len, uint16_t type) 62 { 63 /* Check type present in NSEC typemap with bitmap arg */ 64 /* bitmasks for determining type-lowerbits presence */ 65 uint8_t masks[8] = {0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01}; 66 uint8_t type_window = type>>8; 67 uint8_t type_low = type&0xff; 68 uint8_t win, winlen; 69 /* read each of the type bitmap windows and see if the searched 70 * type is amongst it */ 71 while(len > 0) { 72 if(len < 3) /* bad window, at least window# winlen bitmap */ 73 return 0; 74 win = *bitmap++; 75 winlen = *bitmap++; 76 len -= 2; 77 if(len < winlen || winlen < 1 || winlen > 32) 78 return 0; /* bad window length */ 79 if(win == type_window) { 80 /* search window bitmap for the correct byte */ 81 /* mybyte is 0 if we need the first byte */ 82 size_t mybyte = type_low>>3; 83 if(winlen <= mybyte) 84 return 0; /* window too short */ 85 return (int)(bitmap[mybyte] & masks[type_low&0x7]); 86 } else { 87 /* not the window we are looking for */ 88 bitmap += winlen; 89 len -= winlen; 90 } 91 } 92 /* end of bitmap reached, no type found */ 93 return 0; 94 } 95 96 int 97 nsec_has_type(struct ub_packed_rrset_key* nsec, uint16_t type) 98 { 99 struct packed_rrset_data* d = (struct packed_rrset_data*)nsec-> 100 entry.data; 101 size_t len; 102 if(!d || d->count == 0 || d->rr_len[0] < 2+1) 103 return 0; 104 len = dname_valid(d->rr_data[0]+2, d->rr_len[0]-2); 105 if(!len) 106 return 0; 107 return nsecbitmap_has_type_rdata(d->rr_data[0]+2+len, 108 d->rr_len[0]-2-len, type); 109 } 110 111 /** 112 * Get next owner name from nsec record 113 * @param nsec: the nsec RRset. 114 * If there are multiple RRs, then this will only return one of them. 115 * @param nm: the next name is returned. 116 * @param ln: length of nm is returned. 117 * @return false on a bad NSEC RR (too short, malformed dname). 118 */ 119 static int 120 nsec_get_next(struct ub_packed_rrset_key* nsec, uint8_t** nm, size_t* ln) 121 { 122 struct packed_rrset_data* d = (struct packed_rrset_data*)nsec-> 123 entry.data; 124 if(!d || d->count == 0 || d->rr_len[0] < 2+1) { 125 *nm = 0; 126 *ln = 0; 127 return 0; 128 } 129 *nm = d->rr_data[0]+2; 130 *ln = dname_valid(*nm, d->rr_len[0]-2); 131 if(!*ln) { 132 *nm = 0; 133 *ln = 0; 134 return 0; 135 } 136 return 1; 137 } 138 139 /** 140 * For an NSEC that matches the DS queried for, check absence of DS type. 141 * 142 * @param nsec: NSEC for proof, must be trusted. 143 * @param qinfo: what is queried for. 144 * @return if secure the nsec proves that no DS is present, or 145 * insecure if it proves it is not a delegation point. 146 * or bogus if something was wrong. 147 */ 148 static enum sec_status 149 val_nsec_proves_no_ds(struct ub_packed_rrset_key* nsec, 150 struct query_info* qinfo) 151 { 152 log_assert(qinfo->qtype == LDNS_RR_TYPE_DS); 153 log_assert(ntohs(nsec->rk.type) == LDNS_RR_TYPE_NSEC); 154 155 if(nsec_has_type(nsec, LDNS_RR_TYPE_SOA) && qinfo->qname_len != 1) { 156 /* SOA present means that this is the NSEC from the child, 157 * not the parent (so it is the wrong one). */ 158 return sec_status_bogus; 159 } 160 if(nsec_has_type(nsec, LDNS_RR_TYPE_DS)) { 161 /* DS present means that there should have been a positive 162 * response to the DS query, so there is something wrong. */ 163 return sec_status_bogus; 164 } 165 166 if(!nsec_has_type(nsec, LDNS_RR_TYPE_NS)) { 167 /* If there is no NS at this point at all, then this 168 * doesn't prove anything one way or the other. */ 169 return sec_status_insecure; 170 } 171 /* Otherwise, this proves no DS. */ 172 return sec_status_secure; 173 } 174 175 /** check security status from cache or verify rrset, returns true if secure */ 176 static int 177 nsec_verify_rrset(struct module_env* env, struct val_env* ve, 178 struct ub_packed_rrset_key* nsec, struct key_entry_key* kkey, 179 char** reason) 180 { 181 struct packed_rrset_data* d = (struct packed_rrset_data*) 182 nsec->entry.data; 183 if(d->security == sec_status_secure) 184 return 1; 185 rrset_check_sec_status(env->rrset_cache, nsec, *env->now); 186 if(d->security == sec_status_secure) 187 return 1; 188 d->security = val_verify_rrset_entry(env, ve, nsec, kkey, reason); 189 if(d->security == sec_status_secure) { 190 rrset_update_sec_status(env->rrset_cache, nsec, *env->now); 191 return 1; 192 } 193 return 0; 194 } 195 196 enum sec_status 197 val_nsec_prove_nodata_dsreply(struct module_env* env, struct val_env* ve, 198 struct query_info* qinfo, struct reply_info* rep, 199 struct key_entry_key* kkey, time_t* proof_ttl, char** reason) 200 { 201 struct ub_packed_rrset_key* nsec = reply_find_rrset_section_ns( 202 rep, qinfo->qname, qinfo->qname_len, LDNS_RR_TYPE_NSEC, 203 qinfo->qclass); 204 enum sec_status sec; 205 size_t i; 206 uint8_t* wc = NULL, *ce = NULL; 207 int valid_nsec = 0; 208 struct ub_packed_rrset_key* wc_nsec = NULL; 209 210 /* If we have a NSEC at the same name, it must prove one 211 * of two things 212 * -- 213 * 1) this is a delegation point and there is no DS 214 * 2) this is not a delegation point */ 215 if(nsec) { 216 if(!nsec_verify_rrset(env, ve, nsec, kkey, reason)) { 217 verbose(VERB_ALGO, "NSEC RRset for the " 218 "referral did not verify."); 219 return sec_status_bogus; 220 } 221 sec = val_nsec_proves_no_ds(nsec, qinfo); 222 if(sec == sec_status_bogus) { 223 /* something was wrong. */ 224 *reason = "NSEC does not prove absence of DS"; 225 return sec; 226 } else if(sec == sec_status_insecure) { 227 /* this wasn't a delegation point. */ 228 return sec; 229 } else if(sec == sec_status_secure) { 230 /* this proved no DS. */ 231 *proof_ttl = ub_packed_rrset_ttl(nsec); 232 return sec; 233 } 234 /* if unchecked, fall through to next proof */ 235 } 236 237 /* Otherwise, there is no NSEC at qname. This could be an ENT. 238 * (ENT=empty non terminal). If not, this is broken. */ 239 240 /* verify NSEC rrsets in auth section */ 241 for(i=rep->an_numrrsets; i < rep->an_numrrsets+rep->ns_numrrsets; 242 i++) { 243 if(rep->rrsets[i]->rk.type != htons(LDNS_RR_TYPE_NSEC)) 244 continue; 245 if(!nsec_verify_rrset(env, ve, rep->rrsets[i], kkey, reason)) { 246 verbose(VERB_ALGO, "NSEC for empty non-terminal " 247 "did not verify."); 248 return sec_status_bogus; 249 } 250 if(nsec_proves_nodata(rep->rrsets[i], qinfo, &wc)) { 251 verbose(VERB_ALGO, "NSEC for empty non-terminal " 252 "proved no DS."); 253 *proof_ttl = rrset_get_ttl(rep->rrsets[i]); 254 if(wc && dname_is_wild(rep->rrsets[i]->rk.dname)) 255 wc_nsec = rep->rrsets[i]; 256 valid_nsec = 1; 257 } 258 if(val_nsec_proves_name_error(rep->rrsets[i], qinfo->qname)) { 259 ce = nsec_closest_encloser(qinfo->qname, 260 rep->rrsets[i]); 261 } 262 } 263 if(wc && !ce) 264 valid_nsec = 0; 265 else if(wc && ce) { 266 /* ce and wc must match */ 267 if(query_dname_compare(wc, ce) != 0) 268 valid_nsec = 0; 269 else if(!wc_nsec) 270 valid_nsec = 0; 271 } 272 if(valid_nsec) { 273 if(wc) { 274 /* check if this is a delegation */ 275 *reason = "NSEC for wildcard does not prove absence of DS"; 276 return val_nsec_proves_no_ds(wc_nsec, qinfo); 277 } 278 /* valid nsec proves empty nonterminal */ 279 return sec_status_insecure; 280 } 281 282 /* NSEC proof did not conlusively point to DS or no DS */ 283 return sec_status_unchecked; 284 } 285 286 int nsec_proves_nodata(struct ub_packed_rrset_key* nsec, 287 struct query_info* qinfo, uint8_t** wc) 288 { 289 log_assert(wc); 290 if(query_dname_compare(nsec->rk.dname, qinfo->qname) != 0) { 291 uint8_t* nm; 292 size_t ln; 293 294 /* empty-non-terminal checking. 295 * Done before wildcard, because this is an exact match, 296 * and would prevent a wildcard from matching. */ 297 298 /* If the nsec is proving that qname is an ENT, the nsec owner 299 * will be less than qname, and the next name will be a child 300 * domain of the qname. */ 301 if(!nsec_get_next(nsec, &nm, &ln)) 302 return 0; /* bad nsec */ 303 if(dname_strict_subdomain_c(nm, qinfo->qname) && 304 dname_canonical_compare(nsec->rk.dname, 305 qinfo->qname) < 0) { 306 return 1; /* proves ENT */ 307 } 308 309 /* wildcard checking. */ 310 311 /* If this is a wildcard NSEC, make sure that a) it was 312 * possible to have generated qname from the wildcard and 313 * b) the type map does not contain qtype. Note that this 314 * does NOT prove that this wildcard was the applicable 315 * wildcard. */ 316 if(dname_is_wild(nsec->rk.dname)) { 317 /* the purported closest encloser. */ 318 uint8_t* ce = nsec->rk.dname; 319 size_t ce_len = nsec->rk.dname_len; 320 dname_remove_label(&ce, &ce_len); 321 322 /* The qname must be a strict subdomain of the 323 * closest encloser, for the wildcard to apply 324 */ 325 if(dname_strict_subdomain_c(qinfo->qname, ce)) { 326 /* here we have a matching NSEC for the qname, 327 * perform matching NSEC checks */ 328 if(nsec_has_type(nsec, LDNS_RR_TYPE_CNAME)) { 329 /* should have gotten the wildcard CNAME */ 330 return 0; 331 } 332 if(nsec_has_type(nsec, LDNS_RR_TYPE_NS) && 333 !nsec_has_type(nsec, LDNS_RR_TYPE_SOA)) { 334 /* wrong parentside (wildcard) NSEC used */ 335 return 0; 336 } 337 if(nsec_has_type(nsec, qinfo->qtype)) { 338 return 0; 339 } 340 *wc = ce; 341 return 1; 342 } 343 } 344 345 /* Otherwise, this NSEC does not prove ENT and is not a 346 * wildcard, so it does not prove NODATA. */ 347 return 0; 348 } 349 350 /* If the qtype exists, then we should have gotten it. */ 351 if(nsec_has_type(nsec, qinfo->qtype)) { 352 return 0; 353 } 354 355 /* if the name is a CNAME node, then we should have gotten the CNAME*/ 356 if(nsec_has_type(nsec, LDNS_RR_TYPE_CNAME)) { 357 return 0; 358 } 359 360 /* If an NS set exists at this name, and NOT a SOA (so this is a 361 * zone cut, not a zone apex), then we should have gotten a 362 * referral (or we just got the wrong NSEC). 363 * The reverse of this check is used when qtype is DS, since that 364 * must use the NSEC from above the zone cut. */ 365 if(qinfo->qtype != LDNS_RR_TYPE_DS && 366 nsec_has_type(nsec, LDNS_RR_TYPE_NS) && 367 !nsec_has_type(nsec, LDNS_RR_TYPE_SOA)) { 368 return 0; 369 } else if(qinfo->qtype == LDNS_RR_TYPE_DS && 370 nsec_has_type(nsec, LDNS_RR_TYPE_SOA) && 371 !dname_is_root(qinfo->qname)) { 372 return 0; 373 } 374 375 return 1; 376 } 377 378 int 379 val_nsec_proves_name_error(struct ub_packed_rrset_key* nsec, uint8_t* qname) 380 { 381 uint8_t* owner = nsec->rk.dname; 382 uint8_t* next; 383 size_t nlen; 384 if(!nsec_get_next(nsec, &next, &nlen)) 385 return 0; 386 387 /* If NSEC owner == qname, then this NSEC proves that qname exists. */ 388 if(query_dname_compare(qname, owner) == 0) { 389 return 0; 390 } 391 392 /* If NSEC is a parent of qname, we need to check the type map 393 * If the parent name has a DNAME or is a delegation point, then 394 * this NSEC is being misused. */ 395 if(dname_subdomain_c(qname, owner) && 396 (nsec_has_type(nsec, LDNS_RR_TYPE_DNAME) || 397 (nsec_has_type(nsec, LDNS_RR_TYPE_NS) 398 && !nsec_has_type(nsec, LDNS_RR_TYPE_SOA)) 399 )) { 400 return 0; 401 } 402 403 if(query_dname_compare(owner, next) == 0) { 404 /* this nsec is the only nsec */ 405 /* zone.name NSEC zone.name, disproves everything else */ 406 /* but only for subdomains of that zone */ 407 if(dname_strict_subdomain_c(qname, next)) 408 return 1; 409 } 410 else if(dname_canonical_compare(owner, next) > 0) { 411 /* this is the last nsec, ....(bigger) NSEC zonename(smaller) */ 412 /* the names after the last (owner) name do not exist 413 * there are no names before the zone name in the zone 414 * but the qname must be a subdomain of the zone name(next). */ 415 if(dname_canonical_compare(owner, qname) < 0 && 416 dname_strict_subdomain_c(qname, next)) 417 return 1; 418 } else { 419 /* regular NSEC, (smaller) NSEC (larger) */ 420 if(dname_canonical_compare(owner, qname) < 0 && 421 dname_canonical_compare(qname, next) < 0) { 422 return 1; 423 } 424 } 425 return 0; 426 } 427 428 int val_nsec_proves_insecuredelegation(struct ub_packed_rrset_key* nsec, 429 struct query_info* qinfo) 430 { 431 if(nsec_has_type(nsec, LDNS_RR_TYPE_NS) && 432 !nsec_has_type(nsec, LDNS_RR_TYPE_DS) && 433 !nsec_has_type(nsec, LDNS_RR_TYPE_SOA)) { 434 /* see if nsec signals an insecure delegation */ 435 if(qinfo->qtype == LDNS_RR_TYPE_DS) { 436 /* if type is DS and qname is equal to nsec, then it 437 * is an exact match nsec, result not insecure */ 438 if(dname_strict_subdomain_c(qinfo->qname, 439 nsec->rk.dname)) 440 return 1; 441 } else { 442 if(dname_subdomain_c(qinfo->qname, nsec->rk.dname)) 443 return 1; 444 } 445 } 446 return 0; 447 } 448 449 uint8_t* 450 nsec_closest_encloser(uint8_t* qname, struct ub_packed_rrset_key* nsec) 451 { 452 uint8_t* next; 453 size_t nlen; 454 uint8_t* common1, *common2; 455 if(!nsec_get_next(nsec, &next, &nlen)) 456 return NULL; 457 /* longest common with owner or next name */ 458 common1 = dname_get_shared_topdomain(nsec->rk.dname, qname); 459 common2 = dname_get_shared_topdomain(next, qname); 460 if(dname_count_labels(common1) > dname_count_labels(common2)) 461 return common1; 462 return common2; 463 } 464 465 int val_nsec_proves_positive_wildcard(struct ub_packed_rrset_key* nsec, 466 struct query_info* qinf, uint8_t* wc) 467 { 468 uint8_t* ce; 469 /* 1) prove that qname doesn't exist and 470 * 2) that the correct wildcard was used 471 * nsec has been verified already. */ 472 if(!val_nsec_proves_name_error(nsec, qinf->qname)) 473 return 0; 474 /* check wildcard name */ 475 ce = nsec_closest_encloser(qinf->qname, nsec); 476 if(!ce) 477 return 0; 478 if(query_dname_compare(wc, ce) != 0) { 479 return 0; 480 } 481 return 1; 482 } 483 484 int 485 val_nsec_proves_no_wc(struct ub_packed_rrset_key* nsec, uint8_t* qname, 486 size_t qnamelen) 487 { 488 /* Determine if a NSEC record proves the non-existence of a 489 * wildcard that could have produced qname. */ 490 int labs; 491 int i; 492 uint8_t* ce = nsec_closest_encloser(qname, nsec); 493 uint8_t* strip; 494 size_t striplen; 495 uint8_t buf[LDNS_MAX_DOMAINLEN+3]; 496 if(!ce) 497 return 0; 498 /* we can subtract the closest encloser count - since that is the 499 * largest shared topdomain with owner and next NSEC name, 500 * because the NSEC is no proof for names shorter than the owner 501 * and next names. */ 502 labs = dname_count_labels(qname) - dname_count_labels(ce); 503 504 for(i=labs; i>0; i--) { 505 /* i is number of labels to strip off qname, prepend * wild */ 506 strip = qname; 507 striplen = qnamelen; 508 dname_remove_labels(&strip, &striplen, i); 509 if(striplen > LDNS_MAX_DOMAINLEN-2) 510 continue; /* too long to prepend wildcard */ 511 buf[0] = 1; 512 buf[1] = (uint8_t)'*'; 513 memmove(buf+2, strip, striplen); 514 if(val_nsec_proves_name_error(nsec, buf)) { 515 return 1; 516 } 517 } 518 return 0; 519 } 520 521 /** 522 * Find shared topdomain that exists 523 */ 524 static void 525 dlv_topdomain(struct ub_packed_rrset_key* nsec, uint8_t* qname, 526 uint8_t** nm, size_t* nm_len) 527 { 528 /* make sure reply is part of nm */ 529 /* take shared topdomain with left of NSEC. */ 530 531 /* because, if empty nonterminal, then right is subdomain of qname. 532 * and any shared topdomain would be empty nonterminals. 533 * 534 * If nxdomain, then the right is bigger, and could have an 535 * interesting shared topdomain, but if it does have one, it is 536 * an empty nonterminal. An empty nonterminal shared with the left 537 * one. */ 538 int n; 539 uint8_t* common = dname_get_shared_topdomain(qname, nsec->rk.dname); 540 n = dname_count_labels(*nm) - dname_count_labels(common); 541 dname_remove_labels(nm, nm_len, n); 542 } 543 544 int val_nsec_check_dlv(struct query_info* qinfo, 545 struct reply_info* rep, uint8_t** nm, size_t* nm_len) 546 { 547 uint8_t* next; 548 size_t i, nlen; 549 int c; 550 /* we should now have a NOERROR/NODATA or NXDOMAIN message */ 551 if(rep->an_numrrsets != 0) { 552 return 0; 553 } 554 /* is this NOERROR ? */ 555 if(FLAGS_GET_RCODE(rep->flags) == LDNS_RCODE_NOERROR) { 556 /* it can be a plain NSEC match - go up one more level. */ 557 /* or its an empty nonterminal - go up to nonempty level */ 558 for(i=0; i<rep->ns_numrrsets; i++) { 559 if(htons(rep->rrsets[i]->rk.type)!=LDNS_RR_TYPE_NSEC || 560 !nsec_get_next(rep->rrsets[i], &next, &nlen)) 561 continue; 562 c = dname_canonical_compare( 563 rep->rrsets[i]->rk.dname, qinfo->qname); 564 if(c == 0) { 565 /* plain match */ 566 if(nsec_has_type(rep->rrsets[i], 567 LDNS_RR_TYPE_DLV)) 568 return 0; 569 dname_remove_label(nm, nm_len); 570 return 1; 571 } else if(c < 0 && 572 dname_strict_subdomain_c(next, qinfo->qname)) { 573 /* ENT */ 574 dlv_topdomain(rep->rrsets[i], qinfo->qname, 575 nm, nm_len); 576 return 1; 577 } 578 } 579 return 0; 580 } 581 582 /* is this NXDOMAIN ? */ 583 if(FLAGS_GET_RCODE(rep->flags) == LDNS_RCODE_NXDOMAIN) { 584 /* find the qname denial NSEC record. It can tell us 585 * a closest encloser name; or that we not need bother */ 586 for(i=0; i<rep->ns_numrrsets; i++) { 587 if(htons(rep->rrsets[i]->rk.type) != LDNS_RR_TYPE_NSEC) 588 continue; 589 if(val_nsec_proves_name_error(rep->rrsets[i], 590 qinfo->qname)) { 591 log_nametypeclass(VERB_ALGO, "topdomain on", 592 rep->rrsets[i]->rk.dname, 593 ntohs(rep->rrsets[i]->rk.type), 0); 594 dlv_topdomain(rep->rrsets[i], qinfo->qname, 595 nm, nm_len); 596 return 1; 597 } 598 } 599 return 0; 600 } 601 return 0; 602 } 603