1 /* 2 * validator/val_nsec.c - validator NSEC denial of existence 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 existence, 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, struct module_qstate* qstate) 180 { 181 struct packed_rrset_data* d = (struct packed_rrset_data*) 182 nsec->entry.data; 183 if(!d) return 0; 184 if(d->security == sec_status_secure) 185 return 1; 186 rrset_check_sec_status(env->rrset_cache, nsec, *env->now); 187 if(d->security == sec_status_secure) 188 return 1; 189 d->security = val_verify_rrset_entry(env, ve, nsec, kkey, reason, 190 LDNS_SECTION_AUTHORITY, qstate); 191 if(d->security == sec_status_secure) { 192 rrset_update_sec_status(env->rrset_cache, nsec, *env->now); 193 return 1; 194 } 195 return 0; 196 } 197 198 enum sec_status 199 val_nsec_prove_nodata_dsreply(struct module_env* env, struct val_env* ve, 200 struct query_info* qinfo, struct reply_info* rep, 201 struct key_entry_key* kkey, time_t* proof_ttl, char** reason, 202 struct module_qstate* qstate) 203 { 204 struct ub_packed_rrset_key* nsec = reply_find_rrset_section_ns( 205 rep, qinfo->qname, qinfo->qname_len, LDNS_RR_TYPE_NSEC, 206 qinfo->qclass); 207 enum sec_status sec; 208 size_t i; 209 uint8_t* wc = NULL, *ce = NULL; 210 int valid_nsec = 0; 211 struct ub_packed_rrset_key* wc_nsec = NULL; 212 213 /* If we have a NSEC at the same name, it must prove one 214 * of two things 215 * -- 216 * 1) this is a delegation point and there is no DS 217 * 2) this is not a delegation point */ 218 if(nsec) { 219 if(!nsec_verify_rrset(env, ve, nsec, kkey, reason, qstate)) { 220 verbose(VERB_ALGO, "NSEC RRset for the " 221 "referral did not verify."); 222 return sec_status_bogus; 223 } 224 sec = val_nsec_proves_no_ds(nsec, qinfo); 225 if(sec == sec_status_bogus) { 226 /* something was wrong. */ 227 *reason = "NSEC does not prove absence of DS"; 228 return sec; 229 } else if(sec == sec_status_insecure) { 230 /* this wasn't a delegation point. */ 231 return sec; 232 } else if(sec == sec_status_secure) { 233 /* this proved no DS. */ 234 *proof_ttl = ub_packed_rrset_ttl(nsec); 235 return sec; 236 } 237 /* if unchecked, fall through to next proof */ 238 } 239 240 /* Otherwise, there is no NSEC at qname. This could be an ENT. 241 * (ENT=empty non terminal). If not, this is broken. */ 242 243 /* verify NSEC rrsets in auth section */ 244 for(i=rep->an_numrrsets; i < rep->an_numrrsets+rep->ns_numrrsets; 245 i++) { 246 if(rep->rrsets[i]->rk.type != htons(LDNS_RR_TYPE_NSEC)) 247 continue; 248 if(!nsec_verify_rrset(env, ve, rep->rrsets[i], kkey, reason, 249 qstate)) { 250 verbose(VERB_ALGO, "NSEC for empty non-terminal " 251 "did not verify."); 252 return sec_status_bogus; 253 } 254 if(nsec_proves_nodata(rep->rrsets[i], qinfo, &wc)) { 255 verbose(VERB_ALGO, "NSEC for empty non-terminal " 256 "proved no DS."); 257 *proof_ttl = rrset_get_ttl(rep->rrsets[i]); 258 if(wc && dname_is_wild(rep->rrsets[i]->rk.dname)) 259 wc_nsec = rep->rrsets[i]; 260 valid_nsec = 1; 261 } 262 if(val_nsec_proves_name_error(rep->rrsets[i], qinfo->qname)) { 263 ce = nsec_closest_encloser(qinfo->qname, 264 rep->rrsets[i]); 265 } 266 } 267 if(wc && !ce) 268 valid_nsec = 0; 269 else if(wc && ce) { 270 /* ce and wc must match */ 271 if(query_dname_compare(wc, ce) != 0) 272 valid_nsec = 0; 273 else if(!wc_nsec) 274 valid_nsec = 0; 275 } 276 if(valid_nsec) { 277 if(wc) { 278 /* check if this is a delegation */ 279 *reason = "NSEC for wildcard does not prove absence of DS"; 280 return val_nsec_proves_no_ds(wc_nsec, qinfo); 281 } 282 /* valid nsec proves empty nonterminal */ 283 return sec_status_insecure; 284 } 285 286 /* NSEC proof did not conclusively point to DS or no DS */ 287 return sec_status_unchecked; 288 } 289 290 int nsec_proves_nodata(struct ub_packed_rrset_key* nsec, 291 struct query_info* qinfo, uint8_t** wc) 292 { 293 log_assert(wc); 294 if(query_dname_compare(nsec->rk.dname, qinfo->qname) != 0) { 295 uint8_t* nm; 296 size_t ln; 297 298 /* empty-non-terminal checking. 299 * Done before wildcard, because this is an exact match, 300 * and would prevent a wildcard from matching. */ 301 302 /* If the nsec is proving that qname is an ENT, the nsec owner 303 * will be less than qname, and the next name will be a child 304 * domain of the qname. */ 305 if(!nsec_get_next(nsec, &nm, &ln)) 306 return 0; /* bad nsec */ 307 if(dname_strict_subdomain_c(nm, qinfo->qname) && 308 dname_canonical_compare(nsec->rk.dname, 309 qinfo->qname) < 0) { 310 return 1; /* proves ENT */ 311 } 312 313 /* wildcard checking. */ 314 315 /* If this is a wildcard NSEC, make sure that a) it was 316 * possible to have generated qname from the wildcard and 317 * b) the type map does not contain qtype. Note that this 318 * does NOT prove that this wildcard was the applicable 319 * wildcard. */ 320 if(dname_is_wild(nsec->rk.dname)) { 321 /* the purported closest encloser. */ 322 uint8_t* ce = nsec->rk.dname; 323 size_t ce_len = nsec->rk.dname_len; 324 dname_remove_label(&ce, &ce_len); 325 326 /* The qname must be a strict subdomain of the 327 * closest encloser, for the wildcard to apply 328 */ 329 if(dname_strict_subdomain_c(qinfo->qname, ce)) { 330 /* here we have a matching NSEC for the qname, 331 * perform matching NSEC checks */ 332 if(nsec_has_type(nsec, LDNS_RR_TYPE_CNAME)) { 333 /* should have gotten the wildcard CNAME */ 334 return 0; 335 } 336 if(nsec_has_type(nsec, LDNS_RR_TYPE_NS) && 337 !nsec_has_type(nsec, LDNS_RR_TYPE_SOA)) { 338 /* wrong parentside (wildcard) NSEC used */ 339 return 0; 340 } 341 if(nsec_has_type(nsec, qinfo->qtype)) { 342 return 0; 343 } 344 *wc = ce; 345 return 1; 346 } 347 } else { 348 /* See if the next owner name covers a wildcard 349 * empty non-terminal. */ 350 while (dname_canonical_compare(nsec->rk.dname, nm) < 0) { 351 /* wildcard does not apply if qname below 352 * the name that exists under the '*' */ 353 if (dname_subdomain_c(qinfo->qname, nm)) 354 break; 355 /* but if it is a wildcard and qname is below 356 * it, then the wildcard applies. The wildcard 357 * is an empty nonterminal. nodata proven. */ 358 if (dname_is_wild(nm)) { 359 size_t ce_len = ln; 360 uint8_t* ce = nm; 361 dname_remove_label(&ce, &ce_len); 362 if(dname_strict_subdomain_c(qinfo->qname, ce)) { 363 *wc = ce; 364 return 1; 365 } 366 } 367 dname_remove_label(&nm, &ln); 368 } 369 } 370 371 /* Otherwise, this NSEC does not prove ENT and is not a 372 * wildcard, so it does not prove NODATA. */ 373 return 0; 374 } 375 376 /* If the qtype exists, then we should have gotten it. */ 377 if(nsec_has_type(nsec, qinfo->qtype)) { 378 return 0; 379 } 380 381 /* if the name is a CNAME node, then we should have gotten the CNAME*/ 382 if(nsec_has_type(nsec, LDNS_RR_TYPE_CNAME)) { 383 return 0; 384 } 385 386 /* If an NS set exists at this name, and NOT a SOA (so this is a 387 * zone cut, not a zone apex), then we should have gotten a 388 * referral (or we just got the wrong NSEC). 389 * The reverse of this check is used when qtype is DS, since that 390 * must use the NSEC from above the zone cut. */ 391 if(qinfo->qtype != LDNS_RR_TYPE_DS && 392 nsec_has_type(nsec, LDNS_RR_TYPE_NS) && 393 !nsec_has_type(nsec, LDNS_RR_TYPE_SOA)) { 394 return 0; 395 } else if(qinfo->qtype == LDNS_RR_TYPE_DS && 396 nsec_has_type(nsec, LDNS_RR_TYPE_SOA) && 397 !dname_is_root(qinfo->qname)) { 398 return 0; 399 } 400 401 return 1; 402 } 403 404 int 405 val_nsec_proves_name_error(struct ub_packed_rrset_key* nsec, uint8_t* qname) 406 { 407 uint8_t* owner = nsec->rk.dname; 408 uint8_t* next; 409 size_t nlen; 410 if(!nsec_get_next(nsec, &next, &nlen)) 411 return 0; 412 413 /* If NSEC owner == qname, then this NSEC proves that qname exists. */ 414 if(query_dname_compare(qname, owner) == 0) { 415 return 0; 416 } 417 418 /* If NSEC is a parent of qname, we need to check the type map 419 * If the parent name has a DNAME or is a delegation point, then 420 * this NSEC is being misused. */ 421 if(dname_subdomain_c(qname, owner) && 422 (nsec_has_type(nsec, LDNS_RR_TYPE_DNAME) || 423 (nsec_has_type(nsec, LDNS_RR_TYPE_NS) 424 && !nsec_has_type(nsec, LDNS_RR_TYPE_SOA)) 425 )) { 426 return 0; 427 } 428 429 if(query_dname_compare(owner, next) == 0) { 430 /* this nsec is the only nsec */ 431 /* zone.name NSEC zone.name, disproves everything else */ 432 /* but only for subdomains of that zone */ 433 if(dname_strict_subdomain_c(qname, next)) 434 return 1; 435 } 436 else if(dname_canonical_compare(owner, next) > 0) { 437 /* this is the last nsec, ....(bigger) NSEC zonename(smaller) */ 438 /* the names after the last (owner) name do not exist 439 * there are no names before the zone name in the zone 440 * but the qname must be a subdomain of the zone name(next). */ 441 if(dname_canonical_compare(owner, qname) < 0 && 442 dname_strict_subdomain_c(qname, next)) 443 return 1; 444 } else { 445 /* regular NSEC, (smaller) NSEC (larger) */ 446 if(dname_canonical_compare(owner, qname) < 0 && 447 dname_canonical_compare(qname, next) < 0) { 448 return 1; 449 } 450 } 451 return 0; 452 } 453 454 int val_nsec_proves_insecuredelegation(struct ub_packed_rrset_key* nsec, 455 struct query_info* qinfo) 456 { 457 if(nsec_has_type(nsec, LDNS_RR_TYPE_NS) && 458 !nsec_has_type(nsec, LDNS_RR_TYPE_DS) && 459 !nsec_has_type(nsec, LDNS_RR_TYPE_SOA)) { 460 /* see if nsec signals an insecure delegation */ 461 if(qinfo->qtype == LDNS_RR_TYPE_DS) { 462 /* if type is DS and qname is equal to nsec, then it 463 * is an exact match nsec, result not insecure */ 464 if(dname_strict_subdomain_c(qinfo->qname, 465 nsec->rk.dname)) 466 return 1; 467 } else { 468 if(dname_subdomain_c(qinfo->qname, nsec->rk.dname)) 469 return 1; 470 } 471 } 472 return 0; 473 } 474 475 uint8_t* 476 nsec_closest_encloser(uint8_t* qname, struct ub_packed_rrset_key* nsec) 477 { 478 uint8_t* next; 479 size_t nlen; 480 uint8_t* common1, *common2; 481 if(!nsec_get_next(nsec, &next, &nlen)) 482 return NULL; 483 /* longest common with owner or next name */ 484 common1 = dname_get_shared_topdomain(nsec->rk.dname, qname); 485 common2 = dname_get_shared_topdomain(next, qname); 486 if(dname_count_labels(common1) > dname_count_labels(common2)) 487 return common1; 488 return common2; 489 } 490 491 int val_nsec_proves_positive_wildcard(struct ub_packed_rrset_key* nsec, 492 struct query_info* qinf, uint8_t* wc) 493 { 494 uint8_t* ce; 495 /* 1) prove that qname doesn't exist and 496 * 2) that the correct wildcard was used 497 * nsec has been verified already. */ 498 if(!val_nsec_proves_name_error(nsec, qinf->qname)) 499 return 0; 500 /* check wildcard name */ 501 ce = nsec_closest_encloser(qinf->qname, nsec); 502 if(!ce) 503 return 0; 504 if(query_dname_compare(wc, ce) != 0) { 505 return 0; 506 } 507 return 1; 508 } 509 510 int 511 val_nsec_proves_no_wc(struct ub_packed_rrset_key* nsec, uint8_t* qname, 512 size_t qnamelen) 513 { 514 /* Determine if a NSEC record proves the non-existence of a 515 * wildcard that could have produced qname. */ 516 int labs; 517 uint8_t* ce = nsec_closest_encloser(qname, nsec); 518 uint8_t* strip; 519 size_t striplen; 520 uint8_t buf[LDNS_MAX_DOMAINLEN+3]; 521 if(!ce) 522 return 0; 523 /* we can subtract the closest encloser count - since that is the 524 * largest shared topdomain with owner and next NSEC name, 525 * because the NSEC is no proof for names shorter than the owner 526 * and next names. */ 527 labs = dname_count_labels(qname) - dname_count_labels(ce); 528 529 if(labs > 0) { 530 /* i is number of labels to strip off qname, prepend * wild */ 531 strip = qname; 532 striplen = qnamelen; 533 dname_remove_labels(&strip, &striplen, labs); 534 if(striplen > LDNS_MAX_DOMAINLEN-2) 535 return 0; /* too long to prepend wildcard */ 536 buf[0] = 1; 537 buf[1] = (uint8_t)'*'; 538 memmove(buf+2, strip, striplen); 539 if(val_nsec_proves_name_error(nsec, buf)) { 540 return 1; 541 } 542 } 543 return 0; 544 } 545