| 1 | /************************************************* |
| 2 | * Exim - an Internet mail transport agent * |
| 3 | *************************************************/ |
| 4 | |
| 5 | /* Copyright (c) University of Cambridge 1995 - 2013 */ |
| 6 | /* See the file NOTICE for conditions of use and distribution. */ |
| 7 | |
| 8 | /* Functions for interfacing with the DNS. */ |
| 9 | |
| 10 | #include "exim.h" |
| 11 | |
| 12 | |
| 13 | /* Function declaration needed for mutual recursion when A6 records |
| 14 | are supported. */ |
| 15 | |
| 16 | #if HAVE_IPV6 |
| 17 | #ifdef SUPPORT_A6 |
| 18 | static void dns_complete_a6(dns_address ***, dns_answer *, dns_record *, |
| 19 | int, uschar *); |
| 20 | #endif |
| 21 | #endif |
| 22 | |
| 23 | |
| 24 | /************************************************* |
| 25 | * Fake DNS resolver * |
| 26 | *************************************************/ |
| 27 | |
| 28 | /* This function is called instead of res_search() when Exim is running in its |
| 29 | test harness. It recognizes some special domain names, and uses them to force |
| 30 | failure and retry responses (optionally with a delay). Otherwise, it calls an |
| 31 | external utility that mocks-up a nameserver, if it can find the utility. |
| 32 | If not, it passes its arguments on to res_search(). The fake nameserver may |
| 33 | also return a code specifying that the name should be passed on. |
| 34 | |
| 35 | Background: the original test suite required a real nameserver to carry the |
| 36 | test zones, whereas the new test suit has the fake server for portability. This |
| 37 | code supports both. |
| 38 | |
| 39 | Arguments: |
| 40 | domain the domain name |
| 41 | type the DNS record type |
| 42 | answerptr where to put the answer |
| 43 | size size of the answer area |
| 44 | |
| 45 | Returns: length of returned data, or -1 on error (h_errno set) |
| 46 | */ |
| 47 | |
| 48 | static int |
| 49 | fakens_search(uschar *domain, int type, uschar *answerptr, int size) |
| 50 | { |
| 51 | int len = Ustrlen(domain); |
| 52 | int asize = size; /* Locally modified */ |
| 53 | uschar *endname; |
| 54 | uschar name[256]; |
| 55 | uschar utilname[256]; |
| 56 | uschar *aptr = answerptr; /* Locally modified */ |
| 57 | struct stat statbuf; |
| 58 | |
| 59 | /* Remove terminating dot. */ |
| 60 | |
| 61 | if (domain[len - 1] == '.') len--; |
| 62 | Ustrncpy(name, domain, len); |
| 63 | name[len] = 0; |
| 64 | endname = name + len; |
| 65 | |
| 66 | /* This code, for forcing TRY_AGAIN and NO_RECOVERY, is here so that it works |
| 67 | for the old test suite that uses a real nameserver. When the old test suite is |
| 68 | eventually abandoned, this code could be moved into the fakens utility. */ |
| 69 | |
| 70 | if (len >= 14 && Ustrcmp(endname - 14, "test.again.dns") == 0) |
| 71 | { |
| 72 | int delay = Uatoi(name); /* digits at the start of the name */ |
| 73 | DEBUG(D_dns) debug_printf("Return from DNS lookup of %s (%s) faked for testing\n", |
| 74 | name, dns_text_type(type)); |
| 75 | if (delay > 0) |
| 76 | { |
| 77 | DEBUG(D_dns) debug_printf("delaying %d seconds\n", delay); |
| 78 | sleep(delay); |
| 79 | } |
| 80 | h_errno = TRY_AGAIN; |
| 81 | return -1; |
| 82 | } |
| 83 | |
| 84 | if (len >= 13 && Ustrcmp(endname - 13, "test.fail.dns") == 0) |
| 85 | { |
| 86 | DEBUG(D_dns) debug_printf("Return from DNS lookup of %s (%s) faked for testing\n", |
| 87 | name, dns_text_type(type)); |
| 88 | h_errno = NO_RECOVERY; |
| 89 | return -1; |
| 90 | } |
| 91 | |
| 92 | /* Look for the fakens utility, and if it exists, call it. */ |
| 93 | |
| 94 | (void)string_format(utilname, sizeof(utilname), "%s/../bin/fakens", |
| 95 | spool_directory); |
| 96 | |
| 97 | if (stat(CS utilname, &statbuf) >= 0) |
| 98 | { |
| 99 | pid_t pid; |
| 100 | int infd, outfd, rc; |
| 101 | uschar *argv[5]; |
| 102 | |
| 103 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) using fakens\n", |
| 104 | name, dns_text_type(type)); |
| 105 | |
| 106 | argv[0] = utilname; |
| 107 | argv[1] = spool_directory; |
| 108 | argv[2] = name; |
| 109 | argv[3] = dns_text_type(type); |
| 110 | argv[4] = NULL; |
| 111 | |
| 112 | pid = child_open(argv, NULL, 0000, &infd, &outfd, FALSE); |
| 113 | if (pid < 0) |
| 114 | log_write(0, LOG_MAIN|LOG_PANIC_DIE, "failed to run fakens: %s", |
| 115 | strerror(errno)); |
| 116 | |
| 117 | len = 0; |
| 118 | rc = -1; |
| 119 | while (asize > 0 && (rc = read(outfd, aptr, asize)) > 0) |
| 120 | { |
| 121 | len += rc; |
| 122 | aptr += rc; /* Don't modify the actual arguments, because they */ |
| 123 | asize -= rc; /* may need to be passed on to res_search(). */ |
| 124 | } |
| 125 | |
| 126 | if (rc < 0) |
| 127 | log_write(0, LOG_MAIN|LOG_PANIC_DIE, "read from fakens failed: %s", |
| 128 | strerror(errno)); |
| 129 | |
| 130 | switch(child_close(pid, 0)) |
| 131 | { |
| 132 | case 0: return len; |
| 133 | case 1: h_errno = HOST_NOT_FOUND; return -1; |
| 134 | case 2: h_errno = TRY_AGAIN; return -1; |
| 135 | default: |
| 136 | case 3: h_errno = NO_RECOVERY; return -1; |
| 137 | case 4: h_errno = NO_DATA; return -1; |
| 138 | case 5: /* Pass on to res_search() */ |
| 139 | DEBUG(D_dns) debug_printf("fakens returned PASS_ON\n"); |
| 140 | } |
| 141 | } |
| 142 | |
| 143 | /* fakens utility not found, or it returned "pass on" */ |
| 144 | |
| 145 | DEBUG(D_dns) debug_printf("passing %s on to res_search()\n", domain); |
| 146 | |
| 147 | return res_search(CS domain, C_IN, type, answerptr, size); |
| 148 | } |
| 149 | |
| 150 | |
| 151 | |
| 152 | /************************************************* |
| 153 | * Initialize and configure resolver * |
| 154 | *************************************************/ |
| 155 | |
| 156 | /* Initialize the resolver and the storage for holding DNS answers if this is |
| 157 | the first time we have been here, and set the resolver options. |
| 158 | |
| 159 | Arguments: |
| 160 | qualify_single TRUE to set the RES_DEFNAMES option |
| 161 | search_parents TRUE to set the RES_DNSRCH option |
| 162 | |
| 163 | Returns: nothing |
| 164 | */ |
| 165 | |
| 166 | void |
| 167 | dns_init(BOOL qualify_single, BOOL search_parents) |
| 168 | { |
| 169 | res_state resp = os_get_dns_resolver_res(); |
| 170 | |
| 171 | if ((resp->options & RES_INIT) == 0) |
| 172 | { |
| 173 | DEBUG(D_resolver) resp->options |= RES_DEBUG; /* For Cygwin */ |
| 174 | os_put_dns_resolver_res(resp); |
| 175 | res_init(); |
| 176 | DEBUG(D_resolver) resp->options |= RES_DEBUG; |
| 177 | os_put_dns_resolver_res(resp); |
| 178 | } |
| 179 | |
| 180 | resp->options &= ~(RES_DNSRCH | RES_DEFNAMES); |
| 181 | resp->options |= (qualify_single? RES_DEFNAMES : 0) | |
| 182 | (search_parents? RES_DNSRCH : 0); |
| 183 | if (dns_retrans > 0) resp->retrans = dns_retrans; |
| 184 | if (dns_retry > 0) resp->retry = dns_retry; |
| 185 | |
| 186 | #ifdef RES_USE_EDNS0 |
| 187 | if (dns_use_edns0 >= 0) |
| 188 | { |
| 189 | if (dns_use_edns0) |
| 190 | resp->options |= RES_USE_EDNS0; |
| 191 | else |
| 192 | resp->options &= ~RES_USE_EDNS0; |
| 193 | DEBUG(D_resolver) |
| 194 | debug_printf("Coerced resolver EDNS0 support %s.\n", |
| 195 | dns_use_edns0 ? "on" : "off"); |
| 196 | } |
| 197 | #else |
| 198 | if (dns_use_edns0 >= 0) |
| 199 | DEBUG(D_resolver) |
| 200 | debug_printf("Unable to %sset EDNS0 without resolver support.\n", |
| 201 | dns_use_edns0 ? "" : "un"); |
| 202 | #endif |
| 203 | |
| 204 | #ifndef DISABLE_DNSSEC |
| 205 | # ifdef RES_USE_DNSSEC |
| 206 | # ifndef RES_USE_EDNS0 |
| 207 | # error Have RES_USE_DNSSEC but not RES_USE_EDNS0? Something hinky ... |
| 208 | # endif |
| 209 | if (dns_dnssec_ok >= 0) |
| 210 | { |
| 211 | if (dns_use_edns0 == 0 && dns_dnssec_ok != 0) |
| 212 | { |
| 213 | DEBUG(D_resolver) |
| 214 | debug_printf("CONFLICT: dns_use_edns0 forced false, dns_dnssec_ok forced true, ignoring latter!\n"); |
| 215 | } |
| 216 | else |
| 217 | { |
| 218 | if (dns_dnssec_ok) |
| 219 | resp->options |= RES_USE_DNSSEC; |
| 220 | else |
| 221 | resp->options &= ~RES_USE_DNSSEC; |
| 222 | DEBUG(D_resolver) debug_printf("Coerced resolver DNSSEC support %s.\n", |
| 223 | dns_dnssec_ok ? "on" : "off"); |
| 224 | } |
| 225 | } |
| 226 | # else |
| 227 | if (dns_dnssec_ok >= 0) |
| 228 | DEBUG(D_resolver) |
| 229 | debug_printf("Unable to %sset DNSSEC without resolver support.\n", |
| 230 | dns_dnssec_ok ? "" : "un"); |
| 231 | # endif |
| 232 | #endif /* DISABLE_DNSSEC */ |
| 233 | |
| 234 | os_put_dns_resolver_res(resp); |
| 235 | } |
| 236 | |
| 237 | |
| 238 | |
| 239 | /************************************************* |
| 240 | * Build key name for PTR records * |
| 241 | *************************************************/ |
| 242 | |
| 243 | /* This function inverts an IP address and adds the relevant domain, to produce |
| 244 | a name that can be used to look up PTR records. |
| 245 | |
| 246 | Arguments: |
| 247 | string the IP address as a string |
| 248 | buffer a suitable buffer, long enough to hold the result |
| 249 | |
| 250 | Returns: nothing |
| 251 | */ |
| 252 | |
| 253 | void |
| 254 | dns_build_reverse(uschar *string, uschar *buffer) |
| 255 | { |
| 256 | uschar *p = string + Ustrlen(string); |
| 257 | uschar *pp = buffer; |
| 258 | |
| 259 | /* Handle IPv4 address */ |
| 260 | |
| 261 | #if HAVE_IPV6 |
| 262 | if (Ustrchr(string, ':') == NULL) |
| 263 | #endif |
| 264 | { |
| 265 | int i; |
| 266 | for (i = 0; i < 4; i++) |
| 267 | { |
| 268 | uschar *ppp = p; |
| 269 | while (ppp > string && ppp[-1] != '.') ppp--; |
| 270 | Ustrncpy(pp, ppp, p - ppp); |
| 271 | pp += p - ppp; |
| 272 | *pp++ = '.'; |
| 273 | p = ppp - 1; |
| 274 | } |
| 275 | Ustrcpy(pp, "in-addr.arpa"); |
| 276 | } |
| 277 | |
| 278 | /* Handle IPv6 address; convert to binary so as to fill out any |
| 279 | abbreviation in the textual form. */ |
| 280 | |
| 281 | #if HAVE_IPV6 |
| 282 | else |
| 283 | { |
| 284 | int i; |
| 285 | int v6[4]; |
| 286 | (void)host_aton(string, v6); |
| 287 | |
| 288 | /* The original specification for IPv6 reverse lookup was to invert each |
| 289 | nibble, and look in the ip6.int domain. The domain was subsequently |
| 290 | changed to ip6.arpa. */ |
| 291 | |
| 292 | for (i = 3; i >= 0; i--) |
| 293 | { |
| 294 | int j; |
| 295 | for (j = 0; j < 32; j += 4) |
| 296 | { |
| 297 | sprintf(CS pp, "%x.", (v6[i] >> j) & 15); |
| 298 | pp += 2; |
| 299 | } |
| 300 | } |
| 301 | Ustrcpy(pp, "ip6.arpa."); |
| 302 | |
| 303 | /* Another way of doing IPv6 reverse lookups was proposed in conjunction |
| 304 | with A6 records. However, it fell out of favour when they did. The |
| 305 | alternative was to construct a binary key, and look in ip6.arpa. I tried |
| 306 | to make this code do that, but I could not make it work on Solaris 8. The |
| 307 | resolver seems to lose the initial backslash somehow. However, now that |
| 308 | this style of reverse lookup has been dropped, it doesn't matter. These |
| 309 | lines are left here purely for historical interest. */ |
| 310 | |
| 311 | /************************************************** |
| 312 | Ustrcpy(pp, "\\[x"); |
| 313 | pp += 3; |
| 314 | |
| 315 | for (i = 0; i < 4; i++) |
| 316 | { |
| 317 | sprintf(pp, "%08X", v6[i]); |
| 318 | pp += 8; |
| 319 | } |
| 320 | Ustrcpy(pp, "].ip6.arpa."); |
| 321 | **************************************************/ |
| 322 | |
| 323 | } |
| 324 | #endif |
| 325 | } |
| 326 | |
| 327 | |
| 328 | |
| 329 | |
| 330 | /************************************************* |
| 331 | * Get next DNS record from answer block * |
| 332 | *************************************************/ |
| 333 | |
| 334 | /* Call this with reset == RESET_ANSWERS to scan the answer block, reset == |
| 335 | RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to |
| 336 | scan the additional records, and reset == RESET_NEXT to get the next record. |
| 337 | The result is in static storage which must be copied if it is to be preserved. |
| 338 | |
| 339 | Arguments: |
| 340 | dnsa pointer to dns answer block |
| 341 | dnss pointer to dns scan block |
| 342 | reset option specifing what portion to scan, as described above |
| 343 | |
| 344 | Returns: next dns record, or NULL when no more |
| 345 | */ |
| 346 | |
| 347 | dns_record * |
| 348 | dns_next_rr(dns_answer *dnsa, dns_scan *dnss, int reset) |
| 349 | { |
| 350 | HEADER *h = (HEADER *)dnsa->answer; |
| 351 | int namelen; |
| 352 | |
| 353 | /* Reset the saved data when requested to, and skip to the first required RR */ |
| 354 | |
| 355 | if (reset != RESET_NEXT) |
| 356 | { |
| 357 | dnss->rrcount = ntohs(h->qdcount); |
| 358 | dnss->aptr = dnsa->answer + sizeof(HEADER); |
| 359 | |
| 360 | /* Skip over questions; failure to expand the name just gives up */ |
| 361 | |
| 362 | while (dnss->rrcount-- > 0) |
| 363 | { |
| 364 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, |
| 365 | dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME); |
| 366 | if (namelen < 0) { dnss->rrcount = 0; return NULL; } |
| 367 | dnss->aptr += namelen + 4; /* skip name & type & class */ |
| 368 | } |
| 369 | |
| 370 | /* Get the number of answer records. */ |
| 371 | |
| 372 | dnss->rrcount = ntohs(h->ancount); |
| 373 | |
| 374 | /* Skip over answers if we want to look at the authority section. Also skip |
| 375 | the NS records (i.e. authority section) if wanting to look at the additional |
| 376 | records. */ |
| 377 | |
| 378 | if (reset == RESET_ADDITIONAL) dnss->rrcount += ntohs(h->nscount); |
| 379 | |
| 380 | if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL) |
| 381 | { |
| 382 | while (dnss->rrcount-- > 0) |
| 383 | { |
| 384 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, |
| 385 | dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME); |
| 386 | if (namelen < 0) { dnss->rrcount = 0; return NULL; } |
| 387 | dnss->aptr += namelen + 8; /* skip name, type, class & TTL */ |
| 388 | GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */ |
| 389 | dnss->aptr += dnss->srr.size; /* skip over it */ |
| 390 | } |
| 391 | dnss->rrcount = (reset == RESET_AUTHORITY) |
| 392 | ? ntohs(h->nscount) : ntohs(h->arcount); |
| 393 | } |
| 394 | } |
| 395 | |
| 396 | /* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount |
| 397 | contains the number of RR records left. */ |
| 398 | |
| 399 | if (dnss->rrcount-- <= 0) return NULL; |
| 400 | |
| 401 | /* If expanding the RR domain name fails, behave as if no more records |
| 402 | (something safe). */ |
| 403 | |
| 404 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr, |
| 405 | (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME); |
| 406 | if (namelen < 0) { dnss->rrcount = 0; return NULL; } |
| 407 | |
| 408 | /* Move the pointer past the name and fill in the rest of the data structure |
| 409 | from the following bytes. */ |
| 410 | |
| 411 | dnss->aptr += namelen; |
| 412 | GETSHORT(dnss->srr.type, dnss->aptr); /* Record type */ |
| 413 | dnss->aptr += 6; /* Don't want class or TTL */ |
| 414 | GETSHORT(dnss->srr.size, dnss->aptr); /* Size of data portion */ |
| 415 | dnss->srr.data = dnss->aptr; /* The record's data follows */ |
| 416 | dnss->aptr += dnss->srr.size; /* Advance to next RR */ |
| 417 | |
| 418 | /* Return a pointer to the dns_record structure within the dns_answer. This is |
| 419 | for convenience so that the scans can use nice-looking for loops. */ |
| 420 | |
| 421 | return &(dnss->srr); |
| 422 | } |
| 423 | |
| 424 | |
| 425 | |
| 426 | |
| 427 | /************************************************* |
| 428 | * Return whether AD bit set in DNS result * |
| 429 | *************************************************/ |
| 430 | |
| 431 | /* We do not perform DNSSEC work ourselves; if the administrator has installed |
| 432 | a verifying resolver which sets AD as appropriate, though, we'll use that. |
| 433 | (AD = Authentic Data) |
| 434 | |
| 435 | Argument: pointer to dns answer block |
| 436 | Returns: bool indicating presence of AD bit |
| 437 | */ |
| 438 | |
| 439 | BOOL |
| 440 | dns_is_secure(dns_answer *dnsa) |
| 441 | { |
| 442 | #ifdef DISABLE_DNSSEC |
| 443 | DEBUG(D_dns) |
| 444 | debug_printf("DNSSEC support disabled at build-time; dns_is_secure() false\n"); |
| 445 | return FALSE; |
| 446 | #else |
| 447 | HEADER *h = (HEADER *)dnsa->answer; |
| 448 | return h->ad ? TRUE : FALSE; |
| 449 | #endif |
| 450 | } |
| 451 | |
| 452 | |
| 453 | |
| 454 | |
| 455 | /************************************************* |
| 456 | * Turn DNS type into text * |
| 457 | *************************************************/ |
| 458 | |
| 459 | /* Turn the coded record type into a string for printing. All those that Exim |
| 460 | uses should be included here. |
| 461 | |
| 462 | Argument: record type |
| 463 | Returns: pointer to string |
| 464 | */ |
| 465 | |
| 466 | uschar * |
| 467 | dns_text_type(int t) |
| 468 | { |
| 469 | switch(t) |
| 470 | { |
| 471 | case T_A: return US"A"; |
| 472 | case T_MX: return US"MX"; |
| 473 | case T_AAAA: return US"AAAA"; |
| 474 | case T_A6: return US"A6"; |
| 475 | case T_TXT: return US"TXT"; |
| 476 | case T_SPF: return US"SPF"; |
| 477 | case T_PTR: return US"PTR"; |
| 478 | case T_SOA: return US"SOA"; |
| 479 | case T_SRV: return US"SRV"; |
| 480 | case T_NS: return US"NS"; |
| 481 | case T_CNAME: return US"CNAME"; |
| 482 | default: return US"?"; |
| 483 | } |
| 484 | } |
| 485 | |
| 486 | |
| 487 | |
| 488 | /************************************************* |
| 489 | * Cache a failed DNS lookup result * |
| 490 | *************************************************/ |
| 491 | |
| 492 | /* We cache failed lookup results so as not to experience timeouts many |
| 493 | times for the same domain. We need to retain the resolver options because they |
| 494 | may change. For successful lookups, we rely on resolver and/or name server |
| 495 | caching. |
| 496 | |
| 497 | Arguments: |
| 498 | name the domain name |
| 499 | type the lookup type |
| 500 | rc the return code |
| 501 | |
| 502 | Returns: the return code |
| 503 | */ |
| 504 | |
| 505 | static int |
| 506 | dns_return(uschar *name, int type, int rc) |
| 507 | { |
| 508 | res_state resp = os_get_dns_resolver_res(); |
| 509 | tree_node *node = store_get_perm(sizeof(tree_node) + 290); |
| 510 | sprintf(CS node->name, "%.255s-%s-%lx", name, dns_text_type(type), |
| 511 | resp->options); |
| 512 | node->data.val = rc; |
| 513 | (void)tree_insertnode(&tree_dns_fails, node); |
| 514 | return rc; |
| 515 | } |
| 516 | |
| 517 | |
| 518 | |
| 519 | /************************************************* |
| 520 | * Do basic DNS lookup * |
| 521 | *************************************************/ |
| 522 | |
| 523 | /* Call the resolver to look up the given domain name, using the given type, |
| 524 | and check the result. The error code TRY_AGAIN is documented as meaning "non- |
| 525 | Authoritive Host not found, or SERVERFAIL". Sometimes there are badly set |
| 526 | up nameservers that produce this error continually, so there is the option of |
| 527 | providing a list of domains for which this is treated as a non-existent |
| 528 | host. |
| 529 | |
| 530 | Arguments: |
| 531 | dnsa pointer to dns_answer structure |
| 532 | name name to look up |
| 533 | type type of DNS record required (T_A, T_MX, etc) |
| 534 | |
| 535 | Returns: DNS_SUCCEED successful lookup |
| 536 | DNS_NOMATCH name not found (NXDOMAIN) |
| 537 | or name contains illegal characters (if checking) |
| 538 | or name is an IP address (for IP address lookup) |
| 539 | DNS_NODATA domain exists, but no data for this type (NODATA) |
| 540 | DNS_AGAIN soft failure, try again later |
| 541 | DNS_FAIL DNS failure |
| 542 | */ |
| 543 | |
| 544 | int |
| 545 | dns_basic_lookup(dns_answer *dnsa, uschar *name, int type) |
| 546 | { |
| 547 | #ifndef STAND_ALONE |
| 548 | int rc = -1; |
| 549 | uschar *save; |
| 550 | #endif |
| 551 | res_state resp = os_get_dns_resolver_res(); |
| 552 | |
| 553 | tree_node *previous; |
| 554 | uschar node_name[290]; |
| 555 | |
| 556 | /* DNS lookup failures of any kind are cached in a tree. This is mainly so that |
| 557 | a timeout on one domain doesn't happen time and time again for messages that |
| 558 | have many addresses in the same domain. We rely on the resolver and name server |
| 559 | caching for successful lookups. */ |
| 560 | |
| 561 | sprintf(CS node_name, "%.255s-%s-%lx", name, dns_text_type(type), |
| 562 | resp->options); |
| 563 | previous = tree_search(tree_dns_fails, node_name); |
| 564 | if (previous != NULL) |
| 565 | { |
| 566 | DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n", |
| 567 | name, dns_text_type(type), |
| 568 | (previous->data.val == DNS_NOMATCH)? "DNS_NOMATCH" : |
| 569 | (previous->data.val == DNS_NODATA)? "DNS_NODATA" : |
| 570 | (previous->data.val == DNS_AGAIN)? "DNS_AGAIN" : |
| 571 | (previous->data.val == DNS_FAIL)? "DNS_FAIL" : "??"); |
| 572 | return previous->data.val; |
| 573 | } |
| 574 | |
| 575 | /* If configured, check the hygene of the name passed to lookup. Otherwise, |
| 576 | although DNS lookups may give REFUSED at the lower level, some resolvers |
| 577 | turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such |
| 578 | domains cannot be in the DNS. The check is now done by a regular expression; |
| 579 | give it space for substring storage to save it having to get its own if the |
| 580 | regex has substrings that are used - the default uses a conditional. |
| 581 | |
| 582 | This test is omitted for PTR records. These occur only in calls from the dnsdb |
| 583 | lookup, which constructs the names itself, so they should be OK. Besides, |
| 584 | bitstring labels don't conform to normal name syntax. (But the aren't used any |
| 585 | more.) |
| 586 | |
| 587 | For SRV records, we omit the initial _smtp._tcp. components at the start. */ |
| 588 | |
| 589 | #ifndef STAND_ALONE /* Omit this for stand-alone tests */ |
| 590 | |
| 591 | if (check_dns_names_pattern[0] != 0 && type != T_PTR && type != T_TXT) |
| 592 | { |
| 593 | uschar *checkname = name; |
| 594 | int ovector[3*(EXPAND_MAXN+1)]; |
| 595 | |
| 596 | if (regex_check_dns_names == NULL) |
| 597 | regex_check_dns_names = |
| 598 | regex_must_compile(check_dns_names_pattern, FALSE, TRUE); |
| 599 | |
| 600 | /* For an SRV lookup, skip over the first two components (the service and |
| 601 | protocol names, which both start with an underscore). */ |
| 602 | |
| 603 | if (type == T_SRV) |
| 604 | { |
| 605 | while (*checkname++ != '.'); |
| 606 | while (*checkname++ != '.'); |
| 607 | } |
| 608 | |
| 609 | if (pcre_exec(regex_check_dns_names, NULL, CS checkname, Ustrlen(checkname), |
| 610 | 0, PCRE_EOPT, ovector, sizeof(ovector)/sizeof(int)) < 0) |
| 611 | { |
| 612 | DEBUG(D_dns) |
| 613 | debug_printf("DNS name syntax check failed: %s (%s)\n", name, |
| 614 | dns_text_type(type)); |
| 615 | host_find_failed_syntax = TRUE; |
| 616 | return DNS_NOMATCH; |
| 617 | } |
| 618 | } |
| 619 | |
| 620 | #endif /* STAND_ALONE */ |
| 621 | |
| 622 | /* Call the resolver; for an overlong response, res_search() will return the |
| 623 | number of bytes the message would need, so we need to check for this case. The |
| 624 | effect is to truncate overlong data. |
| 625 | |
| 626 | On some systems, res_search() will recognize "A-for-A" queries and return |
| 627 | the IP address instead of returning -1 with h_error=HOST_NOT_FOUND. Some |
| 628 | nameservers are also believed to do this. It is, of course, contrary to the |
| 629 | specification of the DNS, so we lock it out. */ |
| 630 | |
| 631 | if (( |
| 632 | #ifdef SUPPORT_A6 |
| 633 | type == T_A6 || |
| 634 | #endif |
| 635 | type == T_A || type == T_AAAA) && |
| 636 | string_is_ip_address(name, NULL) != 0) |
| 637 | return DNS_NOMATCH; |
| 638 | |
| 639 | /* If we are running in the test harness, instead of calling the normal resolver |
| 640 | (res_search), we call fakens_search(), which recognizes certain special |
| 641 | domains, and interfaces to a fake nameserver for certain special zones. */ |
| 642 | |
| 643 | if (running_in_test_harness) |
| 644 | dnsa->answerlen = fakens_search(name, type, dnsa->answer, MAXPACKET); |
| 645 | else |
| 646 | dnsa->answerlen = res_search(CS name, C_IN, type, dnsa->answer, MAXPACKET); |
| 647 | |
| 648 | if (dnsa->answerlen > MAXPACKET) |
| 649 | { |
| 650 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) resulted in overlong packet (size %d), truncating to %d.\n", |
| 651 | name, dns_text_type(type), dnsa->answerlen, MAXPACKET); |
| 652 | dnsa->answerlen = MAXPACKET; |
| 653 | } |
| 654 | |
| 655 | if (dnsa->answerlen < 0) switch (h_errno) |
| 656 | { |
| 657 | case HOST_NOT_FOUND: |
| 658 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n" |
| 659 | "returning DNS_NOMATCH\n", name, dns_text_type(type)); |
| 660 | return dns_return(name, type, DNS_NOMATCH); |
| 661 | |
| 662 | case TRY_AGAIN: |
| 663 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n", |
| 664 | name, dns_text_type(type)); |
| 665 | |
| 666 | /* Cut this out for various test programs */ |
| 667 | #ifndef STAND_ALONE |
| 668 | save = deliver_domain; |
| 669 | deliver_domain = name; /* set $domain */ |
| 670 | rc = match_isinlist(name, &dns_again_means_nonexist, 0, NULL, NULL, |
| 671 | MCL_DOMAIN, TRUE, NULL); |
| 672 | deliver_domain = save; |
| 673 | if (rc != OK) |
| 674 | { |
| 675 | DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n"); |
| 676 | return dns_return(name, type, DNS_AGAIN); |
| 677 | } |
| 678 | DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning " |
| 679 | "DNS_NOMATCH\n", name); |
| 680 | return dns_return(name, type, DNS_NOMATCH); |
| 681 | |
| 682 | #else /* For stand-alone tests */ |
| 683 | return dns_return(name, type, DNS_AGAIN); |
| 684 | #endif |
| 685 | |
| 686 | case NO_RECOVERY: |
| 687 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n" |
| 688 | "returning DNS_FAIL\n", name, dns_text_type(type)); |
| 689 | return dns_return(name, type, DNS_FAIL); |
| 690 | |
| 691 | case NO_DATA: |
| 692 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n" |
| 693 | "returning DNS_NODATA\n", name, dns_text_type(type)); |
| 694 | return dns_return(name, type, DNS_NODATA); |
| 695 | |
| 696 | default: |
| 697 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n" |
| 698 | "returning DNS_FAIL\n", name, dns_text_type(type), h_errno); |
| 699 | return dns_return(name, type, DNS_FAIL); |
| 700 | } |
| 701 | |
| 702 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n", |
| 703 | name, dns_text_type(type)); |
| 704 | |
| 705 | return DNS_SUCCEED; |
| 706 | } |
| 707 | |
| 708 | |
| 709 | |
| 710 | |
| 711 | /************************************************ |
| 712 | * Do a DNS lookup and handle CNAMES * |
| 713 | ************************************************/ |
| 714 | |
| 715 | /* Look up the given domain name, using the given type. Follow CNAMEs if |
| 716 | necessary, but only so many times. There aren't supposed to be CNAME chains in |
| 717 | the DNS, but you are supposed to cope with them if you find them. |
| 718 | |
| 719 | The assumption is made that if the resolver gives back records of the |
| 720 | requested type *and* a CNAME, we don't need to make another call to look up |
| 721 | the CNAME. I can't see how it could return only some of the right records. If |
| 722 | it's done a CNAME lookup in the past, it will have all of them; if not, it |
| 723 | won't return any. |
| 724 | |
| 725 | If fully_qualified_name is not NULL, set it to point to the full name |
| 726 | returned by the resolver, if this is different to what it is given, unless |
| 727 | the returned name starts with "*" as some nameservers seem to be returning |
| 728 | wildcards in this form. |
| 729 | |
| 730 | Arguments: |
| 731 | dnsa pointer to dns_answer structure |
| 732 | name domain name to look up |
| 733 | type DNS record type (T_A, T_MX, etc) |
| 734 | fully_qualified_name if not NULL, return the returned name here if its |
| 735 | contents are different (i.e. it must be preset) |
| 736 | |
| 737 | Returns: DNS_SUCCEED successful lookup |
| 738 | DNS_NOMATCH name not found |
| 739 | DNS_NODATA no data found |
| 740 | DNS_AGAIN soft failure, try again later |
| 741 | DNS_FAIL DNS failure |
| 742 | */ |
| 743 | |
| 744 | int |
| 745 | dns_lookup(dns_answer *dnsa, uschar *name, int type, uschar **fully_qualified_name) |
| 746 | { |
| 747 | int i; |
| 748 | uschar *orig_name = name; |
| 749 | |
| 750 | /* Loop to follow CNAME chains so far, but no further... */ |
| 751 | |
| 752 | for (i = 0; i < 10; i++) |
| 753 | { |
| 754 | uschar data[256]; |
| 755 | dns_record *rr, cname_rr, type_rr; |
| 756 | dns_scan dnss; |
| 757 | int datalen, rc; |
| 758 | |
| 759 | /* DNS lookup failures get passed straight back. */ |
| 760 | |
| 761 | if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED) return rc; |
| 762 | |
| 763 | /* We should have either records of the required type, or a CNAME record, |
| 764 | or both. We need to know whether both exist for getting the fully qualified |
| 765 | name, but avoid scanning more than necessary. Note that we must copy the |
| 766 | contents of any rr blocks returned by dns_next_rr() as they use the same |
| 767 | area in the dnsa block. */ |
| 768 | |
| 769 | cname_rr.data = type_rr.data = NULL; |
| 770 | for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); |
| 771 | rr != NULL; |
| 772 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) |
| 773 | { |
| 774 | if (rr->type == type) |
| 775 | { |
| 776 | if (type_rr.data == NULL) type_rr = *rr; |
| 777 | if (cname_rr.data != NULL) break; |
| 778 | } |
| 779 | else if (rr->type == T_CNAME) cname_rr = *rr; |
| 780 | } |
| 781 | |
| 782 | /* For the first time round this loop, if a CNAME was found, take the fully |
| 783 | qualified name from it; otherwise from the first data record, if present. */ |
| 784 | |
| 785 | if (i == 0 && fully_qualified_name != NULL) |
| 786 | { |
| 787 | if (cname_rr.data != NULL) |
| 788 | { |
| 789 | if (Ustrcmp(cname_rr.name, *fully_qualified_name) != 0 && |
| 790 | cname_rr.name[0] != '*') |
| 791 | *fully_qualified_name = string_copy_dnsdomain(cname_rr.name); |
| 792 | } |
| 793 | else if (type_rr.data != NULL) |
| 794 | { |
| 795 | if (Ustrcmp(type_rr.name, *fully_qualified_name) != 0 && |
| 796 | type_rr.name[0] != '*') |
| 797 | *fully_qualified_name = string_copy_dnsdomain(type_rr.name); |
| 798 | } |
| 799 | } |
| 800 | |
| 801 | /* If any data records of the correct type were found, we are done. */ |
| 802 | |
| 803 | if (type_rr.data != NULL) return DNS_SUCCEED; |
| 804 | |
| 805 | /* If there are no data records, we need to re-scan the DNS using the |
| 806 | domain given in the CNAME record, which should exist (otherwise we should |
| 807 | have had a failure from dns_lookup). However code against the possibility of |
| 808 | its not existing. */ |
| 809 | |
| 810 | if (cname_rr.data == NULL) return DNS_FAIL; |
| 811 | datalen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, |
| 812 | cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, 256); |
| 813 | if (datalen < 0) return DNS_FAIL; |
| 814 | name = data; |
| 815 | |
| 816 | DEBUG(D_dns) debug_printf("CNAME found: change to %s\n", name); |
| 817 | } /* Loop back to do another lookup */ |
| 818 | |
| 819 | /*Control reaches here after 10 times round the CNAME loop. Something isn't |
| 820 | right... */ |
| 821 | |
| 822 | log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name); |
| 823 | return DNS_FAIL; |
| 824 | } |
| 825 | |
| 826 | |
| 827 | |
| 828 | |
| 829 | |
| 830 | |
| 831 | /************************************************ |
| 832 | * Do a DNS lookup and handle virtual types * |
| 833 | ************************************************/ |
| 834 | |
| 835 | /* This function handles some invented "lookup types" that synthesize feature |
| 836 | not available in the basic types. The special types all have negative values. |
| 837 | Positive type values are passed straight on to dns_lookup(). |
| 838 | |
| 839 | Arguments: |
| 840 | dnsa pointer to dns_answer structure |
| 841 | name domain name to look up |
| 842 | type DNS record type (T_A, T_MX, etc or a "special") |
| 843 | fully_qualified_name if not NULL, return the returned name here if its |
| 844 | contents are different (i.e. it must be preset) |
| 845 | |
| 846 | Returns: DNS_SUCCEED successful lookup |
| 847 | DNS_NOMATCH name not found |
| 848 | DNS_NODATA no data found |
| 849 | DNS_AGAIN soft failure, try again later |
| 850 | DNS_FAIL DNS failure |
| 851 | */ |
| 852 | |
| 853 | int |
| 854 | dns_special_lookup(dns_answer *dnsa, uschar *name, int type, |
| 855 | uschar **fully_qualified_name) |
| 856 | { |
| 857 | if (type >= 0) return dns_lookup(dnsa, name, type, fully_qualified_name); |
| 858 | |
| 859 | /* The "mx hosts only" type doesn't require any special action here */ |
| 860 | |
| 861 | if (type == T_MXH) return dns_lookup(dnsa, name, T_MX, fully_qualified_name); |
| 862 | |
| 863 | /* Find nameservers for the domain or the nearest enclosing zone, excluding the |
| 864 | root servers. */ |
| 865 | |
| 866 | if (type == T_ZNS) |
| 867 | { |
| 868 | uschar *d = name; |
| 869 | while (d != 0) |
| 870 | { |
| 871 | int rc = dns_lookup(dnsa, d, T_NS, fully_qualified_name); |
| 872 | if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc; |
| 873 | while (*d != 0 && *d != '.') d++; |
| 874 | if (*d++ == 0) break; |
| 875 | } |
| 876 | return DNS_NOMATCH; |
| 877 | } |
| 878 | |
| 879 | /* Try to look up the Client SMTP Authorization SRV record for the name. If |
| 880 | there isn't one, search from the top downwards for a CSA record in a parent |
| 881 | domain, which might be making assertions about subdomains. If we find a record |
| 882 | we set fully_qualified_name to whichever lookup succeeded, so that the caller |
| 883 | can tell whether to look at the explicit authorization field or the subdomain |
| 884 | assertion field. */ |
| 885 | |
| 886 | if (type == T_CSA) |
| 887 | { |
| 888 | uschar *srvname, *namesuff, *tld, *p; |
| 889 | int priority, weight, port; |
| 890 | int limit, rc, i; |
| 891 | BOOL ipv6; |
| 892 | dns_record *rr; |
| 893 | dns_scan dnss; |
| 894 | |
| 895 | DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name); |
| 896 | |
| 897 | srvname = string_sprintf("_client._smtp.%s", name); |
| 898 | rc = dns_lookup(dnsa, srvname, T_SRV, NULL); |
| 899 | if (rc == DNS_SUCCEED || rc == DNS_AGAIN) |
| 900 | { |
| 901 | if (rc == DNS_SUCCEED) *fully_qualified_name = name; |
| 902 | return rc; |
| 903 | } |
| 904 | |
| 905 | /* Search for CSA subdomain assertion SRV records from the top downwards, |
| 906 | starting with the 2nd level domain. This order maximizes cache-friendliness. |
| 907 | We skip the top level domains to avoid loading their nameservers and because |
| 908 | we know they'll never have CSA SRV records. */ |
| 909 | |
| 910 | namesuff = Ustrrchr(name, '.'); |
| 911 | if (namesuff == NULL) return DNS_NOMATCH; |
| 912 | tld = namesuff + 1; |
| 913 | ipv6 = FALSE; |
| 914 | limit = dns_csa_search_limit; |
| 915 | |
| 916 | /* Use more appropriate search parameters if we are in the reverse DNS. */ |
| 917 | |
| 918 | if (strcmpic(namesuff, US".arpa") == 0) |
| 919 | { |
| 920 | if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0) |
| 921 | { |
| 922 | namesuff -= 8; |
| 923 | tld = namesuff + 1; |
| 924 | limit = 3; |
| 925 | } |
| 926 | else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0) |
| 927 | { |
| 928 | namesuff -= 4; |
| 929 | tld = namesuff + 1; |
| 930 | ipv6 = TRUE; |
| 931 | limit = 3; |
| 932 | } |
| 933 | } |
| 934 | |
| 935 | DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld); |
| 936 | |
| 937 | /* Do not perform the search if the top level or 2nd level domains do not |
| 938 | exist. This is quite common, and when it occurs all the search queries would |
| 939 | go to the root or TLD name servers, which is not friendly. So we check the |
| 940 | AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then |
| 941 | the TLD or the 2LD (respectively) doesn't exist and we can skip the search. |
| 942 | If the TLD and the 2LD exist but the explicit CSA record lookup failed, then |
| 943 | the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */ |
| 944 | |
| 945 | if (rc == DNS_NOMATCH) |
| 946 | { |
| 947 | /* This is really gross. The successful return value from res_search() is |
| 948 | the packet length, which is stored in dnsa->answerlen. If we get a |
| 949 | negative DNS reply then res_search() returns -1, which causes the bounds |
| 950 | checks for name decompression to fail when it is treated as a packet |
| 951 | length, which in turn causes the authority search to fail. The correct |
| 952 | packet length has been lost inside libresolv, so we have to guess a |
| 953 | replacement value. (The only way to fix this properly would be to |
| 954 | re-implement res_search() and res_query() so that they don't muddle their |
| 955 | success and packet length return values.) For added safety we only reset |
| 956 | the packet length if the packet header looks plausible. */ |
| 957 | |
| 958 | HEADER *h = (HEADER *)dnsa->answer; |
| 959 | if (h->qr == 1 && h->opcode == QUERY && h->tc == 0 |
| 960 | && (h->rcode == NOERROR || h->rcode == NXDOMAIN) |
| 961 | && ntohs(h->qdcount) == 1 && ntohs(h->ancount) == 0 |
| 962 | && ntohs(h->nscount) >= 1) |
| 963 | dnsa->answerlen = MAXPACKET; |
| 964 | |
| 965 | for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY); |
| 966 | rr != NULL; |
| 967 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) |
| 968 | if (rr->type != T_SOA) continue; |
| 969 | else if (strcmpic(rr->name, US"") == 0 || |
| 970 | strcmpic(rr->name, tld) == 0) return DNS_NOMATCH; |
| 971 | else break; |
| 972 | } |
| 973 | |
| 974 | for (i = 0; i < limit; i++) |
| 975 | { |
| 976 | if (ipv6) |
| 977 | { |
| 978 | /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP |
| 979 | address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */ |
| 980 | namesuff -= 8; |
| 981 | if (namesuff <= name) return DNS_NOMATCH; |
| 982 | } |
| 983 | else |
| 984 | /* Find the start of the preceding domain name label. */ |
| 985 | do |
| 986 | if (--namesuff <= name) return DNS_NOMATCH; |
| 987 | while (*namesuff != '.'); |
| 988 | |
| 989 | DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1); |
| 990 | |
| 991 | srvname = string_sprintf("_client._smtp.%s", namesuff + 1); |
| 992 | rc = dns_lookup(dnsa, srvname, T_SRV, NULL); |
| 993 | if (rc == DNS_AGAIN) return rc; |
| 994 | if (rc != DNS_SUCCEED) continue; |
| 995 | |
| 996 | /* Check that the SRV record we have found is worth returning. We don't |
| 997 | just return the first one we find, because some lower level SRV record |
| 998 | might make stricter assertions than its parent domain. */ |
| 999 | |
| 1000 | for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); |
| 1001 | rr != NULL; |
| 1002 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) |
| 1003 | { |
| 1004 | if (rr->type != T_SRV) continue; |
| 1005 | |
| 1006 | /* Extract the numerical SRV fields (p is incremented) */ |
| 1007 | p = rr->data; |
| 1008 | GETSHORT(priority, p); |
| 1009 | GETSHORT(weight, p); |
| 1010 | GETSHORT(port, p); |
| 1011 | |
| 1012 | /* Check the CSA version number */ |
| 1013 | if (priority != 1) continue; |
| 1014 | |
| 1015 | /* If it's making an interesting assertion, return this response. */ |
| 1016 | if (port & 1) |
| 1017 | { |
| 1018 | *fully_qualified_name = namesuff + 1; |
| 1019 | return DNS_SUCCEED; |
| 1020 | } |
| 1021 | } |
| 1022 | } |
| 1023 | return DNS_NOMATCH; |
| 1024 | } |
| 1025 | |
| 1026 | /* Control should never reach here */ |
| 1027 | |
| 1028 | return DNS_FAIL; |
| 1029 | } |
| 1030 | |
| 1031 | |
| 1032 | |
| 1033 | /* Support for A6 records has been commented out since they were demoted to |
| 1034 | experimental status at IETF 51. */ |
| 1035 | |
| 1036 | #if HAVE_IPV6 && defined(SUPPORT_A6) |
| 1037 | |
| 1038 | /************************************************* |
| 1039 | * Search DNS block for prefix RRs * |
| 1040 | *************************************************/ |
| 1041 | |
| 1042 | /* Called from dns_complete_a6() to search an additional section or a main |
| 1043 | answer section for required prefix records to complete an IPv6 address obtained |
| 1044 | from an A6 record. For each prefix record, a recursive call to dns_complete_a6 |
| 1045 | is made, with a new copy of the address so far. |
| 1046 | |
| 1047 | Arguments: |
| 1048 | dnsa the DNS answer block |
| 1049 | which RESET_ADDITIONAL or RESET_ANSWERS |
| 1050 | name name of prefix record |
| 1051 | yptrptr pointer to the pointer that points to where to hang the next |
| 1052 | dns_address structure |
| 1053 | bits number of bits we have already got |
| 1054 | bitvec the bits we have already got |
| 1055 | |
| 1056 | Returns: TRUE if any records were found |
| 1057 | */ |
| 1058 | |
| 1059 | static BOOL |
| 1060 | dns_find_prefix(dns_answer *dnsa, int which, uschar *name, dns_address |
| 1061 | ***yptrptr, int bits, uschar *bitvec) |
| 1062 | { |
| 1063 | BOOL yield = FALSE; |
| 1064 | dns_record *rr; |
| 1065 | dns_scan dnss; |
| 1066 | |
| 1067 | for (rr = dns_next_rr(dnsa, &dnss, which); |
| 1068 | rr != NULL; |
| 1069 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) |
| 1070 | { |
| 1071 | uschar cbitvec[16]; |
| 1072 | if (rr->type != T_A6 || strcmpic(rr->name, name) != 0) continue; |
| 1073 | yield = TRUE; |
| 1074 | memcpy(cbitvec, bitvec, sizeof(cbitvec)); |
| 1075 | dns_complete_a6(yptrptr, dnsa, rr, bits, cbitvec); |
| 1076 | } |
| 1077 | |
| 1078 | return yield; |
| 1079 | } |
| 1080 | |
| 1081 | |
| 1082 | |
| 1083 | /************************************************* |
| 1084 | * Follow chains of A6 records * |
| 1085 | *************************************************/ |
| 1086 | |
| 1087 | /* A6 records may be incomplete, with pointers to other records containing more |
| 1088 | bits of the address. There can be a tree structure, leading to a number of |
| 1089 | addresses originating from a single initial A6 record. |
| 1090 | |
| 1091 | Arguments: |
| 1092 | yptrptr pointer to the pointer that points to where to hang the next |
| 1093 | dns_address structure |
| 1094 | dnsa the current DNS answer block |
| 1095 | rr the RR we have at present |
| 1096 | bits number of bits we have already got |
| 1097 | bitvec the bits we have already got |
| 1098 | |
| 1099 | Returns: nothing |
| 1100 | */ |
| 1101 | |
| 1102 | static void |
| 1103 | dns_complete_a6(dns_address ***yptrptr, dns_answer *dnsa, dns_record *rr, |
| 1104 | int bits, uschar *bitvec) |
| 1105 | { |
| 1106 | static uschar bitmask[] = { 0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80 }; |
| 1107 | uschar *p = (uschar *)(rr->data); |
| 1108 | int prefix_len, suffix_len; |
| 1109 | int i, j, k; |
| 1110 | uschar *chainptr; |
| 1111 | uschar chain[264]; |
| 1112 | dns_answer cdnsa; |
| 1113 | |
| 1114 | /* The prefix length is the first byte. It defines the prefix which is missing |
| 1115 | from the data in this record as a number of bits. Zero means this is the end of |
| 1116 | a chain. The suffix is the data in this record; only sufficient bytes to hold |
| 1117 | it are supplied. There may be zero bytes. We have to ignore trailing bits that |
| 1118 | we have already obtained from earlier RRs in the chain. */ |
| 1119 | |
| 1120 | prefix_len = *p++; /* bits */ |
| 1121 | suffix_len = (128 - prefix_len + 7)/8; /* bytes */ |
| 1122 | |
| 1123 | /* If the prefix in this record is greater than the prefix in the previous |
| 1124 | record in the chain, we have to ignore the record (RFC 2874). */ |
| 1125 | |
| 1126 | if (prefix_len > 128 - bits) return; |
| 1127 | |
| 1128 | /* In this little loop, the number of bits up to and including the current byte |
| 1129 | is held in k. If we have none of the bits in this byte, we can just or it into |
| 1130 | the current data. If we have all of the bits in this byte, we skip it. |
| 1131 | Otherwise, some masking has to be done. */ |
| 1132 | |
| 1133 | for (i = suffix_len - 1, j = 15, k = 8; i >= 0; i--) |
| 1134 | { |
| 1135 | int required = k - bits; |
| 1136 | if (required >= 8) bitvec[j] |= p[i]; |
| 1137 | else if (required > 0) bitvec[j] |= p[i] & bitmask[required]; |
| 1138 | j--; /* I tried putting these in the "for" statement, but gcc muttered */ |
| 1139 | k += 8; /* about computed values not being used. */ |
| 1140 | } |
| 1141 | |
| 1142 | /* If the prefix_length is zero, we are at the end of a chain. Build a |
| 1143 | dns_address item with the current data, hang it onto the end of the chain, |
| 1144 | adjust the hanging pointer, and we are done. */ |
| 1145 | |
| 1146 | if (prefix_len == 0) |
| 1147 | { |
| 1148 | dns_address *new = store_get(sizeof(dns_address) + 50); |
| 1149 | inet_ntop(AF_INET6, bitvec, CS new->address, 50); |
| 1150 | new->next = NULL; |
| 1151 | **yptrptr = new; |
| 1152 | *yptrptr = &(new->next); |
| 1153 | return; |
| 1154 | } |
| 1155 | |
| 1156 | /* Prefix length is not zero. Reset the number of bits that we have collected |
| 1157 | so far, and extract the chain name. */ |
| 1158 | |
| 1159 | bits = 128 - prefix_len; |
| 1160 | p += suffix_len; |
| 1161 | |
| 1162 | chainptr = chain; |
| 1163 | while ((i = *p++) != 0) |
| 1164 | { |
| 1165 | if (chainptr != chain) *chainptr++ = '.'; |
| 1166 | memcpy(chainptr, p, i); |
| 1167 | chainptr += i; |
| 1168 | p += i; |
| 1169 | } |
| 1170 | *chainptr = 0; |
| 1171 | chainptr = chain; |
| 1172 | |
| 1173 | /* Now scan the current DNS response record to see if the additional section |
| 1174 | contains the records we want. This processing can be cut out for testing |
| 1175 | purposes. */ |
| 1176 | |
| 1177 | if (dns_find_prefix(dnsa, RESET_ADDITIONAL, chainptr, yptrptr, bits, bitvec)) |
| 1178 | return; |
| 1179 | |
| 1180 | /* No chain records were found in the current DNS response block. Do a new DNS |
| 1181 | lookup to try to find these records. This opens up the possibility of DNS |
| 1182 | failures. We ignore them at this point; if all branches of the tree fail, there |
| 1183 | will be no addresses at the end. */ |
| 1184 | |
| 1185 | if (dns_lookup(&cdnsa, chainptr, T_A6, NULL) == DNS_SUCCEED) |
| 1186 | (void)dns_find_prefix(&cdnsa, RESET_ANSWERS, chainptr, yptrptr, bits, bitvec); |
| 1187 | } |
| 1188 | #endif /* HAVE_IPV6 && defined(SUPPORT_A6) */ |
| 1189 | |
| 1190 | |
| 1191 | |
| 1192 | |
| 1193 | /************************************************* |
| 1194 | * Get address(es) from DNS record * |
| 1195 | *************************************************/ |
| 1196 | |
| 1197 | /* The record type is either T_A for an IPv4 address or T_AAAA (or T_A6 when |
| 1198 | supported) for an IPv6 address. In the A6 case, there may be several addresses, |
| 1199 | generated by following chains. A recursive function does all the hard work. A6 |
| 1200 | records now look like passing into history, so the code is only included when |
| 1201 | explicitly asked for. |
| 1202 | |
| 1203 | Argument: |
| 1204 | dnsa the DNS answer block |
| 1205 | rr the RR |
| 1206 | |
| 1207 | Returns: pointer a chain of dns_address items |
| 1208 | */ |
| 1209 | |
| 1210 | dns_address * |
| 1211 | dns_address_from_rr(dns_answer *dnsa, dns_record *rr) |
| 1212 | { |
| 1213 | dns_address *yield = NULL; |
| 1214 | |
| 1215 | #if HAVE_IPV6 && defined(SUPPORT_A6) |
| 1216 | dns_address **yieldptr = &yield; |
| 1217 | uschar bitvec[16]; |
| 1218 | #else |
| 1219 | dnsa = dnsa; /* Stop picky compilers warning */ |
| 1220 | #endif |
| 1221 | |
| 1222 | if (rr->type == T_A) |
| 1223 | { |
| 1224 | uschar *p = (uschar *)(rr->data); |
| 1225 | yield = store_get(sizeof(dns_address) + 20); |
| 1226 | (void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]); |
| 1227 | yield->next = NULL; |
| 1228 | } |
| 1229 | |
| 1230 | #if HAVE_IPV6 |
| 1231 | |
| 1232 | #ifdef SUPPORT_A6 |
| 1233 | else if (rr->type == T_A6) |
| 1234 | { |
| 1235 | memset(bitvec, 0, sizeof(bitvec)); |
| 1236 | dns_complete_a6(&yieldptr, dnsa, rr, 0, bitvec); |
| 1237 | } |
| 1238 | #endif /* SUPPORT_A6 */ |
| 1239 | |
| 1240 | else |
| 1241 | { |
| 1242 | yield = store_get(sizeof(dns_address) + 50); |
| 1243 | inet_ntop(AF_INET6, (uschar *)(rr->data), CS yield->address, 50); |
| 1244 | yield->next = NULL; |
| 1245 | } |
| 1246 | #endif /* HAVE_IPV6 */ |
| 1247 | |
| 1248 | return yield; |
| 1249 | } |
| 1250 | |
| 1251 | /* End of dns.c */ |