| 1 | /* $Cambridge: exim/src/src/dns.c,v 1.8 2005/06/10 13:38:06 tom Exp $ */ |
| 2 | |
| 3 | /************************************************* |
| 4 | * Exim - an Internet mail transport agent * |
| 5 | *************************************************/ |
| 6 | |
| 7 | /* Copyright (c) University of Cambridge 1995 - 2005 */ |
| 8 | /* See the file NOTICE for conditions of use and distribution. */ |
| 9 | |
| 10 | /* Functions for interfacing with the DNS. */ |
| 11 | |
| 12 | #include "exim.h" |
| 13 | |
| 14 | |
| 15 | /* Function declaration needed for mutual recursion when A6 records |
| 16 | are supported. */ |
| 17 | |
| 18 | #if HAVE_IPV6 |
| 19 | #ifdef SUPPORT_A6 |
| 20 | static void dns_complete_a6(dns_address ***, dns_answer *, dns_record *, |
| 21 | int, uschar *); |
| 22 | #endif |
| 23 | #endif |
| 24 | |
| 25 | |
| 26 | |
| 27 | /************************************************* |
| 28 | * Initialize and configure resolver * |
| 29 | *************************************************/ |
| 30 | |
| 31 | /* Initialize the resolver and the storage for holding DNS answers if this is |
| 32 | the first time we have been here, and set the resolver options. |
| 33 | |
| 34 | Arguments: |
| 35 | qualify_single TRUE to set the RES_DEFNAMES option |
| 36 | search_parents TRUE to set the RES_DNSRCH option |
| 37 | |
| 38 | Returns: nothing |
| 39 | */ |
| 40 | |
| 41 | void |
| 42 | dns_init(BOOL qualify_single, BOOL search_parents) |
| 43 | { |
| 44 | if ((_res.options & RES_INIT) == 0) |
| 45 | { |
| 46 | DEBUG(D_resolver) _res.options |= RES_DEBUG; /* For Cygwin */ |
| 47 | res_init(); |
| 48 | DEBUG(D_resolver) _res.options |= RES_DEBUG; |
| 49 | } |
| 50 | |
| 51 | _res.options &= ~(RES_DNSRCH | RES_DEFNAMES); |
| 52 | _res.options |= (qualify_single? RES_DEFNAMES : 0) | |
| 53 | (search_parents? RES_DNSRCH : 0); |
| 54 | if (dns_retrans > 0) _res.retrans = dns_retrans; |
| 55 | if (dns_retry > 0) _res.retry = dns_retry; |
| 56 | } |
| 57 | |
| 58 | |
| 59 | |
| 60 | /************************************************* |
| 61 | * Build key name for PTR records * |
| 62 | *************************************************/ |
| 63 | |
| 64 | /* This function inverts an IP address and adds the relevant domain, to produce |
| 65 | a name that can be used to look up PTR records. |
| 66 | |
| 67 | Arguments: |
| 68 | string the IP address as a string |
| 69 | buffer a suitable buffer, long enough to hold the result |
| 70 | |
| 71 | Returns: nothing |
| 72 | */ |
| 73 | |
| 74 | void |
| 75 | dns_build_reverse(uschar *string, uschar *buffer) |
| 76 | { |
| 77 | uschar *p = string + Ustrlen(string); |
| 78 | uschar *pp = buffer; |
| 79 | |
| 80 | /* Handle IPv4 address */ |
| 81 | |
| 82 | #if HAVE_IPV6 |
| 83 | if (Ustrchr(string, ':') == NULL) |
| 84 | #endif |
| 85 | { |
| 86 | int i; |
| 87 | for (i = 0; i < 4; i++) |
| 88 | { |
| 89 | uschar *ppp = p; |
| 90 | while (ppp > string && ppp[-1] != '.') ppp--; |
| 91 | Ustrncpy(pp, ppp, p - ppp); |
| 92 | pp += p - ppp; |
| 93 | *pp++ = '.'; |
| 94 | p = ppp - 1; |
| 95 | } |
| 96 | Ustrcpy(pp, "in-addr.arpa"); |
| 97 | } |
| 98 | |
| 99 | /* Handle IPv6 address; convert to binary so as to fill out any |
| 100 | abbreviation in the textual form. */ |
| 101 | |
| 102 | #if HAVE_IPV6 |
| 103 | else |
| 104 | { |
| 105 | int i; |
| 106 | int v6[4]; |
| 107 | (void)host_aton(string, v6); |
| 108 | |
| 109 | /* The original specification for IPv6 reverse lookup was to invert each |
| 110 | nibble, and look in the ip6.int domain. The domain was subsequently |
| 111 | changed to ip6.arpa. */ |
| 112 | |
| 113 | for (i = 3; i >= 0; i--) |
| 114 | { |
| 115 | int j; |
| 116 | for (j = 0; j < 32; j += 4) |
| 117 | { |
| 118 | sprintf(CS pp, "%x.", (v6[i] >> j) & 15); |
| 119 | pp += 2; |
| 120 | } |
| 121 | } |
| 122 | Ustrcpy(pp, "ip6.arpa."); |
| 123 | |
| 124 | /* Another way of doing IPv6 reverse lookups was proposed in conjunction |
| 125 | with A6 records. However, it fell out of favour when they did. The |
| 126 | alternative was to construct a binary key, and look in ip6.arpa. I tried |
| 127 | to make this code do that, but I could not make it work on Solaris 8. The |
| 128 | resolver seems to lose the initial backslash somehow. However, now that |
| 129 | this style of reverse lookup has been dropped, it doesn't matter. These |
| 130 | lines are left here purely for historical interest. */ |
| 131 | |
| 132 | /************************************************** |
| 133 | Ustrcpy(pp, "\\[x"); |
| 134 | pp += 3; |
| 135 | |
| 136 | for (i = 0; i < 4; i++) |
| 137 | { |
| 138 | sprintf(pp, "%08X", v6[i]); |
| 139 | pp += 8; |
| 140 | } |
| 141 | Ustrcpy(pp, "].ip6.arpa."); |
| 142 | **************************************************/ |
| 143 | |
| 144 | } |
| 145 | #endif |
| 146 | } |
| 147 | |
| 148 | |
| 149 | |
| 150 | |
| 151 | /************************************************* |
| 152 | * Get next DNS record from answer block * |
| 153 | *************************************************/ |
| 154 | |
| 155 | /* Call this with reset == RESET_ANSWERS to scan the answer block, reset == |
| 156 | RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to |
| 157 | scan the additional records, and reset == RESET_NEXT to get the next record. |
| 158 | The result is in static storage which must be copied if it is to be preserved. |
| 159 | |
| 160 | Arguments: |
| 161 | dnsa pointer to dns answer block |
| 162 | dnss pointer to dns scan block |
| 163 | reset option specifing what portion to scan, as described above |
| 164 | |
| 165 | Returns: next dns record, or NULL when no more |
| 166 | */ |
| 167 | |
| 168 | dns_record * |
| 169 | dns_next_rr(dns_answer *dnsa, dns_scan *dnss, int reset) |
| 170 | { |
| 171 | HEADER *h = (HEADER *)dnsa->answer; |
| 172 | int namelen; |
| 173 | |
| 174 | /* Reset the saved data when requested to, and skip to the first required RR */ |
| 175 | |
| 176 | if (reset != RESET_NEXT) |
| 177 | { |
| 178 | dnss->rrcount = ntohs(h->qdcount); |
| 179 | dnss->aptr = dnsa->answer + sizeof(HEADER); |
| 180 | |
| 181 | /* Skip over questions; failure to expand the name just gives up */ |
| 182 | |
| 183 | while (dnss->rrcount-- > 0) |
| 184 | { |
| 185 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, |
| 186 | dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME); |
| 187 | if (namelen < 0) { dnss->rrcount = 0; return NULL; } |
| 188 | dnss->aptr += namelen + 4; /* skip name & type & class */ |
| 189 | } |
| 190 | |
| 191 | /* Get the number of answer records. */ |
| 192 | |
| 193 | dnss->rrcount = ntohs(h->ancount); |
| 194 | |
| 195 | /* Skip over answers if we want to look at the authority section. Also skip |
| 196 | the NS records (i.e. authority section) if wanting to look at the additional |
| 197 | records. */ |
| 198 | |
| 199 | if (reset == RESET_ADDITIONAL) dnss->rrcount += ntohs(h->nscount); |
| 200 | |
| 201 | if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL) |
| 202 | { |
| 203 | while (dnss->rrcount-- > 0) |
| 204 | { |
| 205 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, |
| 206 | dnss->aptr, (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME); |
| 207 | if (namelen < 0) { dnss->rrcount = 0; return NULL; } |
| 208 | dnss->aptr += namelen + 8; /* skip name, type, class & TTL */ |
| 209 | GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */ |
| 210 | dnss->aptr += dnss->srr.size; /* skip over it */ |
| 211 | } |
| 212 | dnss->rrcount = (reset == RESET_AUTHORITY) |
| 213 | ? ntohs(h->nscount) : ntohs(h->arcount); |
| 214 | } |
| 215 | } |
| 216 | |
| 217 | /* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount |
| 218 | contains the number of RR records left. */ |
| 219 | |
| 220 | if (dnss->rrcount-- <= 0) return NULL; |
| 221 | |
| 222 | /* If expanding the RR domain name fails, behave as if no more records |
| 223 | (something safe). */ |
| 224 | |
| 225 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr, |
| 226 | (DN_EXPAND_ARG4_TYPE) &(dnss->srr.name), DNS_MAXNAME); |
| 227 | if (namelen < 0) { dnss->rrcount = 0; return NULL; } |
| 228 | |
| 229 | /* Move the pointer past the name and fill in the rest of the data structure |
| 230 | from the following bytes. */ |
| 231 | |
| 232 | dnss->aptr += namelen; |
| 233 | GETSHORT(dnss->srr.type, dnss->aptr); /* Record type */ |
| 234 | dnss->aptr += 6; /* Don't want class or TTL */ |
| 235 | GETSHORT(dnss->srr.size, dnss->aptr); /* Size of data portion */ |
| 236 | dnss->srr.data = dnss->aptr; /* The record's data follows */ |
| 237 | dnss->aptr += dnss->srr.size; /* Advance to next RR */ |
| 238 | |
| 239 | /* Return a pointer to the dns_record structure within the dns_answer. This is |
| 240 | for convenience so that the scans can use nice-looking for loops. */ |
| 241 | |
| 242 | return &(dnss->srr); |
| 243 | } |
| 244 | |
| 245 | |
| 246 | |
| 247 | |
| 248 | /************************************************* |
| 249 | * Turn DNS type into text * |
| 250 | *************************************************/ |
| 251 | |
| 252 | /* Turn the coded record type into a string for printing. |
| 253 | |
| 254 | Argument: record type |
| 255 | Returns: pointer to string |
| 256 | */ |
| 257 | |
| 258 | uschar * |
| 259 | dns_text_type(int t) |
| 260 | { |
| 261 | switch(t) |
| 262 | { |
| 263 | case T_A: return US"A"; |
| 264 | case T_MX: return US"MX"; |
| 265 | case T_AAAA: return US"AAAA"; |
| 266 | case T_A6: return US"A6"; |
| 267 | case T_TXT: return US"TXT"; |
| 268 | case T_PTR: return US"PTR"; |
| 269 | case T_SRV: return US"SRV"; |
| 270 | case T_NS: return US"NS"; |
| 271 | case T_CNAME: return US"CNAME"; |
| 272 | default: return US"?"; |
| 273 | } |
| 274 | } |
| 275 | |
| 276 | |
| 277 | |
| 278 | /************************************************* |
| 279 | * Cache a failed DNS lookup result * |
| 280 | *************************************************/ |
| 281 | |
| 282 | /* We cache failed lookup results so as not to experience timeouts many |
| 283 | times for the same domain. We need to retain the resolver options because they |
| 284 | may change. For successful lookups, we rely on resolver and/or name server |
| 285 | caching. |
| 286 | |
| 287 | Arguments: |
| 288 | name the domain name |
| 289 | type the lookup type |
| 290 | rc the return code |
| 291 | |
| 292 | Returns: the return code |
| 293 | */ |
| 294 | |
| 295 | static int |
| 296 | dns_return(uschar *name, int type, int rc) |
| 297 | { |
| 298 | tree_node *node = store_get_perm(sizeof(tree_node) + 290); |
| 299 | sprintf(CS node->name, "%.255s-%s-%lx", name, dns_text_type(type), |
| 300 | _res.options); |
| 301 | node->data.val = rc; |
| 302 | (void)tree_insertnode(&tree_dns_fails, node); |
| 303 | return rc; |
| 304 | } |
| 305 | |
| 306 | |
| 307 | |
| 308 | /************************************************* |
| 309 | * Do basic DNS lookup * |
| 310 | *************************************************/ |
| 311 | |
| 312 | /* Call the resolver to look up the given domain name, using the given type, |
| 313 | and check the result. The error code TRY_AGAIN is documented as meaning "non- |
| 314 | Authoritive Host not found, or SERVERFAIL". Sometimes there are badly set |
| 315 | up nameservers that produce this error continually, so there is the option of |
| 316 | providing a list of domains for which this is treated as a non-existent |
| 317 | host. |
| 318 | |
| 319 | Arguments: |
| 320 | dnsa pointer to dns_answer structure |
| 321 | name name to look up |
| 322 | type type of DNS record required (T_A, T_MX, etc) |
| 323 | |
| 324 | Returns: DNS_SUCCEED successful lookup |
| 325 | DNS_NOMATCH name not found (NXDOMAIN) |
| 326 | or name contains illegal characters (if checking) |
| 327 | DNS_NODATA domain exists, but no data for this type (NODATA) |
| 328 | DNS_AGAIN soft failure, try again later |
| 329 | DNS_FAIL DNS failure |
| 330 | */ |
| 331 | |
| 332 | int |
| 333 | dns_basic_lookup(dns_answer *dnsa, uschar *name, int type) |
| 334 | { |
| 335 | #ifndef STAND_ALONE |
| 336 | int rc; |
| 337 | uschar *save; |
| 338 | #endif |
| 339 | |
| 340 | tree_node *previous; |
| 341 | uschar node_name[290]; |
| 342 | |
| 343 | /* DNS lookup failures of any kind are cached in a tree. This is mainly so that |
| 344 | a timeout on one domain doesn't happen time and time again for messages that |
| 345 | have many addresses in the same domain. We rely on the resolver and name server |
| 346 | caching for successful lookups. */ |
| 347 | |
| 348 | sprintf(CS node_name, "%.255s-%s-%lx", name, dns_text_type(type), |
| 349 | _res.options); |
| 350 | previous = tree_search(tree_dns_fails, node_name); |
| 351 | if (previous != NULL) |
| 352 | { |
| 353 | DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n", |
| 354 | name, dns_text_type(type), |
| 355 | (previous->data.val == DNS_NOMATCH)? "DNS_NOMATCH" : |
| 356 | (previous->data.val == DNS_NODATA)? "DNS_NODATA" : |
| 357 | (previous->data.val == DNS_AGAIN)? "DNS_AGAIN" : |
| 358 | (previous->data.val == DNS_FAIL)? "DNS_FAIL" : "??"); |
| 359 | return previous->data.val; |
| 360 | } |
| 361 | |
| 362 | /* If we are running in the test harness, recognize a couple of special |
| 363 | names that always give error returns. This makes it straightforward to |
| 364 | test the handling of DNS errors. */ |
| 365 | |
| 366 | if (running_in_test_harness) |
| 367 | { |
| 368 | uschar *endname = name + Ustrlen(name); |
| 369 | if (Ustrcmp(endname - 14, "test.again.dns") == 0) |
| 370 | { |
| 371 | int delay = Uatoi(name); /* digits at the start of the name */ |
| 372 | DEBUG(D_dns) debug_printf("Real DNS lookup of %s (%s) bypassed for testing\n", |
| 373 | name, dns_text_type(type)); |
| 374 | if (delay > 0) |
| 375 | { |
| 376 | DEBUG(D_dns) debug_printf("delaying %d seconds\n", delay); |
| 377 | sleep(delay); |
| 378 | } |
| 379 | DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n"); |
| 380 | return dns_return(name, type, DNS_AGAIN); |
| 381 | } |
| 382 | if (Ustrcmp(endname - 13, "test.fail.dns") == 0) |
| 383 | { |
| 384 | DEBUG(D_dns) debug_printf("Real DNS lookup of %s (%s) bypassed for testing\n", |
| 385 | name, dns_text_type(type)); |
| 386 | DEBUG(D_dns) debug_printf("returning DNS_FAIL\n"); |
| 387 | return dns_return(name, type, DNS_FAIL); |
| 388 | } |
| 389 | } |
| 390 | |
| 391 | /* If configured, check the hygene of the name passed to lookup. Otherwise, |
| 392 | although DNS lookups may give REFUSED at the lower level, some resolvers |
| 393 | turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such |
| 394 | domains cannot be in the DNS. The check is now done by a regular expression; |
| 395 | give it space for substring storage to save it having to get its own if the |
| 396 | regex has substrings that are used - the default uses a conditional. |
| 397 | |
| 398 | This test is omitted for PTR records. These occur only in calls from the dnsdb |
| 399 | lookup, which constructs the names itself, so they should be OK. Besides, |
| 400 | bitstring labels don't conform to normal name syntax. (But the aren't used any |
| 401 | more.) |
| 402 | |
| 403 | For SRV records, we omit the initial _smtp._tcp. components at the start. */ |
| 404 | |
| 405 | #ifndef STAND_ALONE /* Omit this for stand-alone tests */ |
| 406 | |
| 407 | if (check_dns_names_pattern[0] != 0 && type != T_PTR) |
| 408 | { |
| 409 | uschar *checkname = name; |
| 410 | int ovector[3*(EXPAND_MAXN+1)]; |
| 411 | |
| 412 | if (regex_check_dns_names == NULL) |
| 413 | regex_check_dns_names = |
| 414 | regex_must_compile(check_dns_names_pattern, FALSE, TRUE); |
| 415 | |
| 416 | /* For an SRV lookup, skip over the first two components (the service and |
| 417 | protocol names, which both start with an underscore). */ |
| 418 | |
| 419 | if (type == T_SRV) |
| 420 | { |
| 421 | while (*checkname++ != '.'); |
| 422 | while (*checkname++ != '.'); |
| 423 | } |
| 424 | |
| 425 | if (pcre_exec(regex_check_dns_names, NULL, CS checkname, Ustrlen(checkname), |
| 426 | 0, PCRE_EOPT, ovector, sizeof(ovector)/sizeof(int)) < 0) |
| 427 | { |
| 428 | DEBUG(D_dns) |
| 429 | debug_printf("DNS name syntax check failed: %s (%s)\n", name, |
| 430 | dns_text_type(type)); |
| 431 | host_find_failed_syntax = TRUE; |
| 432 | return DNS_NOMATCH; |
| 433 | } |
| 434 | } |
| 435 | |
| 436 | #endif /* STAND_ALONE */ |
| 437 | |
| 438 | /* Call the resolver; for an overlong response, res_search() will return the |
| 439 | number of bytes the message would need, so we need to check for this case. |
| 440 | The effect is to truncate overlong data. */ |
| 441 | |
| 442 | dnsa->answerlen = res_search(CS name, C_IN, type, dnsa->answer, MAXPACKET); |
| 443 | if (dnsa->answerlen > MAXPACKET) dnsa->answerlen = MAXPACKET; |
| 444 | |
| 445 | if (dnsa->answerlen < 0) switch (h_errno) |
| 446 | { |
| 447 | case HOST_NOT_FOUND: |
| 448 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n" |
| 449 | "returning DNS_NOMATCH\n", name, dns_text_type(type)); |
| 450 | return dns_return(name, type, DNS_NOMATCH); |
| 451 | |
| 452 | case TRY_AGAIN: |
| 453 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n", |
| 454 | name, dns_text_type(type)); |
| 455 | |
| 456 | /* Cut this out for various test programs */ |
| 457 | #ifndef STAND_ALONE |
| 458 | save = deliver_domain; |
| 459 | deliver_domain = name; /* set $domain */ |
| 460 | rc = match_isinlist(name, &dns_again_means_nonexist, 0, NULL, NULL, |
| 461 | MCL_DOMAIN, TRUE, NULL); |
| 462 | deliver_domain = save; |
| 463 | if (rc != OK) |
| 464 | { |
| 465 | DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n"); |
| 466 | return dns_return(name, type, DNS_AGAIN); |
| 467 | } |
| 468 | DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning " |
| 469 | "DNS_NOMATCH\n", name); |
| 470 | return dns_return(name, type, DNS_NOMATCH); |
| 471 | |
| 472 | #else /* For stand-alone tests */ |
| 473 | return dns_return(name, type, DNS_AGAIN); |
| 474 | #endif |
| 475 | |
| 476 | case NO_RECOVERY: |
| 477 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n" |
| 478 | "returning DNS_FAIL\n", name, dns_text_type(type)); |
| 479 | return dns_return(name, type, DNS_FAIL); |
| 480 | |
| 481 | case NO_DATA: |
| 482 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n" |
| 483 | "returning DNS_NODATA\n", name, dns_text_type(type)); |
| 484 | return dns_return(name, type, DNS_NODATA); |
| 485 | |
| 486 | default: |
| 487 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n" |
| 488 | "returning DNS_FAIL\n", name, dns_text_type(type), h_errno); |
| 489 | return dns_return(name, type, DNS_FAIL); |
| 490 | } |
| 491 | |
| 492 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n", |
| 493 | name, dns_text_type(type)); |
| 494 | |
| 495 | return DNS_SUCCEED; |
| 496 | } |
| 497 | |
| 498 | |
| 499 | |
| 500 | |
| 501 | /************************************************ |
| 502 | * Do a DNS lookup and handle CNAMES * |
| 503 | ************************************************/ |
| 504 | |
| 505 | /* Look up the given domain name, using the given type. Follow CNAMEs if |
| 506 | necessary, but only so many times. There aren't supposed to be CNAME chains in |
| 507 | the DNS, but you are supposed to cope with them if you find them. |
| 508 | |
| 509 | The assumption is made that if the resolver gives back records of the |
| 510 | requested type *and* a CNAME, we don't need to make another call to look up |
| 511 | the CNAME. I can't see how it could return only some of the right records. If |
| 512 | it's done a CNAME lookup in the past, it will have all of them; if not, it |
| 513 | won't return any. |
| 514 | |
| 515 | If fully_qualified_name is not NULL, set it to point to the full name |
| 516 | returned by the resolver, if this is different to what it is given, unless |
| 517 | the returned name starts with "*" as some nameservers seem to be returning |
| 518 | wildcards in this form. |
| 519 | |
| 520 | Arguments: |
| 521 | dnsa pointer to dns_answer structure |
| 522 | name domain name to look up |
| 523 | type DNS record type (T_A, T_MX, etc) |
| 524 | fully_qualified_name if not NULL, return the returned name here if its |
| 525 | contents are different (i.e. it must be preset) |
| 526 | |
| 527 | Returns: DNS_SUCCEED successful lookup |
| 528 | DNS_NOMATCH name not found |
| 529 | DNS_NODATA no data found |
| 530 | DNS_AGAIN soft failure, try again later |
| 531 | DNS_FAIL DNS failure |
| 532 | */ |
| 533 | |
| 534 | int |
| 535 | dns_lookup(dns_answer *dnsa, uschar *name, int type, uschar **fully_qualified_name) |
| 536 | { |
| 537 | int i; |
| 538 | uschar *orig_name = name; |
| 539 | |
| 540 | /* Loop to follow CNAME chains so far, but no further... */ |
| 541 | |
| 542 | for (i = 0; i < 10; i++) |
| 543 | { |
| 544 | uschar data[256]; |
| 545 | dns_record *rr, cname_rr, type_rr; |
| 546 | dns_scan dnss; |
| 547 | int datalen, rc; |
| 548 | |
| 549 | /* DNS lookup failures get passed straight back. */ |
| 550 | |
| 551 | if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED) return rc; |
| 552 | |
| 553 | /* We should have either records of the required type, or a CNAME record, |
| 554 | or both. We need to know whether both exist for getting the fully qualified |
| 555 | name, but avoid scanning more than necessary. Note that we must copy the |
| 556 | contents of any rr blocks returned by dns_next_rr() as they use the same |
| 557 | area in the dnsa block. */ |
| 558 | |
| 559 | cname_rr.data = type_rr.data = NULL; |
| 560 | for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); |
| 561 | rr != NULL; |
| 562 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) |
| 563 | { |
| 564 | if (rr->type == type) |
| 565 | { |
| 566 | if (type_rr.data == NULL) type_rr = *rr; |
| 567 | if (cname_rr.data != NULL) break; |
| 568 | } |
| 569 | else if (rr->type == T_CNAME) cname_rr = *rr; |
| 570 | } |
| 571 | |
| 572 | /* If a CNAME was found, take the fully qualified name from it; otherwise |
| 573 | from the first data record, if present. For testing, there is a magic name |
| 574 | that gets its casing adjusted, because my resolver doesn't seem to pass back |
| 575 | upper case letters in domain names. */ |
| 576 | |
| 577 | if (fully_qualified_name != NULL) |
| 578 | { |
| 579 | if (cname_rr.data != NULL) |
| 580 | { |
| 581 | if (Ustrcmp(cname_rr.name, *fully_qualified_name) != 0 && |
| 582 | cname_rr.name[0] != '*') |
| 583 | *fully_qualified_name = string_copy_dnsdomain(cname_rr.name); |
| 584 | } |
| 585 | else if (type_rr.data != NULL) |
| 586 | { |
| 587 | if (running_in_test_harness && |
| 588 | Ustrcmp(type_rr.name, "uppercase.test.ex") == 0) |
| 589 | *fully_qualified_name = US"UpperCase.test.ex"; |
| 590 | else |
| 591 | { |
| 592 | if (Ustrcmp(type_rr.name, *fully_qualified_name) != 0 && |
| 593 | type_rr.name[0] != '*') |
| 594 | *fully_qualified_name = string_copy_dnsdomain(type_rr.name); |
| 595 | } |
| 596 | } |
| 597 | } |
| 598 | |
| 599 | /* If any data records of the correct type were found, we are done. */ |
| 600 | |
| 601 | if (type_rr.data != NULL) return DNS_SUCCEED; |
| 602 | |
| 603 | /* If there are no data records, we need to re-scan the DNS using the |
| 604 | domain given in the CNAME record, which should exist (otherwise we should |
| 605 | have had a failure from dns_lookup). However code against the possibility of |
| 606 | its not existing. */ |
| 607 | |
| 608 | if (cname_rr.data == NULL) return DNS_FAIL; |
| 609 | datalen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, |
| 610 | cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, 256); |
| 611 | if (datalen < 0) return DNS_FAIL; |
| 612 | name = data; |
| 613 | } /* Loop back to do another lookup */ |
| 614 | |
| 615 | /*Control reaches here after 10 times round the CNAME loop. Something isn't |
| 616 | right... */ |
| 617 | |
| 618 | log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name); |
| 619 | return DNS_FAIL; |
| 620 | } |
| 621 | |
| 622 | |
| 623 | |
| 624 | |
| 625 | |
| 626 | |
| 627 | /************************************************ |
| 628 | * Do a DNS lookup and handle virtual types * |
| 629 | ************************************************/ |
| 630 | |
| 631 | /* This function handles some invented "lookup types" that synthesize feature |
| 632 | not available in the basic types. The special types all have negative values. |
| 633 | Positive type values are passed straight on to dns_lookup(). |
| 634 | |
| 635 | Arguments: |
| 636 | dnsa pointer to dns_answer structure |
| 637 | name domain name to look up |
| 638 | type DNS record type (T_A, T_MX, etc or a "special") |
| 639 | fully_qualified_name if not NULL, return the returned name here if its |
| 640 | contents are different (i.e. it must be preset) |
| 641 | |
| 642 | Returns: DNS_SUCCEED successful lookup |
| 643 | DNS_NOMATCH name not found |
| 644 | DNS_NODATA no data found |
| 645 | DNS_AGAIN soft failure, try again later |
| 646 | DNS_FAIL DNS failure |
| 647 | */ |
| 648 | |
| 649 | int |
| 650 | dns_special_lookup(dns_answer *dnsa, uschar *name, int type, |
| 651 | uschar **fully_qualified_name) |
| 652 | { |
| 653 | if (type >= 0) return dns_lookup(dnsa, name, type, fully_qualified_name); |
| 654 | |
| 655 | /* The "mx hosts only" type doesn't require any special action here */ |
| 656 | |
| 657 | if (type == T_MXH) return dns_lookup(dnsa, name, T_MX, fully_qualified_name); |
| 658 | |
| 659 | /* Find nameservers for the domain or the nearest enclosing zone, excluding the |
| 660 | root servers. */ |
| 661 | |
| 662 | if (type == T_ZNS) |
| 663 | { |
| 664 | uschar *d = name; |
| 665 | while (d != 0) |
| 666 | { |
| 667 | int rc = dns_lookup(dnsa, d, T_NS, fully_qualified_name); |
| 668 | if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc; |
| 669 | while (*d != 0 && *d != '.') d++; |
| 670 | if (*d++ == 0) break; |
| 671 | } |
| 672 | return DNS_NOMATCH; |
| 673 | } |
| 674 | |
| 675 | /* Try to look up the Client SMTP Authorization SRV record for the name. If |
| 676 | there isn't one, search from the top downwards for a CSA record in a parent |
| 677 | domain, which might be making assertions about subdomains. If we find a record |
| 678 | we set fully_qualified_name to whichever lookup succeeded, so that the caller |
| 679 | can tell whether to look at the explicit authorization field or the subdomain |
| 680 | assertion field. */ |
| 681 | |
| 682 | if (type == T_CSA) |
| 683 | { |
| 684 | uschar *srvname, *namesuff, *tld, *p; |
| 685 | int priority, weight, port; |
| 686 | int limit, rc, i; |
| 687 | BOOL ipv6; |
| 688 | dns_record *rr; |
| 689 | dns_scan dnss; |
| 690 | |
| 691 | DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name); |
| 692 | |
| 693 | srvname = string_sprintf("_client._smtp.%s", name); |
| 694 | rc = dns_lookup(dnsa, srvname, T_SRV, NULL); |
| 695 | if (rc == DNS_SUCCEED || rc == DNS_AGAIN) |
| 696 | { |
| 697 | if (rc == DNS_SUCCEED) *fully_qualified_name = name; |
| 698 | return rc; |
| 699 | } |
| 700 | |
| 701 | /* Search for CSA subdomain assertion SRV records from the top downwards, |
| 702 | starting with the 2nd level domain. This order maximizes cache-friendliness. |
| 703 | We skip the top level domains to avoid loading their nameservers and because |
| 704 | we know they'll never have CSA SRV records. */ |
| 705 | |
| 706 | namesuff = Ustrrchr(name, '.'); |
| 707 | if (namesuff == NULL) return DNS_NOMATCH; |
| 708 | tld = namesuff + 1; |
| 709 | ipv6 = FALSE; |
| 710 | limit = dns_csa_search_limit; |
| 711 | |
| 712 | /* Use more appropriate search parameters if we are in the reverse DNS. */ |
| 713 | |
| 714 | if (strcmpic(namesuff, US".arpa") == 0) |
| 715 | { |
| 716 | if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0) |
| 717 | { |
| 718 | namesuff -= 8; |
| 719 | tld = namesuff + 1; |
| 720 | limit = 3; |
| 721 | } |
| 722 | else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0) |
| 723 | { |
| 724 | namesuff -= 4; |
| 725 | tld = namesuff + 1; |
| 726 | ipv6 = TRUE; |
| 727 | limit = 3; |
| 728 | } |
| 729 | } |
| 730 | |
| 731 | DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld); |
| 732 | |
| 733 | /* Do not perform the search if the top level or 2nd level domains do not |
| 734 | exist. This is quite common, and when it occurs all the search queries would |
| 735 | go to the root or TLD name servers, which is not friendly. So we check the |
| 736 | AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then |
| 737 | the TLD or the 2LD (respectively) doesn't exist and we can skip the search. |
| 738 | If the TLD and the 2LD exist but the explicit CSA record lookup failed, then |
| 739 | the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */ |
| 740 | |
| 741 | if (rc == DNS_NOMATCH) |
| 742 | { |
| 743 | /* This is really gross. The successful return value from res_search() is |
| 744 | the packet length, which is stored in dnsa->answerlen. If we get a |
| 745 | negative DNS reply then res_search() returns -1, which causes the bounds |
| 746 | checks for name decompression to fail when it is treated as a packet |
| 747 | length, which in turn causes the authority search to fail. The correct |
| 748 | packet length has been lost inside libresolv, so we have to guess a |
| 749 | replacement value. (The only way to fix this properly would be to |
| 750 | re-implement res_search() and res_query() so that they don't muddle their |
| 751 | success and packet length return values.) For added safety we only reset |
| 752 | the packet length if the packet header looks plausible. */ |
| 753 | |
| 754 | HEADER *h = (HEADER *)dnsa->answer; |
| 755 | if (h->qr == 1 && h->opcode == QUERY && h->tc == 0 |
| 756 | && (h->rcode == NOERROR || h->rcode == NXDOMAIN) |
| 757 | && ntohs(h->qdcount) == 1 && ntohs(h->ancount) == 0 |
| 758 | && ntohs(h->nscount) >= 1) |
| 759 | dnsa->answerlen = MAXPACKET; |
| 760 | |
| 761 | for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY); |
| 762 | rr != NULL; |
| 763 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) |
| 764 | if (rr->type != T_SOA) continue; |
| 765 | else if (strcmpic(rr->name, US"") == 0 || |
| 766 | strcmpic(rr->name, tld) == 0) return DNS_NOMATCH; |
| 767 | else break; |
| 768 | } |
| 769 | |
| 770 | for (i = 0; i < limit; i++) |
| 771 | { |
| 772 | if (ipv6) |
| 773 | { |
| 774 | /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP |
| 775 | address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */ |
| 776 | namesuff -= 8; |
| 777 | if (namesuff <= name) return DNS_NOMATCH; |
| 778 | } |
| 779 | else |
| 780 | /* Find the start of the preceding domain name label. */ |
| 781 | do |
| 782 | if (--namesuff <= name) return DNS_NOMATCH; |
| 783 | while (*namesuff != '.'); |
| 784 | |
| 785 | DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1); |
| 786 | |
| 787 | srvname = string_sprintf("_client._smtp.%s", namesuff + 1); |
| 788 | rc = dns_lookup(dnsa, srvname, T_SRV, NULL); |
| 789 | if (rc == DNS_AGAIN) return rc; |
| 790 | if (rc != DNS_SUCCEED) continue; |
| 791 | |
| 792 | /* Check that the SRV record we have found is worth returning. We don't |
| 793 | just return the first one we find, because some lower level SRV record |
| 794 | might make stricter assertions than its parent domain. */ |
| 795 | |
| 796 | for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); |
| 797 | rr != NULL; |
| 798 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) |
| 799 | { |
| 800 | if (rr->type != T_SRV) continue; |
| 801 | |
| 802 | /* Extract the numerical SRV fields (p is incremented) */ |
| 803 | p = rr->data; |
| 804 | GETSHORT(priority, p); |
| 805 | GETSHORT(weight, p); |
| 806 | GETSHORT(port, p); |
| 807 | |
| 808 | /* Check the CSA version number */ |
| 809 | if (priority != 1) continue; |
| 810 | |
| 811 | /* If it's making an interesting assertion, return this response. */ |
| 812 | if (port & 1) |
| 813 | { |
| 814 | *fully_qualified_name = namesuff + 1; |
| 815 | return DNS_SUCCEED; |
| 816 | } |
| 817 | } |
| 818 | } |
| 819 | return DNS_NOMATCH; |
| 820 | } |
| 821 | |
| 822 | /* Control should never reach here */ |
| 823 | |
| 824 | return DNS_FAIL; |
| 825 | } |
| 826 | |
| 827 | |
| 828 | |
| 829 | /* Support for A6 records has been commented out since they were demoted to |
| 830 | experimental status at IETF 51. */ |
| 831 | |
| 832 | #if HAVE_IPV6 && defined(SUPPORT_A6) |
| 833 | |
| 834 | /************************************************* |
| 835 | * Search DNS block for prefix RRs * |
| 836 | *************************************************/ |
| 837 | |
| 838 | /* Called from dns_complete_a6() to search an additional section or a main |
| 839 | answer section for required prefix records to complete an IPv6 address obtained |
| 840 | from an A6 record. For each prefix record, a recursive call to dns_complete_a6 |
| 841 | is made, with a new copy of the address so far. |
| 842 | |
| 843 | Arguments: |
| 844 | dnsa the DNS answer block |
| 845 | which RESET_ADDITIONAL or RESET_ANSWERS |
| 846 | name name of prefix record |
| 847 | yptrptr pointer to the pointer that points to where to hang the next |
| 848 | dns_address structure |
| 849 | bits number of bits we have already got |
| 850 | bitvec the bits we have already got |
| 851 | |
| 852 | Returns: TRUE if any records were found |
| 853 | */ |
| 854 | |
| 855 | static BOOL |
| 856 | dns_find_prefix(dns_answer *dnsa, int which, uschar *name, dns_address |
| 857 | ***yptrptr, int bits, uschar *bitvec) |
| 858 | { |
| 859 | BOOL yield = FALSE; |
| 860 | dns_record *rr; |
| 861 | dns_scan dnss; |
| 862 | |
| 863 | for (rr = dns_next_rr(dnsa, &dnss, which); |
| 864 | rr != NULL; |
| 865 | rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) |
| 866 | { |
| 867 | uschar cbitvec[16]; |
| 868 | if (rr->type != T_A6 || strcmpic(rr->name, name) != 0) continue; |
| 869 | yield = TRUE; |
| 870 | memcpy(cbitvec, bitvec, sizeof(cbitvec)); |
| 871 | dns_complete_a6(yptrptr, dnsa, rr, bits, cbitvec); |
| 872 | } |
| 873 | |
| 874 | return yield; |
| 875 | } |
| 876 | |
| 877 | |
| 878 | |
| 879 | /************************************************* |
| 880 | * Follow chains of A6 records * |
| 881 | *************************************************/ |
| 882 | |
| 883 | /* A6 records may be incomplete, with pointers to other records containing more |
| 884 | bits of the address. There can be a tree structure, leading to a number of |
| 885 | addresses originating from a single initial A6 record. |
| 886 | |
| 887 | Arguments: |
| 888 | yptrptr pointer to the pointer that points to where to hang the next |
| 889 | dns_address structure |
| 890 | dnsa the current DNS answer block |
| 891 | rr the RR we have at present |
| 892 | bits number of bits we have already got |
| 893 | bitvec the bits we have already got |
| 894 | |
| 895 | Returns: nothing |
| 896 | */ |
| 897 | |
| 898 | static void |
| 899 | dns_complete_a6(dns_address ***yptrptr, dns_answer *dnsa, dns_record *rr, |
| 900 | int bits, uschar *bitvec) |
| 901 | { |
| 902 | static uschar bitmask[] = { 0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80 }; |
| 903 | uschar *p = (uschar *)(rr->data); |
| 904 | int prefix_len, suffix_len; |
| 905 | int i, j, k; |
| 906 | uschar *chainptr; |
| 907 | uschar chain[264]; |
| 908 | dns_answer cdnsa; |
| 909 | |
| 910 | /* The prefix length is the first byte. It defines the prefix which is missing |
| 911 | from the data in this record as a number of bits. Zero means this is the end of |
| 912 | a chain. The suffix is the data in this record; only sufficient bytes to hold |
| 913 | it are supplied. There may be zero bytes. We have to ignore trailing bits that |
| 914 | we have already obtained from earlier RRs in the chain. */ |
| 915 | |
| 916 | prefix_len = *p++; /* bits */ |
| 917 | suffix_len = (128 - prefix_len + 7)/8; /* bytes */ |
| 918 | |
| 919 | /* If the prefix in this record is greater than the prefix in the previous |
| 920 | record in the chain, we have to ignore the record (RFC 2874). */ |
| 921 | |
| 922 | if (prefix_len > 128 - bits) return; |
| 923 | |
| 924 | /* In this little loop, the number of bits up to and including the current byte |
| 925 | is held in k. If we have none of the bits in this byte, we can just or it into |
| 926 | the current data. If we have all of the bits in this byte, we skip it. |
| 927 | Otherwise, some masking has to be done. */ |
| 928 | |
| 929 | for (i = suffix_len - 1, j = 15, k = 8; i >= 0; i--) |
| 930 | { |
| 931 | int required = k - bits; |
| 932 | if (required >= 8) bitvec[j] |= p[i]; |
| 933 | else if (required > 0) bitvec[j] |= p[i] & bitmask[required]; |
| 934 | j--; /* I tried putting these in the "for" statement, but gcc muttered */ |
| 935 | k += 8; /* about computed values not being used. */ |
| 936 | } |
| 937 | |
| 938 | /* If the prefix_length is zero, we are at the end of a chain. Build a |
| 939 | dns_address item with the current data, hang it onto the end of the chain, |
| 940 | adjust the hanging pointer, and we are done. */ |
| 941 | |
| 942 | if (prefix_len == 0) |
| 943 | { |
| 944 | dns_address *new = store_get(sizeof(dns_address) + 50); |
| 945 | inet_ntop(AF_INET6, bitvec, CS new->address, 50); |
| 946 | new->next = NULL; |
| 947 | **yptrptr = new; |
| 948 | *yptrptr = &(new->next); |
| 949 | return; |
| 950 | } |
| 951 | |
| 952 | /* Prefix length is not zero. Reset the number of bits that we have collected |
| 953 | so far, and extract the chain name. */ |
| 954 | |
| 955 | bits = 128 - prefix_len; |
| 956 | p += suffix_len; |
| 957 | |
| 958 | chainptr = chain; |
| 959 | while ((i = *p++) != 0) |
| 960 | { |
| 961 | if (chainptr != chain) *chainptr++ = '.'; |
| 962 | memcpy(chainptr, p, i); |
| 963 | chainptr += i; |
| 964 | p += i; |
| 965 | } |
| 966 | *chainptr = 0; |
| 967 | chainptr = chain; |
| 968 | |
| 969 | /* Now scan the current DNS response record to see if the additional section |
| 970 | contains the records we want. This processing can be cut out for testing |
| 971 | purposes. */ |
| 972 | |
| 973 | if (dns_find_prefix(dnsa, RESET_ADDITIONAL, chainptr, yptrptr, bits, bitvec)) |
| 974 | return; |
| 975 | |
| 976 | /* No chain records were found in the current DNS response block. Do a new DNS |
| 977 | lookup to try to find these records. This opens up the possibility of DNS |
| 978 | failures. We ignore them at this point; if all branches of the tree fail, there |
| 979 | will be no addresses at the end. */ |
| 980 | |
| 981 | if (dns_lookup(&cdnsa, chainptr, T_A6, NULL) == DNS_SUCCEED) |
| 982 | (void)dns_find_prefix(&cdnsa, RESET_ANSWERS, chainptr, yptrptr, bits, bitvec); |
| 983 | } |
| 984 | #endif /* HAVE_IPV6 && defined(SUPPORT_A6) */ |
| 985 | |
| 986 | |
| 987 | |
| 988 | |
| 989 | /************************************************* |
| 990 | * Get address(es) from DNS record * |
| 991 | *************************************************/ |
| 992 | |
| 993 | /* The record type is either T_A for an IPv4 address or T_AAAA (or T_A6 when |
| 994 | supported) for an IPv6 address. In the A6 case, there may be several addresses, |
| 995 | generated by following chains. A recursive function does all the hard work. A6 |
| 996 | records now look like passing into history, so the code is only included when |
| 997 | explicitly asked for. |
| 998 | |
| 999 | Argument: |
| 1000 | dnsa the DNS answer block |
| 1001 | rr the RR |
| 1002 | |
| 1003 | Returns: pointer a chain of dns_address items |
| 1004 | */ |
| 1005 | |
| 1006 | dns_address * |
| 1007 | dns_address_from_rr(dns_answer *dnsa, dns_record *rr) |
| 1008 | { |
| 1009 | dns_address *yield = NULL; |
| 1010 | |
| 1011 | #if HAVE_IPV6 && defined(SUPPORT_A6) |
| 1012 | dns_address **yieldptr = &yield; |
| 1013 | uschar bitvec[16]; |
| 1014 | #else |
| 1015 | dnsa = dnsa; /* Stop picky compilers warning */ |
| 1016 | #endif |
| 1017 | |
| 1018 | if (rr->type == T_A) |
| 1019 | { |
| 1020 | uschar *p = (uschar *)(rr->data); |
| 1021 | yield = store_get(sizeof(dns_address) + 20); |
| 1022 | (void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]); |
| 1023 | yield->next = NULL; |
| 1024 | } |
| 1025 | |
| 1026 | #if HAVE_IPV6 |
| 1027 | |
| 1028 | #ifdef SUPPORT_A6 |
| 1029 | else if (rr->type == T_A6) |
| 1030 | { |
| 1031 | memset(bitvec, 0, sizeof(bitvec)); |
| 1032 | dns_complete_a6(&yieldptr, dnsa, rr, 0, bitvec); |
| 1033 | } |
| 1034 | #endif /* SUPPORT_A6 */ |
| 1035 | |
| 1036 | else |
| 1037 | { |
| 1038 | yield = store_get(sizeof(dns_address) + 50); |
| 1039 | inet_ntop(AF_INET6, (uschar *)(rr->data), CS yield->address, 50); |
| 1040 | yield->next = NULL; |
| 1041 | } |
| 1042 | #endif /* HAVE_IPV6 */ |
| 1043 | |
| 1044 | return yield; |
| 1045 | } |
| 1046 | |
| 1047 | /* End of dns.c */ |