src/src/lookups/dnsdb.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2015 */
   6 /* See the file NOTICE for conditions of use and distribution. */
   7
   8 #include "../exim.h"
   9 #include "lf_functions.h"
  10
  11
  12
  13 /* Ancient systems (e.g. SunOS4) don't appear to have T_TXT defined in their
  14 header files. */
  15
  16 #ifndef T_TXT
  17 #define T_TXT 16
  18 #endif
  19
  20 /* Many systems do not have T_SPF. */
  21 #ifndef T_SPF
  22 #define T_SPF 99
  23 #endif
  24
  25 /* New TLSA record for DANE */
  26 #ifndef T_TLSA
  27 #define T_TLSA 52
  28 #endif
  29
  30 /* Table of recognized DNS record types and their integer values. */
  31
  32 static const char *type_names[] = {
  33   "a",
  34 #if HAVE_IPV6
  35   "a+",
  36   "aaaa",
  37 #endif
  38   "cname",
  39   "csa",
  40   "mx",
  41   "mxh",
  42   "ns",
  43   "ptr",
  44   "soa",
  45   "spf",
  46   "srv",
  47   "tlsa",
  48   "txt",
  49   "zns"
  50 };
  51
  52 static int type_values[] = {
  53   T_A,
  54 #if HAVE_IPV6
  55   T_ADDRESSES,     /* Private type for AAAA + A */
  56   T_AAAA,
  57 #endif
  58   T_CNAME,
  59   T_CSA,     /* Private type for "Client SMTP Authorization". */
  60   T_MX,
  61   T_MXH,     /* Private type for "MX hostnames" */
  62   T_NS,
  63   T_PTR,
  64   T_SOA,
  65   T_SPF,
  66   T_SRV,
  67   T_TLSA,
  68   T_TXT,
  69   T_ZNS      /* Private type for "zone nameservers" */
  70 };
  71
  72
  73 /*************************************************
  74 *              Open entry point                  *
  75 *************************************************/
  76
  77 /* See local README for interface description. */
  78
  79 static void *
  80 dnsdb_open(uschar *filename, uschar **errmsg)
  81 {
  82 filename = filename;   /* Keep picky compilers happy */
  83 errmsg = errmsg;       /* Ditto */
  84 return (void *)(-1);   /* Any non-0 value */
  85 }
  86
  87
  88
  89 /*************************************************
  90 *           Find entry point for dnsdb           *
  91 *************************************************/
  92
  93 /* See local README for interface description. The query in the "keystring" may
  94 consist of a number of parts.
  95
  96 (a) If the first significant character is '>' then the next character is the
  97 separator character that is used when multiple records are found. The default
  98 separator is newline.
  99
 100 (b) If the next character is ',' then the next character is the separator
 101 character used for multiple items of text in "TXT" records. Alternatively,
 102 if the next character is ';' then these multiple items are concatenated with
 103 no separator. With neither of these options specified, only the first item
 104 is output.  Similarly for "SPF" records, but the default for joining multiple
 105 items in one SPF record is the empty string, for direct concatenation.
 106
 107 (c) Options, all comma-terminated, in any order.  Any unrecognised option
 108 terminates option processing.  Recognised options are:
 109
 110 - 'defer_FOO':  set the defer behaviour to FOO.  The possible behaviours are:
 111 'strict', where any defer causes the whole lookup to defer; 'lax', where a defer
 112 causes the whole lookup to defer only if none of the DNS queries succeeds; and
 113 'never', where all defers are as if the lookup failed. The default is 'lax'.
 114
 115 - 'dnssec_FOO', with 'strict', 'lax' and 'never' (default).  The meanings are
 116 require, try and don't-try dnssec respectively.
 117
 118 - 'retrans_VAL', set the timeout value.  VAL is an Exim time specification
 119 (eg "5s").  The default is set by the main configuration option 'dns_retrans'.
 120
 121 - 'retry_VAL', set the retry count on timeouts.  VAL is an integer.  The
 122 default is set by the main configuration option "dns_retry".
 123
 124 (d) If the next sequence of characters is a sequence of letters and digits
 125 followed by '=', it is interpreted as the name of the DNS record type. The
 126 default is "TXT".
 127
 128 (e) Then there follows list of domain names. This is a generalized Exim list,
 129 which may start with '<' in order to set a specific separator. The default
 130 separator, as always, is colon. */
 131
 132 static int
 133 dnsdb_find(void *handle, uschar *filename, const uschar *keystring, int length,
 134   uschar **result, uschar **errmsg, uint *do_cache)
 135 {
 136 int rc;
 137 int size = 256;
 138 int ptr = 0;
 139 int sep = 0;
 140 int defer_mode = PASS;
 141 int dnssec_mode = OK;
 142 int save_retrans = dns_retrans;
 143 int save_retry =   dns_retry;
 144 int type;
 145 int failrc = FAIL;
 146 const uschar *outsep = CUS"\n";
 147 const uschar *outsep2 = NULL;
 148 uschar *equals, *domain, *found;
 149
 150 /* Because we're the working in the search pool, we try to reclaim as much
 151 store as possible later, so we preallocate the result here */
 152
 153 uschar *yield = store_get(size);
 154
 155 dns_record *rr;
 156 dns_answer dnsa;
 157 dns_scan dnss;
 158
 159 handle = handle;           /* Keep picky compilers happy */
 160 filename = filename;
 161 length = length;
 162 do_cache = do_cache;
 163
 164 /* If the string starts with '>' we change the output separator.
 165 If it's followed by ';' or ',' we set the TXT output separator. */
 166
 167 while (isspace(*keystring)) keystring++;
 168 if (*keystring == '>')
 169   {
 170   outsep = keystring + 1;
 171   keystring += 2;
 172   if (*keystring == ',')
 173     {
 174     outsep2 = keystring + 1;
 175     keystring += 2;
 176     }
 177   else if (*keystring == ';')
 178     {
 179     outsep2 = US"";
 180     keystring++;
 181     }
 182   while (isspace(*keystring)) keystring++;
 183   }
 184
 185 /* Check for a modifier keyword. */
 186
 187 for (;;)
 188   {
 189   if (strncmpic(keystring, US"defer_", 6) == 0)
 190     {
 191     keystring += 6;
 192     if (strncmpic(keystring, US"strict", 6) == 0)
 193       { defer_mode = DEFER; keystring += 6; }
 194     else if (strncmpic(keystring, US"lax", 3) == 0)
 195       { defer_mode = PASS; keystring += 3; }
 196     else if (strncmpic(keystring, US"never", 5) == 0)
 197       { defer_mode = OK; keystring += 5; }
 198     else
 199       {
 200       *errmsg = US"unsupported dnsdb defer behaviour";
 201       return DEFER;
 202       }
 203     }
 204   else if (strncmpic(keystring, US"dnssec_", 7) == 0)
 205     {
 206     keystring += 7;
 207     if (strncmpic(keystring, US"strict", 6) == 0)
 208       { dnssec_mode = DEFER; keystring += 6; }
 209     else if (strncmpic(keystring, US"lax", 3) == 0)
 210       { dnssec_mode = PASS; keystring += 3; }
 211     else if (strncmpic(keystring, US"never", 5) == 0)
 212       { dnssec_mode = OK; keystring += 5; }
 213     else
 214       {
 215       *errmsg = US"unsupported dnsdb dnssec behaviour";
 216       return DEFER;
 217       }
 218     }
 219   else if (strncmpic(keystring, US"retrans_", 8) == 0)
 220     {
 221     int timeout_sec;
 222     if ((timeout_sec = readconf_readtime(keystring += 8, ',', FALSE)) <= 0)
 223       {
 224       *errmsg = US"unsupported dnsdb timeout value";
 225       return DEFER;
 226       }
 227     dns_retrans = timeout_sec;
 228     while (*keystring != ',') keystring++;
 229     }
 230   else if (strncmpic(keystring, US"retry_", 6) == 0)
 231     {
 232     int retries;
 233     if ((retries = (int)strtol(CCS keystring + 6, CSS &keystring, 0)) < 0)
 234       {
 235       *errmsg = US"unsupported dnsdb retry count";
 236       return DEFER;
 237       }
 238     dns_retry = retries;
 239     }
 240   else
 241     break;
 242
 243   while (isspace(*keystring)) keystring++;
 244   if (*keystring++ != ',')
 245     {
 246     *errmsg = US"dnsdb modifier syntax error";
 247     return DEFER;
 248     }
 249   while (isspace(*keystring)) keystring++;
 250   }
 251
 252 /* Figure out the "type" value if it is not T_TXT.
 253 If the keystring contains an = this must be preceded by a valid type name. */
 254
 255 type = T_TXT;
 256 if ((equals = Ustrchr(keystring, '=')) != NULL)
 257   {
 258   int i, len;
 259   uschar *tend = equals;
 260
 261   while (tend > keystring && isspace(tend[-1])) tend--;
 262   len = tend - keystring;
 263
 264   for (i = 0; i < sizeof(type_names)/sizeof(uschar *); i++)
 265     {
 266     if (len == Ustrlen(type_names[i]) &&
 267         strncmpic(keystring, US type_names[i], len) == 0)
 268       {
 269       type = type_values[i];
 270       break;
 271       }
 272     }
 273
 274   if (i >= sizeof(type_names)/sizeof(uschar *))
 275     {
 276     *errmsg = US"unsupported DNS record type";
 277     return DEFER;
 278     }
 279
 280   keystring = equals + 1;
 281   while (isspace(*keystring)) keystring++;
 282   }
 283
 284 /* Initialize the resolver in case this is the first time it has been used. */
 285
 286 dns_init(FALSE, FALSE, dnssec_mode != OK);
 287
 288 /* The remainder of the string must be a list of domains. As long as the lookup
 289 for at least one of them succeeds, we return success. Failure means that none
 290 of them were found.
 291
 292 The original implementation did not support a list of domains. Adding the list
 293 feature is compatible, except in one case: when PTR records are being looked up
 294 for a single IPv6 address. Fortunately, we can hack in a compatibility feature
 295 here: If the type is PTR and no list separator is specified, and the entire
 296 remaining string is valid as an IP address, set an impossible separator so that
 297 it is treated as one item. */
 298
 299 if (type == T_PTR && keystring[0] != '<' &&
 300     string_is_ip_address(keystring, NULL) != 0)
 301   sep = -1;
 302
 303 /* SPF strings should be concatenated without a separator, thus make
 304 it the default if not defined (see RFC 4408 section 3.1.3).
 305 Multiple SPF records are forbidden (section 3.1.2) but are currently
 306 not handled specially, thus they are concatenated with \n by default.
 307 MX priority and value are space-separated by default.
 308 SRV and TLSA record parts are space-separated by default. */
 309
 310 if (!outsep2) switch(type)
 311   {
 312   case T_SPF:                         outsep2 = US"";  break;
 313   case T_SRV: case T_MX: case T_TLSA: outsep2 = US" "; break;
 314   }
 315
 316 /* Now scan the list and do a lookup for each item */
 317
 318 while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
 319   {
 320   uschar rbuffer[256];
 321   int searchtype = (type == T_CSA)? T_SRV :         /* record type we want */
 322                    (type == T_MXH)? T_MX :
 323                    (type == T_ZNS)? T_NS : type;
 324
 325   /* If the type is PTR or CSA, we have to construct the relevant magic lookup
 326   key if the original is an IP address (some experimental protocols are using
 327   PTR records for different purposes where the key string is a host name, and
 328   Exim's extended CSA can be keyed by domains or IP addresses). This code for
 329   doing the reversal is now in a separate function. */
 330
 331   if ((type == T_PTR || type == T_CSA) &&
 332       string_is_ip_address(domain, NULL) != 0)
 333     {
 334     dns_build_reverse(domain, rbuffer);
 335     domain = rbuffer;
 336     }
 337
 338   do
 339     {
 340     DEBUG(D_lookup) debug_printf("dnsdb key: %s\n", domain);
 341
 342     /* Do the lookup and sort out the result. There are four special types that
 343     are handled specially: T_CSA, T_ZNS, T_ADDRESSES and T_MXH.
 344     The first two are handled in a special lookup function so that the facility
 345     could be used from other parts of the Exim code. T_ADDRESSES is handled by looping
 346     over the types of A lookup.  T_MXH affects only what happens later on in
 347     this function, but for tidiness it is handled by the "special". If the
 348     lookup fails, continue with the next domain. In the case of DEFER, adjust
 349     the final "nothing found" result, but carry on to the next domain. */
 350
 351     found = domain;
 352 #if HAVE_IPV6
 353     if (type == T_ADDRESSES)            /* NB cannot happen unless HAVE_IPV6 */
 354       {
 355       if (searchtype == T_ADDRESSES) searchtype = T_AAAA;
 356       else if (searchtype == T_AAAA) searchtype = T_A;
 357       rc = dns_special_lookup(&dnsa, domain, searchtype, CUSS &found);
 358       }
 359     else
 360 #endif
 361       rc = dns_special_lookup(&dnsa, domain, type, CUSS &found);
 362
 363     lookup_dnssec_authenticated = dnssec_mode==OK ? NULL
 364       : dns_is_secure(&dnsa) ? US"yes" : US"no";
 365
 366     if (rc == DNS_NOMATCH || rc == DNS_NODATA) continue;
 367     if (  rc != DNS_SUCCEED
 368        || (dnssec_mode == DEFER && !dns_is_secure(&dnsa))
 369        )
 370       {
 371       if (defer_mode == DEFER)
 372         {
 373         dns_retrans = save_retrans;
 374         dns_retry = save_retry;
 375         dns_init(FALSE, FALSE, FALSE);                  /* clr dnssec bit */
 376         return DEFER;                                   /* always defer */
 377         }
 378       if (defer_mode == PASS) failrc = DEFER;         /* defer only if all do */
 379       continue;                                       /* treat defer as fail */
 380       }
 381
 382
 383     /* Search the returned records */
 384
 385     for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS);
 386          rr != NULL;
 387          rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT))
 388       {
 389       if (rr->type != searchtype) continue;
 390
 391       if (*do_cache > rr->ttl)
 392         *do_cache = rr->ttl;
 393
 394       if (type == T_A || type == T_AAAA || type == T_ADDRESSES)
 395         {
 396         dns_address *da;
 397         for (da = dns_address_from_rr(&dnsa, rr); da; da = da->next)
 398           {
 399           if (ptr != 0) yield = string_cat(yield, &size, &ptr, outsep, 1);
 400           yield = string_cat(yield, &size, &ptr, da->address,
 401             Ustrlen(da->address));
 402           }
 403         continue;
 404         }
 405
 406       /* Other kinds of record just have one piece of data each, but there may be
 407       several of them, of course. */
 408
 409       if (ptr != 0) yield = string_cat(yield, &size, &ptr, outsep, 1);
 410
 411       if (type == T_TXT || type == T_SPF)
 412         {
 413         if (outsep2 == NULL)
 414           {
 415           /* output only the first item of data */
 416           yield = string_cat(yield, &size, &ptr, (uschar *)(rr->data+1),
 417             (rr->data)[0]);
 418           }
 419         else
 420           {
 421           /* output all items */
 422           int data_offset = 0;
 423           while (data_offset < rr->size)
 424             {
 425             uschar chunk_len = (rr->data)[data_offset++];
 426             if (outsep2[0] != '\0' && data_offset != 1)
 427               yield = string_cat(yield, &size, &ptr, outsep2, 1);
 428             yield = string_cat(yield, &size, &ptr,
 429                              (uschar *)((rr->data)+data_offset), chunk_len);
 430             data_offset += chunk_len;
 431             }
 432           }
 433         }
 434       else if (type == T_TLSA)
 435         {
 436         uint8_t usage, selector, matching_type;
 437         uint16_t i, payload_length;
 438         uschar s[MAX_TLSA_EXPANDED_SIZE];
 439         uschar * sp = s;
 440         uschar * p = US rr->data;
 441
 442         usage = *p++;
 443         selector = *p++;
 444         matching_type = *p++;
 445         /* What's left after removing the first 3 bytes above */
 446         payload_length = rr->size - 3;
 447         sp += sprintf(CS s, "%d%c%d%c%d%c", usage, *outsep2,
 448                 selector, *outsep2, matching_type, *outsep2);
 449         /* Now append the cert/identifier, one hex char at a time */
 450         for (i=0;
 451              i < payload_length && sp-s < (MAX_TLSA_EXPANDED_SIZE - 4);
 452              i++)
 453           sp += sprintf(CS sp, "%02x", (unsigned char)p[i]);
 454
 455         yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 456         }
 457       else   /* T_CNAME, T_CSA, T_MX, T_MXH, T_NS, T_PTR, T_SOA, T_SRV */
 458         {
 459         int priority, weight, port;
 460         uschar s[264];
 461         uschar * p = US rr->data;
 462
 463         switch (type)
 464           {
 465           case T_MXH:
 466             /* mxh ignores the priority number and includes only the hostnames */
 467             GETSHORT(priority, p);
 468             break;
 469
 470           case T_MX:
 471             GETSHORT(priority, p);
 472             sprintf(CS s, "%d%c", priority, *outsep2);
 473             yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 474             break;
 475
 476           case T_SRV:
 477             GETSHORT(priority, p);
 478             GETSHORT(weight, p);
 479             GETSHORT(port, p);
 480             sprintf(CS s, "%d%c%d%c%d%c", priority, *outsep2,
 481                               weight, *outsep2, port, *outsep2);
 482             yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 483             break;
 484
 485           case T_CSA:
 486             /* See acl_verify_csa() for more comments about CSA. */
 487             GETSHORT(priority, p);
 488             GETSHORT(weight, p);
 489             GETSHORT(port, p);
 490
 491             if (priority != 1) continue;      /* CSA version must be 1 */
 492
 493             /* If the CSA record we found is not the one we asked for, analyse
 494             the subdomain assertions in the port field, else analyse the direct
 495             authorization status in the weight field. */
 496
 497             if (Ustrcmp(found, domain) != 0)
 498               {
 499               if (port & 1) *s = 'X';         /* explicit authorization required */
 500               else *s = '?';                  /* no subdomain assertions here */
 501               }
 502             else
 503               {
 504               if (weight < 2) *s = 'N';       /* not authorized */
 505               else if (weight == 2) *s = 'Y'; /* authorized */
 506               else if (weight == 3) *s = '?'; /* unauthorizable */
 507               else continue;                  /* invalid */
 508               }
 509
 510             s[1] = ' ';
 511             yield = string_cat(yield, &size, &ptr, s, 2);
 512             break;
 513
 514           default:
 515             break;
 516           }
 517
 518         /* GETSHORT() has advanced the pointer to the target domain. */
 519
 520         rc = dn_expand(dnsa.answer, dnsa.answer + dnsa.answerlen, p,
 521           (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 522
 523         /* If an overlong response was received, the data will have been
 524         truncated and dn_expand may fail. */
 525
 526         if (rc < 0)
 527           {
 528           log_write(0, LOG_MAIN, "host name alias list truncated: type=%s "
 529             "domain=%s", dns_text_type(type), domain);
 530           break;
 531           }
 532         else yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 533
 534         if (type == T_SOA && outsep2 != NULL)
 535           {
 536           unsigned long serial, refresh, retry, expire, minimum;
 537
 538           p += rc;
 539           yield = string_cat(yield, &size, &ptr, outsep2, 1);
 540
 541           rc = dn_expand(dnsa.answer, dnsa.answer + dnsa.answerlen, p,
 542             (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 543           if (rc < 0)
 544             {
 545             log_write(0, LOG_MAIN, "responsible-mailbox truncated: type=%s "
 546               "domain=%s", dns_text_type(type), domain);
 547             break;
 548             }
 549           else yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 550
 551           p += rc;
 552           GETLONG(serial, p); GETLONG(refresh, p);
 553           GETLONG(retry,  p); GETLONG(expire,  p); GETLONG(minimum, p);
 554           sprintf(CS s, "%c%lu%c%lu%c%lu%c%lu%c%lu",
 555             *outsep2, serial, *outsep2, refresh,
 556             *outsep2, retry,  *outsep2, expire,  *outsep2, minimum);
 557           yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
 558           }
 559         }
 560       }    /* Loop for list of returned records */
 561
 562            /* Loop for set of A-lookupu types */
 563     } while (type == T_ADDRESSES && searchtype != T_A);
 564
 565   }        /* Loop for list of domains */
 566
 567 /* Reclaim unused memory */
 568
 569 store_reset(yield + ptr + 1);
 570
 571 /* If ptr == 0 we have not found anything. Otherwise, insert the terminating
 572 zero and return the result. */
 573
 574 dns_retrans = save_retrans;
 575 dns_retry = save_retry;
 576 dns_init(FALSE, FALSE, FALSE);  /* clear the dnssec bit for getaddrbyname */
 577
 578 if (ptr == 0) return failrc;
 579 yield[ptr] = 0;
 580 *result = yield;
 581 return OK;
 582 }
 583
 584
 585
 586 /*************************************************
 587 *         Version reporting entry point          *
 588 *************************************************/
 589
 590 /* See local README for interface description. */
 591
 592 #include "../version.h"
 593
 594 void
 595 dnsdb_version_report(FILE *f)
 596 {
 597 #ifdef DYNLOOKUP
 598 fprintf(f, "Library version: DNSDB: Exim version %s\n", EXIM_VERSION_STR);
 599 #endif
 600 }
 601
 602
 603 static lookup_info _lookup_info = {
 604   US"dnsdb",                     /* lookup name */
 605   lookup_querystyle,             /* query style */
 606   dnsdb_open,                    /* open function */
 607   NULL,                          /* check function */
 608   dnsdb_find,                    /* find function */
 609   NULL,                          /* no close function */
 610   NULL,                          /* no tidy function */
 611   NULL,                          /* no quoting function */
 612   dnsdb_version_report           /* version reporting */
 613 };
 614
 615 #ifdef DYNLOOKUP
 616 #define dnsdb_lookup_module_info _lookup_module_info
 617 #endif
 618
 619 static lookup_info *_lookup_list[] = { &_lookup_info };
 620 lookup_module_info dnsdb_lookup_module_info = { LOOKUP_MODULE_INFO_MAGIC, _lookup_list, 1 };
 621
 622 /* vi: aw ai sw=2
 623 */
 624 /* End of lookups/dnsdb.c */