src/lookups/dnsdb.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2018 */
   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 sep = 0;
 138 int defer_mode = PASS;
 139 int dnssec_mode = OK;
 140 int save_retrans = dns_retrans;
 141 int save_retry =   dns_retry;
 142 int type;
 143 int failrc = FAIL;
 144 const uschar *outsep = CUS"\n";
 145 const uschar *outsep2 = NULL;
 146 uschar *equals, *domain, *found;
 147
 148 /* Because we're working in the search pool, we try to reclaim as much
 149 store as possible later, so we preallocate the result here */
 150
 151 gstring * yield = string_get(256);
 152
 153 dns_record * rr;
 154 dns_answer dnsa;
 155 dns_scan dnss;
 156
 157 handle = handle;           /* Keep picky compilers happy */
 158 filename = filename;
 159 length = length;
 160 do_cache = do_cache;
 161
 162 /* If the string starts with '>' we change the output separator.
 163 If it's followed by ';' or ',' we set the TXT output separator. */
 164
 165 while (isspace(*keystring)) keystring++;
 166 if (*keystring == '>')
 167   {
 168   outsep = keystring + 1;
 169   keystring += 2;
 170   if (*keystring == ',')
 171     {
 172     outsep2 = keystring + 1;
 173     keystring += 2;
 174     }
 175   else if (*keystring == ';')
 176     {
 177     outsep2 = US"";
 178     keystring++;
 179     }
 180   while (isspace(*keystring)) keystring++;
 181   }
 182
 183 /* Check for a modifier keyword. */
 184
 185 for (;;)
 186   {
 187   if (strncmpic(keystring, US"defer_", 6) == 0)
 188     {
 189     keystring += 6;
 190     if (strncmpic(keystring, US"strict", 6) == 0)
 191       { defer_mode = DEFER; keystring += 6; }
 192     else if (strncmpic(keystring, US"lax", 3) == 0)
 193       { defer_mode = PASS; keystring += 3; }
 194     else if (strncmpic(keystring, US"never", 5) == 0)
 195       { defer_mode = OK; keystring += 5; }
 196     else
 197       {
 198       *errmsg = US"unsupported dnsdb defer behaviour";
 199       return DEFER;
 200       }
 201     }
 202   else if (strncmpic(keystring, US"dnssec_", 7) == 0)
 203     {
 204     keystring += 7;
 205     if (strncmpic(keystring, US"strict", 6) == 0)
 206       { dnssec_mode = DEFER; keystring += 6; }
 207     else if (strncmpic(keystring, US"lax", 3) == 0)
 208       { dnssec_mode = PASS; keystring += 3; }
 209     else if (strncmpic(keystring, US"never", 5) == 0)
 210       { dnssec_mode = OK; keystring += 5; }
 211     else
 212       {
 213       *errmsg = US"unsupported dnsdb dnssec behaviour";
 214       return DEFER;
 215       }
 216     }
 217   else if (strncmpic(keystring, US"retrans_", 8) == 0)
 218     {
 219     int timeout_sec;
 220     if ((timeout_sec = readconf_readtime(keystring += 8, ',', FALSE)) <= 0)
 221       {
 222       *errmsg = US"unsupported dnsdb timeout value";
 223       return DEFER;
 224       }
 225     dns_retrans = timeout_sec;
 226     while (*keystring != ',') keystring++;
 227     }
 228   else if (strncmpic(keystring, US"retry_", 6) == 0)
 229     {
 230     int retries;
 231     if ((retries = (int)strtol(CCS keystring + 6, CSS &keystring, 0)) < 0)
 232       {
 233       *errmsg = US"unsupported dnsdb retry count";
 234       return DEFER;
 235       }
 236     dns_retry = retries;
 237     }
 238   else
 239     break;
 240
 241   while (isspace(*keystring)) keystring++;
 242   if (*keystring++ != ',')
 243     {
 244     *errmsg = US"dnsdb modifier syntax error";
 245     return DEFER;
 246     }
 247   while (isspace(*keystring)) keystring++;
 248   }
 249
 250 /* Figure out the "type" value if it is not T_TXT.
 251 If the keystring contains an = this must be preceded by a valid type name. */
 252
 253 type = T_TXT;
 254 if ((equals = Ustrchr(keystring, '=')) != NULL)
 255   {
 256   int i, len;
 257   uschar *tend = equals;
 258
 259   while (tend > keystring && isspace(tend[-1])) tend--;
 260   len = tend - keystring;
 261
 262   for (i = 0; i < nelem(type_names); i++)
 263     if (len == Ustrlen(type_names[i]) &&
 264         strncmpic(keystring, US type_names[i], len) == 0)
 265       {
 266       type = type_values[i];
 267       break;
 268       }
 269
 270   if (i >= nelem(type_names))
 271     {
 272     *errmsg = US"unsupported DNS record type";
 273     return DEFER;
 274     }
 275
 276   keystring = equals + 1;
 277   while (isspace(*keystring)) keystring++;
 278   }
 279
 280 /* Initialize the resolver in case this is the first time it has been used. */
 281
 282 dns_init(FALSE, FALSE, dnssec_mode != OK);
 283
 284 /* The remainder of the string must be a list of domains. As long as the lookup
 285 for at least one of them succeeds, we return success. Failure means that none
 286 of them were found.
 287
 288 The original implementation did not support a list of domains. Adding the list
 289 feature is compatible, except in one case: when PTR records are being looked up
 290 for a single IPv6 address. Fortunately, we can hack in a compatibility feature
 291 here: If the type is PTR and no list separator is specified, and the entire
 292 remaining string is valid as an IP address, set an impossible separator so that
 293 it is treated as one item. */
 294
 295 if (type == T_PTR && keystring[0] != '<' &&
 296     string_is_ip_address(keystring, NULL) != 0)
 297   sep = -1;
 298
 299 /* SPF strings should be concatenated without a separator, thus make
 300 it the default if not defined (see RFC 4408 section 3.1.3).
 301 Multiple SPF records are forbidden (section 3.1.2) but are currently
 302 not handled specially, thus they are concatenated with \n by default.
 303 MX priority and value are space-separated by default.
 304 SRV and TLSA record parts are space-separated by default. */
 305
 306 if (!outsep2) switch(type)
 307   {
 308   case T_SPF:                         outsep2 = US"";  break;
 309   case T_SRV: case T_MX: case T_TLSA: outsep2 = US" "; break;
 310   }
 311
 312 /* Now scan the list and do a lookup for each item */
 313
 314 while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
 315   {
 316   uschar rbuffer[256];
 317   int searchtype = (type == T_CSA)? T_SRV :         /* record type we want */
 318                    (type == T_MXH)? T_MX :
 319                    (type == T_ZNS)? T_NS : type;
 320
 321   /* If the type is PTR or CSA, we have to construct the relevant magic lookup
 322   key if the original is an IP address (some experimental protocols are using
 323   PTR records for different purposes where the key string is a host name, and
 324   Exim's extended CSA can be keyed by domains or IP addresses). This code for
 325   doing the reversal is now in a separate function. */
 326
 327   if ((type == T_PTR || type == T_CSA) &&
 328       string_is_ip_address(domain, NULL) != 0)
 329     {
 330     dns_build_reverse(domain, rbuffer);
 331     domain = rbuffer;
 332     }
 333
 334   do
 335     {
 336     DEBUG(D_lookup) debug_printf("dnsdb key: %s\n", domain);
 337
 338     /* Do the lookup and sort out the result. There are four special types that
 339     are handled specially: T_CSA, T_ZNS, T_ADDRESSES and T_MXH.
 340     The first two are handled in a special lookup function so that the facility
 341     could be used from other parts of the Exim code. T_ADDRESSES is handled by looping
 342     over the types of A lookup.  T_MXH affects only what happens later on in
 343     this function, but for tidiness it is handled by the "special". If the
 344     lookup fails, continue with the next domain. In the case of DEFER, adjust
 345     the final "nothing found" result, but carry on to the next domain. */
 346
 347     found = domain;
 348 #if HAVE_IPV6
 349     if (type == T_ADDRESSES)            /* NB cannot happen unless HAVE_IPV6 */
 350       {
 351       if (searchtype == T_ADDRESSES) searchtype = T_AAAA;
 352       else if (searchtype == T_AAAA) searchtype = T_A;
 353       rc = dns_special_lookup(&dnsa, domain, searchtype, CUSS &found);
 354       }
 355     else
 356 #endif
 357       rc = dns_special_lookup(&dnsa, domain, type, CUSS &found);
 358
 359     lookup_dnssec_authenticated = dnssec_mode==OK ? NULL
 360       : dns_is_secure(&dnsa) ? US"yes" : US"no";
 361
 362     if (rc == DNS_NOMATCH || rc == DNS_NODATA) continue;
 363     if (  rc != DNS_SUCCEED
 364        || (dnssec_mode == DEFER && !dns_is_secure(&dnsa))
 365        )
 366       {
 367       if (defer_mode == DEFER)
 368         {
 369         dns_retrans = save_retrans;
 370         dns_retry = save_retry;
 371         dns_init(FALSE, FALSE, FALSE);                  /* clr dnssec bit */
 372         return DEFER;                                   /* always defer */
 373         }
 374       if (defer_mode == PASS) failrc = DEFER;         /* defer only if all do */
 375       continue;                                       /* treat defer as fail */
 376       }
 377
 378
 379     /* Search the returned records */
 380
 381     for (rr = dns_next_rr(&dnsa, &dnss, RESET_ANSWERS); rr;
 382          rr = dns_next_rr(&dnsa, &dnss, RESET_NEXT)) if (rr->type == searchtype)
 383       {
 384       if (*do_cache > rr->ttl)
 385         *do_cache = rr->ttl;
 386
 387       if (type == T_A || type == T_AAAA || type == T_ADDRESSES)
 388         {
 389         dns_address *da;
 390         for (da = dns_address_from_rr(&dnsa, rr); da; da = da->next)
 391           {
 392           if (yield->ptr) yield = string_catn(yield, outsep, 1);
 393           yield = string_cat(yield, da->address);
 394           }
 395         continue;
 396         }
 397
 398       /* Other kinds of record just have one piece of data each, but there may be
 399       several of them, of course. */
 400
 401       if (yield->ptr) yield = string_catn(yield, outsep, 1);
 402
 403       if (type == T_TXT || type == T_SPF)
 404         {
 405         if (outsep2 == NULL)    /* output only the first item of data */
 406           yield = string_catn(yield, US (rr->data+1), (rr->data)[0]);
 407         else
 408           {
 409           /* output all items */
 410           int data_offset = 0;
 411           while (data_offset < rr->size)
 412             {
 413             uschar chunk_len = (rr->data)[data_offset++];
 414             if (outsep2[0] != '\0' && data_offset != 1)
 415               yield = string_catn(yield, outsep2, 1);
 416             yield = string_catn(yield, US ((rr->data)+data_offset), chunk_len);
 417             data_offset += chunk_len;
 418             }
 419           }
 420         }
 421       else if (type == T_TLSA)
 422         {
 423         uint8_t usage, selector, matching_type;
 424         uint16_t payload_length;
 425         uschar s[MAX_TLSA_EXPANDED_SIZE];
 426         uschar * sp = s;
 427         uschar * p = US rr->data;
 428
 429         usage = *p++;
 430         selector = *p++;
 431         matching_type = *p++;
 432         /* What's left after removing the first 3 bytes above */
 433         payload_length = rr->size - 3;
 434         sp += sprintf(CS s, "%d%c%d%c%d%c", usage, *outsep2,
 435                 selector, *outsep2, matching_type, *outsep2);
 436         /* Now append the cert/identifier, one hex char at a time */
 437         while (payload_length-- > 0 && sp-s < (MAX_TLSA_EXPANDED_SIZE - 4))
 438           sp += sprintf(CS sp, "%02x", *p++);
 439
 440         yield = string_cat(yield, s);
 441         }
 442       else   /* T_CNAME, T_CSA, T_MX, T_MXH, T_NS, T_PTR, T_SOA, T_SRV */
 443         {
 444         int priority, weight, port;
 445         uschar s[264];
 446         uschar * p = US rr->data;
 447
 448         switch (type)
 449           {
 450           case T_MXH:
 451             /* mxh ignores the priority number and includes only the hostnames */
 452             GETSHORT(priority, p);
 453             break;
 454
 455           case T_MX:
 456             GETSHORT(priority, p);
 457             sprintf(CS s, "%d%c", priority, *outsep2);
 458             yield = string_cat(yield, s);
 459             break;
 460
 461           case T_SRV:
 462             GETSHORT(priority, p);
 463             GETSHORT(weight, p);
 464             GETSHORT(port, p);
 465             sprintf(CS s, "%d%c%d%c%d%c", priority, *outsep2,
 466                               weight, *outsep2, port, *outsep2);
 467             yield = string_cat(yield, s);
 468             break;
 469
 470           case T_CSA:
 471             /* See acl_verify_csa() for more comments about CSA. */
 472             GETSHORT(priority, p);
 473             GETSHORT(weight, p);
 474             GETSHORT(port, p);
 475
 476             if (priority != 1) continue;      /* CSA version must be 1 */
 477
 478             /* If the CSA record we found is not the one we asked for, analyse
 479             the subdomain assertions in the port field, else analyse the direct
 480             authorization status in the weight field. */
 481
 482             if (Ustrcmp(found, domain) != 0)
 483               {
 484               if (port & 1) *s = 'X';         /* explicit authorization required */
 485               else *s = '?';                  /* no subdomain assertions here */
 486               }
 487             else
 488               {
 489               if (weight < 2) *s = 'N';       /* not authorized */
 490               else if (weight == 2) *s = 'Y'; /* authorized */
 491               else if (weight == 3) *s = '?'; /* unauthorizable */
 492               else continue;                  /* invalid */
 493               }
 494
 495             s[1] = ' ';
 496             yield = string_catn(yield, s, 2);
 497             break;
 498
 499           default:
 500             break;
 501           }
 502
 503         /* GETSHORT() has advanced the pointer to the target domain. */
 504
 505         rc = dn_expand(dnsa.answer, dnsa.answer + dnsa.answerlen, p,
 506           (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 507
 508         /* If an overlong response was received, the data will have been
 509         truncated and dn_expand may fail. */
 510
 511         if (rc < 0)
 512           {
 513           log_write(0, LOG_MAIN, "host name alias list truncated: type=%s "
 514             "domain=%s", dns_text_type(type), domain);
 515           break;
 516           }
 517         else yield = string_cat(yield, s);
 518
 519         if (type == T_SOA && outsep2 != NULL)
 520           {
 521           unsigned long serial, refresh, retry, expire, minimum;
 522
 523           p += rc;
 524           yield = string_catn(yield, outsep2, 1);
 525
 526           rc = dn_expand(dnsa.answer, dnsa.answer + dnsa.answerlen, p,
 527             (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 528           if (rc < 0)
 529             {
 530             log_write(0, LOG_MAIN, "responsible-mailbox truncated: type=%s "
 531               "domain=%s", dns_text_type(type), domain);
 532             break;
 533             }
 534           else yield = string_cat(yield, s);
 535
 536           p += rc;
 537           GETLONG(serial, p); GETLONG(refresh, p);
 538           GETLONG(retry,  p); GETLONG(expire,  p); GETLONG(minimum, p);
 539           sprintf(CS s, "%c%lu%c%lu%c%lu%c%lu%c%lu",
 540             *outsep2, serial, *outsep2, refresh,
 541             *outsep2, retry,  *outsep2, expire,  *outsep2, minimum);
 542           yield = string_cat(yield, s);
 543           }
 544         }
 545       }    /* Loop for list of returned records */
 546
 547            /* Loop for set of A-lookup types */
 548     } while (type == T_ADDRESSES && searchtype != T_A);
 549
 550   }        /* Loop for list of domains */
 551
 552 /* Reclaim unused memory */
 553
 554 store_reset(yield->s + yield->ptr + 1);
 555
 556 /* If yield NULL we have not found anything. Otherwise, insert the terminating
 557 zero and return the result. */
 558
 559 dns_retrans = save_retrans;
 560 dns_retry = save_retry;
 561 dns_init(FALSE, FALSE, FALSE);  /* clear the dnssec bit for getaddrbyname */
 562
 563 if (!yield || !yield->ptr) return failrc;
 564
 565 *result = string_from_gstring(yield);
 566 return OK;
 567 }
 568
 569
 570
 571 /*************************************************
 572 *         Version reporting entry point          *
 573 *************************************************/
 574
 575 /* See local README for interface description. */
 576
 577 #include "../version.h"
 578
 579 void
 580 dnsdb_version_report(FILE *f)
 581 {
 582 #ifdef DYNLOOKUP
 583 fprintf(f, "Library version: DNSDB: Exim version %s\n", EXIM_VERSION_STR);
 584 #endif
 585 }
 586
 587
 588 static lookup_info _lookup_info = {
 589   US"dnsdb",                     /* lookup name */
 590   lookup_querystyle,             /* query style */
 591   dnsdb_open,                    /* open function */
 592   NULL,                          /* check function */
 593   dnsdb_find,                    /* find function */
 594   NULL,                          /* no close function */
 595   NULL,                          /* no tidy function */
 596   NULL,                          /* no quoting function */
 597   dnsdb_version_report           /* version reporting */
 598 };
 599
 600 #ifdef DYNLOOKUP
 601 #define dnsdb_lookup_module_info _lookup_module_info
 602 #endif
 603
 604 static lookup_info *_lookup_list[] = { &_lookup_info };
 605 lookup_module_info dnsdb_lookup_module_info = { LOOKUP_MODULE_INFO_MAGIC, _lookup_list, 1 };
 606
 607 /* vi: aw ai sw=2
 608 */
 609 /* End of lookups/dnsdb.c */