src/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(const 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' (default), and 'never'.  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, const uschar * filename, const uschar * keystring,
 134  int length, uschar ** result, uschar ** errmsg, uint * do_cache)
 135 {
 136 int rc;
 137 int sep = 0;
 138 int defer_mode = PASS;
 139 int dnssec_mode = PASS;
 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 dns_answer * dnsa = store_get_dns_answer();
 149 dns_scan dnss;
 150
 151 /* Because we're working in the search pool, we try to reclaim as much
 152 store as possible later, so we preallocate the result here */
 153
 154 gstring * yield = string_get(256);
 155
 156 handle = handle;           /* Keep picky compilers happy */
 157 filename = filename;
 158 length = length;
 159 do_cache = do_cache;
 160
 161 /* If the string starts with '>' we change the output separator.
 162 If it's followed by ';' or ',' we set the TXT output separator. */
 163
 164 while (isspace(*keystring)) keystring++;
 165 if (*keystring == '>')
 166   {
 167   outsep = keystring + 1;
 168   keystring += 2;
 169   if (*keystring == ',')
 170     {
 171     outsep2 = keystring + 1;
 172     keystring += 2;
 173     }
 174   else if (*keystring == ';')
 175     {
 176     outsep2 = US"";
 177     keystring++;
 178     }
 179   while (isspace(*keystring)) keystring++;
 180   }
 181
 182 /* Check for a modifier keyword. */
 183
 184 for (;;)
 185   {
 186   if (strncmpic(keystring, US"defer_", 6) == 0)
 187     {
 188     keystring += 6;
 189     if (strncmpic(keystring, US"strict", 6) == 0)
 190       { defer_mode = DEFER; keystring += 6; }
 191     else if (strncmpic(keystring, US"lax", 3) == 0)
 192       { defer_mode = PASS; keystring += 3; }
 193     else if (strncmpic(keystring, US"never", 5) == 0)
 194       { defer_mode = OK; keystring += 5; }
 195     else
 196       {
 197       *errmsg = US"unsupported dnsdb defer behaviour";
 198       return DEFER;
 199       }
 200     }
 201   else if (strncmpic(keystring, US"dnssec_", 7) == 0)
 202     {
 203     keystring += 7;
 204     if (strncmpic(keystring, US"strict", 6) == 0)
 205       { dnssec_mode = DEFER; keystring += 6; }
 206     else if (strncmpic(keystring, US"lax", 3) == 0)
 207       { dnssec_mode = PASS; keystring += 3; }
 208     else if (strncmpic(keystring, US"never", 5) == 0)
 209       { dnssec_mode = OK; keystring += 5; }
 210     else
 211       {
 212       *errmsg = US"unsupported dnsdb dnssec behaviour";
 213       return DEFER;
 214       }
 215     }
 216   else if (strncmpic(keystring, US"retrans_", 8) == 0)
 217     {
 218     int timeout_sec;
 219     if ((timeout_sec = readconf_readtime(keystring += 8, ',', FALSE)) <= 0)
 220       {
 221       *errmsg = US"unsupported dnsdb timeout value";
 222       return DEFER;
 223       }
 224     dns_retrans = timeout_sec;
 225     while (*keystring != ',') keystring++;
 226     }
 227   else if (strncmpic(keystring, US"retry_", 6) == 0)
 228     {
 229     int retries;
 230     if ((retries = (int)strtol(CCS keystring + 6, CSS &keystring, 0)) < 0)
 231       {
 232       *errmsg = US"unsupported dnsdb retry count";
 233       return DEFER;
 234       }
 235     dns_retry = retries;
 236     }
 237   else
 238     break;
 239
 240   while (isspace(*keystring)) keystring++;
 241   if (*keystring++ != ',')
 242     {
 243     *errmsg = US"dnsdb modifier syntax error";
 244     return DEFER;
 245     }
 246   while (isspace(*keystring)) keystring++;
 247   }
 248
 249 /* Figure out the "type" value if it is not T_TXT.
 250 If the keystring contains an = this must be preceded by a valid type name. */
 251
 252 type = T_TXT;
 253 if ((equals = Ustrchr(keystring, '=')) != NULL)
 254   {
 255   int i, len;
 256   uschar *tend = equals;
 257
 258   while (tend > keystring && isspace(tend[-1])) tend--;
 259   len = tend - keystring;
 260
 261   for (i = 0; i < nelem(type_names); i++)
 262     if (len == Ustrlen(type_names[i]) &&
 263         strncmpic(keystring, US type_names[i], len) == 0)
 264       {
 265       type = type_values[i];
 266       break;
 267       }
 268
 269   if (i >= nelem(type_names))
 270     {
 271     *errmsg = US"unsupported DNS record type";
 272     return DEFER;
 273     }
 274
 275   keystring = equals + 1;
 276   while (isspace(*keystring)) keystring++;
 277   }
 278
 279 /* Initialize the resolver in case this is the first time it has been used. */
 280
 281 dns_init(FALSE, FALSE, dnssec_mode != OK);
 282
 283 /* The remainder of the string must be a list of domains. As long as the lookup
 284 for at least one of them succeeds, we return success. Failure means that none
 285 of them were found.
 286
 287 The original implementation did not support a list of domains. Adding the list
 288 feature is compatible, except in one case: when PTR records are being looked up
 289 for a single IPv6 address. Fortunately, we can hack in a compatibility feature
 290 here: If the type is PTR and no list separator is specified, and the entire
 291 remaining string is valid as an IP address, set an impossible separator so that
 292 it is treated as one item. */
 293
 294 if (type == T_PTR && keystring[0] != '<' &&
 295     string_is_ip_address(keystring, NULL) != 0)
 296   sep = -1;
 297
 298 /* SPF strings should be concatenated without a separator, thus make
 299 it the default if not defined (see RFC 4408 section 3.1.3).
 300 Multiple SPF records are forbidden (section 3.1.2) but are currently
 301 not handled specially, thus they are concatenated with \n by default.
 302 MX priority and value are space-separated by default.
 303 SRV and TLSA record parts are space-separated by default. */
 304
 305 if (!outsep2) switch(type)
 306   {
 307   case T_SPF:                         outsep2 = US"";  break;
 308   case T_SRV: case T_MX: case T_TLSA: outsep2 = US" "; break;
 309   }
 310
 311 /* Now scan the list and do a lookup for each item */
 312
 313 while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
 314   {
 315   int searchtype = type == T_CSA ? T_SRV :         /* record type we want */
 316                    type == T_MXH ? T_MX :
 317                    type == T_ZNS ? T_NS : type;
 318
 319   /* If the type is PTR or CSA, we have to construct the relevant magic lookup
 320   key if the original is an IP address (some experimental protocols are using
 321   PTR records for different purposes where the key string is a host name, and
 322   Exim's extended CSA can be keyed by domains or IP addresses). This code for
 323   doing the reversal is now in a separate function. */
 324
 325   if ((type == T_PTR || type == T_CSA) &&
 326       string_is_ip_address(domain, NULL) != 0)
 327     domain = dns_build_reverse(domain);
 328
 329   do
 330     {
 331     DEBUG(D_lookup) debug_printf_indent("dnsdb key: %s\n", domain);
 332
 333     /* Do the lookup and sort out the result. There are four special types that
 334     are handled specially: T_CSA, T_ZNS, T_ADDRESSES and T_MXH.
 335     The first two are handled in a special lookup function so that the facility
 336     could be used from other parts of the Exim code. T_ADDRESSES is handled by looping
 337     over the types of A lookup.  T_MXH affects only what happens later on in
 338     this function, but for tidiness it is handled by the "special". If the
 339     lookup fails, continue with the next domain. In the case of DEFER, adjust
 340     the final "nothing found" result, but carry on to the next domain. */
 341
 342     found = domain;
 343 #if HAVE_IPV6
 344     if (type == T_ADDRESSES)            /* NB cannot happen unless HAVE_IPV6 */
 345       {
 346       if (searchtype == T_ADDRESSES) searchtype = T_AAAA;
 347       else if (searchtype == T_AAAA) searchtype = T_A;
 348       rc = dns_special_lookup(dnsa, domain, searchtype, CUSS &found);
 349       }
 350     else
 351 #endif
 352       rc = dns_special_lookup(dnsa, domain, type, CUSS &found);
 353
 354     lookup_dnssec_authenticated = dnssec_mode==OK ? NULL
 355       : dns_is_secure(dnsa) ? US"yes" : US"no";
 356
 357     if (rc == DNS_NOMATCH || rc == DNS_NODATA) continue;
 358     if (  rc != DNS_SUCCEED
 359        || (dnssec_mode == DEFER && !dns_is_secure(dnsa))
 360        )
 361       {
 362       if (defer_mode == DEFER)
 363         {
 364         dns_retrans = save_retrans;
 365         dns_retry = save_retry;
 366         dns_init(FALSE, FALSE, FALSE);                  /* clr dnssec bit */
 367         return DEFER;                                   /* always defer */
 368         }
 369       if (defer_mode == PASS) failrc = DEFER;         /* defer only if all do */
 370       continue;                                       /* treat defer as fail */
 371       }
 372
 373
 374     /* Search the returned records */
 375
 376     for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); rr;
 377          rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) if (rr->type == searchtype)
 378       {
 379       if (*do_cache > rr->ttl)
 380         *do_cache = rr->ttl;
 381
 382       if (type == T_A || type == T_AAAA || type == T_ADDRESSES)
 383         {
 384         for (dns_address * da = dns_address_from_rr(dnsa, rr); da; da = da->next)
 385           {
 386           if (yield->ptr) yield = string_catn(yield, outsep, 1);
 387           yield = string_cat(yield, da->address);
 388           }
 389         continue;
 390         }
 391
 392       /* Other kinds of record just have one piece of data each, but there may be
 393       several of them, of course. */
 394
 395       if (yield->ptr) yield = string_catn(yield, outsep, 1);
 396
 397       if (type == T_TXT || type == T_SPF)
 398         {
 399         if (outsep2 == NULL)    /* output only the first item of data */
 400           yield = string_catn(yield, US (rr->data+1), (rr->data)[0]);
 401         else
 402           {
 403           /* output all items */
 404           int data_offset = 0;
 405           while (data_offset < rr->size)
 406             {
 407             uschar chunk_len = (rr->data)[data_offset++];
 408             if (outsep2[0] != '\0' && data_offset != 1)
 409               yield = string_catn(yield, outsep2, 1);
 410             yield = string_catn(yield, US ((rr->data)+data_offset), chunk_len);
 411             data_offset += chunk_len;
 412             }
 413           }
 414         }
 415       else if (type == T_TLSA)
 416         {
 417         uint8_t usage, selector, matching_type;
 418         uint16_t payload_length;
 419         uschar s[MAX_TLSA_EXPANDED_SIZE];
 420         uschar * sp = s;
 421         uschar * p = US rr->data;
 422
 423         usage = *p++;
 424         selector = *p++;
 425         matching_type = *p++;
 426         /* What's left after removing the first 3 bytes above */
 427         payload_length = rr->size - 3;
 428         sp += sprintf(CS s, "%d%c%d%c%d%c", usage, *outsep2,
 429                 selector, *outsep2, matching_type, *outsep2);
 430         /* Now append the cert/identifier, one hex char at a time */
 431         while (payload_length-- > 0 && sp-s < (MAX_TLSA_EXPANDED_SIZE - 4))
 432           sp += sprintf(CS sp, "%02x", *p++);
 433
 434         yield = string_cat(yield, s);
 435         }
 436       else   /* T_CNAME, T_CSA, T_MX, T_MXH, T_NS, T_PTR, T_SOA, T_SRV */
 437         {
 438         int priority, weight, port;
 439         uschar s[264];
 440         uschar * p = US rr->data;
 441
 442         switch (type)
 443           {
 444           case T_MXH:
 445             /* mxh ignores the priority number and includes only the hostnames */
 446             GETSHORT(priority, p);
 447             break;
 448
 449           case T_MX:
 450             GETSHORT(priority, p);
 451             sprintf(CS s, "%d%c", priority, *outsep2);
 452             yield = string_cat(yield, s);
 453             break;
 454
 455           case T_SRV:
 456             GETSHORT(priority, p);
 457             GETSHORT(weight, p);
 458             GETSHORT(port, p);
 459             sprintf(CS s, "%d%c%d%c%d%c", priority, *outsep2,
 460                               weight, *outsep2, port, *outsep2);
 461             yield = string_cat(yield, s);
 462             break;
 463
 464           case T_CSA:
 465             /* See acl_verify_csa() for more comments about CSA. */
 466             GETSHORT(priority, p);
 467             GETSHORT(weight, p);
 468             GETSHORT(port, p);
 469
 470             if (priority != 1) continue;      /* CSA version must be 1 */
 471
 472             /* If the CSA record we found is not the one we asked for, analyse
 473             the subdomain assertions in the port field, else analyse the direct
 474             authorization status in the weight field. */
 475
 476             if (Ustrcmp(found, domain) != 0)
 477               {
 478               if (port & 1) *s = 'X';         /* explicit authorization required */
 479               else *s = '?';                  /* no subdomain assertions here */
 480               }
 481             else
 482               {
 483               if (weight < 2) *s = 'N';       /* not authorized */
 484               else if (weight == 2) *s = 'Y'; /* authorized */
 485               else if (weight == 3) *s = '?'; /* unauthorizable */
 486               else continue;                  /* invalid */
 487               }
 488
 489             s[1] = ' ';
 490             yield = string_catn(yield, s, 2);
 491             break;
 492
 493           default:
 494             break;
 495           }
 496
 497         /* GETSHORT() has advanced the pointer to the target domain. */
 498
 499         rc = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, p,
 500           (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 501
 502         /* If an overlong response was received, the data will have been
 503         truncated and dn_expand may fail. */
 504
 505         if (rc < 0)
 506           {
 507           log_write(0, LOG_MAIN, "host name alias list truncated: type=%s "
 508             "domain=%s", dns_text_type(type), domain);
 509           break;
 510           }
 511         else yield = string_cat(yield, s);
 512
 513         if (type == T_SOA && outsep2 != NULL)
 514           {
 515           unsigned long serial, refresh, retry, expire, minimum;
 516
 517           p += rc;
 518           yield = string_catn(yield, outsep2, 1);
 519
 520           rc = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, p,
 521             (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 522           if (rc < 0)
 523             {
 524             log_write(0, LOG_MAIN, "responsible-mailbox truncated: type=%s "
 525               "domain=%s", dns_text_type(type), domain);
 526             break;
 527             }
 528           else yield = string_cat(yield, s);
 529
 530           p += rc;
 531           GETLONG(serial, p); GETLONG(refresh, p);
 532           GETLONG(retry,  p); GETLONG(expire,  p); GETLONG(minimum, p);
 533           sprintf(CS s, "%c%lu%c%lu%c%lu%c%lu%c%lu",
 534             *outsep2, serial, *outsep2, refresh,
 535             *outsep2, retry,  *outsep2, expire,  *outsep2, minimum);
 536           yield = string_cat(yield, s);
 537           }
 538         }
 539       }    /* Loop for list of returned records */
 540
 541            /* Loop for set of A-lookup types */
 542     } while (type == T_ADDRESSES && searchtype != T_A);
 543
 544   }        /* Loop for list of domains */
 545
 546 /* Reclaim unused memory */
 547
 548 gstring_release_unused(yield);
 549
 550 /* If yield NULL we have not found anything. Otherwise, insert the terminating
 551 zero and return the result. */
 552
 553 dns_retrans = save_retrans;
 554 dns_retry = save_retry;
 555 dns_init(FALSE, FALSE, FALSE);  /* clear the dnssec bit for getaddrbyname */
 556
 557 if (!yield || !yield->ptr) return failrc;
 558
 559 *result = string_from_gstring(yield);
 560 return OK;
 561 }
 562
 563
 564
 565 /*************************************************
 566 *         Version reporting entry point          *
 567 *************************************************/
 568
 569 /* See local README for interface description. */
 570
 571 #include "../version.h"
 572
 573 void
 574 dnsdb_version_report(FILE *f)
 575 {
 576 #ifdef DYNLOOKUP
 577 fprintf(f, "Library version: DNSDB: Exim version %s\n", EXIM_VERSION_STR);
 578 #endif
 579 }
 580
 581
 582 static lookup_info _lookup_info = {
 583   US"dnsdb",                     /* lookup name */
 584   lookup_querystyle,             /* query style */
 585   dnsdb_open,                    /* open function */
 586   NULL,                          /* check function */
 587   dnsdb_find,                    /* find function */
 588   NULL,                          /* no close function */
 589   NULL,                          /* no tidy function */
 590   NULL,                          /* no quoting function */
 591   dnsdb_version_report           /* version reporting */
 592 };
 593
 594 #ifdef DYNLOOKUP
 595 #define dnsdb_lookup_module_info _lookup_module_info
 596 #endif
 597
 598 static lookup_info *_lookup_list[] = { &_lookup_info };
 599 lookup_module_info dnsdb_lookup_module_info = { LOOKUP_MODULE_INFO_MAGIC, _lookup_list, 1 };
 600
 601 /* vi: aw ai sw=2
 602 */
 603 /* End of lookups/dnsdb.c */