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  const uschar * opts)
 136 {
 137 int rc;
 138 int sep = 0;
 139 int defer_mode = PASS;
 140 int dnssec_mode = PASS;
 141 int save_retrans = dns_retrans;
 142 int save_retry =   dns_retry;
 143 int type;
 144 int failrc = FAIL;
 145 const uschar *outsep = CUS"\n";
 146 const uschar *outsep2 = NULL;
 147 uschar *equals, *domain, *found;
 148
 149 dns_answer * dnsa = store_get_dns_answer();
 150 dns_scan dnss;
 151
 152 /* Because we're working in the search pool, we try to reclaim as much
 153 store as possible later, so we preallocate the result here */
 154
 155 gstring * yield = string_get(256);
 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   int searchtype = type == T_CSA ? T_SRV :         /* record type we want */
 317                    type == T_MXH ? T_MX :
 318                    type == T_ZNS ? T_NS : type;
 319
 320   /* If the type is PTR or CSA, we have to construct the relevant magic lookup
 321   key if the original is an IP address (some experimental protocols are using
 322   PTR records for different purposes where the key string is a host name, and
 323   Exim's extended CSA can be keyed by domains or IP addresses). This code for
 324   doing the reversal is now in a separate function. */
 325
 326   if ((type == T_PTR || type == T_CSA) &&
 327       string_is_ip_address(domain, NULL) != 0)
 328     domain = dns_build_reverse(domain);
 329
 330   do
 331     {
 332     DEBUG(D_lookup) debug_printf_indent("dnsdb key: %s\n", domain);
 333
 334     /* Do the lookup and sort out the result. There are four special types that
 335     are handled specially: T_CSA, T_ZNS, T_ADDRESSES and T_MXH.
 336     The first two are handled in a special lookup function so that the facility
 337     could be used from other parts of the Exim code. T_ADDRESSES is handled by looping
 338     over the types of A lookup.  T_MXH affects only what happens later on in
 339     this function, but for tidiness it is handled by the "special". If the
 340     lookup fails, continue with the next domain. In the case of DEFER, adjust
 341     the final "nothing found" result, but carry on to the next domain. */
 342
 343     found = domain;
 344 #if HAVE_IPV6
 345     if (type == T_ADDRESSES)            /* NB cannot happen unless HAVE_IPV6 */
 346       {
 347       if (searchtype == T_ADDRESSES) searchtype = T_AAAA;
 348       else if (searchtype == T_AAAA) searchtype = T_A;
 349       rc = dns_special_lookup(dnsa, domain, searchtype, CUSS &found);
 350       }
 351     else
 352 #endif
 353       rc = dns_special_lookup(dnsa, domain, type, CUSS &found);
 354
 355     lookup_dnssec_authenticated = dnssec_mode==OK ? NULL
 356       : dns_is_secure(dnsa) ? US"yes" : US"no";
 357
 358     if (rc == DNS_NOMATCH || rc == DNS_NODATA) continue;
 359     if (  rc != DNS_SUCCEED
 360        || (dnssec_mode == DEFER && !dns_is_secure(dnsa))
 361        )
 362       {
 363       if (defer_mode == DEFER)
 364         {
 365         dns_retrans = save_retrans;
 366         dns_retry = save_retry;
 367         dns_init(FALSE, FALSE, FALSE);                  /* clr dnssec bit */
 368         return DEFER;                                   /* always defer */
 369         }
 370       if (defer_mode == PASS) failrc = DEFER;         /* defer only if all do */
 371       continue;                                       /* treat defer as fail */
 372       }
 373
 374
 375     /* Search the returned records */
 376
 377     for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); rr;
 378          rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) if (rr->type == searchtype)
 379       {
 380       if (*do_cache > rr->ttl)
 381         *do_cache = rr->ttl;
 382
 383       if (type == T_A || type == T_AAAA || type == T_ADDRESSES)
 384         {
 385         for (dns_address * da = dns_address_from_rr(dnsa, rr); da; da = da->next)
 386           {
 387           if (yield->ptr) yield = string_catn(yield, outsep, 1);
 388           yield = string_cat(yield, da->address);
 389           }
 390         continue;
 391         }
 392
 393       /* Other kinds of record just have one piece of data each, but there may be
 394       several of them, of course. */
 395
 396       if (yield->ptr) yield = string_catn(yield, outsep, 1);
 397
 398       if (type == T_TXT || type == T_SPF)
 399         {
 400         if (outsep2 == NULL)    /* output only the first item of data */
 401           yield = string_catn(yield, US (rr->data+1), (rr->data)[0]);
 402         else
 403           {
 404           /* output all items */
 405           int data_offset = 0;
 406           while (data_offset < rr->size)
 407             {
 408             uschar chunk_len = (rr->data)[data_offset++];
 409             if (outsep2[0] != '\0' && data_offset != 1)
 410               yield = string_catn(yield, outsep2, 1);
 411             yield = string_catn(yield, US ((rr->data)+data_offset), chunk_len);
 412             data_offset += chunk_len;
 413             }
 414           }
 415         }
 416       else if (type == T_TLSA)
 417         {
 418         uint8_t usage, selector, matching_type;
 419         uint16_t payload_length;
 420         uschar s[MAX_TLSA_EXPANDED_SIZE];
 421         uschar * sp = s;
 422         uschar * p = US rr->data;
 423
 424         usage = *p++;
 425         selector = *p++;
 426         matching_type = *p++;
 427         /* What's left after removing the first 3 bytes above */
 428         payload_length = rr->size - 3;
 429         sp += sprintf(CS s, "%d%c%d%c%d%c", usage, *outsep2,
 430                 selector, *outsep2, matching_type, *outsep2);
 431         /* Now append the cert/identifier, one hex char at a time */
 432         while (payload_length-- > 0 && sp-s < (MAX_TLSA_EXPANDED_SIZE - 4))
 433           sp += sprintf(CS sp, "%02x", *p++);
 434
 435         yield = string_cat(yield, s);
 436         }
 437       else   /* T_CNAME, T_CSA, T_MX, T_MXH, T_NS, T_PTR, T_SOA, T_SRV */
 438         {
 439         int priority, weight, port;
 440         uschar s[264];
 441         uschar * p = US rr->data;
 442
 443         switch (type)
 444           {
 445           case T_MXH:
 446             /* mxh ignores the priority number and includes only the hostnames */
 447             GETSHORT(priority, p);
 448             break;
 449
 450           case T_MX:
 451             GETSHORT(priority, p);
 452             sprintf(CS s, "%d%c", priority, *outsep2);
 453             yield = string_cat(yield, s);
 454             break;
 455
 456           case T_SRV:
 457             GETSHORT(priority, p);
 458             GETSHORT(weight, p);
 459             GETSHORT(port, p);
 460             sprintf(CS s, "%d%c%d%c%d%c", priority, *outsep2,
 461                               weight, *outsep2, port, *outsep2);
 462             yield = string_cat(yield, s);
 463             break;
 464
 465           case T_CSA:
 466             /* See acl_verify_csa() for more comments about CSA. */
 467             GETSHORT(priority, p);
 468             GETSHORT(weight, p);
 469             GETSHORT(port, p);
 470
 471             if (priority != 1) continue;      /* CSA version must be 1 */
 472
 473             /* If the CSA record we found is not the one we asked for, analyse
 474             the subdomain assertions in the port field, else analyse the direct
 475             authorization status in the weight field. */
 476
 477             if (Ustrcmp(found, domain) != 0)
 478               {
 479               if (port & 1) *s = 'X';         /* explicit authorization required */
 480               else *s = '?';                  /* no subdomain assertions here */
 481               }
 482             else
 483               {
 484               if (weight < 2) *s = 'N';       /* not authorized */
 485               else if (weight == 2) *s = 'Y'; /* authorized */
 486               else if (weight == 3) *s = '?'; /* unauthorizable */
 487               else continue;                  /* invalid */
 488               }
 489
 490             s[1] = ' ';
 491             yield = string_catn(yield, s, 2);
 492             break;
 493
 494           default:
 495             break;
 496           }
 497
 498         /* GETSHORT() has advanced the pointer to the target domain. */
 499
 500         rc = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, p,
 501           (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 502
 503         /* If an overlong response was received, the data will have been
 504         truncated and dn_expand may fail. */
 505
 506         if (rc < 0)
 507           {
 508           log_write(0, LOG_MAIN, "host name alias list truncated: type=%s "
 509             "domain=%s", dns_text_type(type), domain);
 510           break;
 511           }
 512         else yield = string_cat(yield, s);
 513
 514         if (type == T_SOA && outsep2 != NULL)
 515           {
 516           unsigned long serial, refresh, retry, expire, minimum;
 517
 518           p += rc;
 519           yield = string_catn(yield, outsep2, 1);
 520
 521           rc = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, p,
 522             (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 523           if (rc < 0)
 524             {
 525             log_write(0, LOG_MAIN, "responsible-mailbox truncated: type=%s "
 526               "domain=%s", dns_text_type(type), domain);
 527             break;
 528             }
 529           else yield = string_cat(yield, s);
 530
 531           p += rc;
 532           GETLONG(serial, p); GETLONG(refresh, p);
 533           GETLONG(retry,  p); GETLONG(expire,  p); GETLONG(minimum, p);
 534           sprintf(CS s, "%c%lu%c%lu%c%lu%c%lu%c%lu",
 535             *outsep2, serial, *outsep2, refresh,
 536             *outsep2, retry,  *outsep2, expire,  *outsep2, minimum);
 537           yield = string_cat(yield, s);
 538           }
 539         }
 540       }    /* Loop for list of returned records */
 541
 542            /* Loop for set of A-lookup types */
 543     } while (type == T_ADDRESSES && searchtype != T_A);
 544
 545   }        /* Loop for list of domains */
 546
 547 /* Reclaim unused memory */
 548
 549 gstring_release_unused(yield);
 550
 551 /* If yield NULL we have not found anything. Otherwise, insert the terminating
 552 zero and return the result. */
 553
 554 dns_retrans = save_retrans;
 555 dns_retry = save_retry;
 556 dns_init(FALSE, FALSE, FALSE);  /* clear the dnssec bit for getaddrbyname */
 557
 558 if (!yield || !yield->ptr) return failrc;
 559
 560 *result = string_from_gstring(yield);
 561 return OK;
 562 }
 563
 564
 565
 566 /*************************************************
 567 *         Version reporting entry point          *
 568 *************************************************/
 569
 570 /* See local README for interface description. */
 571
 572 #include "../version.h"
 573
 574 void
 575 dnsdb_version_report(FILE *f)
 576 {
 577 #ifdef DYNLOOKUP
 578 fprintf(f, "Library version: DNSDB: Exim version %s\n", EXIM_VERSION_STR);
 579 #endif
 580 }
 581
 582
 583 static lookup_info _lookup_info = {
 584   .name = US"dnsdb",                    /* lookup name */
 585   .type = lookup_querystyle,            /* query style */
 586   .open = dnsdb_open,                   /* open function */
 587   .check = NULL,                        /* check function */
 588   .find = dnsdb_find,                   /* find function */
 589   .close = NULL,                        /* no close function */
 590   .tidy = NULL,                         /* no tidy function */
 591   .quote = NULL,                        /* no quoting function */
 592   .version_report = dnsdb_version_report           /* version reporting */
 593 };
 594
 595 #ifdef DYNLOOKUP
 596 #define dnsdb_lookup_module_info _lookup_module_info
 597 #endif
 598
 599 static lookup_info *_lookup_list[] = { &_lookup_info };
 600 lookup_module_info dnsdb_lookup_module_info = { LOOKUP_MODULE_INFO_MAGIC, _lookup_list, 1 };
 601
 602 /* vi: aw ai sw=2
 603 */
 604 /* End of lookups/dnsdb.c */