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(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 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   uschar rbuffer[256];
 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     {
 329     dns_build_reverse(domain, rbuffer);
 330     domain = rbuffer;
 331     }
 332
 333   do
 334     {
 335     DEBUG(D_lookup) debug_printf_indent("dnsdb key: %s\n", domain);
 336
 337     /* Do the lookup and sort out the result. There are four special types that
 338     are handled specially: T_CSA, T_ZNS, T_ADDRESSES and T_MXH.
 339     The first two are handled in a special lookup function so that the facility
 340     could be used from other parts of the Exim code. T_ADDRESSES is handled by looping
 341     over the types of A lookup.  T_MXH affects only what happens later on in
 342     this function, but for tidiness it is handled by the "special". If the
 343     lookup fails, continue with the next domain. In the case of DEFER, adjust
 344     the final "nothing found" result, but carry on to the next domain. */
 345
 346     found = domain;
 347 #if HAVE_IPV6
 348     if (type == T_ADDRESSES)            /* NB cannot happen unless HAVE_IPV6 */
 349       {
 350       if (searchtype == T_ADDRESSES) searchtype = T_AAAA;
 351       else if (searchtype == T_AAAA) searchtype = T_A;
 352       rc = dns_special_lookup(dnsa, domain, searchtype, CUSS &found);
 353       }
 354     else
 355 #endif
 356       rc = dns_special_lookup(dnsa, domain, type, CUSS &found);
 357
 358     lookup_dnssec_authenticated = dnssec_mode==OK ? NULL
 359       : dns_is_secure(dnsa) ? US"yes" : US"no";
 360
 361     if (rc == DNS_NOMATCH || rc == DNS_NODATA) continue;
 362     if (  rc != DNS_SUCCEED
 363        || (dnssec_mode == DEFER && !dns_is_secure(dnsa))
 364        )
 365       {
 366       if (defer_mode == DEFER)
 367         {
 368         dns_retrans = save_retrans;
 369         dns_retry = save_retry;
 370         dns_init(FALSE, FALSE, FALSE);                  /* clr dnssec bit */
 371         return DEFER;                                   /* always defer */
 372         }
 373       if (defer_mode == PASS) failrc = DEFER;         /* defer only if all do */
 374       continue;                                       /* treat defer as fail */
 375       }
 376
 377
 378     /* Search the returned records */
 379
 380     for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); rr;
 381          rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) if (rr->type == searchtype)
 382       {
 383       if (*do_cache > rr->ttl)
 384         *do_cache = rr->ttl;
 385
 386       if (type == T_A || type == T_AAAA || type == T_ADDRESSES)
 387         {
 388         for (dns_address * da = dns_address_from_rr(dnsa, rr); da; da = da->next)
 389           {
 390           if (yield->ptr) yield = string_catn(yield, outsep, 1);
 391           yield = string_cat(yield, da->address);
 392           }
 393         continue;
 394         }
 395
 396       /* Other kinds of record just have one piece of data each, but there may be
 397       several of them, of course. */
 398
 399       if (yield->ptr) yield = string_catn(yield, outsep, 1);
 400
 401       if (type == T_TXT || type == T_SPF)
 402         {
 403         if (outsep2 == NULL)    /* output only the first item of data */
 404           yield = string_catn(yield, US (rr->data+1), (rr->data)[0]);
 405         else
 406           {
 407           /* output all items */
 408           int data_offset = 0;
 409           while (data_offset < rr->size)
 410             {
 411             uschar chunk_len = (rr->data)[data_offset++];
 412             if (outsep2[0] != '\0' && data_offset != 1)
 413               yield = string_catn(yield, outsep2, 1);
 414             yield = string_catn(yield, US ((rr->data)+data_offset), chunk_len);
 415             data_offset += chunk_len;
 416             }
 417           }
 418         }
 419       else if (type == T_TLSA)
 420         {
 421         uint8_t usage, selector, matching_type;
 422         uint16_t payload_length;
 423         uschar s[MAX_TLSA_EXPANDED_SIZE];
 424         uschar * sp = s;
 425         uschar * p = US rr->data;
 426
 427         usage = *p++;
 428         selector = *p++;
 429         matching_type = *p++;
 430         /* What's left after removing the first 3 bytes above */
 431         payload_length = rr->size - 3;
 432         sp += sprintf(CS s, "%d%c%d%c%d%c", usage, *outsep2,
 433                 selector, *outsep2, matching_type, *outsep2);
 434         /* Now append the cert/identifier, one hex char at a time */
 435         while (payload_length-- > 0 && sp-s < (MAX_TLSA_EXPANDED_SIZE - 4))
 436           sp += sprintf(CS sp, "%02x", *p++);
 437
 438         yield = string_cat(yield, s);
 439         }
 440       else   /* T_CNAME, T_CSA, T_MX, T_MXH, T_NS, T_PTR, T_SOA, T_SRV */
 441         {
 442         int priority, weight, port;
 443         uschar s[264];
 444         uschar * p = US rr->data;
 445
 446         switch (type)
 447           {
 448           case T_MXH:
 449             /* mxh ignores the priority number and includes only the hostnames */
 450             GETSHORT(priority, p);
 451             break;
 452
 453           case T_MX:
 454             GETSHORT(priority, p);
 455             sprintf(CS s, "%d%c", priority, *outsep2);
 456             yield = string_cat(yield, s);
 457             break;
 458
 459           case T_SRV:
 460             GETSHORT(priority, p);
 461             GETSHORT(weight, p);
 462             GETSHORT(port, p);
 463             sprintf(CS s, "%d%c%d%c%d%c", priority, *outsep2,
 464                               weight, *outsep2, port, *outsep2);
 465             yield = string_cat(yield, s);
 466             break;
 467
 468           case T_CSA:
 469             /* See acl_verify_csa() for more comments about CSA. */
 470             GETSHORT(priority, p);
 471             GETSHORT(weight, p);
 472             GETSHORT(port, p);
 473
 474             if (priority != 1) continue;      /* CSA version must be 1 */
 475
 476             /* If the CSA record we found is not the one we asked for, analyse
 477             the subdomain assertions in the port field, else analyse the direct
 478             authorization status in the weight field. */
 479
 480             if (Ustrcmp(found, domain) != 0)
 481               {
 482               if (port & 1) *s = 'X';         /* explicit authorization required */
 483               else *s = '?';                  /* no subdomain assertions here */
 484               }
 485             else
 486               {
 487               if (weight < 2) *s = 'N';       /* not authorized */
 488               else if (weight == 2) *s = 'Y'; /* authorized */
 489               else if (weight == 3) *s = '?'; /* unauthorizable */
 490               else continue;                  /* invalid */
 491               }
 492
 493             s[1] = ' ';
 494             yield = string_catn(yield, s, 2);
 495             break;
 496
 497           default:
 498             break;
 499           }
 500
 501         /* GETSHORT() has advanced the pointer to the target domain. */
 502
 503         rc = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, p,
 504           (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 505
 506         /* If an overlong response was received, the data will have been
 507         truncated and dn_expand may fail. */
 508
 509         if (rc < 0)
 510           {
 511           log_write(0, LOG_MAIN, "host name alias list truncated: type=%s "
 512             "domain=%s", dns_text_type(type), domain);
 513           break;
 514           }
 515         else yield = string_cat(yield, s);
 516
 517         if (type == T_SOA && outsep2 != NULL)
 518           {
 519           unsigned long serial, refresh, retry, expire, minimum;
 520
 521           p += rc;
 522           yield = string_catn(yield, outsep2, 1);
 523
 524           rc = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, p,
 525             (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 526           if (rc < 0)
 527             {
 528             log_write(0, LOG_MAIN, "responsible-mailbox truncated: type=%s "
 529               "domain=%s", dns_text_type(type), domain);
 530             break;
 531             }
 532           else yield = string_cat(yield, s);
 533
 534           p += rc;
 535           GETLONG(serial, p); GETLONG(refresh, p);
 536           GETLONG(retry,  p); GETLONG(expire,  p); GETLONG(minimum, p);
 537           sprintf(CS s, "%c%lu%c%lu%c%lu%c%lu%c%lu",
 538             *outsep2, serial, *outsep2, refresh,
 539             *outsep2, retry,  *outsep2, expire,  *outsep2, minimum);
 540           yield = string_cat(yield, s);
 541           }
 542         }
 543       }    /* Loop for list of returned records */
 544
 545            /* Loop for set of A-lookup types */
 546     } while (type == T_ADDRESSES && searchtype != T_A);
 547
 548   }        /* Loop for list of domains */
 549
 550 /* Reclaim unused memory */
 551
 552 gstring_release_unused(yield);
 553
 554 /* If yield NULL we have not found anything. Otherwise, insert the terminating
 555 zero and return the result. */
 556
 557 dns_retrans = save_retrans;
 558 dns_retry = save_retry;
 559 dns_init(FALSE, FALSE, FALSE);  /* clear the dnssec bit for getaddrbyname */
 560
 561 if (!yield || !yield->ptr) return failrc;
 562
 563 *result = string_from_gstring(yield);
 564 return OK;
 565 }
 566
 567
 568
 569 /*************************************************
 570 *         Version reporting entry point          *
 571 *************************************************/
 572
 573 /* See local README for interface description. */
 574
 575 #include "../version.h"
 576
 577 void
 578 dnsdb_version_report(FILE *f)
 579 {
 580 #ifdef DYNLOOKUP
 581 fprintf(f, "Library version: DNSDB: Exim version %s\n", EXIM_VERSION_STR);
 582 #endif
 583 }
 584
 585
 586 static lookup_info _lookup_info = {
 587   US"dnsdb",                     /* lookup name */
 588   lookup_querystyle,             /* query style */
 589   dnsdb_open,                    /* open function */
 590   NULL,                          /* check function */
 591   dnsdb_find,                    /* find function */
 592   NULL,                          /* no close function */
 593   NULL,                          /* no tidy function */
 594   NULL,                          /* no quoting function */
 595   dnsdb_version_report           /* version reporting */
 596 };
 597
 598 #ifdef DYNLOOKUP
 599 #define dnsdb_lookup_module_info _lookup_module_info
 600 #endif
 601
 602 static lookup_info *_lookup_list[] = { &_lookup_info };
 603 lookup_module_info dnsdb_lookup_module_info = { LOOKUP_MODULE_INFO_MAGIC, _lookup_list, 1 };
 604
 605 /* vi: aw ai sw=2
 606 */
 607 /* End of lookups/dnsdb.c */