src/src/lookups/dnsdb.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2018 */
   6 /* Copyright (c) The Exim Maintainers 2020 */
   7 /* See the file NOTICE for conditions of use and distribution. */
   8
   9 #include "../exim.h"
  10 #include "lf_functions.h"
  11
  12
  13
  14 /* Ancient systems (e.g. SunOS4) don't appear to have T_TXT defined in their
  15 header files. */
  16
  17 #ifndef T_TXT
  18 # define T_TXT 16
  19 #endif
  20
  21 /* Many systems do not have T_SPF. */
  22 #ifndef T_SPF
  23 # define T_SPF 99
  24 #endif
  25
  26 /* New TLSA record for DANE */
  27 #ifndef T_TLSA
  28 # define T_TLSA 52
  29 #endif
  30
  31 /* Table of recognized DNS record types and their integer values. */
  32
  33 static const char *type_names[] = {
  34   "a",
  35 #if HAVE_IPV6
  36   "a+",
  37   "aaaa",
  38 #endif
  39   "cname",
  40   "csa",
  41   "mx",
  42   "mxh",
  43   "ns",
  44   "ptr",
  45   "soa",
  46   "spf",
  47   "srv",
  48   "tlsa",
  49   "txt",
  50   "zns"
  51 };
  52
  53 static int type_values[] = {
  54   T_A,
  55 #if HAVE_IPV6
  56   T_ADDRESSES,     /* Private type for AAAA + A */
  57   T_AAAA,
  58 #endif
  59   T_CNAME,
  60   T_CSA,     /* Private type for "Client SMTP Authorization". */
  61   T_MX,
  62   T_MXH,     /* Private type for "MX hostnames" */
  63   T_NS,
  64   T_PTR,
  65   T_SOA,
  66   T_SPF,
  67   T_SRV,
  68   T_TLSA,
  69   T_TXT,
  70   T_ZNS      /* Private type for "zone nameservers" */
  71 };
  72
  73
  74 /*************************************************
  75 *              Open entry point                  *
  76 *************************************************/
  77
  78 /* See local README for interface description. */
  79
  80 static void *
  81 dnsdb_open(const uschar * filename, uschar **errmsg)
  82 {
  83 filename = filename;   /* Keep picky compilers happy */
  84 errmsg = errmsg;       /* Ditto */
  85 return (void *)(-1);   /* Any non-0 value */
  86 }
  87
  88
  89
  90 /*************************************************
  91 *           Find entry point for dnsdb           *
  92 *************************************************/
  93
  94 /* See local README for interface description. The query in the "keystring" may
  95 consist of a number of parts.
  96
  97 (a) If the first significant character is '>' then the next character is the
  98 separator character that is used when multiple records are found. The default
  99 separator is newline.
 100
 101 (b) If the next character is ',' then the next character is the separator
 102 character used for multiple items of text in "TXT" records. Alternatively,
 103 if the next character is ';' then these multiple items are concatenated with
 104 no separator. With neither of these options specified, only the first item
 105 is output.  Similarly for "SPF" records, but the default for joining multiple
 106 items in one SPF record is the empty string, for direct concatenation.
 107
 108 (c) Options, all comma-terminated, in any order.  Any unrecognised option
 109 terminates option processing.  Recognised options are:
 110
 111 - 'defer_FOO':  set the defer behaviour to FOO.  The possible behaviours are:
 112 'strict', where any defer causes the whole lookup to defer; 'lax', where a defer
 113 causes the whole lookup to defer only if none of the DNS queries succeeds; and
 114 'never', where all defers are as if the lookup failed. The default is 'lax'.
 115
 116 - 'dnssec_FOO', with 'strict', 'lax' (default), and 'never'.  The meanings are
 117 require, try and don't-try dnssec respectively.
 118
 119 - 'retrans_VAL', set the timeout value.  VAL is an Exim time specification
 120 (eg "5s").  The default is set by the main configuration option 'dns_retrans'.
 121
 122 - 'retry_VAL', set the retry count on timeouts.  VAL is an integer.  The
 123 default is set by the main configuration option "dns_retry".
 124
 125 (d) If the next sequence of characters is a sequence of letters and digits
 126 followed by '=', it is interpreted as the name of the DNS record type. The
 127 default is "TXT".
 128
 129 (e) Then there follows list of domain names. This is a generalized Exim list,
 130 which may start with '<' in order to set a specific separator. The default
 131 separator, as always, is colon. */
 132
 133 static int
 134 dnsdb_find(void * handle, const uschar * filename, const uschar * keystring,
 135  int length, uschar ** result, uschar ** errmsg, uint * do_cache,
 136  const uschar * opts)
 137 {
 138 int rc;
 139 int sep = 0;
 140 int defer_mode = PASS;
 141 int dnssec_mode = PASS;
 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 dns_answer * dnsa = store_get_dns_answer();
 151 dns_scan dnss;
 152
 153 /* Because we're working in the search pool, we try to reclaim as much
 154 store as possible later, so we preallocate the result here */
 155
 156 gstring * yield = string_get(256);
 157
 158 handle = handle;           /* Keep picky compilers happy */
 159 filename = filename;
 160 length = length;
 161 do_cache = do_cache;
 162
 163 /* If the string starts with '>' we change the output separator.
 164 If it's followed by ';' or ',' we set the TXT output separator. */
 165
 166 while (isspace(*keystring)) keystring++;
 167 if (*keystring == '>')
 168   {
 169   outsep = keystring + 1;
 170   keystring += 2;
 171   if (*keystring == ',')
 172     {
 173     outsep2 = keystring + 1;
 174     keystring += 2;
 175     }
 176   else if (*keystring == ';')
 177     {
 178     outsep2 = US"";
 179     keystring++;
 180     }
 181   while (isspace(*keystring)) keystring++;
 182   }
 183
 184 /* Check for a modifier keyword. */
 185
 186 for (;;)
 187   {
 188   if (strncmpic(keystring, US"defer_", 6) == 0)
 189     {
 190     keystring += 6;
 191     if (strncmpic(keystring, US"strict", 6) == 0)
 192       { defer_mode = DEFER; keystring += 6; }
 193     else if (strncmpic(keystring, US"lax", 3) == 0)
 194       { defer_mode = PASS; keystring += 3; }
 195     else if (strncmpic(keystring, US"never", 5) == 0)
 196       { defer_mode = OK; keystring += 5; }
 197     else
 198       {
 199       *errmsg = US"unsupported dnsdb defer behaviour";
 200       return DEFER;
 201       }
 202     }
 203   else if (strncmpic(keystring, US"dnssec_", 7) == 0)
 204     {
 205     keystring += 7;
 206     if (strncmpic(keystring, US"strict", 6) == 0)
 207       { dnssec_mode = DEFER; keystring += 6; }
 208     else if (strncmpic(keystring, US"lax", 3) == 0)
 209       { dnssec_mode = PASS; keystring += 3; }
 210     else if (strncmpic(keystring, US"never", 5) == 0)
 211       { dnssec_mode = OK; keystring += 5; }
 212     else
 213       {
 214       *errmsg = US"unsupported dnsdb dnssec behaviour";
 215       return DEFER;
 216       }
 217     }
 218   else if (strncmpic(keystring, US"retrans_", 8) == 0)
 219     {
 220     int timeout_sec;
 221     if ((timeout_sec = readconf_readtime(keystring += 8, ',', FALSE)) <= 0)
 222       {
 223       *errmsg = US"unsupported dnsdb timeout value";
 224       return DEFER;
 225       }
 226     dns_retrans = timeout_sec;
 227     while (*keystring != ',') keystring++;
 228     }
 229   else if (strncmpic(keystring, US"retry_", 6) == 0)
 230     {
 231     int retries;
 232     if ((retries = (int)strtol(CCS keystring + 6, CSS &keystring, 0)) < 0)
 233       {
 234       *errmsg = US"unsupported dnsdb retry count";
 235       return DEFER;
 236       }
 237     dns_retry = retries;
 238     }
 239   else
 240     break;
 241
 242   while (isspace(*keystring)) keystring++;
 243   if (*keystring++ != ',')
 244     {
 245     *errmsg = US"dnsdb modifier syntax error";
 246     return DEFER;
 247     }
 248   while (isspace(*keystring)) keystring++;
 249   }
 250
 251 /* Figure out the "type" value if it is not T_TXT.
 252 If the keystring contains an = this must be preceded by a valid type name. */
 253
 254 type = T_TXT;
 255 if ((equals = Ustrchr(keystring, '=')) != NULL)
 256   {
 257   int i, len;
 258   uschar *tend = equals;
 259
 260   while (tend > keystring && isspace(tend[-1])) tend--;
 261   len = tend - keystring;
 262
 263   for (i = 0; i < nelem(type_names); i++)
 264     if (len == Ustrlen(type_names[i]) &&
 265         strncmpic(keystring, US type_names[i], len) == 0)
 266       {
 267       type = type_values[i];
 268       break;
 269       }
 270
 271   if (i >= nelem(type_names))
 272     {
 273     *errmsg = US"unsupported DNS record type";
 274     return DEFER;
 275     }
 276
 277   keystring = equals + 1;
 278   while (isspace(*keystring)) keystring++;
 279   }
 280
 281 /* Initialize the resolver in case this is the first time it has been used. */
 282
 283 dns_init(FALSE, FALSE, dnssec_mode != OK);
 284
 285 /* The remainder of the string must be a list of domains. As long as the lookup
 286 for at least one of them succeeds, we return success. Failure means that none
 287 of them were found.
 288
 289 The original implementation did not support a list of domains. Adding the list
 290 feature is compatible, except in one case: when PTR records are being looked up
 291 for a single IPv6 address. Fortunately, we can hack in a compatibility feature
 292 here: If the type is PTR and no list separator is specified, and the entire
 293 remaining string is valid as an IP address, set an impossible separator so that
 294 it is treated as one item. */
 295
 296 if (type == T_PTR && keystring[0] != '<' &&
 297     string_is_ip_address(keystring, NULL) != 0)
 298   sep = -1;
 299
 300 /* SPF strings should be concatenated without a separator, thus make
 301 it the default if not defined (see RFC 4408 section 3.1.3).
 302 Multiple SPF records are forbidden (section 3.1.2) but are currently
 303 not handled specially, thus they are concatenated with \n by default.
 304 MX priority and value are space-separated by default.
 305 SRV and TLSA record parts are space-separated by default. */
 306
 307 if (!outsep2) switch(type)
 308   {
 309   case T_SPF:                         outsep2 = US"";  break;
 310   case T_SRV: case T_MX: case T_TLSA: outsep2 = US" "; break;
 311   }
 312
 313 /* Now scan the list and do a lookup for each item */
 314
 315 while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
 316   {
 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     domain = dns_build_reverse(domain);
 330
 331   do
 332     {
 333     DEBUG(D_lookup) debug_printf_indent("dnsdb key: %s\n", domain);
 334
 335     /* Do the lookup and sort out the result. There are four special types that
 336     are handled specially: T_CSA, T_ZNS, T_ADDRESSES and T_MXH.
 337     The first two are handled in a special lookup function so that the facility
 338     could be used from other parts of the Exim code. T_ADDRESSES is handled by looping
 339     over the types of A lookup.  T_MXH affects only what happens later on in
 340     this function, but for tidiness it is handled by the "special". If the
 341     lookup fails, continue with the next domain. In the case of DEFER, adjust
 342     the final "nothing found" result, but carry on to the next domain. */
 343
 344     found = domain;
 345 #if HAVE_IPV6
 346     if (type == T_ADDRESSES)            /* NB cannot happen unless HAVE_IPV6 */
 347       {
 348       if (searchtype == T_ADDRESSES) searchtype = T_AAAA;
 349       else if (searchtype == T_AAAA) searchtype = T_A;
 350       rc = dns_special_lookup(dnsa, domain, searchtype, CUSS &found);
 351       }
 352     else
 353 #endif
 354       rc = dns_special_lookup(dnsa, domain, type, CUSS &found);
 355
 356     lookup_dnssec_authenticated = dnssec_mode==OK ? NULL
 357       : dns_is_secure(dnsa) ? US"yes" : US"no";
 358
 359     if (rc == DNS_NOMATCH || rc == DNS_NODATA) continue;
 360     if (  rc != DNS_SUCCEED
 361        || (dnssec_mode == DEFER && !dns_is_secure(dnsa))
 362        )
 363       {
 364       if (defer_mode == DEFER)
 365         {
 366         dns_retrans = save_retrans;
 367         dns_retry = save_retry;
 368         dns_init(FALSE, FALSE, FALSE);                  /* clr dnssec bit */
 369         return DEFER;                                   /* always defer */
 370         }
 371       if (defer_mode == PASS) failrc = DEFER;         /* defer only if all do */
 372       continue;                                       /* treat defer as fail */
 373       }
 374
 375
 376     /* Search the returned records */
 377
 378     for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); rr;
 379          rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) if (rr->type == searchtype)
 380       {
 381       if (*do_cache > rr->ttl)
 382         *do_cache = rr->ttl;
 383
 384       if (type == T_A || type == T_AAAA || type == T_ADDRESSES)
 385         {
 386         for (dns_address * da = dns_address_from_rr(dnsa, rr); da; da = da->next)
 387           {
 388           if (yield->ptr) yield = string_catn(yield, outsep, 1);
 389           yield = string_cat(yield, da->address);
 390           }
 391         continue;
 392         }
 393
 394       /* Other kinds of record just have one piece of data each, but there may be
 395       several of them, of course. */
 396
 397       if (yield->ptr) yield = string_catn(yield, outsep, 1);
 398
 399       if (type == T_TXT || type == T_SPF)
 400         {
 401         if (outsep2 == NULL)    /* output only the first item of data */
 402           yield = string_catn(yield, US (rr->data+1), (rr->data)[0]);
 403         else
 404           {
 405           /* output all items */
 406           int data_offset = 0;
 407           while (data_offset < rr->size)
 408             {
 409             uschar chunk_len = (rr->data)[data_offset++];
 410             if (outsep2[0] != '\0' && data_offset != 1)
 411               yield = string_catn(yield, outsep2, 1);
 412             yield = string_catn(yield, US ((rr->data)+data_offset), chunk_len);
 413             data_offset += chunk_len;
 414             }
 415           }
 416         }
 417       else if (type == T_TLSA)
 418         {
 419         uint8_t usage, selector, matching_type;
 420         uint16_t payload_length;
 421         uschar s[MAX_TLSA_EXPANDED_SIZE];
 422         uschar * sp = s;
 423         uschar * p = US rr->data;
 424
 425         usage = *p++;
 426         selector = *p++;
 427         matching_type = *p++;
 428         /* What's left after removing the first 3 bytes above */
 429         payload_length = rr->size - 3;
 430         sp += sprintf(CS s, "%d%c%d%c%d%c", usage, *outsep2,
 431                 selector, *outsep2, matching_type, *outsep2);
 432         /* Now append the cert/identifier, one hex char at a time */
 433         while (payload_length-- > 0 && sp-s < (MAX_TLSA_EXPANDED_SIZE - 4))
 434           sp += sprintf(CS sp, "%02x", *p++);
 435
 436         yield = string_cat(yield, s);
 437         }
 438       else   /* T_CNAME, T_CSA, T_MX, T_MXH, T_NS, T_PTR, T_SOA, T_SRV */
 439         {
 440         int priority, weight, port;
 441         uschar s[264];
 442         uschar * p = US rr->data;
 443
 444         switch (type)
 445           {
 446           case T_MXH:
 447             /* mxh ignores the priority number and includes only the hostnames */
 448             GETSHORT(priority, p);
 449             break;
 450
 451           case T_MX:
 452             GETSHORT(priority, p);
 453             sprintf(CS s, "%d%c", priority, *outsep2);
 454             yield = string_cat(yield, s);
 455             break;
 456
 457           case T_SRV:
 458             GETSHORT(priority, p);
 459             GETSHORT(weight, p);
 460             GETSHORT(port, p);
 461             sprintf(CS s, "%d%c%d%c%d%c", priority, *outsep2,
 462                               weight, *outsep2, port, *outsep2);
 463             yield = string_cat(yield, s);
 464             break;
 465
 466           case T_CSA:
 467             /* See acl_verify_csa() for more comments about CSA. */
 468             GETSHORT(priority, p);
 469             GETSHORT(weight, p);
 470             GETSHORT(port, p);
 471
 472             if (priority != 1) continue;      /* CSA version must be 1 */
 473
 474             /* If the CSA record we found is not the one we asked for, analyse
 475             the subdomain assertions in the port field, else analyse the direct
 476             authorization status in the weight field. */
 477
 478             if (Ustrcmp(found, domain) != 0)
 479               {
 480               if (port & 1) *s = 'X';         /* explicit authorization required */
 481               else *s = '?';                  /* no subdomain assertions here */
 482               }
 483             else
 484               {
 485               if (weight < 2) *s = 'N';       /* not authorized */
 486               else if (weight == 2) *s = 'Y'; /* authorized */
 487               else if (weight == 3) *s = '?'; /* unauthorizable */
 488               else continue;                  /* invalid */
 489               }
 490
 491             s[1] = ' ';
 492             yield = string_catn(yield, s, 2);
 493             break;
 494
 495           default:
 496             break;
 497           }
 498
 499         /* GETSHORT() has advanced the pointer to the target domain. */
 500
 501         rc = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, p,
 502           (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 503
 504         /* If an overlong response was received, the data will have been
 505         truncated and dn_expand may fail. */
 506
 507         if (rc < 0)
 508           {
 509           log_write(0, LOG_MAIN, "host name alias list truncated: type=%s "
 510             "domain=%s", dns_text_type(type), domain);
 511           break;
 512           }
 513         else yield = string_cat(yield, s);
 514
 515         if (type == T_SOA && outsep2 != NULL)
 516           {
 517           unsigned long serial, refresh, retry, expire, minimum;
 518
 519           p += rc;
 520           yield = string_catn(yield, outsep2, 1);
 521
 522           rc = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, p,
 523             (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
 524           if (rc < 0)
 525             {
 526             log_write(0, LOG_MAIN, "responsible-mailbox truncated: type=%s "
 527               "domain=%s", dns_text_type(type), domain);
 528             break;
 529             }
 530           else yield = string_cat(yield, s);
 531
 532           p += rc;
 533           GETLONG(serial, p); GETLONG(refresh, p);
 534           GETLONG(retry,  p); GETLONG(expire,  p); GETLONG(minimum, p);
 535           sprintf(CS s, "%c%lu%c%lu%c%lu%c%lu%c%lu",
 536             *outsep2, serial, *outsep2, refresh,
 537             *outsep2, retry,  *outsep2, expire,  *outsep2, minimum);
 538           yield = string_cat(yield, s);
 539           }
 540         }
 541       }    /* Loop for list of returned records */
 542
 543            /* Loop for set of A-lookup types */
 544     } while (type == T_ADDRESSES && searchtype != T_A);
 545
 546   }        /* Loop for list of domains */
 547
 548 /* Reclaim unused memory */
 549
 550 gstring_release_unused(yield);
 551
 552 /* If yield NULL we have not found anything. Otherwise, insert the terminating
 553 zero and return the result. */
 554
 555 dns_retrans = save_retrans;
 556 dns_retry = save_retry;
 557 dns_init(FALSE, FALSE, FALSE);  /* clear the dnssec bit for getaddrbyname */
 558
 559 if (!yield || !yield->ptr) return failrc;
 560
 561 *result = string_from_gstring(yield);
 562 return OK;
 563 }
 564
 565
 566
 567 /*************************************************
 568 *         Version reporting entry point          *
 569 *************************************************/
 570
 571 /* See local README for interface description. */
 572
 573 #include "../version.h"
 574
 575 void
 576 dnsdb_version_report(FILE *f)
 577 {
 578 #ifdef DYNLOOKUP
 579 fprintf(f, "Library version: DNSDB: Exim version %s\n", EXIM_VERSION_STR);
 580 #endif
 581 }
 582
 583
 584 static lookup_info _lookup_info = {
 585   .name = US"dnsdb",                    /* lookup name */
 586   .type = lookup_querystyle,            /* query style */
 587   .open = dnsdb_open,                   /* open function */
 588   .check = NULL,                        /* check function */
 589   .find = dnsdb_find,                   /* find function */
 590   .close = NULL,                        /* no close function */
 591   .tidy = NULL,                         /* no tidy function */
 592   .quote = NULL,                        /* no quoting function */
 593   .version_report = dnsdb_version_report           /* version reporting */
 594 };
 595
 596 #ifdef DYNLOOKUP
 597 #define dnsdb_lookup_module_info _lookup_module_info
 598 #endif
 599
 600 static lookup_info *_lookup_list[] = { &_lookup_info };
 601 lookup_module_info dnsdb_lookup_module_info = { LOOKUP_MODULE_INFO_MAGIC, _lookup_list, 1 };
 602
 603 /* vi: aw ai sw=2
 604 */
 605 /* End of lookups/dnsdb.c */