src/src/routers/dnslookup.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 "rf_functions.h"
  10 #include "dnslookup.h"
  11
  12
  13
  14 /* Options specific to the dnslookup router. */
  15
  16 optionlist dnslookup_router_options[] = {
  17   { "check_secondary_mx", opt_bool,
  18       (void *)(offsetof(dnslookup_router_options_block, check_secondary_mx)) },
  19   { "check_srv",          opt_stringptr,
  20       (void *)(offsetof(dnslookup_router_options_block, check_srv)) },
  21   { "fail_defer_domains", opt_stringptr,
  22       (void *)(offsetof(dnslookup_router_options_block, fail_defer_domains)) },
  23   { "ipv4_only",          opt_stringptr,
  24       (void *)(offsetof(dnslookup_router_options_block, ipv4_only)) },
  25   { "ipv4_prefer",        opt_stringptr,
  26       (void *)(offsetof(dnslookup_router_options_block, ipv4_prefer)) },
  27   { "mx_domains",         opt_stringptr,
  28       (void *)(offsetof(dnslookup_router_options_block, mx_domains)) },
  29   { "mx_fail_domains",    opt_stringptr,
  30       (void *)(offsetof(dnslookup_router_options_block, mx_fail_domains)) },
  31   { "qualify_single",     opt_bool,
  32       (void *)(offsetof(dnslookup_router_options_block, qualify_single)) },
  33   { "rewrite_headers",    opt_bool,
  34       (void *)(offsetof(dnslookup_router_options_block, rewrite_headers)) },
  35   { "same_domain_copy_routing", opt_bool|opt_public,
  36       (void *)(offsetof(router_instance, same_domain_copy_routing)) },
  37   { "search_parents",     opt_bool,
  38       (void *)(offsetof(dnslookup_router_options_block, search_parents)) },
  39   { "srv_fail_domains",   opt_stringptr,
  40       (void *)(offsetof(dnslookup_router_options_block, srv_fail_domains)) },
  41   { "widen_domains",      opt_stringptr,
  42       (void *)(offsetof(dnslookup_router_options_block, widen_domains)) }
  43 };
  44
  45 /* Size of the options list. An extern variable has to be used so that its
  46 address can appear in the tables drtables.c. */
  47
  48 int dnslookup_router_options_count =
  49   sizeof(dnslookup_router_options)/sizeof(optionlist);
  50
  51
  52 #ifdef MACRO_PREDEF
  53
  54 /* Dummy entries */
  55 dnslookup_router_options_block dnslookup_router_option_defaults = {0};
  56 void dnslookup_router_init(router_instance *rblock) {}
  57 int dnslookup_router_entry(router_instance *rblock, address_item *addr,
  58   struct passwd *pw, int verify, address_item **addr_local,
  59   address_item **addr_remote, address_item **addr_new,
  60   address_item **addr_succeed) {return 0;}
  61
  62 #else   /*!MACRO_PREDEF*/
  63
  64
  65
  66
  67 /* Default private options block for the dnslookup router. */
  68
  69 dnslookup_router_options_block dnslookup_router_option_defaults = {
  70   .check_secondary_mx = FALSE,
  71   .qualify_single =     TRUE,
  72   .search_parents =     FALSE,
  73   .rewrite_headers =    TRUE,
  74   .widen_domains =      NULL,
  75   .mx_domains =         NULL,
  76   .mx_fail_domains =    NULL,
  77   .srv_fail_domains =   NULL,
  78   .check_srv =          NULL,
  79   .fail_defer_domains = NULL,
  80   .ipv4_only =          NULL,
  81   .ipv4_prefer =        NULL,
  82 };
  83
  84
  85
  86 /*************************************************
  87 *          Initialization entry point            *
  88 *************************************************/
  89
  90 /* Called for each instance, after its options have been read, to enable
  91 consistency checks to be done, or anything else that needs to be set up. */
  92
  93 void
  94 dnslookup_router_init(router_instance *rblock)
  95 {
  96 /*
  97 dnslookup_router_options_block *ob =
  98   (dnslookup_router_options_block *)(rblock->options_block);
  99 */
 100 rblock = rblock;
 101 }
 102
 103
 104
 105 /*************************************************
 106 *              Main entry point                  *
 107 *************************************************/
 108
 109 /* See local README for interface details. This router returns:
 110
 111 DECLINE
 112   . the domain does not exist in the DNS
 113   . MX records point to non-existent hosts (including RHS = IP address)
 114   . a single SRV record has a host name of "." (=> no service)
 115   . syntactically invalid mail domain
 116   . check_secondary_mx set, and local host not in host list
 117
 118 DEFER
 119   . lookup defer for mx_domains
 120   . timeout etc on DNS lookup
 121   . verifying the errors address caused a deferment or a big disaster such
 122       as an expansion failure (rf_get_errors_address)
 123   . expanding a headers_{add,remove} string caused a deferment or another
 124       expansion error (rf_get_munge_headers)
 125   . a problem in rf_get_transport: no transport when one is needed;
 126       failed to expand dynamic transport; failed to find dynamic transport
 127   . failure to expand or find a uid/gid (rf_get_ugid via rf_queue_add)
 128   . self = "freeze", self = "defer"
 129
 130 PASS
 131   . timeout etc on DNS lookup and pass_on_timeout set
 132   . self = "pass"
 133
 134 REROUTED
 135   . routed to local host, but name was expanded by DNS lookup, so a
 136       re-routing should take place
 137   . self = "reroute"
 138
 139   In both cases the new address will have been set up as a child
 140
 141 FAIL
 142   . self = "fail"
 143
 144 OK
 145   added address to addr_local or addr_remote, as appropriate for the
 146   type of transport; this includes the self="send" case.
 147 */
 148
 149 int
 150 dnslookup_router_entry(
 151   router_instance *rblock,        /* data for this instantiation */
 152   address_item *addr,             /* address we are working on */
 153   struct passwd *pw,              /* passwd entry after check_local_user */
 154   int verify,                     /* v_none/v_recipient/v_sender/v_expn */
 155   address_item **addr_local,      /* add it to this if it's local */
 156   address_item **addr_remote,     /* add it to this if it's remote */
 157   address_item **addr_new,        /* put new addresses on here */
 158   address_item **addr_succeed)    /* put old address here on success */
 159 {
 160 host_item h;
 161 int rc;
 162 int widen_sep = 0;
 163 int whichrrs = HOST_FIND_BY_MX | HOST_FIND_BY_A | HOST_FIND_BY_AAAA;
 164 dnslookup_router_options_block *ob =
 165   (dnslookup_router_options_block *)(rblock->options_block);
 166 uschar *srv_service = NULL;
 167 uschar *widen = NULL;
 168 const uschar *pre_widen = addr->domain;
 169 const uschar *post_widen = NULL;
 170 const uschar *fully_qualified_name;
 171 const uschar *listptr;
 172 uschar widen_buffer[256];
 173
 174 addr_new = addr_new;          /* Keep picky compilers happy */
 175 addr_succeed = addr_succeed;
 176
 177 DEBUG(D_route)
 178   debug_printf("%s router called for %s\n  domain = %s\n",
 179     rblock->name, addr->address, addr->domain);
 180
 181 /* If an SRV check is required, expand the service name */
 182
 183 if (ob->check_srv)
 184   {
 185   if (  !(srv_service = expand_string(ob->check_srv))
 186      && !expand_string_forcedfail)
 187     {
 188     addr->message = string_sprintf("%s router: failed to expand \"%s\": %s",
 189       rblock->name, ob->check_srv, expand_string_message);
 190     return DEFER;
 191     }
 192   else whichrrs |= HOST_FIND_BY_SRV;
 193   }
 194
 195 /* Set up the first of any widening domains. The code further down copes with
 196 either pre- or post-widening, but at present there is no way to turn on
 197 pre-widening, as actually doing so seems like a rather bad idea, and nobody has
 198 requested it. Pre-widening would cause local abbreviated names to take
 199 precedence over global names. For example, if the domain is "xxx.ch" it might
 200 be something in the "ch" toplevel domain, but it also might be xxx.ch.xyz.com.
 201 The choice of pre- or post-widening affects which takes precedence. If ever
 202 somebody comes up with some kind of requirement for pre-widening, presumably
 203 with some conditions under which it is done, it can be selected here.
 204
 205 The rewrite_headers option works only when routing an address at transport
 206 time, because the alterations to the headers are not persistent so must be
 207 worked out immediately before they are used. Sender addresses are routed for
 208 verification purposes, but never at transport time, so any header changes that
 209 you might expect as a result of sender domain widening do not occur. Therefore
 210 we do not perform widening when verifying sender addresses; however, widening
 211 sender addresses is OK if we do not have to rewrite the headers. A corollary
 212 of this is that if the current address is not the original address, then it
 213 does not appear in the message header so it is also OK to widen. The
 214 suppression of widening for sender addresses is silent because it is the
 215 normal desirable behaviour. */
 216
 217 if (  ob->widen_domains
 218    && (verify != v_sender || !ob->rewrite_headers || addr->parent))
 219   {
 220   listptr = ob->widen_domains;
 221   widen = string_nextinlist(&listptr, &widen_sep, widen_buffer,
 222     sizeof(widen_buffer));
 223
 224 /****
 225   if (some condition requiring pre-widening)
 226     {
 227     post_widen = pre_widen;
 228     pre_widen = NULL;
 229     }
 230 ****/
 231   }
 232
 233 /* Loop to cope with explicit widening of domains as configured. This code
 234 copes with widening that may happen before or after the original name. The
 235 decision as to which is taken above. */
 236
 237 for (;;)
 238   {
 239   int flags = whichrrs;
 240   BOOL removed = FALSE;
 241
 242   if (pre_widen)
 243     {
 244     h.name = pre_widen;
 245     pre_widen = NULL;
 246     }
 247   else if (widen)
 248     {
 249     h.name = string_sprintf("%s.%s", addr->domain, widen);
 250     widen = string_nextinlist(&listptr, &widen_sep, widen_buffer,
 251       sizeof(widen_buffer));
 252     DEBUG(D_route) debug_printf("%s router widened %s to %s\n", rblock->name,
 253       addr->domain, h.name);
 254     }
 255   else if (post_widen)
 256     {
 257     h.name = post_widen;
 258     post_widen = NULL;
 259     DEBUG(D_route) debug_printf("%s router trying %s after widening failed\n",
 260       rblock->name, h.name);
 261     }
 262   else return DECLINE;
 263
 264   /* Check if we must request only. or prefer, ipv4 */
 265
 266   if (  ob->ipv4_only
 267      && expand_check_condition(ob->ipv4_only, rblock->name, US"router"))
 268     flags = flags & ~HOST_FIND_BY_AAAA | HOST_FIND_IPV4_ONLY;
 269   else if (search_find_defer)
 270     return DEFER;
 271   if (  ob->ipv4_prefer
 272      && expand_check_condition(ob->ipv4_prefer, rblock->name, US"router"))
 273     flags |= HOST_FIND_IPV4_FIRST;
 274   else if (search_find_defer)
 275     return DEFER;
 276
 277   /* Set up the rest of the initial host item. Others may get chained on if
 278   there is more than one IP address. We set it up here instead of outside the
 279   loop so as to re-initialize if a previous try succeeded but was rejected
 280   because of not having an MX record. */
 281
 282   h.next = NULL;
 283   h.address = NULL;
 284   h.port = PORT_NONE;
 285   h.mx = MX_NONE;
 286   h.status = hstatus_unknown;
 287   h.why = hwhy_unknown;
 288   h.last_try = 0;
 289
 290   /* Unfortunately, we cannot set the mx_only option in advance, because the
 291   DNS lookup may extend an unqualified name. Therefore, we must do the test
 292   stoubsequently. We use the same logic as that for widen_domains above to avoid
 293   requesting a header rewrite that cannot work. */
 294
 295   if (verify != v_sender || !ob->rewrite_headers || addr->parent)
 296     {
 297     if (ob->qualify_single) flags |= HOST_FIND_QUALIFY_SINGLE;
 298     if (ob->search_parents) flags |= HOST_FIND_SEARCH_PARENTS;
 299     }
 300
 301   rc = host_find_bydns(&h, CUS rblock->ignore_target_hosts, flags,
 302     srv_service, ob->srv_fail_domains, ob->mx_fail_domains,
 303     &rblock->dnssec, &fully_qualified_name, &removed);
 304   if (removed) setflag(addr, af_local_host_removed);
 305
 306   /* If host found with only address records, test for the domain's being in
 307   the mx_domains list. Note that this applies also to SRV records; the name of
 308   the option is historical. */
 309
 310   if ((rc == HOST_FOUND || rc == HOST_FOUND_LOCAL) && h.mx < 0 &&
 311        ob->mx_domains)
 312     switch(match_isinlist(fully_qualified_name,
 313           CUSS &(ob->mx_domains), 0,
 314           &domainlist_anchor, addr->domain_cache, MCL_DOMAIN, TRUE, NULL))
 315       {
 316       case DEFER:
 317       addr->message = US"lookup defer for mx_domains";
 318       return DEFER;
 319
 320       case OK:
 321       DEBUG(D_route) debug_printf("%s router rejected %s: no MX record(s)\n",
 322         rblock->name, fully_qualified_name);
 323       continue;
 324       }
 325
 326   /* Deferral returns forthwith, and anything other than failure breaks the
 327   loop. */
 328
 329   if (rc == HOST_FIND_SECURITY)
 330     {
 331     addr->message = US"host lookup done insecurely";
 332     return DEFER;
 333     }
 334   if (rc == HOST_FIND_AGAIN)
 335     {
 336     if (rblock->pass_on_timeout)
 337       {
 338       DEBUG(D_route) debug_printf("%s router timed out, and pass_on_timeout is set\n",
 339         rblock->name);
 340       return PASS;
 341       }
 342     addr->message = US"host lookup did not complete";
 343     return DEFER;
 344     }
 345
 346   if (rc != HOST_FIND_FAILED) break;
 347
 348   if (ob->fail_defer_domains)
 349     switch(match_isinlist(fully_qualified_name,
 350           CUSS &ob->fail_defer_domains, 0,
 351           &domainlist_anchor, addr->domain_cache, MCL_DOMAIN, TRUE, NULL))
 352       {
 353       case DEFER:
 354         addr->message = US"lookup defer for fail_defer_domains option";
 355         return DEFER;
 356
 357       case OK:
 358         DEBUG(D_route) debug_printf("%s router: matched fail_defer_domains\n",
 359           rblock->name);
 360         addr->message = US"missing MX, or all MXs point to missing A records,"
 361           " and defer requested";
 362         return DEFER;
 363       }
 364   /* Check to see if the failure is the result of MX records pointing to
 365   non-existent domains, and if so, set an appropriate error message; the case
 366   of an MX or SRV record pointing to "." is another special case that we can
 367   detect. Otherwise "unknown mail domain" is used, which is confusing. Also, in
 368   this case don't do the widening. We need check only the first host to see if
 369   its MX has been filled in, but there is no address, because if there were any
 370   usable addresses returned, we would not have had HOST_FIND_FAILED.
 371
 372   As a common cause of this problem is MX records with IP addresses on the
 373   RHS, give a special message in this case. */
 374
 375   if (h.mx >= 0 && h.address == NULL)
 376     {
 377     setflag(addr, af_pass_message);   /* This is not a security risk */
 378     if (h.name[0] == 0)
 379       addr->message = US"an MX or SRV record indicated no SMTP service";
 380     else
 381       {
 382       addr->basic_errno = ERRNO_UNKNOWNHOST;
 383       addr->message = US"all relevant MX records point to non-existent hosts";
 384       if (!allow_mx_to_ip && string_is_ip_address(h.name, NULL) != 0)
 385         {
 386         addr->user_message =
 387           string_sprintf("It appears that the DNS operator for %s\n"
 388             "has installed an invalid MX record with an IP address\n"
 389             "instead of a domain name on the right hand side.", addr->domain);
 390         addr->message = string_sprintf("%s or (invalidly) to IP addresses",
 391           addr->message);
 392         }
 393       }
 394     return DECLINE;
 395     }
 396
 397   /* If there's a syntax error, do not continue with any widening, and note
 398   the error. */
 399
 400   if (host_find_failed_syntax)
 401     {
 402     addr->message = string_sprintf("mail domain \"%s\" is syntactically "
 403       "invalid", h.name);
 404     return DECLINE;
 405     }
 406   }
 407
 408 /* If the original domain name has been changed as a result of the host lookup,
 409 set up a child address for rerouting and request header rewrites if so
 410 configured. Then yield REROUTED. However, if the only change is a change of
 411 case in the domain name, which some resolvers yield (others don't), just change
 412 the domain name in the original address so that the official version is used in
 413 RCPT commands. */
 414
 415 if (Ustrcmp(addr->domain, fully_qualified_name) != 0)
 416   {
 417   if (strcmpic(addr->domain, fully_qualified_name) == 0)
 418     {
 419     uschar *at = Ustrrchr(addr->address, '@');
 420     memcpy(at+1, fully_qualified_name, Ustrlen(at+1));
 421     }
 422   else
 423     {
 424     rf_change_domain(addr, fully_qualified_name, ob->rewrite_headers, addr_new);
 425     return REROUTED;
 426     }
 427   }
 428
 429 /* If the yield is HOST_FOUND_LOCAL, the remote domain name either found MX
 430 records with the lowest numbered one pointing to a host with an IP address that
 431 is set on one of the interfaces of this machine, or found A records or got
 432 addresses from gethostbyname() that contain one for this machine. This can
 433 happen quite legitimately if the original name was a shortened form of a
 434 domain, but we will have picked that up already via the name change test above.
 435
 436 Otherwise, the action to be taken can be configured by the self option, the
 437 handling of which is in a separate function, as it is also required for other
 438 routers. */
 439
 440 if (rc == HOST_FOUND_LOCAL)
 441   {
 442   rc = rf_self_action(addr, &h, rblock->self_code, rblock->self_rewrite,
 443     rblock->self, addr_new);
 444   if (rc != OK) return rc;
 445   }
 446
 447 /* Otherwise, insist on being a secondary MX if so configured */
 448
 449 else if (ob->check_secondary_mx && !testflag(addr, af_local_host_removed))
 450   {
 451   DEBUG(D_route) debug_printf("check_secondary_mx set and local host not secondary\n");
 452   return DECLINE;
 453   }
 454
 455 /* Set up the errors address, if any. */
 456
 457 rc = rf_get_errors_address(addr, rblock, verify, &addr->prop.errors_address);
 458 if (rc != OK) return rc;
 459
 460 /* Set up the additional and removeable headers for this address. */
 461
 462 rc = rf_get_munge_headers(addr, rblock, &addr->prop.extra_headers,
 463   &addr->prop.remove_headers);
 464 if (rc != OK) return rc;
 465
 466 /* Get store in which to preserve the original host item, chained on
 467 to the address. */
 468
 469 addr->host_list = store_get(sizeof(host_item));
 470 addr->host_list[0] = h;
 471
 472 /* Fill in the transport and queue the address for delivery. */
 473
 474 if (!rf_get_transport(rblock->transport_name, &(rblock->transport),
 475       addr, rblock->name, NULL))
 476   return DEFER;
 477
 478 addr->transport = rblock->transport;
 479
 480 return rf_queue_add(addr, addr_local, addr_remote, rblock, pw)?
 481   OK : DEFER;
 482 }
 483
 484 #endif   /*!MACRO_PREDEF*/
 485 /* End of routers/dnslookup.c */
 486 /* vi: aw ai sw=2
 487 */