src/routers/dnslookup.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2015 */
   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   { "mx_domains",         opt_stringptr,
  24       (void *)(offsetof(dnslookup_router_options_block, mx_domains)) },
  25   { "mx_fail_domains",    opt_stringptr,
  26       (void *)(offsetof(dnslookup_router_options_block, mx_fail_domains)) },
  27   { "qualify_single",     opt_bool,
  28       (void *)(offsetof(dnslookup_router_options_block, qualify_single)) },
  29   { "rewrite_headers",    opt_bool,
  30       (void *)(offsetof(dnslookup_router_options_block, rewrite_headers)) },
  31   { "same_domain_copy_routing", opt_bool|opt_public,
  32       (void *)(offsetof(router_instance, same_domain_copy_routing)) },
  33   { "search_parents",     opt_bool,
  34       (void *)(offsetof(dnslookup_router_options_block, search_parents)) },
  35   { "srv_fail_domains",   opt_stringptr,
  36       (void *)(offsetof(dnslookup_router_options_block, srv_fail_domains)) },
  37   { "widen_domains",      opt_stringptr,
  38       (void *)(offsetof(dnslookup_router_options_block, widen_domains)) }
  39 };
  40
  41 /* Size of the options list. An extern variable has to be used so that its
  42 address can appear in the tables drtables.c. */
  43
  44 int dnslookup_router_options_count =
  45   sizeof(dnslookup_router_options)/sizeof(optionlist);
  46
  47 /* Default private options block for the dnslookup router. */
  48
  49 dnslookup_router_options_block dnslookup_router_option_defaults = {
  50   FALSE,           /* check_secondary_mx */
  51   TRUE,            /* qualify_single */
  52   FALSE,           /* search_parents */
  53   TRUE,            /* rewrite_headers */
  54   NULL,            /* widen_domains */
  55   NULL,            /* mx_domains */
  56   NULL,            /* mx_fail_domains */
  57   NULL,            /* srv_fail_domains */
  58   NULL,            /* check_srv */
  59   NULL             /* fail_defer_domains */
  60 };
  61
  62
  63
  64 /*************************************************
  65 *          Initialization entry point            *
  66 *************************************************/
  67
  68 /* Called for each instance, after its options have been read, to enable
  69 consistency checks to be done, or anything else that needs to be set up. */
  70
  71 void
  72 dnslookup_router_init(router_instance *rblock)
  73 {
  74 /*
  75 dnslookup_router_options_block *ob =
  76   (dnslookup_router_options_block *)(rblock->options_block);
  77 */
  78 rblock = rblock;
  79 }
  80
  81
  82
  83 /*************************************************
  84 *              Main entry point                  *
  85 *************************************************/
  86
  87 /* See local README for interface details. This router returns:
  88
  89 DECLINE
  90   . the domain does not exist in the DNS
  91   . MX records point to non-existent hosts (including RHS = IP address)
  92   . a single SRV record has a host name of "." (=> no service)
  93   . syntactically invalid mail domain
  94   . check_secondary_mx set, and local host not in host list
  95
  96 DEFER
  97   . lookup defer for mx_domains
  98   . timeout etc on DNS lookup
  99   . verifying the errors address caused a deferment or a big disaster such
 100       as an expansion failure (rf_get_errors_address)
 101   . expanding a headers_{add,remove} string caused a deferment or another
 102       expansion error (rf_get_munge_headers)
 103   . a problem in rf_get_transport: no transport when one is needed;
 104       failed to expand dynamic transport; failed to find dynamic transport
 105   . failure to expand or find a uid/gid (rf_get_ugid via rf_queue_add)
 106   . self = "freeze", self = "defer"
 107
 108 PASS
 109   . timeout etc on DNS lookup and pass_on_timeout set
 110   . self = "pass"
 111
 112 REROUTED
 113   . routed to local host, but name was expanded by DNS lookup, so a
 114       re-routing should take place
 115   . self = "reroute"
 116
 117   In both cases the new address will have been set up as a child
 118
 119 FAIL
 120   . self = "fail"
 121
 122 OK
 123   added address to addr_local or addr_remote, as appropriate for the
 124   type of transport; this includes the self="send" case.
 125 */
 126
 127 int
 128 dnslookup_router_entry(
 129   router_instance *rblock,        /* data for this instantiation */
 130   address_item *addr,             /* address we are working on */
 131   struct passwd *pw,              /* passwd entry after check_local_user */
 132   int verify,                     /* v_none/v_recipient/v_sender/v_expn */
 133   address_item **addr_local,      /* add it to this if it's local */
 134   address_item **addr_remote,     /* add it to this if it's remote */
 135   address_item **addr_new,        /* put new addresses on here */
 136   address_item **addr_succeed)    /* put old address here on success */
 137 {
 138 host_item h;
 139 int rc;
 140 int widen_sep = 0;
 141 int whichrrs = HOST_FIND_BY_MX | HOST_FIND_BY_A;
 142 dnslookup_router_options_block *ob =
 143   (dnslookup_router_options_block *)(rblock->options_block);
 144 uschar *srv_service = NULL;
 145 uschar *widen = NULL;
 146 const uschar *pre_widen = addr->domain;
 147 const uschar *post_widen = NULL;
 148 const uschar *fully_qualified_name;
 149 const uschar *listptr;
 150 uschar widen_buffer[256];
 151
 152 addr_new = addr_new;          /* Keep picky compilers happy */
 153 addr_succeed = addr_succeed;
 154
 155 DEBUG(D_route)
 156   debug_printf("%s router called for %s\n  domain = %s\n",
 157     rblock->name, addr->address, addr->domain);
 158
 159 /* If an SRV check is required, expand the service name */
 160
 161 if (ob->check_srv)
 162   {
 163   if (  !(srv_service = expand_string(ob->check_srv))
 164      && !expand_string_forcedfail)
 165     {
 166     addr->message = string_sprintf("%s router: failed to expand \"%s\": %s",
 167       rblock->name, ob->check_srv, expand_string_message);
 168     return DEFER;
 169     }
 170   else whichrrs |= HOST_FIND_BY_SRV;
 171   }
 172
 173 /* Set up the first of any widening domains. The code further down copes with
 174 either pre- or post-widening, but at present there is no way to turn on
 175 pre-widening, as actually doing so seems like a rather bad idea, and nobody has
 176 requested it. Pre-widening would cause local abbreviated names to take
 177 precedence over global names. For example, if the domain is "xxx.ch" it might
 178 be something in the "ch" toplevel domain, but it also might be xxx.ch.xyz.com.
 179 The choice of pre- or post-widening affects which takes precedence. If ever
 180 somebody comes up with some kind of requirement for pre-widening, presumably
 181 with some conditions under which it is done, it can be selected here.
 182
 183 The rewrite_headers option works only when routing an address at transport
 184 time, because the alterations to the headers are not persistent so must be
 185 worked out immediately before they are used. Sender addresses are routed for
 186 verification purposes, but never at transport time, so any header changes that
 187 you might expect as a result of sender domain widening do not occur. Therefore
 188 we do not perform widening when verifying sender addresses; however, widening
 189 sender addresses is OK if we do not have to rewrite the headers. A corollary
 190 of this is that if the current address is not the original address, then it
 191 does not appear in the message header so it is also OK to widen. The
 192 suppression of widening for sender addresses is silent because it is the
 193 normal desirable behaviour. */
 194
 195 if (  ob->widen_domains
 196    && (verify != v_sender || !ob->rewrite_headers || addr->parent))
 197   {
 198   listptr = ob->widen_domains;
 199   widen = string_nextinlist(&listptr, &widen_sep, widen_buffer,
 200     sizeof(widen_buffer));
 201
 202 /****
 203   if (some condition requiring pre-widening)
 204     {
 205     post_widen = pre_widen;
 206     pre_widen = NULL;
 207     }
 208 ****/
 209   }
 210
 211 /* Loop to cope with explicit widening of domains as configured. This code
 212 copes with widening that may happen before or after the original name. The
 213 decision as to which is taken above. */
 214
 215 for (;;)
 216   {
 217   int flags = whichrrs;
 218   BOOL removed = FALSE;
 219
 220   if (pre_widen)
 221     {
 222     h.name = pre_widen;
 223     pre_widen = NULL;
 224     }
 225   else if (widen)
 226     {
 227     h.name = string_sprintf("%s.%s", addr->domain, widen);
 228     widen = string_nextinlist(&listptr, &widen_sep, widen_buffer,
 229       sizeof(widen_buffer));
 230     DEBUG(D_route) debug_printf("%s router widened %s to %s\n", rblock->name,
 231       addr->domain, h.name);
 232     }
 233   else if (post_widen)
 234     {
 235     h.name = post_widen;
 236     post_widen = NULL;
 237     DEBUG(D_route) debug_printf("%s router trying %s after widening failed\n",
 238       rblock->name, h.name);
 239     }
 240   else return DECLINE;
 241
 242   /* Set up the rest of the initial host item. Others may get chained on if
 243   there is more than one IP address. We set it up here instead of outside the
 244   loop so as to re-initialize if a previous try succeeded but was rejected
 245   because of not having an MX record. */
 246
 247   h.next = NULL;
 248   h.address = NULL;
 249   h.port = PORT_NONE;
 250   h.mx = MX_NONE;
 251   h.status = hstatus_unknown;
 252   h.why = hwhy_unknown;
 253   h.last_try = 0;
 254
 255   /* Unfortunately, we cannot set the mx_only option in advance, because the
 256   DNS lookup may extend an unqualified name. Therefore, we must do the test
 257   subsequently. We use the same logic as that for widen_domains above to avoid
 258   requesting a header rewrite that cannot work. */
 259
 260   if (verify != v_sender || !ob->rewrite_headers || addr->parent)
 261     {
 262     if (ob->qualify_single) flags |= HOST_FIND_QUALIFY_SINGLE;
 263     if (ob->search_parents) flags |= HOST_FIND_SEARCH_PARENTS;
 264     }
 265
 266   rc = host_find_bydns(&h, CUS rblock->ignore_target_hosts, flags, srv_service,
 267     ob->srv_fail_domains, ob->mx_fail_domains,
 268     &rblock->dnssec, &fully_qualified_name, &removed);
 269   if (removed) setflag(addr, af_local_host_removed);
 270
 271   /* If host found with only address records, test for the domain's being in
 272   the mx_domains list. Note that this applies also to SRV records; the name of
 273   the option is historical. */
 274
 275   if ((rc == HOST_FOUND || rc == HOST_FOUND_LOCAL) && h.mx < 0 &&
 276        ob->mx_domains)
 277     switch(match_isinlist(fully_qualified_name,
 278           CUSS &(ob->mx_domains), 0,
 279           &domainlist_anchor, addr->domain_cache, MCL_DOMAIN, TRUE, NULL))
 280       {
 281       case DEFER:
 282       addr->message = US"lookup defer for mx_domains";
 283       return DEFER;
 284
 285       case OK:
 286       DEBUG(D_route) debug_printf("%s router rejected %s: no MX record(s)\n",
 287         rblock->name, fully_qualified_name);
 288       continue;
 289       }
 290
 291   /* Deferral returns forthwith, and anything other than failure breaks the
 292   loop. */
 293
 294   if (rc == HOST_FIND_AGAIN)
 295     {
 296     if (rblock->pass_on_timeout)
 297       {
 298       DEBUG(D_route) debug_printf("%s router timed out, and pass_on_timeout is set\n",
 299         rblock->name);
 300       return PASS;
 301       }
 302     addr->message = US"host lookup did not complete";
 303     return DEFER;
 304     }
 305
 306   if (rc != HOST_FIND_FAILED) break;
 307
 308   if (ob->fail_defer_domains)
 309     switch(match_isinlist(fully_qualified_name,
 310           CUSS &ob->fail_defer_domains, 0,
 311           &domainlist_anchor, addr->domain_cache, MCL_DOMAIN, TRUE, NULL))
 312       {
 313       case DEFER:
 314         addr->message = US"lookup defer for fail_defer_domains option";
 315         return DEFER;
 316
 317       case OK:
 318         DEBUG(D_route) debug_printf("%s router: matched fail_defer_domains\n",
 319           rblock->name);
 320         addr->message = US"missing MX, or all MXs point to missing A records,"
 321           " and defer requested";
 322         return DEFER;
 323       }
 324   /* Check to see if the failure is the result of MX records pointing to
 325   non-existent domains, and if so, set an appropriate error message; the case
 326   of an MX or SRV record pointing to "." is another special case that we can
 327   detect. Otherwise "unknown mail domain" is used, which is confusing. Also, in
 328   this case don't do the widening. We need check only the first host to see if
 329   its MX has been filled in, but there is no address, because if there were any
 330   usable addresses returned, we would not have had HOST_FIND_FAILED.
 331
 332   As a common cause of this problem is MX records with IP addresses on the
 333   RHS, give a special message in this case. */
 334
 335   if (h.mx >= 0 && h.address == NULL)
 336     {
 337     setflag(addr, af_pass_message);   /* This is not a security risk */
 338     if (h.name[0] == 0)
 339       addr->message = US"an MX or SRV record indicated no SMTP service";
 340     else
 341       {
 342       addr->basic_errno = ERRNO_UNKNOWNHOST;
 343       addr->message = US"all relevant MX records point to non-existent hosts";
 344       if (!allow_mx_to_ip && string_is_ip_address(h.name, NULL) != 0)
 345         {
 346         addr->user_message =
 347           string_sprintf("It appears that the DNS operator for %s\n"
 348             "has installed an invalid MX record with an IP address\n"
 349             "instead of a domain name on the right hand side.", addr->domain);
 350         addr->message = string_sprintf("%s or (invalidly) to IP addresses",
 351           addr->message);
 352         }
 353       }
 354     return DECLINE;
 355     }
 356
 357   /* If there's a syntax error, do not continue with any widening, and note
 358   the error. */
 359
 360   if (host_find_failed_syntax)
 361     {
 362     addr->message = string_sprintf("mail domain \"%s\" is syntactically "
 363       "invalid", h.name);
 364     return DECLINE;
 365     }
 366   }
 367
 368 /* If the original domain name has been changed as a result of the host lookup,
 369 set up a child address for rerouting and request header rewrites if so
 370 configured. Then yield REROUTED. However, if the only change is a change of
 371 case in the domain name, which some resolvers yield (others don't), just change
 372 the domain name in the original address so that the official version is used in
 373 RCPT commands. */
 374
 375 if (Ustrcmp(addr->domain, fully_qualified_name) != 0)
 376   {
 377   if (strcmpic(addr->domain, fully_qualified_name) == 0)
 378     {
 379     uschar *at = Ustrrchr(addr->address, '@');
 380     memcpy(at+1, fully_qualified_name, Ustrlen(at+1));
 381     }
 382   else
 383     {
 384     rf_change_domain(addr, fully_qualified_name, ob->rewrite_headers, addr_new);
 385     return REROUTED;
 386     }
 387   }
 388
 389 /* If the yield is HOST_FOUND_LOCAL, the remote domain name either found MX
 390 records with the lowest numbered one pointing to a host with an IP address that
 391 is set on one of the interfaces of this machine, or found A records or got
 392 addresses from gethostbyname() that contain one for this machine. This can
 393 happen quite legitimately if the original name was a shortened form of a
 394 domain, but we will have picked that up already via the name change test above.
 395
 396 Otherwise, the action to be taken can be configured by the self option, the
 397 handling of which is in a separate function, as it is also required for other
 398 routers. */
 399
 400 if (rc == HOST_FOUND_LOCAL)
 401   {
 402   rc = rf_self_action(addr, &h, rblock->self_code, rblock->self_rewrite,
 403     rblock->self, addr_new);
 404   if (rc != OK) return rc;
 405   }
 406
 407 /* Otherwise, insist on being a secondary MX if so configured */
 408
 409 else if (ob->check_secondary_mx && !testflag(addr, af_local_host_removed))
 410   {
 411   DEBUG(D_route) debug_printf("check_secondary_mx set and local host not secondary\n");
 412   return DECLINE;
 413   }
 414
 415 /* Set up the errors address, if any. */
 416
 417 rc = rf_get_errors_address(addr, rblock, verify, &addr->prop.errors_address);
 418 if (rc != OK) return rc;
 419
 420 /* Set up the additional and removeable headers for this address. */
 421
 422 rc = rf_get_munge_headers(addr, rblock, &addr->prop.extra_headers,
 423   &addr->prop.remove_headers);
 424 if (rc != OK) return rc;
 425
 426 /* Get store in which to preserve the original host item, chained on
 427 to the address. */
 428
 429 addr->host_list = store_get(sizeof(host_item));
 430 addr->host_list[0] = h;
 431
 432 /* Fill in the transport and queue the address for delivery. */
 433
 434 if (!rf_get_transport(rblock->transport_name, &(rblock->transport),
 435       addr, rblock->name, NULL))
 436   return DEFER;
 437
 438 addr->transport = rblock->transport;
 439
 440 return rf_queue_add(addr, addr_local, addr_remote, rblock, pw)?
 441   OK : DEFER;
 442 }
 443
 444 /* End of routers/dnslookup.c */
 445 /* vi: aw ai sw=2
 446 */