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