1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
5 /* Copyright (c) The Exim Maintainers 2020 - 2022 */
6 /* Copyright (c) University of Cambridge 1995 - 2018 */
7 /* See the file NOTICE for conditions of use and distribution. */
8 /* SPDX-License-Identifier: GPL-2.0-or-later */
11 #include "rf_functions.h"
12 #include "dnslookup.h"
16 /* Options specific to the dnslookup router. */
17 #define LOFF(field) OPT_OFF(dnslookup_router_options_block, field)
19 optionlist dnslookup_router_options[] = {
20 { "check_secondary_mx", opt_bool, LOFF(check_secondary_mx) },
21 { "check_srv", opt_stringptr, LOFF(check_srv) },
22 { "fail_defer_domains", opt_stringptr, LOFF(fail_defer_domains) },
23 { "ipv4_only", opt_stringptr, LOFF(ipv4_only) },
24 { "ipv4_prefer", opt_stringptr, LOFF(ipv4_prefer) },
25 { "mx_domains", opt_stringptr, LOFF(mx_domains) },
26 { "mx_fail_domains", opt_stringptr, LOFF(mx_fail_domains) },
27 { "qualify_single", opt_bool, LOFF(qualify_single) },
28 { "rewrite_headers", opt_bool, LOFF(rewrite_headers) },
29 { "same_domain_copy_routing", opt_bool|opt_public, OPT_OFF(router_instance, same_domain_copy_routing) },
30 { "search_parents", opt_bool, LOFF(search_parents) },
31 { "srv_fail_domains", opt_stringptr, LOFF(srv_fail_domains) },
32 { "widen_domains", opt_stringptr, LOFF(widen_domains) }
35 /* Size of the options list. An extern variable has to be used so that its
36 address can appear in the tables drtables.c. */
38 int dnslookup_router_options_count =
39 sizeof(dnslookup_router_options)/sizeof(optionlist);
45 dnslookup_router_options_block dnslookup_router_option_defaults = {0};
46 void dnslookup_router_init(router_instance *rblock) {}
47 int dnslookup_router_entry(router_instance *rblock, address_item *addr,
48 struct passwd *pw, int verify, address_item **addr_local,
49 address_item **addr_remote, address_item **addr_new,
50 address_item **addr_succeed) {return 0;}
52 #else /*!MACRO_PREDEF*/
57 /* Default private options block for the dnslookup router. */
59 dnslookup_router_options_block dnslookup_router_option_defaults = {
60 .check_secondary_mx = FALSE,
61 .qualify_single = TRUE,
62 .search_parents = FALSE,
63 .rewrite_headers = TRUE,
64 .widen_domains = NULL,
66 .mx_fail_domains = NULL,
67 .srv_fail_domains = NULL,
69 .fail_defer_domains = NULL,
76 /*************************************************
77 * Initialization entry point *
78 *************************************************/
80 /* Called for each instance, after its options have been read, to enable
81 consistency checks to be done, or anything else that needs to be set up. */
84 dnslookup_router_init(router_instance *rblock)
87 dnslookup_router_options_block *ob =
88 (dnslookup_router_options_block *)(rblock->options_block);
95 /*************************************************
97 *************************************************/
99 /* See local README for interface details. This router returns:
102 . the domain does not exist in the DNS
103 . MX records point to non-existent hosts (including RHS = IP address)
104 . a single SRV record has a host name of "." (=> no service)
105 . syntactically invalid mail domain
106 . check_secondary_mx set, and local host not in host list
109 . lookup defer for mx_domains
110 . timeout etc on DNS lookup
111 . verifying the errors address caused a deferment or a big disaster such
112 as an expansion failure (rf_get_errors_address)
113 . expanding a headers_{add,remove} string caused a deferment or another
114 expansion error (rf_get_munge_headers)
115 . a problem in rf_get_transport: no transport when one is needed;
116 failed to expand dynamic transport; failed to find dynamic transport
117 . failure to expand or find a uid/gid (rf_get_ugid via rf_queue_add)
118 . self = "freeze", self = "defer"
121 . timeout etc on DNS lookup and pass_on_timeout set
125 . routed to local host, but name was expanded by DNS lookup, so a
126 re-routing should take place
129 In both cases the new address will have been set up as a child
135 added address to addr_local or addr_remote, as appropriate for the
136 type of transport; this includes the self="send" case.
140 dnslookup_router_entry(
141 router_instance *rblock, /* data for this instantiation */
142 address_item *addr, /* address we are working on */
143 struct passwd *pw, /* passwd entry after check_local_user */
144 int verify, /* v_none/v_recipient/v_sender/v_expn */
145 address_item **addr_local, /* add it to this if it's local */
146 address_item **addr_remote, /* add it to this if it's remote */
147 address_item **addr_new, /* put new addresses on here */
148 address_item **addr_succeed) /* put old address here on success */
153 int whichrrs = HOST_FIND_BY_MX | HOST_FIND_BY_A | HOST_FIND_BY_AAAA;
154 dnslookup_router_options_block * ob =
155 (dnslookup_router_options_block *)(rblock->options_block);
156 uschar * srv_service = NULL, * widen = NULL;
157 const uschar * pre_widen = addr->domain, * post_widen = NULL;
158 const uschar * fully_qualified_name, * listptr;
159 uschar widen_buffer[256];
162 debug_printf("%s router called for %s\n domain = %s\n",
163 rblock->name, addr->address, addr->domain);
165 /* If an SRV check is required, expand the service name */
167 GET_OPTION("check_srv");
169 if ( !(srv_service = expand_string(ob->check_srv))
170 && !f.expand_string_forcedfail)
172 addr->message = string_sprintf("%s router: failed to expand \"%s\": %s",
173 rblock->name, ob->check_srv, expand_string_message);
177 whichrrs |= HOST_FIND_BY_SRV;
179 /* Set up the first of any widening domains. The code further down copes with
180 either pre- or post-widening, but at present there is no way to turn on
181 pre-widening, as actually doing so seems like a rather bad idea, and nobody has
182 requested it. Pre-widening would cause local abbreviated names to take
183 precedence over global names. For example, if the domain is "xxx.ch" it might
184 be something in the "ch" toplevel domain, but it also might be xxx.ch.xyz.com.
185 The choice of pre- or post-widening affects which takes precedence. If ever
186 somebody comes up with some kind of requirement for pre-widening, presumably
187 with some conditions under which it is done, it can be selected here.
189 The rewrite_headers option works only when routing an address at transport
190 time, because the alterations to the headers are not persistent so must be
191 worked out immediately before they are used. Sender addresses are routed for
192 verification purposes, but never at transport time, so any header changes that
193 you might expect as a result of sender domain widening do not occur. Therefore
194 we do not perform widening when verifying sender addresses; however, widening
195 sender addresses is OK if we do not have to rewrite the headers. A corollary
196 of this is that if the current address is not the original address, then it
197 does not appear in the message header so it is also OK to widen. The
198 suppression of widening for sender addresses is silent because it is the
199 normal desirable behaviour. */
201 if ( ob->widen_domains
202 && (verify != v_sender || !ob->rewrite_headers || addr->parent))
204 listptr = ob->widen_domains;
205 /* not expanded so should never be tainted */
206 widen = string_nextinlist(&listptr, &widen_sep, widen_buffer,
207 sizeof(widen_buffer));
210 if (some condition requiring pre-widening)
212 post_widen = pre_widen;
218 /* Loop to cope with explicit widening of domains as configured. This code
219 copes with widening that may happen before or after the original name. The
220 decision as to which is taken above. */
224 int flags = whichrrs;
225 BOOL removed = FALSE;
234 h.name = string_sprintf("%s.%s", addr->domain, widen);
235 /* not expanded so should never be tainted */
236 widen = string_nextinlist(&listptr, &widen_sep, widen_buffer,
237 sizeof(widen_buffer));
238 DEBUG(D_route) debug_printf("%s router widened %s to %s\n", rblock->name,
239 addr->domain, h.name);
245 DEBUG(D_route) debug_printf("%s router trying %s after widening failed\n",
246 rblock->name, h.name);
250 /* Check if we must request only. or prefer, ipv4 */
253 && expand_check_condition(ob->ipv4_only, rblock->name, US"router"))
254 flags = flags & ~HOST_FIND_BY_AAAA | HOST_FIND_IPV4_ONLY;
255 else if (f.search_find_defer)
258 && expand_check_condition(ob->ipv4_prefer, rblock->name, US"router"))
259 flags |= HOST_FIND_IPV4_FIRST;
260 else if (f.search_find_defer)
263 /* Set up the rest of the initial host item. Others may get chained on if
264 there is more than one IP address. We set it up here instead of outside the
265 loop so as to re-initialize if a previous try succeeded but was rejected
266 because of not having an MX record. */
272 h.status = hstatus_unknown;
273 h.why = hwhy_unknown;
276 /* Unfortunately, we cannot set the mx_only option in advance, because the
277 DNS lookup may extend an unqualified name. Therefore, we must do the test
278 subsequently. We use the same logic as that for widen_domains above to avoid
279 requesting a header rewrite that cannot work. */
281 if (verify != v_sender || !ob->rewrite_headers || addr->parent)
283 if (ob->qualify_single) flags |= HOST_FIND_QUALIFY_SINGLE;
284 if (ob->search_parents) flags |= HOST_FIND_SEARCH_PARENTS;
287 rc = host_find_bydns(&h, CUS rblock->ignore_target_hosts, flags,
288 srv_service, ob->srv_fail_domains, ob->mx_fail_domains,
290 &fully_qualified_name, &removed);
292 if (removed) setflag(addr, af_local_host_removed);
294 /* If host found with only address records, test for the domain's being in
295 the mx_domains list. Note that this applies also to SRV records; the name of
296 the option is historical. */
298 if ((rc == HOST_FOUND || rc == HOST_FOUND_LOCAL) && h.mx < 0 &&
300 switch(match_isinlist(fully_qualified_name,
301 CUSS &(ob->mx_domains), 0,
302 &domainlist_anchor, addr->domain_cache, MCL_DOMAIN, TRUE, NULL))
305 addr->message = US"lookup defer for mx_domains";
309 DEBUG(D_route) debug_printf("%s router rejected %s: no MX record(s)\n",
310 rblock->name, fully_qualified_name);
314 /* Deferral returns forthwith, and anything other than failure breaks the
317 if (rc == HOST_FIND_SECURITY)
319 addr->message = US"host lookup done insecurely";
322 if (rc == HOST_FIND_AGAIN)
324 if (rblock->pass_on_timeout)
326 DEBUG(D_route) debug_printf("%s router timed out, and pass_on_timeout is set\n",
330 addr->message = US"host lookup did not complete";
334 if (rc != HOST_FIND_FAILED) break;
336 if (ob->fail_defer_domains)
337 switch(match_isinlist(fully_qualified_name,
338 CUSS &ob->fail_defer_domains, 0,
339 &domainlist_anchor, addr->domain_cache, MCL_DOMAIN, TRUE, NULL))
342 addr->message = US"lookup defer for fail_defer_domains option";
346 DEBUG(D_route) debug_printf("%s router: matched fail_defer_domains\n",
348 addr->message = US"missing MX, or all MXs point to missing A records,"
349 " and defer requested";
352 /* Check to see if the failure is the result of MX records pointing to
353 non-existent domains, and if so, set an appropriate error message; the case
354 of an MX or SRV record pointing to "." is another special case that we can
355 detect. Otherwise "unknown mail domain" is used, which is confusing. Also, in
356 this case don't do the widening. We need check only the first host to see if
357 its MX has been filled in, but there is no address, because if there were any
358 usable addresses returned, we would not have had HOST_FIND_FAILED.
360 As a common cause of this problem is MX records with IP addresses on the
361 RHS, give a special message in this case. */
363 if (h.mx >= 0 && h.address == NULL)
365 setflag(addr, af_pass_message); /* This is not a security risk */
367 addr->message = US"an MX or SRV record indicated no SMTP service";
370 addr->basic_errno = ERRNO_UNKNOWNHOST;
371 addr->message = US"all relevant MX records point to non-existent hosts";
372 if (!allow_mx_to_ip && string_is_ip_address(h.name, NULL) != 0)
375 string_sprintf("It appears that the DNS operator for %s\n"
376 "has installed an invalid MX record with an IP address\n"
377 "instead of a domain name on the right hand side.", addr->domain);
378 addr->message = string_sprintf("%s or (invalidly) to IP addresses",
385 /* If there's a syntax error, do not continue with any widening, and note
388 if (f.host_find_failed_syntax)
390 addr->message = string_sprintf("mail domain \"%s\" is syntactically "
396 /* If the original domain name has been changed as a result of the host lookup,
397 set up a child address for rerouting and request header rewrites if so
398 configured. Then yield REROUTED. However, if the only change is a change of
399 case in the domain name, which some resolvers yield (others don't), just change
400 the domain name in the original address so that the official version is used in
403 if (Ustrcmp(addr->domain, fully_qualified_name) != 0)
405 if (strcmpic(addr->domain, fully_qualified_name) == 0)
407 uschar *at = Ustrrchr(addr->address, '@');
408 memcpy(at+1, fully_qualified_name, Ustrlen(at+1));
412 rf_change_domain(addr, fully_qualified_name, ob->rewrite_headers, addr_new);
417 /* If the yield is HOST_FOUND_LOCAL, the remote domain name either found MX
418 records with the lowest numbered one pointing to a host with an IP address that
419 is set on one of the interfaces of this machine, or found A records or got
420 addresses from gethostbyname() that contain one for this machine. This can
421 happen quite legitimately if the original name was a shortened form of a
422 domain, but we will have picked that up already via the name change test above.
424 Otherwise, the action to be taken can be configured by the self option, the
425 handling of which is in a separate function, as it is also required for other
428 if (rc == HOST_FOUND_LOCAL)
430 rc = rf_self_action(addr, &h, rblock->self_code, rblock->self_rewrite,
431 rblock->self, addr_new);
432 if (rc != OK) return rc;
435 /* Otherwise, insist on being a secondary MX if so configured */
437 else if (ob->check_secondary_mx && !testflag(addr, af_local_host_removed))
439 DEBUG(D_route) debug_printf("check_secondary_mx set and local host not secondary\n");
443 /* Set up the errors address, if any. */
445 rc = rf_get_errors_address(addr, rblock, verify, &addr->prop.errors_address);
446 if (rc != OK) return rc;
448 /* Set up the additional and removable headers for this address. */
450 rc = rf_get_munge_headers(addr, rblock, &addr->prop.extra_headers,
451 &addr->prop.remove_headers);
452 if (rc != OK) return rc;
454 /* Get store in which to preserve the original host item, chained on
457 addr->host_list = store_get(sizeof(host_item), GET_UNTAINTED);
458 addr->host_list[0] = h;
460 /* Fill in the transport and queue the address for delivery. */
462 if (!rf_get_transport(rblock->transport_name, &(rblock->transport),
463 addr, rblock->name, NULL))
466 addr->transport = rblock->transport;
468 return rf_queue_add(addr, addr_local, addr_remote, rblock, pw)?
472 #endif /*!MACRO_PREDEF*/
473 /* End of routers/dnslookup.c */