| 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 | */ |