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-only */
11 #include "lf_functions.h"
15 /* Ancient systems (e.g. SunOS4) don't appear to have T_TXT defined in their
22 /* Many systems do not have T_SPF. */
27 /* New TLSA record for DANE */
32 /* Table of recognized DNS record types and their integer values. */
34 static const char *type_names[] = {
54 static int type_values[] = {
57 T_ADDRESSES, /* Private type for AAAA + A */
61 T_CSA, /* Private type for "Client SMTP Authorization". */
63 T_MXH, /* Private type for "MX hostnames" */
71 T_ZNS /* Private type for "zone nameservers" */
75 /*************************************************
77 *************************************************/
79 /* See local README for interface description. */
82 dnsdb_open(const uschar * filename, uschar **errmsg)
84 return (void *)(-1); /* Any non-0 value */
89 /*************************************************
90 * Find entry point for dnsdb *
91 *************************************************/
93 /* See local README for interface description. The query in the "keystring" may
94 consist of a number of parts.
96 (a) If the first significant character is '>' then the next character is the
97 separator character that is used when multiple records are found. The default
100 (b) If the next character is ',' then the next character is the separator
101 character used for multiple items of text in "TXT" records. Alternatively,
102 if the next character is ';' then these multiple items are concatenated with
103 no separator. With neither of these options specified, only the first item
104 is output. Similarly for "SPF" records, but the default for joining multiple
105 items in one SPF record is the empty string, for direct concatenation.
107 (c) Options, all comma-terminated, in any order. Any unrecognised option
108 terminates option processing. Recognised options are:
110 - 'defer_FOO': set the defer behaviour to FOO. The possible behaviours are:
111 'strict', where any defer causes the whole lookup to defer; 'lax', where a defer
112 causes the whole lookup to defer only if none of the DNS queries succeeds; and
113 'never', where all defers are as if the lookup failed. The default is 'lax'.
115 - 'dnssec_FOO', with 'strict', 'lax' (default), and 'never'. The meanings are
116 require, try and don't-try dnssec respectively.
118 - 'retrans_VAL', set the timeout value. VAL is an Exim time specification
119 (eg "5s"). The default is set by the main configuration option 'dns_retrans'.
121 - 'retry_VAL', set the retry count on timeouts. VAL is an integer. The
122 default is set by the main configuration option "dns_retry".
124 (d) If the next sequence of characters is a sequence of letters and digits
125 followed by '=', it is interpreted as the name of the DNS record type. The
128 (e) Then there follows list of domain names. This is a generalized Exim list,
129 which may start with '<' in order to set a specific separator. The default
130 separator, as always, is colon. */
133 dnsdb_find(void * handle, const uschar * filename, const uschar * keystring,
134 int length, uschar ** result, uschar ** errmsg, uint * do_cache,
139 int defer_mode = PASS;
140 int dnssec_mode = PASS;
141 int save_retrans = dns_retrans;
142 int save_retry = dns_retry;
145 const uschar *outsep = CUS"\n";
146 const uschar *outsep2 = NULL;
147 uschar *equals, *domain, *found;
149 dns_answer * dnsa = store_get_dns_answer();
152 /* Because we're working in the search pool, we try to reclaim as much
153 store as possible later, so we preallocate the result here */
155 gstring * yield = string_get(256);
157 /* If the string starts with '>' we change the output separator.
158 If it's followed by ';' or ',' we set the TXT output separator. */
160 while (isspace(*keystring)) keystring++;
161 if (*keystring == '>')
163 outsep = keystring + 1;
165 if (*keystring == ',')
167 outsep2 = keystring + 1;
170 else if (*keystring == ';')
175 while (isspace(*keystring)) keystring++;
178 /* Check for a modifier keyword. */
182 if (strncmpic(keystring, US"defer_", 6) == 0)
185 if (strncmpic(keystring, US"strict", 6) == 0)
186 { defer_mode = DEFER; keystring += 6; }
187 else if (strncmpic(keystring, US"lax", 3) == 0)
188 { defer_mode = PASS; keystring += 3; }
189 else if (strncmpic(keystring, US"never", 5) == 0)
190 { defer_mode = OK; keystring += 5; }
193 *errmsg = US"unsupported dnsdb defer behaviour";
198 else if (strncmpic(keystring, US"dnssec_", 7) == 0)
201 if (strncmpic(keystring, US"strict", 6) == 0)
202 { dnssec_mode = DEFER; keystring += 6; }
203 else if (strncmpic(keystring, US"lax", 3) == 0)
204 { dnssec_mode = PASS; keystring += 3; }
205 else if (strncmpic(keystring, US"never", 5) == 0)
206 { dnssec_mode = OK; keystring += 5; }
209 *errmsg = US"unsupported dnsdb dnssec behaviour";
214 else if (strncmpic(keystring, US"retrans_", 8) == 0)
217 if ((timeout_sec = readconf_readtime(keystring += 8, ',', FALSE)) <= 0)
219 *errmsg = US"unsupported dnsdb timeout value";
223 dns_retrans = timeout_sec;
224 while (*keystring != ',') keystring++;
226 else if (strncmpic(keystring, US"retry_", 6) == 0)
229 if ((retries = (int)strtol(CCS keystring + 6, CSS &keystring, 0)) < 0)
231 *errmsg = US"unsupported dnsdb retry count";
240 while (isspace(*keystring)) keystring++;
241 if (*keystring++ != ',')
243 *errmsg = US"dnsdb modifier syntax error";
247 while (isspace(*keystring)) keystring++;
250 /* Figure out the "type" value if it is not T_TXT.
251 If the keystring contains an = this must be preceded by a valid type name. */
254 if ((equals = Ustrchr(keystring, '=')) != NULL)
257 uschar *tend = equals;
259 while (tend > keystring && isspace(tend[-1])) tend--;
260 len = tend - keystring;
262 for (i = 0; i < nelem(type_names); i++)
263 if (len == Ustrlen(type_names[i]) &&
264 strncmpic(keystring, US type_names[i], len) == 0)
266 type = type_values[i];
270 if (i >= nelem(type_names))
272 *errmsg = US"unsupported DNS record type";
277 keystring = equals + 1;
278 while (isspace(*keystring)) keystring++;
281 /* Initialize the resolver in case this is the first time it has been used. */
283 dns_init(FALSE, FALSE, dnssec_mode != OK);
285 /* The remainder of the string must be a list of domains. As long as the lookup
286 for at least one of them succeeds, we return success. Failure means that none
289 The original implementation did not support a list of domains. Adding the list
290 feature is compatible, except in one case: when PTR records are being looked up
291 for a single IPv6 address. Fortunately, we can hack in a compatibility feature
292 here: If the type is PTR and no list separator is specified, and the entire
293 remaining string is valid as an IP address, set an impossible separator so that
294 it is treated as one item. */
296 if (type == T_PTR && keystring[0] != '<' &&
297 string_is_ip_address(keystring, NULL) != 0)
300 /* SPF strings should be concatenated without a separator, thus make
301 it the default if not defined (see RFC 4408 section 3.1.3).
302 Multiple SPF records are forbidden (section 3.1.2) but are currently
303 not handled specially, thus they are concatenated with \n by default.
304 MX priority and value are space-separated by default.
305 SRV and TLSA record parts are space-separated by default. */
307 if (!outsep2) switch(type)
309 case T_SPF: outsep2 = US""; break;
310 case T_SRV: case T_MX: case T_TLSA: outsep2 = US" "; break;
313 /* Now scan the list and do a lookup for each item */
315 while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
317 int searchtype = type == T_CSA ? T_SRV : /* record type we want */
318 type == T_MXH ? T_MX :
319 type == T_ZNS ? T_NS : type;
321 /* If the type is PTR or CSA, we have to construct the relevant magic lookup
322 key if the original is an IP address (some experimental protocols are using
323 PTR records for different purposes where the key string is a host name, and
324 Exim's extended CSA can be keyed by domains or IP addresses). This code for
325 doing the reversal is now in a separate function. */
327 if ((type == T_PTR || type == T_CSA) &&
328 string_is_ip_address(domain, NULL) != 0)
329 domain = dns_build_reverse(domain);
333 DEBUG(D_lookup) debug_printf_indent("dnsdb key: %s\n", domain);
335 /* Do the lookup and sort out the result. There are four special types that
336 are handled specially: T_CSA, T_ZNS, T_ADDRESSES and T_MXH.
337 The first two are handled in a special lookup function so that the facility
338 could be used from other parts of the Exim code. T_ADDRESSES is handled by looping
339 over the types of A lookup. T_MXH affects only what happens later on in
340 this function, but for tidiness it is handled by the "special". If the
341 lookup fails, continue with the next domain. In the case of DEFER, adjust
342 the final "nothing found" result, but carry on to the next domain. */
346 if (type == T_ADDRESSES) /* NB cannot happen unless HAVE_IPV6 */
348 if (searchtype == T_ADDRESSES) searchtype = T_AAAA;
349 else if (searchtype == T_AAAA) searchtype = T_A;
350 rc = dns_special_lookup(dnsa, domain, searchtype, CUSS &found);
354 rc = dns_special_lookup(dnsa, domain, type, CUSS &found);
356 lookup_dnssec_authenticated = dnssec_mode==OK ? NULL
357 : dns_is_secure(dnsa) ? US"yes" : US"no";
359 if (rc == DNS_NOMATCH || rc == DNS_NODATA) continue;
360 if ( rc != DNS_SUCCEED
361 || (dnssec_mode == DEFER && !dns_is_secure(dnsa))
364 if (defer_mode == DEFER)
366 dns_retrans = save_retrans;
367 dns_retry = save_retry;
368 dns_init(FALSE, FALSE, FALSE); /* clr dnssec bit */
369 rc = DEFER; /* always defer */
372 if (defer_mode == PASS) failrc = DEFER; /* defer only if all do */
373 continue; /* treat defer as fail */
377 /* Search the returned records */
379 for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); rr;
380 rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) if (rr->type == searchtype)
382 if (*do_cache > rr->ttl)
385 if (type == T_A || type == T_AAAA || type == T_ADDRESSES)
387 for (dns_address * da = dns_address_from_rr(dnsa, rr); da; da = da->next)
389 if (yield->ptr) yield = string_catn(yield, outsep, 1);
390 yield = string_cat(yield, da->address);
395 /* Other kinds of record just have one piece of data each, but there may be
396 several of them, of course. */
398 if (yield->ptr) yield = string_catn(yield, outsep, 1);
400 if (type == T_TXT || type == T_SPF)
402 if (outsep2 == NULL) /* output only the first item of data */
403 yield = string_catn(yield, US (rr->data+1), (rr->data)[0]);
406 /* output all items */
408 while (data_offset < rr->size)
410 uschar chunk_len = (rr->data)[data_offset++];
411 if (outsep2[0] != '\0' && data_offset != 1)
412 yield = string_catn(yield, outsep2, 1);
413 yield = string_catn(yield, US ((rr->data)+data_offset), chunk_len);
414 data_offset += chunk_len;
418 else if (type == T_TLSA)
420 uint8_t usage, selector, matching_type;
421 uint16_t payload_length;
422 uschar s[MAX_TLSA_EXPANDED_SIZE];
424 uschar * p = US rr->data;
428 matching_type = *p++;
429 /* What's left after removing the first 3 bytes above */
430 payload_length = rr->size - 3;
431 sp += sprintf(CS s, "%d%c%d%c%d%c", usage, *outsep2,
432 selector, *outsep2, matching_type, *outsep2);
433 /* Now append the cert/identifier, one hex char at a time */
434 while (payload_length-- > 0 && sp-s < (MAX_TLSA_EXPANDED_SIZE - 4))
435 sp += sprintf(CS sp, "%02x", *p++);
437 yield = string_cat(yield, s);
439 else /* T_CNAME, T_CSA, T_MX, T_MXH, T_NS, T_PTR, T_SOA, T_SRV */
441 int priority, weight, port;
443 uschar * p = US rr->data;
448 /* mxh ignores the priority number and includes only the hostnames */
449 GETSHORT(priority, p);
453 GETSHORT(priority, p);
454 sprintf(CS s, "%d%c", priority, *outsep2);
455 yield = string_cat(yield, s);
459 GETSHORT(priority, p);
462 sprintf(CS s, "%d%c%d%c%d%c", priority, *outsep2,
463 weight, *outsep2, port, *outsep2);
464 yield = string_cat(yield, s);
468 /* See acl_verify_csa() for more comments about CSA. */
469 GETSHORT(priority, p);
473 if (priority != 1) continue; /* CSA version must be 1 */
475 /* If the CSA record we found is not the one we asked for, analyse
476 the subdomain assertions in the port field, else analyse the direct
477 authorization status in the weight field. */
479 if (Ustrcmp(found, domain) != 0)
481 if (port & 1) *s = 'X'; /* explicit authorization required */
482 else *s = '?'; /* no subdomain assertions here */
486 if (weight < 2) *s = 'N'; /* not authorized */
487 else if (weight == 2) *s = 'Y'; /* authorized */
488 else if (weight == 3) *s = '?'; /* unauthorizable */
489 else continue; /* invalid */
493 yield = string_catn(yield, s, 2);
500 /* GETSHORT() has advanced the pointer to the target domain. */
502 rc = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, p,
503 (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
505 /* If an overlong response was received, the data will have been
506 truncated and dn_expand may fail. */
510 log_write(0, LOG_MAIN, "host name alias list truncated: type=%s "
511 "domain=%s", dns_text_type(type), domain);
514 else yield = string_cat(yield, s);
516 if (type == T_SOA && outsep2 != NULL)
518 unsigned long serial, refresh, retry, expire, minimum;
521 yield = string_catn(yield, outsep2, 1);
523 rc = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, p,
524 (DN_EXPAND_ARG4_TYPE)s, sizeof(s));
527 log_write(0, LOG_MAIN, "responsible-mailbox truncated: type=%s "
528 "domain=%s", dns_text_type(type), domain);
531 else yield = string_cat(yield, s);
534 GETLONG(serial, p); GETLONG(refresh, p);
535 GETLONG(retry, p); GETLONG(expire, p); GETLONG(minimum, p);
536 sprintf(CS s, "%c%lu%c%lu%c%lu%c%lu%c%lu",
537 *outsep2, serial, *outsep2, refresh,
538 *outsep2, retry, *outsep2, expire, *outsep2, minimum);
539 yield = string_cat(yield, s);
542 } /* Loop for list of returned records */
544 /* Loop for set of A-lookup types */
545 } while (type == T_ADDRESSES && searchtype != T_A);
547 } /* Loop for list of domains */
549 /* Reclaim unused memory */
551 gstring_release_unused(yield);
553 /* If yield NULL we have not found anything. Otherwise, insert the terminating
554 zero and return the result. */
556 dns_retrans = save_retrans;
557 dns_retry = save_retry;
558 dns_init(FALSE, FALSE, FALSE); /* clear the dnssec bit for getaddrbyname */
560 if (!yield || !yield->ptr)
564 *result = string_from_gstring(yield);
570 store_free_dns_answer(dnsa);
576 /*************************************************
577 * Version reporting entry point *
578 *************************************************/
580 /* See local README for interface description. */
582 #include "../version.h"
585 dnsdb_version_report(gstring * g)
588 g = string_fmt_append(g, "Library version: DNSDB: Exim version %s\n", EXIM_VERSION_STR);
594 static lookup_info _lookup_info = {
595 .name = US"dnsdb", /* lookup name */
596 .type = lookup_querystyle, /* query style */
597 .open = dnsdb_open, /* open function */
598 .check = NULL, /* check function */
599 .find = dnsdb_find, /* find function */
600 .close = NULL, /* no close function */
601 .tidy = NULL, /* no tidy function */
602 .quote = NULL, /* no quoting function */
603 .version_report = dnsdb_version_report /* version reporting */
607 #define dnsdb_lookup_module_info _lookup_module_info
610 static lookup_info *_lookup_list[] = { &_lookup_info };
611 lookup_module_info dnsdb_lookup_module_info = { LOOKUP_MODULE_INFO_MAGIC, _lookup_list, 1 };
615 /* End of lookups/dnsdb.c */