Commit | Line | Data |
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420a0d19 CE |
1 | /************************************************* |
2 | * Exim - an Internet mail transport agent * | |
3 | *************************************************/ | |
4 | ||
2813c06e | 5 | /* Copyright (c) University of Cambridge 1995 - 2017 */ |
420a0d19 CE |
6 | /* See the file NOTICE for conditions of use and distribution. */ |
7 | ||
8 | /* Functions for interfacing with the DNS. */ | |
9 | ||
10 | #include "exim.h" | |
11 | ||
12 | ||
420a0d19 CE |
13 | |
14 | /************************************************* | |
15 | * Fake DNS resolver * | |
16 | *************************************************/ | |
17 | ||
18 | /* This function is called instead of res_search() when Exim is running in its | |
19 | test harness. It recognizes some special domain names, and uses them to force | |
20 | failure and retry responses (optionally with a delay). Otherwise, it calls an | |
21 | external utility that mocks-up a nameserver, if it can find the utility. | |
22 | If not, it passes its arguments on to res_search(). The fake nameserver may | |
23 | also return a code specifying that the name should be passed on. | |
24 | ||
25 | Background: the original test suite required a real nameserver to carry the | |
2813c06e | 26 | test zones, whereas the new test suite has the fake server for portability. This |
420a0d19 CE |
27 | code supports both. |
28 | ||
29 | Arguments: | |
30 | domain the domain name | |
31 | type the DNS record type | |
32 | answerptr where to put the answer | |
33 | size size of the answer area | |
34 | ||
35 | Returns: length of returned data, or -1 on error (h_errno set) | |
36 | */ | |
37 | ||
38 | static int | |
2813c06e | 39 | fakens_search(const uschar *domain, int type, uschar *answerptr, int size) |
420a0d19 CE |
40 | { |
41 | int len = Ustrlen(domain); | |
42 | int asize = size; /* Locally modified */ | |
420a0d19 CE |
43 | uschar name[256]; |
44 | uschar utilname[256]; | |
45 | uschar *aptr = answerptr; /* Locally modified */ | |
46 | struct stat statbuf; | |
47 | ||
48 | /* Remove terminating dot. */ | |
49 | ||
50 | if (domain[len - 1] == '.') len--; | |
51 | Ustrncpy(name, domain, len); | |
52 | name[len] = 0; | |
420a0d19 CE |
53 | |
54 | /* Look for the fakens utility, and if it exists, call it. */ | |
55 | ||
2813c06e CE |
56 | (void)string_format(utilname, sizeof(utilname), "%s/bin/fakens", |
57 | config_main_directory); | |
420a0d19 CE |
58 | |
59 | if (stat(CS utilname, &statbuf) >= 0) | |
60 | { | |
61 | pid_t pid; | |
62 | int infd, outfd, rc; | |
63 | uschar *argv[5]; | |
64 | ||
2813c06e | 65 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) using fakens\n", name, dns_text_type(type)); |
420a0d19 CE |
66 | |
67 | argv[0] = utilname; | |
2813c06e | 68 | argv[1] = config_main_directory; |
420a0d19 CE |
69 | argv[2] = name; |
70 | argv[3] = dns_text_type(type); | |
71 | argv[4] = NULL; | |
72 | ||
73 | pid = child_open(argv, NULL, 0000, &infd, &outfd, FALSE); | |
74 | if (pid < 0) | |
75 | log_write(0, LOG_MAIN|LOG_PANIC_DIE, "failed to run fakens: %s", | |
76 | strerror(errno)); | |
77 | ||
78 | len = 0; | |
79 | rc = -1; | |
80 | while (asize > 0 && (rc = read(outfd, aptr, asize)) > 0) | |
81 | { | |
82 | len += rc; | |
83 | aptr += rc; /* Don't modify the actual arguments, because they */ | |
84 | asize -= rc; /* may need to be passed on to res_search(). */ | |
85 | } | |
86 | ||
2813c06e CE |
87 | /* If we ran out of output buffer before exhausting the return, |
88 | carry on reading and counting it. */ | |
89 | ||
90 | if (asize == 0) | |
91 | while ((rc = read(outfd, name, sizeof(name))) > 0) | |
92 | len += rc; | |
93 | ||
420a0d19 CE |
94 | if (rc < 0) |
95 | log_write(0, LOG_MAIN|LOG_PANIC_DIE, "read from fakens failed: %s", | |
96 | strerror(errno)); | |
97 | ||
98 | switch(child_close(pid, 0)) | |
99 | { | |
100 | case 0: return len; | |
101 | case 1: h_errno = HOST_NOT_FOUND; return -1; | |
102 | case 2: h_errno = TRY_AGAIN; return -1; | |
103 | default: | |
104 | case 3: h_errno = NO_RECOVERY; return -1; | |
105 | case 4: h_errno = NO_DATA; return -1; | |
106 | case 5: /* Pass on to res_search() */ | |
107 | DEBUG(D_dns) debug_printf("fakens returned PASS_ON\n"); | |
108 | } | |
109 | } | |
2813c06e CE |
110 | else |
111 | { | |
112 | DEBUG(D_dns) debug_printf("fakens (%s) not found\n", utilname); | |
113 | } | |
420a0d19 CE |
114 | |
115 | /* fakens utility not found, or it returned "pass on" */ | |
116 | ||
117 | DEBUG(D_dns) debug_printf("passing %s on to res_search()\n", domain); | |
118 | ||
119 | return res_search(CS domain, C_IN, type, answerptr, size); | |
120 | } | |
121 | ||
122 | ||
123 | ||
124 | /************************************************* | |
125 | * Initialize and configure resolver * | |
126 | *************************************************/ | |
127 | ||
128 | /* Initialize the resolver and the storage for holding DNS answers if this is | |
129 | the first time we have been here, and set the resolver options. | |
130 | ||
131 | Arguments: | |
132 | qualify_single TRUE to set the RES_DEFNAMES option | |
133 | search_parents TRUE to set the RES_DNSRCH option | |
134 | use_dnssec TRUE to set the RES_USE_DNSSEC option | |
135 | ||
136 | Returns: nothing | |
137 | */ | |
138 | ||
139 | void | |
140 | dns_init(BOOL qualify_single, BOOL search_parents, BOOL use_dnssec) | |
141 | { | |
142 | res_state resp = os_get_dns_resolver_res(); | |
143 | ||
144 | if ((resp->options & RES_INIT) == 0) | |
145 | { | |
146 | DEBUG(D_resolver) resp->options |= RES_DEBUG; /* For Cygwin */ | |
147 | os_put_dns_resolver_res(resp); | |
148 | res_init(); | |
149 | DEBUG(D_resolver) resp->options |= RES_DEBUG; | |
150 | os_put_dns_resolver_res(resp); | |
151 | } | |
152 | ||
153 | resp->options &= ~(RES_DNSRCH | RES_DEFNAMES); | |
154 | resp->options |= (qualify_single? RES_DEFNAMES : 0) | | |
155 | (search_parents? RES_DNSRCH : 0); | |
156 | if (dns_retrans > 0) resp->retrans = dns_retrans; | |
157 | if (dns_retry > 0) resp->retry = dns_retry; | |
158 | ||
159 | #ifdef RES_USE_EDNS0 | |
160 | if (dns_use_edns0 >= 0) | |
161 | { | |
162 | if (dns_use_edns0) | |
163 | resp->options |= RES_USE_EDNS0; | |
164 | else | |
165 | resp->options &= ~RES_USE_EDNS0; | |
166 | DEBUG(D_resolver) | |
167 | debug_printf("Coerced resolver EDNS0 support %s.\n", | |
168 | dns_use_edns0 ? "on" : "off"); | |
169 | } | |
170 | #else | |
171 | if (dns_use_edns0 >= 0) | |
172 | DEBUG(D_resolver) | |
173 | debug_printf("Unable to %sset EDNS0 without resolver support.\n", | |
174 | dns_use_edns0 ? "" : "un"); | |
175 | #endif | |
176 | ||
177 | #ifndef DISABLE_DNSSEC | |
178 | # ifdef RES_USE_DNSSEC | |
179 | # ifndef RES_USE_EDNS0 | |
180 | # error Have RES_USE_DNSSEC but not RES_USE_EDNS0? Something hinky ... | |
181 | # endif | |
182 | if (use_dnssec) | |
183 | resp->options |= RES_USE_DNSSEC; | |
184 | if (dns_dnssec_ok >= 0) | |
185 | { | |
186 | if (dns_use_edns0 == 0 && dns_dnssec_ok != 0) | |
187 | { | |
188 | DEBUG(D_resolver) | |
189 | debug_printf("CONFLICT: dns_use_edns0 forced false, dns_dnssec_ok forced true, ignoring latter!\n"); | |
190 | } | |
191 | else | |
192 | { | |
193 | if (dns_dnssec_ok) | |
194 | resp->options |= RES_USE_DNSSEC; | |
195 | else | |
196 | resp->options &= ~RES_USE_DNSSEC; | |
197 | DEBUG(D_resolver) debug_printf("Coerced resolver DNSSEC support %s.\n", | |
198 | dns_dnssec_ok ? "on" : "off"); | |
199 | } | |
200 | } | |
201 | # else | |
202 | if (dns_dnssec_ok >= 0) | |
203 | DEBUG(D_resolver) | |
204 | debug_printf("Unable to %sset DNSSEC without resolver support.\n", | |
205 | dns_dnssec_ok ? "" : "un"); | |
206 | if (use_dnssec) | |
207 | DEBUG(D_resolver) | |
208 | debug_printf("Unable to set DNSSEC without resolver support.\n"); | |
209 | # endif | |
210 | #endif /* DISABLE_DNSSEC */ | |
211 | ||
212 | os_put_dns_resolver_res(resp); | |
213 | } | |
214 | ||
215 | ||
216 | ||
217 | /************************************************* | |
218 | * Build key name for PTR records * | |
219 | *************************************************/ | |
220 | ||
221 | /* This function inverts an IP address and adds the relevant domain, to produce | |
222 | a name that can be used to look up PTR records. | |
223 | ||
224 | Arguments: | |
225 | string the IP address as a string | |
226 | buffer a suitable buffer, long enough to hold the result | |
227 | ||
228 | Returns: nothing | |
229 | */ | |
230 | ||
231 | void | |
2813c06e | 232 | dns_build_reverse(const uschar *string, uschar *buffer) |
420a0d19 | 233 | { |
2813c06e | 234 | const uschar *p = string + Ustrlen(string); |
420a0d19 CE |
235 | uschar *pp = buffer; |
236 | ||
237 | /* Handle IPv4 address */ | |
238 | ||
239 | #if HAVE_IPV6 | |
240 | if (Ustrchr(string, ':') == NULL) | |
241 | #endif | |
242 | { | |
243 | int i; | |
244 | for (i = 0; i < 4; i++) | |
245 | { | |
2813c06e | 246 | const uschar *ppp = p; |
420a0d19 CE |
247 | while (ppp > string && ppp[-1] != '.') ppp--; |
248 | Ustrncpy(pp, ppp, p - ppp); | |
249 | pp += p - ppp; | |
250 | *pp++ = '.'; | |
251 | p = ppp - 1; | |
252 | } | |
253 | Ustrcpy(pp, "in-addr.arpa"); | |
254 | } | |
255 | ||
256 | /* Handle IPv6 address; convert to binary so as to fill out any | |
257 | abbreviation in the textual form. */ | |
258 | ||
259 | #if HAVE_IPV6 | |
260 | else | |
261 | { | |
262 | int i; | |
263 | int v6[4]; | |
264 | (void)host_aton(string, v6); | |
265 | ||
266 | /* The original specification for IPv6 reverse lookup was to invert each | |
267 | nibble, and look in the ip6.int domain. The domain was subsequently | |
268 | changed to ip6.arpa. */ | |
269 | ||
270 | for (i = 3; i >= 0; i--) | |
271 | { | |
272 | int j; | |
273 | for (j = 0; j < 32; j += 4) | |
274 | { | |
275 | sprintf(CS pp, "%x.", (v6[i] >> j) & 15); | |
276 | pp += 2; | |
277 | } | |
278 | } | |
279 | Ustrcpy(pp, "ip6.arpa."); | |
280 | ||
281 | /* Another way of doing IPv6 reverse lookups was proposed in conjunction | |
282 | with A6 records. However, it fell out of favour when they did. The | |
283 | alternative was to construct a binary key, and look in ip6.arpa. I tried | |
284 | to make this code do that, but I could not make it work on Solaris 8. The | |
285 | resolver seems to lose the initial backslash somehow. However, now that | |
286 | this style of reverse lookup has been dropped, it doesn't matter. These | |
287 | lines are left here purely for historical interest. */ | |
288 | ||
289 | /************************************************** | |
290 | Ustrcpy(pp, "\\[x"); | |
291 | pp += 3; | |
292 | ||
293 | for (i = 0; i < 4; i++) | |
294 | { | |
295 | sprintf(pp, "%08X", v6[i]); | |
296 | pp += 8; | |
297 | } | |
298 | Ustrcpy(pp, "].ip6.arpa."); | |
299 | **************************************************/ | |
300 | ||
301 | } | |
302 | #endif | |
303 | } | |
304 | ||
305 | ||
306 | ||
307 | ||
2813c06e CE |
308 | /* Increment the aptr in dnss, checking against dnsa length. |
309 | Return: TRUE for a bad result | |
310 | */ | |
311 | static BOOL | |
312 | dnss_inc_aptr(const dns_answer * dnsa, dns_scan * dnss, unsigned delta) | |
313 | { | |
314 | return (dnss->aptr += delta) >= dnsa->answer + dnsa->answerlen; | |
315 | } | |
316 | ||
420a0d19 CE |
317 | /************************************************* |
318 | * Get next DNS record from answer block * | |
319 | *************************************************/ | |
320 | ||
321 | /* Call this with reset == RESET_ANSWERS to scan the answer block, reset == | |
322 | RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to | |
323 | scan the additional records, and reset == RESET_NEXT to get the next record. | |
324 | The result is in static storage which must be copied if it is to be preserved. | |
325 | ||
326 | Arguments: | |
327 | dnsa pointer to dns answer block | |
328 | dnss pointer to dns scan block | |
2813c06e | 329 | reset option specifying what portion to scan, as described above |
420a0d19 CE |
330 | |
331 | Returns: next dns record, or NULL when no more | |
332 | */ | |
333 | ||
334 | dns_record * | |
2813c06e | 335 | dns_next_rr(const dns_answer *dnsa, dns_scan *dnss, int reset) |
420a0d19 | 336 | { |
2813c06e | 337 | const HEADER * h = (const HEADER *)dnsa->answer; |
420a0d19 CE |
338 | int namelen; |
339 | ||
2813c06e CE |
340 | char * trace = NULL; |
341 | #ifdef rr_trace | |
342 | # define TRACE DEBUG(D_dns) | |
343 | #else | |
344 | trace = trace; | |
345 | # define TRACE if (FALSE) | |
346 | #endif | |
347 | ||
420a0d19 CE |
348 | /* Reset the saved data when requested to, and skip to the first required RR */ |
349 | ||
350 | if (reset != RESET_NEXT) | |
351 | { | |
352 | dnss->rrcount = ntohs(h->qdcount); | |
2813c06e | 353 | TRACE debug_printf("%s: reset (Q rrcount %d)\n", __FUNCTION__, dnss->rrcount); |
420a0d19 CE |
354 | dnss->aptr = dnsa->answer + sizeof(HEADER); |
355 | ||
356 | /* Skip over questions; failure to expand the name just gives up */ | |
357 | ||
358 | while (dnss->rrcount-- > 0) | |
359 | { | |
2813c06e | 360 | TRACE trace = "Q-namelen"; |
420a0d19 | 361 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, |
2813c06e CE |
362 | dnss->aptr, (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME); |
363 | if (namelen < 0) goto null_return; | |
364 | /* skip name & type & class */ | |
365 | TRACE trace = "Q-skip"; | |
366 | if (dnss_inc_aptr(dnsa, dnss, namelen+4)) goto null_return; | |
420a0d19 CE |
367 | } |
368 | ||
369 | /* Get the number of answer records. */ | |
370 | ||
371 | dnss->rrcount = ntohs(h->ancount); | |
2813c06e | 372 | TRACE debug_printf("%s: reset (A rrcount %d)\n", __FUNCTION__, dnss->rrcount); |
420a0d19 CE |
373 | |
374 | /* Skip over answers if we want to look at the authority section. Also skip | |
375 | the NS records (i.e. authority section) if wanting to look at the additional | |
376 | records. */ | |
377 | ||
2813c06e CE |
378 | if (reset == RESET_ADDITIONAL) |
379 | { | |
380 | TRACE debug_printf("%s: additional\n", __FUNCTION__); | |
381 | dnss->rrcount += ntohs(h->nscount); | |
382 | TRACE debug_printf("%s: reset (NS rrcount %d)\n", __FUNCTION__, dnss->rrcount); | |
383 | } | |
420a0d19 CE |
384 | |
385 | if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL) | |
386 | { | |
2813c06e CE |
387 | TRACE if (reset == RESET_AUTHORITY) |
388 | debug_printf("%s: authority\n", __FUNCTION__); | |
420a0d19 CE |
389 | while (dnss->rrcount-- > 0) |
390 | { | |
2813c06e | 391 | TRACE trace = "A-namelen"; |
420a0d19 | 392 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, |
2813c06e CE |
393 | dnss->aptr, (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME); |
394 | if (namelen < 0) goto null_return; | |
395 | /* skip name, type, class & TTL */ | |
396 | TRACE trace = "A-hdr"; | |
397 | if (dnss_inc_aptr(dnsa, dnss, namelen+8)) goto null_return; | |
420a0d19 | 398 | GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */ |
2813c06e CE |
399 | /* skip over it */ |
400 | TRACE trace = "A-skip"; | |
401 | if (dnss_inc_aptr(dnsa, dnss, dnss->srr.size)) goto null_return; | |
420a0d19 | 402 | } |
2813c06e | 403 | dnss->rrcount = reset == RESET_AUTHORITY |
420a0d19 | 404 | ? ntohs(h->nscount) : ntohs(h->arcount); |
2813c06e CE |
405 | TRACE debug_printf("%s: reset (%s rrcount %d)\n", __FUNCTION__, |
406 | reset == RESET_AUTHORITY ? "NS" : "AR", dnss->rrcount); | |
420a0d19 | 407 | } |
2813c06e | 408 | TRACE debug_printf("%s: %d RRs to read\n", __FUNCTION__, dnss->rrcount); |
420a0d19 | 409 | } |
2813c06e CE |
410 | else |
411 | TRACE debug_printf("%s: next (%d left)\n", __FUNCTION__, dnss->rrcount); | |
420a0d19 CE |
412 | |
413 | /* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount | |
414 | contains the number of RR records left. */ | |
415 | ||
416 | if (dnss->rrcount-- <= 0) return NULL; | |
417 | ||
418 | /* If expanding the RR domain name fails, behave as if no more records | |
419 | (something safe). */ | |
420 | ||
2813c06e | 421 | TRACE trace = "R-namelen"; |
420a0d19 | 422 | namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr, |
2813c06e CE |
423 | (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME); |
424 | if (namelen < 0) goto null_return; | |
420a0d19 CE |
425 | |
426 | /* Move the pointer past the name and fill in the rest of the data structure | |
427 | from the following bytes. */ | |
428 | ||
2813c06e CE |
429 | TRACE trace = "R-name"; |
430 | if (dnss_inc_aptr(dnsa, dnss, namelen)) goto null_return; | |
431 | ||
432 | GETSHORT(dnss->srr.type, dnss->aptr); /* Record type */ | |
433 | TRACE trace = "R-class"; | |
434 | if (dnss_inc_aptr(dnsa, dnss, 2)) goto null_return; /* Don't want class */ | |
435 | GETLONG(dnss->srr.ttl, dnss->aptr); /* TTL */ | |
436 | GETSHORT(dnss->srr.size, dnss->aptr); /* Size of data portion */ | |
437 | dnss->srr.data = dnss->aptr; /* The record's data follows */ | |
438 | ||
439 | /* Unchecked increment ok here since no further access on this iteration; | |
440 | will be checked on next at "R-name". */ | |
441 | ||
442 | dnss->aptr += dnss->srr.size; /* Advance to next RR */ | |
420a0d19 CE |
443 | |
444 | /* Return a pointer to the dns_record structure within the dns_answer. This is | |
445 | for convenience so that the scans can use nice-looking for loops. */ | |
446 | ||
2813c06e CE |
447 | return &dnss->srr; |
448 | ||
449 | null_return: | |
450 | TRACE debug_printf("%s: terminate (%d RRs left). Last op: %s; errno %d %s\n", | |
451 | __FUNCTION__, dnss->rrcount, trace, errno, strerror(errno)); | |
452 | dnss->rrcount = 0; | |
453 | return NULL; | |
454 | } | |
455 | ||
456 | ||
457 | /* Extract the AUTHORITY information from the answer. If the answer isn't | |
458 | authoritative (AA not set), we do not extract anything. | |
459 | ||
460 | The AUTHORITY section contains NS records if the name in question was found, | |
461 | it contains a SOA record otherwise. (This is just from experience and some | |
462 | tests, is there some spec?) | |
463 | ||
464 | Scan the whole AUTHORITY section, since it may contain other records | |
465 | (e.g. NSEC3) too. | |
466 | ||
467 | Return: name for the authority, in an allocated string, or NULL if none found */ | |
468 | ||
469 | static const uschar * | |
470 | dns_extract_auth_name(const dns_answer * dnsa) /* FIXME: const dns_answer */ | |
471 | { | |
472 | dns_scan dnss; | |
473 | dns_record * rr; | |
474 | const HEADER * h = (const HEADER *) dnsa->answer; | |
475 | ||
476 | if (h->nscount && h->aa) | |
477 | for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY); | |
478 | rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) | |
479 | if (rr->type == (h->ancount ? T_NS : T_SOA)) | |
480 | return string_copy(rr->name); | |
481 | return NULL; | |
420a0d19 CE |
482 | } |
483 | ||
484 | ||
485 | ||
486 | ||
487 | /************************************************* | |
488 | * Return whether AD bit set in DNS result * | |
489 | *************************************************/ | |
490 | ||
491 | /* We do not perform DNSSEC work ourselves; if the administrator has installed | |
492 | a verifying resolver which sets AD as appropriate, though, we'll use that. | |
2813c06e | 493 | (AD = Authentic Data, AA = Authoritative Answer) |
420a0d19 CE |
494 | |
495 | Argument: pointer to dns answer block | |
496 | Returns: bool indicating presence of AD bit | |
497 | */ | |
498 | ||
499 | BOOL | |
2813c06e | 500 | dns_is_secure(const dns_answer * dnsa) |
420a0d19 CE |
501 | { |
502 | #ifdef DISABLE_DNSSEC | |
503 | DEBUG(D_dns) | |
504 | debug_printf("DNSSEC support disabled at build-time; dns_is_secure() false\n"); | |
505 | return FALSE; | |
506 | #else | |
2813c06e CE |
507 | const HEADER * h = (const HEADER *) dnsa->answer; |
508 | const uschar * auth_name; | |
509 | const uschar * trusted; | |
510 | ||
511 | if (h->ad) return TRUE; | |
512 | ||
513 | /* If the resolver we ask is authoritative for the domain in question, it | |
514 | * may not set the AD but the AA bit. If we explicitly trust | |
515 | * the resolver for that domain (via a domainlist in dns_trust_aa), | |
516 | * we return TRUE to indicate a secure answer. | |
517 | */ | |
518 | ||
519 | if ( !h->aa | |
520 | || !dns_trust_aa | |
521 | || !(trusted = expand_string(dns_trust_aa)) | |
522 | || !*trusted | |
523 | || !(auth_name = dns_extract_auth_name(dnsa)) | |
524 | || OK != match_isinlist(auth_name, &trusted, 0, NULL, NULL, | |
525 | MCL_DOMAIN, TRUE, NULL) | |
526 | ) | |
527 | return FALSE; | |
528 | ||
529 | DEBUG(D_dns) debug_printf("DNS faked the AD bit " | |
530 | "(got AA and matched with dns_trust_aa (%s in %s))\n", | |
531 | auth_name, dns_trust_aa); | |
532 | ||
533 | return TRUE; | |
534 | #endif | |
535 | } | |
536 | ||
537 | static void | |
538 | dns_set_insecure(dns_answer * dnsa) | |
539 | { | |
540 | #ifndef DISABLE_DNSSEC | |
541 | HEADER * h = (HEADER *)dnsa->answer; | |
542 | h->aa = h->ad = 0; | |
420a0d19 CE |
543 | #endif |
544 | } | |
545 | ||
2813c06e CE |
546 | /************************************************ |
547 | * Check whether the AA bit is set * | |
548 | * We need this to warn if we requested AD * | |
549 | * from an authoritative server * | |
550 | ************************************************/ | |
551 | ||
552 | BOOL | |
553 | dns_is_aa(const dns_answer *dnsa) | |
554 | { | |
555 | #ifdef DISABLE_DNSSEC | |
556 | return FALSE; | |
557 | #else | |
558 | return ((const HEADER*)dnsa->answer)->aa; | |
559 | #endif | |
560 | } | |
420a0d19 CE |
561 | |
562 | ||
563 | ||
564 | /************************************************* | |
565 | * Turn DNS type into text * | |
566 | *************************************************/ | |
567 | ||
568 | /* Turn the coded record type into a string for printing. All those that Exim | |
569 | uses should be included here. | |
570 | ||
571 | Argument: record type | |
572 | Returns: pointer to string | |
573 | */ | |
574 | ||
575 | uschar * | |
576 | dns_text_type(int t) | |
577 | { | |
578 | switch(t) | |
579 | { | |
580 | case T_A: return US"A"; | |
581 | case T_MX: return US"MX"; | |
582 | case T_AAAA: return US"AAAA"; | |
583 | case T_A6: return US"A6"; | |
584 | case T_TXT: return US"TXT"; | |
585 | case T_SPF: return US"SPF"; | |
586 | case T_PTR: return US"PTR"; | |
587 | case T_SOA: return US"SOA"; | |
588 | case T_SRV: return US"SRV"; | |
589 | case T_NS: return US"NS"; | |
590 | case T_CNAME: return US"CNAME"; | |
591 | case T_TLSA: return US"TLSA"; | |
592 | default: return US"?"; | |
593 | } | |
594 | } | |
595 | ||
596 | ||
597 | ||
598 | /************************************************* | |
599 | * Cache a failed DNS lookup result * | |
600 | *************************************************/ | |
601 | ||
602 | /* We cache failed lookup results so as not to experience timeouts many | |
603 | times for the same domain. We need to retain the resolver options because they | |
604 | may change. For successful lookups, we rely on resolver and/or name server | |
605 | caching. | |
606 | ||
607 | Arguments: | |
608 | name the domain name | |
609 | type the lookup type | |
610 | rc the return code | |
611 | ||
612 | Returns: the return code | |
613 | */ | |
614 | ||
615 | static int | |
2813c06e | 616 | dns_return(const uschar * name, int type, int rc) |
420a0d19 CE |
617 | { |
618 | res_state resp = os_get_dns_resolver_res(); | |
619 | tree_node *node = store_get_perm(sizeof(tree_node) + 290); | |
620 | sprintf(CS node->name, "%.255s-%s-%lx", name, dns_text_type(type), | |
2813c06e | 621 | (unsigned long) resp->options); |
420a0d19 CE |
622 | node->data.val = rc; |
623 | (void)tree_insertnode(&tree_dns_fails, node); | |
624 | return rc; | |
625 | } | |
626 | ||
420a0d19 CE |
627 | /************************************************* |
628 | * Do basic DNS lookup * | |
629 | *************************************************/ | |
630 | ||
631 | /* Call the resolver to look up the given domain name, using the given type, | |
632 | and check the result. The error code TRY_AGAIN is documented as meaning "non- | |
2813c06e | 633 | Authoritative Host not found, or SERVERFAIL". Sometimes there are badly set |
420a0d19 CE |
634 | up nameservers that produce this error continually, so there is the option of |
635 | providing a list of domains for which this is treated as a non-existent | |
636 | host. | |
637 | ||
638 | Arguments: | |
639 | dnsa pointer to dns_answer structure | |
640 | name name to look up | |
641 | type type of DNS record required (T_A, T_MX, etc) | |
642 | ||
643 | Returns: DNS_SUCCEED successful lookup | |
644 | DNS_NOMATCH name not found (NXDOMAIN) | |
645 | or name contains illegal characters (if checking) | |
646 | or name is an IP address (for IP address lookup) | |
647 | DNS_NODATA domain exists, but no data for this type (NODATA) | |
648 | DNS_AGAIN soft failure, try again later | |
649 | DNS_FAIL DNS failure | |
650 | */ | |
651 | ||
652 | int | |
2813c06e | 653 | dns_basic_lookup(dns_answer *dnsa, const uschar *name, int type) |
420a0d19 CE |
654 | { |
655 | #ifndef STAND_ALONE | |
656 | int rc = -1; | |
2813c06e | 657 | const uschar *save_domain; |
420a0d19 CE |
658 | #endif |
659 | res_state resp = os_get_dns_resolver_res(); | |
660 | ||
661 | tree_node *previous; | |
662 | uschar node_name[290]; | |
663 | ||
664 | /* DNS lookup failures of any kind are cached in a tree. This is mainly so that | |
665 | a timeout on one domain doesn't happen time and time again for messages that | |
666 | have many addresses in the same domain. We rely on the resolver and name server | |
667 | caching for successful lookups. */ | |
668 | ||
669 | sprintf(CS node_name, "%.255s-%s-%lx", name, dns_text_type(type), | |
2813c06e CE |
670 | (unsigned long) resp->options); |
671 | if ((previous = tree_search(tree_dns_fails, node_name))) | |
420a0d19 CE |
672 | { |
673 | DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: using cached value %s\n", | |
674 | name, dns_text_type(type), | |
675 | (previous->data.val == DNS_NOMATCH)? "DNS_NOMATCH" : | |
676 | (previous->data.val == DNS_NODATA)? "DNS_NODATA" : | |
677 | (previous->data.val == DNS_AGAIN)? "DNS_AGAIN" : | |
678 | (previous->data.val == DNS_FAIL)? "DNS_FAIL" : "??"); | |
679 | return previous->data.val; | |
680 | } | |
681 | ||
2813c06e CE |
682 | #ifdef SUPPORT_I18N |
683 | /* Convert all names to a-label form before doing lookup */ | |
684 | { | |
685 | uschar * alabel; | |
686 | uschar * errstr = NULL; | |
687 | DEBUG(D_dns) if (string_is_utf8(name)) | |
688 | debug_printf("convert utf8 '%s' to alabel for for lookup\n", name); | |
689 | if ((alabel = string_domain_utf8_to_alabel(name, &errstr)), errstr) | |
690 | { | |
691 | DEBUG(D_dns) | |
692 | debug_printf("DNS name '%s' utf8 conversion to alabel failed: %s\n", name, | |
693 | errstr); | |
694 | host_find_failed_syntax = TRUE; | |
695 | return DNS_NOMATCH; | |
696 | } | |
697 | name = alabel; | |
698 | } | |
699 | #endif | |
700 | ||
701 | /* If configured, check the hygiene of the name passed to lookup. Otherwise, | |
420a0d19 CE |
702 | although DNS lookups may give REFUSED at the lower level, some resolvers |
703 | turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such | |
704 | domains cannot be in the DNS. The check is now done by a regular expression; | |
705 | give it space for substring storage to save it having to get its own if the | |
706 | regex has substrings that are used - the default uses a conditional. | |
707 | ||
708 | This test is omitted for PTR records. These occur only in calls from the dnsdb | |
709 | lookup, which constructs the names itself, so they should be OK. Besides, | |
710 | bitstring labels don't conform to normal name syntax. (But the aren't used any | |
711 | more.) | |
712 | ||
713 | For SRV records, we omit the initial _smtp._tcp. components at the start. */ | |
714 | ||
715 | #ifndef STAND_ALONE /* Omit this for stand-alone tests */ | |
716 | ||
717 | if (check_dns_names_pattern[0] != 0 && type != T_PTR && type != T_TXT) | |
718 | { | |
2813c06e | 719 | const uschar *checkname = name; |
420a0d19 CE |
720 | int ovector[3*(EXPAND_MAXN+1)]; |
721 | ||
2813c06e | 722 | dns_pattern_init(); |
420a0d19 CE |
723 | |
724 | /* For an SRV lookup, skip over the first two components (the service and | |
725 | protocol names, which both start with an underscore). */ | |
726 | ||
2813c06e | 727 | if (type == T_SRV || type == T_TLSA) |
420a0d19 CE |
728 | { |
729 | while (*checkname++ != '.'); | |
730 | while (*checkname++ != '.'); | |
731 | } | |
732 | ||
2813c06e CE |
733 | if (pcre_exec(regex_check_dns_names, NULL, CCS checkname, Ustrlen(checkname), |
734 | 0, PCRE_EOPT, ovector, nelem(ovector)) < 0) | |
420a0d19 CE |
735 | { |
736 | DEBUG(D_dns) | |
737 | debug_printf("DNS name syntax check failed: %s (%s)\n", name, | |
738 | dns_text_type(type)); | |
739 | host_find_failed_syntax = TRUE; | |
740 | return DNS_NOMATCH; | |
741 | } | |
742 | } | |
743 | ||
744 | #endif /* STAND_ALONE */ | |
745 | ||
746 | /* Call the resolver; for an overlong response, res_search() will return the | |
747 | number of bytes the message would need, so we need to check for this case. The | |
748 | effect is to truncate overlong data. | |
749 | ||
750 | On some systems, res_search() will recognize "A-for-A" queries and return | |
751 | the IP address instead of returning -1 with h_error=HOST_NOT_FOUND. Some | |
752 | nameservers are also believed to do this. It is, of course, contrary to the | |
753 | specification of the DNS, so we lock it out. */ | |
754 | ||
2813c06e | 755 | if ((type == T_A || type == T_AAAA) && string_is_ip_address(name, NULL) != 0) |
420a0d19 CE |
756 | return DNS_NOMATCH; |
757 | ||
758 | /* If we are running in the test harness, instead of calling the normal resolver | |
759 | (res_search), we call fakens_search(), which recognizes certain special | |
760 | domains, and interfaces to a fake nameserver for certain special zones. */ | |
761 | ||
2813c06e CE |
762 | dnsa->answerlen = running_in_test_harness |
763 | ? fakens_search(name, type, dnsa->answer, sizeof(dnsa->answer)) | |
764 | : res_search(CCS name, C_IN, type, dnsa->answer, sizeof(dnsa->answer)); | |
420a0d19 | 765 | |
2813c06e | 766 | if (dnsa->answerlen > (int) sizeof(dnsa->answer)) |
420a0d19 | 767 | { |
2813c06e CE |
768 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) resulted in overlong packet" |
769 | " (size %d), truncating to %u.\n", | |
770 | name, dns_text_type(type), dnsa->answerlen, (unsigned int) sizeof(dnsa->answer)); | |
771 | dnsa->answerlen = sizeof(dnsa->answer); | |
420a0d19 CE |
772 | } |
773 | ||
774 | if (dnsa->answerlen < 0) switch (h_errno) | |
775 | { | |
776 | case HOST_NOT_FOUND: | |
2813c06e CE |
777 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n" |
778 | "returning DNS_NOMATCH\n", name, dns_text_type(type)); | |
779 | return dns_return(name, type, DNS_NOMATCH); | |
420a0d19 CE |
780 | |
781 | case TRY_AGAIN: | |
2813c06e CE |
782 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n", |
783 | name, dns_text_type(type)); | |
420a0d19 | 784 | |
2813c06e CE |
785 | /* Cut this out for various test programs */ |
786 | #ifndef STAND_ALONE | |
787 | save_domain = deliver_domain; | |
788 | deliver_domain = string_copy(name); /* set $domain */ | |
789 | rc = match_isinlist(name, (const uschar **)&dns_again_means_nonexist, 0, NULL, NULL, | |
790 | MCL_DOMAIN, TRUE, NULL); | |
791 | deliver_domain = save_domain; | |
792 | if (rc != OK) | |
793 | { | |
794 | DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n"); | |
795 | return dns_return(name, type, DNS_AGAIN); | |
796 | } | |
797 | DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning " | |
798 | "DNS_NOMATCH\n", name); | |
799 | return dns_return(name, type, DNS_NOMATCH); | |
800 | ||
801 | #else /* For stand-alone tests */ | |
802 | return dns_return(name, type, DNS_AGAIN); | |
803 | #endif | |
420a0d19 CE |
804 | |
805 | case NO_RECOVERY: | |
2813c06e CE |
806 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n" |
807 | "returning DNS_FAIL\n", name, dns_text_type(type)); | |
808 | return dns_return(name, type, DNS_FAIL); | |
420a0d19 CE |
809 | |
810 | case NO_DATA: | |
2813c06e CE |
811 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n" |
812 | "returning DNS_NODATA\n", name, dns_text_type(type)); | |
813 | return dns_return(name, type, DNS_NODATA); | |
420a0d19 CE |
814 | |
815 | default: | |
2813c06e CE |
816 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n" |
817 | "returning DNS_FAIL\n", name, dns_text_type(type), h_errno); | |
818 | return dns_return(name, type, DNS_FAIL); | |
420a0d19 CE |
819 | } |
820 | ||
821 | DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n", | |
822 | name, dns_text_type(type)); | |
823 | ||
824 | return DNS_SUCCEED; | |
825 | } | |
826 | ||
827 | ||
828 | ||
829 | ||
830 | /************************************************ | |
831 | * Do a DNS lookup and handle CNAMES * | |
832 | ************************************************/ | |
833 | ||
834 | /* Look up the given domain name, using the given type. Follow CNAMEs if | |
835 | necessary, but only so many times. There aren't supposed to be CNAME chains in | |
836 | the DNS, but you are supposed to cope with them if you find them. | |
837 | ||
838 | The assumption is made that if the resolver gives back records of the | |
839 | requested type *and* a CNAME, we don't need to make another call to look up | |
840 | the CNAME. I can't see how it could return only some of the right records. If | |
841 | it's done a CNAME lookup in the past, it will have all of them; if not, it | |
842 | won't return any. | |
843 | ||
844 | If fully_qualified_name is not NULL, set it to point to the full name | |
845 | returned by the resolver, if this is different to what it is given, unless | |
846 | the returned name starts with "*" as some nameservers seem to be returning | |
2813c06e CE |
847 | wildcards in this form. In international mode "different" means "alabel |
848 | forms are different". | |
420a0d19 CE |
849 | |
850 | Arguments: | |
851 | dnsa pointer to dns_answer structure | |
852 | name domain name to look up | |
853 | type DNS record type (T_A, T_MX, etc) | |
854 | fully_qualified_name if not NULL, return the returned name here if its | |
855 | contents are different (i.e. it must be preset) | |
856 | ||
857 | Returns: DNS_SUCCEED successful lookup | |
858 | DNS_NOMATCH name not found | |
859 | DNS_NODATA no data found | |
860 | DNS_AGAIN soft failure, try again later | |
861 | DNS_FAIL DNS failure | |
862 | */ | |
863 | ||
864 | int | |
2813c06e CE |
865 | dns_lookup(dns_answer *dnsa, const uschar *name, int type, |
866 | const uschar **fully_qualified_name) | |
420a0d19 CE |
867 | { |
868 | int i; | |
2813c06e CE |
869 | const uschar *orig_name = name; |
870 | BOOL secure_so_far = TRUE; | |
420a0d19 CE |
871 | |
872 | /* Loop to follow CNAME chains so far, but no further... */ | |
873 | ||
874 | for (i = 0; i < 10; i++) | |
875 | { | |
2813c06e | 876 | uschar * data; |
420a0d19 CE |
877 | dns_record *rr, cname_rr, type_rr; |
878 | dns_scan dnss; | |
879 | int datalen, rc; | |
880 | ||
881 | /* DNS lookup failures get passed straight back. */ | |
882 | ||
2813c06e CE |
883 | if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED) |
884 | return rc; | |
420a0d19 CE |
885 | |
886 | /* We should have either records of the required type, or a CNAME record, | |
887 | or both. We need to know whether both exist for getting the fully qualified | |
888 | name, but avoid scanning more than necessary. Note that we must copy the | |
889 | contents of any rr blocks returned by dns_next_rr() as they use the same | |
890 | area in the dnsa block. */ | |
891 | ||
892 | cname_rr.data = type_rr.data = NULL; | |
893 | for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); | |
2813c06e | 894 | rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) |
420a0d19 CE |
895 | if (rr->type == type) |
896 | { | |
897 | if (type_rr.data == NULL) type_rr = *rr; | |
898 | if (cname_rr.data != NULL) break; | |
899 | } | |
2813c06e CE |
900 | else if (rr->type == T_CNAME) |
901 | cname_rr = *rr; | |
420a0d19 CE |
902 | |
903 | /* For the first time round this loop, if a CNAME was found, take the fully | |
904 | qualified name from it; otherwise from the first data record, if present. */ | |
905 | ||
2813c06e | 906 | if (i == 0 && fully_qualified_name) |
420a0d19 | 907 | { |
2813c06e CE |
908 | uschar * rr_name = cname_rr.data |
909 | ? cname_rr.name : type_rr.data ? type_rr.name : NULL; | |
910 | if ( rr_name | |
911 | && Ustrcmp(rr_name, *fully_qualified_name) != 0 | |
912 | && rr_name[0] != '*' | |
913 | #ifdef SUPPORT_I18N | |
914 | && ( !string_is_utf8(*fully_qualified_name) | |
915 | || Ustrcmp(rr_name, | |
916 | string_domain_utf8_to_alabel(*fully_qualified_name, NULL)) != 0 | |
917 | ) | |
918 | #endif | |
919 | ) | |
920 | *fully_qualified_name = string_copy_dnsdomain(rr_name); | |
420a0d19 CE |
921 | } |
922 | ||
923 | /* If any data records of the correct type were found, we are done. */ | |
924 | ||
2813c06e CE |
925 | if (type_rr.data) |
926 | { | |
927 | if (!secure_so_far) /* mark insecure if any element of CNAME chain was */ | |
928 | dns_set_insecure(dnsa); | |
929 | return DNS_SUCCEED; | |
930 | } | |
420a0d19 CE |
931 | |
932 | /* If there are no data records, we need to re-scan the DNS using the | |
933 | domain given in the CNAME record, which should exist (otherwise we should | |
934 | have had a failure from dns_lookup). However code against the possibility of | |
935 | its not existing. */ | |
936 | ||
2813c06e CE |
937 | if (!cname_rr.data) |
938 | return DNS_FAIL; | |
939 | ||
940 | data = store_get(256); | |
941 | if ((datalen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, | |
942 | cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, 256)) < 0) | |
943 | return DNS_FAIL; | |
420a0d19 CE |
944 | name = data; |
945 | ||
2813c06e CE |
946 | if (!dns_is_secure(dnsa)) |
947 | secure_so_far = FALSE; | |
948 | ||
420a0d19 CE |
949 | DEBUG(D_dns) debug_printf("CNAME found: change to %s\n", name); |
950 | } /* Loop back to do another lookup */ | |
951 | ||
952 | /*Control reaches here after 10 times round the CNAME loop. Something isn't | |
953 | right... */ | |
954 | ||
955 | log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name); | |
956 | return DNS_FAIL; | |
957 | } | |
958 | ||
959 | ||
960 | ||
961 | ||
962 | ||
963 | ||
964 | /************************************************ | |
965 | * Do a DNS lookup and handle virtual types * | |
966 | ************************************************/ | |
967 | ||
2813c06e | 968 | /* This function handles some invented "lookup types" that synthesize features |
420a0d19 CE |
969 | not available in the basic types. The special types all have negative values. |
970 | Positive type values are passed straight on to dns_lookup(). | |
971 | ||
972 | Arguments: | |
973 | dnsa pointer to dns_answer structure | |
974 | name domain name to look up | |
975 | type DNS record type (T_A, T_MX, etc or a "special") | |
976 | fully_qualified_name if not NULL, return the returned name here if its | |
977 | contents are different (i.e. it must be preset) | |
978 | ||
979 | Returns: DNS_SUCCEED successful lookup | |
980 | DNS_NOMATCH name not found | |
981 | DNS_NODATA no data found | |
982 | DNS_AGAIN soft failure, try again later | |
983 | DNS_FAIL DNS failure | |
984 | */ | |
985 | ||
986 | int | |
2813c06e CE |
987 | dns_special_lookup(dns_answer *dnsa, const uschar *name, int type, |
988 | const uschar **fully_qualified_name) | |
420a0d19 | 989 | { |
2813c06e | 990 | switch (type) |
420a0d19 | 991 | { |
2813c06e CE |
992 | /* The "mx hosts only" type doesn't require any special action here */ |
993 | case T_MXH: | |
994 | return dns_lookup(dnsa, name, T_MX, fully_qualified_name); | |
995 | ||
996 | /* Find nameservers for the domain or the nearest enclosing zone, excluding | |
997 | the root servers. */ | |
998 | case T_ZNS: | |
999 | type = T_NS; | |
1000 | /* FALLTHROUGH */ | |
1001 | case T_SOA: | |
420a0d19 | 1002 | { |
2813c06e CE |
1003 | const uschar *d = name; |
1004 | while (d != 0) | |
1005 | { | |
1006 | int rc = dns_lookup(dnsa, d, type, fully_qualified_name); | |
1007 | if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc; | |
1008 | while (*d != 0 && *d != '.') d++; | |
1009 | if (*d++ == 0) break; | |
1010 | } | |
1011 | return DNS_NOMATCH; | |
420a0d19 | 1012 | } |
420a0d19 | 1013 | |
2813c06e CE |
1014 | /* Try to look up the Client SMTP Authorization SRV record for the name. If |
1015 | there isn't one, search from the top downwards for a CSA record in a parent | |
1016 | domain, which might be making assertions about subdomains. If we find a record | |
1017 | we set fully_qualified_name to whichever lookup succeeded, so that the caller | |
1018 | can tell whether to look at the explicit authorization field or the subdomain | |
1019 | assertion field. */ | |
1020 | case T_CSA: | |
420a0d19 | 1021 | { |
2813c06e CE |
1022 | uschar *srvname, *namesuff, *tld, *p; |
1023 | int priority, weight, port; | |
1024 | int limit, rc, i; | |
1025 | BOOL ipv6; | |
1026 | dns_record *rr; | |
1027 | dns_scan dnss; | |
420a0d19 | 1028 | |
2813c06e | 1029 | DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name); |
420a0d19 | 1030 | |
2813c06e CE |
1031 | srvname = string_sprintf("_client._smtp.%s", name); |
1032 | rc = dns_lookup(dnsa, srvname, T_SRV, NULL); | |
1033 | if (rc == DNS_SUCCEED || rc == DNS_AGAIN) | |
420a0d19 | 1034 | { |
2813c06e CE |
1035 | if (rc == DNS_SUCCEED) *fully_qualified_name = string_copy(name); |
1036 | return rc; | |
420a0d19 | 1037 | } |
420a0d19 | 1038 | |
2813c06e CE |
1039 | /* Search for CSA subdomain assertion SRV records from the top downwards, |
1040 | starting with the 2nd level domain. This order maximizes cache-friendliness. | |
1041 | We skip the top level domains to avoid loading their nameservers and because | |
1042 | we know they'll never have CSA SRV records. */ | |
1043 | ||
1044 | namesuff = Ustrrchr(name, '.'); | |
1045 | if (namesuff == NULL) return DNS_NOMATCH; | |
1046 | tld = namesuff + 1; | |
1047 | ipv6 = FALSE; | |
1048 | limit = dns_csa_search_limit; | |
1049 | ||
1050 | /* Use more appropriate search parameters if we are in the reverse DNS. */ | |
1051 | ||
1052 | if (strcmpic(namesuff, US".arpa") == 0) | |
1053 | if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0) | |
1054 | { | |
1055 | namesuff -= 8; | |
1056 | tld = namesuff + 1; | |
1057 | limit = 3; | |
1058 | } | |
1059 | else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0) | |
1060 | { | |
1061 | namesuff -= 4; | |
1062 | tld = namesuff + 1; | |
1063 | ipv6 = TRUE; | |
1064 | limit = 3; | |
1065 | } | |
1066 | ||
1067 | DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld); | |
1068 | ||
1069 | /* Do not perform the search if the top level or 2nd level domains do not | |
1070 | exist. This is quite common, and when it occurs all the search queries would | |
1071 | go to the root or TLD name servers, which is not friendly. So we check the | |
1072 | AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then | |
1073 | the TLD or the 2LD (respectively) doesn't exist and we can skip the search. | |
1074 | If the TLD and the 2LD exist but the explicit CSA record lookup failed, then | |
1075 | the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */ | |
1076 | ||
1077 | if (rc == DNS_NOMATCH) | |
420a0d19 | 1078 | { |
2813c06e CE |
1079 | /* This is really gross. The successful return value from res_search() is |
1080 | the packet length, which is stored in dnsa->answerlen. If we get a | |
1081 | negative DNS reply then res_search() returns -1, which causes the bounds | |
1082 | checks for name decompression to fail when it is treated as a packet | |
1083 | length, which in turn causes the authority search to fail. The correct | |
1084 | packet length has been lost inside libresolv, so we have to guess a | |
1085 | replacement value. (The only way to fix this properly would be to | |
1086 | re-implement res_search() and res_query() so that they don't muddle their | |
1087 | success and packet length return values.) For added safety we only reset | |
1088 | the packet length if the packet header looks plausible. */ | |
1089 | ||
1090 | const HEADER * h = (const HEADER *)dnsa->answer; | |
1091 | if (h->qr == 1 && h->opcode == QUERY && h->tc == 0 | |
1092 | && (h->rcode == NOERROR || h->rcode == NXDOMAIN) | |
1093 | && ntohs(h->qdcount) == 1 && ntohs(h->ancount) == 0 | |
1094 | && ntohs(h->nscount) >= 1) | |
1095 | dnsa->answerlen = MAXPACKET; | |
1096 | ||
1097 | for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY); | |
1098 | rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT) | |
1099 | ) | |
1100 | if (rr->type != T_SOA) continue; | |
1101 | else if (strcmpic(rr->name, US"") == 0 || | |
1102 | strcmpic(rr->name, tld) == 0) return DNS_NOMATCH; | |
1103 | else break; | |
420a0d19 | 1104 | } |
420a0d19 | 1105 | |
2813c06e | 1106 | for (i = 0; i < limit; i++) |
420a0d19 | 1107 | { |
2813c06e CE |
1108 | if (ipv6) |
1109 | { | |
1110 | /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP | |
1111 | address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */ | |
1112 | namesuff -= 8; | |
1113 | if (namesuff <= name) return DNS_NOMATCH; | |
1114 | } | |
1115 | else | |
1116 | /* Find the start of the preceding domain name label. */ | |
1117 | do | |
1118 | if (--namesuff <= name) return DNS_NOMATCH; | |
1119 | while (*namesuff != '.'); | |
1120 | ||
1121 | DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1); | |
1122 | ||
1123 | srvname = string_sprintf("_client._smtp.%s", namesuff + 1); | |
1124 | rc = dns_lookup(dnsa, srvname, T_SRV, NULL); | |
1125 | if (rc == DNS_AGAIN) return rc; | |
1126 | if (rc != DNS_SUCCEED) continue; | |
1127 | ||
1128 | /* Check that the SRV record we have found is worth returning. We don't | |
1129 | just return the first one we find, because some lower level SRV record | |
1130 | might make stricter assertions than its parent domain. */ | |
1131 | ||
1132 | for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); | |
1133 | rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) if (rr->type == T_SRV) | |
1134 | { | |
1135 | const uschar * p = rr->data; | |
1136 | ||
1137 | /* Extract the numerical SRV fields (p is incremented) */ | |
1138 | GETSHORT(priority, p); | |
1139 | GETSHORT(weight, p); weight = weight; /* compiler quietening */ | |
1140 | GETSHORT(port, p); | |
1141 | ||
1142 | /* Check the CSA version number */ | |
1143 | if (priority != 1) continue; | |
1144 | ||
1145 | /* If it's making an interesting assertion, return this response. */ | |
1146 | if (port & 1) | |
1147 | { | |
1148 | *fully_qualified_name = namesuff + 1; | |
1149 | return DNS_SUCCEED; | |
1150 | } | |
1151 | } | |
420a0d19 | 1152 | } |
2813c06e | 1153 | return DNS_NOMATCH; |
420a0d19 | 1154 | } |
2813c06e CE |
1155 | |
1156 | default: | |
1157 | if (type >= 0) | |
1158 | return dns_lookup(dnsa, name, type, fully_qualified_name); | |
420a0d19 CE |
1159 | } |
1160 | ||
1161 | /* Control should never reach here */ | |
1162 | ||
1163 | return DNS_FAIL; | |
1164 | } | |
1165 | ||
1166 | ||
1167 | ||
420a0d19 CE |
1168 | |
1169 | ||
1170 | /************************************************* | |
1171 | * Get address(es) from DNS record * | |
1172 | *************************************************/ | |
1173 | ||
2813c06e | 1174 | /* The record type is either T_A for an IPv4 address or T_AAAA for an IPv6 address. |
420a0d19 CE |
1175 | |
1176 | Argument: | |
1177 | dnsa the DNS answer block | |
1178 | rr the RR | |
1179 | ||
2813c06e | 1180 | Returns: pointer to a chain of dns_address items; NULL when the dnsa was overrun |
420a0d19 CE |
1181 | */ |
1182 | ||
1183 | dns_address * | |
1184 | dns_address_from_rr(dns_answer *dnsa, dns_record *rr) | |
1185 | { | |
2813c06e CE |
1186 | dns_address * yield = NULL; |
1187 | uschar * dnsa_lim = dnsa->answer + dnsa->answerlen; | |
420a0d19 CE |
1188 | |
1189 | if (rr->type == T_A) | |
1190 | { | |
2813c06e CE |
1191 | uschar *p = US rr->data; |
1192 | if (p + 4 <= dnsa_lim) | |
1193 | { | |
1194 | yield = store_get(sizeof(dns_address) + 20); | |
1195 | (void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]); | |
1196 | yield->next = NULL; | |
1197 | } | |
420a0d19 CE |
1198 | } |
1199 | ||
1200 | #if HAVE_IPV6 | |
1201 | ||
420a0d19 CE |
1202 | else |
1203 | { | |
2813c06e CE |
1204 | if (rr->data + 16 <= dnsa_lim) |
1205 | { | |
1206 | struct in6_addr in6; | |
1207 | int i; | |
1208 | for (i = 0; i < 16; i++) in6.s6_addr[i] = rr->data[i]; | |
1209 | yield = store_get(sizeof(dns_address) + 50); | |
1210 | inet_ntop(AF_INET6, &in6, CS yield->address, 50); | |
1211 | yield->next = NULL; | |
1212 | } | |
420a0d19 CE |
1213 | } |
1214 | #endif /* HAVE_IPV6 */ | |
1215 | ||
1216 | return yield; | |
1217 | } | |
1218 | ||
2813c06e CE |
1219 | |
1220 | ||
1221 | void | |
1222 | dns_pattern_init(void) | |
1223 | { | |
1224 | if (check_dns_names_pattern[0] != 0 && !regex_check_dns_names) | |
1225 | regex_check_dns_names = | |
1226 | regex_must_compile(check_dns_names_pattern, FALSE, TRUE); | |
1227 | } | |
1228 | ||
420a0d19 CE |
1229 | /* vi: aw ai sw=2 |
1230 | */ | |
1231 | /* End of dns.c */ |