DNS: do not skip initial two components of SRV & TLSA lookups before checking name...
[exim.git] / src / src / dns.c
CommitLineData
059ec3d9
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1/*************************************************
2* Exim - an Internet mail transport agent *
3*************************************************/
4
f9ba5e22 5/* Copyright (c) University of Cambridge 1995 - 2018 */
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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
bef5a11f
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13/*************************************************
14* Fake DNS resolver *
15*************************************************/
16
17/* This function is called instead of res_search() when Exim is running in its
18test harness. It recognizes some special domain names, and uses them to force
433a2980
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19failure and retry responses (optionally with a delay). Otherwise, it calls an
20external utility that mocks-up a nameserver, if it can find the utility.
21If not, it passes its arguments on to res_search(). The fake nameserver may
22also return a code specifying that the name should be passed on.
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23
24Background: the original test suite required a real nameserver to carry the
8e013028 25test zones, whereas the new test suite has the fake server for portability. This
e7726cbf 26code supports both.
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27
28Arguments:
e7726cbf 29 domain the domain name
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30 type the DNS record type
31 answerptr where to put the answer
32 size size of the answer area
33
34Returns: length of returned data, or -1 on error (h_errno set)
35*/
36
37static int
1dc92d5a 38fakens_search(const uschar *domain, int type, uschar *answerptr, int size)
bef5a11f 39{
e7726cbf 40int len = Ustrlen(domain);
433a2980 41int asize = size; /* Locally modified */
f3ebb786 42uschar * name;
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43uschar utilname[256];
44uschar *aptr = answerptr; /* Locally modified */
45struct stat statbuf;
46
47/* Remove terminating dot. */
e7726cbf
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48
49if (domain[len - 1] == '.') len--;
f3ebb786 50name = string_copyn(domain, len);
bef5a11f 51
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52/* Look for the fakens utility, and if it exists, call it. */
53
5f3d0983
HSHR
54(void)string_format(utilname, sizeof(utilname), "%s/bin/fakens",
55 config_main_directory);
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56
57if (stat(CS utilname, &statbuf) >= 0)
bef5a11f 58 {
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59 pid_t pid;
60 int infd, outfd, rc;
61 uschar *argv[5];
62
3735e326 63 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) using fakens\n", name, dns_text_type(type));
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64
65 argv[0] = utilname;
5f3d0983 66 argv[1] = config_main_directory;
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67 argv[2] = name;
68 argv[3] = dns_text_type(type);
69 argv[4] = NULL;
70
71 pid = child_open(argv, NULL, 0000, &infd, &outfd, FALSE);
72 if (pid < 0)
73 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "failed to run fakens: %s",
74 strerror(errno));
75
76 len = 0;
77 rc = -1;
78 while (asize > 0 && (rc = read(outfd, aptr, asize)) > 0)
79 {
80 len += rc;
81 aptr += rc; /* Don't modify the actual arguments, because they */
82 asize -= rc; /* may need to be passed on to res_search(). */
83 }
bef5a11f 84
aa7751be 85 /* If we ran out of output buffer before exhausting the return,
1fb7660f
JH
86 carry on reading and counting it. */
87
88 if (asize == 0)
89 while ((rc = read(outfd, name, sizeof(name))) > 0)
90 len += rc;
91
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92 if (rc < 0)
93 log_write(0, LOG_MAIN|LOG_PANIC_DIE, "read from fakens failed: %s",
94 strerror(errno));
bef5a11f 95
433a2980 96 switch(child_close(pid, 0))
bef5a11f 97 {
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98 case 0: return len;
99 case 1: h_errno = HOST_NOT_FOUND; return -1;
100 case 2: h_errno = TRY_AGAIN; return -1;
101 default:
102 case 3: h_errno = NO_RECOVERY; return -1;
103 case 4: h_errno = NO_DATA; return -1;
104 case 5: /* Pass on to res_search() */
105 DEBUG(D_dns) debug_printf("fakens returned PASS_ON\n");
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106 }
107 }
8e013028
HSHR
108else
109 {
4cea764f 110 DEBUG(D_dns) debug_printf("fakens (%s) not found\n", utilname);
8e013028 111 }
bef5a11f 112
433a2980 113/* fakens utility not found, or it returned "pass on" */
bef5a11f 114
433a2980 115DEBUG(D_dns) debug_printf("passing %s on to res_search()\n", domain);
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116
117return res_search(CS domain, C_IN, type, answerptr, size);
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118}
119
120
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121
122/*************************************************
123* Initialize and configure resolver *
124*************************************************/
125
126/* Initialize the resolver and the storage for holding DNS answers if this is
127the first time we have been here, and set the resolver options.
128
129Arguments:
130 qualify_single TRUE to set the RES_DEFNAMES option
131 search_parents TRUE to set the RES_DNSRCH option
8c51eead 132 use_dnssec TRUE to set the RES_USE_DNSSEC option
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133
134Returns: nothing
135*/
136
137void
8c51eead 138dns_init(BOOL qualify_single, BOOL search_parents, BOOL use_dnssec)
059ec3d9 139{
5bfb4cdf
PP
140res_state resp = os_get_dns_resolver_res();
141
142if ((resp->options & RES_INIT) == 0)
059ec3d9 143 {
5bfb4cdf
PP
144 DEBUG(D_resolver) resp->options |= RES_DEBUG; /* For Cygwin */
145 os_put_dns_resolver_res(resp);
059ec3d9 146 res_init();
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PP
147 DEBUG(D_resolver) resp->options |= RES_DEBUG;
148 os_put_dns_resolver_res(resp);
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149 }
150
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PP
151resp->options &= ~(RES_DNSRCH | RES_DEFNAMES);
152resp->options |= (qualify_single? RES_DEFNAMES : 0) |
059ec3d9 153 (search_parents? RES_DNSRCH : 0);
5bfb4cdf
PP
154if (dns_retrans > 0) resp->retrans = dns_retrans;
155if (dns_retry > 0) resp->retry = dns_retry;
e97d1f08
PP
156
157#ifdef RES_USE_EDNS0
158if (dns_use_edns0 >= 0)
159 {
160 if (dns_use_edns0)
5bfb4cdf 161 resp->options |= RES_USE_EDNS0;
e97d1f08 162 else
5bfb4cdf 163 resp->options &= ~RES_USE_EDNS0;
e97d1f08
PP
164 DEBUG(D_resolver)
165 debug_printf("Coerced resolver EDNS0 support %s.\n",
166 dns_use_edns0 ? "on" : "off");
167 }
168#else
169if (dns_use_edns0 >= 0)
170 DEBUG(D_resolver)
171 debug_printf("Unable to %sset EDNS0 without resolver support.\n",
172 dns_use_edns0 ? "" : "un");
173#endif
5bfb4cdf 174
1f4a55da
PP
175#ifndef DISABLE_DNSSEC
176# ifdef RES_USE_DNSSEC
177# ifndef RES_USE_EDNS0
178# error Have RES_USE_DNSSEC but not RES_USE_EDNS0? Something hinky ...
179# endif
8c51eead
JH
180if (use_dnssec)
181 resp->options |= RES_USE_DNSSEC;
0fbd9bff 182if (dns_dnssec_ok >= 0)
1f4a55da 183 {
0fbd9bff 184 if (dns_use_edns0 == 0 && dns_dnssec_ok != 0)
1f4a55da
PP
185 {
186 DEBUG(D_resolver)
0fbd9bff 187 debug_printf("CONFLICT: dns_use_edns0 forced false, dns_dnssec_ok forced true, ignoring latter!\n");
1f4a55da
PP
188 }
189 else
190 {
0fbd9bff 191 if (dns_dnssec_ok)
1f4a55da
PP
192 resp->options |= RES_USE_DNSSEC;
193 else
194 resp->options &= ~RES_USE_DNSSEC;
195 DEBUG(D_resolver) debug_printf("Coerced resolver DNSSEC support %s.\n",
0fbd9bff 196 dns_dnssec_ok ? "on" : "off");
1f4a55da
PP
197 }
198 }
199# else
0fbd9bff 200if (dns_dnssec_ok >= 0)
1f4a55da
PP
201 DEBUG(D_resolver)
202 debug_printf("Unable to %sset DNSSEC without resolver support.\n",
0fbd9bff 203 dns_dnssec_ok ? "" : "un");
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204if (use_dnssec)
205 DEBUG(D_resolver)
93d4b03a 206 debug_printf("Unable to set DNSSEC without resolver support.\n");
1f4a55da
PP
207# endif
208#endif /* DISABLE_DNSSEC */
209
5bfb4cdf 210os_put_dns_resolver_res(resp);
059ec3d9
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211}
212
213
214
215/*************************************************
216* Build key name for PTR records *
217*************************************************/
218
219/* This function inverts an IP address and adds the relevant domain, to produce
220a name that can be used to look up PTR records.
221
222Arguments:
223 string the IP address as a string
224 buffer a suitable buffer, long enough to hold the result
225
226Returns: nothing
227*/
228
229void
55414b25 230dns_build_reverse(const uschar *string, uschar *buffer)
059ec3d9 231{
55414b25 232const uschar *p = string + Ustrlen(string);
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233uschar *pp = buffer;
234
235/* Handle IPv4 address */
236
237#if HAVE_IPV6
238if (Ustrchr(string, ':') == NULL)
239#endif
240 {
d7978c0f 241 for (int i = 0; i < 4; i++)
059ec3d9 242 {
55414b25 243 const uschar *ppp = p;
059ec3d9
PH
244 while (ppp > string && ppp[-1] != '.') ppp--;
245 Ustrncpy(pp, ppp, p - ppp);
246 pp += p - ppp;
247 *pp++ = '.';
248 p = ppp - 1;
249 }
f3ebb786 250 Ustrcpy(pp, US"in-addr.arpa");
059ec3d9
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251 }
252
253/* Handle IPv6 address; convert to binary so as to fill out any
254abbreviation in the textual form. */
255
256#if HAVE_IPV6
257else
258 {
059ec3d9
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259 int v6[4];
260 (void)host_aton(string, v6);
261
262 /* The original specification for IPv6 reverse lookup was to invert each
263 nibble, and look in the ip6.int domain. The domain was subsequently
264 changed to ip6.arpa. */
265
d7978c0f
JH
266 for (int i = 3; i >= 0; i--)
267 for (int j = 0; j < 32; j += 4)
5976eb99 268 pp += sprintf(CS pp, "%x.", (v6[i] >> j) & 15);
f3ebb786 269 Ustrcpy(pp, US"ip6.arpa.");
059ec3d9
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270
271 /* Another way of doing IPv6 reverse lookups was proposed in conjunction
272 with A6 records. However, it fell out of favour when they did. The
273 alternative was to construct a binary key, and look in ip6.arpa. I tried
274 to make this code do that, but I could not make it work on Solaris 8. The
275 resolver seems to lose the initial backslash somehow. However, now that
276 this style of reverse lookup has been dropped, it doesn't matter. These
277 lines are left here purely for historical interest. */
278
279 /**************************************************
280 Ustrcpy(pp, "\\[x");
281 pp += 3;
282
d7978c0f 283 for (int i = 0; i < 4; i++)
059ec3d9
PH
284 {
285 sprintf(pp, "%08X", v6[i]);
286 pp += 8;
287 }
f3ebb786 288 Ustrcpy(pp, US"].ip6.arpa.");
059ec3d9
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289 **************************************************/
290
291 }
292#endif
293}
294
295
296
297
2a407b17
JH
298/* Increment the aptr in dnss, checking against dnsa length.
299Return: TRUE for a bad result
300*/
301static BOOL
dd708fd7 302dnss_inc_aptr(const dns_answer * dnsa, dns_scan * dnss, unsigned delta)
2a407b17
JH
303{
304return (dnss->aptr += delta) >= dnsa->answer + dnsa->answerlen;
305}
306
059ec3d9
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307/*************************************************
308* Get next DNS record from answer block *
309*************************************************/
310
311/* Call this with reset == RESET_ANSWERS to scan the answer block, reset ==
e5a9dba6
PH
312RESET_AUTHORITY to scan the authority records, reset == RESET_ADDITIONAL to
313scan the additional records, and reset == RESET_NEXT to get the next record.
314The result is in static storage which must be copied if it is to be preserved.
059ec3d9
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315
316Arguments:
317 dnsa pointer to dns answer block
318 dnss pointer to dns scan block
4c04137d 319 reset option specifying what portion to scan, as described above
059ec3d9
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320
321Returns: next dns record, or NULL when no more
322*/
323
324dns_record *
dd708fd7 325dns_next_rr(const dns_answer *dnsa, dns_scan *dnss, int reset)
059ec3d9 326{
dd708fd7 327const HEADER * h = (const HEADER *)dnsa->answer;
059ec3d9
PH
328int namelen;
329
2a407b17
JH
330char * trace = NULL;
331#ifdef rr_trace
332# define TRACE DEBUG(D_dns)
333#else
334trace = trace;
335# define TRACE if (FALSE)
336#endif
337
059ec3d9
PH
338/* Reset the saved data when requested to, and skip to the first required RR */
339
340if (reset != RESET_NEXT)
341 {
342 dnss->rrcount = ntohs(h->qdcount);
d093f8e5 343 TRACE debug_printf("%s: reset (Q rrcount %d)\n", __FUNCTION__, dnss->rrcount);
059ec3d9
PH
344 dnss->aptr = dnsa->answer + sizeof(HEADER);
345
346 /* Skip over questions; failure to expand the name just gives up */
347
348 while (dnss->rrcount-- > 0)
349 {
2a407b17 350 TRACE trace = "Q-namelen";
059ec3d9 351 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
2a407b17
JH
352 dnss->aptr, (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME);
353 if (namelen < 0) goto null_return;
354 /* skip name & type & class */
355 TRACE trace = "Q-skip";
dd708fd7 356 if (dnss_inc_aptr(dnsa, dnss, namelen+4)) goto null_return;
059ec3d9
PH
357 }
358
359 /* Get the number of answer records. */
360
361 dnss->rrcount = ntohs(h->ancount);
d093f8e5 362 TRACE debug_printf("%s: reset (A rrcount %d)\n", __FUNCTION__, dnss->rrcount);
059ec3d9 363
e5a9dba6
PH
364 /* Skip over answers if we want to look at the authority section. Also skip
365 the NS records (i.e. authority section) if wanting to look at the additional
059ec3d9
PH
366 records. */
367
2a407b17
JH
368 if (reset == RESET_ADDITIONAL)
369 {
370 TRACE debug_printf("%s: additional\n", __FUNCTION__);
371 dnss->rrcount += ntohs(h->nscount);
d093f8e5 372 TRACE debug_printf("%s: reset (NS rrcount %d)\n", __FUNCTION__, dnss->rrcount);
2a407b17 373 }
e5a9dba6
PH
374
375 if (reset == RESET_AUTHORITY || reset == RESET_ADDITIONAL)
059ec3d9 376 {
2a407b17
JH
377 TRACE if (reset == RESET_AUTHORITY)
378 debug_printf("%s: authority\n", __FUNCTION__);
059ec3d9
PH
379 while (dnss->rrcount-- > 0)
380 {
2a407b17 381 TRACE trace = "A-namelen";
059ec3d9 382 namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
2a407b17
JH
383 dnss->aptr, (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME);
384 if (namelen < 0) goto null_return;
385 /* skip name, type, class & TTL */
386 TRACE trace = "A-hdr";
dd708fd7 387 if (dnss_inc_aptr(dnsa, dnss, namelen+8)) goto null_return;
059ec3d9 388 GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */
2a407b17
JH
389 /* skip over it */
390 TRACE trace = "A-skip";
dd708fd7 391 if (dnss_inc_aptr(dnsa, dnss, dnss->srr.size)) goto null_return;
059ec3d9 392 }
2a407b17 393 dnss->rrcount = reset == RESET_AUTHORITY
e5a9dba6 394 ? ntohs(h->nscount) : ntohs(h->arcount);
d093f8e5
JH
395 TRACE debug_printf("%s: reset (%s rrcount %d)\n", __FUNCTION__,
396 reset == RESET_AUTHORITY ? "NS" : "AR", dnss->rrcount);
059ec3d9 397 }
2a407b17 398 TRACE debug_printf("%s: %d RRs to read\n", __FUNCTION__, dnss->rrcount);
059ec3d9 399 }
2a407b17
JH
400else
401 TRACE debug_printf("%s: next (%d left)\n", __FUNCTION__, dnss->rrcount);
059ec3d9 402
059ec3d9
PH
403/* The variable dnss->aptr is now pointing at the next RR, and dnss->rrcount
404contains the number of RR records left. */
405
406if (dnss->rrcount-- <= 0) return NULL;
407
408/* If expanding the RR domain name fails, behave as if no more records
409(something safe). */
410
2a407b17 411TRACE trace = "R-namelen";
059ec3d9 412namelen = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen, dnss->aptr,
2a407b17
JH
413 (DN_EXPAND_ARG4_TYPE) &dnss->srr.name, DNS_MAXNAME);
414if (namelen < 0) goto null_return;
059ec3d9
PH
415
416/* Move the pointer past the name and fill in the rest of the data structure
417from the following bytes. */
418
2a407b17 419TRACE trace = "R-name";
dd708fd7 420if (dnss_inc_aptr(dnsa, dnss, namelen)) goto null_return;
2a407b17
JH
421
422GETSHORT(dnss->srr.type, dnss->aptr); /* Record type */
423TRACE trace = "R-class";
dd708fd7 424if (dnss_inc_aptr(dnsa, dnss, 2)) goto null_return; /* Don't want class */
2a407b17
JH
425GETLONG(dnss->srr.ttl, dnss->aptr); /* TTL */
426GETSHORT(dnss->srr.size, dnss->aptr); /* Size of data portion */
427dnss->srr.data = dnss->aptr; /* The record's data follows */
428
429/* Unchecked increment ok here since no further access on this iteration;
430will be checked on next at "R-name". */
431
432dnss->aptr += dnss->srr.size; /* Advance to next RR */
059ec3d9
PH
433
434/* Return a pointer to the dns_record structure within the dns_answer. This is
435for convenience so that the scans can use nice-looking for loops. */
436
7d8d08c4 437TRACE debug_printf("%s: return %s\n", __FUNCTION__, dns_text_type(dnss->srr.type));
2a407b17
JH
438return &dnss->srr;
439
440null_return:
d093f8e5
JH
441 TRACE debug_printf("%s: terminate (%d RRs left). Last op: %s; errno %d %s\n",
442 __FUNCTION__, dnss->rrcount, trace, errno, strerror(errno));
2a407b17
JH
443 dnss->rrcount = 0;
444 return NULL;
059ec3d9
PH
445}
446
447
8688d177 448/* Extract the AUTHORITY information from the answer. If the answer isn't
4c04137d 449authoritative (AA not set), we do not extract anything.
8db90b31 450
4c04137d 451The AUTHORITY section contains NS records if the name in question was found,
8688d177
JH
452it contains a SOA record otherwise. (This is just from experience and some
453tests, is there some spec?)
8db90b31 454
8688d177
JH
455Scan the whole AUTHORITY section, since it may contain other records
456(e.g. NSEC3) too.
457
458Return: name for the authority, in an allocated string, or NULL if none found */
09b80b4e
JH
459
460static const uschar *
461dns_extract_auth_name(const dns_answer * dnsa) /* FIXME: const dns_answer */
9820a77f 462{
09b80b4e 463dns_scan dnss;
dd708fd7 464const HEADER * h = (const HEADER *) dnsa->answer;
09b80b4e 465
8688d177 466if (h->nscount && h->aa)
d7978c0f 467 for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
8688d177
JH
468 rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
469 if (rr->type == (h->ancount ? T_NS : T_SOA))
470 return string_copy(rr->name);
09b80b4e 471return NULL;
9820a77f
HSHR
472}
473
474
059ec3d9
PH
475
476
477/*************************************************
1f4a55da
PP
478* Return whether AD bit set in DNS result *
479*************************************************/
480
481/* We do not perform DNSSEC work ourselves; if the administrator has installed
482a verifying resolver which sets AD as appropriate, though, we'll use that.
4c04137d 483(AD = Authentic Data, AA = Authoritative Answer)
1f4a55da
PP
484
485Argument: pointer to dns answer block
486Returns: bool indicating presence of AD bit
487*/
488
489BOOL
4a142059 490dns_is_secure(const dns_answer * dnsa)
1f4a55da
PP
491{
492#ifdef DISABLE_DNSSEC
493DEBUG(D_dns)
494 debug_printf("DNSSEC support disabled at build-time; dns_is_secure() false\n");
495return FALSE;
496#else
dd708fd7 497const HEADER * h = (const HEADER *) dnsa->answer;
09b80b4e
JH
498const uschar * auth_name;
499const uschar * trusted;
9820a77f
HSHR
500
501if (h->ad) return TRUE;
9820a77f 502
4c04137d 503/* If the resolver we ask is authoritative for the domain in question, it
09b80b4e
JH
504* may not set the AD but the AA bit. If we explicitly trust
505* the resolver for that domain (via a domainlist in dns_trust_aa),
506* we return TRUE to indicate a secure answer.
507*/
9820a77f 508
09b80b4e
JH
509if ( !h->aa
510 || !dns_trust_aa
25bf2076
HSHR
511 || !(trusted = expand_string(dns_trust_aa))
512 || !*trusted
09b80b4e
JH
513 || !(auth_name = dns_extract_auth_name(dnsa))
514 || OK != match_isinlist(auth_name, &trusted, 0, NULL, NULL,
94431adb 515 MCL_DOMAIN, TRUE, NULL)
09b80b4e
JH
516 )
517 return FALSE;
9820a77f 518
09b80b4e
JH
519DEBUG(D_dns) debug_printf("DNS faked the AD bit "
520 "(got AA and matched with dns_trust_aa (%s in %s))\n",
521 auth_name, dns_trust_aa);
9820a77f 522
09b80b4e 523return TRUE;
1f4a55da
PP
524#endif
525}
526
4a142059
JH
527static void
528dns_set_insecure(dns_answer * dnsa)
529{
e87c01c7 530#ifndef DISABLE_DNSSEC
4a142059 531HEADER * h = (HEADER *)dnsa->answer;
8688d177 532h->aa = h->ad = 0;
e87c01c7 533#endif
4a142059
JH
534}
535
221dff13
HSHR
536/************************************************
537 * Check whether the AA bit is set *
538 * We need this to warn if we requested AD *
4c04137d 539 * from an authoritative server *
221dff13
HSHR
540 ************************************************/
541
542BOOL
543dns_is_aa(const dns_answer *dnsa)
544{
e87c01c7
MH
545#ifdef DISABLE_DNSSEC
546return FALSE;
547#else
dd708fd7 548return ((const HEADER*)dnsa->answer)->aa;
e87c01c7 549#endif
221dff13 550}
1f4a55da
PP
551
552
553
554/*************************************************
059ec3d9
PH
555* Turn DNS type into text *
556*************************************************/
557
885ccd3e
PH
558/* Turn the coded record type into a string for printing. All those that Exim
559uses should be included here.
059ec3d9
PH
560
561Argument: record type
562Returns: pointer to string
563*/
564
565uschar *
566dns_text_type(int t)
567{
568switch(t)
569 {
33397d19
PH
570 case T_A: return US"A";
571 case T_MX: return US"MX";
572 case T_AAAA: return US"AAAA";
573 case T_A6: return US"A6";
574 case T_TXT: return US"TXT";
eae0036b 575 case T_SPF: return US"SPF";
33397d19 576 case T_PTR: return US"PTR";
885ccd3e 577 case T_SOA: return US"SOA";
33397d19
PH
578 case T_SRV: return US"SRV";
579 case T_NS: return US"NS";
8e669ac1 580 case T_CNAME: return US"CNAME";
1e06383a 581 case T_TLSA: return US"TLSA";
33397d19 582 default: return US"?";
059ec3d9
PH
583 }
584}
585
586
587
588/*************************************************
589* Cache a failed DNS lookup result *
590*************************************************/
591
cabf3e99
JH
592static void
593dns_fail_tag(uschar * buf, const uschar * name, int dns_type)
594{
595res_state resp = os_get_dns_resolver_res();
7d8d08c4
JH
596
597/*XX buf needs to be 255 +1 + (max(typetext) == 5) +1 + max(chars_for_long-max) +1
598We truncate the name here for safety... could use a dynamic string. */
599
cabf3e99
JH
600sprintf(CS buf, "%.255s-%s-%lx", name, dns_text_type(dns_type),
601 (unsigned long) resp->options);
602}
603
604
059ec3d9
PH
605/* We cache failed lookup results so as not to experience timeouts many
606times for the same domain. We need to retain the resolver options because they
607may change. For successful lookups, we rely on resolver and/or name server
608caching.
609
610Arguments:
611 name the domain name
612 type the lookup type
7d8d08c4 613 expiry time TTL expires, or zero for unlimited
059ec3d9
PH
614 rc the return code
615
616Returns: the return code
617*/
618
3a2feed8 619/* we need: 255 +1 + (max(typetext) == 5) +1 + max(chars_for_long-max) +1 */
7d8d08c4 620#define DNS_FAILTAG_MAX 290
927e32d4 621#define DNS_FAILNODE_SIZE \
3a2feed8 622 (sizeof(expiring_data) + sizeof(tree_node) + DNS_FAILTAG_MAX)
7d8d08c4
JH
623
624static int
625dns_fail_return(const uschar * name, int type, time_t expiry, int rc)
626{
627uschar node_name[DNS_FAILTAG_MAX];
628tree_node * previous, * new;
629expiring_data * e;
630
631dns_fail_tag(node_name, name, type);
632if ((previous = tree_search(tree_dns_fails, node_name)))
633 e = previous->data.ptr;
634else
635 {
3a2feed8
JH
636 e = store_get_perm(DNS_FAILNODE_SIZE, is_tainted(name));
637 new = (void *)(e+1);
7d8d08c4 638 dns_fail_tag(new->name, name, type);
7d8d08c4
JH
639 new->data.ptr = e;
640 (void)tree_insertnode(&tree_dns_fails, new);
641 }
642
643DEBUG(D_dns) debug_printf(" %s neg-cache entry for %s, ttl %d\n",
644 previous ? "update" : "writing",
645 node_name, expiry ? (int)(expiry - time(NULL)) : -1);
646e->expiry = expiry;
647e->data.val = rc;
648return rc;
649}
650
651
652/* Return the cached result of a known-bad lookup, or -1.
653*/
059ec3d9 654static int
7d8d08c4 655dns_fail_cache_hit(const uschar * name, int type)
059ec3d9 656{
7d8d08c4
JH
657uschar node_name[DNS_FAILTAG_MAX];
658tree_node * previous;
659expiring_data * e;
660int val, rc;
661
662dns_fail_tag(node_name, name, type);
663if (!(previous = tree_search(tree_dns_fails, node_name)))
664 return -1;
665
666e = previous->data.ptr;
667val = e->data.val;
668rc = e->expiry && e->expiry <= time(NULL) ? -1 : val;
669
670DEBUG(D_dns) debug_printf("DNS lookup of %.255s-%s: %scached value %s%s\n",
671 name, dns_text_type(type),
672 rc == -1 ? "" : "using ",
673 val == DNS_NOMATCH ? "DNS_NOMATCH" :
674 val == DNS_NODATA ? "DNS_NODATA" :
675 val == DNS_AGAIN ? "DNS_AGAIN" :
676 val == DNS_FAIL ? "DNS_FAIL" : "??",
677 rc == -1 ? " past valid time" : "");
678
059ec3d9
PH
679return rc;
680}
681
7d8d08c4
JH
682
683
684/* Return the TTL suitable for an NXDOMAIN result, which is given
685in the SOA. We hope that one was returned in the lookup, and do not
686bother doing a separate lookup; if not found return a forever TTL.
687*/
688
3462da30 689time_t
7d8d08c4
JH
690dns_expire_from_soa(dns_answer * dnsa)
691{
692const HEADER * h = (const HEADER *)dnsa->answer;
693dns_scan dnss;
694
695/* This is really gross. The successful return value from res_search() is
696the packet length, which is stored in dnsa->answerlen. If we get a
697negative DNS reply then res_search() returns -1, which causes the bounds
698checks for name decompression to fail when it is treated as a packet
699length, which in turn causes the authority search to fail. The correct
700packet length has been lost inside libresolv, so we have to guess a
701replacement value. (The only way to fix this properly would be to
702re-implement res_search() and res_query() so that they don't muddle their
703success and packet length return values.) For added safety we only reset
704the packet length if the packet header looks plausible. */
705
706if ( h->qr == 1 && h->opcode == QUERY && h->tc == 0
707 && (h->rcode == NOERROR || h->rcode == NXDOMAIN)
708 && (ntohs(h->qdcount) == 1 || f.running_in_test_harness)
709 && ntohs(h->ancount) == 0
710 && ntohs(h->nscount) >= 1)
711 dnsa->answerlen = sizeof(dnsa->answer);
712
713for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
714 rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)
715 ) if (rr->type == T_SOA)
716 {
717 const uschar * p = rr->data;
718 uschar discard_buf[256];
719 int len;
720 unsigned long ttl;
721
722 /* Skip the mname & rname strings */
723
724 if ((len = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
725 p, (DN_EXPAND_ARG4_TYPE)discard_buf, 256)) < 0)
726 break;
727 p += len;
728 if ((len = dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
729 p, (DN_EXPAND_ARG4_TYPE)discard_buf, 256)) < 0)
730 break;
731 p += len;
732
733 /* Skip the SOA serial, refresh, retry & expire. Grab the TTL */
734
d70fc283 735 if (p > dnsa->answer + dnsa->answerlen - 5 * INT32SZ)
7d8d08c4 736 break;
d70fc283 737 p += 4 * INT32SZ;
7d8d08c4
JH
738 GETLONG(ttl, p);
739
740 return time(NULL) + ttl;
741 }
742DEBUG(D_dns) debug_printf("DNS: no SOA record found for neg-TTL\n");
743return 0;
744}
745
746
059ec3d9
PH
747/*************************************************
748* Do basic DNS lookup *
749*************************************************/
750
751/* Call the resolver to look up the given domain name, using the given type,
752and check the result. The error code TRY_AGAIN is documented as meaning "non-
4c04137d 753Authoritative Host not found, or SERVERFAIL". Sometimes there are badly set
059ec3d9
PH
754up nameservers that produce this error continually, so there is the option of
755providing a list of domains for which this is treated as a non-existent
756host.
757
75c121f0
JH
758The dns_answer structure is pretty big; enough to hold a max-sized DNS message
759- so best allocated from fast-release memory. As of writing, all our callers
760use a stack-auto variable.
761
059ec3d9
PH
762Arguments:
763 dnsa pointer to dns_answer structure
764 name name to look up
765 type type of DNS record required (T_A, T_MX, etc)
766
767Returns: DNS_SUCCEED successful lookup
768 DNS_NOMATCH name not found (NXDOMAIN)
769 or name contains illegal characters (if checking)
30e18802 770 or name is an IP address (for IP address lookup)
059ec3d9
PH
771 DNS_NODATA domain exists, but no data for this type (NODATA)
772 DNS_AGAIN soft failure, try again later
773 DNS_FAIL DNS failure
774*/
775
776int
7d8d08c4 777dns_basic_lookup(dns_answer * dnsa, const uschar * name, int type)
059ec3d9 778{
7d8d08c4 779int rc;
059ec3d9 780#ifndef STAND_ALONE
7d8d08c4 781const uschar * save_domain;
059ec3d9
PH
782#endif
783
059ec3d9
PH
784/* DNS lookup failures of any kind are cached in a tree. This is mainly so that
785a timeout on one domain doesn't happen time and time again for messages that
786have many addresses in the same domain. We rely on the resolver and name server
7d8d08c4
JH
787caching for successful lookups.
788*/
059ec3d9 789
7d8d08c4
JH
790if ((rc = dns_fail_cache_hit(name, type)) > 0)
791 return rc;
059ec3d9 792
8c5d388a 793#ifdef SUPPORT_I18N
9d4319df
JH
794/* Convert all names to a-label form before doing lookup */
795 {
796 uschar * alabel;
797 uschar * errstr = NULL;
766e7a65
JH
798 DEBUG(D_dns) if (string_is_utf8(name))
799 debug_printf("convert utf8 '%s' to alabel for for lookup\n", name);
9d4319df
JH
800 if ((alabel = string_domain_utf8_to_alabel(name, &errstr)), errstr)
801 {
802 DEBUG(D_dns)
37bf366e 803 debug_printf("DNS name '%s' utf8 conversion to alabel failed: %s\n", name,
9d4319df 804 errstr);
8768d548 805 f.host_find_failed_syntax = TRUE;
9d4319df
JH
806 return DNS_NOMATCH;
807 }
808 name = alabel;
809 }
810#endif
811
4c04137d 812/* If configured, check the hygiene of the name passed to lookup. Otherwise,
059ec3d9
PH
813although DNS lookups may give REFUSED at the lower level, some resolvers
814turn this into TRY_AGAIN, which is silly. Give a NOMATCH return, since such
815domains cannot be in the DNS. The check is now done by a regular expression;
816give it space for substring storage to save it having to get its own if the
817regex has substrings that are used - the default uses a conditional.
818
819This test is omitted for PTR records. These occur only in calls from the dnsdb
820lookup, which constructs the names itself, so they should be OK. Besides,
6219e0ec
SA
821bitstring labels don't conform to normal name syntax. (But they aren't used any
822more.) */
059ec3d9
PH
823
824#ifndef STAND_ALONE /* Omit this for stand-alone tests */
825
482d1455 826if (check_dns_names_pattern[0] != 0 && type != T_PTR && type != T_TXT)
059ec3d9 827 {
059ec3d9
PH
828 int ovector[3*(EXPAND_MAXN+1)];
829
476be7e2 830 dns_pattern_init();
6219e0ec 831 if (pcre_exec(regex_check_dns_names, NULL, CCS name, Ustrlen(name),
d093f8e5 832 0, PCRE_EOPT, ovector, nelem(ovector)) < 0)
059ec3d9
PH
833 {
834 DEBUG(D_dns)
835 debug_printf("DNS name syntax check failed: %s (%s)\n", name,
836 dns_text_type(type));
8768d548 837 f.host_find_failed_syntax = TRUE;
059ec3d9
PH
838 return DNS_NOMATCH;
839 }
840 }
841
842#endif /* STAND_ALONE */
843
844/* Call the resolver; for an overlong response, res_search() will return the
bef5a11f
PH
845number of bytes the message would need, so we need to check for this case. The
846effect is to truncate overlong data.
847
30e18802
PH
848On some systems, res_search() will recognize "A-for-A" queries and return
849the IP address instead of returning -1 with h_error=HOST_NOT_FOUND. Some
850nameservers are also believed to do this. It is, of course, contrary to the
851specification of the DNS, so we lock it out. */
852
cc00f4af 853if ((type == T_A || type == T_AAAA) && string_is_ip_address(name, NULL) != 0)
30e18802
PH
854 return DNS_NOMATCH;
855
856/* If we are running in the test harness, instead of calling the normal resolver
bef5a11f
PH
857(res_search), we call fakens_search(), which recognizes certain special
858domains, and interfaces to a fake nameserver for certain special zones. */
859
8768d548 860dnsa->answerlen = f.running_in_test_harness
d093f8e5
JH
861 ? fakens_search(name, type, dnsa->answer, sizeof(dnsa->answer))
862 : res_search(CCS name, C_IN, type, dnsa->answer, sizeof(dnsa->answer));
059ec3d9 863
d093f8e5 864if (dnsa->answerlen > (int) sizeof(dnsa->answer))
80a47a2c 865 {
9e7e0f6a
JH
866 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) resulted in overlong packet"
867 " (size %d), truncating to %u.\n",
868 name, dns_text_type(type), dnsa->answerlen, (unsigned int) sizeof(dnsa->answer));
d093f8e5 869 dnsa->answerlen = sizeof(dnsa->answer);
80a47a2c 870 }
059ec3d9
PH
871
872if (dnsa->answerlen < 0) switch (h_errno)
873 {
874 case HOST_NOT_FOUND:
4b0fe319
JH
875 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave HOST_NOT_FOUND\n"
876 "returning DNS_NOMATCH\n", name, dns_text_type(type));
7d8d08c4 877 return dns_fail_return(name, type, dns_expire_from_soa(dnsa), DNS_NOMATCH);
059ec3d9
PH
878
879 case TRY_AGAIN:
4b0fe319
JH
880 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave TRY_AGAIN\n",
881 name, dns_text_type(type));
059ec3d9 882
4b0fe319 883 /* Cut this out for various test programs */
1dc92d5a 884#ifndef STAND_ALONE
4b0fe319
JH
885 save_domain = deliver_domain;
886 deliver_domain = string_copy(name); /* set $domain */
887 rc = match_isinlist(name, (const uschar **)&dns_again_means_nonexist, 0, NULL, NULL,
888 MCL_DOMAIN, TRUE, NULL);
889 deliver_domain = save_domain;
890 if (rc != OK)
891 {
892 DEBUG(D_dns) debug_printf("returning DNS_AGAIN\n");
7d8d08c4 893 return dns_fail_return(name, type, 0, DNS_AGAIN);
4b0fe319
JH
894 }
895 DEBUG(D_dns) debug_printf("%s is in dns_again_means_nonexist: returning "
896 "DNS_NOMATCH\n", name);
7d8d08c4 897 return dns_fail_return(name, type, dns_expire_from_soa(dnsa), DNS_NOMATCH);
059ec3d9 898
1dc92d5a 899#else /* For stand-alone tests */
7d8d08c4 900 return dns_fail_return(name, type, 0, DNS_AGAIN);
1dc92d5a 901#endif
059ec3d9
PH
902
903 case NO_RECOVERY:
4b0fe319
JH
904 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_RECOVERY\n"
905 "returning DNS_FAIL\n", name, dns_text_type(type));
7d8d08c4 906 return dns_fail_return(name, type, 0, DNS_FAIL);
059ec3d9
PH
907
908 case NO_DATA:
4b0fe319
JH
909 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave NO_DATA\n"
910 "returning DNS_NODATA\n", name, dns_text_type(type));
7d8d08c4 911 return dns_fail_return(name, type, dns_expire_from_soa(dnsa), DNS_NODATA);
059ec3d9
PH
912
913 default:
4b0fe319
JH
914 DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) gave unknown DNS error %d\n"
915 "returning DNS_FAIL\n", name, dns_text_type(type), h_errno);
7d8d08c4 916 return dns_fail_return(name, type, 0, DNS_FAIL);
059ec3d9
PH
917 }
918
919DEBUG(D_dns) debug_printf("DNS lookup of %s (%s) succeeded\n",
920 name, dns_text_type(type));
921
922return DNS_SUCCEED;
923}
924
925
926
927
928/************************************************
929* Do a DNS lookup and handle CNAMES *
930************************************************/
931
932/* Look up the given domain name, using the given type. Follow CNAMEs if
933necessary, but only so many times. There aren't supposed to be CNAME chains in
934the DNS, but you are supposed to cope with them if you find them.
d8d9f930
JH
935By default, follow one CNAME since a resolver has been seen, faced with
936an MX request and a CNAME (to an A) but no MX present, returning the CNAME.
059ec3d9
PH
937
938The assumption is made that if the resolver gives back records of the
939requested type *and* a CNAME, we don't need to make another call to look up
940the CNAME. I can't see how it could return only some of the right records. If
941it's done a CNAME lookup in the past, it will have all of them; if not, it
942won't return any.
943
944If fully_qualified_name is not NULL, set it to point to the full name
945returned by the resolver, if this is different to what it is given, unless
946the returned name starts with "*" as some nameservers seem to be returning
766e7a65
JH
947wildcards in this form. In international mode "different" means "alabel
948forms are different".
059ec3d9
PH
949
950Arguments:
951 dnsa pointer to dns_answer structure
952 name domain name to look up
953 type DNS record type (T_A, T_MX, etc)
954 fully_qualified_name if not NULL, return the returned name here if its
955 contents are different (i.e. it must be preset)
956
957Returns: DNS_SUCCEED successful lookup
958 DNS_NOMATCH name not found
959 DNS_NODATA no data found
960 DNS_AGAIN soft failure, try again later
961 DNS_FAIL DNS failure
962*/
963
964int
1dc92d5a 965dns_lookup(dns_answer *dnsa, const uschar *name, int type,
55414b25 966 const uschar **fully_qualified_name)
059ec3d9 967{
1dc92d5a 968const uschar *orig_name = name;
c85b3043 969BOOL secure_so_far = TRUE;
059ec3d9 970
d8d9f930
JH
971/* By default, assume the resolver follows CNAME chains (and returns NODATA for
972an unterminated one). If it also does that for a CNAME loop, fine; if it returns
973a CNAME (maybe the last?) whine about it. However, retain the coding for dumb
974resolvers hiding behind a config variable. Loop to follow CNAME chains so far,
975but no further... The testsuite tests the latter case, mostly assuming that the
976former will work. */
059ec3d9 977
d7978c0f 978for (int i = 0; i <= dns_cname_loops; i++)
059ec3d9 979 {
806c3df9 980 uschar * data;
d7978c0f 981 dns_record cname_rr, type_rr;
059ec3d9 982 dns_scan dnss;
1b76ad22 983 int rc;
059ec3d9
PH
984
985 /* DNS lookup failures get passed straight back. */
986
dd708fd7
JH
987 if ((rc = dns_basic_lookup(dnsa, name, type)) != DNS_SUCCEED)
988 return rc;
059ec3d9
PH
989
990 /* We should have either records of the required type, or a CNAME record,
991 or both. We need to know whether both exist for getting the fully qualified
992 name, but avoid scanning more than necessary. Note that we must copy the
993 contents of any rr blocks returned by dns_next_rr() as they use the same
994 area in the dnsa block. */
995
996 cname_rr.data = type_rr.data = NULL;
d7978c0f 997 for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
8688d177 998 rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT))
059ec3d9
PH
999 if (rr->type == type)
1000 {
1001 if (type_rr.data == NULL) type_rr = *rr;
1002 if (cname_rr.data != NULL) break;
1003 }
dd708fd7
JH
1004 else if (rr->type == T_CNAME)
1005 cname_rr = *rr;
059ec3d9 1006
a2042e78
PH
1007 /* For the first time round this loop, if a CNAME was found, take the fully
1008 qualified name from it; otherwise from the first data record, if present. */
059ec3d9 1009
dd708fd7 1010 if (i == 0 && fully_qualified_name)
059ec3d9 1011 {
dd708fd7
JH
1012 uschar * rr_name = cname_rr.data
1013 ? cname_rr.name : type_rr.data ? type_rr.name : NULL;
766e7a65
JH
1014 if ( rr_name
1015 && Ustrcmp(rr_name, *fully_qualified_name) != 0
1016 && rr_name[0] != '*'
8c5d388a 1017#ifdef SUPPORT_I18N
766e7a65
JH
1018 && ( !string_is_utf8(*fully_qualified_name)
1019 || Ustrcmp(rr_name,
1020 string_domain_utf8_to_alabel(*fully_qualified_name, NULL)) != 0
1021 )
1022#endif
1023 )
1024 *fully_qualified_name = string_copy_dnsdomain(rr_name);
059ec3d9
PH
1025 }
1026
1027 /* If any data records of the correct type were found, we are done. */
1028
806c3df9 1029 if (type_rr.data)
c85b3043
JH
1030 {
1031 if (!secure_so_far) /* mark insecure if any element of CNAME chain was */
4a142059 1032 dns_set_insecure(dnsa);
c85b3043
JH
1033 return DNS_SUCCEED;
1034 }
059ec3d9
PH
1035
1036 /* If there are no data records, we need to re-scan the DNS using the
1037 domain given in the CNAME record, which should exist (otherwise we should
1038 have had a failure from dns_lookup). However code against the possibility of
1039 its not existing. */
1040
806c3df9
JH
1041 if (!cname_rr.data)
1042 return DNS_FAIL;
1043
f3ebb786
JH
1044 /* DNS data comes from the outside, hence tainted */
1045 data = store_get(256, TRUE);
1b76ad22
JH
1046 if (dn_expand(dnsa->answer, dnsa->answer + dnsa->answerlen,
1047 cname_rr.data, (DN_EXPAND_ARG4_TYPE)data, 256) < 0)
806c3df9 1048 return DNS_FAIL;
059ec3d9 1049 name = data;
a2042e78 1050
c85b3043
JH
1051 if (!dns_is_secure(dnsa))
1052 secure_so_far = FALSE;
1053
a2042e78 1054 DEBUG(D_dns) debug_printf("CNAME found: change to %s\n", name);
059ec3d9
PH
1055 } /* Loop back to do another lookup */
1056
1057/*Control reaches here after 10 times round the CNAME loop. Something isn't
1058right... */
1059
1060log_write(0, LOG_MAIN, "CNAME loop for %s encountered", orig_name);
1061return DNS_FAIL;
1062}
1063
1064
1065
33397d19
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1066
1067
1068
1069/************************************************
1070* Do a DNS lookup and handle virtual types *
1071************************************************/
1072
9820a77f 1073/* This function handles some invented "lookup types" that synthesize features
8e669ac1 1074not available in the basic types. The special types all have negative values.
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1075Positive type values are passed straight on to dns_lookup().
1076
1077Arguments:
1078 dnsa pointer to dns_answer structure
1079 name domain name to look up
1080 type DNS record type (T_A, T_MX, etc or a "special")
1081 fully_qualified_name if not NULL, return the returned name here if its
1082 contents are different (i.e. it must be preset)
1083
1084Returns: DNS_SUCCEED successful lookup
1085 DNS_NOMATCH name not found
1086 DNS_NODATA no data found
1087 DNS_AGAIN soft failure, try again later
1088 DNS_FAIL DNS failure
1089*/
1090
1091int
1dc92d5a 1092dns_special_lookup(dns_answer *dnsa, const uschar *name, int type,
55414b25 1093 const uschar **fully_qualified_name)
33397d19 1094{
d2a2c69b 1095switch (type)
e5a9dba6 1096 {
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1097 /* The "mx hosts only" type doesn't require any special action here */
1098 case T_MXH:
1705dd20 1099 return dns_lookup(dnsa, name, T_MX, fully_qualified_name);
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1100
1101 /* Find nameservers for the domain or the nearest enclosing zone, excluding
1102 the root servers. */
1103 case T_ZNS:
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1104 type = T_NS;
1105 /* FALLTHROUGH */
d2a2c69b 1106 case T_SOA:
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1107 {
1108 const uschar *d = name;
1109 while (d != 0)
1110 {
1111 int rc = dns_lookup(dnsa, d, type, fully_qualified_name);
1112 if (rc != DNS_NOMATCH && rc != DNS_NODATA) return rc;
1113 while (*d != 0 && *d != '.') d++;
1114 if (*d++ == 0) break;
1115 }
1116 return DNS_NOMATCH;
1117 }
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1118
1119 /* Try to look up the Client SMTP Authorization SRV record for the name. If
1120 there isn't one, search from the top downwards for a CSA record in a parent
1121 domain, which might be making assertions about subdomains. If we find a record
1122 we set fully_qualified_name to whichever lookup succeeded, so that the caller
1123 can tell whether to look at the explicit authorization field or the subdomain
1124 assertion field. */
1125 case T_CSA:
1705dd20 1126 {
cab0c277 1127 uschar *srvname, *namesuff, *tld;
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1128 int priority, weight, port;
1129 int limit, rc, i;
1130 BOOL ipv6;
1131 dns_record *rr;
1132 dns_scan dnss;
1133
1134 DEBUG(D_dns) debug_printf("CSA lookup of %s\n", name);
1135
1136 srvname = string_sprintf("_client._smtp.%s", name);
1137 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
1138 if (rc == DNS_SUCCEED || rc == DNS_AGAIN)
1139 {
1140 if (rc == DNS_SUCCEED) *fully_qualified_name = string_copy(name);
1141 return rc;
1142 }
d2a2c69b 1143
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1144 /* Search for CSA subdomain assertion SRV records from the top downwards,
1145 starting with the 2nd level domain. This order maximizes cache-friendliness.
1146 We skip the top level domains to avoid loading their nameservers and because
1147 we know they'll never have CSA SRV records. */
d2a2c69b 1148
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1149 namesuff = Ustrrchr(name, '.');
1150 if (namesuff == NULL) return DNS_NOMATCH;
1151 tld = namesuff + 1;
1152 ipv6 = FALSE;
1153 limit = dns_csa_search_limit;
1154
1155 /* Use more appropriate search parameters if we are in the reverse DNS. */
1156
1157 if (strcmpic(namesuff, US".arpa") == 0)
1158 if (namesuff - 8 > name && strcmpic(namesuff - 8, US".in-addr.arpa") == 0)
1159 {
1160 namesuff -= 8;
d2a2c69b 1161 tld = namesuff + 1;
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1162 limit = 3;
1163 }
1164 else if (namesuff - 4 > name && strcmpic(namesuff - 4, US".ip6.arpa") == 0)
1165 {
1166 namesuff -= 4;
1167 tld = namesuff + 1;
1168 ipv6 = TRUE;
1169 limit = 3;
1170 }
d2a2c69b 1171
1705dd20 1172 DEBUG(D_dns) debug_printf("CSA TLD %s\n", tld);
d2a2c69b 1173
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1174 /* Do not perform the search if the top level or 2nd level domains do not
1175 exist. This is quite common, and when it occurs all the search queries would
1176 go to the root or TLD name servers, which is not friendly. So we check the
1177 AUTHORITY section; if it contains the root's SOA record or the TLD's SOA then
1178 the TLD or the 2LD (respectively) doesn't exist and we can skip the search.
1179 If the TLD and the 2LD exist but the explicit CSA record lookup failed, then
1180 the AUTHORITY SOA will be the 2LD's or a subdomain thereof. */
1181
1182 if (rc == DNS_NOMATCH)
1183 {
1184 /* This is really gross. The successful return value from res_search() is
1185 the packet length, which is stored in dnsa->answerlen. If we get a
1186 negative DNS reply then res_search() returns -1, which causes the bounds
1187 checks for name decompression to fail when it is treated as a packet
1188 length, which in turn causes the authority search to fail. The correct
1189 packet length has been lost inside libresolv, so we have to guess a
1190 replacement value. (The only way to fix this properly would be to
1191 re-implement res_search() and res_query() so that they don't muddle their
1192 success and packet length return values.) For added safety we only reset
1193 the packet length if the packet header looks plausible. */
1194
dd708fd7 1195 const HEADER * h = (const HEADER *)dnsa->answer;
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1196 if (h->qr == 1 && h->opcode == QUERY && h->tc == 0
1197 && (h->rcode == NOERROR || h->rcode == NXDOMAIN)
1198 && ntohs(h->qdcount) == 1 && ntohs(h->ancount) == 0
1199 && ntohs(h->nscount) >= 1)
75c121f0 1200 dnsa->answerlen = sizeof(dnsa->answer);
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1201
1202 for (rr = dns_next_rr(dnsa, &dnss, RESET_AUTHORITY);
8688d177 1203 rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)
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1204 )
1205 if (rr->type != T_SOA) continue;
1206 else if (strcmpic(rr->name, US"") == 0 ||
1207 strcmpic(rr->name, tld) == 0) return DNS_NOMATCH;
1208 else break;
1209 }
d2a2c69b 1210
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1211 for (i = 0; i < limit; i++)
1212 {
1213 if (ipv6)
1214 {
1215 /* Scan through the IPv6 reverse DNS in chunks of 16 bits worth of IP
1216 address, i.e. 4 hex chars and 4 dots, i.e. 8 chars. */
1217 namesuff -= 8;
1218 if (namesuff <= name) return DNS_NOMATCH;
1219 }
1220 else
1221 /* Find the start of the preceding domain name label. */
1222 do
1223 if (--namesuff <= name) return DNS_NOMATCH;
1224 while (*namesuff != '.');
1225
1226 DEBUG(D_dns) debug_printf("CSA parent search at %s\n", namesuff + 1);
1227
1228 srvname = string_sprintf("_client._smtp.%s", namesuff + 1);
1229 rc = dns_lookup(dnsa, srvname, T_SRV, NULL);
1230 if (rc == DNS_AGAIN) return rc;
1231 if (rc != DNS_SUCCEED) continue;
1232
1233 /* Check that the SRV record we have found is worth returning. We don't
1234 just return the first one we find, because some lower level SRV record
1235 might make stricter assertions than its parent domain. */
1236
1237 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
8688d177 1238 rr; rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)) if (rr->type == T_SRV)
1705dd20 1239 {
dd708fd7 1240 const uschar * p = rr->data;
d2a2c69b 1241
1705dd20 1242 /* Extract the numerical SRV fields (p is incremented) */
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1243 GETSHORT(priority, p);
1244 GETSHORT(weight, p); weight = weight; /* compiler quietening */
1245 GETSHORT(port, p);
d2a2c69b 1246
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1247 /* Check the CSA version number */
1248 if (priority != 1) continue;
d2a2c69b 1249
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1250 /* If it's making an interesting assertion, return this response. */
1251 if (port & 1)
d2a2c69b 1252 {
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1253 *fully_qualified_name = namesuff + 1;
1254 return DNS_SUCCEED;
d2a2c69b 1255 }
d2a2c69b 1256 }
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1257 }
1258 return DNS_NOMATCH;
1259 }
e5a9dba6 1260
d2a2c69b 1261 default:
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1262 if (type >= 0)
1263 return dns_lookup(dnsa, name, type, fully_qualified_name);
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1264 }
1265
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1266/* Control should never reach here */
1267
1268return DNS_FAIL;
1269}
1270
1271
1272
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1273
1274
1275/*************************************************
1276* Get address(es) from DNS record *
1277*************************************************/
1278
d57d474f 1279/* The record type is either T_A for an IPv4 address or T_AAAA for an IPv6 address.
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1280
1281Argument:
1282 dnsa the DNS answer block
1283 rr the RR
1284
e1a3f32f 1285Returns: pointer to a chain of dns_address items; NULL when the dnsa was overrun
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1286*/
1287
1288dns_address *
1289dns_address_from_rr(dns_answer *dnsa, dns_record *rr)
1290{
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1291dns_address * yield = NULL;
1292uschar * dnsa_lim = dnsa->answer + dnsa->answerlen;
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1293
1294if (rr->type == T_A)
1295 {
d2a2c69b 1296 uschar *p = US rr->data;
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1297 if (p + 4 <= dnsa_lim)
1298 {
f3ebb786
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1299 /* the IP is not regarded as tainted */
1300 yield = store_get(sizeof(dns_address) + 20, FALSE);
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1301 (void)sprintf(CS yield->address, "%d.%d.%d.%d", p[0], p[1], p[2], p[3]);
1302 yield->next = NULL;
1303 }
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1304 }
1305
1306#if HAVE_IPV6
1307
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1308else
1309 {
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1310 if (rr->data + 16 <= dnsa_lim)
1311 {
d57d474f 1312 struct in6_addr in6;
d7978c0f 1313 for (int i = 0; i < 16; i++) in6.s6_addr[i] = rr->data[i];
f3ebb786 1314 yield = store_get(sizeof(dns_address) + 50, FALSE);
d57d474f 1315 inet_ntop(AF_INET6, &in6, CS yield->address, 50);
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1316 yield->next = NULL;
1317 }
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1318 }
1319#endif /* HAVE_IPV6 */
1320
1321return yield;
1322}
1323
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1324
1325
1326void
1327dns_pattern_init(void)
1328{
1329if (check_dns_names_pattern[0] != 0 && !regex_check_dns_names)
1330 regex_check_dns_names =
1331 regex_must_compile(check_dns_names_pattern, FALSE, TRUE);
1332}
1333
8c51eead
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1334/* vi: aw ai sw=2
1335*/
059ec3d9 1336/* End of dns.c */