1 /* $NetBSD: res_query.c,v 1.7 2006/01/24 17:41:25 christos Exp $ */
2
3 /*
4 * Copyright (c) 1988, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. All advertising materials mentioning features or use of this software
16 * must display the following acknowledgement:
17 * This product includes software developed by the University of
18 * California, Berkeley and its contributors.
19 * 4. Neither the name of the University nor the names of its contributors
20 * may be used to endorse or promote products derived from this software
21 * without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 */
35
36 /*
37 * Portions Copyright (c) 1993 by Digital Equipment Corporation.
38 *
39 * Permission to use, copy, modify, and distribute this software for any
40 * purpose with or without fee is hereby granted, provided that the above
41 * copyright notice and this permission notice appear in all copies, and that
42 * the name of Digital Equipment Corporation not be used in advertising or
43 * publicity pertaining to distribution of the document or software without
44 * specific, written prior permission.
45 *
46 * THE SOFTWARE IS PROVIDED "AS IS" AND DIGITAL EQUIPMENT CORP. DISCLAIMS ALL
47 * WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES
48 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL DIGITAL EQUIPMENT
49 * CORPORATION BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
50 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
51 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
52 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
53 * SOFTWARE.
54 */
55
56 /*
57 * Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
58 * Portions Copyright (c) 1996-1999 by Internet Software Consortium.
59 *
60 * Permission to use, copy, modify, and distribute this software for any
61 * purpose with or without fee is hereby granted, provided that the above
62 * copyright notice and this permission notice appear in all copies.
63 *
64 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
65 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
66 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR
67 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
68 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
69 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
70 * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
71 */
72
73 #define LOG_TAG "resolv"
74
75 #include <arpa/inet.h>
76 #include <arpa/nameser.h>
77 #include <ctype.h>
78 #include <errno.h>
79 #include <netdb.h>
80 #include <netinet/in.h>
81 #include <sys/param.h>
82 #include <stdlib.h>
83 #include <string.h>
84 #include <unistd.h>
85
86 #include <android-base/logging.h>
87
88 #include "res_debug.h"
89 #include "resolv_cache.h"
90 #include "resolv_private.h"
91
92 /*
93 * Formulate a normal query, send, and await answer.
94 * Returned answer is placed in supplied buffer "answer".
95 * Perform preliminary check of answer, returning success only
96 * if no error is indicated and the answer count is nonzero.
97 * Return the size of the response on success, -1 on error.
98 * Error number is left in *herrno.
99 *
100 * Caller must parse answer and determine whether it answers the question.
101 */
res_nquery(res_state statp,const char * name,int cl,int type,uint8_t * answer,int anslen,int * herrno)102 int res_nquery(res_state statp, const char* name, // domain name
103 int cl, int type, // class and type of query
104 uint8_t* answer, // buffer to put answer
105 int anslen, // size of answer buffer
106 int* herrno) // legacy and extended h_errno
107 // NETD_RESOLV_H_ERRNO_EXT_*
108 {
109 uint8_t buf[MAXPACKET];
110 HEADER* hp = (HEADER*) (void*) answer;
111 int n;
112 int rcode = NOERROR;
113 bool retried = false;
114
115 again:
116 hp->rcode = NOERROR; // default
117
118 LOG(DEBUG) << __func__ << ": (" << cl << ", " << type << ")";
119
120 n = res_nmkquery(QUERY, name, cl, type, /*data=*/nullptr, 0, buf, sizeof(buf),
121 statp->netcontext_flags);
122 if (n > 0 &&
123 (statp->netcontext_flags &
124 (NET_CONTEXT_FLAG_USE_DNS_OVER_TLS | NET_CONTEXT_FLAG_USE_EDNS)) &&
125 !retried)
126 n = res_nopt(statp, n, buf, sizeof(buf), anslen);
127 if (n <= 0) {
128 LOG(DEBUG) << __func__ << ": mkquery failed";
129 *herrno = NO_RECOVERY;
130 return n;
131 }
132 n = res_nsend(statp, buf, n, answer, anslen, &rcode, 0);
133 if (n < 0) {
134 // If the query choked with EDNS0, retry without EDNS0 that when the server
135 // has no response, resovler won't retry and do nothing. Even fallback to UDP,
136 // we also has the same symptom if EDNS is enabled.
137 if ((statp->netcontext_flags &
138 (NET_CONTEXT_FLAG_USE_DNS_OVER_TLS | NET_CONTEXT_FLAG_USE_EDNS)) &&
139 (statp->_flags & RES_F_EDNS0ERR) && !retried) {
140 LOG(DEBUG) << __func__ << ": retry without EDNS0";
141 retried = true;
142 goto again;
143 }
144 LOG(DEBUG) << __func__ << ": send error";
145
146 // Note that rcodes SERVFAIL, NOTIMP, REFUSED may cause res_nquery() to return a general
147 // error code EAI_AGAIN, but mapping the error code from rcode as res_queryN() does for
148 // getaddrinfo(). Different rcodes trigger different behaviors:
149 //
150 // - SERVFAIL, NOTIMP, REFUSED
151 // These result in send_dg() returning 0, causing res_nsend() to try the next
152 // nameserver. After all nameservers failed, res_nsend() returns -ETIMEDOUT, causing
153 // res_nquery() to return EAI_AGAIN here regardless of the rcode from the DNS response.
154 //
155 // - NXDOMAIN, FORMERR
156 // These rcodes may cause res_nsend() to return successfully (i.e. the result is a
157 // positive integer). In this case, res_nquery() returns error number by referring
158 // the rcode from the DNS response.
159 switch (rcode) {
160 case RCODE_TIMEOUT: // Not defined in RFC.
161 // DNS metrics monitors DNS query timeout.
162 *herrno = NETD_RESOLV_H_ERRNO_EXT_TIMEOUT; // extended h_errno.
163 break;
164 default:
165 *herrno = TRY_AGAIN;
166 break;
167 }
168 return n;
169 }
170
171 if (hp->rcode != NOERROR || ntohs(hp->ancount) == 0) {
172 LOG(DEBUG) << __func__ << ": rcode = (" << p_rcode(hp->rcode)
173 << "), counts = an:" << ntohs(hp->ancount) << " ns:" << ntohs(hp->nscount)
174 << " ar:" << ntohs(hp->arcount);
175
176 switch (hp->rcode) {
177 case NXDOMAIN:
178 *herrno = HOST_NOT_FOUND;
179 break;
180 case SERVFAIL:
181 *herrno = TRY_AGAIN;
182 break;
183 case NOERROR:
184 *herrno = NO_DATA;
185 break;
186 case FORMERR:
187 case NOTIMP:
188 case REFUSED:
189 default:
190 *herrno = NO_RECOVERY;
191 break;
192 }
193 return -1;
194 }
195 return n;
196 }
197
198 /*
199 * Formulate a normal query, send, and retrieve answer in supplied buffer.
200 * Return the size of the response on success, -1 on error.
201 * If enabled, implement search rules until answer or unrecoverable failure
202 * is detected. Error code, if any, is left in *herrno.
203 */
res_nsearch(res_state statp,const char * name,int cl,int type,uint8_t * answer,int anslen,int * herrno)204 int res_nsearch(res_state statp, const char* name, /* domain name */
205 int cl, int type, /* class and type of query */
206 uint8_t* answer, /* buffer to put answer */
207 int anslen, /* size of answer */
208 int* herrno) /* legacy and extended
209 h_errno NETD_RESOLV_H_ERRNO_EXT_* */
210 {
211 const char* cp;
212 HEADER* hp = (HEADER*) (void*) answer;
213 uint32_t dots;
214 int ret, saved_herrno;
215 int got_nodata = 0, got_servfail = 0, root_on_list = 0;
216 int tried_as_is = 0;
217
218 errno = 0;
219 *herrno = HOST_NOT_FOUND; /* True if we never query. */
220
221 dots = 0;
222 for (cp = name; *cp != '\0'; cp++) dots += (*cp == '.');
223 const bool trailing_dot = (cp > name && *--cp == '.') ? true : false;
224
225 /*
226 * If there are enough dots in the name, let's just give it a
227 * try 'as is'. The threshold can be set with the "ndots" option.
228 * Also, query 'as is', if there is a trailing dot in the name.
229 */
230 saved_herrno = -1;
231 if (dots >= statp->ndots || trailing_dot) {
232 ret = res_nquerydomain(statp, name, NULL, cl, type, answer, anslen, herrno);
233 if (ret > 0 || trailing_dot) return ret;
234 saved_herrno = *herrno;
235 tried_as_is++;
236 }
237
238 /*
239 * We do at least one level of search if
240 * - there is no dot, or
241 * - there is at least one dot and there is no trailing dot.
242 */
243 if ((!dots) || (dots && !trailing_dot)) {
244 int done = 0;
245
246 /* Unfortunately we need to load network-specific info
247 * (dns servers, search domains) before
248 * the domain stuff is tried. Will have a better
249 * fix after thread pools are used as this will
250 * be loaded once for the thread instead of each
251 * time a query is tried.
252 */
253 resolv_populate_res_for_net(statp);
254
255 for (const auto& domain : statp->search_domains) {
256 if (domain == "." || domain == "") ++root_on_list;
257
258 ret = res_nquerydomain(statp, name, domain.c_str(), cl, type, answer, anslen, herrno);
259 if (ret > 0) return ret;
260
261 /*
262 * If no server present, give up.
263 * If name isn't found in this domain,
264 * keep trying higher domains in the search list
265 * (if that's enabled).
266 * On a NO_DATA error, keep trying, otherwise
267 * a wildcard entry of another type could keep us
268 * from finding this entry higher in the domain.
269 * If we get some other error (negative answer or
270 * server failure), then stop searching up,
271 * but try the input name below in case it's
272 * fully-qualified.
273 */
274 if (errno == ECONNREFUSED) {
275 *herrno = TRY_AGAIN;
276 return -1;
277 }
278
279 switch (*herrno) {
280 case NO_DATA:
281 got_nodata++;
282 break;
283 case HOST_NOT_FOUND:
284 /* keep trying */
285 break;
286 case TRY_AGAIN:
287 if (hp->rcode == SERVFAIL) {
288 /* try next search element, if any */
289 got_servfail++;
290 break;
291 }
292 [[fallthrough]];
293 default:
294 /* anything else implies that we're done */
295 done++;
296 }
297 }
298 }
299
300 // if we have not already tried the name "as is", do that now.
301 // note that we do this regardless of how many dots were in the
302 // name or whether it ends with a dot.
303 if (!tried_as_is && !root_on_list) {
304 ret = res_nquerydomain(statp, name, NULL, cl, type, answer, anslen, herrno);
305 if (ret > 0) return ret;
306 }
307
308 /* if we got here, we didn't satisfy the search.
309 * if we did an initial full query, return that query's H_ERRNO
310 * (note that we wouldn't be here if that query had succeeded).
311 * else if we ever got a nodata, send that back as the reason.
312 * else send back meaningless H_ERRNO, that being the one from
313 * the last DNSRCH we did.
314 */
315 if (saved_herrno != -1)
316 *herrno = saved_herrno;
317 else if (got_nodata)
318 *herrno = NO_DATA;
319 else if (got_servfail)
320 *herrno = TRY_AGAIN;
321 return -1;
322 }
323
324 /*
325 * Perform a call on res_query on the concatenation of name and domain,
326 * removing a trailing dot from name if domain is NULL.
327 */
res_nquerydomain(res_state statp,const char * name,const char * domain,int cl,int type,uint8_t * answer,int anslen,int * herrno)328 int res_nquerydomain(res_state statp, const char* name, const char* domain, int cl,
329 int type, /* class and type of query */
330 uint8_t* answer, /* buffer to put answer */
331 int anslen, /* size of answer */
332 int* herrno) /* legacy and extended h_errno NETD_RESOLV_H_ERRNO_EXT_* */
333 {
334 char nbuf[MAXDNAME];
335 const char* longname = nbuf;
336 int n, d;
337
338 if (domain == NULL) {
339 LOG(DEBUG) << __func__ << ": (null, " << cl << ", " << type << ")";
340 /*
341 * Check for trailing '.';
342 * copy without '.' if present.
343 */
344 n = strlen(name);
345 if (n >= MAXDNAME) {
346 *herrno = NO_RECOVERY;
347 return -1;
348 }
349 n--;
350 if (n >= 0 && name[n] == '.') {
351 strncpy(nbuf, name, (size_t) n);
352 nbuf[n] = '\0';
353 } else
354 longname = name;
355 } else {
356 LOG(DEBUG) << __func__ << ": (" << cl << ", " << type << ")";
357 n = strlen(name);
358 d = strlen(domain);
359 if (n + d + 1 >= MAXDNAME) {
360 *herrno = NO_RECOVERY;
361 return -1;
362 }
363 snprintf(nbuf, sizeof(nbuf), "%s.%s", name, domain);
364 }
365 return res_nquery(statp, longname, cl, type, answer, anslen, herrno);
366 }
367