86e5ea3aaa6c7f44cc4d52d4082b8ec9580046e0
[project/mdnsd.git] / dns.c
1 /*
2 * Copyright (C) 2014 John Crispin <blogic@openwrt.org>
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU Lesser General Public License version 2.1
6 * as published by the Free Software Foundation
7 *
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11 * GNU General Public License for more details.
12 */
13
14 #include <sys/types.h>
15 #include <sys/stat.h>
16
17 #include <fcntl.h>
18 #include <ifaddrs.h>
19 #include <time.h>
20 #include <stdio.h>
21 #include <unistd.h>
22 #include <sys/types.h>
23 #include <sys/socket.h>
24 #include <netinet/in.h>
25 #include <arpa/inet.h>
26 #include <arpa/nameser.h>
27 #include <resolv.h>
28 #include <stdlib.h>
29 #include <string.h>
30
31 #include <libubox/uloop.h>
32 #include <libubox/usock.h>
33 #include <libubox/utils.h>
34
35 #include "announce.h"
36 #include "util.h"
37 #include "dns.h"
38 #include "cache.h"
39 #include "service.h"
40 #include "interface.h"
41
42 static char name_buffer[MAX_NAME_LEN + 1];
43 static char dns_buffer[MAX_NAME_LEN];
44 static struct blob_buf ans_buf;
45
46 const char*
47 dns_type_string(uint16_t type)
48 {
49 static const struct {
50 uint16_t type;
51 char str[5];
52 } type_str[] = {
53 { TYPE_A, "A" },
54 { TYPE_AAAA, "AAAA" },
55 { TYPE_PTR, "PTR" },
56 { TYPE_TXT, "TXT" },
57 { TYPE_SRV, "SRV" },
58 { TYPE_ANY, "ANY" },
59 };
60 int i;
61
62 for (i = 0; i < ARRAY_SIZE(type_str); i++) {
63 if (type == type_str[i].type)
64 return type_str[i].str;
65 }
66
67 return "N/A";
68 }
69
70 void
71 dns_send_question(struct interface *iface, struct sockaddr *to,
72 const char *question, int type, int multicast)
73 {
74 static struct dns_header h;
75 static struct dns_question q;
76 static struct iovec iov[] = {
77 {
78 .iov_base = &h,
79 .iov_len = sizeof(h),
80 },
81 {
82 .iov_base = dns_buffer,
83 },
84 {
85 .iov_base = &q,
86 .iov_len = sizeof(q),
87 }
88 };
89 int len;
90
91 h.questions = cpu_to_be16(1);
92 q.class = cpu_to_be16((multicast ? 0 : CLASS_UNICAST) | 1);
93 q.type = cpu_to_be16(type);
94
95 len = dn_comp(question, (void *) dns_buffer, sizeof(dns_buffer), NULL, NULL);
96 if (len < 1)
97 return;
98
99 iov[1].iov_len = len;
100
101 DBG(1, "Q <- %s %s\n", dns_type_string(type), question);
102 if (interface_send_packet(iface, to, iov, ARRAY_SIZE(iov)) < 0)
103 perror("failed to send question");
104 }
105
106
107 struct dns_reply {
108 int type;
109 struct dns_answer a;
110 uint16_t rdlength;
111 uint8_t *rdata;
112 char *buffer;
113 };
114
115 static int dns_answer_cnt;
116
117 void
118 dns_init_answer(void)
119 {
120 dns_answer_cnt = 0;
121 blob_buf_init(&ans_buf, 0);
122 }
123
124 void
125 dns_add_answer(int type, const uint8_t *rdata, uint16_t rdlength, int ttl)
126 {
127 struct blob_attr *attr;
128 struct dns_answer *a;
129
130 attr = blob_new(&ans_buf, 0, sizeof(*a) + rdlength);
131 a = blob_data(attr);
132 a->type = cpu_to_be16(type);
133 a->class = cpu_to_be16(1);
134 a->ttl = cpu_to_be32(ttl);
135 a->rdlength = cpu_to_be16(rdlength);
136 memcpy(a + 1, rdata, rdlength);
137
138 dns_answer_cnt++;
139 }
140
141 void
142 dns_send_answer(struct interface *iface, struct sockaddr *to, const char *answer)
143 {
144 uint8_t buffer[256];
145 struct blob_attr *attr;
146 struct dns_header h = { 0 };
147 struct iovec *iov;
148 int answer_len, rem;
149 int n_iov = 0;
150
151 if (!dns_answer_cnt)
152 return;
153
154 h.answers = cpu_to_be16(dns_answer_cnt);
155 h.flags = cpu_to_be16(0x8400);
156
157 iov = alloca(sizeof(struct iovec) * ((dns_answer_cnt * 2) + 1));
158
159 iov[n_iov].iov_base = &h;
160 iov[n_iov].iov_len = sizeof(struct dns_header);
161 n_iov++;
162
163 answer_len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
164 if (answer_len < 1)
165 return;
166
167 blob_for_each_attr(attr, ans_buf.head, rem) {
168 struct dns_answer *a = blob_data(attr);
169
170 iov[n_iov].iov_base = buffer;
171 iov[n_iov].iov_len = answer_len;
172 n_iov++;
173
174 iov[n_iov].iov_base = blob_data(attr);
175 iov[n_iov].iov_len = blob_len(attr);
176 n_iov++;
177
178 DBG(1, "A <- %s %s\n", dns_type_string(be16_to_cpu(a->type)), answer);
179 }
180
181 if (interface_send_packet(iface, to, iov, n_iov) < 0)
182 perror("failed to send answer");
183 }
184
185 void
186 dns_reply_a(struct interface *iface, struct sockaddr *to, int ttl)
187 {
188 struct ifaddrs *ifap, *ifa;
189 struct sockaddr_in *sa;
190 struct sockaddr_in6 *sa6;
191
192 getifaddrs(&ifap);
193
194 dns_init_answer();
195 for (ifa = ifap; ifa; ifa = ifa->ifa_next) {
196 if (strcmp(ifa->ifa_name, iface->name))
197 continue;
198 if (ifa->ifa_addr->sa_family == AF_INET) {
199 sa = (struct sockaddr_in *) ifa->ifa_addr;
200 dns_add_answer(TYPE_A, (uint8_t *) &sa->sin_addr, 4, ttl);
201 }
202 if (ifa->ifa_addr->sa_family == AF_INET6) {
203 uint8_t ll_prefix[] = {0xfe, 0x80 };
204 sa6 = (struct sockaddr_in6 *) ifa->ifa_addr;
205 if (!memcmp(&sa6->sin6_addr, &ll_prefix, 2))
206 dns_add_answer(TYPE_AAAA, (uint8_t *) &sa6->sin6_addr, 16, ttl);
207 }
208 }
209 dns_send_answer(iface, to, mdns_hostname_local);
210
211 freeifaddrs(ifap);
212 }
213
214 static int
215 scan_name(const uint8_t *buffer, int len)
216 {
217 int offset = 0;
218
219 while (len && (*buffer != '\0')) {
220 int l = *buffer;
221
222 if (IS_COMPRESSED(l))
223 return offset + 2;
224
225 len -= l + 1;
226 offset += l + 1;
227 buffer += l + 1;
228 }
229
230 if (!len || !offset || (*buffer != '\0'))
231 return -1;
232
233 return offset + 1;
234 }
235
236 static struct dns_header*
237 dns_consume_header(uint8_t **data, int *len)
238 {
239 struct dns_header *h = (struct dns_header *) *data;
240
241 if (*len < sizeof(struct dns_header))
242 return NULL;
243
244 h->id = be16_to_cpu(h->id);
245 h->flags = be16_to_cpu(h->flags);
246 h->questions = be16_to_cpu(h->questions);
247 h->answers = be16_to_cpu(h->answers);
248 h->authority = be16_to_cpu(h->authority);
249 h->additional = be16_to_cpu(h->additional);
250
251 *len -= sizeof(struct dns_header);
252 *data += sizeof(struct dns_header);
253
254 return h;
255 }
256
257 static struct dns_question*
258 dns_consume_question(uint8_t **data, int *len)
259 {
260 struct dns_question *q = (struct dns_question *) *data;
261
262 if (*len < sizeof(struct dns_question))
263 return NULL;
264
265 q->type = be16_to_cpu(q->type);
266 q->class = be16_to_cpu(q->class);
267
268 *len -= sizeof(struct dns_question);
269 *data += sizeof(struct dns_question);
270
271 return q;
272 }
273
274 static struct dns_answer*
275 dns_consume_answer(uint8_t **data, int *len)
276 {
277 struct dns_answer *a = (struct dns_answer *) *data;
278
279 if (*len < sizeof(struct dns_answer))
280 return NULL;
281
282 a->type = be16_to_cpu(a->type);
283 a->class = be16_to_cpu(a->class);
284 a->ttl = be32_to_cpu(a->ttl);
285 a->rdlength = be16_to_cpu(a->rdlength);
286
287 *len -= sizeof(struct dns_answer);
288 *data += sizeof(struct dns_answer);
289
290 return a;
291 }
292
293 static char *
294 dns_consume_name(const uint8_t *base, int blen, uint8_t **data, int *len)
295 {
296 int nlen = scan_name(*data, *len);
297
298 if (nlen < 1)
299 return NULL;
300
301 if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
302 perror("dns_consume_name/dn_expand");
303 return NULL;
304 }
305
306 *len -= nlen;
307 *data += nlen;
308
309 return name_buffer;
310 }
311
312 static int parse_answer(struct interface *iface, struct sockaddr *from,
313 uint8_t *buffer, int len, uint8_t **b, int *rlen,
314 int cache)
315 {
316 char *name = dns_consume_name(buffer, len, b, rlen);
317 struct dns_answer *a;
318 uint8_t *rdata;
319
320 if (!name) {
321 fprintf(stderr, "dropping: bad question\n");
322 return -1;
323 }
324
325 a = dns_consume_answer(b, rlen);
326 if (!a) {
327 fprintf(stderr, "dropping: bad question\n");
328 return -1;
329 }
330
331 if ((a->class & ~CLASS_FLUSH) != CLASS_IN)
332 return -1;
333
334 rdata = *b;
335 if (a->rdlength > *rlen) {
336 fprintf(stderr, "dropping: bad question\n");
337 return -1;
338 }
339
340 *rlen -= a->rdlength;
341 *b += a->rdlength;
342
343 if (cache)
344 cache_answer(iface, from, buffer, len, name, a, rdata, a->class & CLASS_FLUSH);
345
346 return 0;
347 }
348
349 static void
350 parse_question(struct interface *iface, struct sockaddr *from, char *name, struct dns_question *q)
351 {
352 struct sockaddr *to = NULL;
353 char *host;
354
355 /* TODO: Multicast if more than one quarter of TTL has passed */
356 if (q->class & CLASS_UNICAST) {
357 to = from;
358 if (iface->multicast)
359 iface = iface->peer;
360 }
361
362 DBG(1, "Q -> %s %s\n", dns_type_string(q->type), name);
363
364 switch (q->type) {
365 case TYPE_ANY:
366 if (!strcmp(name, mdns_hostname_local)) {
367 dns_reply_a(iface, to, announce_ttl);
368 service_reply(iface, to, NULL, NULL, announce_ttl);
369 }
370 break;
371
372 case TYPE_PTR:
373 if (!strcmp(name, C_DNS_SD)) {
374 dns_reply_a(iface, to, announce_ttl);
375 service_announce_services(iface, to, announce_ttl);
376 } else {
377 if (name[0] == '_') {
378 service_reply(iface, to, NULL, name, announce_ttl);
379 } else {
380 /* First dot separates instance name from the rest */
381 char *dot = strchr(name, '.');
382
383 if (dot) {
384 *dot = '\0';
385 service_reply(iface, to, name, dot + 1, announce_ttl);
386 *dot = '.';
387 }
388 }
389 }
390 break;
391
392 case TYPE_AAAA:
393 case TYPE_A:
394 host = strstr(name, ".local");
395 if (host)
396 *host = '\0';
397 if (!strcmp(umdns_host_label, name))
398 dns_reply_a(iface, to, announce_ttl);
399 break;
400 };
401 }
402
403 void
404 dns_handle_packet(struct interface *iface, struct sockaddr *from, uint16_t port, uint8_t *buffer, int len)
405 {
406 struct dns_header *h;
407 uint8_t *b = buffer;
408 int rlen = len;
409
410 h = dns_consume_header(&b, &rlen);
411 if (!h) {
412 fprintf(stderr, "dropping: bad header\n");
413 return;
414 }
415
416 if (h->questions && !iface->multicast && port != MCAST_PORT)
417 /* silently drop unicast questions that dont originate from port 5353 */
418 return;
419
420 while (h->questions-- > 0) {
421 char *name = dns_consume_name(buffer, len, &b, &rlen);
422 struct dns_question *q;
423
424 if (!name) {
425 fprintf(stderr, "dropping: bad name\n");
426 return;
427 }
428
429 q = dns_consume_question(&b, &rlen);
430 if (!q) {
431 fprintf(stderr, "dropping: bad question\n");
432 return;
433 }
434
435 if (!(h->flags & FLAG_RESPONSE))
436 parse_question(iface, from, name, q);
437 }
438
439 if (!(h->flags & FLAG_RESPONSE))
440 return;
441
442 while (h->answers-- > 0)
443 if (parse_answer(iface, from, buffer, len, &b, &rlen, 1))
444 return;
445
446 while (h->authority-- > 0)
447 if (parse_answer(iface, from, buffer, len, &b, &rlen, 1))
448 return;
449
450 while (h->additional-- > 0)
451 if (parse_answer(iface, from, buffer, len, &b, &rlen, 1))
452 return;
453
454 }