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, const char *hostname)
 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                         sa6 = (struct sockaddr_in6 *) ifa->ifa_addr;
 204                         dns_add_answer(TYPE_AAAA, (uint8_t *) &sa6->sin6_addr, 16, ttl);
 205                 }
 206         }
 207         dns_send_answer(iface, to, hostname ? hostname : mdns_hostname_local);
 208
 209         freeifaddrs(ifap);
 210 }
 211
 212 void
 213 dns_reply_a_additional(struct interface *iface, struct sockaddr *to, int ttl)
 214 {
 215         struct hostname *h;
 216
 217         vlist_for_each_element(&hostnames, h, node)
 218                 dns_reply_a(iface, to, ttl, h->hostname);
 219 }
 220
 221 static int
 222 scan_name(const uint8_t *buffer, int len)
 223 {
 224         int offset = 0;
 225
 226         while (len && (*buffer != '\0')) {
 227                 int l = *buffer;
 228
 229                 if (IS_COMPRESSED(l))
 230                         return offset + 2;
 231
 232                 if (l + 1 > len) return -1;
 233                 len -= l + 1;
 234                 offset += l + 1;
 235                 buffer += l + 1;
 236         }
 237
 238         if (!len || !offset || (*buffer != '\0'))
 239                 return -1;
 240
 241         return offset + 1;
 242 }
 243
 244 static struct dns_header*
 245 dns_consume_header(uint8_t **data, int *len)
 246 {
 247         struct dns_header *h = (struct dns_header *) *data;
 248
 249         if (*len < sizeof(struct dns_header))
 250                 return NULL;
 251
 252         h->id = be16_to_cpu(h->id);
 253         h->flags = be16_to_cpu(h->flags);
 254         h->questions = be16_to_cpu(h->questions);
 255         h->answers = be16_to_cpu(h->answers);
 256         h->authority = be16_to_cpu(h->authority);
 257         h->additional = be16_to_cpu(h->additional);
 258
 259         *len -= sizeof(struct dns_header);
 260         *data += sizeof(struct dns_header);
 261
 262         return h;
 263 }
 264
 265 static struct dns_question*
 266 dns_consume_question(uint8_t **data, int *len)
 267 {
 268         struct dns_question *q = (struct dns_question *) *data;
 269
 270         if (*len < sizeof(struct dns_question))
 271                 return NULL;
 272
 273         q->type = be16_to_cpu(q->type);
 274         q->class = be16_to_cpu(q->class);
 275
 276         *len -= sizeof(struct dns_question);
 277         *data += sizeof(struct dns_question);
 278
 279         return q;
 280 }
 281
 282 static struct dns_answer*
 283 dns_consume_answer(uint8_t **data, int *len)
 284 {
 285         struct dns_answer *a = (struct dns_answer *) *data;
 286
 287         if (*len < sizeof(struct dns_answer))
 288                 return NULL;
 289
 290         a->type = be16_to_cpu(a->type);
 291         a->class = be16_to_cpu(a->class);
 292         a->ttl = be32_to_cpu(a->ttl);
 293         a->rdlength = be16_to_cpu(a->rdlength);
 294
 295         *len -= sizeof(struct dns_answer);
 296         *data += sizeof(struct dns_answer);
 297
 298         return a;
 299 }
 300
 301 static char *
 302 dns_consume_name(const uint8_t *base, int blen, uint8_t **data, int *len)
 303 {
 304         int nlen = scan_name(*data, *len);
 305
 306         if (nlen < 1)
 307                 return NULL;
 308
 309         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 310                 perror("dns_consume_name/dn_expand");
 311                 return NULL;
 312         }
 313
 314         *len -= nlen;
 315         *data += nlen;
 316
 317         return name_buffer;
 318 }
 319
 320 static int parse_answer(struct interface *iface, struct sockaddr *from,
 321                         uint8_t *buffer, int len, uint8_t **b, int *rlen,
 322                         int cache)
 323 {
 324         char *name = dns_consume_name(buffer, len, b, rlen);
 325         struct dns_answer *a;
 326         uint8_t *rdata;
 327
 328         if (!name || *rlen < 0) {
 329                 fprintf(stderr, "dropping: bad question\n");
 330                 return -1;
 331         }
 332
 333         a = dns_consume_answer(b, rlen);
 334         if (!a) {
 335                 fprintf(stderr, "dropping: bad question\n");
 336                 return -1;
 337         }
 338
 339         if ((a->class & ~CLASS_FLUSH) != CLASS_IN)
 340                 return -1;
 341
 342         rdata = *b;
 343         if (a->rdlength > *rlen) {
 344                 fprintf(stderr, "dropping: bad question\n");
 345                 return -1;
 346         }
 347
 348         *rlen -= a->rdlength;
 349         *b += a->rdlength;
 350
 351         if (cache)
 352                 cache_answer(iface, from, buffer, len, name, a, rdata, a->class & CLASS_FLUSH);
 353
 354         return 0;
 355 }
 356
 357 static void
 358 parse_question(struct interface *iface, struct sockaddr *from, char *name, struct dns_question *q)
 359 {
 360         struct sockaddr *to = NULL;
 361         char *host;
 362
 363         /* TODO: Multicast if more than one quarter of TTL has passed */
 364         if (q->class & CLASS_UNICAST) {
 365                 to = from;
 366                 if (interface_multicast(iface))
 367                         iface = interface_get(iface->name, iface->type | SOCKTYPE_BIT_UNICAST);
 368         }
 369
 370         DBG(1, "Q -> %s %s\n", dns_type_string(q->type), name);
 371
 372         switch (q->type) {
 373         case TYPE_ANY:
 374                 if (!strcmp(name, mdns_hostname_local)) {
 375                         dns_reply_a(iface, to, announce_ttl, NULL);
 376                         dns_reply_a_additional(iface, to, announce_ttl);
 377                         service_reply(iface, to, NULL, NULL, announce_ttl);
 378                 }
 379                 break;
 380
 381         case TYPE_PTR:
 382                 if (!strcmp(name, C_DNS_SD)) {
 383                         dns_reply_a(iface, to, announce_ttl, NULL);
 384                         dns_reply_a_additional(iface, to, announce_ttl);
 385                         service_announce_services(iface, to, announce_ttl);
 386                 } else {
 387                         if (name[0] == '_') {
 388                                 service_reply(iface, to, NULL, name, announce_ttl);
 389                         } else {
 390                                 /* First dot separates instance name from the rest */
 391                                 char *dot = strchr(name, '.');
 392
 393                                 if (dot) {
 394                                         *dot = '\0';
 395                                         service_reply(iface, to, name, dot + 1, announce_ttl);
 396                                         *dot = '.';
 397                                 }
 398                         }
 399                 }
 400                 break;
 401
 402         case TYPE_AAAA:
 403         case TYPE_A:
 404                 host = strstr(name, ".local");
 405                 if (host)
 406                         *host = '\0';
 407                 if (!strcmp(umdns_host_label, name))
 408                         dns_reply_a(iface, to, announce_ttl, NULL);
 409                 break;
 410         };
 411 }
 412
 413 void
 414 dns_handle_packet(struct interface *iface, struct sockaddr *from, uint16_t port, uint8_t *buffer, int len)
 415 {
 416         struct dns_header *h;
 417         uint8_t *b = buffer;
 418         int rlen = len;
 419
 420         h = dns_consume_header(&b, &rlen);
 421         if (!h) {
 422                 fprintf(stderr, "dropping: bad header\n");
 423                 return;
 424         }
 425
 426         if (h->questions && !interface_multicast(iface) && port != MCAST_PORT)
 427                 /* silently drop unicast questions that dont originate from port 5353 */
 428                 return;
 429
 430         while (h->questions-- > 0) {
 431                 char *name = dns_consume_name(buffer, len, &b, &rlen);
 432                 struct dns_question *q;
 433
 434                 if (!name || rlen < 0) {
 435                         fprintf(stderr, "dropping: bad name\n");
 436                         return;
 437                 }
 438
 439                 q = dns_consume_question(&b, &rlen);
 440                 if (!q) {
 441                         fprintf(stderr, "dropping: bad question\n");
 442                         return;
 443                 }
 444
 445                 if (!(h->flags & FLAG_RESPONSE))
 446                         parse_question(iface, from, name, q);
 447         }
 448
 449         if (!(h->flags & FLAG_RESPONSE))
 450                 return;
 451
 452         while (h->answers-- > 0)
 453                 if (parse_answer(iface, from, buffer, len, &b, &rlen, 1))
 454                         return;
 455
 456         while (h->authority-- > 0)
 457                 if (parse_answer(iface, from, buffer, len, &b, &rlen, 1))
 458                         return;
 459
 460         while (h->additional-- > 0)
 461                 if (parse_answer(iface, from, buffer, len, &b, &rlen, 1))
 462                         return;
 463
 464 }