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