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 <time.h>
  19 #include <stdio.h>
  20 #include <unistd.h>
  21 #include <sys/types.h>
  22 #include <sys/socket.h>
  23 #include <netinet/in.h>
  24 #include <arpa/inet.h>
  25 #include <arpa/nameser.h>
  26 #include <resolv.h>
  27 #include <stdlib.h>
  28 #include <string.h>
  29
  30 #include <libubox/uloop.h>
  31 #include <libubox/usock.h>
  32 #include <libubox/utils.h>
  33
  34 #include "announce.h"
  35 #include "util.h"
  36 #include "dns.h"
  37 #include "cache.h"
  38 #include "service.h"
  39 #include "interface.h"
  40
  41 static char name_buffer[MAX_NAME_LEN + 1];
  42 static char dns_buffer[MAX_NAME_LEN];
  43 static struct blob_buf ans_buf;
  44
  45 const char*
  46 dns_type_string(uint16_t type)
  47 {
  48         static const struct {
  49                 uint16_t type;
  50                 char str[5];
  51         } type_str[] = {
  52                 { TYPE_A, "A" },
  53                 { TYPE_AAAA, "AAAA" },
  54                 { TYPE_PTR, "PTR" },
  55                 { TYPE_TXT, "TXT" },
  56                 { TYPE_SRV, "SRV" },
  57                 { TYPE_ANY, "ANY" },
  58         };
  59         int i;
  60
  61         for (i = 0; i < ARRAY_SIZE(type_str); i++) {
  62                 if (type == type_str[i].type)
  63                         return type_str[i].str;
  64         }
  65
  66         return "N/A";
  67 }
  68
  69 void
  70 dns_send_question(struct interface *iface, const char *question, int type, int multicast)
  71 {
  72         static struct dns_header h;
  73         static struct dns_question q;
  74         static struct iovec iov[] = {
  75                 {
  76                         .iov_base = &h,
  77                         .iov_len = sizeof(h),
  78                 },
  79                 {
  80                         .iov_base = dns_buffer,
  81                 },
  82                 {
  83                         .iov_base = &q,
  84                         .iov_len = sizeof(q),
  85                 }
  86         };
  87         int len;
  88
  89         h.questions = cpu_to_be16(1);
  90         q.class = cpu_to_be16((multicast ? 0 : CLASS_UNICAST) | 1);
  91         q.type = cpu_to_be16(type);
  92
  93         len = dn_comp(question, (void *) dns_buffer, sizeof(dns_buffer), NULL, NULL);
  94         if (len < 1)
  95                 return;
  96
  97         iov[1].iov_len = len;
  98
  99         DBG(1, "Q <- %s %s\n", dns_type_string(type), question);
 100         if (interface_send_packet(iface, iov, ARRAY_SIZE(iov)) < 0)
 101                 perror("failed to send question :");
 102 }
 103
 104
 105 struct dns_reply {
 106         int type;
 107         struct dns_answer a;
 108         uint16_t rdlength;
 109         uint8_t *rdata;
 110         char *buffer;
 111 };
 112
 113 static int dns_answer_cnt;
 114
 115 void
 116 dns_init_answer(void)
 117 {
 118         dns_answer_cnt = 0;
 119         blob_buf_init(&ans_buf, 0);
 120 }
 121
 122 void
 123 dns_add_answer(int type, const uint8_t *rdata, uint16_t rdlength, int ttl)
 124 {
 125         struct blob_attr *attr;
 126         struct dns_answer *a;
 127
 128         attr = blob_new(&ans_buf, 0, sizeof(*a) + rdlength);
 129         a = blob_data(attr);
 130         a->type = cpu_to_be16(type);
 131         a->class = cpu_to_be16(1);
 132         a->ttl = cpu_to_be32(ttl);
 133         a->rdlength = cpu_to_be16(rdlength);
 134         memcpy(a + 1, rdata, rdlength);
 135
 136         dns_answer_cnt++;
 137 }
 138
 139 void
 140 dns_send_answer(struct interface *iface, const char *answer)
 141 {
 142         uint8_t buffer[256];
 143         struct blob_attr *attr;
 144         struct dns_header h = { 0 };
 145         struct iovec *iov;
 146         int answer_len, rem;
 147         int n_iov = 0;
 148
 149         if (!dns_answer_cnt)
 150                 return;
 151
 152         h.answers = cpu_to_be16(dns_answer_cnt);
 153         h.flags = cpu_to_be16(0x8400);
 154
 155         iov = alloca(sizeof(struct iovec) * ((dns_answer_cnt * 2) + 1));
 156
 157         iov[n_iov].iov_base = &h;
 158         iov[n_iov].iov_len = sizeof(struct dns_header);
 159         n_iov++;
 160
 161         answer_len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
 162         if (answer_len < 1)
 163                 return;
 164
 165         blob_for_each_attr(attr, ans_buf.head, rem) {
 166                 struct dns_answer *a = blob_data(attr);
 167
 168                 iov[n_iov].iov_base = buffer;
 169                 iov[n_iov].iov_len = answer_len;
 170                 n_iov++;
 171
 172                 iov[n_iov].iov_base = blob_data(attr);
 173                 iov[n_iov].iov_len = blob_len(attr);
 174                 n_iov++;
 175
 176                 DBG(1, "A <- %s %s\n", dns_type_string(be16_to_cpu(a->type)), answer);
 177         }
 178
 179         if (interface_send_packet(iface, iov, n_iov) < 0)
 180                 fprintf(stderr, "failed to send question\n");
 181 }
 182
 183 static int
 184 scan_name(const uint8_t *buffer, int len)
 185 {
 186         int offset = 0;
 187
 188         while (len && (*buffer != '\0')) {
 189                 int l = *buffer;
 190
 191                 if (IS_COMPRESSED(l))
 192                         return offset + 2;
 193
 194                 len -= l + 1;
 195                 offset += l + 1;
 196                 buffer += l + 1;
 197         }
 198
 199         if (!len || !offset || (*buffer != '\0'))
 200                 return -1;
 201
 202         return offset + 1;
 203 }
 204
 205 static struct dns_header*
 206 dns_consume_header(uint8_t **data, int *len)
 207 {
 208         struct dns_header *h = (struct dns_header *) *data;
 209         uint16_t *swap = (uint16_t *) h;
 210         int endianess = 6;
 211
 212         if (*len < sizeof(struct dns_header))
 213                 return NULL;
 214
 215         while (endianess--) {
 216                 *swap = be16_to_cpu(*swap);
 217                 swap++;
 218         }
 219
 220         *len -= sizeof(struct dns_header);
 221         *data += sizeof(struct dns_header);
 222
 223         return h;
 224 }
 225
 226 static struct dns_question*
 227 dns_consume_question(uint8_t **data, int *len)
 228 {
 229         struct dns_question *q = (struct dns_question *) *data;
 230         uint16_t *swap = (uint16_t *) q;
 231         int endianess = 2;
 232
 233         if (*len < sizeof(struct dns_question))
 234                 return NULL;
 235
 236         while (endianess--) {
 237                 *swap = be16_to_cpu(*swap);
 238                 swap++;
 239         }
 240
 241         *len -= sizeof(struct dns_question);
 242         *data += sizeof(struct dns_question);
 243
 244         return q;
 245 }
 246
 247 static struct dns_answer*
 248 dns_consume_answer(uint8_t **data, int *len)
 249 {
 250         struct dns_answer *a = (struct dns_answer *) *data;
 251
 252         if (*len < sizeof(struct dns_answer))
 253                 return NULL;
 254
 255         a->type = be16_to_cpu(a->type);
 256         a->class = be16_to_cpu(a->class);
 257         a->ttl = be32_to_cpu(a->ttl);
 258         a->rdlength = be16_to_cpu(a->rdlength);
 259
 260         *len -= sizeof(struct dns_answer);
 261         *data += sizeof(struct dns_answer);
 262
 263         return a;
 264 }
 265
 266 static char *
 267 dns_consume_name(const uint8_t *base, int blen, uint8_t **data, int *len)
 268 {
 269         int nlen = scan_name(*data, *len);
 270
 271         if (nlen < 1)
 272                 return NULL;
 273
 274         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 275                 perror("dns_consume_name/dn_expand");
 276                 return NULL;
 277         }
 278
 279         *len -= nlen;
 280         *data += nlen;
 281
 282         return name_buffer;
 283 }
 284
 285 static int
 286 parse_answer(struct interface *iface, uint8_t *buffer, int len, uint8_t **b, int *rlen, int cache)
 287 {
 288         char *name = dns_consume_name(buffer, len, b, rlen);
 289         struct dns_answer *a;
 290         uint8_t *rdata;
 291
 292         if (!name) {
 293                 fprintf(stderr, "dropping: bad question\n");
 294                 return -1;
 295         }
 296
 297         a = dns_consume_answer(b, rlen);
 298         if (!a) {
 299                 fprintf(stderr, "dropping: bad question\n");
 300                 return -1;
 301         }
 302
 303         if ((a->class & ~CLASS_FLUSH) != CLASS_IN)
 304                 return -1;
 305
 306         rdata = *b;
 307         if (a->rdlength > *rlen) {
 308                 fprintf(stderr, "dropping: bad question\n");
 309                 return -1;
 310         }
 311
 312         *rlen -= a->rdlength;
 313         *b += a->rdlength;
 314
 315         if (cache)
 316                 cache_answer(iface, buffer, len, name, a, rdata, a->class & CLASS_FLUSH);
 317
 318         return 0;
 319 }
 320
 321 static void
 322 parse_question(struct interface *iface, char *name, struct dns_question *q)
 323 {
 324         char *host;
 325
 326         if ((q->class & CLASS_UNICAST) && iface->multicast)
 327                 iface = iface->peer;
 328
 329         DBG(1, "Q -> %s %s\n", dns_type_string(q->type), name);
 330
 331         switch (q->type) {
 332         case TYPE_ANY:
 333                 if (!strcmp(name, mdns_hostname_local))
 334                         service_reply(iface, NULL, announce_ttl);
 335                 break;
 336
 337         case TYPE_PTR:
 338                 service_announce_services(iface, name, announce_ttl);
 339                 service_reply(iface, name, announce_ttl);
 340                 break;
 341
 342         case TYPE_AAAA:
 343         case TYPE_A:
 344                 host = strstr(name, ".local");
 345                 if (host)
 346                         *host = '\0';
 347                 if (!strcmp(mdns_hostname, name))
 348                         service_reply_a(iface, announce_ttl);
 349                 break;
 350         };
 351 }
 352
 353 void
 354 dns_handle_packet(struct interface *iface, struct sockaddr *s, uint16_t port, uint8_t *buffer, int len)
 355 {
 356         struct dns_header *h;
 357         uint8_t *b = buffer;
 358         int rlen = len;
 359
 360         h = dns_consume_header(&b, &rlen);
 361         if (!h) {
 362                 fprintf(stderr, "dropping: bad header\n");
 363                 return;
 364         }
 365
 366         if (h->questions && !iface->multicast && port != 5353)
 367                 // silently drop unicast questions that dont originate from port 5353
 368                 return;
 369
 370         while (h->questions-- > 0) {
 371                 char *name = dns_consume_name(buffer, len, &b, &rlen);
 372                 struct dns_question *q;
 373
 374                 if (!name) {
 375                         fprintf(stderr, "dropping: bad name\n");
 376                         return;
 377                 }
 378
 379                 q = dns_consume_question(&b, &rlen);
 380                 if (!q) {
 381                         fprintf(stderr, "dropping: bad question\n");
 382                         return;
 383                 }
 384
 385                 if (!(h->flags & FLAG_RESPONSE))
 386                         parse_question(iface, name, q);
 387         }
 388
 389         if (!(h->flags & FLAG_RESPONSE))
 390                 return;
 391
 392         while (h->answers-- > 0)
 393                 if (parse_answer(iface, buffer, len, &b, &rlen, 1))
 394                         return;
 395
 396         while (h->authority-- > 0)
 397                 if (parse_answer(iface, buffer, len, &b, &rlen, 1))
 398                         return;
 399
 400         while (h->additional-- > 0)
 401                 if (parse_answer(iface, buffer, len, &b, &rlen, 1))
 402                         return;
 403
 404 }