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 <asm/byteorder.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
  44 const char*
  45 dns_type_string(uint16_t type)
  46 {
  47         static const struct {
  48                 uint16_t type;
  49                 char str[5];
  50         } type_str[] = {
  51                 { TYPE_A, "A" },
  52                 { TYPE_AAAA, "AAAA" },
  53                 { TYPE_PTR, "PTR" },
  54                 { TYPE_TXT, "TXT" },
  55                 { TYPE_SRV, "SRV" },
  56                 { TYPE_ANY, "ANY" },
  57         };
  58         int i;
  59
  60         for (i = 0; i < ARRAY_SIZE(type_str); i++) {
  61                 if (type == type_str[i].type)
  62                         return type_str[i].str;
  63         }
  64
  65         return "N/A";
  66 }
  67
  68 void
  69 dns_send_question(struct interface *iface, const char *question, int type)
  70 {
  71         static struct dns_header h = {
  72                 .questions = cpu_to_be16(1),
  73         };
  74         static struct dns_question q = {
  75                 .class = cpu_to_be16(1),
  76         };
  77         static struct iovec iov[] = {
  78                 {
  79                         .iov_base = &h,
  80                         .iov_len = sizeof(h),
  81                 },
  82                 {
  83                         .iov_base = name_buffer,
  84                 },
  85                 {
  86                         .iov_base = &q,
  87                         .iov_len = sizeof(q),
  88                 }
  89         };
  90         int len;
  91
  92         q.type = __cpu_to_be16(type);
  93
  94         len = dn_comp(question, (void *) name_buffer, sizeof(name_buffer), NULL, NULL);
  95         if (len < 1)
  96                 return;
  97
  98         iov[1].iov_len = len;
  99
 100         if (interface_send_packet(iface, iov, ARRAY_SIZE(iov)) < 0)
 101                 fprintf(stderr, "failed to send question\n");
 102         else
 103                 DBG(1, "Q <- %s %s\n", dns_type_string(type), 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 #define MAX_ANSWER      8
 116 static struct dns_reply dns_reply[1 + (MAX_ANSWER * 3)];
 117 static int dns_answer_cnt;
 118
 119 void
 120 dns_init_answer(void)
 121 {
 122         dns_answer_cnt = 0;
 123 }
 124
 125 void
 126 dns_add_answer(int type, const uint8_t *rdata, uint16_t rdlength)
 127 {
 128         struct dns_reply *a = &dns_reply[dns_answer_cnt];
 129         if (dns_answer_cnt == MAX_ANSWER)
 130                 return;
 131         a->rdata = memdup(rdata, rdlength);
 132         a->type = type;
 133         a->rdlength = rdlength;
 134         dns_answer_cnt++;
 135 }
 136
 137 void
 138 dns_send_answer(struct interface *iface, const char *answer)
 139 {
 140         uint8_t buffer[256];
 141         struct dns_header h = { 0 };
 142         struct iovec *iov;
 143         int len, i;
 144
 145         if (!dns_answer_cnt)
 146                 return;
 147
 148         h.answers = __cpu_to_be16(dns_answer_cnt);
 149         h.flags = __cpu_to_be16(0x8400);
 150
 151         iov = alloca(sizeof(struct iovec) * ((dns_answer_cnt * 3) + 1));
 152         iov[0].iov_base = &h;
 153         iov[0].iov_len = sizeof(struct dns_header);
 154
 155         for (i = 0; i < dns_answer_cnt; i++) {
 156                 struct dns_answer *a = &dns_reply[i].a;
 157                 int id = (i * 3) + 1;
 158
 159                 memset(a, 0, sizeof(*a));
 160                 a->type = __cpu_to_be16(dns_reply[i].type);
 161                 a->class = __cpu_to_be16(1);
 162                 a->ttl = __cpu_to_be32(announce_ttl);
 163                 a->rdlength = __cpu_to_be16(dns_reply[i].rdlength);
 164
 165                 len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
 166                 if (len < 1)
 167                         return;
 168
 169                 dns_reply[i].buffer = iov[id].iov_base = memdup(buffer, len);
 170                 iov[id].iov_len = len;
 171
 172                 iov[id + 1].iov_base = a;
 173                 iov[id + 1].iov_len = sizeof(struct dns_answer);
 174
 175                 iov[id + 2].iov_base = dns_reply[i].rdata;
 176                 iov[id + 2].iov_len = dns_reply[i].rdlength;
 177
 178                 DBG(1, "A <- %s %s\n", dns_type_string(dns_reply[i].type), answer);
 179         }
 180
 181         if (interface_send_packet(iface, iov, (dns_answer_cnt * 3) + 1) < 0)
 182                 fprintf(stderr, "failed to send question\n");
 183
 184         for (i = 0; i < dns_answer_cnt; i++) {
 185                 free(dns_reply[i].buffer);
 186                 free(dns_reply[i].rdata);
 187         }
 188         dns_answer_cnt = 0;
 189 }
 190
 191 static int
 192 scan_name(const uint8_t *buffer, int len)
 193 {
 194         int offset = 0;
 195
 196         while (len && (*buffer != '\0')) {
 197                 int l = *buffer;
 198
 199                 if (IS_COMPRESSED(l))
 200                         return offset + 2;
 201
 202                 len -= l + 1;
 203                 offset += l + 1;
 204                 buffer += l + 1;
 205         }
 206
 207         if (!len || !offset || (*buffer != '\0'))
 208                 return -1;
 209
 210         return offset + 1;
 211 }
 212
 213 static struct dns_header*
 214 dns_consume_header(uint8_t **data, int *len)
 215 {
 216         struct dns_header *h = (struct dns_header *) *data;
 217         uint16_t *swap = (uint16_t *) h;
 218         int endianess = 6;
 219
 220         if (*len < sizeof(struct dns_header))
 221                 return NULL;
 222
 223         while (endianess--) {
 224                 *swap = __be16_to_cpu(*swap);
 225                 swap++;
 226         }
 227
 228         *len -= sizeof(struct dns_header);
 229         *data += sizeof(struct dns_header);
 230
 231         return h;
 232 }
 233
 234 static struct dns_question*
 235 dns_consume_question(uint8_t **data, int *len)
 236 {
 237         struct dns_question *q = (struct dns_question *) *data;
 238         uint16_t *swap = (uint16_t *) q;
 239         int endianess = 2;
 240
 241         if (*len < sizeof(struct dns_question))
 242                 return NULL;
 243
 244         while (endianess--) {
 245                 *swap = __be16_to_cpu(*swap);
 246                 swap++;
 247         }
 248
 249         *len -= sizeof(struct dns_question);
 250         *data += sizeof(struct dns_question);
 251
 252         return q;
 253 }
 254
 255 static struct dns_answer*
 256 dns_consume_answer(uint8_t **data, int *len)
 257 {
 258         struct dns_answer *a = (struct dns_answer *) *data;
 259
 260         if (*len < sizeof(struct dns_answer))
 261                 return NULL;
 262
 263         a->type = __be16_to_cpu(a->type);
 264         a->class = __be16_to_cpu(a->class);
 265         a->ttl = __be32_to_cpu(a->ttl);
 266         a->rdlength = __be16_to_cpu(a->rdlength);
 267
 268         *len -= sizeof(struct dns_answer);
 269         *data += sizeof(struct dns_answer);
 270
 271         return a;
 272 }
 273
 274 static char *
 275 dns_consume_name(const uint8_t *base, int blen, uint8_t **data, int *len)
 276 {
 277         int nlen = scan_name(*data, *len);
 278
 279         if (nlen < 1)
 280                 return NULL;
 281
 282         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 283                 perror("dns_consume_name/dn_expand");
 284                 return NULL;
 285         }
 286
 287         *len -= nlen;
 288         *data += nlen;
 289
 290         return name_buffer;
 291 }
 292
 293 static int
 294 parse_answer(struct interface *iface, uint8_t *buffer, int len, uint8_t **b, int *rlen, int cache)
 295 {
 296         char *name = dns_consume_name(buffer, len, b, rlen);
 297         struct dns_answer *a;
 298         uint8_t *rdata;
 299
 300         if (!name) {
 301                 fprintf(stderr, "dropping: bad question\n");
 302                 return -1;
 303         }
 304
 305         a = dns_consume_answer(b, rlen);
 306         if (!a) {
 307                 fprintf(stderr, "dropping: bad question\n");
 308                 return -1;
 309         }
 310
 311         rdata = *b;
 312         if (a->rdlength > *rlen) {
 313                 fprintf(stderr, "dropping: bad question\n");
 314                 return -1;
 315         }
 316
 317         *rlen -= a->rdlength;
 318         *b += a->rdlength;
 319
 320         if (cache)
 321                 cache_answer(iface, buffer, len, name, a, rdata);
 322
 323         return 0;
 324 }
 325
 326 static void
 327 parse_question(struct interface *iface, char *name, struct dns_question *q)
 328 {
 329         char *host;
 330
 331         DBG(1, "Q -> %s %s\n", dns_type_string(q->type), name);
 332
 333         switch (q->type) {
 334         case TYPE_ANY:
 335                 if (!strcmp(name, mdns_hostname_local))
 336                         service_reply(iface, NULL);
 337                 break;
 338
 339         case TYPE_PTR:
 340                 service_announce_services(iface, name);
 341                 service_reply(iface, name);
 342                 break;
 343
 344         case TYPE_AAAA:
 345         case TYPE_A:
 346                 host = strstr(name, ".local");
 347                 if (host)
 348                         *host = '\0';
 349                 if (!strcmp(mdns_hostname, name))
 350                         service_reply_a(iface, q->type);
 351                 break;
 352         };
 353 }
 354
 355 void
 356 dns_handle_packet(struct interface *iface, uint8_t *buffer, int len)
 357 {
 358         struct dns_header *h;
 359         uint8_t *b = buffer;
 360         int rlen = len;
 361
 362         h = dns_consume_header(&b, &rlen);
 363         if (!h) {
 364                 fprintf(stderr, "dropping: bad header\n");
 365                 return;
 366         }
 367
 368         while (h->questions-- > 0) {
 369                 char *name = dns_consume_name(buffer, len, &b, &rlen);
 370                 struct dns_question *q;
 371
 372                 if (!name) {
 373                         fprintf(stderr, "dropping: bad name\n");
 374                         return;
 375                 }
 376
 377                 q = dns_consume_question(&b, &rlen);
 378                 if (!q) {
 379                         fprintf(stderr, "dropping: bad question\n");
 380                         return;
 381                 }
 382
 383                 if (!(h->flags & FLAG_RESPONSE))
 384                         parse_question(iface, name, q);
 385         }
 386
 387         if (!(h->flags & FLAG_RESPONSE))
 388                 return;
 389
 390         while (h->answers-- > 0)
 391                 parse_answer(iface, buffer, len, &b, &rlen, 1);
 392
 393         while (h->authority-- > 0)
 394                 parse_answer(iface, buffer, len, &b, &rlen, 0);
 395
 396         while (h->additional-- > 0)
 397                 parse_answer(iface, buffer, len, &b, &rlen, 1);
 398 }