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         switch (type) {
  48         case TYPE_A:
  49                 return "A";
  50
  51         case TYPE_AAAA:
  52                 return "AAAA";
  53
  54         case TYPE_PTR:
  55                 return "PTR";
  56
  57         case TYPE_TXT:
  58                 return "TXT";
  59
  60         case TYPE_SRV:
  61                 return "SRV";
  62
  63         case TYPE_ANY:
  64                 return "ANY";
  65         }
  66
  67         return "N/A";
  68 }
  69
  70 void
  71 dns_send_question(struct interface *iface, const char *question, int type)
  72 {
  73         static struct dns_header h = {
  74                 .questions = cpu_to_be16(1),
  75         };
  76         static struct dns_question q = {
  77                 .class = cpu_to_be16(1),
  78         };
  79         static struct iovec iov[] = {
  80                 {
  81                         .iov_base = &h,
  82                         .iov_len = sizeof(h),
  83                 },
  84                 {
  85                         .iov_base = name_buffer,
  86                 },
  87                 {
  88                         .iov_base = &q,
  89                         .iov_len = sizeof(q),
  90                 }
  91         };
  92         int len;
  93
  94         q.type = __cpu_to_be16(type);
  95
  96         len = dn_comp(question, (void *) name_buffer, sizeof(name_buffer), NULL, NULL);
  97         if (len < 1)
  98                 return;
  99
 100         iov[1].iov_len = len;
 101
 102         if (interface_send_packet(iface, iov, ARRAY_SIZE(iov)) < 0)
 103                 fprintf(stderr, "failed to send question\n");
 104         else
 105                 DBG(1, "Q <- %s %s\n", dns_type_string(type), question);
 106 }
 107
 108
 109 struct dns_reply {
 110         int type;
 111         struct dns_answer a;
 112         uint16_t rdlength;
 113         uint8_t *rdata;
 114         char *buffer;
 115 };
 116
 117 #define MAX_ANSWER      8
 118 static struct dns_reply dns_reply[1 + (MAX_ANSWER * 3)];
 119 static int dns_answer_cnt;
 120
 121 void
 122 dns_init_answer(void)
 123 {
 124         dns_answer_cnt = 0;
 125 }
 126
 127 void
 128 dns_add_answer(int type, const uint8_t *rdata, uint16_t rdlength)
 129 {
 130         struct dns_reply *a = &dns_reply[dns_answer_cnt];
 131         if (dns_answer_cnt == MAX_ANSWER)
 132                 return;
 133         a->rdata = memdup(rdata, rdlength);
 134         a->type = type;
 135         a->rdlength = rdlength;
 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 dns_header h = { 0 };
 144         struct iovec *iov;
 145         int len, i;
 146
 147         if (!dns_answer_cnt)
 148                 return;
 149
 150         h.answers = __cpu_to_be16(dns_answer_cnt);
 151         h.flags = __cpu_to_be16(0x8400);
 152
 153         iov = alloca(sizeof(struct iovec) * ((dns_answer_cnt * 3) + 1));
 154         iov[0].iov_base = &h;
 155         iov[0].iov_len = sizeof(struct dns_header);
 156
 157         for (i = 0; i < dns_answer_cnt; i++) {
 158                 struct dns_answer *a = &dns_reply[i].a;
 159                 int id = (i * 3) + 1;
 160
 161                 memset(a, 0, sizeof(*a));
 162                 a->type = __cpu_to_be16(dns_reply[i].type);
 163                 a->class = __cpu_to_be16(1);
 164                 a->ttl = __cpu_to_be32(announce_ttl);
 165                 a->rdlength = __cpu_to_be16(dns_reply[i].rdlength);
 166
 167                 len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
 168                 if (len < 1)
 169                         return;
 170
 171                 dns_reply[i].buffer = iov[id].iov_base = memdup(buffer, len);
 172                 iov[id].iov_len = len;
 173
 174                 iov[id + 1].iov_base = a;
 175                 iov[id + 1].iov_len = sizeof(struct dns_answer);
 176
 177                 iov[id + 2].iov_base = dns_reply[i].rdata;
 178                 iov[id + 2].iov_len = dns_reply[i].rdlength;
 179
 180                 DBG(1, "A <- %s %s\n", dns_type_string(dns_reply[i].type), answer);
 181         }
 182
 183         if (interface_send_packet(iface, iov, (dns_answer_cnt * 3) + 1) < 0)
 184                 fprintf(stderr, "failed to send question\n");
 185
 186         for (i = 0; i < dns_answer_cnt; i++) {
 187                 free(dns_reply[i].buffer);
 188                 free(dns_reply[i].rdata);
 189         }
 190         dns_answer_cnt = 0;
 191 }
 192
 193 static int
 194 scan_name(const uint8_t *buffer, int len)
 195 {
 196         int offset = 0;
 197
 198         while (len && (*buffer != '\0')) {
 199                 int l = *buffer;
 200
 201                 if (IS_COMPRESSED(l))
 202                         return offset + 2;
 203
 204                 len -= l + 1;
 205                 offset += l + 1;
 206                 buffer += l + 1;
 207         }
 208
 209         if (!len || !offset || (*buffer != '\0'))
 210                 return -1;
 211
 212         return offset + 1;
 213 }
 214
 215 static struct dns_header*
 216 dns_consume_header(uint8_t **data, int *len)
 217 {
 218         struct dns_header *h = (struct dns_header *) *data;
 219         uint16_t *swap = (uint16_t *) h;
 220         int endianess = 6;
 221
 222         if (*len < sizeof(struct dns_header))
 223                 return NULL;
 224
 225         while (endianess--) {
 226                 *swap = __be16_to_cpu(*swap);
 227                 swap++;
 228         }
 229
 230         *len -= sizeof(struct dns_header);
 231         *data += sizeof(struct dns_header);
 232
 233         return h;
 234 }
 235
 236 static struct dns_question*
 237 dns_consume_question(uint8_t **data, int *len)
 238 {
 239         struct dns_question *q = (struct dns_question *) *data;
 240         uint16_t *swap = (uint16_t *) q;
 241         int endianess = 2;
 242
 243         if (*len < sizeof(struct dns_question))
 244                 return NULL;
 245
 246         while (endianess--) {
 247                 *swap = __be16_to_cpu(*swap);
 248                 swap++;
 249         }
 250
 251         *len -= sizeof(struct dns_question);
 252         *data += sizeof(struct dns_question);
 253
 254         return q;
 255 }
 256
 257 static struct dns_answer*
 258 dns_consume_answer(uint8_t **data, int *len)
 259 {
 260         struct dns_answer *a = (struct dns_answer *) *data;
 261
 262         if (*len < sizeof(struct dns_answer))
 263                 return NULL;
 264
 265         a->type = __be16_to_cpu(a->type);
 266         a->class = __be16_to_cpu(a->class);
 267         a->ttl = __be32_to_cpu(a->ttl);
 268         a->rdlength = __be16_to_cpu(a->rdlength);
 269
 270         *len -= sizeof(struct dns_answer);
 271         *data += sizeof(struct dns_answer);
 272
 273         return a;
 274 }
 275
 276 static char *
 277 dns_consume_name(const uint8_t *base, int blen, uint8_t **data, int *len)
 278 {
 279         int nlen = scan_name(*data, *len);
 280
 281         if (nlen < 1)
 282                 return NULL;
 283
 284         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 285                 perror("dns_consume_name/dn_expand");
 286                 return NULL;
 287         }
 288
 289         *len -= nlen;
 290         *data += nlen;
 291
 292         return name_buffer;
 293 }
 294
 295 static int
 296 parse_answer(struct interface *iface, uint8_t *buffer, int len, uint8_t **b, int *rlen, int cache)
 297 {
 298         char *name = dns_consume_name(buffer, len, b, rlen);
 299         struct dns_answer *a;
 300         uint8_t *rdata;
 301
 302         if (!name) {
 303                 fprintf(stderr, "dropping: bad question\n");
 304                 return -1;
 305         }
 306
 307         a = dns_consume_answer(b, rlen);
 308         if (!a) {
 309                 fprintf(stderr, "dropping: bad question\n");
 310                 return -1;
 311         }
 312
 313         rdata = *b;
 314         if (a->rdlength > *rlen) {
 315                 fprintf(stderr, "dropping: bad question\n");
 316                 return -1;
 317         }
 318
 319         *rlen -= a->rdlength;
 320         *b += a->rdlength;
 321
 322         if (cache)
 323                 cache_answer(iface, buffer, len, name, a, rdata);
 324
 325         return 0;
 326 }
 327
 328 static void
 329 parse_question(struct interface *iface, char *name, struct dns_question *q)
 330 {
 331         char *host;
 332
 333         DBG(1, "Q -> %s %s\n", dns_type_string(q->type), name);
 334
 335         switch (q->type) {
 336         case TYPE_ANY:
 337                 if (!strcmp(name, mdns_hostname_local))
 338                         service_reply(iface, NULL);
 339                 break;
 340
 341         case TYPE_PTR:
 342                 service_announce_services(iface, name);
 343                 service_reply(iface, name);
 344                 break;
 345
 346         case TYPE_AAAA:
 347         case TYPE_A:
 348                 host = strstr(name, ".local");
 349                 if (host)
 350                         *host = '\0';
 351                 if (!strcmp(mdns_hostname, name))
 352                         service_reply_a(iface, q->type);
 353                 break;
 354         };
 355 }
 356
 357 void
 358 dns_handle_packet(struct interface *iface, uint8_t *buffer, int len)
 359 {
 360         struct dns_header *h;
 361         uint8_t *b = buffer;
 362         int rlen = len;
 363
 364         h = dns_consume_header(&b, &rlen);
 365         if (!h) {
 366                 fprintf(stderr, "dropping: bad header\n");
 367                 return;
 368         }
 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                 parse_answer(iface, buffer, len, &b, &rlen, 1);
 394
 395         while (h->authority-- > 0)
 396                 parse_answer(iface, buffer, len, &b, &rlen, 0);
 397
 398         while (h->additional-- > 0)
 399                 parse_answer(iface, buffer, len, &b, &rlen, 1);
 400 }