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 char rdata_buffer[MAX_DATA_LEN + 1];
  43 static char name_buffer[MAX_NAME_LEN + 1];
  44
  45 const char*
  46 dns_type_string(uint16_t type)
  47 {
  48         switch (type) {
  49         case TYPE_A:
  50                 return "A";
  51
  52         case TYPE_AAAA:
  53                 return "AAAA";
  54
  55         case TYPE_PTR:
  56                 return "PTR";
  57
  58         case TYPE_TXT:
  59                 return "TXT";
  60
  61         case TYPE_SRV:
  62                 return "SRV";
  63
  64         case TYPE_ANY:
  65                 return "ANY";
  66         }
  67
  68         return "N/A";
  69 }
  70
  71 void
  72 dns_send_question(struct interface *iface, const char *question, int type)
  73 {
  74         static struct dns_header h = {
  75                 .questions = cpu_to_be16(1),
  76         };
  77         static struct dns_question q = {
  78                 .class = cpu_to_be16(1),
  79         };
  80         static struct iovec iov[] = {
  81                 {
  82                         .iov_base = &h,
  83                         .iov_len = sizeof(h),
  84                 },
  85                 {
  86                         .iov_base = name_buffer,
  87                 },
  88                 {
  89                         .iov_base = &q,
  90                         .iov_len = sizeof(q),
  91                 }
  92         };
  93         int len;
  94
  95         q.type = __cpu_to_be16(type);
  96
  97         len = dn_comp(question, (void *) name_buffer, sizeof(name_buffer), NULL, NULL);
  98         if (len < 1)
  99                 return;
 100
 101         iov[1].iov_len = len;
 102
 103         if (interface_send_packet(iface, iov, ARRAY_SIZE(iov)) < 0)
 104                 fprintf(stderr, "failed to send question\n");
 105         else
 106                 DBG(1, "Q <- %s %s\n", dns_type_string(type), question);
 107 }
 108
 109
 110 struct dns_reply {
 111         int type;
 112         struct dns_answer a;
 113         uint16_t rdlength;
 114         uint8_t *rdata;
 115         char *buffer;
 116 };
 117
 118 #define MAX_ANSWER      8
 119 static struct dns_reply dns_reply[1 + (MAX_ANSWER * 3)];
 120 static int dns_answer_cnt;
 121
 122 void
 123 dns_init_answer(void)
 124 {
 125         dns_answer_cnt = 0;
 126 }
 127
 128 void
 129 dns_add_answer(int type, const uint8_t *rdata, uint16_t rdlength)
 130 {
 131         struct dns_reply *a = &dns_reply[dns_answer_cnt];
 132         if (dns_answer_cnt == MAX_ANSWER)
 133                 return;
 134         a->rdata = memdup(rdata, rdlength);
 135         a->type = type;
 136         a->rdlength = rdlength;
 137         dns_answer_cnt++;
 138 }
 139
 140 void
 141 dns_send_answer(struct interface *iface, const char *answer)
 142 {
 143         uint8_t buffer[256];
 144         struct dns_header h = { 0 };
 145         struct iovec *iov;
 146         int len, i;
 147
 148         if (!dns_answer_cnt)
 149                 return;
 150
 151         h.answers = __cpu_to_be16(dns_answer_cnt);
 152         h.flags = __cpu_to_be16(0x8400);
 153
 154         iov = alloca(sizeof(struct iovec) * ((dns_answer_cnt * 3) + 1));
 155         iov[0].iov_base = &h;
 156         iov[0].iov_len = sizeof(struct dns_header);
 157
 158         for (i = 0; i < dns_answer_cnt; i++) {
 159                 struct dns_answer *a = &dns_reply[i].a;
 160                 int id = (i * 3) + 1;
 161
 162                 memset(a, 0, sizeof(*a));
 163                 a->type = __cpu_to_be16(dns_reply[i].type);
 164                 a->class = __cpu_to_be16(1);
 165                 a->ttl = __cpu_to_be32(announce_ttl);
 166                 a->rdlength = __cpu_to_be16(dns_reply[i].rdlength);
 167
 168                 len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
 169                 if (len < 1)
 170                         return;
 171
 172                 dns_reply[i].buffer = iov[id].iov_base = memdup(buffer, len);
 173                 iov[id].iov_len = len;
 174
 175                 iov[id + 1].iov_base = a;
 176                 iov[id + 1].iov_len = sizeof(struct dns_answer);
 177
 178                 iov[id + 2].iov_base = dns_reply[i].rdata;
 179                 iov[id + 2].iov_len = dns_reply[i].rdlength;
 180
 181                 DBG(1, "A <- %s %s\n", dns_type_string(dns_reply[i].type), answer);
 182         }
 183
 184         if (interface_send_packet(iface, iov, (dns_answer_cnt * 3) + 1) < 0)
 185                 fprintf(stderr, "failed to send question\n");
 186
 187         for (i = 0; i < dns_answer_cnt; i++) {
 188                 free(dns_reply[i].buffer);
 189                 free(dns_reply[i].rdata);
 190         }
 191         dns_answer_cnt = 0;
 192 }
 193
 194 static int
 195 scan_name(const uint8_t *buffer, int len)
 196 {
 197         int offset = 0;
 198
 199         while (len && (*buffer != '\0')) {
 200                 int l = *buffer;
 201
 202                 if (IS_COMPRESSED(l))
 203                         return offset + 2;
 204
 205                 len -= l + 1;
 206                 offset += l + 1;
 207                 buffer += l + 1;
 208         }
 209
 210         if (!len || !offset || (*buffer != '\0'))
 211                 return -1;
 212
 213         return offset + 1;
 214 }
 215
 216 static struct dns_header*
 217 dns_consume_header(uint8_t **data, int *len)
 218 {
 219         struct dns_header *h = (struct dns_header *) *data;
 220         uint16_t *swap = (uint16_t *) h;
 221         int endianess = 6;
 222
 223         if (*len < sizeof(struct dns_header))
 224                 return NULL;
 225
 226         while (endianess--) {
 227                 *swap = __be16_to_cpu(*swap);
 228                 swap++;
 229         }
 230
 231         *len -= sizeof(struct dns_header);
 232         *data += sizeof(struct dns_header);
 233
 234         return h;
 235 }
 236
 237 static struct dns_question*
 238 dns_consume_question(uint8_t **data, int *len)
 239 {
 240         struct dns_question *q = (struct dns_question *) *data;
 241         uint16_t *swap = (uint16_t *) q;
 242         int endianess = 2;
 243
 244         if (*len < sizeof(struct dns_question))
 245                 return NULL;
 246
 247         while (endianess--) {
 248                 *swap = __be16_to_cpu(*swap);
 249                 swap++;
 250         }
 251
 252         *len -= sizeof(struct dns_question);
 253         *data += sizeof(struct dns_question);
 254
 255         return q;
 256 }
 257
 258 static struct dns_answer*
 259 dns_consume_answer(uint8_t **data, int *len)
 260 {
 261         struct dns_answer *a = (struct dns_answer *) *data;
 262
 263         if (*len < sizeof(struct dns_answer))
 264                 return NULL;
 265
 266         a->type = __be16_to_cpu(a->type);
 267         a->class = __be16_to_cpu(a->class);
 268         a->ttl = __be32_to_cpu(a->ttl);
 269         a->rdlength = __be16_to_cpu(a->rdlength);
 270
 271         *len -= sizeof(struct dns_answer);
 272         *data += sizeof(struct dns_answer);
 273
 274         return a;
 275 }
 276
 277 static char *
 278 dns_consume_name(const uint8_t *base, int blen, uint8_t **data, int *len)
 279 {
 280         int nlen = scan_name(*data, *len);
 281
 282         if (nlen < 1)
 283                 return NULL;
 284
 285         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 286                 perror("dns_consume_name/dn_expand");
 287                 return NULL;
 288         }
 289
 290         *len -= nlen;
 291         *data += nlen;
 292
 293         return name_buffer;
 294 }
 295
 296 static int
 297 parse_answer(struct interface *iface, uint8_t *buffer, int len, uint8_t **b, int *rlen, int cache)
 298 {
 299         char *name = dns_consume_name(buffer, len, b, rlen);
 300         struct dns_answer *a;
 301         uint8_t *rdata;
 302
 303         if (!name) {
 304                 fprintf(stderr, "dropping: bad question\n");
 305                 return -1;
 306         }
 307
 308         a = dns_consume_answer(b, rlen);
 309         if (!a) {
 310                 fprintf(stderr, "dropping: bad question\n");
 311                 return -1;
 312         }
 313
 314         rdata = *b;
 315         if (a->rdlength > *rlen) {
 316                 fprintf(stderr, "dropping: bad question\n");
 317                 return -1;
 318         }
 319
 320         *rlen -= a->rdlength;
 321         *b += a->rdlength;
 322
 323         if (cache)
 324                 cache_answer(iface, buffer, len, name, a, rdata);
 325
 326         return 0;
 327 }
 328
 329 static void
 330 parse_question(struct interface *iface, char *name, struct dns_question *q)
 331 {
 332         char *host;
 333
 334         DBG(1, "Q -> %s %s\n", dns_type_string(q->type), name);
 335
 336         switch (q->type) {
 337         case TYPE_ANY:
 338                 host = service_name("local");
 339                 if (!strcmp(name, host))
 340                         service_reply(iface, NULL);
 341                 break;
 342
 343         case TYPE_PTR:
 344                 service_announce_services(iface, name);
 345                 service_reply(iface, name);
 346                 break;
 347
 348         case TYPE_AAAA:
 349         case TYPE_A:
 350                 host = strstr(name, ".local");
 351                 if (host)
 352                         *host = '\0';
 353                 if (!strcmp(hostname, name))
 354                         service_reply_a(iface, q->type);
 355                 break;
 356         };
 357 }
 358
 359 void
 360 dns_handle_packet(struct interface *iface, uint8_t *buffer, int len)
 361 {
 362         struct dns_header *h;
 363         uint8_t *b = buffer;
 364         int rlen = len;
 365
 366         h = dns_consume_header(&b, &rlen);
 367         if (!h) {
 368                 fprintf(stderr, "dropping: bad header\n");
 369                 return;
 370         }
 371
 372         while (h->questions-- > 0) {
 373                 char *name = dns_consume_name(buffer, len, &b, &rlen);
 374                 struct dns_question *q;
 375
 376                 if (!name) {
 377                         fprintf(stderr, "dropping: bad name\n");
 378                         return;
 379                 }
 380
 381                 q = dns_consume_question(&b, &rlen);
 382                 if (!q) {
 383                         fprintf(stderr, "dropping: bad question\n");
 384                         return;
 385                 }
 386
 387                 if (!(h->flags & FLAG_RESPONSE))
 388                         parse_question(iface, name, q);
 389         }
 390
 391         if (!(h->flags & FLAG_RESPONSE))
 392                 return;
 393
 394         while (h->answers-- > 0)
 395                 parse_answer(iface, buffer, len, &b, &rlen, 1);
 396
 397         while (h->authority-- > 0)
 398                 parse_answer(iface, buffer, len, &b, &rlen, 0);
 399
 400         while (h->additional-- > 0)
 401                 parse_answer(iface, buffer, len, &b, &rlen, 1);
 402 }