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