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         if (unicast == iface->multicast)
  99                 iface = iface->peer;
 100
 101         if (interface_send_packet(iface, iov, ARRAY_SIZE(iov)) < 0)
 102                 fprintf(stderr, "failed to send question\n");
 103         else
 104                 DBG(1, "Q <- %s %s\n", dns_type_string(type), question);
 105 }
 106
 107
 108 struct dns_reply {
 109         int type;
 110         struct dns_answer a;
 111         uint16_t rdlength;
 112         uint8_t *rdata;
 113         char *buffer;
 114 };
 115
 116 static int dns_answer_cnt;
 117
 118 void
 119 dns_init_answer(void)
 120 {
 121         dns_answer_cnt = 0;
 122         blob_buf_init(&ans_buf, 0);
 123 }
 124
 125 void
 126 dns_add_answer(int type, const uint8_t *rdata, uint16_t rdlength, int ttl)
 127 {
 128         struct blob_attr *attr;
 129         struct dns_answer *a;
 130
 131         attr = blob_new(&ans_buf, 0, sizeof(*a) + rdlength);
 132         a = blob_data(attr);
 133         a->type = cpu_to_be16(type);
 134         a->class = cpu_to_be16(1);
 135         a->ttl = cpu_to_be32(ttl);
 136         a->rdlength = cpu_to_be16(rdlength);
 137         memcpy(a + 1, rdata, rdlength);
 138
 139         dns_answer_cnt++;
 140 }
 141
 142 void
 143 dns_send_answer(struct interface *iface, const char *answer)
 144 {
 145         uint8_t buffer[256];
 146         struct blob_attr *attr;
 147         struct dns_header h = { 0 };
 148         struct iovec *iov;
 149         int answer_len, rem;
 150         int n_iov = 0;
 151
 152         if (!dns_answer_cnt)
 153                 return;
 154
 155         h.answers = cpu_to_be16(dns_answer_cnt);
 156         h.flags = cpu_to_be16(0x8400);
 157
 158         iov = alloca(sizeof(struct iovec) * ((dns_answer_cnt * 2) + 1));
 159
 160         iov[n_iov].iov_base = &h;
 161         iov[n_iov].iov_len = sizeof(struct dns_header);
 162         n_iov++;
 163
 164         answer_len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
 165         if (answer_len < 1)
 166                 return;
 167
 168         blob_for_each_attr(attr, ans_buf.head, rem) {
 169                 struct dns_answer *a = blob_data(attr);
 170
 171                 iov[n_iov].iov_base = buffer;
 172                 iov[n_iov].iov_len = answer_len;
 173                 n_iov++;
 174
 175                 iov[n_iov].iov_base = blob_data(attr);
 176                 iov[n_iov].iov_len = blob_len(attr);
 177                 n_iov++;
 178
 179                 DBG(1, "A <- %s %s\n", dns_type_string(be16_to_cpu(a->type)), answer);
 180         }
 181
 182         if (interface_send_packet(iface, iov, n_iov) < 0)
 183                 fprintf(stderr, "failed to send question\n");
 184 }
 185
 186 static int
 187 scan_name(const uint8_t *buffer, int len)
 188 {
 189         int offset = 0;
 190
 191         while (len && (*buffer != '\0')) {
 192                 int l = *buffer;
 193
 194                 if (IS_COMPRESSED(l))
 195                         return offset + 2;
 196
 197                 len -= l + 1;
 198                 offset += l + 1;
 199                 buffer += l + 1;
 200         }
 201
 202         if (!len || !offset || (*buffer != '\0'))
 203                 return -1;
 204
 205         return offset + 1;
 206 }
 207
 208 static struct dns_header*
 209 dns_consume_header(uint8_t **data, int *len)
 210 {
 211         struct dns_header *h = (struct dns_header *) *data;
 212         uint16_t *swap = (uint16_t *) h;
 213         int endianess = 6;
 214
 215         if (*len < sizeof(struct dns_header))
 216                 return NULL;
 217
 218         while (endianess--) {
 219                 *swap = be16_to_cpu(*swap);
 220                 swap++;
 221         }
 222
 223         *len -= sizeof(struct dns_header);
 224         *data += sizeof(struct dns_header);
 225
 226         return h;
 227 }
 228
 229 static struct dns_question*
 230 dns_consume_question(uint8_t **data, int *len)
 231 {
 232         struct dns_question *q = (struct dns_question *) *data;
 233         uint16_t *swap = (uint16_t *) q;
 234         int endianess = 2;
 235
 236         if (*len < sizeof(struct dns_question))
 237                 return NULL;
 238
 239         while (endianess--) {
 240                 *swap = be16_to_cpu(*swap);
 241                 swap++;
 242         }
 243
 244         *len -= sizeof(struct dns_question);
 245         *data += sizeof(struct dns_question);
 246
 247         return q;
 248 }
 249
 250 static struct dns_answer*
 251 dns_consume_answer(uint8_t **data, int *len)
 252 {
 253         struct dns_answer *a = (struct dns_answer *) *data;
 254
 255         if (*len < sizeof(struct dns_answer))
 256                 return NULL;
 257
 258         a->type = be16_to_cpu(a->type);
 259         a->class = be16_to_cpu(a->class);
 260         a->ttl = be32_to_cpu(a->ttl);
 261         a->rdlength = be16_to_cpu(a->rdlength);
 262
 263         *len -= sizeof(struct dns_answer);
 264         *data += sizeof(struct dns_answer);
 265
 266         return a;
 267 }
 268
 269 static char *
 270 dns_consume_name(const uint8_t *base, int blen, uint8_t **data, int *len)
 271 {
 272         int nlen = scan_name(*data, *len);
 273
 274         if (nlen < 1)
 275                 return NULL;
 276
 277         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 278                 perror("dns_consume_name/dn_expand");
 279                 return NULL;
 280         }
 281
 282         *len -= nlen;
 283         *data += nlen;
 284
 285         return name_buffer;
 286 }
 287
 288 static int
 289 parse_answer(struct interface *iface, uint8_t *buffer, int len, uint8_t **b, int *rlen, int cache)
 290 {
 291         char *name = dns_consume_name(buffer, len, b, rlen);
 292         struct dns_answer *a;
 293         uint8_t *rdata;
 294
 295         if (!name) {
 296                 fprintf(stderr, "dropping: bad question\n");
 297                 return -1;
 298         }
 299
 300         a = dns_consume_answer(b, rlen);
 301         if (!a) {
 302                 fprintf(stderr, "dropping: bad question\n");
 303                 return -1;
 304         }
 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);
 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);
 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, q->type, announce_ttl);
 349                 break;
 350         };
 351 }
 352
 353 void
 354 dns_handle_packet(struct interface *iface, uint8_t *buffer, int len, int unicast)
 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         while (h->questions-- > 0) {
 367                 char *name = dns_consume_name(buffer, len, &b, &rlen);
 368                 struct dns_question *q;
 369
 370                 if (!name) {
 371                         fprintf(stderr, "dropping: bad name\n");
 372                         return;
 373                 }
 374
 375                 q = dns_consume_question(&b, &rlen);
 376                 if (!q) {
 377                         fprintf(stderr, "dropping: bad question\n");
 378                         return;
 379                 }
 380
 381                 if (!(h->flags & FLAG_RESPONSE))
 382                         parse_question(iface, name, q);
 383         }
 384
 385         if (!(h->flags & FLAG_RESPONSE))
 386                 return;
 387
 388         while (h->answers-- > 0)
 389                 if (parse_answer(iface, buffer, len, &b, &rlen, 1))
 390                         return;
 391
 392         while (h->authority-- > 0)
 393                 if (parse_answer(iface, buffer, len, &b, &rlen, 1))
 394                         return;
 395
 396         while (h->additional-- > 0)
 397                 if (parse_answer(iface, buffer, len, &b, &rlen, 1))
 398                         return;
 399
 400 }