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
  39 char rdata_buffer[MAX_DATA_LEN + 1];
  40 static char name_buffer[MAX_NAME_LEN + 1];
  41
  42 const char*
  43 dns_type_string(uint16_t type)
  44 {
  45         switch (type) {
  46         case TYPE_A:
  47                 return "A";
  48
  49         case TYPE_AAAA:
  50                 return "AAAA";
  51
  52         case TYPE_PTR:
  53                 return "PTR";
  54
  55         case TYPE_TXT:
  56                 return "TXT";
  57
  58         case TYPE_SRV:
  59                 return "SRV";
  60
  61         case TYPE_ANY:
  62                 return "ANY";
  63         }
  64
  65         return "N/A";
  66 }
  67
  68 static int
  69 dns_send_packet(int fd, struct iovec *iov, int iov_len)
  70 {
  71         static size_t cmsg_data[( CMSG_SPACE(sizeof(struct in_pktinfo)) / sizeof(size_t)) + 1];
  72         static struct sockaddr_in a = {
  73                 .sin_family = AF_INET,
  74                 .sin_port = htons(MCAST_PORT),
  75         };
  76         static struct msghdr m = {
  77                 .msg_name = (struct sockaddr *) &a,
  78                 .msg_namelen = sizeof(a),
  79                 .msg_control = cmsg_data,
  80                 .msg_controllen = CMSG_LEN(sizeof(struct in_pktinfo)),
  81         };
  82         struct in_pktinfo *pkti;
  83         struct cmsghdr *cmsg;
  84
  85         m.msg_iov = iov;
  86         m.msg_iovlen = iov_len;
  87
  88         memset(cmsg_data, 0, sizeof(cmsg_data));
  89         cmsg = CMSG_FIRSTHDR(&m);
  90         cmsg->cmsg_len = m.msg_controllen;
  91         cmsg->cmsg_level = IPPROTO_IP;
  92         cmsg->cmsg_type = IP_PKTINFO;
  93
  94         pkti = (struct in_pktinfo*) CMSG_DATA(cmsg);
  95         pkti->ipi_ifindex = iface_index;
  96
  97         a.sin_addr.s_addr = inet_addr(MCAST_ADDR);
  98
  99         return sendmsg(fd, &m, 0);
 100 }
 101
 102 void
 103 dns_send_question(struct uloop_fd *u, char *question, int type)
 104 {
 105         static struct dns_header h = {
 106                 .questions = cpu_to_be16(1),
 107         };
 108         static struct dns_question q = {
 109                 .class = cpu_to_be16(1),
 110         };
 111         static struct iovec iov[] = {
 112                 {
 113                         .iov_base = &h,
 114                         .iov_len = sizeof(h),
 115                 },
 116                 {
 117                         .iov_base = name_buffer,
 118                 },
 119                 {
 120                         .iov_base = &q,
 121                         .iov_len = sizeof(q),
 122                 }
 123         };
 124         int len;
 125
 126         q.type = __cpu_to_be16(type);
 127
 128         len = dn_comp(question, (void *) name_buffer, sizeof(name_buffer), NULL, NULL);
 129         if (len < 1)
 130                 return;
 131
 132         iov[1].iov_len = len;
 133
 134         if (dns_send_packet(u->fd, iov, ARRAY_SIZE(iov)) < 0)
 135                 fprintf(stderr, "failed to send question\n");
 136         else
 137                 DBG(1, "Q <- %s %s\n", dns_type_string(type), question);
 138 }
 139
 140
 141 struct dns_reply {
 142         int type;
 143         struct dns_answer a;
 144         uint16_t rdlength;
 145         uint8_t *rdata;
 146         char *buffer;
 147 };
 148
 149 #define MAX_ANSWER      8
 150 static struct dns_reply dns_reply[1 + (MAX_ANSWER * 3)];
 151 static int dns_answer_cnt;
 152
 153 void
 154 dns_init_answer(void)
 155 {
 156         dns_answer_cnt = 0;
 157 }
 158
 159 void
 160 dns_add_answer(int type, uint8_t *rdata, uint16_t rdlength)
 161 {
 162         struct dns_reply *a = &dns_reply[dns_answer_cnt];
 163         if (dns_answer_cnt == MAX_ANSWER)
 164                 return;
 165         a->rdata = memdup(rdata, rdlength);
 166         a->type = type;
 167         a->rdlength = rdlength;
 168         dns_answer_cnt++;
 169 }
 170
 171 void
 172 dns_send_answer(struct uloop_fd *u, char *answer)
 173 {
 174         uint8_t buffer[256];
 175         struct dns_header h = { 0 };
 176         struct iovec *iov;
 177         int len, i;
 178
 179         if (!dns_answer_cnt)
 180                 return;
 181
 182         h.answers = __cpu_to_be16(dns_answer_cnt);
 183         h.flags = __cpu_to_be16(0x8400);
 184
 185         iov = malloc(sizeof(struct iovec) * ((dns_answer_cnt * 3) + 1));
 186         if (!iov)
 187                 return;
 188
 189         iov[0].iov_base = &h;
 190         iov[0].iov_len = sizeof(struct dns_header);
 191
 192         for (i = 0; i < dns_answer_cnt; i++) {
 193                 struct dns_answer *a = &dns_reply[i].a;
 194                 int id = (i * 3) + 1;
 195
 196                 memset(a, 0, sizeof(*a));
 197                 a->type = __cpu_to_be16(dns_reply[i].type);
 198                 a->class = __cpu_to_be16(1);
 199                 a->ttl = __cpu_to_be32(announce_ttl);
 200                 a->rdlength = __cpu_to_be16(dns_reply[i].rdlength);
 201
 202                 len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
 203                 if (len < 1)
 204                         return;
 205
 206                 dns_reply[i].buffer = iov[id].iov_base = memdup(buffer, len);
 207                 iov[id].iov_len = len;
 208
 209                 iov[id + 1].iov_base = a;
 210                 iov[id + 1].iov_len = sizeof(struct dns_answer);
 211
 212                 iov[id + 2].iov_base = dns_reply[i].rdata;
 213                 iov[id + 2].iov_len = dns_reply[i].rdlength;
 214
 215                 DBG(1, "A <- %s %s\n", dns_type_string(dns_reply[i].type), answer);
 216         }
 217
 218         if (dns_send_packet(u->fd, iov, (dns_answer_cnt * 3) + 1) < 0)
 219                 fprintf(stderr, "failed to send question\n");
 220
 221         for (i = 0; i < dns_answer_cnt; i++) {
 222                 free(dns_reply[i].buffer);
 223                 free(dns_reply[i].rdata);
 224         }
 225         dns_answer_cnt = 0;
 226 }
 227
 228 static int
 229 scan_name(uint8_t *buffer, int len)
 230 {
 231         int offset = 0;
 232
 233         while (len && (*buffer != '\0')) {
 234                 int l = *buffer;
 235
 236                 if (IS_COMPRESSED(l))
 237                         return offset + 2;
 238
 239                 len -= l + 1;
 240                 offset += l + 1;
 241                 buffer += l + 1;
 242         }
 243
 244         if (!len || !offset || (*buffer != '\0'))
 245                 return -1;
 246
 247         return offset + 1;
 248 }
 249
 250 struct dns_header*
 251 dns_consume_header(uint8_t **data, int *len)
 252 {
 253         struct dns_header *h = (struct dns_header *) *data;
 254         uint16_t *swap = (uint16_t *) h;
 255         int endianess = 6;
 256
 257         if (*len < sizeof(struct dns_header))
 258                 return NULL;
 259
 260         while (endianess--) {
 261                 *swap = __be16_to_cpu(*swap);
 262                 swap++;
 263         }
 264
 265         *len -= sizeof(struct dns_header);
 266         *data += sizeof(struct dns_header);
 267
 268         return h;
 269 }
 270
 271 struct dns_question*
 272 dns_consume_question(uint8_t **data, int *len)
 273 {
 274         struct dns_question *q = (struct dns_question *) *data;
 275         uint16_t *swap = (uint16_t *) q;
 276         int endianess = 2;
 277
 278         if (*len < sizeof(struct dns_question))
 279                 return NULL;
 280
 281         while (endianess--) {
 282                 *swap = __be16_to_cpu(*swap);
 283                 swap++;
 284         }
 285
 286         *len -= sizeof(struct dns_question);
 287         *data += sizeof(struct dns_question);
 288
 289         return q;
 290 }
 291
 292 struct dns_answer*
 293 dns_consume_answer(uint8_t **data, int *len)
 294 {
 295         struct dns_answer *a = (struct dns_answer *) *data;
 296
 297         if (*len < sizeof(struct dns_answer))
 298                 return NULL;
 299
 300         a->type = __be16_to_cpu(a->type);
 301         a->class = __be16_to_cpu(a->class);
 302         a->ttl = __be32_to_cpu(a->ttl);
 303         a->rdlength = __be16_to_cpu(a->rdlength);
 304
 305         *len -= sizeof(struct dns_answer);
 306         *data += sizeof(struct dns_answer);
 307
 308         return a;
 309 }
 310
 311 char*
 312 dns_consume_name(uint8_t *base, int blen, uint8_t **data, int *len)
 313 {
 314         int nlen = scan_name(*data, *len);
 315
 316         if (nlen < 1)
 317                 return NULL;
 318
 319         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 320                 perror("dns_consume_name/dn_expand");
 321                 return NULL;
 322         }
 323
 324         *len -= nlen;
 325         *data += nlen;
 326
 327         return name_buffer;
 328 }