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
  34 #include "announce.h"
  35 #include "util.h"
  36 #include "dns.h"
  37
  38 char *rdata_buffer;
  39 static char *name_buffer;
  40
  41 const char*
  42 dns_type_string(uint16_t type)
  43 {
  44         switch (type) {
  45         case TYPE_A:
  46                 return "A";
  47
  48         case TYPE_AAAA:
  49                 return "AAAA";
  50
  51         case TYPE_PTR:
  52                 return "PTR";
  53
  54         case TYPE_TXT:
  55                 return "TXT";
  56
  57         case TYPE_SRV:
  58                 return "SRV";
  59
  60         case TYPE_ANY:
  61                 return "ANY";
  62         }
  63
  64         return "N/A";
  65 }
  66
  67 void
  68 dns_send_question(struct uloop_fd *u, char *question, int type)
  69 {
  70         unsigned char buffer[MAX_NAME_LEN];
  71         struct dns_header h = { 0 };
  72         struct dns_question q = { 0 };
  73         struct msghdr m = { 0 };
  74         struct iovec iov[3] = { {0}, {0}, {0} };
  75         struct sockaddr_in a = { 0 };
  76         int len;
  77
  78         a.sin_family = AF_INET;
  79         a.sin_addr.s_addr = inet_addr(MCAST_ADDR);
  80         a.sin_port = htons(MCAST_PORT);
  81
  82         h.questions = __cpu_to_be16(1);
  83         q.type = __cpu_to_be16(type);
  84         q.class = __cpu_to_be16(1);
  85
  86         len = dn_comp(question, buffer, MAX_NAME_LEN, NULL, NULL);
  87         if (len < 1)
  88                 return;
  89
  90         m.msg_name = &a;
  91         m.msg_namelen = sizeof(struct sockaddr_in);
  92         m.msg_iov = iov;
  93         m.msg_iovlen = 3;
  94
  95         iov[0].iov_base = &h;
  96         iov[0].iov_len = sizeof(struct dns_header);
  97
  98         iov[1].iov_base = buffer;
  99         iov[1].iov_len = len;
 100
 101         iov[2].iov_base = &q;
 102         iov[2].iov_len = sizeof(struct dns_question);
 103
 104         if (sendmsg(u->fd, &m, 0) < 0)
 105                 fprintf(stderr, "failed to send question\n");
 106         else
 107                 DBG(1, "Q <- %s %s\n", dns_type_string(type), question);
 108 }
 109
 110
 111 struct dns_reply {
 112         int type;
 113         struct dns_answer a;
 114         uint16_t rdlength;
 115         uint8_t *rdata;
 116         char *buffer;
 117 };
 118
 119 #define MAX_ANSWER      8
 120 static struct dns_reply dns_reply[1 + (MAX_ANSWER * 3)];
 121 static int dns_answer_cnt;
 122
 123 void
 124 dns_init_answer(void)
 125 {
 126         dns_answer_cnt = 0;
 127 }
 128
 129 void
 130 dns_add_answer(int type, uint8_t *rdata, uint16_t rdlength)
 131 {
 132         struct dns_reply *a = &dns_reply[dns_answer_cnt];
 133         if (dns_answer_cnt == MAX_ANSWER)
 134                 return;
 135         a->rdata = memdup(rdata, rdlength);
 136         a->type = type;
 137         a->rdlength = rdlength;
 138         dns_answer_cnt++;
 139 }
 140
 141 void
 142 dns_send_answer(struct uloop_fd *u, char *answer)
 143 {
 144         uint8_t buffer[256];
 145         struct dns_header h = { 0 };
 146         struct msghdr m = { 0 };
 147         struct iovec *iov;
 148         struct sockaddr_in in = { 0 };
 149         int len, i;
 150
 151         if (!dns_answer_cnt)
 152                 return;
 153
 154         in.sin_family = AF_INET;
 155         in.sin_addr.s_addr = inet_addr(MCAST_ADDR);
 156         in.sin_port = htons(MCAST_PORT);
 157
 158         h.answers = __cpu_to_be16(dns_answer_cnt);
 159         h.flags = __cpu_to_be16(0x8400);
 160
 161         iov = malloc(sizeof(struct iovec) * ((dns_answer_cnt * 3) + 1));
 162         if (!iov)
 163                 return;
 164
 165         m.msg_name = &in;
 166         m.msg_namelen = sizeof(struct sockaddr_in);
 167         m.msg_iov = iov;
 168         m.msg_iovlen = (dns_answer_cnt * 3) + 1;
 169
 170         iov[0].iov_base = &h;
 171         iov[0].iov_len = sizeof(struct dns_header);
 172
 173         for (i = 0; i < dns_answer_cnt; i++) {
 174                 struct dns_answer *a = &dns_reply[i].a;
 175                 int id = (i * 3) + 1;
 176
 177                 memset(a, 0, sizeof(*a));
 178                 a->type = __cpu_to_be16(dns_reply[i].type);
 179                 a->class = __cpu_to_be16(1);
 180                 a->ttl = __cpu_to_be32(announce_ttl);
 181                 a->rdlength = __cpu_to_be16(dns_reply[i].rdlength);
 182
 183                 len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
 184                 if (len < 1)
 185                         return;
 186
 187                 dns_reply[i].buffer = iov[id].iov_base = memdup(buffer, len);
 188                 iov[id].iov_len = len;
 189
 190                 iov[id + 1].iov_base = a;
 191                 iov[id + 1].iov_len = sizeof(struct dns_answer);
 192
 193                 iov[id + 2].iov_base = dns_reply[i].rdata;
 194                 iov[id + 2].iov_len = dns_reply[i].rdlength;
 195
 196                 DBG(1, "A <- %s %s\n", dns_type_string(dns_reply[i].type), answer);
 197         }
 198
 199         if (sendmsg(u->fd, &m, 0) < 0)
 200                 fprintf(stderr, "failed to send question\n");
 201
 202         for (i = 0; i < dns_answer_cnt; i++) {
 203                 free(dns_reply[i].buffer);
 204                 free(dns_reply[i].rdata);
 205         }
 206         dns_answer_cnt = 0;
 207 }
 208
 209 static int
 210 scan_name(uint8_t *buffer, int len)
 211 {
 212         int offset = 0;
 213
 214         while (len && (*buffer != '\0')) {
 215                 int l = *buffer;
 216
 217                 if (IS_COMPRESSED(l))
 218                         return offset + 2;
 219
 220                 len -= l + 1;
 221                 offset += l + 1;
 222                 buffer += l + 1;
 223         }
 224
 225         if (!len || !offset || (*buffer != '\0'))
 226                 return -1;
 227
 228         return offset + 1;
 229 }
 230
 231 struct dns_header*
 232 dns_consume_header(uint8_t **data, int *len)
 233 {
 234         struct dns_header *h = (struct dns_header *) *data;
 235         uint16_t *swap = (uint16_t *) h;
 236         int endianess = 6;
 237
 238         if (*len < sizeof(struct dns_header))
 239                 return NULL;
 240
 241         while (endianess--) {
 242                 *swap = __be16_to_cpu(*swap);
 243                 swap++;
 244         }
 245
 246         *len -= sizeof(struct dns_header);
 247         *data += sizeof(struct dns_header);
 248
 249         return h;
 250 }
 251
 252 struct dns_question*
 253 dns_consume_question(uint8_t **data, int *len)
 254 {
 255         struct dns_question *q = (struct dns_question *) *data;
 256         uint16_t *swap = (uint16_t *) q;
 257         int endianess = 2;
 258
 259         if (*len < sizeof(struct dns_question))
 260                 return NULL;
 261
 262         while (endianess--) {
 263                 *swap = __be16_to_cpu(*swap);
 264                 swap++;
 265         }
 266
 267         *len -= sizeof(struct dns_question);
 268         *data += sizeof(struct dns_question);
 269
 270         return q;
 271 }
 272
 273 struct dns_answer*
 274 dns_consume_answer(uint8_t **data, int *len)
 275 {
 276         struct dns_answer *a = (struct dns_answer *) *data;
 277
 278         if (*len < sizeof(struct dns_answer))
 279                 return NULL;
 280
 281         a->type = __be16_to_cpu(a->type);
 282         a->class = __be16_to_cpu(a->class);
 283         a->ttl = __be32_to_cpu(a->ttl);
 284         a->rdlength = __be16_to_cpu(a->rdlength);
 285
 286         *len -= sizeof(struct dns_answer);
 287         *data += sizeof(struct dns_answer);
 288
 289         return a;
 290 }
 291
 292 char*
 293 dns_consume_name(uint8_t *base, int blen, uint8_t **data, int *len)
 294 {
 295         int nlen = scan_name(*data, *len);
 296
 297         if (nlen < 1)
 298                 return NULL;
 299
 300         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 301                 perror("dns_consume_name/dn_expand");
 302                 return NULL;
 303         }
 304
 305         *len -= nlen;
 306         *data += nlen;
 307
 308         return name_buffer;
 309 }
 310
 311 int
 312 dns_init(void)
 313 {
 314         name_buffer = malloc(MAX_NAME_LEN + 1);
 315         rdata_buffer = malloc(MAX_DATA_LEN + 1);
 316
 317         if (!name_buffer || !rdata_buffer)
 318                 return -1;
 319
 320         memset(name_buffer, 0, MAX_NAME_LEN + 1);
 321         memset(rdata_buffer, 0, MAX_NAME_LEN + 1);
 322
 323         return 0;
 324 }
 325
 326 void
 327 dns_cleanup(void)
 328 {
 329         free(name_buffer);
 330         free(rdata_buffer);
 331 }