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         size_t cmsg_data[( CMSG_SPACE(sizeof(struct in_pktinfo)) / sizeof(size_t)) + 1];
  71         unsigned char buffer[MAX_NAME_LEN];
  72         struct dns_header h = { 0 };
  73         struct dns_question q = { 0 };
  74         struct msghdr m = { 0 };
  75         struct iovec iov[3] = { {0}, {0}, {0} };
  76         struct sockaddr_in a = { 0 };
  77         struct in_pktinfo *pkti;
  78         struct cmsghdr *cmsg;
  79         struct in_addr in;
  80         int len;
  81
  82         a.sin_family = AF_INET;
  83         a.sin_addr.s_addr = inet_addr(MCAST_ADDR);
  84         a.sin_port = htons(MCAST_PORT);
  85
  86         h.questions = __cpu_to_be16(1);
  87         q.type = __cpu_to_be16(type);
  88         q.class = __cpu_to_be16(1);
  89
  90         len = dn_comp(question, buffer, MAX_NAME_LEN, NULL, NULL);
  91         if (len < 1)
  92                 return;
  93
  94         m.msg_name = &a;
  95         m.msg_namelen = sizeof(struct sockaddr_in);
  96         m.msg_iov = iov;
  97         m.msg_iovlen = 3;
  98
  99         memset(cmsg_data, 0, sizeof(cmsg_data));
 100         m.msg_control = cmsg_data;
 101         m.msg_controllen = CMSG_LEN(sizeof(struct in_pktinfo));
 102
 103         cmsg = CMSG_FIRSTHDR(&m);
 104         cmsg->cmsg_len = m.msg_controllen;
 105         cmsg->cmsg_level = IPPROTO_IP;
 106         cmsg->cmsg_type = IP_PKTINFO;
 107
 108         inet_aton(iface_ip, &in);
 109
 110         pkti = (struct in_pktinfo*) CMSG_DATA(cmsg);
 111         pkti->ipi_ifindex = iface_index;
 112
 113         iov[0].iov_base = &h;
 114         iov[0].iov_len = sizeof(struct dns_header);
 115
 116         iov[1].iov_base = buffer;
 117         iov[1].iov_len = len;
 118
 119         iov[2].iov_base = &q;
 120         iov[2].iov_len = sizeof(struct dns_question);
 121
 122         if (sendmsg(u->fd, &m, 0) < 0)
 123                 fprintf(stderr, "failed to send question\n");
 124         else
 125                 DBG(1, "Q <- %s %s\n", dns_type_string(type), question);
 126 }
 127
 128
 129 struct dns_reply {
 130         int type;
 131         struct dns_answer a;
 132         uint16_t rdlength;
 133         uint8_t *rdata;
 134         char *buffer;
 135 };
 136
 137 #define MAX_ANSWER      8
 138 static struct dns_reply dns_reply[1 + (MAX_ANSWER * 3)];
 139 static int dns_answer_cnt;
 140
 141 void
 142 dns_init_answer(void)
 143 {
 144         dns_answer_cnt = 0;
 145 }
 146
 147 void
 148 dns_add_answer(int type, uint8_t *rdata, uint16_t rdlength)
 149 {
 150         struct dns_reply *a = &dns_reply[dns_answer_cnt];
 151         if (dns_answer_cnt == MAX_ANSWER)
 152                 return;
 153         a->rdata = memdup(rdata, rdlength);
 154         a->type = type;
 155         a->rdlength = rdlength;
 156         dns_answer_cnt++;
 157 }
 158
 159 void
 160 dns_send_answer(struct uloop_fd *u, char *answer)
 161 {
 162         uint8_t buffer[256];
 163         struct dns_header h = { 0 };
 164         struct msghdr m = { 0 };
 165         struct iovec *iov;
 166         struct sockaddr_in in = { 0 };
 167         int len, i;
 168
 169         if (!dns_answer_cnt)
 170                 return;
 171
 172         in.sin_family = AF_INET;
 173         in.sin_addr.s_addr = inet_addr(MCAST_ADDR);
 174         in.sin_port = htons(MCAST_PORT);
 175
 176         h.answers = __cpu_to_be16(dns_answer_cnt);
 177         h.flags = __cpu_to_be16(0x8400);
 178
 179         iov = malloc(sizeof(struct iovec) * ((dns_answer_cnt * 3) + 1));
 180         if (!iov)
 181                 return;
 182
 183         m.msg_name = &in;
 184         m.msg_namelen = sizeof(struct sockaddr_in);
 185         m.msg_iov = iov;
 186         m.msg_iovlen = (dns_answer_cnt * 3) + 1;
 187
 188         iov[0].iov_base = &h;
 189         iov[0].iov_len = sizeof(struct dns_header);
 190
 191         for (i = 0; i < dns_answer_cnt; i++) {
 192                 struct dns_answer *a = &dns_reply[i].a;
 193                 int id = (i * 3) + 1;
 194
 195                 memset(a, 0, sizeof(*a));
 196                 a->type = __cpu_to_be16(dns_reply[i].type);
 197                 a->class = __cpu_to_be16(1);
 198                 a->ttl = __cpu_to_be32(announce_ttl);
 199                 a->rdlength = __cpu_to_be16(dns_reply[i].rdlength);
 200
 201                 len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
 202                 if (len < 1)
 203                         return;
 204
 205                 dns_reply[i].buffer = iov[id].iov_base = memdup(buffer, len);
 206                 iov[id].iov_len = len;
 207
 208                 iov[id + 1].iov_base = a;
 209                 iov[id + 1].iov_len = sizeof(struct dns_answer);
 210
 211                 iov[id + 2].iov_base = dns_reply[i].rdata;
 212                 iov[id + 2].iov_len = dns_reply[i].rdlength;
 213
 214                 DBG(1, "A <- %s %s\n", dns_type_string(dns_reply[i].type), answer);
 215         }
 216
 217         if (sendmsg(u->fd, &m, 0) < 0)
 218                 fprintf(stderr, "failed to send question\n");
 219
 220         for (i = 0; i < dns_answer_cnt; i++) {
 221                 free(dns_reply[i].buffer);
 222                 free(dns_reply[i].rdata);
 223         }
 224         dns_answer_cnt = 0;
 225 }
 226
 227 static int
 228 scan_name(uint8_t *buffer, int len)
 229 {
 230         int offset = 0;
 231
 232         while (len && (*buffer != '\0')) {
 233                 int l = *buffer;
 234
 235                 if (IS_COMPRESSED(l))
 236                         return offset + 2;
 237
 238                 len -= l + 1;
 239                 offset += l + 1;
 240                 buffer += l + 1;
 241         }
 242
 243         if (!len || !offset || (*buffer != '\0'))
 244                 return -1;
 245
 246         return offset + 1;
 247 }
 248
 249 struct dns_header*
 250 dns_consume_header(uint8_t **data, int *len)
 251 {
 252         struct dns_header *h = (struct dns_header *) *data;
 253         uint16_t *swap = (uint16_t *) h;
 254         int endianess = 6;
 255
 256         if (*len < sizeof(struct dns_header))
 257                 return NULL;
 258
 259         while (endianess--) {
 260                 *swap = __be16_to_cpu(*swap);
 261                 swap++;
 262         }
 263
 264         *len -= sizeof(struct dns_header);
 265         *data += sizeof(struct dns_header);
 266
 267         return h;
 268 }
 269
 270 struct dns_question*
 271 dns_consume_question(uint8_t **data, int *len)
 272 {
 273         struct dns_question *q = (struct dns_question *) *data;
 274         uint16_t *swap = (uint16_t *) q;
 275         int endianess = 2;
 276
 277         if (*len < sizeof(struct dns_question))
 278                 return NULL;
 279
 280         while (endianess--) {
 281                 *swap = __be16_to_cpu(*swap);
 282                 swap++;
 283         }
 284
 285         *len -= sizeof(struct dns_question);
 286         *data += sizeof(struct dns_question);
 287
 288         return q;
 289 }
 290
 291 struct dns_answer*
 292 dns_consume_answer(uint8_t **data, int *len)
 293 {
 294         struct dns_answer *a = (struct dns_answer *) *data;
 295
 296         if (*len < sizeof(struct dns_answer))
 297                 return NULL;
 298
 299         a->type = __be16_to_cpu(a->type);
 300         a->class = __be16_to_cpu(a->class);
 301         a->ttl = __be32_to_cpu(a->ttl);
 302         a->rdlength = __be16_to_cpu(a->rdlength);
 303
 304         *len -= sizeof(struct dns_answer);
 305         *data += sizeof(struct dns_answer);
 306
 307         return a;
 308 }
 309
 310 char*
 311 dns_consume_name(uint8_t *base, int blen, uint8_t **data, int *len)
 312 {
 313         int nlen = scan_name(*data, *len);
 314
 315         if (nlen < 1)
 316                 return NULL;
 317
 318         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 319                 perror("dns_consume_name/dn_expand");
 320                 return NULL;
 321         }
 322
 323         *len -= nlen;
 324         *data += nlen;
 325
 326         return name_buffer;
 327 }
 328
 329 int
 330 dns_init(void)
 331 {
 332         name_buffer = malloc(MAX_NAME_LEN + 1);
 333         rdata_buffer = malloc(MAX_DATA_LEN + 1);
 334
 335         if (!name_buffer || !rdata_buffer)
 336                 return -1;
 337
 338         memset(name_buffer, 0, MAX_NAME_LEN + 1);
 339         memset(rdata_buffer, 0, MAX_NAME_LEN + 1);
 340
 341         return 0;
 342 }
 343
 344 void
 345 dns_cleanup(void)
 346 {
 347         free(name_buffer);
 348         free(rdata_buffer);
 349 }