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 void
  69 dns_send_question(struct uloop_fd *u, char *question, int type)
  70 {
  71         static size_t cmsg_data[( CMSG_SPACE(sizeof(struct in_pktinfo)) / sizeof(size_t)) + 1];
  72         static struct dns_header h = {
  73                 .questions = cpu_to_be16(1),
  74         };
  75         static struct dns_question q = {
  76                 .class = cpu_to_be16(1),
  77         };
  78         static struct iovec iov[] = {
  79                 {
  80                         .iov_base = &h,
  81                         .iov_len = sizeof(h),
  82                 },
  83                 {
  84                         .iov_base = name_buffer,
  85                 },
  86                 {
  87                         .iov_base = &q,
  88                         .iov_len = sizeof(q),
  89                 }
  90         };
  91         static struct sockaddr_in a = {
  92                 .sin_family = AF_INET,
  93                 .sin_port = htons(MCAST_PORT),
  94         };
  95         static struct msghdr m = {
  96                 .msg_name = (struct sockaddr *) &a,
  97                 .msg_namelen = sizeof(a),
  98                 .msg_iov = iov,
  99                 .msg_iovlen = ARRAY_SIZE(iov),
 100                 .msg_control = cmsg_data,
 101                 .msg_controllen = CMSG_LEN(sizeof(struct in_pktinfo)),
 102         };
 103         struct in_pktinfo *pkti;
 104         struct cmsghdr *cmsg;
 105         int len;
 106
 107         a.sin_addr.s_addr = inet_addr(MCAST_ADDR);
 108         q.type = __cpu_to_be16(type);
 109
 110         len = dn_comp(question, (void *) name_buffer, sizeof(name_buffer), NULL, NULL);
 111         if (len < 1)
 112                 return;
 113
 114         iov[1].iov_len = len;
 115
 116         memset(cmsg_data, 0, sizeof(cmsg_data));
 117
 118         cmsg = CMSG_FIRSTHDR(&m);
 119         cmsg->cmsg_len = m.msg_controllen;
 120         cmsg->cmsg_level = IPPROTO_IP;
 121         cmsg->cmsg_type = IP_PKTINFO;
 122
 123         pkti = (struct in_pktinfo*) CMSG_DATA(cmsg);
 124         pkti->ipi_ifindex = iface_index;
 125
 126         if (sendmsg(u->fd, &m, 0) < 0)
 127                 fprintf(stderr, "failed to send question\n");
 128         else
 129                 DBG(1, "Q <- %s %s\n", dns_type_string(type), question);
 130 }
 131
 132
 133 struct dns_reply {
 134         int type;
 135         struct dns_answer a;
 136         uint16_t rdlength;
 137         uint8_t *rdata;
 138         char *buffer;
 139 };
 140
 141 #define MAX_ANSWER      8
 142 static struct dns_reply dns_reply[1 + (MAX_ANSWER * 3)];
 143 static int dns_answer_cnt;
 144
 145 void
 146 dns_init_answer(void)
 147 {
 148         dns_answer_cnt = 0;
 149 }
 150
 151 void
 152 dns_add_answer(int type, uint8_t *rdata, uint16_t rdlength)
 153 {
 154         struct dns_reply *a = &dns_reply[dns_answer_cnt];
 155         if (dns_answer_cnt == MAX_ANSWER)
 156                 return;
 157         a->rdata = memdup(rdata, rdlength);
 158         a->type = type;
 159         a->rdlength = rdlength;
 160         dns_answer_cnt++;
 161 }
 162
 163 void
 164 dns_send_answer(struct uloop_fd *u, char *answer)
 165 {
 166         uint8_t buffer[256];
 167         struct dns_header h = { 0 };
 168         struct msghdr m = { 0 };
 169         struct iovec *iov;
 170         struct sockaddr_in in = { 0 };
 171         int len, i;
 172
 173         if (!dns_answer_cnt)
 174                 return;
 175
 176         in.sin_family = AF_INET;
 177         in.sin_addr.s_addr = inet_addr(MCAST_ADDR);
 178         in.sin_port = htons(MCAST_PORT);
 179
 180         h.answers = __cpu_to_be16(dns_answer_cnt);
 181         h.flags = __cpu_to_be16(0x8400);
 182
 183         iov = malloc(sizeof(struct iovec) * ((dns_answer_cnt * 3) + 1));
 184         if (!iov)
 185                 return;
 186
 187         m.msg_name = &in;
 188         m.msg_namelen = sizeof(struct sockaddr_in);
 189         m.msg_iov = iov;
 190         m.msg_iovlen = (dns_answer_cnt * 3) + 1;
 191
 192         iov[0].iov_base = &h;
 193         iov[0].iov_len = sizeof(struct dns_header);
 194
 195         for (i = 0; i < dns_answer_cnt; i++) {
 196                 struct dns_answer *a = &dns_reply[i].a;
 197                 int id = (i * 3) + 1;
 198
 199                 memset(a, 0, sizeof(*a));
 200                 a->type = __cpu_to_be16(dns_reply[i].type);
 201                 a->class = __cpu_to_be16(1);
 202                 a->ttl = __cpu_to_be32(announce_ttl);
 203                 a->rdlength = __cpu_to_be16(dns_reply[i].rdlength);
 204
 205                 len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
 206                 if (len < 1)
 207                         return;
 208
 209                 dns_reply[i].buffer = iov[id].iov_base = memdup(buffer, len);
 210                 iov[id].iov_len = len;
 211
 212                 iov[id + 1].iov_base = a;
 213                 iov[id + 1].iov_len = sizeof(struct dns_answer);
 214
 215                 iov[id + 2].iov_base = dns_reply[i].rdata;
 216                 iov[id + 2].iov_len = dns_reply[i].rdlength;
 217
 218                 DBG(1, "A <- %s %s\n", dns_type_string(dns_reply[i].type), answer);
 219         }
 220
 221         if (sendmsg(u->fd, &m, 0) < 0)
 222                 fprintf(stderr, "failed to send question\n");
 223
 224         for (i = 0; i < dns_answer_cnt; i++) {
 225                 free(dns_reply[i].buffer);
 226                 free(dns_reply[i].rdata);
 227         }
 228         dns_answer_cnt = 0;
 229 }
 230
 231 static int
 232 scan_name(uint8_t *buffer, int len)
 233 {
 234         int offset = 0;
 235
 236         while (len && (*buffer != '\0')) {
 237                 int l = *buffer;
 238
 239                 if (IS_COMPRESSED(l))
 240                         return offset + 2;
 241
 242                 len -= l + 1;
 243                 offset += l + 1;
 244                 buffer += l + 1;
 245         }
 246
 247         if (!len || !offset || (*buffer != '\0'))
 248                 return -1;
 249
 250         return offset + 1;
 251 }
 252
 253 struct dns_header*
 254 dns_consume_header(uint8_t **data, int *len)
 255 {
 256         struct dns_header *h = (struct dns_header *) *data;
 257         uint16_t *swap = (uint16_t *) h;
 258         int endianess = 6;
 259
 260         if (*len < sizeof(struct dns_header))
 261                 return NULL;
 262
 263         while (endianess--) {
 264                 *swap = __be16_to_cpu(*swap);
 265                 swap++;
 266         }
 267
 268         *len -= sizeof(struct dns_header);
 269         *data += sizeof(struct dns_header);
 270
 271         return h;
 272 }
 273
 274 struct dns_question*
 275 dns_consume_question(uint8_t **data, int *len)
 276 {
 277         struct dns_question *q = (struct dns_question *) *data;
 278         uint16_t *swap = (uint16_t *) q;
 279         int endianess = 2;
 280
 281         if (*len < sizeof(struct dns_question))
 282                 return NULL;
 283
 284         while (endianess--) {
 285                 *swap = __be16_to_cpu(*swap);
 286                 swap++;
 287         }
 288
 289         *len -= sizeof(struct dns_question);
 290         *data += sizeof(struct dns_question);
 291
 292         return q;
 293 }
 294
 295 struct dns_answer*
 296 dns_consume_answer(uint8_t **data, int *len)
 297 {
 298         struct dns_answer *a = (struct dns_answer *) *data;
 299
 300         if (*len < sizeof(struct dns_answer))
 301                 return NULL;
 302
 303         a->type = __be16_to_cpu(a->type);
 304         a->class = __be16_to_cpu(a->class);
 305         a->ttl = __be32_to_cpu(a->ttl);
 306         a->rdlength = __be16_to_cpu(a->rdlength);
 307
 308         *len -= sizeof(struct dns_answer);
 309         *data += sizeof(struct dns_answer);
 310
 311         return a;
 312 }
 313
 314 char*
 315 dns_consume_name(uint8_t *base, int blen, uint8_t **data, int *len)
 316 {
 317         int nlen = scan_name(*data, *len);
 318
 319         if (nlen < 1)
 320                 return NULL;
 321
 322         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 323                 perror("dns_consume_name/dn_expand");
 324                 return NULL;
 325         }
 326
 327         *len -= nlen;
 328         *data += nlen;
 329
 330         return name_buffer;
 331 }