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 unsigned char buffer[MAX_NAME_LEN];
  73         static struct dns_header h = {
  74                 .questions = cpu_to_be16(1),
  75         };
  76         static struct dns_question q = {
  77                 .class = cpu_to_be16(1),
  78         };
  79         static struct iovec iov[] = {
  80                 {
  81                         .iov_base = &h,
  82                         .iov_len = sizeof(h),
  83                 },
  84                 {
  85                         .iov_base = buffer,
  86                 },
  87                 {
  88                         .iov_base = &q,
  89                         .iov_len = sizeof(q),
  90                 }
  91         };
  92         static struct sockaddr_in a = {
  93                 .sin_family = AF_INET,
  94                 .sin_port = htons(MCAST_PORT),
  95         };
  96         static struct msghdr m = {
  97                 .msg_name = (struct sockaddr *) &a,
  98                 .msg_namelen = sizeof(a),
  99                 .msg_iov = iov,
 100                 .msg_iovlen = ARRAY_SIZE(iov),
 101                 .msg_control = cmsg_data,
 102                 .msg_controllen = CMSG_LEN(sizeof(struct in_pktinfo)),
 103         };
 104         struct in_pktinfo *pkti;
 105         struct cmsghdr *cmsg;
 106         int len;
 107
 108         a.sin_addr.s_addr = inet_addr(MCAST_ADDR);
 109         q.type = __cpu_to_be16(type);
 110
 111         len = dn_comp(question, buffer, MAX_NAME_LEN, NULL, NULL);
 112         if (len < 1)
 113                 return;
 114
 115         iov[1].iov_len = len;
 116
 117         memset(cmsg_data, 0, sizeof(cmsg_data));
 118
 119         cmsg = CMSG_FIRSTHDR(&m);
 120         cmsg->cmsg_len = m.msg_controllen;
 121         cmsg->cmsg_level = IPPROTO_IP;
 122         cmsg->cmsg_type = IP_PKTINFO;
 123
 124         pkti = (struct in_pktinfo*) CMSG_DATA(cmsg);
 125         pkti->ipi_ifindex = iface_index;
 126
 127         if (sendmsg(u->fd, &m, 0) < 0)
 128                 fprintf(stderr, "failed to send question\n");
 129         else
 130                 DBG(1, "Q <- %s %s\n", dns_type_string(type), question);
 131 }
 132
 133
 134 struct dns_reply {
 135         int type;
 136         struct dns_answer a;
 137         uint16_t rdlength;
 138         uint8_t *rdata;
 139         char *buffer;
 140 };
 141
 142 #define MAX_ANSWER      8
 143 static struct dns_reply dns_reply[1 + (MAX_ANSWER * 3)];
 144 static int dns_answer_cnt;
 145
 146 void
 147 dns_init_answer(void)
 148 {
 149         dns_answer_cnt = 0;
 150 }
 151
 152 void
 153 dns_add_answer(int type, uint8_t *rdata, uint16_t rdlength)
 154 {
 155         struct dns_reply *a = &dns_reply[dns_answer_cnt];
 156         if (dns_answer_cnt == MAX_ANSWER)
 157                 return;
 158         a->rdata = memdup(rdata, rdlength);
 159         a->type = type;
 160         a->rdlength = rdlength;
 161         dns_answer_cnt++;
 162 }
 163
 164 void
 165 dns_send_answer(struct uloop_fd *u, char *answer)
 166 {
 167         uint8_t buffer[256];
 168         struct dns_header h = { 0 };
 169         struct msghdr m = { 0 };
 170         struct iovec *iov;
 171         struct sockaddr_in in = { 0 };
 172         int len, i;
 173
 174         if (!dns_answer_cnt)
 175                 return;
 176
 177         in.sin_family = AF_INET;
 178         in.sin_addr.s_addr = inet_addr(MCAST_ADDR);
 179         in.sin_port = htons(MCAST_PORT);
 180
 181         h.answers = __cpu_to_be16(dns_answer_cnt);
 182         h.flags = __cpu_to_be16(0x8400);
 183
 184         iov = malloc(sizeof(struct iovec) * ((dns_answer_cnt * 3) + 1));
 185         if (!iov)
 186                 return;
 187
 188         m.msg_name = &in;
 189         m.msg_namelen = sizeof(struct sockaddr_in);
 190         m.msg_iov = iov;
 191         m.msg_iovlen = (dns_answer_cnt * 3) + 1;
 192
 193         iov[0].iov_base = &h;
 194         iov[0].iov_len = sizeof(struct dns_header);
 195
 196         for (i = 0; i < dns_answer_cnt; i++) {
 197                 struct dns_answer *a = &dns_reply[i].a;
 198                 int id = (i * 3) + 1;
 199
 200                 memset(a, 0, sizeof(*a));
 201                 a->type = __cpu_to_be16(dns_reply[i].type);
 202                 a->class = __cpu_to_be16(1);
 203                 a->ttl = __cpu_to_be32(announce_ttl);
 204                 a->rdlength = __cpu_to_be16(dns_reply[i].rdlength);
 205
 206                 len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
 207                 if (len < 1)
 208                         return;
 209
 210                 dns_reply[i].buffer = iov[id].iov_base = memdup(buffer, len);
 211                 iov[id].iov_len = len;
 212
 213                 iov[id + 1].iov_base = a;
 214                 iov[id + 1].iov_len = sizeof(struct dns_answer);
 215
 216                 iov[id + 2].iov_base = dns_reply[i].rdata;
 217                 iov[id + 2].iov_len = dns_reply[i].rdlength;
 218
 219                 DBG(1, "A <- %s %s\n", dns_type_string(dns_reply[i].type), answer);
 220         }
 221
 222         if (sendmsg(u->fd, &m, 0) < 0)
 223                 fprintf(stderr, "failed to send question\n");
 224
 225         for (i = 0; i < dns_answer_cnt; i++) {
 226                 free(dns_reply[i].buffer);
 227                 free(dns_reply[i].rdata);
 228         }
 229         dns_answer_cnt = 0;
 230 }
 231
 232 static int
 233 scan_name(uint8_t *buffer, int len)
 234 {
 235         int offset = 0;
 236
 237         while (len && (*buffer != '\0')) {
 238                 int l = *buffer;
 239
 240                 if (IS_COMPRESSED(l))
 241                         return offset + 2;
 242
 243                 len -= l + 1;
 244                 offset += l + 1;
 245                 buffer += l + 1;
 246         }
 247
 248         if (!len || !offset || (*buffer != '\0'))
 249                 return -1;
 250
 251         return offset + 1;
 252 }
 253
 254 struct dns_header*
 255 dns_consume_header(uint8_t **data, int *len)
 256 {
 257         struct dns_header *h = (struct dns_header *) *data;
 258         uint16_t *swap = (uint16_t *) h;
 259         int endianess = 6;
 260
 261         if (*len < sizeof(struct dns_header))
 262                 return NULL;
 263
 264         while (endianess--) {
 265                 *swap = __be16_to_cpu(*swap);
 266                 swap++;
 267         }
 268
 269         *len -= sizeof(struct dns_header);
 270         *data += sizeof(struct dns_header);
 271
 272         return h;
 273 }
 274
 275 struct dns_question*
 276 dns_consume_question(uint8_t **data, int *len)
 277 {
 278         struct dns_question *q = (struct dns_question *) *data;
 279         uint16_t *swap = (uint16_t *) q;
 280         int endianess = 2;
 281
 282         if (*len < sizeof(struct dns_question))
 283                 return NULL;
 284
 285         while (endianess--) {
 286                 *swap = __be16_to_cpu(*swap);
 287                 swap++;
 288         }
 289
 290         *len -= sizeof(struct dns_question);
 291         *data += sizeof(struct dns_question);
 292
 293         return q;
 294 }
 295
 296 struct dns_answer*
 297 dns_consume_answer(uint8_t **data, int *len)
 298 {
 299         struct dns_answer *a = (struct dns_answer *) *data;
 300
 301         if (*len < sizeof(struct dns_answer))
 302                 return NULL;
 303
 304         a->type = __be16_to_cpu(a->type);
 305         a->class = __be16_to_cpu(a->class);
 306         a->ttl = __be32_to_cpu(a->ttl);
 307         a->rdlength = __be16_to_cpu(a->rdlength);
 308
 309         *len -= sizeof(struct dns_answer);
 310         *data += sizeof(struct dns_answer);
 311
 312         return a;
 313 }
 314
 315 char*
 316 dns_consume_name(uint8_t *base, int blen, uint8_t **data, int *len)
 317 {
 318         int nlen = scan_name(*data, *len);
 319
 320         if (nlen < 1)
 321                 return NULL;
 322
 323         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 324                 perror("dns_consume_name/dn_expand");
 325                 return NULL;
 326         }
 327
 328         *len -= nlen;
 329         *data += nlen;
 330
 331         return name_buffer;
 332 }