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 #include "interface.h"
  39
  40 char rdata_buffer[MAX_DATA_LEN + 1];
  41 static char name_buffer[MAX_NAME_LEN + 1];
  42
  43 const char*
  44 dns_type_string(uint16_t type)
  45 {
  46         switch (type) {
  47         case TYPE_A:
  48                 return "A";
  49
  50         case TYPE_AAAA:
  51                 return "AAAA";
  52
  53         case TYPE_PTR:
  54                 return "PTR";
  55
  56         case TYPE_TXT:
  57                 return "TXT";
  58
  59         case TYPE_SRV:
  60                 return "SRV";
  61
  62         case TYPE_ANY:
  63                 return "ANY";
  64         }
  65
  66         return "N/A";
  67 }
  68
  69 void
  70 dns_send_question(struct interface *iface, const char *question, int type)
  71 {
  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         int len;
  92
  93         q.type = __cpu_to_be16(type);
  94
  95         len = dn_comp(question, (void *) name_buffer, sizeof(name_buffer), NULL, NULL);
  96         if (len < 1)
  97                 return;
  98
  99         iov[1].iov_len = len;
 100
 101         if (interface_send_packet(iface, iov, ARRAY_SIZE(iov)) < 0)
 102                 fprintf(stderr, "failed to send question\n");
 103         else
 104                 DBG(1, "Q <- %s %s\n", dns_type_string(type), question);
 105 }
 106
 107
 108 struct dns_reply {
 109         int type;
 110         struct dns_answer a;
 111         uint16_t rdlength;
 112         uint8_t *rdata;
 113         char *buffer;
 114 };
 115
 116 #define MAX_ANSWER      8
 117 static struct dns_reply dns_reply[1 + (MAX_ANSWER * 3)];
 118 static int dns_answer_cnt;
 119
 120 void
 121 dns_init_answer(void)
 122 {
 123         dns_answer_cnt = 0;
 124 }
 125
 126 void
 127 dns_add_answer(int type, const uint8_t *rdata, uint16_t rdlength)
 128 {
 129         struct dns_reply *a = &dns_reply[dns_answer_cnt];
 130         if (dns_answer_cnt == MAX_ANSWER)
 131                 return;
 132         a->rdata = memdup(rdata, rdlength);
 133         a->type = type;
 134         a->rdlength = rdlength;
 135         dns_answer_cnt++;
 136 }
 137
 138 void
 139 dns_send_answer(struct interface *iface, const char *answer)
 140 {
 141         uint8_t buffer[256];
 142         struct dns_header h = { 0 };
 143         struct iovec *iov;
 144         int len, i;
 145
 146         if (!dns_answer_cnt)
 147                 return;
 148
 149         h.answers = __cpu_to_be16(dns_answer_cnt);
 150         h.flags = __cpu_to_be16(0x8400);
 151
 152         iov = alloca(sizeof(struct iovec) * ((dns_answer_cnt * 3) + 1));
 153         iov[0].iov_base = &h;
 154         iov[0].iov_len = sizeof(struct dns_header);
 155
 156         for (i = 0; i < dns_answer_cnt; i++) {
 157                 struct dns_answer *a = &dns_reply[i].a;
 158                 int id = (i * 3) + 1;
 159
 160                 memset(a, 0, sizeof(*a));
 161                 a->type = __cpu_to_be16(dns_reply[i].type);
 162                 a->class = __cpu_to_be16(1);
 163                 a->ttl = __cpu_to_be32(announce_ttl);
 164                 a->rdlength = __cpu_to_be16(dns_reply[i].rdlength);
 165
 166                 len = dn_comp(answer, buffer, sizeof(buffer), NULL, NULL);
 167                 if (len < 1)
 168                         return;
 169
 170                 dns_reply[i].buffer = iov[id].iov_base = memdup(buffer, len);
 171                 iov[id].iov_len = len;
 172
 173                 iov[id + 1].iov_base = a;
 174                 iov[id + 1].iov_len = sizeof(struct dns_answer);
 175
 176                 iov[id + 2].iov_base = dns_reply[i].rdata;
 177                 iov[id + 2].iov_len = dns_reply[i].rdlength;
 178
 179                 DBG(1, "A <- %s %s\n", dns_type_string(dns_reply[i].type), answer);
 180         }
 181
 182         if (interface_send_packet(iface, iov, (dns_answer_cnt * 3) + 1) < 0)
 183                 fprintf(stderr, "failed to send question\n");
 184
 185         for (i = 0; i < dns_answer_cnt; i++) {
 186                 free(dns_reply[i].buffer);
 187                 free(dns_reply[i].rdata);
 188         }
 189         dns_answer_cnt = 0;
 190 }
 191
 192 static int
 193 scan_name(const uint8_t *buffer, int len)
 194 {
 195         int offset = 0;
 196
 197         while (len && (*buffer != '\0')) {
 198                 int l = *buffer;
 199
 200                 if (IS_COMPRESSED(l))
 201                         return offset + 2;
 202
 203                 len -= l + 1;
 204                 offset += l + 1;
 205                 buffer += l + 1;
 206         }
 207
 208         if (!len || !offset || (*buffer != '\0'))
 209                 return -1;
 210
 211         return offset + 1;
 212 }
 213
 214 struct dns_header*
 215 dns_consume_header(uint8_t **data, int *len)
 216 {
 217         struct dns_header *h = (struct dns_header *) *data;
 218         uint16_t *swap = (uint16_t *) h;
 219         int endianess = 6;
 220
 221         if (*len < sizeof(struct dns_header))
 222                 return NULL;
 223
 224         while (endianess--) {
 225                 *swap = __be16_to_cpu(*swap);
 226                 swap++;
 227         }
 228
 229         *len -= sizeof(struct dns_header);
 230         *data += sizeof(struct dns_header);
 231
 232         return h;
 233 }
 234
 235 struct dns_question*
 236 dns_consume_question(uint8_t **data, int *len)
 237 {
 238         struct dns_question *q = (struct dns_question *) *data;
 239         uint16_t *swap = (uint16_t *) q;
 240         int endianess = 2;
 241
 242         if (*len < sizeof(struct dns_question))
 243                 return NULL;
 244
 245         while (endianess--) {
 246                 *swap = __be16_to_cpu(*swap);
 247                 swap++;
 248         }
 249
 250         *len -= sizeof(struct dns_question);
 251         *data += sizeof(struct dns_question);
 252
 253         return q;
 254 }
 255
 256 struct dns_answer*
 257 dns_consume_answer(uint8_t **data, int *len)
 258 {
 259         struct dns_answer *a = (struct dns_answer *) *data;
 260
 261         if (*len < sizeof(struct dns_answer))
 262                 return NULL;
 263
 264         a->type = __be16_to_cpu(a->type);
 265         a->class = __be16_to_cpu(a->class);
 266         a->ttl = __be32_to_cpu(a->ttl);
 267         a->rdlength = __be16_to_cpu(a->rdlength);
 268
 269         *len -= sizeof(struct dns_answer);
 270         *data += sizeof(struct dns_answer);
 271
 272         return a;
 273 }
 274
 275 char*
 276 dns_consume_name(const uint8_t *base, int blen, uint8_t **data, int *len)
 277 {
 278         int nlen = scan_name(*data, *len);
 279
 280         if (nlen < 1)
 281                 return NULL;
 282
 283         if (dn_expand(base, base + blen, *data, name_buffer, MAX_NAME_LEN) < 0) {
 284                 perror("dns_consume_name/dn_expand");
 285                 return NULL;
 286         }
 287
 288         *len -= nlen;
 289         *data += nlen;
 290
 291         return name_buffer;
 292 }