1/*
2 * Copyright 2011 Daniel Drown
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 *
16 * dns64.c - find the nat64 prefix with a dns64 lookup
17 */
18
19#include <sys/socket.h>
20#include <netinet/in.h>
21#include <arpa/inet.h>
22#include <netdb.h>
23#include <strings.h>
24#include <stdio.h>
25#include <stdlib.h>
26#include <unistd.h>
27
28#include "dns64.h"
29#include "logging.h"
30#include "resolv_netid.h"
31
32/* function: plat_prefix
33 * looks up an ipv4-only hostname and looks for a nat64 /96 prefix, returns 1 on success, 0 on failure
34 * ipv4_name  - name to lookup
35 * net_id     - (optional) netId to use, NETID_UNSET indicates use of default network
36 * prefix     - the plat /96 prefix
37 */
38int plat_prefix(const char *ipv4_name, unsigned net_id, struct in6_addr *prefix) {
39  const struct addrinfo hints = {
40    .ai_family = AF_INET6,
41  };
42  int status;
43  struct addrinfo *result = NULL;
44  struct in6_addr plat_addr;
45  char plat_addr_str[INET6_ADDRSTRLEN];
46
47  logmsg(ANDROID_LOG_INFO, "Detecting NAT64 prefix from DNS...");
48
49  status = android_getaddrinfofornet(ipv4_name, NULL, &hints, net_id, MARK_UNSET, &result);
50  if (status != 0 || result == NULL) {
51    logmsg(ANDROID_LOG_ERROR, "plat_prefix/dns(%s) status = %d/%s",
52           ipv4_name, status, gai_strerror(status));
53    return 0;
54  }
55
56  // Use only the first result.  If other records are present, possibly with
57  // differing DNS64 prefixes they are ignored (there is very little sensible
58  // that could be done with them at this time anyway).
59
60  if (result->ai_family != AF_INET6) {
61    logmsg(ANDROID_LOG_WARN, "plat_prefix/unexpected address family: %d", result->ai_family);
62    return 0;
63  }
64  plat_addr = ((struct sockaddr_in6 *)result->ai_addr)->sin6_addr;
65  // Only /96 DNS64 prefixes are supported at this time.
66  plat_addr.s6_addr32[3] = 0;
67  freeaddrinfo(result);
68
69  logmsg(ANDROID_LOG_INFO, "Detected NAT64 prefix %s/96",
70         inet_ntop(AF_INET6, &plat_addr, plat_addr_str, sizeof(plat_addr_str)));
71  *prefix = plat_addr;
72  return 1;
73}
74