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 "NetdClient.h"
31#include "resolv_netid.h"
32
33/* function: plat_prefix
34 * looks up an ipv4-only hostname and looks for a nat64 /96 prefix, returns 1 on success, 0 on failure
35 * ipv4_name  - name to lookup
36 * net_id     - (optional) netId to use, NETID_UNSET indicates use of default network
37 * prefix     - the plat /96 prefix
38 */
39int plat_prefix(const char *ipv4_name, unsigned net_id, struct in6_addr *prefix) {
40  const struct addrinfo hints = {
41    .ai_family = AF_INET6,
42  };
43  int status;
44  struct addrinfo *result = NULL;
45  struct in6_addr plat_addr;
46  char plat_addr_str[INET6_ADDRSTRLEN];
47
48  logmsg(ANDROID_LOG_INFO, "Detecting NAT64 prefix from DNS...");
49
50  // Be sure to query local DNS64 servers, bypassing Private DNS (if enabled).
51  if (net_id != NETID_UNSET) {
52    net_id |= NETID_USE_LOCAL_NAMESERVERS;
53  }
54
55  status = android_getaddrinfofornet(ipv4_name, NULL, &hints, net_id, MARK_UNSET, &result);
56  if (status != 0 || result == NULL) {
57    logmsg(ANDROID_LOG_ERROR, "plat_prefix/dns(%s) status = %d/%s",
58           ipv4_name, status, gai_strerror(status));
59    return 0;
60  }
61
62  // Use only the first result.  If other records are present, possibly with
63  // differing DNS64 prefixes they are ignored (there is very little sensible
64  // that could be done with them at this time anyway).
65
66  if (result->ai_family != AF_INET6) {
67    logmsg(ANDROID_LOG_WARN, "plat_prefix/unexpected address family: %d", result->ai_family);
68    return 0;
69  }
70  plat_addr = ((struct sockaddr_in6 *)result->ai_addr)->sin6_addr;
71  // Only /96 DNS64 prefixes are supported at this time.
72  plat_addr.s6_addr32[3] = 0;
73  freeaddrinfo(result);
74
75  logmsg(ANDROID_LOG_INFO, "Detected NAT64 prefix %s/96",
76         inet_ntop(AF_INET6, &plat_addr, plat_addr_str, sizeof(plat_addr_str)));
77  *prefix = plat_addr;
78  return 1;
79}
80