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 */
plat_prefix(const char * ipv4_name,unsigned net_id,struct in6_addr * prefix)39 int 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