1 /* 2 * Copyright (C) 2018 The Android Open Source Project 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 17 package com.android.networkstack.tethering; 18 19 import android.annotation.Nullable; 20 import android.net.LinkProperties; 21 import android.net.NetworkCapabilities; 22 import android.net.RouteInfo; 23 import android.net.util.InterfaceSet; 24 25 import com.android.net.module.util.NetUtils; 26 27 import java.net.InetAddress; 28 import java.net.UnknownHostException; 29 30 /** 31 * @hide 32 */ 33 public final class TetheringInterfaceUtils { 34 private static final InetAddress IN6ADDR_ANY = getByAddress( 35 new byte[] {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}); 36 private static final InetAddress INADDR_ANY = getByAddress(new byte[] {0, 0, 0, 0}); 37 38 /** 39 * Get upstream interfaces for tethering based on default routes for IPv4/IPv6. 40 * @return null if there is no usable interface, or a set of at least one interface otherwise. 41 */ getTetheringInterfaces(UpstreamNetworkState ns)42 public static @Nullable InterfaceSet getTetheringInterfaces(UpstreamNetworkState ns) { 43 if (ns == null) { 44 return null; 45 } 46 47 final LinkProperties lp = ns.linkProperties; 48 final String if4 = getInterfaceForDestination(lp, INADDR_ANY); 49 final String if6 = getIPv6Interface(ns); 50 51 return (if4 == null && if6 == null) ? null : new InterfaceSet(if4, if6); 52 } 53 54 /** 55 * Get the upstream interface for IPv6 tethering. 56 * @return null if there is no usable interface, or the interface name otherwise. 57 */ getIPv6Interface(UpstreamNetworkState ns)58 public static @Nullable String getIPv6Interface(UpstreamNetworkState ns) { 59 // Broadly speaking: 60 // 61 // [1] does the upstream have an IPv6 default route? 62 // 63 // and 64 // 65 // [2] does the upstream have one or more global IPv6 /64s 66 // dedicated to this device? 67 // 68 // In lieu of Prefix Delegation and other evaluation of whether a 69 // prefix may or may not be dedicated to this device, for now just 70 // check whether the upstream is TRANSPORT_CELLULAR. This works 71 // because "[t]he 3GPP network allocates each default bearer a unique 72 // /64 prefix", per RFC 6459, Section 5.2. 73 final boolean canTether = 74 (ns != null) && (ns.network != null) 75 && (ns.linkProperties != null) && (ns.networkCapabilities != null) 76 // At least one upstream DNS server: 77 && ns.linkProperties.hasIpv6DnsServer() 78 // Minimal amount of IPv6 provisioning: 79 && ns.linkProperties.hasGlobalIpv6Address() 80 // Temporary approximation of "dedicated prefix": 81 && ns.networkCapabilities.hasTransport(NetworkCapabilities.TRANSPORT_CELLULAR); 82 83 return canTether 84 ? getInterfaceForDestination(ns.linkProperties, IN6ADDR_ANY) 85 : null; 86 } 87 getInterfaceForDestination(LinkProperties lp, InetAddress dst)88 private static String getInterfaceForDestination(LinkProperties lp, InetAddress dst) { 89 final RouteInfo ri = (lp != null) 90 ? NetUtils.selectBestRoute(lp.getAllRoutes(), dst) 91 : null; 92 return (ri != null) ? ri.getInterface() : null; 93 } 94 getByAddress(final byte[] addr)95 private static InetAddress getByAddress(final byte[] addr) { 96 try { 97 return InetAddress.getByAddress(null, addr); 98 } catch (UnknownHostException e) { 99 throw new AssertionError("illegal address length" + addr.length); 100 } 101 } 102 } 103