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.server.connectivity.tethering; 18 19 import android.annotation.Nullable; 20 import android.net.LinkProperties; 21 import android.net.NetworkCapabilities; 22 import android.net.NetworkState; 23 import android.net.RouteInfo; 24 import android.net.util.InterfaceSet; 25 26 import java.net.Inet4Address; 27 import java.net.Inet6Address; 28 import java.net.InetAddress; 29 30 /** 31 * @hide 32 */ 33 public final class TetheringInterfaceUtils { 34 /** 35 * Get upstream interfaces for tethering based on default routes for IPv4/IPv6. 36 * @return null if there is no usable interface, or a set of at least one interface otherwise. 37 */ 38 public static @Nullable InterfaceSet getTetheringInterfaces(NetworkState ns) { 39 if (ns == null) { 40 return null; 41 } 42 43 final LinkProperties lp = ns.linkProperties; 44 final String if4 = getInterfaceForDestination(lp, Inet4Address.ANY); 45 final String if6 = getIPv6Interface(ns); 46 47 return (if4 == null && if6 == null) ? null : new InterfaceSet(if4, if6); 48 } 49 50 /** 51 * Get the upstream interface for IPv6 tethering. 52 * @return null if there is no usable interface, or the interface name otherwise. 53 */ 54 public static @Nullable String getIPv6Interface(NetworkState ns) { 55 // Broadly speaking: 56 // 57 // [1] does the upstream have an IPv6 default route? 58 // 59 // and 60 // 61 // [2] does the upstream have one or more global IPv6 /64s 62 // dedicated to this device? 63 // 64 // In lieu of Prefix Delegation and other evaluation of whether a 65 // prefix may or may not be dedicated to this device, for now just 66 // check whether the upstream is TRANSPORT_CELLULAR. This works 67 // because "[t]he 3GPP network allocates each default bearer a unique 68 // /64 prefix", per RFC 6459, Section 5.2. 69 final boolean canTether = 70 (ns != null) && (ns.network != null) && 71 (ns.linkProperties != null) && (ns.networkCapabilities != null) && 72 // At least one upstream DNS server: 73 ns.linkProperties.hasIPv6DnsServer() && 74 // Minimal amount of IPv6 provisioning: 75 ns.linkProperties.hasGlobalIPv6Address() && 76 // Temporary approximation of "dedicated prefix": 77 ns.networkCapabilities.hasTransport(NetworkCapabilities.TRANSPORT_CELLULAR); 78 79 return canTether 80 ? getInterfaceForDestination(ns.linkProperties, Inet6Address.ANY) 81 : null; 82 } 83 84 private static String getInterfaceForDestination(LinkProperties lp, InetAddress dst) { 85 final RouteInfo ri = (lp != null) 86 ? RouteInfo.selectBestRoute(lp.getAllRoutes(), dst) 87 : null; 88 return (ri != null) ? ri.getInterface() : null; 89 } 90 } 91
