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/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.networkstack.tethering;
import static android.net.NetworkCapabilities.TRANSPORT_CELLULAR;
import static android.net.NetworkCapabilities.TRANSPORT_TEST;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.net.LinkProperties;
import android.net.NetworkCapabilities;
import android.net.RouteInfo;
import com.android.net.module.util.NetUtils;
import com.android.networkstack.tethering.util.InterfaceSet;
import java.net.InetAddress;
import java.net.UnknownHostException;
/**
* @hide
*/
public final class TetheringInterfaceUtils {
private static final InetAddress IN6ADDR_ANY = getByAddress(
new byte[] {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0});
private static final InetAddress INADDR_ANY = getByAddress(new byte[] {0, 0, 0, 0});
/**
* Get upstream interfaces for tethering based on default routes for IPv4/IPv6.
* @return null if there is no usable interface, or a set of at least one interface otherwise.
*/
public static @Nullable InterfaceSet getTetheringInterfaces(UpstreamNetworkState ns) {
if (ns == null) {
return null;
}
final LinkProperties lp = ns.linkProperties;
final String if4 = getInterfaceForDestination(lp, INADDR_ANY);
final String if6 = getIPv6Interface(ns);
return (if4 == null && if6 == null) ? null : new InterfaceSet(if4, if6);
}
/**
* Get the upstream interface for IPv6 tethering.
* @return null if there is no usable interface, or the interface name otherwise.
*/
public static @Nullable String getIPv6Interface(UpstreamNetworkState ns) {
// Broadly speaking:
//
// [1] does the upstream have an IPv6 default route?
//
// and
//
// [2] does the upstream have one or more global IPv6 /64s
// dedicated to this device?
//
// In lieu of Prefix Delegation and other evaluation of whether a
// prefix may or may not be dedicated to this device, for now just
// check whether the upstream is TRANSPORT_CELLULAR. This works
// because "[t]he 3GPP network allocates each default bearer a unique
// /64 prefix", per RFC 6459, Section 5.2.
final boolean canTether =
(ns != null) && (ns.network != null)
&& (ns.linkProperties != null) && (ns.networkCapabilities != null)
// At least one upstream DNS server:
&& ns.linkProperties.hasIpv6DnsServer()
// Minimal amount of IPv6 provisioning:
&& ns.linkProperties.hasGlobalIpv6Address()
// Temporary approximation of "dedicated prefix":
&& allowIpv6Tethering(ns.networkCapabilities);
return canTether
? getInterfaceForDestination(ns.linkProperties, IN6ADDR_ANY)
: null;
}
private static boolean allowIpv6Tethering(@NonNull final NetworkCapabilities nc) {
return nc.hasTransport(TRANSPORT_CELLULAR) || nc.hasTransport(TRANSPORT_TEST);
}
private static String getInterfaceForDestination(LinkProperties lp, InetAddress dst) {
final RouteInfo ri = (lp != null)
? NetUtils.selectBestRoute(lp.getAllRoutes(), dst)
: null;
return (ri != null) ? ri.getInterface() : null;
}
private static InetAddress getByAddress(final byte[] addr) {
try {
return InetAddress.getByAddress(null, addr);
} catch (UnknownHostException e) {
throw new AssertionError("illegal address length" + addr.length);
}
}
}
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