Experimental support for IPv6 UDP encap.

This is a back-pocket solution only, to ensure that VpnManager
privileged clients can temporarily rely on IPv6 UDP encap if on
certain carriers IPv4 UDP and IPv6 ESP cannot provide acceptable
performance and battery life.

For these reasons IPv6 UDP encap is not a public or system API
and is triggered by passing a port greater than 65535 to the
existing openUdpEncapsulationSocket API.

Bug: 259001350
Test: new CTS tests
Change-Id: I02e0566ba910a300dda6a589cd265a3360add40c
diff --git a/service-t/src/com/android/server/IpSecService.java b/service-t/src/com/android/server/IpSecService.java
index 9e71eb3..1a51e91 100644
--- a/service-t/src/com/android/server/IpSecService.java
+++ b/service-t/src/com/android/server/IpSecService.java
@@ -17,6 +17,7 @@
 package com.android.server;
 
 import static android.Manifest.permission.DUMP;
+import static android.Manifest.permission.NETWORK_SETTINGS;
 import static android.net.IpSecManager.FEATURE_IPSEC_TUNNEL_MIGRATION;
 import static android.net.IpSecManager.INVALID_RESOURCE_ID;
 import static android.system.OsConstants.AF_INET;
@@ -65,6 +66,7 @@
 import com.android.internal.annotations.GuardedBy;
 import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.util.Preconditions;
+import com.android.modules.utils.build.SdkLevel;
 import com.android.net.module.util.BinderUtils;
 import com.android.net.module.util.NetdUtils;
 import com.android.net.module.util.PermissionUtils;
@@ -102,6 +104,7 @@
 
     private static final int NETD_FETCH_TIMEOUT_MS = 5000; // ms
     private static final InetAddress INADDR_ANY;
+    private static final InetAddress IN6ADDR_ANY;
 
     @VisibleForTesting static final int MAX_PORT_BIND_ATTEMPTS = 10;
 
@@ -110,6 +113,8 @@
     static {
         try {
             INADDR_ANY = InetAddress.getByAddress(new byte[] {0, 0, 0, 0});
+            IN6ADDR_ANY = InetAddress.getByAddress(
+                    new byte[] {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0});
         } catch (UnknownHostException e) {
             throw new RuntimeException(e);
         }
@@ -1013,11 +1018,13 @@
     private final class EncapSocketRecord extends OwnedResourceRecord {
         private FileDescriptor mSocket;
         private final int mPort;
+        private final int mFamily;  // TODO: what about IPV6_ADDRFORM?
 
-        EncapSocketRecord(int resourceId, FileDescriptor socket, int port) {
+        EncapSocketRecord(int resourceId, FileDescriptor socket, int port, int family) {
             super(resourceId);
             mSocket = socket;
             mPort = port;
+            mFamily = family;
         }
 
         /** always guarded by IpSecService#this */
@@ -1038,6 +1045,10 @@
             return mSocket;
         }
 
+        public int getFamily() {
+            return mFamily;
+        }
+
         @Override
         protected ResourceTracker getResourceTracker() {
             return getUserRecord().mSocketQuotaTracker;
@@ -1210,15 +1221,16 @@
      * and re-binding, during which the system could *technically* hand that port out to someone
      * else.
      */
-    private int bindToRandomPort(FileDescriptor sockFd) throws IOException {
+    private int bindToRandomPort(FileDescriptor sockFd, int family) throws IOException {
+        final InetAddress any = (family == AF_INET6) ? IN6ADDR_ANY : INADDR_ANY;
         for (int i = MAX_PORT_BIND_ATTEMPTS; i > 0; i--) {
             try {
-                FileDescriptor probeSocket = Os.socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
-                Os.bind(probeSocket, INADDR_ANY, 0);
+                FileDescriptor probeSocket = Os.socket(family, SOCK_DGRAM, IPPROTO_UDP);
+                Os.bind(probeSocket, any, 0);
                 int port = ((InetSocketAddress) Os.getsockname(probeSocket)).getPort();
                 Os.close(probeSocket);
                 Log.v(TAG, "Binding to port " + port);
-                Os.bind(sockFd, INADDR_ANY, port);
+                Os.bind(sockFd, any, port);
                 return port;
             } catch (ErrnoException e) {
                 // Someone miraculously claimed the port just after we closed probeSocket.
@@ -1260,6 +1272,19 @@
     @Override
     public synchronized IpSecUdpEncapResponse openUdpEncapsulationSocket(int port, IBinder binder)
             throws RemoteException {
+        // Experimental support for IPv6 UDP encap.
+        final int family;
+        final InetAddress localAddr;
+        if (SdkLevel.isAtLeastU() && port >= 65536) {
+            PermissionUtils.enforceNetworkStackPermissionOr(mContext, NETWORK_SETTINGS);
+            port -= 65536;
+            family = AF_INET6;
+            localAddr = IN6ADDR_ANY;
+        } else {
+            family = AF_INET;
+            localAddr = INADDR_ANY;
+        }
+
         if (port != 0 && (port < FREE_PORT_MIN || port > PORT_MAX)) {
             throw new IllegalArgumentException(
                     "Specified port number must be a valid non-reserved UDP port");
@@ -1278,7 +1303,7 @@
 
             FileDescriptor sockFd = null;
             try {
-                sockFd = Os.socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+                sockFd = Os.socket(family, SOCK_DGRAM, IPPROTO_UDP);
                 pFd = ParcelFileDescriptor.dup(sockFd);
             } finally {
                 IoUtils.closeQuietly(sockFd);
@@ -1295,15 +1320,16 @@
             mNetd.ipSecSetEncapSocketOwner(pFd, callingUid);
             if (port != 0) {
                 Log.v(TAG, "Binding to port " + port);
-                Os.bind(pFd.getFileDescriptor(), INADDR_ANY, port);
+                Os.bind(pFd.getFileDescriptor(), localAddr, port);
             } else {
-                port = bindToRandomPort(pFd.getFileDescriptor());
+                port = bindToRandomPort(pFd.getFileDescriptor(), family);
             }
 
             userRecord.mEncapSocketRecords.put(
                     resourceId,
                     new RefcountedResource<EncapSocketRecord>(
-                            new EncapSocketRecord(resourceId, pFd.getFileDescriptor(), port),
+                            new EncapSocketRecord(resourceId, pFd.getFileDescriptor(), port,
+                                    family),
                             binder));
             return new IpSecUdpEncapResponse(IpSecManager.Status.OK, resourceId, port,
                     pFd.getFileDescriptor());
@@ -1580,6 +1606,7 @@
      */
     private void checkIpSecConfig(IpSecConfig config) {
         UserRecord userRecord = mUserResourceTracker.getUserRecord(Binder.getCallingUid());
+        EncapSocketRecord encapSocketRecord = null;
 
         switch (config.getEncapType()) {
             case IpSecTransform.ENCAP_NONE:
@@ -1587,7 +1614,7 @@
             case IpSecTransform.ENCAP_ESPINUDP:
             case IpSecTransform.ENCAP_ESPINUDP_NON_IKE:
                 // Retrieve encap socket record; will throw IllegalArgumentException if not found
-                userRecord.mEncapSocketRecords.getResourceOrThrow(
+                encapSocketRecord = userRecord.mEncapSocketRecords.getResourceOrThrow(
                         config.getEncapSocketResourceId());
 
                 int port = config.getEncapRemotePort();
@@ -1641,10 +1668,9 @@
                             + ") have different address families.");
         }
 
-        // Throw an error if UDP Encapsulation is not used in IPv4.
-        if (config.getEncapType() != IpSecTransform.ENCAP_NONE && sourceFamily != AF_INET) {
+        if (encapSocketRecord != null && encapSocketRecord.getFamily() != destinationFamily) {
             throw new IllegalArgumentException(
-                    "UDP Encapsulation is not supported for this address family");
+                    "UDP encapsulation socket and destination address families must match");
         }
 
         switch (config.getMode()) {