Allow MANAGE_TEST_NETWORKS to register limited agents

This puts in force some restrictions against test networks,
and in exchange relaxes the restrictions around registering
a network agent that provides a test network.
Test networks can only ever have transport TEST, and have
only a few capabilities available to them.

This is useful in particular to test CTS. See aosp/1253423
for first, basic usage of this capability.

Test: IpSecManagerTunnelTest
Test: new CTS aosp/1253423
Bug: 139268426
Change-Id: I47600e6097e8519e50ae771daa13bb6bb7640451

core/java/android/net/NetworkCapabilities.java

@@ -411,6 +411,20 @@ public final class NetworkCapabilities implements Parcelable {
             | (1 << NET_CAPABILITY_FOREGROUND)
             | (1 << NET_CAPABILITY_PARTIAL_CONNECTIVITY);
 
+    /**
+     * Capabilities that are allowed for test networks. This list must be set so that it is safe
+     * for an unprivileged user to create a network with these capabilities via shell. As such,
+     * it must never contain capabilities that are generally useful to the system, such as
+     * INTERNET, IMS, SUPL, etc.
+     */
+    private static final long TEST_NETWORKS_ALLOWED_CAPABILITIES =
+            (1 << NET_CAPABILITY_NOT_METERED)
+            | (1 << NET_CAPABILITY_NOT_RESTRICTED)
+            | (1 << NET_CAPABILITY_NOT_VPN)
+            | (1 << NET_CAPABILITY_NOT_ROAMING)
+            | (1 << NET_CAPABILITY_NOT_CONGESTED)
+            | (1 << NET_CAPABILITY_NOT_SUSPENDED);
+
     /**
      * Adds the given capability to this {@code NetworkCapability} instance.
      * Multiple capabilities may be applied sequentially.  Note that when searching
@@ -640,6 +654,21 @@ public final class NetworkCapabilities implements Parcelable {
         }
     }
 
+    /**
+     * Test networks have strong restrictions on what capabilities they can have. Enforce these
+     * restrictions.
+     * @hide
+     */
+    public void restrictCapabilitesForTestNetwork() {
+        final long originalCapabilities = mNetworkCapabilities;
+        final NetworkSpecifier originalSpecifier = mNetworkSpecifier;
+        clearAll();
+        // Reset the transports to only contain TRANSPORT_TEST.
+        mTransportTypes = (1 << TRANSPORT_TEST);
+        mNetworkCapabilities = originalCapabilities & TEST_NETWORKS_ALLOWED_CAPABILITIES;
+        mNetworkSpecifier = originalSpecifier;
+    }
+
     /**
      * Representing the transport type.  Apps should generally not care about transport.  A
      * request for a fast internet connection could be satisfied by a number of different

services/core/java/com/android/server/ConnectivityService.java

@@ -40,6 +40,7 @@ import static android.net.NetworkCapabilities.NET_CAPABILITY_NOT_VPN;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_PARTIAL_CONNECTIVITY;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_VALIDATED;
 import static android.net.NetworkCapabilities.TRANSPORT_CELLULAR;
+import static android.net.NetworkCapabilities.TRANSPORT_TEST;
 import static android.net.NetworkCapabilities.TRANSPORT_VPN;
 import static android.net.NetworkPolicyManager.RULE_NONE;
 import static android.net.NetworkPolicyManager.uidRulesToString;
@@ -52,6 +53,7 @@ import static com.android.internal.util.Preconditions.checkNotNull;
 
 import static java.util.Map.Entry;
 
+import android.Manifest;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.app.AppOpsManager;
@@ -2696,10 +2698,18 @@ public class ConnectivityService extends IConnectivityManager.Stub
 
             switch (msg.what) {
                 case NetworkAgent.EVENT_NETWORK_CAPABILITIES_CHANGED: {
-                    final NetworkCapabilities networkCapabilities = (NetworkCapabilities) msg.obj;
+                    NetworkCapabilities networkCapabilities = (NetworkCapabilities) msg.obj;
                     if (networkCapabilities.hasConnectivityManagedCapability()) {
                         Slog.wtf(TAG, "BUG: " + nai + " has CS-managed capability.");
                     }
+                    if (networkCapabilities.hasTransport(TRANSPORT_TEST)) {
+                        // Make sure the original object is not mutated. NetworkAgent normally
+                        // makes a copy of the capabilities when sending the message through
+                        // the Messenger, but if this ever changes, not making a defensive copy
+                        // here will give attack vectors to clients using this code path.
+                        networkCapabilities = new NetworkCapabilities(networkCapabilities);
+                        networkCapabilities.restrictCapabilitesForTestNetwork();
+                    }
                     updateCapabilities(nai.getCurrentScore(), nai, networkCapabilities);
                     break;
                 }
@@ -5772,7 +5782,16 @@ public class ConnectivityService extends IConnectivityManager.Stub
     public Network registerNetworkAgent(Messenger messenger, NetworkInfo networkInfo,
             LinkProperties linkProperties, NetworkCapabilities networkCapabilities,
             int currentScore, NetworkAgentConfig networkAgentConfig, int providerId) {
-        enforceNetworkFactoryPermission();
+        if (networkCapabilities.hasTransport(TRANSPORT_TEST)) {
+            enforceAnyPermissionOf(Manifest.permission.MANAGE_TEST_NETWORKS);
+            // Strictly, sanitizing here is unnecessary as the capabilities will be sanitized in
+            // the call to mixInCapabilities below anyway, but sanitizing here means the NAI never
+            // sees capabilities that may be malicious, which might prevent mistakes in the future.
+            networkCapabilities = new NetworkCapabilities(networkCapabilities);
+            networkCapabilities.restrictCapabilitesForTestNetwork();
+        } else {
+            enforceNetworkFactoryPermission();
+        }
 
         LinkProperties lp = new LinkProperties(linkProperties);
         lp.ensureDirectlyConnectedRoutes();