TestNetworkService: Add support for toggling carrier on tun/tap

Adds support for setting carrier to on/off for a tun/tap interface. It
turns out that TUNSETCARRIER is also usable by tap interfaces, and
TUNSETLINK does not work as expected.

Test: atest EthernetManagerTest
Change-Id: I39d70e0a65a34e7a4c4df70c53e4cc781a24a213

framework/src/android/net/ITestNetworkManager.aidl

@@ -32,6 +32,8 @@ interface ITestNetworkManager
     TestNetworkInterface createInterface(boolean isTun, boolean bringUp, in LinkAddress[] addrs,
             in @nullable String iface);
 
+    void setCarrierEnabled(in TestNetworkInterface iface, boolean enabled);
+
     void setupTestNetwork(in String iface, in LinkProperties lp, in boolean isMetered,
             in int[] administratorUids, in IBinder binder);
 

framework/src/android/net/TestNetworkManager.java

@@ -231,4 +231,23 @@ public class TestNetworkManager {
             throw e.rethrowFromSystemServer();
         }
     }
+
+    /**
+     * Enable / disable carrier on TestNetworkInterface
+     *
+     * Note: TUNSETCARRIER is not supported until kernel version 5.0.
+     * TODO: add RequiresApi annotation.
+     *
+     * @param iface the interface to configure.
+     * @param enabled true to turn carrier on, false to turn carrier off.
+     * @hide
+     */
+    @RequiresPermission(Manifest.permission.MANAGE_TEST_NETWORKS)
+    public void setCarrierEnabled(@NonNull TestNetworkInterface iface, boolean enabled) {
+        try {
+            mService.setCarrierEnabled(iface, enabled);
+        } catch (RemoteException e) {
+            throw e.rethrowFromSystemServer();
+        }
+    }
 }

service/jni/com_android_server_TestNetworkService.cpp

@@ -51,7 +51,15 @@ static void throwException(JNIEnv* env, int error, const char* action, const cha
     jniThrowException(env, "java/lang/IllegalStateException", msg.c_str());
 }
 
-static int createTunTapInterface(JNIEnv* env, bool isTun, const char* iface) {
+// enable or disable  carrier on tun / tap interface.
+static void setTunTapCarrierEnabledImpl(JNIEnv* env, const char* iface, int tunFd, bool enabled) {
+    uint32_t carrierOn = enabled;
+    if (ioctl(tunFd, TUNSETCARRIER, &carrierOn)) {
+        throwException(env, errno, "set carrier", iface);
+    }
+}
+
+static int createTunTapImpl(JNIEnv* env, bool isTun, const char* iface) {
     base::unique_fd tun(open("/dev/tun", O_RDWR | O_NONBLOCK));
     ifreq ifr{};
 
@@ -79,23 +87,30 @@ static int createTunTapInterface(JNIEnv* env, bool isTun, const char* iface) {
 
 //------------------------------------------------------------------------------
 
-static jint create(JNIEnv* env, jobject /* thiz */, jboolean isTun, jstring jIface) {
+static void setTunTapCarrierEnabled(JNIEnv* env, jclass /* clazz */, jstring
+                                    jIface, jint tunFd, jboolean enabled) {
+    ScopedUtfChars iface(env, jIface);
+    if (!iface.c_str()) {
+        jniThrowNullPointerException(env, "iface");
+    }
+    setTunTapCarrierEnabledImpl(env, iface.c_str(), tunFd, enabled);
+}
+
+static jint createTunTap(JNIEnv* env, jclass /* clazz */, jboolean isTun, jstring jIface) {
     ScopedUtfChars iface(env, jIface);
     if (!iface.c_str()) {
         jniThrowNullPointerException(env, "iface");
         return -1;
     }
 
-    int tun = createTunTapInterface(env, isTun, iface.c_str());
+    return createTunTapImpl(env, isTun, iface.c_str());
-
-    // Any exceptions will be thrown from the createTunTapInterface call
-    return tun;
 }
 
 //------------------------------------------------------------------------------
 
 static const JNINativeMethod gMethods[] = {
-    {"jniCreateTunTap", "(ZLjava/lang/String;)I", (void*)create},
+    {"nativeSetTunTapCarrierEnabled", "(Ljava/lang/String;IZ)V", (void*)setTunTapCarrierEnabled},
+    {"nativeCreateTunTap", "(ZLjava/lang/String;)I", (void*)createTunTap},
 };
 
 int register_com_android_server_TestNetworkService(JNIEnv* env) {

service/src/com/android/server/TestNetworkService.java

@@ -50,6 +50,7 @@ import com.android.internal.annotations.VisibleForTesting;
 import com.android.net.module.util.NetdUtils;
 import com.android.net.module.util.NetworkStackConstants;
 
+import java.io.IOException;
 import java.io.UncheckedIOException;
 import java.net.Inet4Address;
 import java.net.Inet6Address;
@@ -76,7 +77,10 @@ class TestNetworkService extends ITestNetworkManager.Stub {
     @NonNull private final NetworkProvider mNetworkProvider;
 
     // Native method stubs
-    private static native int jniCreateTunTap(boolean isTun, @NonNull String iface);
+    private static native int nativeCreateTunTap(boolean isTun, @NonNull String iface);
+
+    private static native void nativeSetTunTapCarrierEnabled(@NonNull String iface, int tunFd,
+            boolean enabled);
 
     @VisibleForTesting
     protected TestNetworkService(@NonNull Context context) {
@@ -131,7 +135,7 @@ class TestNetworkService extends ITestNetworkManager.Stub {
         final long token = Binder.clearCallingIdentity();
         try {
             ParcelFileDescriptor tunIntf =
-                    ParcelFileDescriptor.adoptFd(jniCreateTunTap(isTun, interfaceName));
+                    ParcelFileDescriptor.adoptFd(nativeCreateTunTap(isTun, interfaceName));
             for (LinkAddress addr : linkAddrs) {
                 mNetd.interfaceAddAddress(
                         interfaceName,
@@ -375,4 +379,20 @@ class TestNetworkService extends ITestNetworkManager.Stub {
     public static void enforceTestNetworkPermissions(@NonNull Context context) {
         context.enforceCallingOrSelfPermission(PERMISSION_NAME, "TestNetworkService");
     }
+
+    /** Enable / disable TestNetworkInterface carrier */
+    @Override
+    public void setCarrierEnabled(@NonNull TestNetworkInterface iface, boolean enabled) {
+        enforceTestNetworkPermissions(mContext);
+        nativeSetTunTapCarrierEnabled(iface.getInterfaceName(), iface.getFileDescriptor().getFd(),
+                enabled);
+        // Explicitly close fd after use to prevent StrictMode from complaining.
+        // Also, explicitly referencing iface guarantees that the object is not garbage collected
+        // before nativeSetTunTapCarrierEnabled() executes.
+        try {
+            iface.getFileDescriptor().close();
+        } catch (IOException e) {
+            // if the close fails, there is not much that can be done -- move on.
+        }
+    }
 }