Do not access MTP devices when disabled.

The USB data transfer is disabled we should not allow access MTP devices
(e.g.
usb sticks). We have two ways of accessing them: Either by mounting them
or by creating a MTPDevice in an app.

Of course an app could implement implement their own MTPDevice
implementation. In this case we cannot enforce the policy without
completely suppressing all MTP USB devices which would be too
restrictive.

Note: When the policy is set we do _not_ disconnect already connected
MTP devices

Fixes: 31472955
Change-Id: I6080c48c49657102774b2b3b4d89ff030245a266

core/java/android/hardware/usb/UsbDeviceConnection.java

@@ -16,8 +16,10 @@
 
 package android.hardware.usb;
 
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.content.Context;
 import android.os.ParcelFileDescriptor;
-
 import java.io.FileDescriptor;
 
 
@@ -31,6 +33,8 @@ public class UsbDeviceConnection {
 
     private final UsbDevice mDevice;
 
+    private Context mContext;
+
     // used by the JNI code
     private long mNativeContext;
 
@@ -42,10 +46,21 @@ public class UsbDeviceConnection {
         mDevice = device;
     }
 
-    /* package */ boolean open(String name, ParcelFileDescriptor pfd) {
+    /* package */ boolean open(String name, ParcelFileDescriptor pfd,  @NonNull Context context) {
+        mContext = context.getApplicationContext();
+
         return native_open(name, pfd.getFileDescriptor());
     }
 
+    /**
+     * @return The application context the connection was created for.
+     *
+     * @hide
+     */
+    public @Nullable Context getContext() {
+        return mContext;
+    }
+
     /**
      * Releases all system resources related to the device.
      * Once the object is closed it cannot be used again.

core/java/android/hardware/usb/UsbManager.java

@@ -330,7 +330,7 @@ public class UsbManager {
             ParcelFileDescriptor pfd = mService.openDevice(deviceName);
             if (pfd != null) {
                 UsbDeviceConnection connection = new UsbDeviceConnection(device);
-                boolean result = connection.open(deviceName, pfd);
+                boolean result = connection.open(deviceName, pfd, mContext);
                 pfd.close();
                 if (result) {
                     return connection;

media/java/android/mtp/MtpDevice.java

@@ -18,11 +18,13 @@ package android.mtp;
 
 import android.annotation.NonNull;
 import android.annotation.Nullable;
+import android.content.Context;
 import android.hardware.usb.UsbDevice;
 import android.hardware.usb.UsbDeviceConnection;
 import android.os.CancellationSignal;
 import android.os.ParcelFileDescriptor;
 
+import android.os.UserManager;
 import com.android.internal.util.Preconditions;
 
 import java.io.IOException;
@@ -62,7 +64,17 @@ public final class MtpDevice {
      * @return true if the device was successfully opened.
      */
     public boolean open(UsbDeviceConnection connection) {
-        boolean result = native_open(mDevice.getDeviceName(), connection.getFileDescriptor());
+        boolean result = false;
+
+        Context context = connection.getContext();
+        if (context != null) {
+            UserManager userManager = (UserManager) context.getSystemService(Context.USER_SERVICE);
+
+            if (!userManager.hasUserRestriction(UserManager.DISALLOW_USB_FILE_TRANSFER)) {
+                result = native_open(mDevice.getDeviceName(), connection.getFileDescriptor());
+            }
+        }
+
         if (!result) {
             connection.close();
         }

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

@@ -1437,13 +1437,22 @@ class MountService extends IMountService.Stub
      * Decide if volume is mountable per device policies.
      */
     private boolean isMountDisallowed(VolumeInfo vol) {
-        if (vol.type == VolumeInfo.TYPE_PUBLIC || vol.type == VolumeInfo.TYPE_PRIVATE) {
+        UserManager userManager = mContext.getSystemService(UserManager.class);
-            final UserManager userManager = mContext.getSystemService(UserManager.class);
+
-            return userManager.hasUserRestriction(UserManager.DISALLOW_MOUNT_PHYSICAL_MEDIA,
+        boolean isUsbRestricted = false;
+        if (vol.disk != null && vol.disk.isUsb()) {
+            isUsbRestricted = userManager.hasUserRestriction(UserManager.DISALLOW_USB_FILE_TRANSFER,
                     Binder.getCallingUserHandle());
-        } else {
-            return false;
         }
+
+        boolean isTypeRestricted = false;
+        if (vol.type == VolumeInfo.TYPE_PUBLIC || vol.type == VolumeInfo.TYPE_PRIVATE) {
+            isTypeRestricted = userManager
+                    .hasUserRestriction(UserManager.DISALLOW_MOUNT_PHYSICAL_MEDIA,
+                    Binder.getCallingUserHandle());
+        }
+
+        return isUsbRestricted || isTypeRestricted;
     }
 
     private void enforceAdminUser() {