【问题描述】
应用点击同意授予权限的弹窗授予了应用USB权限后，设备重启或usb设备拔插后还是需要重新授权
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【问题分析】
USB设备的访问权限需要应用在运行时请求，并且为了确保用户可以知道应用访问了哪个USB设备，每个USB设备都会有一个对话框，用户必须批准该请求才能继续。这确保了用户对哪些应用程序可以访问其 USB 设备有直接的控制权。
为什么每次设备重启或usb设备拔插之后需要重新申请权限？
在 Android 系统中，动态申请的 USB 设备访问权限通常是临时的，意味着它们只在当前的应用中有效。一旦应用被完全关闭后，之前授予的权限就会失效。这样的设计主要是出于安全和隐私的考虑。
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因此，每当应用程序设备重启或usb设备拔插后运行，它需要重新请求对 USB 设备的访问权限。这通常是通过使用 UsbManager 类和相关的 API 完成的。当应用检测到 USB 设备连接时，它可以通过发送一个 PendingIntent 来请求访问权限，系统会向用户显示一个对话框，让用户选择是否授权该权限。
这个流程确保了用户对哪些应用可以访问其 USB 设备有直接的控制，并且在设备重启或usb设备拔插时重新评估这些权限。这种机制有助于防止恶意应用在用户不知情的情况下长期访问 USB 设备。
应用申请USB权限的具体过程？
应用通过requestPermission方法申请USB权限
private void findDeviceAndRequestPermission() {
HashMap deviceList = usbManager.getDeviceList();
UsbDevice device = null; // your logic to get the device
if (device != null) {
if (!usbManager.hasPermission(device)) {
usbManager.requestPermission(device, permissionIntent);
}
}
}
frameworks/base/libs/usb/src/com/android/future/usb/UsbManager.java
public void requestPermission(UsbAccessory accessory, PendingIntent pi) {
try {
mService.requestAccessoryPermission(new android.hardware.usb.UsbAccessory(
accessory.getManufacturer(),accessory.getModel(),
accessory.getDescription(), accessory.getVersion(),
accessory.getUri(), accessory.getSerial()),
mContext.getPackageName(), pi);
} catch (RemoteException e) {
Log.e(TAG, "RemoteException in requestPermission", e);
}
}
frameworks/base/services/usb/java/com/android/server/usb/UsbService.java
public void requestAccessoryPermission(
UsbAccessory accessory, String packageName, PendingIntent pi) {
final int uid = Binder.getCallingUid();
final int userId = UserHandle.getUserId(uid);
final long token = Binder.clearCallingIdentity();
try {
getPermissionsForUser(userId).requestPermission(accessory, packageName, pi, uid);
} finally {
Binder.restoreCallingIdentity(token);
}
}
getPermissionsForUser方法返回的是UsbUserPermissionManager对象，因此实际调用UsbUserPermissionManager类的requestPermission方法
frameworks/base/services/usb/java/com/android/server/usb/UsbUserPermissionManager.java
public void requestPermission(UsbAccessory accessory, String packageName, PendingIntent pi,
int uid) {
// respond immediately if permission has already been granted
if (hasPermission(accessory, uid)) {
Intent intent = new Intent();
intent.putExtra(UsbManager.EXTRA_ACCESSORY, accessory);
intent.putExtra(UsbManager.EXTRA_PERMISSION_GRANTED, true);
try {
pi.send(mContext, 0, intent);
} catch (PendingIntent.CanceledException e) {
if (DEBUG) Slog.d(TAG, "requestPermission PendingIntent was cancelled");
}
return;
}
requestPermissionDialog(null, accessory,
mUsbUserSettingsManager.canBeDefault(accessory, packageName), packageName, pi, uid);
}
因为权限还没有授予，因此执行requestPermissionDialog方法
private void requestPermissionDialog(@Nullable UsbDevice device,
@Nullable UsbAccessory accessory,
boolean canBeDefault,
String packageName,
PendingIntent pi,
int uid) {
// compare uid with packageName to foil apps pretending to be someone else
try {
ApplicationInfo aInfo = mContext.getPackageManager().getApplicationInfo(packageName, 0);
if (aInfo.uid != uid) {
throw new IllegalArgumentException("package " + packageName
+ " does not match caller's uid " + uid);
}
} catch (PackageManager.NameNotFoundException e) {
throw new IllegalArgumentException("package " + packageName + " not found");
}
requestPermissionDialog(device, accessory, canBeDefault, packageName, uid, mContext, pi);
}
执行重载的requestPermissionDialog方法,最终跳转到UsbPermissionActivity
frameworks/base/packages/SystemUI/src/com/android/systemui/usb/UsbPermissionActivity.java
void requestPermissionDialog(@Nullable UsbDevice device,
@Nullable UsbAccessory accessory,
boolean canBeDefault,
@NonNull String packageName,
int uid,
@NonNull Context userContext,
@NonNull PendingIntent pi) {
long identity = Binder.clearCallingIdentity();
Intent intent = new Intent();
if (device != null) {
intent.putExtra(UsbManager.EXTRA_DEVICE, device);
} else {
intent.putExtra(UsbManager.EXTRA_ACCESSORY, accessory);
}
intent.putExtra(Intent.EXTRA_INTENT, pi);
intent.putExtra(Intent.EXTRA_UID, uid);
intent.putExtra(UsbManager.EXTRA_CAN_BE_DEFAULT, canBeDefault);
intent.putExtra(UsbManager.EXTRA_PACKAGE, packageName);
// 跳转到UsbPermissionActivity
intent.setComponent(ComponentName.unflattenFromString(userContext.getResources().getString(
com.android.internal.R.string.config_usbPermissionActivity)));
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
try {
userContext.startActivityAsUser(intent, mUser);
} catch (ActivityNotFoundException e) {
Slog.e(TAG, "unable to start UsbPermissionActivity");
} finally {
Binder.restoreCallingIdentity(identity);
}
}
UsbPermissionActivity 会创建一个对话框，当用户点击同意后，对话框会退出，并授予应用对应的USB权限
@Override
public void onDestroy() {
IBinder b = ServiceManager.getService(USB_SERVICE);
IUsbManager service = IUsbManager.Stub.asInterface(b);
// send response via pending intent
Intent intent = new Intent();
try {
if (mDevice != null) {
intent.putExtra(UsbManager.EXTRA_DEVICE, mDevice);
if (mPermissionGranted) {
service.grantDevicePermission(mDevice, mUid);
if (mAlwaysUse != null && mAlwaysUse.isChecked()) {
final int userId = UserHandle.getUserId(mUid);
service.setDevicePackage(mDevice, mPackageName, userId);
}
}
}
if (mAccessory != null) {
intent.putExtra(UsbManager.EXTRA_ACCESSORY, mAccessory);
if (mPermissionGranted) {
service.grantAccessoryPermission(mAccessory, mUid);
if (mAlwaysUse != null && mAlwaysUse.isChecked()) {
final int userId = UserHandle.getUserId(mUid);
service.setAccessoryPackage(mAccessory, mPackageName, userId);
}
}
}
intent.putExtra(UsbManager.EXTRA_PERMISSION_GRANTED, mPermissionGranted);
mPendingIntent.send(this, 0, intent);
} catch (PendingIntent.CanceledException e) {
Log.w(TAG, "PendingIntent was cancelled");
} catch (RemoteException e) {
Log.e(TAG, "IUsbService connection failed", e);
}
if (mDisconnectedReceiver != null) {
unregisterReceiver(mDisconnectedReceiver);
}
super.onDestroy();
}
public void onClick(DialogInterface dialog, int which) {
if (which == AlertDialog.BUTTON_POSITIVE) {
mPermissionGranted = true;
}
finish();
}
【修改对策】
根据上面分析，申请usb权限使Android系统出于安全原因，在应用被完全关闭、设备重新启动、USB设备断开后重连就需要重新申请USB权限；这其实不是一个BUG，但是因为客户应用不希望终端客户重复授权，觉得这样的操作会给用户带来困惑，因此还是需要更改。
根据上面追踪的代码，可知UsbPermissionActivity在onDestory()时，通过判断mPermissionGranted来决定是否授予权限
对策：针对客户应用修改，在onCreate阶段，通过筛选包名，设置mPermissionGranted为true，然后finish掉当前activity，直接默认授予对应应用USB权限
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
...
// Don't show the "always use" checkbox if the USB/Record warning is in effect
if (!useRecordWarning && canBeDefault && (mDevice != null || mAccessory != null)) {
// add "open when" checkbox
LayoutInflater inflater = (LayoutInflater) getSystemService(
Context.LAYOUT_INFLATER_SERVICE);
ap.mView = inflater.inflate(com.android.internal.R.layout.always_use_checkbox, null);
mAlwaysUse = (CheckBox) ap.mView.findViewById(com.android.internal.R.id.alwaysUse);
if (mDevice == null) {
mAlwaysUse.setText(getString(R.string.always_use_accessory, appName,
mAccessory.getDescription()));
} else {
mAlwaysUse.setText(getString(R.string.always_use_device, appName,
mDevice.getProductName()));
}
mAlwaysUse.setOnCheckedChangeListener(this);
mClearDefaultHint = (TextView)ap.mView.findViewById(
com.android.internal.R.id.clearDefaultHint);
mClearDefaultHint.setVisibility(View.GONE);
}
// grant usb permission to app start
if (!mPackageName.equals("app.package.name")){
setupAlert();
}else{
mPermissionGranted = true;
finish();
}
// grant usb permission to app end
}
