Permission check failed
现象描述
Android 10 手机连接GATT后，读写characteristic结果返回true,但是确没有callback返回，logcat打印如下:
02-20 04:26:15.599 3815 3834 W BtGatt.GattService: writeCharacteristic() - permission check failed!
源码分析
BluetoothGatt#writeCharacteristic
android.bluetooth.BluetoothGatt.java
/**
* Writes a given characteristic and its values to the associated remote device.
*
* <p>Once the write operation has been completed, the
* {@link BluetoothGattCallback#onCharacteristicWrite} callback is invoked,
* reporting the result of the operation.
*
* <p>Requires {@link android.Manifest.permission#BLUETOOTH} permission.
*
* @param characteristic Characteristic to write on the remote device
* @return true, if the write operation was initiated successfully
*/
public boolean writeCharacteristic(BluetoothGattCharacteristic characteristic) {
if ((characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_WRITE) == 0
&& (characteristic.getProperties()
& BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE) == 0) {
return false;
}
if (VDBG) Log.d(TAG, "writeCharacteristic() - uuid: " + characteristic.getUuid());
if (mService == null || mClientIf == 0 || characteristic.getValue() == null) return false;
BluetoothGattService service = characteristic.getService();
if (service == null) return false;
BluetoothDevice device = service.getDevice();
if (device == null) return false;
synchronized (mDeviceBusyLock) {
if (mDeviceBusy) return false;
mDeviceBusy = true;
}
try {
mService.writeCharacteristic(mClientIf, device.getAddress(),
characteristic.getInstanceId(), characteristic.getWriteType(),
AUTHENTICATION_NONE, characteristic.getValue());
} catch (RemoteException e) {
Log.e(TAG, "", e);
mDeviceBusy = false;
return false;
}
return true;
}
GattService#writeCharacteristic
/android/platform/packages/apps/Bluetooth/src/com/android/bluetooth/gatt/GattService.java
void writeCharacteristic(int clientIf, String address, int handle, int writeType, int authReq,
byte[] value) {
enforceCallingOrSelfPermission(BLUETOOTH_PERM, "Need BLUETOOTH permission");
if (VDBG) {
Log.d(TAG, "writeCharacteristic() - address=" + address);
}
if (mReliableQueue.contains(address)) {
writeType = 3; // Prepared write
}
Integer connId = mClientMap.connIdByAddress(clientIf, address);
if (connId == null) {
Log.e(TAG, "writeCharacteristic() - No connection for " + address + "...");
return;
}
if (!permissionCheck(connId, handle)) {
Log.w(TAG, "writeCharacteristic() - permission check failed!");
return;
}
gattClientWriteCharacteristicNative(connId, handle, writeType, authReq, value);
}
从上面的代码可以看到，writeCharacteristic() - permission check failed! 是在permissionCheck(connId, handle)返回失败的情况下才打印的。
permissionCheck
/android/platform/packages/apps/Bluetooth/src/com/android/bluetooth/gatt/GattService.java
private boolean permissionCheck(int connId, int handle) {
Set<Integer> restrictedHandles = mRestrictedHandles.get(connId);
if (restrictedHandles == null || !restrictedHandles.contains(handle)) {
return true;
}
return (checkCallingOrSelfPermission(BLUETOOTH_PRIVILEGED)
== PERMISSION_GRANTED);
}
从上面的代码可以看出检查流程如下：
-
首先检查
restrictedHandles是否包含当前操作的 handle，由于handle对应的UUID在restrictedHandles中，所以开始检查BLUETOOTH_PRIVILEGED权限 -
但是只有系统应用才可以申请获取
BLUETOOTH_PRIVILEGED权限，所以最后依然返回false.
第三方应用是无法获取BLUETOOTH_PRIVILEGED权限的，所以问题应该是出在restrictedHandles上。
restrictedHandles
/**
* Set of restricted (which require a BLUETOOTH_PRIVILEGED permission) handles per connectionId.
*/
private final Map<Integer, Set<Integer>> mRestrictedHandles = new HashMap<>();
void onGetGattDb(int connId, ArrayList<GattDbElement> db) throws RemoteException {
String address = mClientMap.addressByConnId(connId);
if (DBG) {
Log.d(TAG, "onGetGattDb() - address=" + address);
}
ClientMap.App app = mClientMap.getByConnId(connId);
if (app == null || app.callback == null) {
Log.e(TAG, "app or callback is null");
return;
}
List<BluetoothGattService> dbOut = new ArrayList<BluetoothGattService>();
Set<Integer> restrictedIds = new HashSet<>();
BluetoothGattService currSrvc = null;
BluetoothGattCharacteristic currChar = null;
boolean isRestrictedSrvc = false;
boolean isHidSrvc = false;
boolean isRestrictedChar = false;
for (GattDbElement el : db) {
switch (el.type) {
case GattDbElement.TYPE_PRIMARY_SERVICE:
case GattDbElement.TYPE_SECONDARY_SERVICE:
if (DBG) {
Log.d(TAG, "got service with UUID=" + el.uuid + " id: " + el.id);
}
currSrvc = new BluetoothGattService(el.uuid, el.id, el.type);
dbOut.add(currSrvc);
isRestrictedSrvc =
isFidoSrvcUuid(el.uuid) || isAndroidTvRemoteSrvcUuid(el.uuid);
isHidSrvc = isHidSrvcUuid(el.uuid);
if (isRestrictedSrvc) {
restrictedIds.add(el.id);
}
break;
case GattDbElement.TYPE_CHARACTERISTIC:
if (DBG) {
Log.d(TAG, "got characteristic with UUID=" + el.uuid + " id: " + el.id);
}
currChar = new BluetoothGattCharacteristic(el.uuid, el.id, el.properties, 0);
currSrvc.addCharacteristic(currChar);
isRestrictedChar = isRestrictedSrvc || (isHidSrvc && isHidCharUuid(el.uuid));
if (isRestrictedChar) {
restrictedIds.add(el.id);
}
break;
case GattDbElement.TYPE_DESCRIPTOR:
if (DBG) {
Log.d(TAG, "got descriptor with UUID=" + el.uuid + " id: " + el.id);
}
currChar.addDescriptor(new BluetoothGattDescriptor(el.uuid, el.id, 0));
if (isRestrictedChar) {
restrictedIds.add(el.id);
}
break;
case GattDbElement.TYPE_INCLUDED_SERVICE:
if (DBG) {
Log.d(TAG, "got included service with UUID=" + el.uuid + " id: " + el.id
+ " startHandle: " + el.startHandle);
}
currSrvc.addIncludedService(
new BluetoothGattService(el.uuid, el.startHandle, el.type));
break;
default:
Log.e(TAG, "got unknown element with type=" + el.type + " and UUID=" + el.uuid
+ " id: " + el.id);
}
}
if (!restrictedIds.isEmpty()) {
mRestrictedHandles.put(connId, restrictedIds);
}
// Search is complete when there was error, or nothing more to process
app.callback.onSearchComplete(address, dbOut, 0 /* status */);
}
从上面的代码看到restrictedHandles里面包含了需要被过滤的UUID，从前面的permissionCheck已经知道，这些被限制的UUID只有系统应用才可以访问。
我们测试设备的服务里面确实没有需要被限制的UUID为什么也会被过滤？
继续跟踪定位发现，restrictedHandles只有put操作，没有remove或者clear操作。于是怀疑是restrictedHandles缓存导致的，模拟场景如下：
-
首先先连接一个HID设备，查询到的服务里面包含被限制的Service（这里以HID为例），连接成功后，connId=0x09.
-
断开HID设备，connId=0x09被释放。
-
连接一个新的LE设备，服务里面没有需要被限制的Service.连接成功后，connId也是0x09。
-
从前面的
onGetGattDb可以看出，虽然新的设备没有需要被限制的Service，但是由于restrictedHandles没有被清空，两次的connId也是一样的，导致后面判断的时候依然会被过滤。if (!restrictedIds.isEmpty()) { mRestrictedHandles.put(connId, restrictedIds); }
为什么其他Android设备正常，只有 Android 10有问题?
前面我们分析的代码就是Android 10 的。mRestrictedHandles也是在Android 10才加上的。
Android 10 以前版本的 permissionCheck是直接检查UUID，不会受前一次连接的缓存影响。
boolean permissionCheck(int connId, int handle) {
List<BluetoothGattService> db = mGattClientDatabases.get(connId);
if (db == null) {
return true;
}
for (BluetoothGattService service : db) {
for (BluetoothGattCharacteristic characteristic : service.getCharacteristics()) {
if (handle == characteristic.getInstanceId()) {
return !((isRestrictedCharUuid(characteristic.getUuid())
|| isRestrictedSrvcUuid(service.getUuid()))
&& (0 != checkCallingOrSelfPermission(BLUETOOTH_PRIVILEGED)));
}
for (BluetoothGattDescriptor descriptor : characteristic.getDescriptors()) {
if (handle == descriptor.getInstanceId()) {
return !((isRestrictedCharUuid(characteristic.getUuid())
|| isRestrictedSrvcUuid(service.getUuid())) && (0
!= checkCallingOrSelfPermission(BLUETOOTH_PRIVILEGED)));
}
}
}
}
return true;
}
结论
从上面的分析可以知道，这个问题是Android 10 引入的 BUG，Android 10 以前的系统没有这个问题。第三方APP连接LE设备后，如果前一次连接了一个HID设备，且当前连接的connId和上一次连接的connId相同，就会触发这个BUG。
解决方案
-
重新开关蓝牙，这样BluetoothManagerService就会重新bind，缓存会被清除。
-
确保App 或者第三方应用不会去连接HID设备，减小触发BUG的机率。
上面两个方法都不能从根本上解决问题，最终我们还是要等到Google更新patch来修复这个BUG。
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