Android權限管理原理
前言
Android系統在MarshMallow之前，權限都是在安裝的時候授予的，雖然在4.3時，Google就試圖在源碼里面引入AppOpsManager來達到動態控制權限的目的，但由于不太成熟，在Release版本中都是把這個功能給隱藏掉的。在6.0之后，Google為了簡化安裝流程且方便用戶控制權限，正式引入了runtime-permission，允許用戶在運行的時候動態控制權限。對于開發而言就是將targetSdkVersion設置為23，并且在相應的時機動態申請權限，在適配了Android6.0的App運行在Android 6.0+的手機上時，就會調用6.0相關的API，不過在低版本的手機上，仍然是按安裝時權限處理。
AppOpsManager動態權限管理：官方預演的權限管理
AppOpsManager是Google在Android4.3引入的動態權限管理方式，不過，Google覺得不成熟，所以在每個發行版的時候，總是會將這個功能給屏蔽掉。該功能跟國內的權限動態管理表現類似，這里用CyanogenMod12里面的實現講述一下，（國內的ROM源碼拿不到，不過從表現來看，實現應該類似）。AppOpsManager實現的動態管理的本質是：將鑒權放在每個服務內部，比如，如果App要申請定位權限，定位服務LocationManagerService會向AppOpsService查詢是否授予了App定位權限，如果需要授權，就彈出一個系統對話框讓用戶操作，并根據用戶的操作將結果持久化在文件中，如果在Setting里設置了響應的權限，也會去更新相應的權限操作持久化文件/data/system/appops.xml，下次再次申請服務的時候，服務會再次鑒定權限。
舉個栗子-定位服務LocationManagerService: CM12源碼
App在使用定位服務的時候，一般是通過LocationManager的requestLocationUpdates獲取定位，其實是通過Binder請求LocationManagerService去定位。
/android/location/LocationManager.java
private void requestLocationUpdates(LocationRequest request, LocationListener listener,
Looper looper, PendingIntent intent) {
...
try {
mService.requestLocationUpdates(request, transport, intent, packageName);
...
/com/android/server/LocationManagerService.java
@Override
public void requestLocationUpdates(LocationRequest request, ILocationListener listener,
PendingIntent intent, String packageName) {
if (request == null) request = DEFAULT_LOCATION_REQUEST;
checkPackageName(packageName);
<!--關鍵函數 1 ，查詢Manifest文件，是否進行了權限聲明 -->
int allowedResolutionLevel = getCallerAllowedResolutionLevel();
checkResolutionLevelIsSufficientForProviderUse(allowedResolutionLevel,
request.getProvider());
。。。
<!--獲取調用app的pid跟uid-->
final int pid = Binder.getCallingPid();
final int uid = Binder.getCallingUid();
// providers may use public location API's, need to clear identity
long identity = Binder.clearCallingIdentity();
try {
<!--關鍵函數 2 檢查是否動態授權了權限，或者拒絕了權限-->
checkLocationAccess(uid, packageName, allowedResolutionLevel);
synchronized (mLock) {
Receiver receiver = checkListenerOrIntentLocked(listener, intent, pid, uid,
packageName, workSource, hideFromAppOps);
if (receiver != null) {
requestLocationUpdatesLocked(sanitizedRequest, receiver, pid,
uid, packageName);
}
}
} finally {
Binder.restoreCallingIdentity(identity);
}
}</code></pre>
getCallerAllowedResolutionLevel主要通過調用getAllowedResolutionLevel查詢APP是否在Manifest中進行了聲明
private int getCallerAllowedResolutionLevel() {
return getAllowedResolutionLevel(Binder.getCallingPid(), Binder.getCallingUid());
}
private int getAllowedResolutionLevel(int pid, int uid) {
if (mContext.checkPermission(android.Manifest.permission.ACCESS_FINE_LOCATION,
pid, uid) == PackageManager.PERMISSION_GRANTED) {
return RESOLUTION_LEVEL_FINE;
} else if (mContext.checkPermission(android.Manifest.permission.ACCESS_COARSE_LOCATION,
pid, uid) == PackageManager.PERMISSION_GRANTED) {
return RESOLUTION_LEVEL_COARSE;
} else {
return RESOLUTION_LEVEL_NONE;
}
}</code></pre>
checkLocationAccess這里才是動態鑒權的入口，在checkLocationAccess函數中，會調用mAppOps.checkOp去鑒權，mAppOps就是AppOpsManager實例，
boolean checkLocationAccess(int uid, String packageName, int allowedResolutionLevel) {
int op = resolutionLevelToOp(allowedResolutionLevel);
if (op >= 0) {
int mode = mAppOps.checkOp(op, uid, packageName);
if (mode != AppOpsManager.MODE_ALLOWED && mode != AppOpsManager.MODE_ASK ) {
return false;
}
}
return true;
}
進而通過Binder向AppOpsService服務發送鑒權請求
public int noteOp(int op, int uid, String packageName) {
try {
int mode = mService.noteOperation(op, uid, packageName);
if (mode == MODE_ERRORED) {
throw new SecurityException(buildSecurityExceptionMsg(op, uid, packageName));
}
return mode;
} catch (RemoteException e) {
}
return MODE_IGNORED;
}
AppOpsService負責動態權限的鑒定跟更新，接著看noteOperation代碼
@Override
public int noteOperation(int code, int uid, String packageName) {
final Result userDialogResult;
verifyIncomingUid(uid);
verifyIncomingOp(code);
synchronized (this) {
Ops ops = getOpsLocked(uid, packageName, true);
...
<!--關鍵點 1-->
if (switchOp.mode == AppOpsManager.MODE_IGNORED ||
switchOp.mode == AppOpsManager.MODE_ERRORED) {
op.rejectTime = System.currentTimeMillis();
op.ignoredCount++;
return switchOp.mode;
<!--關鍵點 2-->
} else if(switchOp.mode == AppOpsManager.MODE_ALLOWED) {
op.time = System.currentTimeMillis();
op.rejectTime = 0;
op.allowedCount++;
return AppOpsManager.MODE_ALLOWED;
} else {
op.noteOpCount++;
<!--關鍵函數 3-->
userDialogResult = askOperationLocked(code, uid, packageName,
switchOp);
}
}
return userDialogResult.get();
}</code></pre>
在上面的代碼里面，1、2是對已經處理過的場景直接返回已授權，或者已經拒絕，而3就是我們常見授權入口對話框，這里是統一在AppOpsServie中進行授權處理的。askOperationLocked會顯示一個系統對話框，用戶選擇授權或者拒絕后，AppOpsServie會將選擇記錄在案，并通知申請服務提供或者拒絕服務。askOperationLocked通過mHandler發送鑒權Message，看一下實現其實就是新建了一個PermissionDialog授權對話框，并且將AppOpsService的引用傳了進去，授權后會通過mService.notifyOperation通知授權結果。
mHandler = new Handler() {
public void handleMessage(Message msg) {
switch (msg.what) {
case SHOW_PERMISSION_DIALOG: {
HashMap<String, Object> data =
(HashMap<String, Object>) msg.obj;
synchronized (this) {
Op op = (Op) data.get("op");
Result res = (Result) data.get("result");
op.dialogResult.register(res);
if(op.dialogResult.mDialog == null) {
Integer code = (Integer) data.get("code");
Integer uid = (Integer) data.get("uid");
String packageName =
(String) data.get("packageName");
Dialog d = new PermissionDialog(mContext,
AppOpsService.this, code, uid,
packageName);
op.dialogResult.mDialog = (PermissionDialog)d;
d.show();
}
}
}break;
}
}
};
整體流程
Android發行版源碼對于動態權限管理的支持（幾乎為零）
在Android4.3到5.1之間，雖然App可以獲得AppOpsManager的實例，但是真正動態操作權限的接口setMode卻被隱藏，如下
/** @hide */
public void setMode(int code, int uid, String packageName, int mode) {
try {
mService.setMode(code, uid, packageName, mode);
} catch (RemoteException e) {
}
}
遍歷源碼也只有NotificationManagerService這個系統應用使用了setMode，也就是說發行版，只有通知是通過系統的通知管理進行動態管理的。
public void setNotificationsEnabledForPackage(String pkg, int uid, boolean enabled) {
checkCallerIsSystem();
Slog.v(TAG, (enabled?"en":"dis") + "abling notifications for " + pkg);
mAppOps.setMode(AppOpsManager.OP_POST_NOTIFICATION, uid, pkg,
enabled ? AppOpsManager.MODE_ALLOWED : AppOpsManager.MODE_IGNORED);
// Now, cancel any outstanding notifications that are part of a just-disabled app
if (ENABLE_BLOCKED_NOTIFICATIONS && !enabled) {
cancelAllNotificationsInt(pkg, 0, 0, true, UserHandle.getUserId(uid));
}
}</code></pre>
Android 6.0權限管理原理
Android6.0的runtime-permission機制讓用戶在任何時候都可以取消授權，因此，每次在申請系統服務的時候，都要動態查詢是否獲取了相應的權限，如果沒有獲取，就需要動態去申請，首先先看一下權限的查詢：
Android6.0權限查詢
support-v4兼容包里面提供了一個工具類PermissionChecker，可以用來檢查權限獲取情況。
PermissionChecker
public static int checkPermission(@NonNull Context context, @NonNull String permission,
int pid, int uid, String packageName) {
if (context.checkPermission(permission, pid, uid) == PackageManager.PERMISSION_DENIED) {
return PERMISSION_DENIED;
}
String op = AppOpsManagerCompat.permissionToOp(permission);
if (op == null) {
return PERMISSION_GRANTED;
}
if (packageName == null) {
String[] packageNames = context.getPackageManager().getPackagesForUid(uid);
if (packageNames == null || packageNames.length <= 0) {
return PERMISSION_DENIED;
}
packageName = packageNames[0];
}
if (AppOpsManagerCompat.noteProxyOp(context, op, packageName)
!= AppOpsManagerCompat.MODE_ALLOWED) {
return PERMISSION_DENIED_APP_OP;
}
return PERMISSION_GRANTED;
}</code></pre>
這里我們只關心context.checkPermission，從上面對于4.3-5.1的APPOpsManager的分析，我們知道AppOpsManagerCompat本身的一些操作對于權限管理并沒有實際意義，只是用來做一些標記，最多就是對于通知權限有些用，接下來看checkPermission：
ContextImple.java
/** @hide */
@Override
public int checkPermission(String permission, int pid, int uid, IBinder callerToken) {
if (permission == null) {
throw new IllegalArgumentException("permission is null");
}
try {
return ActivityManagerNative.getDefault().checkPermissionWithToken(
permission, pid, uid, callerToken);
} catch (RemoteException e) {
return PackageManager.PERMISSION_DENIED;
}
}
接著往下看
ActivityManagerNative.java
public int checkPermission(String permission, int pid, int uid)
throws RemoteException {
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeString(permission);
data.writeInt(pid);
data.writeInt(uid);
mRemote.transact(CHECK_PERMISSION_TRANSACTION, data, reply, 0);
reply.readException();
int res = reply.readInt();
data.recycle();
reply.recycle();
return res;
}
ActivityManagerService
public int checkPermission(String permission, int pid, int uid) {
if (permission == null) {
return PackageManager.PERMISSION_DENIED;
}
return checkComponentPermission(permission, pid, UserHandle.getAppId(uid), -1, true);
}
進而調用ActivityManager.checkComponentPermission，調用AppGlobals.getPackageManager().checkUidPermission(permission, uid);
ActivityManager.java
/* @hide /
public static int checkComponentPermission(String permission, int uid,
int owningUid, boolean exported) {
// Root, system server get to do everything.
<!--root及System能獲取所有權限-->
if (uid == 0 || uid == Process.SYSTEM_UID) {
return PackageManager.PERMISSION_GRANTED;
}
。。。
<!--普通的權限查詢-->
try {
return AppGlobals.getPackageManager()
.checkUidPermission(permission, uid);
} catch (RemoteException e) {
// Should never happen, but if it does... deny!
Slog.e(TAG, "PackageManager is dead?!?", e);
}
return PackageManager.PERMISSION_DENIED;
}</code></pre>
最終調用PackageManagerService.java去查看是否有權限，到這里，我們只需要知道權限的查詢其實是通過PKMS來進行的。心里先有個底，權限的更新，持久化，恢復都是通過PKMS來進行的。
PKMS不同版本的權限查詢
Android5.0的checkUidPermission
public int checkUidPermission(String permName, int uid) {
final boolean enforcedDefault = isPermissionEnforcedDefault(permName);
synchronized (mPackages) {
<!--PackageManagerService.Setting.mUserIds數組中，根據uid查找uid（也就是package）的權限列表-->
Object obj = mSettings.getUserIdLPr(UserHandle.getAppId(uid));
if (obj != null) {
GrantedPermissions gp = (GrantedPermissions)obj;
if (gp.grantedPermissions.contains(permName)) {
return PackageManager.PERMISSION_GRANTED;
}
} else {
<!--mSystemPermissions記錄一些系統級的應用的 uid 對應的 permission->
HashSet<String> perms = mSystemPermissions.get(uid);
if (perms != null && perms.contains(permName)) {
return PackageManager.PERMISSION_GRANTED;
}
}
if (!isPermissionEnforcedLocked(permName, enforcedDefault)) {
return PackageManager.PERMISSION_GRANTED;
}
}
return PackageManager.PERMISSION_DENIED;
}
Android6.0+的checkUidPermission
@Override
public int checkUidPermission(String permName, int uid) {
final int userId = UserHandle.getUserId(uid);
if (!sUserManager.exists(userId)) {
return PackageManager.PERMISSION_DENIED;
}
synchronized (mPackages) {
Object obj = mSettings.getUserIdLPr(UserHandle.getAppId(uid));
if (obj != null) {
final SettingBase ps = (SettingBase) obj;
final PermissionsState permissionsState = ps.getPermissionsState();
if (permissionsState.hasPermission(permName, userId)) {
return PackageManager.PERMISSION_GRANTED;
}
// Special case: ACCESS_FINE_LOCATION permission includes ACCESS_COARSE_LOCATION
if (Manifest.permission.ACCESS_COARSE_LOCATION.equals(permName) && permissionsState
.hasPermission(Manifest.permission.ACCESS_FINE_LOCATION, userId)) {
return PackageManager.PERMISSION_GRANTED;
}
} else {
ArraySet<String> perms = mSystemPermissions.get(uid);
if (perms != null) {
if (perms.contains(permName)) {
return PackageManager.PERMISSION_GRANTED;
}
if (Manifest.permission.ACCESS_COARSE_LOCATION.equals(permName) && perms
.contains(Manifest.permission.ACCESS_FINE_LOCATION)) {
return PackageManager.PERMISSION_GRANTED;
}
}
}
}
return PackageManager.PERMISSION_DENIED;
}</code></pre>
可以看到Android6.0之后，對權限的操作是PermissionsState
PermissionsState.java (android-6.0\frameworks\base\services\core\java\com\android\server\pm)
public boolean hasPermission(String name, int userId) {
enforceValidUserId(userId);
if (mPermissions == null) {
return false;
}
PermissionData permissionData = mPermissions.get(name);
return permissionData != null && permissionData.isGranted(userId);
}
從上面的代碼可以很清晰看出，6.0之后，除了聲明了權限之外，還必須是授權了的。運行時權限跟install權限有所不同，對于install權限isGranted一直返回是True，這里先不必深究PermissionsState是怎么存進內存，先記住，后面會將講。
權限恢復流程
Android6.0動態申請權限
申請權限可以通過V4包里面的ActivityCompat，它已經對不同版本做了兼容
ActivityCompat.java
public static void requestPermissions(final @NonNull Activity activity,
final @NonNull String[] permissions, final int requestCode) {
if (Build.VERSION.SDK_INT >= 23) {
ActivityCompatApi23.requestPermissions(activity, permissions, requestCode);
} else if (activity instanceof OnRequestPermissionsResultCallback) {
Handler handler = new Handler(Looper.getMainLooper());
handler.post(new Runnable() {
@Override
public void run() {
final int[] grantResults = new int[permissions.length];
PackageManager packageManager = activity.getPackageManager();
String packageName = activity.getPackageName();
final int permissionCount = permissions.length;
for (int i = 0; i < permissionCount; i++) {
grantResults[i] = packageManager.checkPermission(
permissions[i], packageName);
}
((OnRequestPermissionsResultCallback) activity).onRequestPermissionsResult(
requestCode, permissions, grantResults);
}
});
}
}
可以看到，如果是6.0以下，直接通過PKMS查詢是否在Manifest里面申請了權限，并把查詢結果通過onRequestPermissionsResult回調傳給Activity或者Fragment。其實這里只要在Manifest中聲明了，就會默認是Granted。接著往下看：ActivityCompatApi23最終會調用activity.requestPermissions去請求權限。
Activity
public final void requestPermissions(@NonNull String[] permissions, int requestCode) {
Intent intent = getPackageManager().buildRequestPermissionsIntent(permissions);
startActivityForResult(REQUEST_PERMISSIONS_WHO_PREFIX, intent, requestCode, null);
}
Intent其實是通過PackageManager（ApplicationPackageManager實現類）獲取的Intent
public Intent buildRequestPermissionsIntent(@NonNull String[] permissions) {
if (ArrayUtils.isEmpty(permissions)) {
throw new NullPointerException("permission cannot be null or empty");
}
Intent intent = new Intent(ACTION_REQUEST_PERMISSIONS);
intent.putExtra(EXTRA_REQUEST_PERMISSIONS_NAMES, permissions);
intent.setPackage(getPermissionControllerPackageName());
return intent;
}
這里首先是隱式的獲取授權Activity組件相關信息（GrantPermissionsActivity），其實就是對話框樣式的授權Activity，它是PackageInstaller系統應用里面的一個Activity。這里的getPermissionControllerPackageName其實就是獲取相應的包名，
ApplicationPackageManager.java (android-6.0\frameworks\base\core\java\android\app)
@Override
public String getPermissionControllerPackageName() {
synchronized (mLock) {
if (mPermissionsControllerPackageName == null) {
try {
mPermissionsControllerPackageName = mPM.getPermissionControllerPackageName();
} catch (RemoteException e) {
throw new RuntimeException("Package manager has died", e);
}
}
return mPermissionsControllerPackageName;
}
}
最終通過PackageManagerService獲取包名
PackageManagerService.java (android-6.0\frameworks\base\services\core\java\com\android\server\pm)
@Override
public String getPermissionControllerPackageName() {
synchronized (mPackages) {
return mRequiredInstallerPackage;
}
}
mRequiredInstallerPackage這個變量具體賦值是在PMS的構造器中：對于原生Android 6.0，權限管理的APP跟安裝器是同一個
mRequiredInstallerPackage = getRequiredInstallerLPr();
這里會得到PackageInstaller應用的相關信息，PackageInstaller負責應用的安裝與卸載，里面還包含了對授權管理的一些邏輯。startActivityForResult啟動的就是PackageInstaller中的GrantPermissionsActivity，該Activity主要負責權限的授予工作。
<activity android:name=".permission.ui.GrantPermissionsActivity"
android:configChanges="orientation|keyboardHidden|screenSize"
android:excludeFromRecents="true"
android:theme="@style/GrantPermissions">
<intent-filter>
<action android:name="android.content.pm.action.REQUEST_PERMISSIONS" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
這是一個類似于對話框的懸浮窗樣式的Activity
<style name="GrantPermissions" parent="Settings">
<item name="android:windowIsFloating">true</item>
<item name="android:windowElevation">@dimen/action_dialog_z</item>
<item name="android:windowSwipeToDismiss">false</item>
</style>
之后就是動態更新權限流程：
權限恢復流程
如何動態更新RuntimePermission
通過上面的流程，我們進入了GrantPermissionsActivity，在這個Activity里面，如果一開始沒有獲得權限，就會彈出權限申請對話框，根據用戶的操作去更新PKMS中的權限信息，同時將更新的結構持久化到runtime-permissions.xml中去。
GrantPermissionsActivity
GrantPermissionsActivity其實是利用GroupState對象與PKMS通信，遠程更新權限的，當然，如果權限都已經授予了，那么就不需要再次彈出權限申請對話框。
public class GrantPermissionsActivity extends OverlayTouchActivity
implements GrantPermissionsViewHandler.ResultListener {
private LinkedHashMap<String, GroupState> mRequestGrantPermissionGroups = new LinkedHashMap<>();
....
@Override
public void onPermissionGrantResult(String name, boolean granted, boolean doNotAskAgain) {
GroupState groupState = mRequestGrantPermissionGroups.get(name);
if (groupState.mGroup != null) {
if (granted) {
<!--權限更新時機-->
groupState.mGroup.grantRuntimePermissions(doNotAskAgain);
groupState.mState = GroupState.STATE_ALLOWED;
} else {
groupState.mGroup.revokeRuntimePermissions(doNotAskAgain);
groupState.mState = GroupState.STATE_DENIED;
}
updateGrantResults(groupState.mGroup);
}
if (!showNextPermissionGroupGrantRequest()) {
setResultAndFinish();
}
}
具體更新流程：
public boolean grantRuntimePermissions(boolean fixedByTheUser, String[] filterPermissions) {
final int uid = mPackageInfo.applicationInfo.uid;
// We toggle permissions only to apps that support runtime
// permissions, otherwise we toggle the app op corresponding
// to the permission if the permission is granted to the app.
for (Permission permission : mPermissions.values()) {
if (filterPermissions != null
&& !ArrayUtils.contains(filterPermissions, permission.getName())) {
continue;
}
...
<!--一些關鍵點-->
// Grant the permission if needed.
if (!permission.isGranted()) {
permission.setGranted(true);
mPackageManager.grantRuntimePermission(mPackageInfo.packageName,
permission.getName(), mUserHandle);
}
// Update the permission flags.
if (!fixedByTheUser) {
// Now the apps can ask for the permission as the user
// no longer has it fixed in a denied state.
if (permission.isUserFixed() || permission.isUserSet()) {
permission.setUserFixed(false);
permission.setUserSet(true);
mPackageManager.updatePermissionFlags(permission.getName(),
mPackageInfo.packageName,
PackageManager.FLAG_PERMISSION_USER_FIXED
| PackageManager.FLAG_PERMISSION_USER_SET,
0, mUserHandle);
可以看到最終還是調用PackageManager去更新App的運行時權限,最終走進PackageManagerService服務，
PackageManagerService
@Override
public void grantRuntimePermission(String packageName, String name, final int userId) {
if (!sUserManager.exists(userId)) {
Log.e(TAG, "No such user:" + userId);
return;
}
...一些檢查
mContext.enforceCallingOrSelfPermission(
android.Manifest.permission.GRANT_RUNTIME_PERMISSIONS,
"grantRuntimePermission");
enforceCrossUserPermission(Binder.getCallingUid(), userId,
true /* requireFullPermission */, true /* checkShell */,
"grantRuntimePermission");
。。。。。
...
uid = UserHandle.getUid(userId, pkg.applicationInfo.uid);
sb = (SettingBase) pkg.mExtras;
if (sb == null) {
throw new IllegalArgumentException("Unknown package: " + packageName);
}
final PermissionsState permissionsState = sb.getPermissionsState();
...
...授權
final int result = permissionsState.grantRuntimePermission(bp, userId);
switch (result) {
case PermissionsState.PERMISSION_OPERATION_FAILURE: {
return;
}
case PermissionsState.PERMISSION_OPERATION_SUCCESS_GIDS_CHANGED: {
final int appId = UserHandle.getAppId(pkg.applicationInfo.uid);
mHandler.post(new Runnable() {
@Override
public void run() {
killUid(appId, userId, KILL_APP_REASON_GIDS_CHANGED);
}
});
}
break;
}
mOnPermissionChangeListeners.onPermissionsChanged(uid);
<!--持久化-->
// Not critical if that is lost - app has to request again.
mSettings.writeRuntimePermissionsForUserLPr(userId, false);
}
<!--查詢是否在Manifest聲明過權限-->
private static void enforceDeclaredAsUsedAndRuntimeOrDevelopmentPermission(PackageParser.Package pkg,
BasePermission bp) {
int index = pkg.requestedPermissions.indexOf(bp.name);
if (index == -1) {
throw new SecurityException("Package " + pkg.packageName
+ " has not requested permission " + bp.name);
}
if (!bp.isRuntime() && !bp.isDevelopment()) {
throw new SecurityException("Permission " + bp.name
+ " is not a changeable permission type");
}
}
首先要更新內存中的權限授予情況
PermissionsState.java
private int grantPermission(BasePermission permission, int userId) {
if (hasPermission(permission.name, userId)) {
return PERMISSION_OPERATION_FAILURE;
}
final boolean hasGids = !ArrayUtils.isEmpty(permission.computeGids(userId));
final int[] oldGids = hasGids ? computeGids(userId) : NO_GIDS;
PermissionData permissionData = ensurePermissionData(permission);
if (!permissionData.grant(userId)) {
return PERMISSION_OPERATION_FAILURE;
}
if (hasGids) {
final int[] newGids = computeGids(userId);
if (oldGids.length != newGids.length) {
return PERMISSION_OPERATION_SUCCESS_GIDS_CHANGED;
}
}
return PERMISSION_OPERATION_SUCCESS;
}
<!--動態添加更新內存Permison -->
private PermissionData ensurePermissionData(BasePermission permission) {
if (mPermissions == null) {
mPermissions = new ArrayMap<>();
}
PermissionData permissionData = mPermissions.get(permission.name);
if (permissionData == null) {
permissionData = new PermissionData(permission);
mPermissions.put(permission.name, permissionData);
}
return permissionData;
}
下一步，要將更新的權限持久化到文件中去 mSettings.writeRuntimePermissionsForUserLPr
RuntimePermission持久化
Settings.java
public void writeRuntimePermissionsForUserLPr(int userId, boolean sync) {
if (sync) {
mRuntimePermissionsPersistence.writePermissionsForUserSyncLPr(userId);
} else {
mRuntimePermissionsPersistence.writePermissionsForUserAsyncLPr(userId);
}
}
Settings.getPackageLPw這個方法，這是在安裝應用掃描的時候scanPackageDirtyLI方法調用的，里面可以看到Settings類中的mUserIds、mPackages里面存的value還有PackageManagerService中的mPackages.pkg. mExtras都是同一個玩意奏是個PackageSetting。
private File getUserRuntimePermissionsFile(int userId) {
// TODO: Implement a cleaner solution when adding tests.
// This instead of Environment.getUserSystemDirectory(userId) to support testing.
File userDir = new File(new File(mSystemDir, "users"), Integer.toString(userId));
return new File(userDir, RUNTIME_PERMISSIONS_FILE_NAME);
}
在目錄data/system/0/runtime-permissions.xml存放需要運行時申請的權限，Android6.0以上才有
<pkg name="com.snail.labaffinity">
<item name="android.permission.CALL_PHONE" granted="true" flags="0" />
<item name="android.permission.CAMERA" granted="false" flags="1" />
</pkg>
RuntimePermission恢復（其實這里也包含普通權限）
這些持久化的數據會在手機啟動的時候由PMS讀取,開機啟動，PKMS掃描Apk，并更新package信息，檢查/data/system/packages.xml是否存在，這個文件是在解析apk時由writeLP()創建的，里面記錄了系統的permissions，以及每個apk的name,codePath,flags,ts,version,uesrid等信息，這些信息主要通過apk的AndroidManifest.xml解析獲取，解析完apk后將更新信息寫入這個文件并保存到flash，下次開機直接從里面讀取相關信息添加到內存相關列表中，當有apk升級，安裝或刪除時會更新這個文件，packages.xml放的只包括installpermission，runtimepermissiono由runtime-permissions.xml存放。
public PackageManagerService(Context context, Installer installer,
boolean factoryTest, boolean onlyCore) {
....
mSettings = new Settings(mPackages);
//匯總并更新和Permission相關的信息
updatePermissionsLPw(null, null, true,
regrantPermissions,regrantPermissions);
//將信息寫到package.xml、package.list及package-stopped.xml文件中
mSettings.writeLPr();
....
mFirstBoot = !mSettings.readLPw(sUserManager.getUsers(false));
Settings(File dataDir, Object lock) {
mRuntimePermissionsPersistence = new RuntimePermissionPersistence(mLock);
<!--加載package信息-->
根據SettingsFile或者BackupSettingsFile讀取相應的設置信息 生成PackageSetting對象，里面有權限列表字段protected final PermissionsState mPermissionsState;，之后再運行中，動態權限的操作都是針對這個對象
boolean readLPw(@NonNull List<UserInfo> users) {
FileInputStream str = null;
if (mBackupSettingsFilename.exists()) {
try {
str = new FileInputStream(mBackupSettingsFilename);
mReadMessages.append("Reading from backup settings file\n");
...
while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& (type != XmlPullParser.END_TAG || parser.getDepth() > outerDepth)) {
String tagName = parser.getName();
if (tagName.equals("package")) {
!--讀取package信息，包括install權限信息（對于Android6.0package.xml）-->
readPackageLPw(parser);
...
<!--讀取runtime權限信息-->
for (UserInfo user : users) {
mRuntimePermissionsPersistence.readStateForUserSyncLPr(user.id);
}
}
private void readPackageLPw(XmlPullParser parser) throws XmlPullParserException, IOException {
String name = null;
...
(tagName.equals(TAG_PERMISSIONS)) {
readInstallPermissionsLPr(parser,
packageSetting.getPermissionsState());
之后就可以checkpermission了
@Override
public int checkUidPermission(String permName, int uid) {
final int userId = UserHandle.getUserId(uid);
if (!sUserManager.exists(userId)) {
return PackageManager.PERMISSION_DENIED;
}
synchronized (mPackages) {
Object obj = mSettings.getUserIdLPr(UserHandle.getAppId(uid));
if (obj != null) {
final SettingBase ps = (SettingBase) obj;
final PermissionsState permissionsState = ps.getPermissionsState();
if (permissionsState.hasPermission(permName, userId)) {
return PackageManager.PERMISSION_GRANTED;
}
權限恢復流程
原來的權限存放位置在哪？不會都從Android Manifest清單去讀取，只會在啟動時讀取一次。Android6.0之前會吧所有的權限都放置在data/system/packages.xml文件中。Android6.0之后，分為運行時權限跟普通權限，普通權限還是放在data/system/packages.xml中，運行時權限防止在data/system/users/0/runtime-permissions.xml文件中。根據運行時是否動態申請去更新權限。
Android6.0申請普通權限會怎么樣
Android6.0里，普通權限仍然按照運行時權限的模型，只是granted="true"，就是永遠是取得授權的。所以可以直接獲得權限申請成功的回調。如果查看packages.xml，就會發現：如下信息：
<perms>
<item name="android.permission.INTERNET" granted="true" flags="0" />
<item name="android.permission.ACCESS_WIFI_STATE" granted="true" flags="0" />
</perms>
Android的關鍵節點，在哪里？
關鍵節點并不是查詢是否具有該權限，Android6.0之前的 權限查詢是不會觸發權限申請與授權的，只有在請求系統服務的時候，由系統服務調用AppopsManager去查詢是否賦予了該權限，第一次未操作肯定是null，未賦予就可能會觸發權限申請邏輯，這個點在各個系統服務內部，由AppOpsService服務統一管理，不過對于官方的Release版本，其實只有系統通知APP才有動態權限管理的能力，其他都沒有操作能力。
參考文檔
2、 android permission權限與安全機制解析
5、 Android 4.3 隱藏功能 App Ops 分析
9、 CM12源碼
來自：http://www.jianshu.com/p/9938d367b6db