前言
Android6.0以后引入了动态权限机制，一些系统权限的分配需要在app运行中进行分配，而不只是在AndroidManifest中指定。
本篇将针对动态权限的底层分配过程进行分析(基于Android-6.0.1)。
权限分配
我们先看一下请求分配权限的代码
//frameworks/support/v4/java/android/support/v4/app/ActivityCompat.java
public static void requestPermissions(final @NonNull Activity activity,
final @NonNull String[] permissions, final int requestCode) {
if (Build.VERSION.SDK_INT >= 23) {//对于Android M 以及以上的权限的分配
ActivityCompatApi23.requestPermissions(activity, permissions, requestCode);
} else if (activity instanceof OnRequestPermissionsResultCallback) {//Android M以下的权限分配
Handler handler = new Handler(Looper.getMainLooper());
handler.post(new Runnable() {
@Override
public void run() {
//请求分配的权限结果，如分配就是PERMISSION_GRANTED
final int[] grantResults = new int[permissions.length];
PackageManager packageManager = activity.getPackageManager();
String packageName = activity.getPackageName();
final int permissionCount = permissions.length;
//通过包管理的checkPermission来检验是否分配权限
for (int i = 0; i < permissionCount; i++) {
grantResults[i] = packageManager.checkPermission(
permissions[i], packageName);
}
((OnRequestPermissionsResultCallback) activity).onRequestPermissionsResult(
requestCode, permissions, grantResults);
}
});
}
}
requestPermissions对于Android M的前后版本都分别做了处理，Android M以上通过ActivityCompatApi23.requestPermissions进行权限的请求，而Android M以下通过PackageManager来检查Permission的分配情况。
//frameworks/support/v4/api23/android/support/v4/app/ActivityCompat23.java
class ActivityCompatApi23 {
...
public static void requestPermissions(Activity activity, String[] permissions,
int requestCode) {
if (activity instanceof RequestPermissionsRequestCodeValidator) {
((RequestPermissionsRequestCodeValidator) activity)
.validateRequestPermissionsRequestCode(requestCode);
}
//通过Android M的Activity处理
activity.requestPermissions(permissions, requestCode);
}
...
}
//frameworks/base/core/java/android/app/Activity.java
public final void requestPermissions(@NonNull String[] permissions, int requestCode) {
if (mHasCurrentPermissionsRequest) {
Log.w(TAG, "Can reqeust only one set of permissions at a time");
// Dispatch the callback with empty arrays which means a cancellation.
onRequestPermissionsResult(requestCode, new String[0], new int[0]);
return;
}
//通过请求的权限构造Intent，弹出请求的窗口
Intent intent = getPackageManager().buildRequestPermissionsIntent(permissions);
startActivityForResult(REQUEST_PERMISSIONS_WHO_PREFIX, intent, requestCode, null);
mHasCurrentPermissionsRequest = true;
}
ActivityCompat23将请求权限的任务交给Activity来完成，在Activity中，通过请求的permission来构造一个Intent随后启动Activity来弹出请求的界面。Intent的构造是通过PackageManager的buildRequestPermissionsIntent方法构造的。
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;
}
Intent的action是ACTION_REQUEST_PERMISSIONS，它是这么定义的
public static final String ACTION_REQUEST_PERMISSIONS = "android.content.pm.action.REQUEST_PERMISSIONS";
随后一个参数就是具体请求的permission数组和一个权限分派控制的相关的包名。所以activity的请求窗口是通过隐式启动的。
/packages/apps/PackageInstaller/AndroidManifest.xml
从intent-fliter可以看到，这个GrantPermissionsActivity就是我们进行权限分配的弹出窗口。GrantPermissionsActivity它的布局文件定义在packages/apps/PackageInstaller/res/layout/grant_permissions.xml，从GrantPermissionsActivity的实现来看它就是一个长的像Dialog的activity，这里我们重点关注在该Activity中对权限的允许和拒绝的处理。
//packages/apps/PackageInstaller/src/com/android/packageinstaller/permission/ui/GrantPermissionsDefaultViewHandler.java
public void onClick(View view) {
switch (view.getId()) {
case R.id.permission_allow_button://允许
if (mResultListener != null) {
view.clearAccessibilityFocus();
mResultListener.onPermissionGrantResult(mGroupName, true, false);
}
break;
case R.id.permission_deny_button://拒绝
mAllowButton.setEnabled(true);
if (mResultListener != null) {
view.clearAccessibilityFocus();
mResultListener.onPermissionGrantResult(mGroupName, false,
mDoNotAskCheckbox.isChecked());
}
break;
case R.id.do_not_ask_checkbox://不再询问
mAllowButton.setEnabled(!mDoNotAskCheckbox.isChecked());
break;
}
}
这里是通过GrantPermissionsDefaultViewHandler来控制GrantPermissionsActivity的ui视图，按钮的点击事件是通过GrantPermissionsViewHandler.ResultListener接口来处理的，GrantPermissionsActivity实现了该接口。
@Override
public void onPermissionGrantResult(String name, boolean granted, boolean doNotAskAgain) {
if (isObscuredTouch()) {
showOverlayDialog();
finish();
return;
}
GroupState groupState = mRequestGrantPermissionGroups.get(name);
if (groupState.mGroup != null) {
if (granted) {
groupState.mGroup.grantRuntimePermissions(doNotAskAgain);//权限组内部的权限分配
groupState.mState = GroupState.STATE_ALLOWED;//重置权限组的状态
} else {
groupState.mGroup.revokeRuntimePermissions(doNotAskAgain);
groupState.mState = GroupState.STATE_DENIED;
}
updateGrantResults(groupState.mGroup);
}
//下一个组权限的授权
if (!showNextPermissionGroupGrantRequest()) {
setResultAndFinish();
}
}
onPermissionGrantResult的三个参数分别是name代表了权限组的名字，granted表示是否进行权限分配，doNotAskAgain代表是否询问权限。内部的mRequestGrantPermissionGroups是一个LinkedHashMap
//packages/apps/PackageInstaller/src/com/android/packageinstaller/permission/ui/GrantPermissionsActivity.java
public class GrantPermissionsActivity extends OverlayTouchActivity
implements GrantPermissionsViewHandler.ResultListener {
private String[] mRequestedPermissions;//请求的权限数组
private int[] mGrantResults;//权限分配的结果数组
//请求的权限数组对应的权限组Map
private LinkedHashMap mRequestGrantPermissionGroups = new LinkedHashMap<>();
...
@Override
public void onCreate(Bundle icicle) {
...
//加载应用权限组
mAppPermissions = new AppPermissions(this, callingPackageInfo, null, false,
new Runnable() {
@Override
public void run() {
setResultAndFinish();
}
});
//遍历权限组
for (AppPermissionGroup group : mAppPermissions.getPermissionGroups()) {
boolean groupHasRequestedPermission = false;
for (String requestedPermission : mRequestedPermissions) {
//如果请求的权限在该组内则标记groupHasRequestedPermission为true
if (group.hasPermission(requestedPermission)) {
groupHasRequestedPermission = true;
break;
}
}
if (!groupHasRequestedPermission) {
continue;
}
// We allow the user to choose only non-fixed permissions. A permission
// is fixed either by device policy or the user denying with prejudice.
if (!group.isUserFixed() && !group.isPolicyFixed()) {
switch (permissionPolicy) {
case DevicePolicyManager.PERMISSION_POLICY_AUTO_GRANT: {
if (!group.areRuntimePermissionsGranted()) {
group.grantRuntimePermissions(false);
}
group.setPolicyFixed();
} break;
case DevicePolicyManager.PERMISSION_POLICY_AUTO_DENY: {
if (group.areRuntimePermissionsGranted()) {
group.revokeRuntimePermissions(false);
}
group.setPolicyFixed();
} break;
default: {
//权限组是否已经分配了Runtime Permission,如果没有，则添加到mRequestGrantPermissionGroups中
if (!group.areRuntimePermissionsGranted()) {
mRequestGrantPermissionGroups.put(group.getName(),
new GroupState(group));
} else {
group.grantRuntimePermissions(false);
updateGrantResults(group);
}
} break;
}
} else {
// if the permission is fixed, ensure that we return the right request result
updateGrantResults(group);
}
}
...
if (!showNextPermissionGroupGrantRequest()) {
setResultAndFinish();
}
}
}
在GrantPermissionsActivity的onCreate方法中，根据请求的权限计算所属权限组的状态，首先创建AppPermissions对象，这时会去加载应用的权限组。同时遍历用于请求的权限数组并找到其对应的权限组，同时判断该权限组是否已经分配了动态权限，如果未授权则添加到待授权的权限组Map中。到这里我们还未看到真正的授权过程，在前面onPermissionGrantResult方法中，授权是通过GroupState中的成员mGroup的grantRuntimePermissions方法进一步进行权限分配的。而GroupState的定义如下
private static final class GroupState {
static final int STATE_UNKNOWN = 0;
static final int STATE_ALLOWED = 1;
static final int STATE_DENIED = 2;
final AppPermissionGroup mGroup;
int mState = STATE_UNKNOWN;
GroupState(AppPermissionGroup group) {
mGroup = group;
}
}
GroupState有三个状态STATE_UNKNOWN，STATE_ALLOWED，STATE_DENIED，它内部的mGroup实际上是个AppPermissionGroup，这些AppPermissionGroup是在AppPermissions加载的。
//packages/apps/PackageInstaller/src/com/android/packageinstaller/permission/model/AppPermissionGroup.java
public boolean grantRuntimePermissions(boolean fixedByTheUser) {
final boolean isSharedUser = mPackageInfo.sharedUserId != null;
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.
//遍历权限组对应的权限
for (Permission permission : mPermissions.values()) {
if (mAppSupportsRuntimePermissions) {//支持动态权限分配
// Do not touch permissions fixed by the system.
if (permission.isSystemFixed()) {//系统权限则返回
return false;
}
// Ensure the permission app op enabled before the permission grant.
//打开permssion可以被grant的选项
if (permission.hasAppOp() && !permission.isAppOpAllowed()) {
permission.setAppOpAllowed(true);
mAppOps.setUidMode(permission.getAppOp(), uid, AppOpsManager.MODE_ALLOWED);
}
// Grant the permission if needed.
//进行动态分配，通过PMS完成
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);
}
}
} else {//Adnroid M以下的版本权限分配
....
}
}
return true;
}
权限的分配最终是通过PMS的grantRuntimePermission方法来完成的。
//frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java
@Override
public void grantRuntimePermission(String packageName, String name, final int userId) {
...
mContext.enforceCallingOrSelfPermission(
android.Manifest.permission.GRANT_RUNTIME_PERMISSIONS,
"grantRuntimePermission");
enforceCrossUserPermission(Binder.getCallingUid(), userId, true, false,
"grantRuntimePermission");
final int uid;
final SettingBase sb;
synchronized (mPackages) {
//取到Package对象
final PackageParser.Package pkg = mPackages.get(packageName);
if (pkg == null) {
throw new IllegalArgumentException("Unknown package: " + packageName);
}
//取到全局设置中的权限信息
final BasePermission bp = mSettings.mPermissions.get(name);
if (bp == null) {
throw new IllegalArgumentException("Unknown permission: " + name);
}
enforceDeclaredAsUsedAndRuntimeOrDevelopmentPermission(pkg, bp);
uid = UserHandle.getUid(userId, pkg.applicationInfo.uid);
sb = (SettingBase) pkg.mExtras;//从pkg中取到应用的设置信息SettingBase
if (sb == null) {
throw new IllegalArgumentException("Unknown package: " + packageName);
}
//取到权限状态
final PermissionsState permissionsState = sb.getPermissionsState();
final int flags = permissionsState.getPermissionFlags(name, userId);
if ((flags & PackageManager.FLAG_PERMISSION_SYSTEM_FIXED) != 0) {
throw new SecurityException("Cannot grant system fixed permission: "
+ name + " for package: " + packageName);
}
if (bp.isDevelopment()) {
// Development permissions must be handled specially, since they are not
// normal runtime permissions. For now they apply to all users.
if (permissionsState.grantInstallPermission(bp) !=
PermissionsState.PERMISSION_OPERATION_FAILURE) {
scheduleWriteSettingsLocked();
}
return;
}
//通过PermissionsState进行动态权限的分配
final int result = permissionsState.grantRuntimePermission(bp, userId);
....
}
.....
}
在PMS的grantRuntimePermission方法中首先根据包名取到应用安装时的Package对象，这个Package对象中包含了应用的一些设置信息，通过这个设置信息可以取到当前应用的PermissionState，它维护了当前应用的权限授予情况。同时根据参数name,也就是权限名获取全新的配置信息BasePermission对象，它时从mSettings中取到的，mSettings是PMS的全局设置，它在PMS启动的时候初始化，里面包含了平台支持的所有权限。最后权限的分配进一步通过PermissionState来完成
//frameworks/base/services/core/java/com/android/server/pm/PermissionsState.java
//动态权限的分配
public int grantRuntimePermission(BasePermission permission, int userId) {
enforceValidUserId(userId);
if (userId == UserHandle.USER_ALL) {
return PERMISSION_OPERATION_FAILURE;
}
return grantPermission(permission, userId);
}
private int grantPermission(BasePermission permission, int userId) {
if (hasPermission(permission.name, userId)) {
return PERMISSION_OPERATION_FAILURE;
}
//计算用户组id
final boolean hasGids = !ArrayUtils.isEmpty(permission.computeGids(userId));
final int[] oldGids = hasGids ? computeGids(userId) : NO_GIDS;
//将权限包装成PermissionData添加到应用的权限列表中
PermissionData permissionData = ensurePermissionData(permission);
//授予权限，修改PermissionState的mGranted属性
if (!permissionData.grant(userId)) {
return PERMISSION_OPERATION_FAILURE;
}
if (hasGids) {
final int[] newGids = computeGids(userId);//重新计算用户的权限组id
//权限组id是否发生变化
if (oldGids.length != newGids.length) {
return PERMISSION_OPERATION_SUCCESS_GIDS_CHANGED;
}
}
return PERMISSION_OPERATION_SUCCESS;
}
在grantPermission方法中首先会计算当前用户进程当前拥有的组id，然后再通过ensurePermissionData将权限添加到应用的PermissionData列表中，这里返回一个PermissionData，通过该对象的grant方法进行最终的分配，事实上它其实是修改内部PermissionState成员的mGranted状态为true。最后会对用户的组id进行重新计算，如果发生变化则返回PERMISSION_OPERATION_SUCCESS_GIDS_CHANGED，否则返回PERMISSION_OPERATION_SUCCESS
//保证权限被添加到用户列表中
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;
}
//根据用户权限列表计算用户的gid
public int[] computeGids(int userId) {
enforceValidUserId(userId);
int[] gids = mGlobalGids;
if (mPermissions != null) {
final int permissionCount = mPermissions.size();
for (int i = 0; i < permissionCount; i++) {
String permission = mPermissions.keyAt(i);
if (!hasPermission(permission, userId)) {
continue;
}
PermissionData permissionData = mPermissions.valueAt(i);
//取到权限对应的组id数组，可见权限可以通过多个gid描述
final int[] permGids = permissionData.computeGids(userId);
if (permGids != NO_GIDS) {
//将权限对应的组id添加到用户的组id数组中
gids = appendInts(gids, permGids);
}
}
}
return gids;
}
ensurePermissionData方法确保将权限对应的PermissionData添加到PermissonsState的权限列表中，后续通过computeGids计算用户userId对应的组id，并将其添加到用户的组id数组mGlobalGids中。其中内置权限的gid映射是定义在/etc/permission/platform.xml
··· ···
至此，我们明白了权限的本质实际上就是一组gid，这组gid对应的是一些整型，这些映射关系存放在system/core/include/private/android_filesystem_config.h中，其中的定义如下
#define AID_NET_BT_ADMIN 3001 /* bluetooth: create any socket */
#define AID_NET_BT 3002 /* bluetooth: create sco, rfcomm or l2cap sockets */
#define AID_INET 3003 /* can create AF_INET and AF_INET6 sockets */
#define AID_SDCARD_RW 1015 /* external storage write access */
static const struct android_id_info android_ids[] = {
...
{ "bluetooth", AID_BLUETOOTH, },
{ "sdcard_rw", AID_SDCARD_RW, },
{ "net_bt_admin", AID_NET_BT_ADMIN, },
{ "net_bt", AID_NET_BT, },
{ "inet", AID_INET, },
...
}
通过将权限映射成一组gid，然后作为补充gid赋值给用户进程，也就是权限分配的本质。
//PermisssionsState.PermissionData
public boolean grant(int userId) {
if (!isCompatibleUserId(userId)) {
return false;
}
if (isGranted(userId)) {
return false;
}
PermissionState userState = mUserStates.get(userId);
if (userState == null) {
userState = new PermissionState(mPerm.name);
mUserStates.put(userId, userState);
}
//分配权限置true
userState.mGranted = true;
return true;
}
通过PermissionData的grant方法，为对应的用户创建PermissionState，并将mGranted置为true表示分配了该权限给
该用户。
当然权限分配完成后，下次不需要再次分配，当我们重新启动手机后，并需要再次对权限进行分配，这是因为PMS为所有的package记录了权限分配的情况，在Android6.0之前，package所有的权限信息都是存放在data/system/packages.xml配置文件中,在应用中启动时候读取该配置就可以直到权限分配了哪些权限。但在Android6.0后，运行时权限放在了data/system/users/0/runtime-permissions.xml中，而普通权限保持不变依然存放在packages.xml中，而且默认granted就是true。那么在分配完成权限后需要将权限的分配信息持久化到该文件中。
//packages.xml
- ...
在PMS的grantRuntimePermission分配完运行时权限后，最后会调用writeRuntimePermissionsForUserLPr将权限信息持久化到配置文件runtime-permissions.xml中,我们看看这个过程
public void writeRuntimePermissionsForUserLPr(int userId, boolean sync) {
if (sync) {
mRuntimePermissionsPersistence.writePermissionsForUserSyncLPr(userId);
} else {
mRuntimePermissionsPersistence.writePermissionsForUserAsyncLPr(userId);
}
}
无论时同步方式还是异步方式的持久化，最后都会调用下面的方法进行
//写入权限到配置文件
private void writePermissionsSync(int userId) {
//要写入的文件/data/system/users/0/runtime-permissions.xml
AtomicFile destination = new AtomicFile(getUserRuntimePermissionsFile(userId));
ArrayMap> permissionsForPackage = new ArrayMap<>();
ArrayMap> permissionsForSharedUser = new ArrayMap<>();
synchronized (mLock) {
mWriteScheduled.delete(userId);
//对所有的package进行处理
final int packageCount = mPackages.size();
for (int i = 0; i < packageCount; i++) {
String packageName = mPackages.keyAt(i);
//取到PackageSetting
PackageSetting packageSetting = mPackages.valueAt(i);
if (packageSetting.sharedUser == null) {//没有sharedUser的情况
//取到PermissionsState，这个对象描述了包的权限信息
PermissionsState permissionsState = packageSetting.getPermissionsState();
List permissionsStates = permissionsState
.getRuntimePermissionStates(userId);//获取全新分配列表
if (!permissionsStates.isEmpty()) {
//存放在permissionsForPackage这个Map中，以包名为键
permissionsForPackage.put(packageName, permissionsStates);
}
}
}
//有shareUser的情况
final int sharedUserCount = mSharedUsers.size();
for (int i = 0; i < sharedUserCount; i++) {
String sharedUserName = mSharedUsers.keyAt(i);
SharedUserSetting sharedUser = mSharedUsers.valueAt(i);
PermissionsState permissionsState = sharedUser.getPermissionsState();
List permissionsStates = permissionsState
.getRuntimePermissionStates(userId);
if (!permissionsStates.isEmpty()) {
permissionsForSharedUser.put(sharedUserName, permissionsStates);
}
}
}
//写配置
FileOutputStream out = null;
try {
//取到输出流
out = destination.startWrite();
XmlSerializer serializer = Xml.newSerializer();
serializer.setOutput(out, StandardCharsets.UTF_8.name());
serializer.setFeature(
"http://xmlpull.org/v1/doc/features.html#indent-output", true);
serializer.startDocument(null, true);
serializer.startTag(null, TAG_RUNTIME_PERMISSIONS);
String fingerprint = mFingerprints.get(userId);
if (fingerprint != null) {
serializer.attribute(null, ATTR_FINGERPRINT, fingerprint);
}
//先写当前package的permission
final int packageCount = permissionsForPackage.size();
for (int i = 0; i < packageCount; i++) {
String packageName = permissionsForPackage.keyAt(i);
List permissionStates = permissionsForPackage.valueAt(i);
serializer.startTag(null, TAG_PACKAGE);//package
serializer.attribute(null, ATTR_NAME, packageName);
writePermissions(serializer, permissionStates);
serializer.endTag(null, TAG_PACKAGE);
}
//写其shareUser进程的permission
final int sharedUserCount = permissionsForSharedUser.size();
for (int i = 0; i < sharedUserCount; i++) {
String packageName = permissionsForSharedUser.keyAt(i);
List permissionStates = permissionsForSharedUser.valueAt(i);
serializer.startTag(null, TAG_SHARED_USER);
serializer.attribute(null, ATTR_NAME, packageName);
writePermissions(serializer, permissionStates);
serializer.endTag(null, TAG_SHARED_USER);
}
serializer.endTag(null, TAG_RUNTIME_PERMISSIONS);
serializer.endDocument();
destination.finishWrite(out);
if (Build.FINGERPRINT.equals(fingerprint)) {
mDefaultPermissionsGranted.put(userId, true);
}
// Any error while writing is fatal.
} catch (Throwable t) {
Slog.wtf(PackageManagerService.TAG,
"Failed to write settings, restoring backup", t);
destination.failWrite(out);
} finally {
IoUtils.closeQuietly(out);
}
}
writePermissionsSync写配置的过程很简单，先打开配置文件/data/system/users/0/runtime-permissions.xml，随后对PMS中的每个package和sharedUser分别将其对应的权限分配列表按照包名和shareUserName存放在permissionsForPackage和permissionsForSharedUser中，随后打开输出流分别将其对应的运行时权限分配情况写入文件。
private void writePermissions(XmlSerializer serializer,
List permissionStates) throws IOException {
for (PermissionState permissionState : permissionStates) {
serializer.startTag(null, TAG_ITEM);
serializer.attribute(null, ATTR_NAME,permissionState.getName());
serializer.attribute(null, ATTR_GRANTED,
String.valueOf(permissionState.isGranted()));
serializer.attribute(null, ATTR_FLAGS,
Integer.toHexString(permissionState.getFlags()));
serializer.endTag(null, TAG_ITEM);
}
}
writePermissions负责写tag 为package下的一条权限分配信息，如
权限的检测
权限检测是通过Context的checkSelfPermission方法来进行的。我们看下它的实现
@Override
public int checkSelfPermission(String permission) {
if (permission == null) {
throw new IllegalArgumentException("permission is null");
}
return checkPermission(permission, Process.myPid(), Process.myUid());
}
@Override
public int checkPermission(String permission, int pid, int uid) {
if (permission == null) {
throw new IllegalArgumentException("permission is null");
}
try {
return ActivityManagerNative.getDefault().checkPermission(
permission, pid, uid);
} catch (RemoteException e) {
return PackageManager.PERMISSION_DENIED;
}
}
最终还是通过AMS的checkPermission来进行权限检查。
//frameworks/base/core/java/android/app/ActivityManager.java
@Override
public int checkPermission(String permission, int pid, int uid) {
if (permission == null) {
return PackageManager.PERMISSION_DENIED;
}
return checkComponentPermission(permission, pid, uid, -1, true);
}
int checkComponentPermission(String permission, int pid, int uid,
int owningUid, boolean exported) {
if (pid == MY_PID) {
return PackageManager.PERMISSION_GRANTED;
}
return ActivityManager.checkComponentPermission(permission, uid,
owningUid, exported);
}
/** @hide */
public static int checkComponentPermission(String permission, int uid,
int owningUid, boolean exported) {
// Root, system server get to do everything.
final int appId = UserHandle.getAppId(uid);
if (appId == Process.ROOT_UID || appId == Process.SYSTEM_UID) {
return PackageManager.PERMISSION_GRANTED;
}
// Isolated processes don't get any permissions.
if (UserHandle.isIsolated(uid)) {
return PackageManager.PERMISSION_DENIED;
}
// If there is a uid that owns whatever is being accessed, it has
// blanket access to it regardless of the permissions it requires.
if (owningUid >= 0 && UserHandle.isSameApp(uid, owningUid)) {
return PackageManager.PERMISSION_GRANTED;
}
// If the target is not exported, then nobody else can get to it.
if (!exported) {
/*
RuntimeException here = new RuntimeException("here");
here.fillInStackTrace();
Slog.w(TAG, "Permission denied: checkComponentPermission() owningUid=" + owningUid,
here);
*/
return PackageManager.PERMISSION_DENIED;
}
if (permission == null) {
return PackageManager.PERMISSION_GRANTED;
}
//通过PMS进行check
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;
}
在AMS中的一系列调用中，最终的权限还是通过PMS的checkUidPermission来进行check的。
//PMS
@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();
//通过PermissionsState来检查
if (permissionsState.hasPermission(permName, userId)) {
return PackageManager.PERMISSION_GRANTED;
}
//定位权限的检测特殊处理
// 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 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;
}
checkUidPermission首先根据userId从PMS的配置对象中取到SettingBase,然后取到用户对应的PermissionsState，再通过permissionsState的hasPermission判断是否有该权限。
//检测权限
public boolean hasPermission(String name, int userId) {
enforceValidUserId(userId);
if (mPermissions == null) {
return false;
}
//取到权限对应的PermissionData
PermissionData permissionData = mPermissions.get(name);
//通过isGranted来判断
return permissionData != null && permissionData.isGranted(userId);
}
从PermissionsState的权限列表中取到PermissionData，通过PermissionData的PermissionState对象的mGranted成员就知道权限是否分配了。
总结
在Android6.0之前的版本中，应用在安装的时候会将manifest中request的权限(即通过申请的权限)添加到Package对象的PackageSetting中，PMS为每个安装的app创建一个Package对象，这个是在安装过程中创建的，同时在安装过程中也会为每个app创建一个PackageSetting对象，并将其保存在Package对象的mExtra中，在PackageSetting内部保存了应用的签名信息和授予的权限列表，实际上PackageSetting本身就是继承自GrantedPermissions类，这个类从名字看就知道它负责已授权的permission。应用中授权的权限在安装完成后会将应用的信息(包括了权限，签名和应用的基本信息等)写入到pacakge.xml文件中，这样下次系统启动就可以通过读取该文件获取应用的授权信息。
在Aandroid6.0之后，google为了防止应用滥用权限对权限的授予进行了收缩，将危险的权限授予过程交给用户来决定，为了适应这样的变化，必须要将安装权限和运行时权限进行区分处理，安装权限保持原有的逻辑不变，对于动态权限的分配必然要对PackageSetting进行一个大手术，在Android6.0中PackageSetting不再继承自GrantedPermissions，而是继承自于SettingBase，它的内部也比以前复杂了一些，简单来说它内部维护了一个PermissionsState，它负责管理应用的权限，因此它内部存放着应用的授权的权限列表(实际上是一个ArrayMap
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