标签：des android style class blog code
Android系统采用了sandboxes的安全机制，每个app有对应的PID，UID，资源，数据，以及基本的API。当app需要sandbox没有提供的额外API时，需要声明权限。
在本文中，我们将会探究apk申请的权限信息是如何被保存到系统中的。
AndroidManifest.xml位于工程根目录下
在<activity>标签之前声明权限
参考：AndroidDeveloper->SecurityTips->Using Permissions
PKMS中mPackages对应的类型是：
// Keys are String (package name), values are Package. This also serves
// as the lock for the global state. Methods that must be called with
// this lock held have the prefix "LP".
final HashMap<String, PackageParser.Package> mPackages =
new HashMap<String, PackageParser.Package>();
部分属性成员和方法如下：
从上面两个流程，我们可以看到在PackageManagerService（PKMS）启动（即SystemServer启动）与安装apk时，PKMS都会调用PackageParser::parsePackage()和scanPackageLI()方法。
那么下面我们就来分析一下这两个方法的作用：
PackageParser.Package.parsePackage():
private Package parsePackage(
Resources res, XmlResourceParser parser, int flags, String[] outError)
throws XmlPullParserException, IOException {
String pkgName = parsePackageName(parser, attrs, flags, outError);
final Package pkg = new Package(pkgName);
// ...
int outerDepth = parser.getDepth();
while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
&& (type != XmlPullParser.END_TAG || parser.getDepth() > outerDepth)) {
if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
continue;
}
String tagName = parser.getName();
if (tagName.equals("application")) {
// ...
}
} /* ... */ else if (tagName.equals("uses-permission")) {
if (!parseUsesPermission(pkg, res, parser, attrs, outError)) {
return null;
}
}
}
// ...
return pkg;
}
通过AndroidManifest.xml来获得package名字，然后解析xml文件的tag，并调用相应的方法。 如"uses-permission"标签对应调用parseUsesPermission()方法。
PackageParser.parseUsesPermission():
private boolean parseUsesPermission(Package pkg, Resources res, XmlResourceParser parser,
AttributeSet attrs, String[] outError)
throws XmlPullParserException, IOException {
// ...
if ((maxSdkVersion == 0) || (maxSdkVersion >= Build.VERSION.RESOURCES_SDK_INT)) {
if (name != null) {
int index = pkg.requestedPermissions.indexOf(name);
if (index == -1) {
pkg.requestedPermissions.add(name.intern());
pkg.requestedPermissionsRequired.add(required ? Boolean.TRUE : Boolean.FALSE);
} else {
if (pkg.requestedPermissionsRequired.get(index) != required) {
outError[0] = "conflicting <uses-permission> entries";
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
}
}
}
XmlUtils.skipCurrentTag(parser);
return true;
}
parseUsesPermission()判断permission是否已经保存，如果没有则add到pkg的requestedPermissions(ArrayList）中。
下面我们继续看scanPackageLI()方法：
PackageManagerService.scanPackageLI(PackageParser.Package, ...)
private PackageParser.Package scanPackageLI(PackageParser.Package pkg,
int parseFlags, int scanMode, long currentTime, UserHandle user) {
// 判断apk是否已经安装过，跳过重复安装
// 检查非system app的库是否被映射到正确的路径上
// 检查是否需要重命名原来的Package Name
// 为新的apk创建PackageSetting
// 验证apk的signature
// 验证apk的ContentProvider是否与已存在的apk的有冲突
// 把apk的库解压复制到对应目录中
// writer
synchronized (mPackages) {
// We don‘t expect installation to fail beyond this point,
if ((scanMode&SCAN_MONITOR) != 0) {
mAppDirs.put(pkg.mPath, pkg);
}
// Add the new setting to mSettings
mSettings.insertPackageSettingLPw(pkgSetting, pkg);
// Add the new setting to mPackages
mPackages.put(pkg.applicationInfo.packageName, pkg);
// Make sure we don‘t accidentally delete its data.
final Iterator<PackageCleanItem> iter = mSettings.mPackagesToBeCleaned.iterator();
while (iter.hasNext()) {
PackageCleanItem item = iter.next();
if (pkgName.equals(item.packageName)) {
iter.remove();
}
}
// Just create the setting, don‘t add it yet. For already existing packages
// the PkgSetting exists already and doesn‘t have to be created.
// 安装新apk时，会最终调用到newUserIdLPw()
pkgSetting = mSettings.getPackageLPw(pkg, origPackage, realName, suid, destCodeFile,
destResourceFile, pkg.applicationInfo.nativeLibraryDir,
pkg.applicationInfo.flags, user, false);
// ...
}
// ...
}
在Android中有多个名为Settings的类，此Settings为com.android.server.pm.Settings。
其中，mUserIds属性保存着uid的重要信息。
从PKMS构造的时序图可以看出，在PKMS进行scanDirLI之前，会先后调用Settings的addSharedUserLPw()和readLPw()。
public PackageManagerService(Context context, Installer installer,
boolean factoryTest, boolean onlyCore) {
// ...
mSettings = new Settings(context);
mSettings.addSharedUserLPw("android.uid.system",
Process.SYSTEM_UID, ApplicationInfo.FLAG_SYSTEM);
mSettings.addSharedUserLPw("android.uid.phone", RADIO_UID, ApplicationInfo.FLAG_SYSTEM);
mSettings.addSharedUserLPw("android.uid.log", LOG_UID, ApplicationInfo.FLAG_SYSTEM);
mSettings.addSharedUserLPw("android.uid.nfc", NFC_UID, ApplicationInfo.FLAG_SYSTEM);
mSettings.addSharedUserLPw("android.uid.bluetooth", BLUETOOTH_UID, ApplicationInfo.FLAG_SYSTEM);
mSettings.addSharedUserLPw("android.uid.shell", SHELL_UID, ApplicationInfo.FLAG_SYSTEM);
synchronized (mInstallLock) {
// writer
synchronized (mPackages) {
// ...
sUserManager = new UserManagerService(context, this,
mInstallLock, mPackages);
readPermissions();
mFoundPolicyFile = SELinuxMMAC.readInstallPolicy();
mRestoredSettings = mSettings.readLPw(this, sUserManager.getUsers(false),
mSdkVersion, mOnlyCore);
addSharedUserLPw()方法的作用是如果某个app的AndroidManifest中声明android:sharedUserId="com.android.process"，则它的uid与属性值中的进程uid一样。
当然，前提是两者的apk签名（signature）相同。
这样，该进程就能获得uid的权限。
而readLPw()则是创建新的uid。无论是调用addSharedUserLPw()还是readLPw()，最终都会调用到addUserIdLPw()。
private boolean addUserIdLPw(int uid, Object obj, Object name) {
if (uid > Process.LAST_APPLICATION_UID) {
return false;
}
if (uid >= Process.FIRST_APPLICATION_UID) {
int N = mUserIds.size();
final int index = uid - Process.FIRST_APPLICATION_UID;
while (index >= N) {
mUserIds.add(null);
N++;
}
if (mUserIds.get(index) != null) {
PackageManagerService.reportSettingsProblem(Log.ERROR,
"Adding duplicate user id: " + uid
+ " name=" + name);
return false;
}
mUserIds.set(index, obj);
} else {
if (mOtherUserIds.get(uid) != null) {
PackageManagerService.reportSettingsProblem(Log.ERROR,
"Adding duplicate shared id: " + uid
+ " name=" + name);
return false;
}
mOtherUserIds.put(uid, obj);
}
mUserIds是一个ArrayList，以uid减去FIRST_APPLICATION_UID的值为下标索引，而对应的obj是Object类型，实际上是PackageSetting
（PackageSetting继承于PackageSettingBase，
而PackageSettingBase继承于GrantedPermissions。
GrantedPermissions中有一个类型为HashSet的grantedPermissions，存放着权限的String）
上面的addUserIdLPw，是在PKMS启动时调用的。而安装新apk时，调用的是newUserIdLPw。
private PackageParser.Package scanPackageLI(PackageParser.Package pkg,
int parseFlags, int scanMode, long currentTime, UserHandle user) {
// writer
synchronized (mPackages) {
// Just create the setting, don‘t add it yet. For already existing packages
// the PkgSetting exists already and doesn‘t have to be created.
// 为新的APK创建PackageSetting
pkgSetting = mSettings.getPackageLPw(pkg, origPackage, realName, suid, destCodeFile,
destResourceFile, pkg.applicationInfo.nativeLibraryDir,
pkg.applicationInfo.flags, user, false);
if (pkgSetting == null) {
Slog.w(TAG, "Creating application package " + pkg.packageName + " failed");
mLastScanError = PackageManager.INSTALL_FAILED_INSUFFICIENT_STORAGE;
return null;
}
}
}
最终会调用到newUserIdLPw():
private int newUserIdLPw(Object obj) {
// Let‘s be stupidly inefficient for now...
final int N = mUserIds.size();
for (int i = 0; i < N; i++) {
if (mUserIds.get(i) == null) {
mUserIds.set(i, obj);
return Process.FIRST_APPLICATION_UID + i;
}
}
// None left?
if (N > (Process.LAST_APPLICATION_UID-Process.FIRST_APPLICATION_UID)) {
return -1;
}
mUserIds.add(obj);
return Process.FIRST_APPLICATION_UID + N;
}
如果新安装的apk具有android:sharedUserId的话，scanPackageLI()中将会调用getSharedUserLPw()，最终还是会调用到newUserIdLPw()，这一段我们就不再详细探究。
通过以上的分析，我们可以得出以下结论：
保存了apk的信息之后，我们就可以通过PackageManager来间接获得PKMS中的这些信息。 PackageManager.getPackageInfo()是Android API level 1的公开接口：
public abstract PackageInfo getPackageInfo(String packageName, int flags)
通过AIDL，PKMS的getPackageInfo()会被调用到：
PackageManagerService.getPackageInfo()
@Override
public PackageInfo getPackageInfo(String packageName, int flags, int userId) {
if (!sUserManager.exists(userId)) return null;
enforceCrossUserPermission(Binder.getCallingUid(), userId, false, "get package info");
// reader
synchronized (mPackages) {
PackageParser.Package p = mPackages.get(packageName);
if (DEBUG_PACKAGE_INFO)
Log.v(TAG, "getPackageInfo " + packageName + ": " + p);
if (p != null) {
return generatePackageInfo(p, flags, userId);
}
if((flags & PackageManager.GET_UNINSTALLED_PACKAGES) != 0) {
return generatePackageInfoFromSettingsLPw(packageName, flags, userId);
}
}
return null;
}
这样，apk的<uses-permission>信息也就能够被第三方app获取到了。
Android权限机制（一） 权限的申请与保存,布布扣,bubuko.com
标签：des android style class blog code
原文地址：http://www.cnblogs.com/jacobchen/p/3804994.html
