Android(安卓)系统对permision的检测过程

Android 系统对permision的检测过程
RK3288 5.1 中以太网设置静态IP 对permission的检测

简略的调用过程如下：

frameworks\opt\net\ethernet\java\com\android\server\ethernet\EthernetServiceImpl.java

    public void setConfiguration(IpConfiguration config) {        if (!mStarted.get()) {            Log.w(TAG, "System isn't ready enough to change ethernet configuration");        }        enforceChangePermission();        enforceConnectivityInternalPermission();        synchronized (mIpConfiguration) {            mEthernetConfigStore.writeIpAndProxyConfigurations(config);            // TODO: this does not check proxy settings, gateways, etc.            // Fix this by making IpConfiguration a complete representation of static configuration.            if (!config.equals(mIpConfiguration)) {                mIpConfiguration = new IpConfiguration(config);                mTracker.stop();                mTracker.start(mContext, mHandler);            }        }    }   private void enforceConnectivityInternalPermission() {        mContext.enforceCallingOrSelfPermission(                android.Manifest.permission.CONNECTIVITY_INTERNAL,                "ConnectivityService");    }

frameworks\base\core\java\android\app\ContextImpl.java

public void enforceCallingOrSelfPermission(            String permission, String message) {        enforce(permission,                checkCallingOrSelfPermission(permission),                true,                Binder.getCallingUid(),                message);

通过Binder这个类，可以获得调用服务的应用的ID，通过这个ID，可以获得应用的相关信息；

    @Override    public int checkCallingOrSelfPermission(String permission) {        if (permission == null) {            throw new IllegalArgumentException("permission is null");        }        return checkPermission(permission, Binder.getCallingPid(),                Binder.getCallingUid());    }    @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;        }    }

frameworks\base\services\core\java\com\android\server\ActivityManagerService.java

    @Override    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);    }    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);    }

frameworks\base\core\java\android\app\ActivityManager.java

    /** @hide */    public static int checkComponentPermission(String permission, int uid,            int owningUid, boolean exported) {        // Root, system server get to do everything.        if (uid == 0 || uid == 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;        }        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;    }

对于普通应用将通过PackageManagerService中保持的信息进行判断是否具有相应的权限；
base/services/core/java/com/android/server/pm/PackageManagerService.java

    @Override    public int checkUidPermission(String permName, int uid) {        synchronized (mPackages) {            Object obj = mSettings.getUserIdLPr(UserHandle.getAppId(uid));            if (obj != null) {                GrantedPermissions gp = (GrantedPermissions)obj;                if (gp.grantedPermissions.contains(permName)) {                    return PackageManager.PERMISSION_GRANTED;                }            } else {                ArraySet perms = mSystemPermissions.get(uid);                if (perms != null && perms.contains(permName)) {                    return PackageManager.PERMISSION_GRANTED;                }            }        }        return PackageManager.PERMISSION_DENIED;    }

每次开机系统PackageManagerService都会还原现有app的安装信息，这些信息被放在/data/system/packages.xml里，由mSettings管理。另外/data/system/packages.list记录了app的uid和数据路径等信息。

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