Android 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<String> 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。