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      1 /*
      2  * Copyright (C) 2013 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.server.firewall;
     18 
     19 import android.app.AppGlobals;
     20 import android.content.ComponentName;
     21 import android.content.Intent;
     22 import android.content.pm.ApplicationInfo;
     23 import android.content.pm.IPackageManager;
     24 import android.os.Process;
     25 import android.os.RemoteException;
     26 import android.util.Slog;
     27 import org.xmlpull.v1.XmlPullParser;
     28 import org.xmlpull.v1.XmlPullParserException;
     29 
     30 import java.io.IOException;
     31 
     32 class SenderFilter {
     33     private static final String ATTR_TYPE = "type";
     34 
     35     private static final String VAL_SIGNATURE = "signature";
     36     private static final String VAL_SYSTEM = "system";
     37     private static final String VAL_SYSTEM_OR_SIGNATURE = "system|signature";
     38     private static final String VAL_USER_ID = "userId";
     39 
     40     static boolean isPrivilegedApp(int callerUid, int callerPid) {
     41         if (callerUid == Process.SYSTEM_UID || callerUid == 0 ||
     42                 callerPid == Process.myPid() || callerPid == 0) {
     43             return true;
     44         }
     45 
     46         IPackageManager pm = AppGlobals.getPackageManager();
     47         try {
     48             return (pm.getFlagsForUid(callerUid) & ApplicationInfo.FLAG_PRIVILEGED) != 0;
     49         } catch (RemoteException ex) {
     50             Slog.e(IntentFirewall.TAG, "Remote exception while retrieving uid flags",
     51                     ex);
     52         }
     53 
     54         return false;
     55     }
     56 
     57     public static final FilterFactory FACTORY = new FilterFactory("sender") {
     58         @Override
     59         public Filter newFilter(XmlPullParser parser) throws IOException, XmlPullParserException {
     60             String typeString = parser.getAttributeValue(null, ATTR_TYPE);
     61             if (typeString == null) {
     62                 throw new XmlPullParserException("type attribute must be specified for <sender>",
     63                         parser, null);
     64             }
     65             if (typeString.equals(VAL_SYSTEM)) {
     66                 return SYSTEM;
     67             } else if (typeString.equals(VAL_SIGNATURE)) {
     68                 return SIGNATURE;
     69             } else if (typeString.equals(VAL_SYSTEM_OR_SIGNATURE)) {
     70                 return SYSTEM_OR_SIGNATURE;
     71             } else if (typeString.equals(VAL_USER_ID)) {
     72                 return USER_ID;
     73             }
     74             throw new XmlPullParserException(
     75                     "Invalid type attribute for <sender>: " + typeString, parser, null);
     76         }
     77     };
     78 
     79     private static final Filter SIGNATURE = new Filter() {
     80         @Override
     81         public boolean matches(IntentFirewall ifw, ComponentName resolvedComponent, Intent intent,
     82                 int callerUid, int callerPid, String resolvedType, int receivingUid) {
     83             return ifw.signaturesMatch(callerUid, receivingUid);
     84         }
     85     };
     86 
     87     private static final Filter SYSTEM = new Filter() {
     88         @Override
     89         public boolean matches(IntentFirewall ifw, ComponentName resolvedComponent, Intent intent,
     90                 int callerUid, int callerPid, String resolvedType, int receivingUid) {
     91             return isPrivilegedApp(callerUid, callerPid);
     92         }
     93     };
     94 
     95     private static final Filter SYSTEM_OR_SIGNATURE = new Filter() {
     96         @Override
     97         public boolean matches(IntentFirewall ifw, ComponentName resolvedComponent, Intent intent,
     98                 int callerUid, int callerPid, String resolvedType, int receivingUid) {
     99             return isPrivilegedApp(callerUid, callerPid) ||
    100                     ifw.signaturesMatch(callerUid, receivingUid);
    101         }
    102     };
    103 
    104     private static final Filter USER_ID = new Filter() {
    105         @Override
    106         public boolean matches(IntentFirewall ifw, ComponentName resolvedComponent, Intent intent,
    107                 int callerUid, int callerPid, String resolvedType, int receivingUid) {
    108             // This checks whether the caller is either the system process, or has the same user id
    109             // I.e. the same app, or an app that uses the same shared user id.
    110             // This is the same set of applications that would be able to access the component if
    111             // it wasn't exported.
    112             return ifw.checkComponentPermission(null, callerPid, callerUid, receivingUid, false);
    113         }
    114     };
    115 }
    116