1 /*
2  * Copyright (C) 2015 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.example.android.supportv4.media;
18 
19 import android.content.Context;
20 import android.content.pm.PackageInfo;
21 import android.content.pm.PackageManager;
22 import android.content.res.XmlResourceParser;
23 import android.os.Process;
24 import android.util.Base64;
25 import android.util.Log;
26 
27 import com.example.android.supportv4.R;
28 
29 import org.xmlpull.v1.XmlPullParserException;
30 
31 import java.io.IOException;
32 import java.util.ArrayList;
33 import java.util.HashMap;
34 import java.util.Map;
35 
36 /**
37  * Validates that the calling package is authorized to browse a
38  * {@link android.service.media.MediaBrowserService}.
39  *
40  * The list of allowed signing certificates and their corresponding package names is defined in
41  * res/xml/allowed_media_browser_callers.xml.
42  */
43 public class PackageValidator {
44     private static final String TAG = "PackageValidator";
45 
46     /**
47      * Map allowed callers' certificate keys to the expected caller information.
48      *
49      */
50     private final Map<String, ArrayList<CallerInfo>> mValidCertificates;
51 
PackageValidator(Context ctx)52     public PackageValidator(Context ctx) {
53         mValidCertificates = readValidCertificates(ctx.getResources().getXml(
54             R.xml.allowed_media_browser_callers));
55     }
56 
readValidCertificates(XmlResourceParser parser)57     private Map<String, ArrayList<CallerInfo>> readValidCertificates(XmlResourceParser parser) {
58         HashMap<String, ArrayList<CallerInfo>> validCertificates = new HashMap<>();
59         try {
60             int eventType = parser.next();
61             while (eventType != XmlResourceParser.END_DOCUMENT) {
62                 if (eventType == XmlResourceParser.START_TAG
63                         && parser.getName().equals("signing_certificate")) {
64 
65                     String name = parser.getAttributeValue(null, "name");
66                     String packageName = parser.getAttributeValue(null, "package");
67                     boolean isRelease = parser.getAttributeBooleanValue(null, "release", false);
68                     String certificate = parser.nextText().replaceAll("\\s|\\n", "");
69 
70                     CallerInfo info = new CallerInfo(name, packageName, isRelease, certificate);
71 
72                     ArrayList<CallerInfo> infos = validCertificates.get(certificate);
73                     if (infos == null) {
74                         infos = new ArrayList<>();
75                         validCertificates.put(certificate, infos);
76                     }
77                     Log.v(TAG, "Adding allowed caller: " + info.name + " package="
78                             + info.packageName + " release=" + info.release + " certificate="
79                             + certificate);
80                     infos.add(info);
81                 }
82                 eventType = parser.next();
83             }
84         } catch (XmlPullParserException | IOException e) {
85             Log.e(TAG, "Could not read allowed callers from XML.", e);
86         }
87         return validCertificates;
88     }
89 
90     /**
91      * @return false if the caller is not authorized to get data from this MediaBrowserService
92      */
93     @SuppressWarnings("BooleanMethodIsAlwaysInverted")
isCallerAllowed(Context context, String callingPackage, int callingUid)94     public boolean isCallerAllowed(Context context, String callingPackage, int callingUid) {
95         // Always allow calls from the framework, self app or development environment.
96         if (Process.SYSTEM_UID == callingUid || Process.myUid() == callingUid) {
97             return true;
98         }
99         PackageManager packageManager = context.getPackageManager();
100         PackageInfo packageInfo;
101         try {
102             packageInfo = packageManager.getPackageInfo(
103                     callingPackage, PackageManager.GET_SIGNATURES);
104         } catch (PackageManager.NameNotFoundException e) {
105             Log.w(TAG, "Package manager can't find package: " + callingPackage, e);
106             return false;
107         }
108         if (packageInfo.signatures.length != 1) {
109             Log.w(TAG, "Caller has more than one signature certificate!");
110             return false;
111         }
112         String signature = Base64.encodeToString(
113             packageInfo.signatures[0].toByteArray(), Base64.NO_WRAP);
114 
115         // Test for known signatures:
116         ArrayList<CallerInfo> validCallers = mValidCertificates.get(signature);
117         if (validCallers == null) {
118             Log.v(TAG, "Signature for caller " + callingPackage + " is not valid: \n" + signature);
119             if (mValidCertificates.isEmpty()) {
120                 Log.w(TAG, "The list of valid certificates is empty. Either your file"
121                         + " res/xml/allowed_media_browser_callers.xml is empty or there was an"
122                         + " error while reading it. Check previous log messages.");
123             }
124             return false;
125         }
126 
127         // Check if the package name is valid for the certificate:
128         StringBuffer expectedPackages = new StringBuffer();
129         for (CallerInfo info: validCallers) {
130             if (callingPackage.equals(info.packageName)) {
131                 Log.v(TAG, "Valid caller: " + info.name + "  package=" + info.packageName
132                     + " release=" + info.release);
133                 return true;
134             }
135             expectedPackages.append(info.packageName).append(' ');
136         }
137 
138         Log.i(TAG, "Caller has a valid certificate, but its package doesn't match any expected"
139                 + "package for the given certificate. Caller's package is " + callingPackage
140                 + ". Expected packages as defined in res/xml/allowed_media_browser_callers.xml are"
141                 +" (" + expectedPackages + "). This caller's certificate is: \n" + signature);
142 
143         return false;
144     }
145 
146     private final static class CallerInfo {
147         final String name;
148         final String packageName;
149         final boolean release;
150         final String signingCertificate;
151 
CallerInfo(String name, String packageName, boolean release, String signingCertificate)152         public CallerInfo(String name, String packageName, boolean release,
153                           String signingCertificate) {
154             this.name = name;
155             this.packageName = packageName;
156             this.release = release;
157             this.signingCertificate = signingCertificate;
158         }
159     }
160 }
161