4.3.1.1 创建/..
4.3.1.3 创建/..

安卓应用安全指南 (Android Application Secure Design/Secure Coding Guidebook)

4.3.1.2 创建/使用公共内容供应器

公共内容供应器是应该由未指定的大量应用使用的内容供应器。 需要注意的是，由于它不指定客户端，它可能会受到恶意软件的攻击和篡改。 例如，可以通过select()获取保存的数据，可以通过update()更改数据，或者可以通过insert()/ delete()插入/删除假数据。

另外，在使用 Android OS 未提供的自定义公共内容供应器时，需要注意的是，恶意软件可能会接收到请求参数，伪装成自定义公共内容供应器，并且也可能发送攻击数据。 Android OS 提供的联系人和 MediaStore 也是公共内容提供商，但恶意软件不能伪装成它们。

实现公共内容供应器的样例代码展示在下面：

要点（创建内容供应器）：

  1. 将导出的属性显式设置为true。

  2. 仔细安全地处理收到的请求数据。

  3. 返回结果时，请勿包含敏感信息。

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="org.jssec.android.provider.publicprovider">
    
    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        
        <!-- *** POINT 1 *** Explicitly set the exported attribute to true. -->
        <provider
        android:name=".PublicProvider"
        android:authorities="org.jssec.android.provider.publicprovider"
        android:exported="true" />
    </application>
</manifest>

PublicProvider.java

package org.jssec.android.provider.publicprovider;

import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.MatrixCursor;
import android.net.Uri;

public class PublicProvider extends ContentProvider {

    public static final String AUTHORITY = "org.jssec.android.provider.publicprovider";
    public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.org.jssec.contenttype";
    public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.org.jssec.contenttype";
    // Expose the interface that the Content Provider provides.

    public interface Download {
        public static final String PATH = "downloads";
        public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/" + PATH);
    }
    
    public interface Address {
        public static final String PATH = "addresses";
        public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/" + PATH);
    }
    
    // UriMatcher
    private static final int DOWNLOADS_CODE = 1;
    private static final int DOWNLOADS_ID_CODE = 2;
    private static final int ADDRESSES_CODE = 3;
    private static final int ADDRESSES_ID_CODE = 4;
    private static UriMatcher sUriMatcher;
    
    static {
        sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        sUriMatcher.addURI(AUTHORITY, Download.PATH, DOWNLOADS_CODE);
        sUriMatcher.addURI(AUTHORITY, Download.PATH + "/#", DOWNLOADS_ID_CODE);
        sUriMatcher.addURI(AUTHORITY, Address.PATH, ADDRESSES_CODE);
        sUriMatcher.addURI(AUTHORITY, Address.PATH + "/#", ADDRESSES_ID_CODE);
    }
    
    // Since this is a sample program,
    // query method returns the following fixed result always without using database.
    private static MatrixCursor sAddressCursor = new MatrixCursor(new String[] { "_id", "city" });
    
    static {
        sAddressCursor.addRow(new String[] { "1", "New York" });
        sAddressCursor.addRow(new String[] { "2", "London" });
        sAddressCursor.addRow(new String[] { "3", "Paris" });
    }
    
    private static MatrixCursor sDownloadCursor = new MatrixCursor(new String[] { "_id", "path" });
    
    static {
        sDownloadCursor.addRow(new String[] { "1", "/sdcard/downloads/sample.jpg" });
        sDownloadCursor.addRow(new String[] { "2", "/sdcard/downloads/sample.txt" });
    }
    
    @Override
    public boolean onCreate() {
        return true;
    }
    
    @Override
    public String getType(Uri uri) {
        switch (sUriMatcher.match(uri)) {
            case DOWNLOADS_CODE:
            case ADDRESSES_CODE:
                return CONTENT_TYPE;
            case DOWNLOADS_ID_CODE:
            case ADDRESSES_ID_CODE:
                return CONTENT_ITEM_TYPE;
            default:
                throw new IllegalArgumentException("Invalid URI:" + uri);
        }
    }
    
    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
    String[] selectionArgs, String sortOrder) {
        // *** POINT 2 *** Handle the received request data carefully and securely.
        // Here, whether uri is within expectations or not, is verified by UriMatcher#match() and switch case.
        // Checking for other parameters are omitted here, due to sample.
        // Refer to "3.2 Handle Input Data Carefully and Securely."
        // *** POINT 3 *** When returning a result, do not include sensitive information.
        // It depends on application whether the query result has sensitive meaning or not.
        // If no problem when the information is taken by malware, it can be returned as result.
        switch (sUriMatcher.match(uri)) {
            case DOWNLOADS_CODE:
            case DOWNLOADS_ID_CODE:
                return sDownloadCursor;
            case ADDRESSES_CODE:
            case ADDRESSES_ID_CODE:
                return sAddressCursor;
            default:
                throw new IllegalArgumentException("Invalid URI:" + uri);
        }
    }
    
    @Override
    public Uri insert(Uri uri, ContentValues values) {
        // *** POINT 2 *** Handle the received request data carefully and securely.
        // Here, whether uri is within expectations or not, is verified by UriMatcher#match() and switch case.
        // Checking for other parameters are omitted here, due to sample.
        // Refer to "3.2 Handle Input Data Carefully and Securely."
        // *** POINT 3 *** When returning a result, do not include sensitive information.
        // It depends on application whether the issued ID has sensitive meaning or not.
        // If no problem when the information is taken by malware, it can be returned as result.
        switch (sUriMatcher.match(uri)) {
            case DOWNLOADS_CODE:
                return ContentUris.withAppendedId(Download.CONTENT_URI, 3);
            case ADDRESSES_CODE:
                return ContentUris.withAppendedId(Address.CONTENT_URI, 4);
            default:
                throw new IllegalArgumentException("Invalid URI:" + uri);
        }
    }
    
    @Override
    public int update(Uri uri, ContentValues values, String selection,
        String[] selectionArgs) {
        // *** POINT 2 *** Handle the received request data carefully and securely.
        // Here, whether uri is within expectations or not, is verified by UriMatcher#match() and switch case.
        // Checking for other parameters are omitted here, due to sample.
        // Refer to "3.2 Handle Input Data Carefully and Securely."
        // *** POINT 3 *** When returning a result, do not include sensitive information.
        // It depends on application whether the number of updated records has sensitive meaning or not.
        // If no problem when the information is taken by malware, it can be returned as result.
        switch (sUriMatcher.match(uri)) {
            case DOWNLOADS_CODE:
                return 5; // Return number of updated records
            case DOWNLOADS_ID_CODE:
                return 1;
            case ADDRESSES_CODE:
                return 15;
            case ADDRESSES_ID_CODE:
                return 1;
            default:
                throw new IllegalArgumentException("Invalid URI:" + uri);
        }
    }
    
    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        // *** POINT 2 *** Handle the received request data carefully and securely.
        // Here, whether uri is within expectations or not, is verified by UriMatcher#match() and switch case.
        // Checking for other parameters are omitted here, due to sample.
        // Refer to "3.2 Handle Input Data Carefully and Securely."
        // *** POINT 3 *** When returning a result, do not include sensitive information.
        // It depends on application whether the number of deleted records has sensitive meaning or not.
        // If no problem when the information is taken by malware, it can be returned as result.
        switch (sUriMatcher.match(uri)) {
            case DOWNLOADS_CODE:
                return 10; // Return number of deleted records
            case DOWNLOADS_ID_CODE:
                return 1;
            case ADDRESSES_CODE:
                return 20;
            case ADDRESSES_ID_CODE:
                return 1;
            default:
                throw new IllegalArgumentException("Invalid URI:" + uri);
        }
    }
}

下面是使用公共内容供应器的活动示例。

要点（使用内容供应器）：

  1. 不要发送敏感信息

  2. 收到结果时，小心和安全地处理结果数据

PublicUserActivity.java

package org.jssec.android.provider.publicuser;

import android.app.Activity;
import android.content.ContentValues;
import android.content.pm.ProviderInfo;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class PublicUserActivity extends Activity {

    // Target Content Provider Information
    private static final String AUTHORITY = "org.jssec.android.provider.publicprovider";
    
    private interface Address {
        public static final String PATH = "addresses";
        public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/" + PATH);
    }
    
    public void onQueryClick(View view) {
        logLine("[Query]");
        if (!providerExists(Address.CONTENT_URI)) {
            logLine(" Content Provider doesn't exist.");
            return;
        }
        Cursor cursor = null;
        try {
            // *** POINT 4 *** Do not send sensitive information.
            // since the target Content Provider may be malware.
            // If no problem when the information is taken by malware, it can be included in the request.
            cursor = getContentResolver().query(Address.CONTENT_URI, null, null, null, null);
            // *** POINT 5 *** When receiving a result, handle the result data carefully and securely.
            // Omitted, since this is a sample. Please refer to "3.2 Handling Input Data Carefully and Securely."
            if (cursor == null) {
                logLine(" null cursor");
            } else {
                boolean moved = cursor.moveToFirst();
                while (moved) {
                    logLine(String.format(" %d, %s", cursor.getInt(0), cursor.getString(1)));
                    moved = cursor.moveToNext();
                }
            }
        }
        finally {
            if (cursor != null) cursor.close();
        }
    }
    
    public void onInsertClick(View view) {
    logLine("[Insert]");
        if (!providerExists(Address.CONTENT_URI)) {
            logLine(" Content Provider doesn't exist.");
            return;
        }
        // *** POINT 4 *** Do not send sensitive information.
        // since the target Content Provider may be malware.
        // If no problem when the information is taken by malware, it can be included in the request.
        ContentValues values = new ContentValues();
        values.put("city", "Tokyo");
        Uri uri = getContentResolver().insert(Address.CONTENT_URI, values);
        // *** POINT 5 *** When receiving a result, handle the result data carefully and securely.
        // Omitted, since this is a sample. Please refer to "3.2 Handling Input Data Carefully and Securely."
        logLine(" uri:" + uri);
    }
    
    public void onUpdateClick(View view) {
    logLine("[Update]");
        if (!providerExists(Address.CONTENT_URI)) {
            logLine(" Content Provider doesn't exist.");
            return;
        }
        // *** POINT 4 *** Do not send sensitive information.
        // since the target Content Provider may be malware.
        // If no problem when the information is taken by malware, it can be included in the request.
        ContentValues values = new ContentValues();
        values.put("city", "Tokyo");
        String where = "_id = ?";
        String[] args = { "4" };
        int count = getContentResolver().update(Address.CONTENT_URI, values, where, args);
        // *** POINT 5 *** When receiving a result, handle the result data carefully and securely.
        // Omitted, since this is a sample. Please refer to "3.2 Handling Input Data Carefully and Securely."
        logLine(String.format(" %s records updated", count));
    }
    
    public void onDeleteClick(View view) {
    logLine("[Delete]");
        if (!providerExists(Address.CONTENT_URI)) {
            logLine(" Content Provider doesn't exist.");
            return;
        }
        // *** POINT 4 *** Do not send sensitive information.
        // since the target Content Provider may be malware.
        // If no problem when the information is taken by malware, it can be included in the request.
        int count = getContentResolver().delete(Address.CONTENT_URI, null, null);
        // *** POINT 5 *** When receiving a result, handle the result data carefully and securely.
        // Omitted, since this is a sample. Please refer to "3.2 Handling Input Data Carefully and Securely."
        logLine(String.format(" %s records deleted", count));
    }
    
    private boolean providerExists(Uri uri) {
        ProviderInfo pi = getPackageManager().resolveContentProvider(uri.getAuthority(), 0);
        return (pi != null);
    }
    
    private TextView mLogView;
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mLogView = (TextView)findViewById(R.id.logview);
    }
    
    private void logLine(String line) {
        mLogView.append(line);
        mLogView.append("¥n");
    }
}
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