Android 4.4.2 SELinux 与系统关系详解二： mac_permissions.xml 加载及seinfo 提取过程分析

PackageManager 调用mac_permissions.xml内容：

mac_permissions.xml 加载文件位置：/frameworks/base/services/java/com/android/server/pm/SELinuxMMAC.java  

执行加载的函数： private static boolean readInstallPolicy(File[] policyFiles)

根据policyFiles 文件所在路径加载mac_permissions.xml 文件。

                       

[code=java]
   // Locations of potential install policy files.
    private static final File[] INSTALL_POLICY_FILE = {
        new File(Environment.getDataDirectory(), "security/mac_permissions.xml"),
        new File(Environment.getRootDirectory(), "etc/security/mac_permissions.xml"),
        null};
[/code]

加载mac_permissions.xml 函数 readInstallPolicy代码：

 

[code=java]
private static boolean readInstallPolicy(File[] policyFiles) {

        FileReader policyFile = null;
        int i = 0;
        while (policyFile == null && policyFiles != null && policyFiles[i] != null) {
            try {
                policyFile = new FileReader(policyFiles[i]);
                break;
            } catch (FileNotFoundException e) {
                Slog.d(TAG,"Couldn't find install policy " + policyFiles[i].getPath());
            }
            i++;
        }

        if (policyFile == null) {
            Slog.d(TAG, "No policy file found. All seinfo values will be null.");
            return false;
        }

        Slog.d(TAG, "Using install policy file " + policyFiles[i].getPath());

        flushInstallPolicy();

        try {
            XmlPullParser parser = Xml.newPullParser();
            parser.setInput(policyFile);

            XmlUtils.beginDocument(parser, "policy");
            while (true) {
                XmlUtils.nextElement(parser);
                if (parser.getEventType() == XmlPullParser.END_DOCUMENT) {
                    break;
                }

                String tagName = parser.getName();
                if ("signer".equals(tagName)) {
                    String cert = parser.getAttributeValue(null, "signature");
                    if (cert == null) {
                        Slog.w(TAG, "<signer> without signature at "
                               + parser.getPositionDescription());
                        XmlUtils.skipCurrentTag(parser);
                        continue;
                    }
                    Signature signature;
                    try {
                        signature = new Signature(cert);
                    } catch (IllegalArgumentException e) {
                        Slog.w(TAG, "<signer> with bad signature at "
                               + parser.getPositionDescription(), e);
                        XmlUtils.skipCurrentTag(parser);
                        continue;
                    }
                    String seinfo = readSeinfoTag(parser);
                    if (seinfo != null) {
                        if (DEBUG_POLICY_INSTALL)
                            Slog.i(TAG, "<signer> tag: (" + cert + ") assigned seinfo="
                                   + seinfo);

                        sSigSeinfo.put(signature, seinfo);
                    }
                } else if ("default".equals(tagName)) {
                    String seinfo = readSeinfoTag(parser);
                    if (seinfo != null) {
                        if (DEBUG_POLICY_INSTALL)
                            Slog.i(TAG, "<default> tag assigned seinfo=" + seinfo);

                        // The 'null' signature is the default seinfo value
                        sSigSeinfo.put(null, seinfo);
                    }
                } else if ("package".equals(tagName)) {
                    String pkgName = parser.getAttributeValue(null, "name");
                    if (pkgName == null) {
                        Slog.w(TAG, "<package> without name at "
                               + parser.getPositionDescription());
                        XmlUtils.skipCurrentTag(parser);
                        continue;
                    }
                    String seinfo = readSeinfoTag(parser);
                    if (seinfo != null) {
                        if (DEBUG_POLICY_INSTALL)
                            Slog.i(TAG, "<package> tag: (" + pkgName +
                                   ") assigned seinfo=" + seinfo);

                        sPackageSeinfo.put(pkgName, seinfo);
                    }
                } else {
                    XmlUtils.skipCurrentTag(parser);
                    continue;
                }
            }
        } catch (XmlPullParserException e) {
            Slog.w(TAG, "Got execption parsing ", e);
        } catch (IOException e) {
            Slog.w(TAG, "Got execption parsing ", e);
        }
        try {
            policyFile.close();
        } catch (IOException e) {
            //omit
        }
        return true;
    }
[/code]