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Android 根证书管理与证书验证（2）

达芬奇密码2018-08-17 13:43

OpenSSLSocketImpl 的 verifyCertificateChain() 从 sslParameters 获得 X509TrustManager，然后在 Platform.checkServerTrusted() （com.android.org.conscrypt.Platform，位于 external/conscrypt/src/compat/java/org/conscrypt/Platform.java）中执行服务端证书合法有效性的检查：

    public static void checkServerTrusted(X509TrustManager tm, X509Certificate[] chain,
            String authType, OpenSSLSocketImpl socket) throws CertificateException {
        if (!checkTrusted("checkServerTrusted", tm, chain, authType, Socket.class, socket)
                && !checkTrusted("checkServerTrusted", tm, chain, authType, String.class,
                                 socket.getHandshakeSession().getPeerHost())) {
            tm.checkServerTrusted(chain, authType);
        }
    }

Platform.checkServerTrusted() 通过执行 X509TrustManager 的 checkServerTrusted() 方法执行证书有合法性检查。

X509TrustManager 来自于 OpenSSLSocketImpl 的 sslParameters，那 sslParameters 又来自于哪里呢？OpenSSLSocketImpl 的 sslParameters 由对象的创建者传入：

public class OpenSSLSocketImpl
        extends javax.net.ssl.SSLSocket
        implements NativeCrypto.SSLHandshakeCallbacks, SSLParametersImpl.AliasChooser,
        SSLParametersImpl.PSKCallbacks {
. . . . . .
    private final SSLParametersImpl sslParameters;
. . . . . .
    protected OpenSSLSocketImpl(SSLParametersImpl sslParameters) throws IOException {
        this.socket = this;
        this.peerHostname = null;
        this.peerPort = -1;
        this.autoClose = false;
        this.sslParameters = sslParameters;
    }

    protected OpenSSLSocketImpl(String hostname, int port, SSLParametersImpl sslParameters)
            throws IOException {
        super(hostname, port);
        this.socket = this;
        this.peerHostname = hostname;
        this.peerPort = port;
        this.autoClose = false;
        this.sslParameters = sslParameters;
    }

    protected OpenSSLSocketImpl(InetAddress address, int port, SSLParametersImpl sslParameters)
            throws IOException {
        super(address, port);
        this.socket = this;
        this.peerHostname = null;
        this.peerPort = -1;
        this.autoClose = false;
        this.sslParameters = sslParameters;
    }


    protected OpenSSLSocketImpl(String hostname, int port,
                                InetAddress clientAddress, int clientPort,
                                SSLParametersImpl sslParameters) throws IOException {
        super(hostname, port, clientAddress, clientPort);
        this.socket = this;
        this.peerHostname = hostname;
        this.peerPort = port;
        this.autoClose = false;
        this.sslParameters = sslParameters;
    }

    protected OpenSSLSocketImpl(InetAddress address, int port,
                                InetAddress clientAddress, int clientPort,
                                SSLParametersImpl sslParameters) throws IOException {
        super(address, port, clientAddress, clientPort);
        this.socket = this;
        this.peerHostname = null;
        this.peerPort = -1;
        this.autoClose = false;
        this.sslParameters = sslParameters;
    }

    /**
     * Create an SSL socket that wraps another socket. Invoked by
     * OpenSSLSocketImplWrapper constructor.
     */
    protected OpenSSLSocketImpl(Socket socket, String hostname, int port,
            boolean autoClose, SSLParametersImpl sslParameters) throws IOException {
        this.socket = socket;
        this.peerHostname = hostname;
        this.peerPort = port;
        this.autoClose = autoClose;
        this.sslParameters = sslParameters;

        // this.timeout is not set intentionally.
        // OpenSSLSocketImplWrapper.getSoTimeout will delegate timeout
        // to wrapped socket
    }

也就是说，OpenSSLSocketImpl 的 sslParameters 来自于 javax.net.ssl.SSLSocketFactory，即 OpenSSLSocketFactoryImpl。OpenSSLSocketFactoryImpl 定义（位于 external/conscrypt/src/main/java/org/conscrypt/OpenSSLSocketFactoryImpl.java）如下：

package org.conscrypt;

import java.io.IOException;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import java.security.KeyManagementException;

public class OpenSSLSocketFactoryImpl extends javax.net.ssl.SSLSocketFactory {

    private final SSLParametersImpl sslParameters;
    private final IOException instantiationException;

    public OpenSSLSocketFactoryImpl() {
        SSLParametersImpl sslParametersLocal = null;
        IOException instantiationExceptionLocal = null;
        try {
            sslParametersLocal = SSLParametersImpl.getDefault();
        } catch (KeyManagementException e) {
            instantiationExceptionLocal = new IOException("Delayed instantiation exception:");
            instantiationExceptionLocal.initCause(e);
        }
        this.sslParameters = sslParametersLocal;
        this.instantiationException = instantiationExceptionLocal;
    }

    public OpenSSLSocketFactoryImpl(SSLParametersImpl sslParameters) {
        this.sslParameters = sslParameters;
        this.instantiationException = null;
    }

    @Override
    public String[] getDefaultCipherSuites() {
        return sslParameters.getEnabledCipherSuites();
    }

    @Override
    public String[] getSupportedCipherSuites() {
        return NativeCrypto.getSupportedCipherSuites();
    }

    @Override
    public Socket createSocket() throws IOException {
        if (instantiationException != null) {
            throw instantiationException;
        }
        return new OpenSSLSocketImpl((SSLParametersImpl) sslParameters.clone());
    }

    @Override
    public Socket createSocket(String hostname, int port) throws IOException, UnknownHostException {
        return new OpenSSLSocketImpl(hostname, port, (SSLParametersImpl) sslParameters.clone());
    }

    @Override
    public Socket createSocket(String hostname, int port, InetAddress localHost, int localPort)
            throws IOException, UnknownHostException {
        return new OpenSSLSocketImpl(hostname,
                                     port,
                                     localHost,
                                     localPort,
                                     (SSLParametersImpl) sslParameters.clone());
    }

    @Override
    public Socket createSocket(InetAddress address, int port) throws IOException {
        return new OpenSSLSocketImpl(address, port, (SSLParametersImpl) sslParameters.clone());
    }

    @Override
    public Socket createSocket(InetAddress address,
                               int port,
                               InetAddress localAddress,
                               int localPort)
            throws IOException {
        return new OpenSSLSocketImpl(address,
                                     port,
                                     localAddress,
                                     localPort,
                                     (SSLParametersImpl) sslParameters.clone());
    }

    @Override
    public Socket createSocket(Socket s, String hostname, int port, boolean autoClose)
            throws IOException {
        return new OpenSSLSocketImplWrapper(s,
                                            hostname,
                                            port,
                                            autoClose,
                                            (SSLParametersImpl) sslParameters.clone());
    }
}

OpenSSLSocketImpl 最主要的职责，即是将 SSL/TLS 参数 SSLParametersImpl 与 SSLSocket 粘起来。主要来看默认情况下 SSLParametersImpl 的 X509TrustManager 是什么（位于external/conscrypt/src/main/java/org/conscrypt/SSLParametersImpl.java ）：

    /**
     * Initializes the parameters. Naturally this constructor is used
     * in SSLContextImpl.engineInit method which directly passes its
     * parameters. In other words this constructor holds all
     * the functionality provided by SSLContext.init method.
     * See {@link javax.net.ssl.SSLContext#init(KeyManager[],TrustManager[],
     * SecureRandom)} for more information
     */
    protected SSLParametersImpl(KeyManager[] kms, TrustManager[] tms,
            SecureRandom sr, ClientSessionContext clientSessionContext,
            ServerSessionContext serverSessionContext, String[] protocols)
            throws KeyManagementException {
        this.serverSessionContext = serverSessionContext;
        this.clientSessionContext = clientSessionContext;

        // initialize key managers
        if (kms == null) {
            x509KeyManager = getDefaultX509KeyManager();
            // There's no default PSK key manager
            pskKeyManager = null;
        } else {
            x509KeyManager = findFirstX509KeyManager(kms);
            pskKeyManager = findFirstPSKKeyManager(kms);
        }

        // initialize x509TrustManager
        if (tms == null) {
            x509TrustManager = getDefaultX509TrustManager();
        } else {
            x509TrustManager = findFirstX509TrustManager(tms);
        }

        // initialize secure random
        // We simply use the SecureRandom passed in by the caller. If it's
        // null, we don't replace it by a new instance. The native code below
        // then directly accesses /dev/urandom. Not the most elegant solution,
        // but faster than going through the SecureRandom object.
        secureRandom = sr;

        // initialize the list of cipher suites and protocols enabled by default
        enabledProtocols = NativeCrypto.checkEnabledProtocols(
                protocols == null ? NativeCrypto.DEFAULT_PROTOCOLS : protocols).clone();
        boolean x509CipherSuitesNeeded = (x509KeyManager != null) || (x509TrustManager != null);
        boolean pskCipherSuitesNeeded = pskKeyManager != null;
        enabledCipherSuites = getDefaultCipherSuites(
                x509CipherSuitesNeeded, pskCipherSuitesNeeded);
    }

    protected static SSLParametersImpl getDefault() throws KeyManagementException {
        SSLParametersImpl result = defaultParameters;
        if (result == null) {
            // single-check idiom
            defaultParameters = result = new SSLParametersImpl(null,
                                                               null,
                                                               null,
                                                               new ClientSessionContext(),
                                                               new ServerSessionContext(),
                                                               null);
        }
        return (SSLParametersImpl) result.clone();
    }
 . . . . . . 
    /**
     * @return X.509 trust manager or {@code null} for none.
     */
    protected X509TrustManager getX509TrustManager() {
        return x509TrustManager;
    }
 . . . . . . 
    /**
     * Gets the default X.509 trust manager.
     * <p>
     * TODO: Move this to a published API under dalvik.system.
     */
    public static X509TrustManager getDefaultX509TrustManager()
            throws KeyManagementException {
        X509TrustManager result = defaultX509TrustManager;
        if (result == null) {
            // single-check idiom
            defaultX509TrustManager = result = createDefaultX509TrustManager();
        }
        return result;
    }

    private static X509TrustManager createDefaultX509TrustManager()
            throws KeyManagementException {
        try {
            String algorithm = TrustManagerFactory.getDefaultAlgorithm();
            TrustManagerFactory tmf = TrustManagerFactory.getInstance(algorithm);
            tmf.init((KeyStore) null);
            TrustManager[] tms = tmf.getTrustManagers();
            X509TrustManager trustManager = findFirstX509TrustManager(tms);
            if (trustManager == null) {
                throw new KeyManagementException(
                        "No X509TrustManager in among default TrustManagers: "
                                + Arrays.toString(tms));
            }
            return trustManager;
        } catch (NoSuchAlgorithmException e) {
            throw new KeyManagementException(e);
        } catch (KeyStoreException e) {
            throw new KeyManagementException(e);
        }
    }

将 createDefaultX509TrustManager() 的代码复制到我们的应用程序中，就像下面这样：

        private X509TrustManager systemDefaultTrustManager() {
            try {
                TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(
                        TrustManagerFactory.getDefaultAlgorithm());
                trustManagerFactory.init((KeyStore) null);
                TrustManager[] trustManagers = trustManagerFactory.getTrustManagers();
                if (trustManagers.length != 1 || !(trustManagers[0] instanceof X509TrustManager)) {
                    throw new IllegalStateException("Unexpected default trust managers:"
                            + Arrays.toString(trustManagers));
                }
                return (X509TrustManager) trustManagers[0];
            } catch (GeneralSecurityException e) {
                throw new AssertionError(); // The system has no TLS. Just give up.
            }
        }

在应用程序执行时打断点，借助于 Android Studio 确认系统默认的 X509TrustManager 是什么，不难确认，它是 android.security.net.config.RootTrustManager。android.security.net.config.RootTrustManager 的 checkServerTrusted() 定义（位于 frameworks/base/core/java/android/security/net/config/RootTrustManager.java）如下：

    @Override
    public void checkServerTrusted(X509Certificate[] certs, String authType, Socket socket)
            throws CertificateException {
        if (socket instanceof SSLSocket) {
            SSLSocket sslSocket = (SSLSocket) socket;
            SSLSession session = sslSocket.getHandshakeSession();
            if (session == null) {
                throw new CertificateException("Not in handshake; no session available");
            }
            String host = session.getPeerHost();
            NetworkSecurityConfig config = mConfig.getConfigForHostname(host);
            config.getTrustManager().checkServerTrusted(certs, authType, socket);
        } else {
            // Not an SSLSocket, use the hostname unaware checkServerTrusted.
            checkServerTrusted(certs, authType);
        }
    }

    @Override
    public void checkServerTrusted(X509Certificate[] certs, String authType, SSLEngine engine)
            throws CertificateException {
        SSLSession session = engine.getHandshakeSession();
        if (session == null) {
            throw new CertificateException("Not in handshake; no session available");
        }
        String host = session.getPeerHost();
        NetworkSecurityConfig config = mConfig.getConfigForHostname(host);
        config.getTrustManager().checkServerTrusted(certs, authType, engine);
    }

    @Override
    public void checkServerTrusted(X509Certificate[] certs, String authType)
            throws CertificateException {
        if (mConfig.hasPerDomainConfigs()) {
            throw new CertificateException(
                    "Domain specific configurations require that hostname aware"
                    + " checkServerTrusted(X509Certificate[], String, String) is used");
        }
        NetworkSecurityConfig config = mConfig.getConfigForHostname("");
        config.getTrustManager().checkServerTrusted(certs, authType);
    }

    /**
     * Hostname aware version of {@link #checkServerTrusted(X509Certificate[], String)}.
     * This interface is used by conscrypt and android.net.http.X509TrustManagerExtensions do not
     * modify without modifying those callers.
     */
    public List<X509Certificate> checkServerTrusted(X509Certificate[] certs, String authType,
            String hostname) throws CertificateException {
        if (hostname == null && mConfig.hasPerDomainConfigs()) {
            throw new CertificateException(
                    "Domain specific configurations require that the hostname be provided");
        }
        NetworkSecurityConfig config = mConfig.getConfigForHostname(hostname);
        return config.getTrustManager().checkServerTrusted(certs, authType, hostname);
    }

NetworkSecurityConfig 的 getTrustManager() 定义（位于 frameworks/base/core/java/android/security/net/config/NetworkSecurityConfig.java）如下：

    public NetworkSecurityTrustManager getTrustManager() {
        synchronized(mTrustManagerLock) {
            if (mTrustManager == null) {
                mTrustManager = new NetworkSecurityTrustManager(this);
            }
            return mTrustManager;
        }
    }

NetworkSecurityConfig 将管根证书库的组件 SystemCertificateSource 、 UserCertificateSource 和执行证书合法性验证的 NetworkSecurityTrustManager 粘起来：

    public static final Builder getDefaultBuilder(int targetSdkVersion) {
        Builder builder = new Builder()
                .setCleartextTrafficPermitted(DEFAULT_CLEARTEXT_TRAFFIC_PERMITTED)
                .setHstsEnforced(DEFAULT_HSTS_ENFORCED)
                // System certificate store, does not bypass static pins.
                .addCertificatesEntryRef(
                        new CertificatesEntryRef(SystemCertificateSource.getInstance(), false));
        // Applications targeting N and above must opt in into trusting the user added certificate
        // store.
        if (targetSdkVersion <= Build.VERSION_CODES.M) {
            // User certificate store, does not bypass static pins.
            builder.addCertificatesEntryRef(
                    new CertificatesEntryRef(UserCertificateSource.getInstance(), false));
        }
        return builder;
    }

同时 NetworkSecurityConfig 还提供了一些根据特定条件查找根证书的操作：

    public Set<TrustAnchor> getTrustAnchors() {
        synchronized (mAnchorsLock) {
            if (mAnchors != null) {
                return mAnchors;
            }
            // Merge trust anchors based on the X509Certificate.
            // If we see the same certificate in two TrustAnchors, one with overridesPins and one
            // without, the one with overridesPins wins.
            // Because mCertificatesEntryRefs is sorted with all overridesPins anchors coming first
            // this can be simplified to just using the first occurrence of a certificate.
            Map<X509Certificate, TrustAnchor> anchorMap = new ArrayMap<>();
            for (CertificatesEntryRef ref : mCertificatesEntryRefs) {
                Set<TrustAnchor> anchors = ref.getTrustAnchors();
                for (TrustAnchor anchor : anchors) {
                    X509Certificate cert = anchor.certificate;
                    if (!anchorMap.containsKey(cert)) {
                        anchorMap.put(cert, anchor);
                    }
                }
            }
            ArraySet<TrustAnchor> anchors = new ArraySet<TrustAnchor>(anchorMap.size());
            anchors.addAll(anchorMap.values());
            mAnchors = anchors;
            return mAnchors;
        }
    }
. . . . . .
    public NetworkSecurityTrustManager getTrustManager() {
        synchronized(mTrustManagerLock) {
            if (mTrustManager == null) {
                mTrustManager = new NetworkSecurityTrustManager(this);
            }
            return mTrustManager;
        }
    }

    /** @hide */
    public TrustAnchor findTrustAnchorBySubjectAndPublicKey(X509Certificate cert) {
        for (CertificatesEntryRef ref : mCertificatesEntryRefs) {
            TrustAnchor anchor = ref.findBySubjectAndPublicKey(cert);
            if (anchor != null) {
                return anchor;
            }
        }
        return null;
    }

    /** @hide */
    public TrustAnchor findTrustAnchorByIssuerAndSignature(X509Certificate cert) {
        for (CertificatesEntryRef ref : mCertificatesEntryRefs) {
            TrustAnchor anchor = ref.findByIssuerAndSignature(cert);
            if (anchor != null) {
                return anchor;
            }
        }
        return null;
    }

    /** @hide */
    public Set<X509Certificate> findAllCertificatesByIssuerAndSignature(X509Certificate cert) {
        Set<X509Certificate> certs = new ArraySet<X509Certificate>();
        for (CertificatesEntryRef ref : mCertificatesEntryRefs) {
            certs.addAll(ref.findAllCertificatesByIssuerAndSignature(cert));
        }
        return certs;
    }