    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017
    018package org.apache.commons.net.bsd;
    019
    020import java.io.IOException;
    021import java.io.InputStream;
    022import java.io.OutputStream;
    023import java.net.ServerSocket;
    024import java.net.Socket;
    025import java.nio.charset.StandardCharsets;
    026
    027import org.apache.commons.net.SocketClient;
    028import org.apache.commons.net.io.SocketInputStream;
    029import org.apache.commons.net.util.NetConstants;
    030
    031/**
    032 * RExecClient implements the rexec() facility that first appeared in 4.2BSD Unix. This class will probably only be of use for connecting to Unix systems and
    033 * only when the rexecd daemon is configured to run, which is a rarity these days because of the security risks involved. However, rexec() can be very useful
    034 * for performing administrative tasks on a network behind a firewall.
    035 * <p>
    036 * As with virtually all the client classes in org.apache.commons.net, this class derives from SocketClient, inheriting its connection methods. The way to
    037 * use RExecClient is to first connect to the server, call the {@link #rexec rexec()} method, and then fetch the connection's input, output, and optionally
    038 * error streams. Interaction with the remote command is controlled entirely through the I/O streams. Once you have finished processing the streams, you should
    039 * invoke {@link #disconnect disconnect()} to clean up properly.
    040 * <p>
    041 * By default, the standard output and standard error streams of the remote process are transmitted over the same connection, readable from the input stream
    042 * returned by {@link #getInputStream getInputStream()}. However, it is possible to tell the rexecd daemon to return the standard error stream over a separate
    043 * connection, readable from the input stream returned by {@link #getErrorStream getErrorStream()}. You can specify that a separate connection should be created
    044 * for standard error by setting the boolean <code> separateErrorStream </code> parameter of {@link #rexec rexec()} to <code> true </code>. The standard input
    045 * of the remote process can be written to through the output stream returned by {@link #getOutputStream getOutputSream()}.
    046 *
    047 * @see SocketClient
    048 * @see RCommandClient
    049 * @see RLoginClient
    050 */
    051
    052public class RExecClient extends SocketClient {
    053    /**
    054     * @since 3.3
    055     */
    056    protected static final char NULL_CHAR = '\0';
    057
    058    /**
    059     * The default rexec port. Set to 512 in BSD Unix.
    060     */
    061    public static final int DEFAULT_PORT = 512;
    062
    063    private boolean remoteVerificationEnabled;
    064
    065    /**
    066     * If a separate error stream is requested, <code>_errorStream_</code> will point to an InputStream from which the standard error of the remote process can
    067     * be read (after a call to rexec()). Otherwise, <code> _errorStream_ </code> will be null.
    068     */
    069    protected InputStream _errorStream_;
    070
    071    /**
    072     * The default RExecClient constructor. Initializes the default port to <code> DEFAULT_PORT </code>.
    073     */
    074    public RExecClient() {
    075        _errorStream_ = null;
    076        setDefaultPort(DEFAULT_PORT);
    077    }
    078
    079    // This can be overridden in local package to implement port range
    080    // limitations of rcmd and rlogin
    081    InputStream createErrorStream() throws IOException {
    082        final Socket socket;
    083
    084        try (final ServerSocket server = _serverSocketFactory_.createServerSocket(0, 1, getLocalAddress())) {
    085            _output_.write(Integer.toString(server.getLocalPort()).getBytes(StandardCharsets.UTF_8)); // $NON-NLS-1$
    086            _output_.write(NULL_CHAR);
    087            _output_.flush();
    088            socket = server.accept();
    089        }
    090
    091        if (remoteVerificationEnabled && !verifyRemote(socket)) {
    092            socket.close();
    093            throw new IOException("Security violation: unexpected connection attempt by " + socket.getInetAddress().getHostAddress());
    094        }
    095
    096        return new SocketInputStream(socket, socket.getInputStream());
    097    }
    098
    099    /**
    100     * Disconnects from the server, closing all associated open sockets and streams.
    101     *
    102     * @throws IOException If an error occurs while disconnecting.
    103     */
    104    @Override
    105    public void disconnect() throws IOException {
    106        if (_errorStream_ != null) {
    107            _errorStream_.close();
    108        }
    109        _errorStream_ = null;
    110        super.disconnect();
    111    }
    112
    113    /**
    114     * Returns the InputStream from which the standard error of the remote process can be read if a separate error stream is requested from the server.
    115     * Otherwise, null will be returned. The error stream will only be set after a successful rexec() invocation.
    116     *
    117     * @return The InputStream from which the standard error of the remote process can be read if a separate error stream is requested from the server.
    118     *         Otherwise, null will be returned.
    119     */
    120    public InputStream getErrorStream() {
    121        return _errorStream_;
    122    }
    123
    124    /**
    125     * Returns the InputStream from which the standard output of the remote process can be read. The input stream will only be set after a successful rexec()
    126     * invocation.
    127     *
    128     * @return The InputStream from which the standard output of the remote process can be read.
    129     */
    130    public InputStream getInputStream() {
    131        return _input_;
    132    }
    133
    134    /**
    135     * Returns the OutputStream through which the standard input of the remote process can be written. The output stream will only be set after a successful
    136     * rexec() invocation.
    137     *
    138     * @return The OutputStream through which the standard input of the remote process can be written.
    139     */
    140    public OutputStream getOutputStream() {
    141        return _output_;
    142    }
    143
    144    /**
    145     * Return whether or not verification of the remote host providing a separate error stream is enabled. The default behavior is for verification to be
    146     * enabled.
    147     *
    148     * @return True if verification is enabled, false if not.
    149     */
    150    public final boolean isRemoteVerificationEnabled() {
    151        return remoteVerificationEnabled;
    152    }
    153
    154    /**
    155     * Same as <code> rexec(user, password, command, false); </code>
    156     *
    157     * @param user the user name
    158     * @param password the password
    159     * @param command  the command to run
    160     * @throws IOException if an error occurs
    161     */
    162    public void rexec(final String user, final String password, final String command) throws IOException {
    163        rexec(user, password, command, false);
    164    }
    165
    166    /**
    167     * Remotely executes a command through the rexecd daemon on the server to which the RExecClient is connected. After calling this method, you may interact
    168     * with the remote process through its standard input, output, and error streams. You will typically be able to detect the termination of the remote process
    169     * after reaching end of file on its standard output (accessible through {@link #getInputStream getInputStream()}). Disconnecting from the server or closing
    170     * the process streams before reaching end of file will not necessarily terminate the remote process.
    171     * <p>
    172     * If a separate error stream is requested, the remote server will connect to a local socket opened by RExecClient, providing an independent stream through
    173     * which standard error will be transmitted. RExecClient will do a simple security check when it accepts a connection for this error stream. If the
    174     * connection does not originate from the remote server, an IOException will be thrown. This serves as a simple protection against possible hijacking of the
    175     * error stream by an attacker monitoring the rexec() negotiation. You may disable this behavior with {@link #setRemoteVerificationEnabled
    176     * setRemoteVerificationEnabled()} .
    177     *
    178     * @param user            The account name on the server through which to execute the command.
    179     * @param password            The plain text password of the user account.
    180     * @param command             The command, including any arguments, to execute.
    181     * @param separateErrorStream True if you would like the standard error to be transmitted through a different stream than standard output. False if not.
    182     * @throws IOException If the rexec() attempt fails. The exception will contain a message indicating the nature of the failure.
    183     */
    184    public void rexec(final String user, final String password, final String command, final boolean separateErrorStream) throws IOException {
    185        int ch;
    186
    187        if (separateErrorStream) {
    188            _errorStream_ = createErrorStream();
    189        } else {
    190            _output_.write(NULL_CHAR);
    191        }
    192
    193        _output_.write(user.getBytes(getCharset()));
    194        _output_.write(NULL_CHAR);
    195        _output_.write(password.getBytes(getCharset()));
    196        _output_.write(NULL_CHAR);
    197        _output_.write(command.getBytes(getCharset()));
    198        _output_.write(NULL_CHAR);
    199        _output_.flush();
    200
    201        ch = _input_.read();
    202        if (ch > 0) {
    203            final StringBuilder buffer = new StringBuilder();
    204
    205            while ((ch = _input_.read()) != NetConstants.EOS && ch != '\n') {
    206                buffer.append((char) ch);
    207            }
    208
    209            throw new IOException(buffer.toString());
    210        }
    211        if (ch < 0) {
    212            throw new IOException("Server closed connection.");
    213        }
    214    }
    215
    216    /**
    217     * Enable or disable verification that the remote host connecting to create a separate error stream is the same as the host to which the standard out stream
    218     * is connected. The default is for verification to be enabled. You may set this value at any time, whether the client is currently connected or not.
    219     *
    220     * @param enable True to enable verification, false to disable verification.
    221     */
    222    public final void setRemoteVerificationEnabled(final boolean enable) {
    223        remoteVerificationEnabled = enable;
    224    }
    225
    226}