RCommandClient.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.net.bsd;
import java.io.IOException;
import java.io.InputStream;
import java.net.BindException;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.nio.charset.StandardCharsets;
import org.apache.commons.net.io.SocketInputStream;
/**
* RCommandClient is very similar to {@link org.apache.commons.net.bsd.RExecClient}, from which it is derived, and implements the rcmd() facility that first
* appeared in 4.2BSD Unix. rcmd() is the facility used by the rsh (rshell) and other commands to execute a command on another machine from a trusted host
* without issuing a password. The trust relationship between two machines is established by the contents of a machine's /etc/hosts.equiv file and a user's
* .rhosts file. These files specify from which hosts and accounts on those hosts rcmd() requests will be accepted. The only additional measure for establishing
* trust is that all client connections must originate from a port between 512 and 1023. Consequently, there is an upper limit to the number of rcmd connections
* that can be running simultaneously. The required ports are reserved ports on Unix systems, and can only be bound by a process running with root permissions
* (to accomplish this rsh, rlogin, and related commands usualy have the suid bit set). Therefore, on a Unix system, you will only be able to successfully use
* the RCommandClient class if the process runs as root. However, there is no such restriction on Windows95 and some other systems. The security risks are
* obvious. However, when carefully used, rcmd() can be very useful when used behind a firewall.
* <p>
* As with virtually all the client classes in org.apache.commons.net, this class derives from SocketClient. But it overrides most of its connection methods
* so that the local Socket will originate from an acceptable rshell port. The way to use RCommandClient is to first connect to the server, call the
* {@link #rcommand rcommand() } method, and then fetch the connection's input, output, and optionally error streams. Interaction with the remote command is
* controlled entirely through the I/O streams. Once you have finished processing the streams, you should invoke
* {@link org.apache.commons.net.bsd.RExecClient#disconnect disconnect() } to clean up properly.
* </p>
* <p>
* By default, the standard output and standard error streams of the remote process are transmitted over the same connection, readable from the input stream
* returned by {@link org.apache.commons.net.bsd.RExecClient#getInputStream getInputStream() } . However, it is possible to tell the rshd daemon to return the
* standard error stream over a separate connection, readable from the input stream returned by {@link org.apache.commons.net.bsd.RExecClient#getErrorStream
* getErrorStream() } . You can specify that a separate connection should be created for standard error by setting the boolean
* <code> separateErrorStream </code> parameter of {@link #rcommand rcommand() } to <code> true </code>. The standard input of the remote process can be written
* to through the output stream returned by {@link org.apache.commons.net.bsd.RExecClient#getOutputStream getOutputStream() } .
* </p>
*
* @see org.apache.commons.net.SocketClient
* @see RExecClient
* @see RLoginClient
*/
public class RCommandClient extends RExecClient {
/**
* The default rshell port. Set to 514 in BSD Unix.
*/
public static final int DEFAULT_PORT = 514;
/**
* The smallest port number a rcmd client may use. By BSD convention this number is 512.
*/
public static final int MIN_CLIENT_PORT = 512;
/**
* The largest port number a rcmd client may use. By BSD convention this number is 1023.
*/
public static final int MAX_CLIENT_PORT = 1023;
/**
* The default RCommandClient constructor. Initializes the default port to <code> DEFAULT_PORT </code>.
*/
public RCommandClient() {
setDefaultPort(DEFAULT_PORT);
}
/**
* Opens a Socket connected to a remote host at the specified port and originating from the current host at a port in a range acceptable to the BSD rshell
* daemon. Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() } is called to perform connection initialization
* actions.
*
* @param host The remote host.
* @param port The port to connect to on the remote host.
* @throws SocketException If the socket timeout could not be set.
* @throws BindException If all acceptable rshell ports are in use.
* @throws IOException If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from
* it.
*/
@Override
public void connect(final InetAddress host, final int port) throws SocketException, IOException {
connect(host, port, InetAddress.getLocalHost());
}
/**
* Opens a Socket connected to a remote host at the specified port and originating from the specified local address using a port in a range acceptable to
* the BSD rshell daemon. Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() } is called to perform connection
* initialization actions.
*
* @param host The remote host.
* @param port The port to connect to on the remote host.
* @param localAddr The local address to use.
* @throws SocketException If the socket timeout could not be set.
* @throws BindException If all acceptable rshell ports are in use.
* @throws IOException If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from
* it.
*/
public void connect(final InetAddress host, final int port, final InetAddress localAddr) throws SocketException, BindException, IOException {
int localPort;
for (localPort = MAX_CLIENT_PORT; localPort >= MIN_CLIENT_PORT; --localPort) {
try {
_socket_ = _socketFactory_.createSocket(host, port, localAddr, localPort);
} catch (final SocketException e) {
continue;
}
break;
}
if (localPort < MIN_CLIENT_PORT) {
throw new BindException("All ports in use or insufficient permssion.");
}
_connectAction_();
}
/**
* Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port. The local port must lie
* between <code> MIN_CLIENT_PORT </code> and <code> MAX_CLIENT_PORT </code> or an IllegalArgumentException will be thrown. Before returning,
* {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() } is called to perform connection initialization actions.
*
* @param host The remote host.
* @param port The port to connect to on the remote host.
* @param localAddr The local address to use.
* @param localPort The local port to use.
* @throws SocketException If the socket timeout could not be set.
* @throws IOException If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is
* derived from it.
* @throws IllegalArgumentException If an invalid local port number is specified.
*/
@Override
public void connect(final InetAddress host, final int port, final InetAddress localAddr, final int localPort)
throws SocketException, IOException, IllegalArgumentException {
if (localPort < MIN_CLIENT_PORT || localPort > MAX_CLIENT_PORT) {
throw new IllegalArgumentException("Invalid port number " + localPort);
}
super.connect(host, port, localAddr, localPort);
}
/**
* Opens a Socket connected to a remote host at the specified port and originating from the current host at a port in a range acceptable to the BSD rshell
* daemon. Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() } is called to perform connection initialization
* actions.
*
* @param hostname The name of the remote host.
* @param port The port to connect to on the remote host.
* @throws SocketException If the socket timeout could not be set.
* @throws BindException If all acceptable rshell ports are in use.
* @throws IOException If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived
* from it.
* @throws UnknownHostException If the hostname cannot be resolved.
*/
@Override
public void connect(final String hostname, final int port) throws SocketException, IOException, UnknownHostException {
connect(InetAddress.getByName(hostname), port, InetAddress.getLocalHost());
}
/**
* Opens a Socket connected to a remote host at the specified port and originating from the specified local address using a port in a range acceptable to
* the BSD rshell daemon. Before returning, {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() } is called to perform connection
* initialization actions.
*
* @param hostname The remote host.
* @param port The port to connect to on the remote host.
* @param localAddr The local address to use.
* @throws SocketException If the socket timeout could not be set.
* @throws BindException If all acceptable rshell ports are in use.
* @throws IOException If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from
* it.
*/
public void connect(final String hostname, final int port, final InetAddress localAddr) throws SocketException, IOException {
connect(InetAddress.getByName(hostname), port, localAddr);
}
/**
* Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port. The local port must lie
* between <code> MIN_CLIENT_PORT </code> and <code> MAX_CLIENT_PORT </code> or an IllegalArgumentException will be thrown. Before returning,
* {@link org.apache.commons.net.SocketClient#_connectAction_ _connectAction_() } is called to perform connection initialization actions.
*
* @param hostname The name of the remote host.
* @param port The port to connect to on the remote host.
* @param localAddr The local address to use.
* @param localPort The local port to use.
* @throws SocketException If the socket timeout could not be set.
* @throws IOException If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is
* derived from it.
* @throws UnknownHostException If the hostname cannot be resolved.
* @throws IllegalArgumentException If an invalid local port number is specified.
*/
@Override
public void connect(final String hostname, final int port, final InetAddress localAddr, final int localPort)
throws SocketException, IOException, IllegalArgumentException, UnknownHostException {
if (localPort < MIN_CLIENT_PORT || localPort > MAX_CLIENT_PORT) {
throw new IllegalArgumentException("Invalid port number " + localPort);
}
super.connect(hostname, port, localAddr, localPort);
}
// Overrides method in RExecClient in order to implement proper
// port number limitations.
@Override
InputStream createErrorStream() throws IOException {
final Socket socket;
try (ServerSocket server = createServer()) {
_output_.write(Integer.toString(server.getLocalPort()).getBytes(StandardCharsets.UTF_8));
_output_.write(NULL_CHAR);
_output_.flush();
socket = server.accept();
}
if (isRemoteVerificationEnabled() && !verifyRemote(socket)) {
socket.close();
throw new IOException("Security violation: unexpected connection attempt by " + socket.getInetAddress().getHostAddress());
}
return new SocketInputStream(socket, socket.getInputStream());
}
private ServerSocket createServer() throws IOException {
for (int localPort = MAX_CLIENT_PORT; localPort >= MIN_CLIENT_PORT; --localPort) {
try {
return _serverSocketFactory_.createServerSocket(localPort, 1, getLocalAddress());
} catch (final SocketException e) {
continue;
}
}
throw new BindException("All ports in use.");
}
/**
* Same as <code> rcommand(localUsername, remoteUsername, command, false); </code>
*
* @param localUser the local user
* @param remoteUser the remote user
* @param command the command
* @throws IOException on error
*/
public void rcommand(final String localUser, final String remoteUser, final String command) throws IOException {
rcommand(localUser, remoteUser, command, false);
}
/**
* Remotely executes a command through the rshd daemon on the server to which the RCommandClient is connected. After calling this method, you may interact
* 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
* after reaching end of file on its standard output (accessible through {@link #getInputStream getInputStream()}). Disconnecting from the server or closing
* the process streams before reaching end of file will not necessarily terminate the remote process.
* <p>
* If a separate error stream is requested, the remote server will connect to a local socket opened by RCommandClient, providing an independent stream
* through which standard error will be transmitted. The local socket must originate from a secure port (512 - 1023), and rcommand() ensures that this will
* be so. RCommandClient will also do a simple security check when it accepts a connection for this error stream. If the connection does not originate from
* the remote server, an IOException will be thrown. This serves as a simple protection against possible hijacking of the error stream by an attacker
* monitoring the rexec() negotiation. You may disable this behavior with {@link org.apache.commons.net.bsd.RExecClient#setRemoteVerificationEnabled
* setRemoteVerificationEnabled()} .
* </p>
*
* @param localUser The user account on the local machine that is requesting the command execution.
* @param remoteUser The account name on the server through which to execute the command.
* @param command The command, including any arguments, to execute.
* @param separateErrorStream True if you would like the standard error to be transmitted through a different stream than standard output. False if not.
* @throws IOException If the rcommand() attempt fails. The exception will contain a message indicating the nature of the failure.
*/
public void rcommand(final String localUser, final String remoteUser, final String command, final boolean separateErrorStream) throws IOException {
rexec(localUser, remoteUser, command, separateErrorStream);
}
}