readme

基于TCP-WRAP原理的系统监控的c语言实现代码

@(#) README 1.30 97/03/21 19:27:21

This is the 7.6 version of the TCP/IP daemon wrapper package.

Thank you for using this program. If you like it, send me a postcard.
My postal address is at the bottom of this file.

Read the BLURB file for a brief summary of what is new. The CHANGES
file gives a complete account of differences with respect to previous
releases.

Announcements of new releases of this software are posted to Usenet
(comp.security.unix, comp.unix.admin), to the cert-tools mailing list,
and to a dedicated mailing list.  You can subscribe to the dedicated
mailing list by sending an email message to [e-mail]
with in the body (not subject):  subscribe tcp-wrappers-announce.

Table of contents
-----------------

    1 - Introduction
    2 - Disclaimer
    3 - Tutorials
                3.1 - How it works
                3.2 - Where the logging information goes
    4 - Features
                4.1 - Access control
                4.2 - Host name spoofing
                4.3 - Host address spoofing
                4.4 - Client username lookups
                4.5 - Language extensions
		4.6 - Multiple ftp/gopher/www archives on one host
		4.7 - Banner messages
		4.8 - Sequence number guessing
    5 - Other works
                5.1 - Related documents
                5.2 - Related software
    6 - Limitations
                6.1 - Known wrapper limitations
                6.2 - Known system software bugs
    7 - Configuration and installation
                7.1 - Easy configuration and installation
                7.2 - Advanced configuration and installation
                7.3 - Daemons with arbitrary path names
                7.4 - Building and testing the access control rules
                7.5 - Other applications
    8 - Acknowledgements

1 - Introduction
----------------

With this package you can monitor and filter incoming requests for the
SYSTAT, FINGER, FTP, TELNET, RLOGIN, RSH, EXEC, TFTP, TALK, and other
network services.

It supports both 4.3BSD-style sockets and System V.4-style TLI. Praise
yourself lucky if you don't know what that means.

The package provides tiny daemon wrapper programs that can be installed
without any changes to existing software or to existing configuration
files.  The wrappers report the name of the client host and of the
requested service; the wrappers do not exchange information with the
client or server applications, and impose no overhead on the actual
conversation between the client and server applications.

Optional features are: access control to restrict what systems can
connect to what network daemons; client user name lookups with the RFC
931 etc. protocol; additional protection against hosts that pretend to
have someone elses host name; additional protection against hosts that
pretend to have someone elses host address.

The programs are very portable. Build procedures are provided for many
common (and not so common) environments, and guidelines are provided in
case your environment is not among them.

Requirements are that network daemons are spawned by a super server
such as the inetd; a 4.3BSD-style socket programming interface and/or
System V.4-style TLI programming interface; and the availability of a
syslog(3) library and of a syslogd(8) daemon.  The wrappers should run
without modification on any system that satisfies these requirements.
Workarounds have been implemented for several common bugs in systems
software.

What to do if this is your first encounter with the wrapper programs:
1) read the tutorial sections for an introduction to the relevant
concepts and terminology; 2) glance over the security feature sections
in this document; 3) follow the installation instructions (easy or
advanced). I recommend that you first use the default security feature
settings.  Run the wrappers for a few days to become familiar with
their logs, before doing anything drastic such as cutting off access or
installing booby traps.

2 - Disclaimer
--------------

The wrapper programs rely on source address information obtained from
network packets. This information is provided by the client host. It is
not 100 percent reliable, although the wrappers do their best to expose
forgeries.

In the absence of cryptographic protection of message contents, and of
cryptographic authentication of message originators, all data from the
network should be treated with sound scepticism.

THIS RESTRICTION IS BY NO MEANS SPECIFIC TO THE TCP/IP PROTOCOLS.

3 - Tutorials
-------------

The tutorial sections give a gentle introduction to the operation of
the wrapper programs, and introduce some of the terminology that is
used in the remainder of the document: client, server, the inetd and
syslogd daemons, and their configuration files.

3.1 - How it works
------------------

Almost every application of the TCP/IP protocols is based on a client-
server model. For example, when a user invokes the telnet command to
connect to one of your systems, a telnet server process is executed on
the target host. The telnet server process connects the user to a login
process. A few examples of client and server programs are shown in the
table below:

              client   server    application
              --------------------------------
              telnet   telnetd   remote login
              ftp      ftpd      file transfer
              finger   fingerd   show users

The usual approach is to run one single daemon process that waits for
all kinds of incoming network connections. Whenever a connection is
established, this daemon (usually called inetd) runs the appropriate
server program and goes back to sleep, waiting for other connections.

The wrapper programs rely on a simple, but powerful mechanism.  Instead
of directly running the desired server program, the inetd is tricked
into running a small wrapper program. The wrapper logs the client host
name or address and performs some additional checks.  When all is well,
the wrapper executes the desired server program and goes away.

The wrapper programs have no interaction with the client user (or with
the client process).  Nor do the wrappers interact with the server
application. This has two major advantages: 1) the wrappers are
application-independent, so that the same program can protect many
kinds of network services; 2) no interaction also means that the
wrappers are invisible from outside (at least for authorized users).

Another important property is that the wrapper programs are active only
when the initial contact between client and server is established. Once
a wrapper has done its work there is no overhead on the client-server
conversation.

The simple mechanism has one major drawback: the wrappers go away after
the initial contact between client and server processes, so the
wrappers are of little use with network daemons that service more than
one client.  The wrappers would only see the first client attempt to
contact such a server. The NFS mount daemon is a typical example of a
daemon that services requests from multiple clients. See the section on
related software for ways to deal with such server programs.

There are two ways to use the wrapper programs:

1) The easy way: move network daemons to some other directory and fill
   the resulting holes with copies of the wrapper programs.  This
   approach involves no changes to system configuration files, so there
   is very little risk of breaking things.

2) The advanced way: leave the network daemons alone and modify the
   inetd configuration file.  For example, an entry such as:

     tftp  dgram  udp  wait  root  /usr/etc/tcpd  in.tftpd -s /tftpboot

   When a tftp request arrives, inetd will run the wrapper program
   (tcpd) with a process name `in.tftpd'.  This is the name that the
   wrapper will use when logging the request and when scanning the
   optional access control tables.  `in.tftpd' is also the name of the
   server program that the wrapper will attempt to run when all is
   well.  Any arguments (`-s /tftpboot' in this particular example) are
   transparently passed on to the server program.

For an account of the history of the wrapper programs, with real-life
examples, see the section below on related documents.

3.2 - Where the logging information goes
----------------------------------------

The wrapper programs send their logging information to the syslog
daemon (syslogd). The disposition of the wrapper logs is determined by
the syslog configuration file (usually /etc/syslog.conf). Messages are
written to files, to the console, or are forwarded to a @loghost. Some
syslogd versions can even forward messages down a |pipeline.

Older syslog implementations (still found on Ultrix systems) only
support priority levels ranging from 9 (debug-level messages) to 0
(alerts). All logging information of the specified priority level or
more urgent is written to the same destination.  In the syslog.conf
file, priority levels are specified in numerical form.  For example,

    8/usr/spool/mqueue/syslog

causes all messages with priority 8 (informational messages), and
anything that is more urgent, to be appended to the file
/usr/spool/mqueue/syslog.

Newer syslog implementations support message classes in addition to
priority levels.  Examples of message classes are: mail, daemon, auth
and news. In the syslog.conf file, priority levels are specified with
symbolic names: debug, info, notice, ..., emerg. For example,

    mail.debug                  /var/log/syslog

causes all messages of class mail with priority debug (or more urgent)
to be appended to the /var/log/syslog file.

By default, the wrapper logs go to the same place as the transaction
logs of the sendmail daemon. The disposition can be changed by editing
the Makefile and/or the syslog.conf file. Send a `kill -HUP' to the
syslogd after changing its configuration file. Remember that syslogd,
just like sendmail, insists on one or more TABs between the left-hand
side and the right-hand side expressions in its configuration file.

Solaris 2.x note: the syslog daemon depends on the m4 macro processor.
The m4 program is installed as part of the software developer packages.

Trouble shooting note: when the syslogging does not work as expected,
run the program by hand (`syslogd -d') and see what really happens.

4 - Features
------------

4.1 - Access control
--------------------

When compiled with -DHOSTS_ACCESS, the wrapper programs support a
simple form of access control.  Access can be controlled per host, per
service, or combinations thereof. The software provides hooks for the
execution of shell commands when an access control rule fires; this
feature may be used to install "booby traps".  For details, see the
hosts_access.5 manual page, which is in `nroff -man' format. A later
section describes how you can test your access control rules.

Access control can also be used to connect clients to the "right"
service. What is right may depend on the requested service, the origin
of the request, and what host address the client connects to. Examples:

(1) A gopher or www database speaks native language when contacted from
    within the country, otherwise it speaks English.

(2) A service provider offers different ftp, gopher or www services
    with different internet hostnames from one host (section 4.6).

Access control is enabled by default. It can be turned off by editing
the Makefile, or by providing no access control tables. The install
instructions below describe the Makefile editing process.

The hosts_options.5 manual page (`nroff -man' format) documents an
extended version of the access control language. The extensions are
disabled by default. See the section below on language extensions.