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OpenWindows Advanced User's Guide

D.2 More About Security

This section describes some fundamentals of network security that you may find useful as you run applications across the network, including:

D.2.1 Who Should Read this Section

The default security configuration in the OpenWindows Version 3.3 software, or later versions, does not need to be changed unless you run applications in any of the following configurations:

D.2.2 Access Control Mechanisms

An access control mechanism controls which clients or applications have access to the X11 server. Only properly authorized clients can connect to the server; all others are denied access, and are terminated with the following error message. 

Xlib: connection to hostname refused by server
Xlib: Client is not authorized to connect to server

The connection attempt logs to the server console as:

AUDIT: <Date Time Year>: X: client 6 rejected from IP 129.144.152.193 port 3485
	Auth name: MIT-MAGIC-COOKIE-1

There are two different types of access control mechanisms: user-based and host-based. (That is, one mechanism grants access to a particular user's account, while the other grants access to a particular host, or machine.) Unless the -noauth option is used with openwin, both the user-based access control mechanism and the host-based access control mechanism are active. For more information see "D.2.4 Manipulating Access to the Server" in this chapter.

D.2.2.1 User-Based Access

A user-based, or authorization-based mechanism allows you to give access explicitly to a particular user on any host machine. The user's client passes authorization data to the server. If the data match the server's authorization data, the user is allowed access.

D.2.2.2 Host-Based Access

A host-based mechanism is a general purpose mechanism. It allows you to give access to a particular host, in which all users on that host can connect to the server. This is a weaker form of access control: if that host has access to the server, all users on that host are allowed to connect to the server.

The Solaris environment provides the host-based mechanism for backward compatibility. Applications linked with versions of Xlib or libcps older than OpenWindows Version 2 software or X11R4 do not recognize the new user-based access control mechanism. To enable these applications to connect to the server, a user must either switch to the host-based mechanism, or relink with the newer versions of Xlib and libcps.

Note -

If possible, clients linked with older versions of Xlib or libcps should be relinked with newer versions of these libraries to enable them to connect to the server with the new user-based access control mechanism.

D.2.3 Authorization Protocols

Two authorization protocols are supported in this version of the OpenWindows software: MIT-MAGIC-COOKIE-1 and SUN-DES-1. They differ in the authorization data used; they are similar in the access control mechanism used. At any time, the server implements only one protocol. The MIT-MAGIC-COOKIE-1 protocol using the user-based mechanism is the default in the OpenWindows software.

D.2.3.1 MIT-MAGIC-COOKIE-1

The MIT-MAGIC-COOKIE-1 authorization protocol was developed by the Massachusetts Institute of Technology. At server start-up, a magic cookie is created for the server and the user who started the system. On every connection attempt, the user's client sends the magic cookie to the server as part of the connection packet. This magic cookie is compared with the servers' magic cookie. The connection is allowed if the magic cookies match, or denied if they do not match.

D.2.3.2 SUN-DES-1

The SUN-DES-1 authorization protocol, developed by Sun Microsystems, is based on Secure RPC (Remote Procedure Call) and requires DES (Data Encryption Software) support. The authorization information is the machine-independent netname, or network name, of a user. This information is encrypted and sent to the server as part of the connection packet. The server decrypts the information, and if the netname is known, allows the connection.

This protocol provides a higher level of security than the MIT-MAGIC-COOKIE-1 protocol. There is no way for another user to use your machine independent netname to access a server, but it is possible for another user to use the magic cookie to access a server.

This protocol is available only in libraries in the OpenWindows Version 3 and later environments. Any applications built with static libraries, in particular Xlib, in environments prior to OpenWindows Version 3 cannot use this authorization protocol.

"D.2.4.3 Allowing Access When Using SUN-DES-1", in this chapter, describes how to allow another user access to your server by adding their netname to your server's access list.

D.2.3.3 Changing the Default Authorization Protocol

The default authorization protocol, MIT-MAGIC-COOKIE-1, can be changed to SUN_DES-1, the other supported authorization protocol, or to no user-based access mechanism at all. You change the default by supplying options with the openwin command. For example, to change the default from MIT-MAGIC-COOKIE-1 to SUN-DES-1, start the OpenWindows software as follows: 

example% openwin -auth sun-des

If you must run the OpenWindows software without the user-based access mechanism, use the -noauth command line option: 

example% openwin -noauth

Caution - Caution -

Using -noauth weakens security. It is equivalent to running the OpenWindows software with the host-based access control mechanism only; the server inactivates the user-based access control mechanism. Anyone that can run applications on your local machine will be allowed access to your server.

D.2.4 Manipulating Access to the Server

Unless the -noauth option is used with openwin (see "D.2.3.3 Changing the Default Authorization Protocol"), both the user-based access control mechanism and the host-based access control mechanism are active. The server first checks the user-based mechanism, then the host-based mechanism. The default security configuration uses MIT-MAGIC-COOKIE-1 as the user-based mechanism, and an empty list for the host-based mechanism. Since the host-based list is empty, only the user-based mechanism is effectively active. Using the -noauth option instructs the server to inactivate the user-based access control mechanism, and initializes the host-based list by adding the local host.

You can use either of two programs to change a server's access control mechanism: xhost and xauth. For more information, see these man pages. These programs access two binary files created by the authorization protocol. These files contain session-specific authorization data. One file is for server internal use only. The other file is located in the user's $HOME directory: 

.Xauthority 

Client Authority file

Use the xhost program to change the host-based access list in the server. You can add hosts to, or delete hosts from the access list. If you are starting with the default configuration -- an empty host-based access list -- and use xhost to add a machine name, you will lower the level of security. The server will allow access to the host you added, as well as to any user specifying the default authorization protocol. See "D.2.2.2 Host-Based Access" for an explanation of why the host-based access control mechanism is considered a lower level of security.

The xauth program accesses the authorization protocol data in the .Xauthority client file. You can extract this data from your .Xauthority file so that another user can merge the data into their .Xauthority file, thus allowing them access to your server, or to the server to which you connect.

See "D.2.4.2 Allowing Access When Using MIT-MAGIC-COOKIE-1"for examples of how to use xhost and xauth.

D.2.4.1 Client Authority File

The client authority file is .Xauthority. It contains entries of the form: 

connection-protocol          auth-protocol          auth-data

By default, .Xauthority contains MIT-MAGIC-COOKIE-1 as the auth-protocol, and entries for the local display only as the connection-protocol and auth-data. For example, on host anyhost, the .Xauthority file may contain the following entries: 

anyhost:0      MIT-MAGIC-COOKIE-1  82744f2c4850b03fce7ae47176e75localhost:0    MIT-MAGIC-COOKIE-1  82744f2c4850b03fce7ae47176e75anyhost/unix:0 MIT-MAGIC-COOKIE-1   82744f2c4850b03fce7ae47176e75

When the client starts up, an entry corresponding to the connection-protocol is read from .Xauthority, and the auth-protocol and auth-data are sent to the server as part of the connection packet. In the default configuration, xhost returns empty host-based access lists and state that authorization is enabled.

If you have changed the authorization protocol from the default to SUN-DES-1 the entries in .Xauthority contain SUN-DES-1 as the auth-protocol and the netname of the user as auth-data. The netname is in the following form: 

unix.userid@NISdomainname

For example, on host, anyhost the .Xauthority file may contain the following entries, where unix.15339@EBB.Eng.Sun.COM is the machine-independent netname of the user:

anyhost:0        SUN-DES-1            "unix.15339@EBB.Eng.Sun.COM"
localhost:0      SUN-DES-1            "unix.15339@EBB.Eng.Sun.COM"
anyhost/unix:0   SUN-DES-1            "unix.15339@EBB.Eng.Sun.COM"

Note -

If you do not know your network name, or machine independent netname, ask your system administrator.

D.2.4.2 Allowing Access When Using MIT-MAGIC-COOKIE-1

If you are using the MIT-MAGIC-COOKIE-1 authorization protocol, follow these steps to allow another user access to your server:

  1. On the machine running the server, use xauth to extract an entry corresponding to hostname:0 into a file.

    For this example, hostname is anyhost and the file is xauth.info:

    myhost% /usr/openwin/bin/xauth nextract - anyhost:0 > $HOME/xauth.info

  2. Send the file containing the entry to the user requesting access (using Mail Tool, rcp or some other file transfer method).

    Note -

    Mailing the file containing your authorization information is a safer method than using rcp. If you do use rcp, do not place the file in a directory that is easily accessible by another user.

  3. The other user must merge the entry into his/her.Xauthority file.

    For this example, userhost merges xauth.info into the other user's .Xauthority file: 

    userhost% /usr/openwin/bin/xauth nmerge - < xauth.info

    Note -

    The auth-data is session-specific; therefore, it is valid only as long as the server is not restarted.

D.2.4.3 Allowing Access When Using SUN-DES-1

If you are using the SUN-DES-1 authorization protocol, follow these steps to allow another user access to your server:

  1. On the machine running the server, use xhost to make the new user known to the server.

    For this example, to allow new user somebody to run on myhost:

    myhost% xhost + somebody@

  2. The new user must use xauth to add the entry into their .Xauthority file.

    For this example, the new user's machine independent netname is unix.15339@EBB.Eng.Sun.COM. Note that this command should be typed on one line with no carriage return. After the pipe symbol, type a space followed by the remainder of the command. 

    userhost% echo 'add myhost:0 SUN-DES-1 "unix.15339@EBB.Eng.Sun.COM"' |
$OPENWINHOME/bin/xauth

D.2.5 Running Clients Remotely, or Locally as Another User

X clients use the value of the DISPLAY environment variable to get the name of the server to which they should connect.

To run clients remotely, or locally as another user, follow these steps:

  1. On the machine running the server, allow another user access.

    Depending on which authorization protocol you use, follow the steps outlined in either "D.2.4.2 Allowing Access When Using MIT-MAGIC-COOKIE-1"or "D.2.4.3 Allowing Access When Using SUN-DES-1".

  2. Set DISPLAY to the name of the host running the server.

    For this example, the host is remotehost:

    myhost% setenv DISPLAY remotehost:0

  3. Run the client program as shown. 

    myhost% client_program&

    The client is displayed on the remote machine, remotehost.