Controlling Access to Machine Resources

As system administrator, you can control and monitor system activity. You can set limits on who can use what resources. You can log resource use, and you can monitor who is using the resources. You can also set up your machines to minimize improper use of resources.

Limiting and Monitoring Superuser

Your system requires a root password for superuser access. In the default configuration, a user cannot remotely log in to a system as root. When logging in remotely, a user must log in with the user's user name and then use the su command to become root. You can monitor who has been using the su command, especially those users who are trying to gain superuser access. For procedures that monitor superuser and limit access to superuser, see Monitoring and Restricting Superuser (Task Map).

Configuring Role-Based Access Control to Replace Superuser

Role-based access control, or RBAC, is designed to limit the capabilities of superuser. Superuser, the root user, has access to every resource in the system. With RBAC, you can replace root with a set of roles with discrete powers. For example, you can set up one role to handle user account creation, and another role to handle system file modification. When you have established a role to handle a function or set of functions, you can remove those functions from root's capabilities.

Each role requires that a known user log in with their user name and password. After logging in, the user then assumes the role with a specific role password. As a consequence, someone who learns the root password has limited ability to damage your system. For more on RBAC, see Role-Based Access Control (Overview).

Preventing Unintentional Misuse of Machine Resources

You can prevent you and your users from making unintentional errors in the following ways:

• You can keep from running a Trojan horse by correctly setting the PATH variable.

• You can assign a restricted shell to users. A restricted shell prevents user error by steering users to those parts of the system that the users need for their jobs. In fact, through careful setup, you can ensure that users access only those parts of the system that help the users work efficiently.

• You can set restrictive permissions on files that users do not need to access.

Setting the PATH Variable

You should take care to correctly set the PATH variable. Otherwise, you can accidentally run a program that was introduced by someone else. The intruding program can corrupt your data or harm your system. This kind of program, which creates a security hazard, is referred to as a Trojan horse. For example, a substitute su program could be placed in a public directory where you, as system administrator, might run the substitute program. Such a script would look just like the regular su command. Because the script removes itself after execution, you would have little evidence to show that you have actually run a Trojan horse.

The PATH variable is automatically set at login time. The path is set through the startup files: .login, .profile, and .cshrc. When you set up the user search path so that the current directory (.) comes last, you are protected from running this type of Trojan horse. The PATH variable for superuser should not include the current directory at all.

Assigning a Restricted Shell to Users

The standard shell allows a user to open files, execute commands, and so on. The restricted shell limits the ability of a user to change directories and to execute commands. The restricted shell is invoked with the /usr/lib/rsh command. Note that the restricted shell is not the remote shell, which is /usr/sbin/rsh.

The restricted shell differs from the standard shell in the following ways:

• The user is limited to the user's home directory, so the user cannot use the cd command to change directories. Therefore, the user cannot browse system files.

• The user cannot change the PATH variable, so the user can use only commands in the path that is set by the system administrator. The user also cannot execute commands or scripts by using a complete path name.

• The user cannot redirect output with > or >>.

The restricted shell enables you to limit a user's ability to stray into system files. The shell creates a limited environment for a user who needs to perform specific tasks. The restricted shell is not completely secure, however, and is only intended to keep unskilled users from inadvertently doing damage.

For information about the restricted shell, use the man -s1m rsh command to see the rsh(1M) man page.

Restricting Access to Data in Files

Because the Solaris OS is a multiuser environment, file system security is the most basic security risk on a system. You can use traditional UNIX file protections to protect your files. You can also use the more secure access control lists (ACLs).

You might want to allow some users to read some files, and give other users permission to change or delete some files. You might have some data that you do not want anyone else to see. Chapter 7, Controlling Access to Files (Tasks) discusses how to set file permissions.

Restricting setuid Executable Files

Executable files can be security risks. Many executable programs have to be run as root, that is, as superuser, to work properly. These setuid programs run with the user ID set to 0. Anyone who is running these programs runs the programs with the root ID. A program that runs with the root ID creates a potential security problem if the program was not written with security in mind.

Except for the executables that Sun ships with the setuid bit set to root, you should disallow the use of setuid programs. If you cannot disallow the use of setuid programs, then you should at least restrict their use. Secure administration requires few setuid programs.

For more information, see Preventing Executable Files From Compromising Security. For procedures, see Protecting Against Programs With Security Risk (Task Map).

Using the Solaris Security Toolkit

the Solaris Security Toolkit provides a flexible and extensible mechanism to minimize, harden, and secure a Solaris system. The Solaris Security Toolkit, informally known as the JASS toolkit, is a tool that enables the user to perform security modifications to a system. The tool can provide a report on the security status of a system. The tool also has the ability to undo previous runs of the tool. The JASS toolkit can be downloaded from the Sun web site, https://wwws.sun.com/security/jass. The web site contains pointers to online documentation.

The toolkit is described in detail in Securing Systems with the Solaris Security Toolkit, by Alex Noordergraaf and Glenn Brunette, ISBN 0-13-141071-7, June 2003. The book is part of the Sun BluePrints Series, which is published by Sun Microsystems Press.

Using the netservices limited Configuration

By default, when the Solaris 10 release is installed, a large set of network services are enabled. To limit a system's network connectivity, you run the netservices limited command. Then, the only network service that accepts network requests is the sshd daemon. All other network services are disabled or handle local requests only. To enable individual network services, such as ftp, you use the Solaris Service Management Facility (SMF). For more information, see the netservices(1M) and smf(5) man pages.

Using Solaris Resource Management Features

Solaris software provides sophisticated resource management features. Using these features, you can allocate, schedule, monitor, and cap resource use by applications in a server consolidation environment. The resource controls framework enables you to set constraints on system resources that are consumed by processes. Such constraints help to prevent denial-of-service attacks by a script that attempts to flood a system's resources.

With Solaris resource management features, you can designate resources for particular projects. You can also dynamically adjust the resources that are available. For more information, see Part I, Resource Management, in System Administration Guide: Virtualization Using the Solaris Operating System.

Using Solaris Zones

Solaris zones provide an application execution environment in which processes are isolated from the rest of the system within a single instance of the Solaris OS. This isolation prevents processes that are running in one zone from monitoring or affecting processes that are running in other zones. Even a process running with superuser capabilities cannot view or affect activity in other zones.

Solaris zones are ideal for environments that place several applications on a single server. For more information, see Part II, Zones, in System Administration Guide: Virtualization Using the Solaris Operating System.

Monitoring Use of Machine Resources

As a system administrator, you need to monitor system activity. You need to be aware of all aspects of your machines, including the following:

• What is the normal load?

• Who has access to the system?

• When do individuals access the system?

• What programs normally run on the system?

With this kind of knowledge, you can use the available tools to audit system use and monitor the activities of individual users. Monitoring is very useful when a breach in security is suspected. For more information on the auditing service, see Chapter 28, Solaris Auditing (Overview).

Monitoring File Integrity

As a system administrator, you need assurance that the files that were installed on the systems that you administer have not changed in unexpected ways. In large installations, a comparison and reporting tool about the software stack on each of your systems enables you to track your systems. The Basic Audit Reporting Tool (BART) enables you to comprehensively validate systems by performing file-level checks of one or more systems over time. Changes in a BART manifest across systems, or for one system over time, can validate the integrity of your systems. BART provides manifest creation, manifest comparison, and rules for scripting reports. For more information, see Chapter 6, Using the Basic Audit Reporting Tool (Tasks).