Managing Confined Services

Red Hat Enterprise Linux 6

Guide to configuring services under control of SELinux

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Mirek Jahoda

Red Hat Customer Content Services

Robert Krátký

Red Hat Customer Content Services

Barbora Ančincová

Red Hat Customer Content Services

Abstract

This book provides assistance to advanced users and administrators when using and configuring Security-Enhanced Linux (SELinux). It focuses on Red Hat Enterprise Linux and describes the components of SELinux as they pertain to services an advanced user or administrator might need to configure. Also included are real-world examples of configuring those services and demonstrations of how SELinux complements their operation.

Chapter 1. Introduction

Security-Enhanced Linux (SELinux) is an implementation of a mandatory access control mechanism in the Linux kernel, checking for allowed operations after standard discretionary access controls are checked. It was created by the National Security Agency and can enforce rules on files and processes in a Linux system, and on their actions, based on defined policy.
Security-Enhanced Linux (SELinux) refers to files, such as directories and devices, as objects. Processes, such as a user running a command or the Mozilla Firefox application, are referred to as subjects. Most operating systems use a Discretionary Access Control (DAC) system that controls how subjects interact with objects, and how subjects interact with each other. On operating systems using DAC, users control the permissions of files (objects) that they own. For example, on Linux operating systems, users could make their home directories world-readable, inadvertently giving other users and processes (subjects) access to potentially sensitive information.
DAC access decisions are only based on user identity and ownership, ignoring other security-relevant information such as the role of the user, the function and trustworthiness of the program, and the sensitivity and integrity of the data. Each user usually has complete discretion over their files, making it difficult to enforce a system-wide security policy. Furthermore, every program run by a user inherits all of the permissions granted to the user and is free to change access to the user's files, so minimal protection is provided against malicious software. Many system services and privileged programs must run with coarse-grained privileges that far exceed their requirements, so that a flaw in any one of these programs might be exploited to obtain further system access. [1]
The following is an example of permissions used on Linux operating systems that do not run Security-Enhanced Linux (SELinux). The permissions in these examples may differ from your system. Use the ls -l command to view file permissions: 
$ ls -l file1
-rwxrw-r-- 1 user1 group1 0 2010-01-29 09:17 file1
The first three permission bits, rwx, control the access rights that the Linux user1 user (in this case, the owner) has to file1. The next three permission bits, rw-, control the access rights that the Linux group1 group has to file1. The last three permission bits, r--, control the access rights that everyone else has to file1, which includes all users and processes.
Security-Enhanced Linux (SELinux) adds Mandatory Access Control (MAC) to the Linux kernel, and is enabled by default in Red Hat Enterprise Linux. A general purpose MAC architecture needs the ability to enforce an administratively-set security policy over all processes and files in the system, basing decisions on labels containing a variety of security-relevant information. When properly implemented, it enables a system to adequately defend itself and offers critical support for application security by protecting against the tampering with, and bypassing of, secured applications. MAC provides strong separation of applications that permits the safe execution of untrustworthy applications. Its ability to limit the privileges associated with executing processes limits the scope of potential damage that can result from the exploitation of vulnerabilities in applications and system services. MAC enables information to be protected from legitimate users with limited authorization as well as from authorized users who have unwittingly executed malicious applications.[2]
The following is an example of the labels containing security-relevant information that are applied to processes, Linux users, and files, on Linux operating systems that run SELinux. This information is called the SELinux context, and is viewed using the ls -Z command: 
$ ls -Z file1
-rwxrw-r--  user1 group1 unconfined_u:object_r:user_home_t:s0      file1
In this example, SELinux provides a user (unconfined_u), a role (object_r), a type (user_home_t), and a level (s0) for the file1 file. This information is used to make access control decisions. This example also displays the DAC rules, which are shown in the SELinux context via the ls -Z command. SELinux policy rules are checked after DAC rules. SELinux policy rules are not applied if DAC rules deny access first.

Targeted Policy

When SELinux is in enforcing mode, the default policy used in Red Hat Enterprise Linux, is the targeted policy. Processes that are targeted run in a confined domain, and processes that are not targeted run in an unconfined domain. Refer to the Targeted Policy chapter in the Security-Enhanced Linux guide for more information about targeted policy and confined and unconfined processes.

[1] "Integrating Flexible Support for Security Policies into the Linux Operating System", by Peter Loscocco and Stephen Smalley. This paper was originally prepared for the National Security Agency and is, consequently, in the public domain. Refer to the original paper for details.
[2] "Meeting Critical Security Objectives with Security-Enhanced Linux", by Peter Loscocco and Stephen Smalley. This paper was originally prepared for the National Security Agency and is in the public domain. Refer to the original paper for details.

Chapter 2. The Apache HTTP Server

The Apache HTTP Server provides an open-source HTTP server with the current HTTP standards.[3]
In Red Hat Enterprise Linux, the httpd package provides the Apache HTTP Server. Run the rpm -q httpd command to see if the httpd package is installed. If it is not installed and you want to use the Apache HTTP Server, run the following command as the root user to install it: 
~]# yum install httpd

2.1. The Apache HTTP Server and SELinux

When SELinux is enabled, the Apache HTTP Server (httpd) runs confined by default. Confined processes run in their own domains, and are separated from other confined processes. If a confined process is compromised by an attacker, depending on SELinux policy configuration, an attacker's access to resources and the possible damage they can do is limited. The following example demonstrates the httpd processes running in their own domain. This example assumes the httpd, setroubleshoot, setroubleshoot-server and policycoreutils-python packages are installed:
  1. Run the getenforce command to confirm SELinux is running in enforcing mode: 
    ~]$ getenforce
Enforcing
    The getenforce command returns Enforcing when SELinux is running in enforcing mode.
  2. Run the service httpd start command as the root user to start httpd: 
    ~]# service httpd start
Starting httpd:                                            [  OK  ]
  3. Run the ps -eZ | grep httpd command to view the httpd processes: 
    ~]$ ps -eZ | grep httpd
unconfined_u:system_r:httpd_t:s0 2850 ?        00:00:00 httpd
unconfined_u:system_r:httpd_t:s0 2852 ?        00:00:00 httpd
unconfined_u:system_r:httpd_t:s0 2853 ?        00:00:00 httpd
unconfined_u:system_r:httpd_t:s0 2854 ?        00:00:00 httpd
unconfined_u:system_r:httpd_t:s0 2855 ?        00:00:00 httpd
unconfined_u:system_r:httpd_t:s0 2856 ?        00:00:00 httpd
unconfined_u:system_r:httpd_t:s0 2857 ?        00:00:00 httpd
unconfined_u:system_r:httpd_t:s0 2858 ?        00:00:00 httpd
unconfined_u:system_r:httpd_t:s0 2859 ?        00:00:00 httpd
    The SELinux context associated with the httpd processes is unconfined_u:system_r:httpd_t:s0. The second last part of the context, httpd_t, is the type. A type defines a domain for processes and a type for files. In this case, the httpd processes are running in the httpd_t domain.
SELinux policy defines how processes running in confined domains (such as httpd_t) interact with files, other processes, and the system in general. Files must be labeled correctly to allow httpd access to them. For example, httpd can read files labeled with the httpd_sys_content_t type, but cannot write to them, even if Linux (DAC) permissions allow write access. Booleans must be enabled to allow certain behavior, such as allowing scripts network access, allowing httpd access to NFS and CIFS volumes, and httpd being allowed to execute Common Gateway Interface (CGI) scripts.
When /etc/httpd/conf/httpd.conf is configured so httpd listens on a port other than TCP ports 80, 443, 488, 8008, 8009, or 8443, the semanage port command must be used to add the new port number to SELinux policy configuration. The following example demonstrates configuring httpd to listen on a port that is not already defined in SELinux policy configuration for httpd, and, as a consequence, httpd failing to start. This example also demonstrates how to then configure the SELinux system to allow httpd to successfully listen on a non-standard port that is not already defined in the policy. This example assumes the httpd package is installed. Run each command in the example as the root user:
  1. Run the service httpd status command to confirm httpd is not running: 
    ~]# service httpd status
httpd is stopped
    If the output differs, run the service httpd stop command to stop the process: 
    ~]# service httpd stop
Stopping httpd:                                            [  OK  ]
  2. Run the semanage port -l | grep -w http_port_t command to view the ports SELinux allows httpd to listen on: 
    ~]# semanage port -l | grep -w http_port_t
http_port_t                    tcp      80, 443, 488, 8008, 8009, 8443
  3. Edit /etc/httpd/conf/httpd.conf as the root user. Configure the Listen option so it lists a port that is not configured in SELinux policy configuration for httpd. In this example, httpd is configured to listen on port 12345: 
    # Change this to Listen on specific IP addresses as shown below to 
# prevent Apache from glomming onto all bound IP addresses (0.0.0.0)
#
#Listen 12.34.56.78:80
Listen 127.0.0.1:12345
  4. Run the service httpd start command to start httpd: 
    ~]# service httpd start
Starting httpd: (13)Permission denied: make_sock: could not bind to address 127.0.0.1:12345
no listening sockets available, shutting down
Unable to open logs					   [FAILED]
    An SELinux denial similar to the following is logged: 
    setroubleshoot: SELinux is preventing the httpd (httpd_t) from binding to port 12345. For complete SELinux messages. run sealert -l f18bca99-db64-4c16-9719-1db89f0d8c77
  5. For SELinux to allow httpd to listen on port 12345, as used in this example, the following command is required: 
    ~]# semanage port -a -t http_port_t -p tcp 12345
  6. Run service httpd start again to start httpd and have it listen on the new port: 
    ~]# service httpd start
Starting httpd:						   [  OK  ]
  7. Now that SELinux has been configured to allow httpd to listen on a non-standard port (TCP 12345 in this example), httpd starts successfully on this port.
  8. To prove that httpd is listening and communicating on TCP port 12345, open a telnet connection to the specified port and issue a HTTP GET command, as follows: 
    ~]# telnet localhost 12345
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
GET / HTTP/1.0

HTTP/1.1 200 OK
Date: Wed, 02 Dec 2009 14:36:34 GMT
Server: Apache/2.2.13 (Red Hat)
Accept-Ranges: bytes
Content-Length: 3985
Content-Type: text/html; charset=UTF-8
[...continues...]

2.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
The following example creates a new file in the /var/www/html/ directory, and shows the file inheriting the httpd_sys_content_t type from its parent directory (/var/www/html/):
  1. Run the ls -dZ /var/www/html command to view the SELinux context of /var/www/html/: 
    ~]$ ls -dZ /var/www/html
drwxr-xr-x  root root system_u:object_r:httpd_sys_content_t:s0 /var/www/html
    This shows /var/www/html/ is labeled with the httpd_sys_content_t type.
  2. Run the touch /var/www/html/file1 command as the root user to create a new file.
  3. Run the ls -Z /var/www/html/file1 command to view the SELinux context: 
    ~]$ ls -Z /var/www/html/file1
-rw-r--r--  root root unconfined_u:object_r:httpd_sys_content_t:s0 /var/www/html/file1
The ls -Z command shows file1 labeled with the httpd_sys_content_t type. SELinux allows httpd to read files labeled with this type, but not write to them, even if Linux permissions allow write access. SELinux policy defines what types a process running in the httpd_t domain (where httpd runs) can read and write to. This helps prevent processes from accessing files intended for use by another process.
For example, httpd can access files labeled with the httpd_sys_content_t type (intended for the Apache HTTP Server), but by default, cannot access files labeled with the samba_share_t type (intended for Samba). Also, files in user home directories are labeled with the user_home_t type: by default, this prevents httpd from reading or writing to files in user home directories.
The following lists some of the types used with httpd. Different types allow you to configure flexible access:
httpd_sys_content_t
Use this type for static web content, such as .html files used by a static website. Files labeled with this type are accessible (read only) to httpd and scripts executed by httpd. By default, files and directories labeled with this type cannot be written to or modified by httpd or other processes. Note that by default, files created in or copied into /var/www/html/ are labeled with the httpd_sys_content_t type.
httpd_sys_script_exec_t
Use this type for scripts you want httpd to execute. This type is commonly used for Common Gateway Interface (CGI) scripts in /var/www/cgi-bin/. By default, SELinux policy prevents httpd from executing CGI scripts. To allow this, label the scripts with the httpd_sys_script_exec_t type and enable the httpd_enable_cgi Boolean. Scripts labeled with httpd_sys_script_exec_t run in the httpd_sys_script_t domain when executed by httpd. The httpd_sys_script_t domain has access to other system domains, such as postgresql_t and mysqld_t.
httpd_sys_rw_content_t
Files labeled with this type can be written to by scripts labeled with the httpd_sys_script_exec_t type, but cannot be modified by scripts labeled with any other type. You must use the httpd_sys_rw_content_t type to label files that will be read from and written to by scripts labeled with the httpd_sys_script_exec_t type.
httpd_sys_ra_content_t
Files labeled with this type can be appended to by scripts labeled with the httpd_sys_script_exec_t type, but cannot be modified by scripts labeled with any other type. You must use the httpd_sys_ra_content_t type to label files that will be read from and appended to by scripts labeled with the httpd_sys_script_exec_t type.
httpd_unconfined_script_exec_t
Scripts labeled with this type run without SELinux protection. Only use this type for complex scripts, after exhausting all other options. It is better to use this type instead of disabling SELinux protection for httpd, or for the entire system.

Note

To see more of the available types for httpd, run the following command: 
~]$ grep httpd /etc/selinux/targeted/contexts/files/file_contexts

Procedure 2.1. Changing the SELinux Context

The type for files and directories can be changed with the chcon command. Changes made with chcon do not survive a file system relabel or the restorecon command. SELinux policy controls whether users are able to modify the SELinux context for any given file. The following example demonstrates creating a new directory and an index.html file for use by httpd, and labeling that file and directory to allow httpd access to them:
  1. Run the mkdir -p /my/website command as the root user to create a top-level directory structure to store files to be used by httpd.
  2. Files and directories that do not match a pattern in file-context configuration may be labeled with the default_t type. This type is inaccessible to confined services: 
    ~]$ ls -dZ /my
drwxr-xr-x  root root unconfined_u:object_r:default_t:s0 /my
  3. Run the chcon -R -t httpd_sys_content_t /my/ command as the root user to change the type of the /my/ directory and subdirectories, to a type accessible to httpd. Now, files created under /my/website/ inherit the httpd_sys_content_t type, rather than the default_t type, and are therefore accessible to httpd: 
    ~]# chcon -R -t httpd_sys_content_t /my/
~]# touch /my/website/index.html
~]# ls -Z /my/website/index.html
-rw-r--r--  root root unconfined_u:object_r:httpd_sys_content_t:s0 /my/website/index.html
Refer to the Temporary Changes: chcon section of the Red Hat Enterprise Linux 6 SELinux User Guide for further information about chcon.
Use the semanage fcontext command (semanage is provided by the policycoreutils-python package) to make label changes that survive a relabel and the restorecon command. This command adds changes to file-context configuration. Then, run restorecon, which reads file-context configuration, to apply the label change. The following example demonstrates creating a new directory and an index.html file for use by httpd, and persistently changing the label of that directory and file to allow httpd access to them:
  1. Run the mkdir -p /my/website command as the root user to create a top-level directory structure to store files to be used by httpd.
  2. Run the following command as the root user to add the label change to file-context configuration: 
    ~]# semanage fcontext -a -t httpd_sys_content_t "/my(/.*)?"
    The "/my(/.*)?" expression means the label change applies to the /my/ directory and all files and directories under it.
  3. Run the touch /my/website/index.html command as the root user to create a new file.
  4. Run the restorecon -R -v /my/ command as the root user to apply the label changes (restorecon reads file-context configuration, which was modified by the semanage command in step 2): 
    ~]# restorecon -R -v /my/
restorecon reset /my context unconfined_u:object_r:default_t:s0->system_u:object_r:httpd_sys_content_t:s0
restorecon reset /my/website context unconfined_u:object_r:default_t:s0->system_u:object_r:httpd_sys_content_t:s0
restorecon reset /my/website/index.html context unconfined_u:object_r:default_t:s0->system_u:object_r:httpd_sys_content_t:s0
Refer to the Persistent Changes: semanage fcontext section of the Red Hat Enterprise Linux SELinux User Guide for further information on semanage.

2.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. This can be achieved via Booleans that allow parts of SELinux policy to be changed at runtime, without any knowledge of SELinux policy writing. This allows changes, such as allowing services access to NFS volumes, without reloading or recompiling SELinux policy.
To modify the state of a Boolean, use the setsebool command. For example, to enable the allow_httpd_anon_write Boolean, run the following command as the root user: 
~]# setsebool -P allow_httpd_anon_write on
To disable a Boolean, using the same example, simply change on to off in the command, as shown below: 
~]# setsebool -P allow_httpd_anon_write off

Note

Do not use the -P option if you do not want setsebool changes to persist across reboots.
Below is a description of common Booleans available that cater for the way httpd is running:
allow_httpd_anon_write
When disabled, this Boolean allows httpd to only have read access to files labeled with the public_content_rw_t type. Enabling this Boolean will allow httpd to write to files labeled with the public_content_rw_t type, such as a public directory containing files for a public file transfer service.
allow_httpd_mod_auth_ntlm_winbind
Enabling this Boolean allows access to NTLM and Winbind authentication mechanisms via the mod_auth_ntlm_winbind module in httpd.
allow_httpd_mod_auth_pam
Enabling this Boolean allows access to PAM authentication mechanisms via the mod_auth_pam module in httpd.
allow_httpd_sys_script_anon_write
This Boolean defines whether or not HTTP scripts are allowed write access to files labeled with the public_content_rw_t type, as used in a public file transfer service.
httpd_builtin_scripting
This Boolean defines access to httpd scripting. Having this Boolean enabled is often required for PHP content.
httpd_can_network_connect
When disabled, this Boolean prevents HTTP scripts and modules from initiating a connection to a network or remote port. Enable this Boolean to allow this access.
httpd_can_network_connect_db
When disabled, this Boolean prevents HTTP scripts and modules from initiating a connection to database servers. Enable this Boolean to allow this access.
httpd_can_network_relay
Enable this Boolean when httpd is being used as a forward or reverse proxy.
httpd_can_sendmail
When disabled, this Boolean prevents HTTP modules from sending mail. This can prevent spam attacks should a vulnerability be found in httpd. Enable this Boolean to allow HTTP modules to send mail.
httpd_dbus_avahi
When off, this Boolean denies httpd access to the avahi service via D-Bus. Enable this Boolean to allow this access.
httpd_enable_cgi
When disabled, this Boolean prevents httpd from executing CGI scripts. Enable this Boolean to allow httpd to execute CGI scripts (CGI scripts must be labeled with the httpd_sys_script_exec_t type).
httpd_enable_ftp_server
Enabling this Boolean will allow httpd to listen on the FTP port and act as an FTP server.
httpd_enable_homedirs
When disabled, this Boolean prevents httpd from accessing user home directories. Enable this Boolean to allow httpd access to user home directories; for example, content in /home/*/.
httpd_execmem
When enabled, this Boolean allows httpd to execute programs that require memory addresses that are both executable and writable. Enabling this Boolean is not recommended from a security standpoint as it reduces protection against buffer overflows, however certain modules and applications (such as Java and Mono applications) require this privilege.
httpd_ssi_exec
This Boolean defines whether or not server side include (SSI) elements in a web page can be executed.
httpd_tty_comm
This Boolean defines whether or not httpd is allowed access to the controlling terminal. Usually this access is not required, however in cases such as configuring an SSL certificate file, terminal access is required to display and process a password prompt.
httpd_unified
When enabled, this Boolean allows httpd_t complete access to all of the httpd types (that is to execute, read, or write sys_content_t). When disabled, there is separation in place between web content that is read-only, writable or executable. Disabling this Boolean ensures an extra level of security but adds the administrative overhead of having to individually label scripts and other web content based on the file access that each should have.
httpd_use_cifs
Enable this Boolean to allow httpd access to files on CIFS volumes that are labeled with the cifs_t type, such as file systems mounted via Samba.
httpd_use_nfs
Enable this Boolean to allow httpd access to files on NFS volumes that are labeled with the nfs_t type, such as file systems mounted via NFS.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

2.4. Configuration examples

The following examples provide real-world demonstrations of how SELinux complements the Apache HTTP Server and how full function of the Apache HTTP Server can be maintained.

2.4.1. Running a static site

To create a static website, label the .html files for that website with the httpd_sys_content_t type. By default, the Apache HTTP Server cannot write to files that are labeled with the httpd_sys_content_t type. The following example creates a new directory to store files for a read-only website:
  1. Run the mkdir /mywebsite command as the root user to create a top-level directory.
  2. As the root user, create a /mywebsite/index.html file. Copy and paste the following content into /mywebsite/index.html: 
    <html>
<h2>index.html from /mywebsite/</h2>
</html>
  3. To allow the Apache HTTP Server read only access to /mywebsite/, as well as files and subdirectories under it, label /mywebsite/ with the httpd_sys_content_t type. Run the following command as the root user to add the label change to file-context configuration: 
    ~]# semanage fcontext -a -t httpd_sys_content_t "/mywebsite(/.*)?"
  4. Run the restorecon -R -v /mywebsite command as the root user to make the label changes: 
    ~]# restorecon -R -v /mywebsite
restorecon reset /mywebsite context unconfined_u:object_r:default_t:s0->system_u:object_r:httpd_sys_content_t:s0
restorecon reset /mywebsite/index.html context unconfined_u:object_r:default_t:s0->system_u:object_r:httpd_sys_content_t:s0
  5. For this example, edit /etc/httpd/conf/httpd.conf as the root user. Comment out the existing DocumentRoot option. Add a DocumentRoot "/mywebsite" option. After editing, these options should look as follows: 
    #DocumentRoot "/var/www/html"
DocumentRoot "/mywebsite"
  6. Run the service httpd status command as the root user to see the status of the Apache HTTP Server. If the server is stopped, run the service httpd start command as the root user to start it. If the server is running, run the service httpd restart command as the root user to restart the service (this also applies any changes made to httpd.conf).
  7. Use a web browser to navigate to http://localhost/index.html. The following is displayed: 
    index.html from /mywebsite/

2.4.2. Sharing NFS and CIFS volumes

By default, NFS mounts on the client side are labeled with a default context defined by policy for NFS volumes. In common policies, this default context uses the nfs_t type. Also, by default, Samba shares mounted on the client side are labeled with a default context defined by policy. In common policies, this default context uses the cifs_t type.
Depending on policy configuration, services may not be able to read files labeled with the nfs_t or cifs_t types. This may prevent file systems labeled with these types from being mounted and then read or exported by other services. Booleans can be enabled or disabled to control which services are allowed to access the nfs_t and cifs_t types.
Enable the httpd_use_nfs Boolean to allow httpd to access and share NFS volumes (labeled with the nfs_t type). Run the setsebool command as the root user to enable the Boolean: 
~]# setsebool -P httpd_use_nfs on
Enable the httpd_use_cifs Boolean to allow httpd to access and share CIFS volumes (labeled with the cifs_t type). Run the setsebool command as the root user to enable the Boolean: 
~]# setsebool -P httpd_use_cifs on

Note

Do not use the -P option if you do not want setsebool changes to persist across reboots.

2.4.3. Sharing files between services

Type Enforcement helps prevent processes from accessing files intended for use by another process. For example, by default, Samba cannot read files labeled with the httpd_sys_content_t type, which are intended for use by the Apache HTTP Server. Files can be shared between the Apache HTTP Server, FTP, rsync, and Samba, if the desired files are labeled with the public_content_t or public_content_rw_t type.
The following example creates a directory and files, and allows that directory and files to be shared (read only) through the Apache HTTP Server, FTP, rsync, and Samba:
  1. Run the mkdir /shares command as the root user to create a new top-level directory to share files between multiple services.
  2. Files and directories that do not match a pattern in file-context configuration may be labeled with the default_t type. This type is inaccessible to confined services: 
    ~]$ ls -dZ /shares
drwxr-xr-x  root root unconfined_u:object_r:default_t:s0 /shares
  3. As the root user, create a /shares/index.html file. Copy and paste the following content into /shares/index.html: 
    <html>
<body>
<p>Hello</p>
</body>
</html>
  4. Labeling /shares/ with the public_content_t type allows read-only access by the Apache HTTP Server, FTP, rsync, and Samba. Run the following command as the root user to add the label change to file-context configuration: 
    ~]# semanage fcontext -a -t public_content_t "/shares(/.*)?"
  5. Run the restorecon -R -v /shares/ command as the root user to apply the label changes: 
    ~]# restorecon -R -v /shares/
restorecon reset /shares context unconfined_u:object_r:default_t:s0->system_u:object_r:public_content_t:s0
restorecon reset /shares/index.html context unconfined_u:object_r:default_t:s0->system_u:object_r:public_content_t:s0
To share /shares/ through Samba:
  1. Run the rpm -q samba samba-common samba-client command to confirm the samba, samba-common, and samba-client packages are installed (version numbers may differ): 
    ~]$ rpm -q samba samba-common samba-client
samba-3.4.0-0.41.el6.3.i686
samba-common-3.4.0-0.41.el6.3.i686
samba-client-3.4.0-0.41.el6.3.i686
    If any of these packages are not installed, install them by running the yum install package-name command as the root user.
  2. Edit /etc/samba/smb.conf as the root user. Add the following entry to the bottom of this file to share the /shares/ directory through Samba: 
    [shares]
comment = Documents for Apache HTTP Server, FTP, rsync, and Samba
path = /shares
public = yes
writable = no
  3. A Samba account is required to mount a Samba file system. Run the smbpasswd -a username command as the root user to create a Samba account, where username is an existing Linux user. For example, smbpasswd -a testuser creates a Samba account for the Linux testuser user: 
    ~]# smbpasswd -a testuser
New SMB password: Enter a password
Retype new SMB password: Enter the same password again
Added user testuser.
    Running smbpasswd -a username, where username is the user name of a Linux account that does not exist on the system, causes a Cannot locate Unix account for 'username'! error.
  4. Run the service smb start command as the root user to start the Samba service: 
    ~]# service smb start
Starting SMB services:                                     [  OK  ]
  5. Run the smbclient -U username -L localhost command to list the available shares, where username is the Samba account added in step 3. When prompted for a password, enter the password assigned to the Samba account in step 3 (version numbers may differ): 
    ~]$ smbclient -U username -L localhost
Enter username's password:
Domain=[HOSTNAME] OS=[Unix] Server=[Samba 3.4.0-0.41.el6]

Sharename       Type      Comment
---------       ----      -------
shares          Disk      Documents for Apache HTTP Server, FTP, rsync, and Samba
IPC$            IPC       IPC Service (Samba Server Version 3.4.0-0.41.el6)
username        Disk      Home Directories
Domain=[HOSTNAME] OS=[Unix] Server=[Samba 3.4.0-0.41.el6]

Server               Comment
---------            -------

Workgroup            Master
---------            -------
  6. Run the mkdir /test/ command as the root user to create a new directory. This directory will be used to mount the shares Samba share.
  7. Run the following command as the root user to mount the shares Samba share to /test/, replacing username with the user name from step 3: 
    ~]# mount //localhost/shares /test/ -o user=username
    Enter the password for username, which was configured in step 3.
  8. Run the cat /test/index.html command to view the file, which is being shared through Samba: 
    ~]$ cat /test/index.html
<html>
<body>
<p>Hello</p>
</body>
</html>
To share /shares/ through the Apache HTTP Server:
  1. Run the rpm -q httpd command to confirm the httpd package is installed (version number may differ): 
    ~]$ rpm -q httpd
httpd-2.2.11-6.i386
    If this package is not installed, run the yum install httpd command as the root user to install it.
  2. Change into the /var/www/html/ directory. Run the following command as the root user to create a link (named shares) to the /shares/ directory: 
    ~]# ln -s /shares/ shares
  3. Run the service httpd start command as the root user to start the Apache HTTP Server: 
    ~]# service httpd start
Starting httpd:                                            [  OK  ]
  4. Use a web browser to navigate to http://localhost/shares. The /shares/index.html file is displayed.
By default, the Apache HTTP Server reads an index.html file if it exists. If /shares/ did not have index.html, and instead had file1, file2, and file3, a directory listing would occur when accessing http://localhost/shares:
  1. Run the rm -i /shares/index.html command as the root user to remove the index.html file.
  2. Run the touch /shares/file{1,2,3} command as the root user to create three files in /shares/: 
    ~]# touch /shares/file{1,2,3}
~]# ls -Z /shares/
-rw-r--r--  root root system_u:object_r:public_content_t:s0 file1
-rw-r--r--  root root unconfined_u:object_r:public_content_t:s0 file2
-rw-r--r--  root root unconfined_u:object_r:public_content_t:s0 file3
  3. Run the service httpd status command as the root user to see the status of the Apache HTTP Server. If the server is stopped, run service httpd start as the root user to start it.
  4. Use a web browser to navigate to http://localhost/shares. A directory listing is displayed:

2.4.4. Changing port numbers

Depending on policy configuration, services may only be allowed to run on certain port numbers. Attempting to change the port a service runs on without changing policy may result in the service failing to start. Run the semanage port -l | grep -w "http_port_t" command as the root user to list the ports SELinux allows httpd to listen on: 
~]# semanage port -l | grep -w http_port_t
http_port_t                    tcp      80, 443, 488, 8008, 8009, 8443
By default, SELinux allows http to listen on TCP ports 80, 443, 488, 8008, 8009, or 8443. If /etc/httpd/conf/httpd.conf is configured so that httpd listens on any port not listed for http_port_t, httpd fails to start.
To configure httpd to run on a port other than TCP ports 80, 443, 488, 8008, 8009, or 8443:
  1. Edit /etc/httpd/conf/httpd.conf as the root user so the Listen option lists a port that is not configured in SELinux policy for httpd. The following example configures httpd to listen on the 10.0.0.1 IP address, and on TCP port 12345: 
    # Change this to Listen on specific IP addresses as shown below to 
# prevent Apache from glomming onto all bound IP addresses (0.0.0.0)
#
#Listen 12.34.56.78:80
Listen 10.0.0.1:12345
  2. Run the semanage port -a -t http_port_t -p tcp 12345 command as the root user to add the port to SELinux policy configuration.
  3. Run the semanage port -l | grep -w http_port_t command as the root user to confirm the port is added: 
    ~]# semanage port -l | grep -w http_port_t
http_port_t                    tcp      12345, 80, 443, 488, 8008, 8009, 8443
If you no longer run httpd on port 12345, run the semanage port -d -t http_port_t -p tcp 12345 command as the root user to remove the port from policy configuration.

[3] Refer to the Apache HTTP Server Project page for more information.

Chapter 3. Samba

Samba is an open-source implementation of the Server Message Block (SMB) and Common Internet File System (CIFS) protocols that provides file and print services between clients across various operating systems.[4]
In Red Hat Enterprise Linux, the samba package provides the Samba server. Run the rpm -q samba command to see if the samba package is installed. If it is not installed and you want to use Samba, run the following command as the root user to install it: 
~]# yum install samba

3.1. Samba and SELinux

When SELinux is enabled, the Samba server (smbd) runs confined by default. Confined services run in their own domains, and are separated from other confined services. The following example demonstrates the smbd process running in its own domain. This example assumes the samba package is installed:
  1. Run the getenforce command to confirm SELinux is running in enforcing mode: 
    ~]$ getenforce
Enforcing
    The getenforce command returns Enforcing when SELinux is running in enforcing mode.
  2. Run the service smbd start command as the root user to start smbd: 
    ~]# service smb start
Starting SMB services:                                     [  OK  ]
  3. Run the ps -eZ | grep smb command to view the smbd processes: 
    ~]$ ps -eZ | grep smb
unconfined_u:system_r:smbd_t:s0 16420 ?        00:00:00 smbd
unconfined_u:system_r:smbd_t:s0 16422 ?        00:00:00 smbd
    The SELinux context associated with the smbd processes is unconfined_u:system_r:smbd_t:s0. The second last part of the context, smbd_t, is the type. A type defines a domain for processes and a type for files. In this case, the smbd processes are running in the smbd_t domain.
Files must be labeled correctly to allow smbd to access and share them. For example, smbd can read and write to files labeled with the samba_share_t type, but by default, cannot access files labeled with the httpd_sys_content_t type, which is intended for use by the Apache HTTP Server. Booleans must be enabled to allow certain behavior, such as allowing home directories and NFS volumes to be exported through Samba, as well as to allow Samba to act as a domain controller.

3.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
Label files with the samba_share_t type to allow Samba to share them. Only label files you have created, and do not relabel system files with the samba_share_t type: Booleans can be enabled to share such files and directories. SELinux allows Samba to write to files labeled with the samba_share_t type, as long as /etc/samba/smb.conf and Linux permissions are set accordingly.
The samba_etc_t type is used on certain files in /etc/samba/, such as smb.conf. Do not manually label files with the samba_etc_t type. If files in /etc/samba/ are not labeled correctly, run the restorecon -R -v /etc/samba command as the root user to restore such files to their default contexts. If /etc/samba/smb.conf is not labeled with the samba_etc_t type, the service smb start command may fail and an SELinux denial may be logged. The following is an example denial when /etc/samba/smb.conf was labeled with the httpd_sys_content_t type: 
setroubleshoot: SELinux is preventing smbd (smbd_t) "read" to ./smb.conf (httpd_sys_content_t). For complete SELinux messages. run sealert -l deb33473-1069-482b-bb50-e4cd05ab18af

3.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
allow_smbd_anon_write
Having this Boolean enabled allows smbd to write to a public directory, such as an area reserved for common files that otherwise has no special access restrictions.
samba_create_home_dirs
Having this Boolean enabled allows Samba to create new home directories independently. This is often done by mechanisms such as PAM.
samba_domain_controller
When enabled, this Boolean allows Samba to act as a domain controller, as well as giving it permission to execute related commands such as useradd, groupadd and passwd.
samba_enable_home_dirs
Enabling this Boolean allows Samba to share users' home directories.
samba_export_all_ro
Export any file or directory, allowing read-only permissions. This allows files and directories that are not labeled with the samba_share_t type to be shared through Samba. When the samba_export_all_ro Boolean is on, but the samba_export_all_rw Boolean is off, write access to Samba shares is denied, even if write access is configured in /etc/samba/smb.conf, as well as Linux permissions allowing write access.
samba_export_all_rw
Export any file or directory, allowing read and write permissions. This allows files and directories that are not labeled with the samba_share_t type to be exported through Samba. Permissions in /etc/samba/smb.conf and Linux permissions must be configured to allow write access.
samba_run_unconfined
Having this Boolean enabled allows Samba to run unconfined scripts in the /var/lib/samba/scripts/ directory.
samba_share_fusefs
This Boolean must be enabled for Samba to share fusefs file systems.
samba_share_nfs
Disabling this Boolean prevents smbd from having full access to NFS shares via Samba. Enabling this Boolean will allow Samba to share NFS volumes.
use_samba_home_dirs
Enable this Boolean to use a remote server for Samba home directories.
virt_use_samba
Allow virtual machine access to CIFS files.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

3.4. Configuration examples

The following examples provide real-world demonstrations of how SELinux complements the Samba server and how full function of the Samba server can be maintained.

3.4.1. Sharing directories you create

The following example creates a new directory, and shares that directory through Samba:
  1. Run the rpm -q samba samba-common samba-client command to confirm the samba, samba-common, and samba-client packages are installed. If any of these packages are not installed, install them by running the yum install package-name command as the root user.
  2. Run the mkdir /myshare command as the root user to create a new top-level directory to share files through Samba.
  3. Run the touch /myshare/file1 command as the root user to create an empty file. This file is used later to verify the Samba share mounted correctly.
  4. SELinux allows Samba to read and write to files labeled with the samba_share_t type, as long as /etc/samba/smb.conf and Linux permissions are set accordingly. Run the following command as the root user to add the label change to file-context configuration: 
    ~]# semanage fcontext -a -t samba_share_t "/myshare(/.*)?"
  5. Run the restorecon -R -v /myshare command as the root user to apply the label changes: 
    ~]# restorecon -R -v /myshare
restorecon reset /myshare context unconfined_u:object_r:default_t:s0->system_u:object_r:samba_share_t:s0
restorecon reset /myshare/file1 context unconfined_u:object_r:default_t:s0->system_u:object_r:samba_share_t:s0
  6. Edit /etc/samba/smb.conf as the root user. Add the following to the bottom of this file to share the /myshare/ directory through Samba: 
    [myshare]
comment = My share
path = /myshare
public = yes
writable = no
  7. A Samba account is required to mount a Samba file system. Run the smbpasswd -a username command as the root user to create a Samba account, where username is an existing Linux user. For example, smbpasswd -a testuser creates a Samba account for the Linux testuser user: 
    ~]# smbpasswd -a testuser
New SMB password: Enter a password
Retype new SMB password: Enter the same password again
Added user testuser.
    Running smbpasswd -a username, where username is the user name of a Linux account that does not exist on the system, causes a Cannot locate Unix account for 'username'! error.
  8. Run the service smb start command as the root user to start the Samba service: 
    ~]# service smb start
Starting SMB services:                                     [  OK  ]
  9. Run the smbclient -U username -L localhost command to list the available shares, where username is the Samba account added in step 7. When prompted for a password, enter the password assigned to the Samba account in step 7 (version numbers may differ): 
    ~]$ smbclient -U username -L localhost
Enter username's password:
Domain=[HOSTNAME] OS=[Unix] Server=[Samba 3.4.0-0.41.el6]

Sharename       Type      Comment
---------       ----      -------
myshare         Disk      My share
IPC$            IPC       IPC Service (Samba Server Version 3.4.0-0.41.el6)
username        Disk      Home Directories
Domain=[HOSTNAME] OS=[Unix] Server=[Samba 3.4.0-0.41.el6]

Server               Comment
---------            -------

Workgroup            Master
---------            -------
  10. Run the mkdir /test/ command as the root user to create a new directory. This directory will be used to mount the myshare Samba share.
  11. Run the following command as the root user to mount the myshare Samba share to /test/, replacing username with the user name from step 7: 
    ~]# mount //localhost/myshare /test/ -o user=username
    Enter the password for username, which was configured in step 7.
  12. Run the ls /test/ command to view the file1 file created in step 3: 
    ~]$ ls /test/
file1

3.4.2. Sharing a website

It may not be possible to label files with the samba_share_t type, for example, when wanting to share a website in /var/www/html/. For these cases, use the samba_export_all_ro Boolean to share any file or directory (regardless of the current label), allowing read only permissions, or the samba_export_all_rw Boolean to share any file or directory (regardless of the current label), allowing read and write permissions.
The following example creates a file for a website in /var/www/html/, and then shares that file through Samba, allowing read and write permissions. This example assumes the httpd, samba, samba-common, samba-client, and wget packages are installed:
  1. As the root user, create a /var/www/html/file1.html file. Copy and paste the following content into /var/www/html/file1.html: 
    <html>
<h2>File being shared through the Apache HTTP Server and Samba.</h2>
</html>
  2. Run the ls -Z /var/www/html/file1.html command to view the SELinux context of file1.html: 
    ~]$ ls -Z /var/www/html/file1.html
-rw-r--r--. root root unconfined_u:object_r:httpd_sys_content_t:s0 /var/www/html/file1.html
    file1.index.html is labeled with the httpd_sys_content_t. By default, the Apache HTTP Server can access this type, but Samba cannot.
  3. Run the service httpd start command as the root user to start the Apache HTTP Server: 
    ~]# service httpd start
Starting httpd:                                            [  OK  ]
  4. Change into a directory your user has write access to, and run the wget http://localhost/file1.html command. Unless there are changes to the default configuration, this command succeeds: 
    ~]$ wget http://localhost/file1.html
Resolving localhost... 127.0.0.1
Connecting to localhost|127.0.0.1|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 84 [text/html]
Saving to: `file1.html.1'

100%[=======================>] 84          --.-K/s   in 0s      

`file1.html.1' saved [84/84]
  5. Edit /etc/samba/smb.conf as the root user. Add the following to the bottom of this file to share the /var/www/html/ directory through Samba: 
    [website]
comment = Sharing a website
path = /var/www/html/
public = no
writable = no
  6. The /var/www/html/ directory is labeled with the httpd_sys_content_t type. By default, Samba cannot access files and directories labeled with the httpd_sys_content_t type, even if Linux permissions allow it. To allow Samba access, run the following command as the root user to enable the samba_export_all_ro Boolean: 
    ~]# setsebool -P samba_export_all_ro on
    Do not use the -P option if you do not want the change to persist across reboots. Note that enabling the samba_export_all_ro Boolean allows Samba to access any type.
  7. Run service smb start as the root user to start smbd: 
    ~]# service smb start
Starting SMB services:                                     [  OK  ]

[4] Refer to the official Samba website for more information.

Chapter 4. File Transfer Protocol

File Transfer Protocol (FTP) is one of the oldest and most commonly used protocols found on the Internet today. Its purpose is to reliably transfer files between computer hosts on a network without requiring the user to log directly into the remote host or have knowledge of how to use the remote system. It allows users to access files on remote systems using a standard set of simple commands.
The Very Secure FTP Daemon (vsftpd) is designed from the ground up to be fast, stable, and, most importantly, secure. Its ability to handle large numbers of connections efficiently and securely is why vsftpd is the only stand-alone FTP distributed with Red Hat Enterprise Linux.
In Red Hat Enterprise Linux, the vsftpd package provides the Very Secure FTP daemon. Run the rpm -q vsftpd command to see if vsftpd is installed: 
~]$ rpm -q vsftpd
If you want an FTP server and the vsftpd package is not installed, run the following command as the root user to install it: 
~]# yum install vsftpd

4.1. FTP and SELinux

The vsftpd FTP daemon runs confined by default. SELinux policy defines how vsftpd interacts with files, processes, and with the system in general. For example, when an authenticated user logs in via FTP, they cannot read from or write to files in their home directories: SELinux prevents vsftpd from accessing user home directories by default. Also, by default, vsftpd does not have access to NFS or CIFS volumes, and anonymous users do not have write access, even if such write access is configured in /etc/vsftpd/vsftpd.conf. Booleans can be enabled to allow the previously mentioned access.
The following example demonstrates an authenticated user logging in, and an SELinux denial when trying to view files in their home directory:
  1. Run the rpm -q ftp command to see if the ftp package is installed. If it is not, run the yum install ftp command as the root user to install it.
  2. Run the rpm -q vsftpd command to see if the vsftpd package is installed. If it is not, run the yum install vsftpd command as the root user to install it.
  3. In Red Hat Enterprise Linux, vsftpd only allows anonymous users to log in by default. To allow authenticated users to log in, edit /etc/vsftpd/vsftpd.conf as the root user. Make sure the local_enable=YES option is uncommented: 
    # Uncomment this to allow local users to log in.
local_enable=YES
  4. Run the service vsftpd start command as the root user to start vsftpd. If the service was running before editing vsftpd.conf, run the service vsftpd restart command as the root user to apply the configuration changes: 
    ~]# service vsftpd start
Starting vsftpd for vsftpd:                                [  OK  ]
  5. Run the ftp localhost command as the user you are currently logged in with. When prompted for your name, make sure your user name is displayed. If the correct user name is displayed, press Enter, otherwise, enter the correct user name: 
    ~] ftp localhost
Connected to localhost (127.0.0.1).
220 (vsFTPd 2.1.0)
Name (localhost:username):
331 Please specify the password.
Password: Enter your password
500 OOPS: cannot change directory:/home/username
Login failed.
ftp>
  6. An SELinux denial similar to the following is logged: 
    setroubleshoot: SELinux is preventing the ftp daemon from reading users home directories (username). For complete SELinux messages. run sealert -l c366e889-2553-4c16-b73f-92f36a1730ce
  7. Access to home directories has been denied by SELinux. This can be fixed by activating the ftp_home_dir Boolean. Enable this ftp_home_dir Boolean by running the following command as the root user: 
    ~]# setsebool -P ftp_home_dir=1

    Note

    Do not use the -P option if you do not want changes to persist across reboots.
    Try to log in again. Now that SELinux is allowing access to home directories via the ftp_home_dir Boolean, logging in will succeed.

4.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
By default, anonymous users have read access to files in /var/ftp/ when they log in via FTP. This directory is labeled with the public_content_t type, allowing only read access, even if write access is configured in /etc/vsftpd/vsftpd.conf. The public_content_t type is accessible to other services, such as Apache HTTP Server, Samba, and NFS.
Use one of the following types to share files through FTP:
public_content_t
Label files and directories you have created with the public_content_t type to share them read-only through vsftpd. Other services, such as Apache HTTP Server, Samba, and NFS, also have access to files labeled with this type. Files labeled with the public_content_t type cannot be written to, even if Linux permissions allow write access. If you require write access, use the public_content_rw_t type.
public_content_rw_t
Label files and directories you have created with the public_content_rw_t type to share them with read and write permissions through vsftpd. Other services, such as Apache HTTP Server, Samba, and NFS, also have access to files labeled with this type. Remember that Booleans for each service must be enabled before they can write to files labeled with this type.

4.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
allow_ftpd_anon_write
When disabled, this Boolean prevents vsftpd from writing to files and directories labeled with the public_content_rw_t type. Enable this Boolean to allow users to upload files via FTP. The directory where files are uploaded to must be labeled with the public_content_rw_t type and Linux permissions set accordingly.
allow_ftpd_full_access
When this Boolean is on, only Linux (DAC) permissions are used to control access, and authenticated users can read and write to files that are not labeled with the public_content_t or public_content_rw_t types.
allow_ftpd_use_cifs
Having this Boolean enabled allows vsftpd to access files and directories labeled with the cifs_t type; therefore, having this Boolean enabled allows you to share file systems mounted via Samba through vsftpd.
allow_ftpd_use_nfs
Having this Boolean enabled allows vsftpd to access files and directories labeled with the nfs_t type; therefore, having this Boolean enabled allows you to share file systems mounted via NFS through vsftpd.
ftp_home_dir
Having this Boolean enabled allows authenticated users to read and write to files in their home directories. When this Boolean is off, attempting to download a file from a home directory results in an error such as 550 Failed to open file. An SELinux denial is logged.
ftpd_connect_db
Allow FTP daemons to initiate a connection to a database.
httpd_enable_ftp_server
Allow httpd to listen on the FTP port and act as a FTP server.
tftp_anon_write
Having this Boolean enabled allows TFTP access to a public directory, such as an area reserved for common files that otherwise has no special access restrictions.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

4.4. Configuration Examples

4.4.1. Uploading to an FTP site

The following example creates an FTP site that allows a dedicated user to upload files. It creates the directory structure and the required SELinux configuration changes:
  1. Run the setsebool ftp_home_dir=1 command as the root user to enable access to FTP home directories.
  2. Run the mkdir -p /myftp/pub command as the root user to create a new top-level directory.
  3. Set Linux permissions on the /myftp/pub/ directory to allow a Linux user write access. This example changes the owner and group from root to owner user1 and group root. Replace user1 with the user you want to give write access to: 
    ~]# chown user1:root /myftp/pub
~]# chmod 775 /myftp/pub
    The chown command changes the owner and group permissions. The chmod command changes the mode, allowing the user1 user read, write, and execute permissions, and members of the root group read, write, and execute permissions. Everyone else has read and execute permissions, which allows the Apache HTTP Server to read files from this directory.
  4. When running SELinux, files and directories must be labeled correctly to allow access. Setting Linux permissions is not enough. Files labeled with the public_content_t type allow them to be read by FTP, Apache HTTP Server, Samba, and rsync. Files labeled with the public_content_rw_t type can be written to by FTP. Other services, such as Samba, require Booleans to be set before they can write to files labeled with the public_content_rw_t type. Label the top-level directory (/myftp/) with the public_content_t type, to prevent copied or newly-created files under /myftp/ from being written to or modified by services. Run the following command as the root user to add the label change to file-context configuration: 
    ~]# semanage fcontext -a -t public_content_t /myftp
  5. Run the restorecon -R -v /myftp/ command to apply the label change: 
    ~]# restorecon -R -v /myftp/
restorecon reset /myftp context unconfined_u:object_r:default_t:s0->system_u:object_r:public_content_t:s0
  6. Confirm /myftp is labeled with the public_content_t type, and /myftp/pub/ is labeled with the default_t type: 
    ~]$ ls -dZ /myftp/
drwxr-xr-x. root root system_u:object_r:public_content_t:s0 /myftp/
~]$ ls -dZ /myftp/pub/
drwxrwxr-x. user1 root unconfined_u:object_r:default_t:s0 /myftp/pub/
  7. FTP must be allowed to write to a directory before users can upload files via FTP. SELinux allows FTP to write to directories labeled with the public_content_rw_t type. This example uses /myftp/pub/ as the directory FTP can write to. Run the following command as the root user to add the label change to file-context configuration: 
    ~]# semanage fcontext -a -t public_content_rw_t "/myftp/pub(/.*)?"
  8. Run the restorecon -R -v /myftp/pub command as the root user to apply the label change: 
    ~]# restorecon -R -v /myftp/pub
restorecon reset /myftp/pub context system_u:object_r:default_t:s0->system_u:object_r:public_content_rw_t:s0
  9. The allow_ftpd_anon_write Boolean must be on to allow vsftpd to write to files that are labeled with the public_content_rw_t type. Run the following command as the root user to enable this Boolean: 
    ~]# setsebool -P allow_ftpd_anon_write on
    Do not use the -P option if you do not want changes to persist across reboots.
The following example demonstrates logging in via FTP and uploading a file. This example uses the user1 user from the previous example, where user1 is the dedicated owner of the /myftp/pub/ directory:
  1. Run the cd ~/ command to change into your home directory. Then, run the mkdir myftp command to create a directory to store files to upload via FTP.
  2. Run the cd ~/myftp command to change into the ~/myftp/ directory. In this directory, create an ftpupload file. Copy the following contents into this file: 
    File upload via FTP from a home directory.
  3. Run the getsebool allow_ftpd_anon_write command to confirm the allow_ftpd_anon_write Boolean is on: 
    ~]$ getsebool allow_ftpd_anon_write
allow_ftpd_anon_write --> on
    If this Boolean is off, run the setsebool -P allow_ftpd_anon_write on command as the root user to enable it. Do not use the -P option if you do not want the change to persist across reboots.
  4. Run the service vsftpd start command as the root user to start vsftpd: 
    ~]# service vsftpd start
Starting vsftpd for vsftpd:                                [  OK  ]
  5. Run the ftp localhost command. When prompted for a user name, enter the user name of the user who has write access, then, enter the correct password for that user: 
    ~]$ ftp localhost
Connected to localhost (127.0.0.1).
220 (vsFTPd 2.1.0)
Name (localhost:username):
331 Please specify the password.
Password: Enter the correct password
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> cd myftp
250 Directory successfully changed.
ftp> put ftpupload 
local: ftpupload remote: ftpupload
227 Entering Passive Mode (127,0,0,1,241,41).
150 Ok to send data.
226 File receive OK.
ftp> 221 Goodbye.
    The upload succeeds as the allow_ftpd_anon_write Boolean is enabled.

Chapter 5. Network File System

A Network File System (NFS) allows remote hosts to mount file systems over a network and interact with those file systems as though they are mounted locally. This enables system administrators to consolidate resources onto centralized servers on the network.[5]
In Red Hat Enterprise Linux, the nfs-utils package is required for full NFS support. Run the rpm -q nfs-utils command to see if the nfs-utils is installed. If it is not installed and you want to use NFS, run the following command as the root user to install it: 
~]# yum install nfs-utils

5.1. NFS and SELinux

When running SELinux, the NFS daemons are confined by default. SELinux policy allows NFS to share files by default.

5.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
By default, mounted NFS volumes on the client side are labeled with a default context defined by policy for NFS. In common policies, this default context uses the nfs_t type. The following types are used with NFS. Different types allow you to configure flexible access:
var_lib_nfs_t
This type is used for existing and new files copied to or created in the /var/lib/nfs/ directory. This type should not need to be changed in normal operation. To restore changes to the default settings, run the restorecon -R -v /var/lib/nfs command as the root user.
nfsd_exec_t
The /usr/sbin/rpc.nfsd file is labeled with the nfsd_exec_t, as are other system executables and libraries related to NFS. Users should not label any files with this type. nfsd_exec_t will transition to nfsd_t.

5.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
allow_ftpd_use_nfs
When enabled, this Boolean allows the ftpd daemon to access NFS volumes.
cobbler_use_nfs
When enabled, this Boolean allows the cobblerd daemon to access NFS volumes.
git_system_use_nfs
When enabled, this Boolean allows the Git system daemon to read system shared repositories on NFS volumes.
httpd_use_nfs
When enabled, this Boolean allows the httpd daemon to access files stored on NFS volumes.
qemu_use_nfs
When enabled, this Boolean allows Qemu to use NFS volumes.
rsync_use_nfs
When enabled, this Boolean allows rsync servers to share NFS volumes.
samba_share_nfs
When enabled, this Boolean allows the smbd daemon to share NFS volumes. When disabled, this Boolean prevents smbd from having full access to NFS shares via Samba.
sanlock_use_nfs
When enabled, this Boolean allows the sanlock daemon to manage NFS volumes.
sge_use_nfs
When enabled, this Boolean allows the sge scheduler to access NFS volumes.
use_nfs_home_dirs
When enabled, this Boolean adds support for NFS home directories.
virt_use_nfs
When enabled, this Boolean allows confident virtual guests to manage files on NFS volumes.
xen_use_nfs
When enabled, this Boolean allows Xen to manage files on NFS volumes.
git_cgi_use_nfs
When enabled, this Boolean allows the Git Common Gateway Interface (CGI) to access NFS volumes.
tftp_use_nfs
When enabled, this Boolean allows The Trivial File Transfer Protocol (TFTP) to read from NFS volumes for public file transfer services.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

[5] Refer to the Storage Administration Guide for more information.

Chapter 6. Berkeley Internet Name Domain

BIND performs name resolution services via the named daemon. BIND lets users locate computer resources and services by name instead of numerical addresses.
In Red Hat Enterprise Linux, the bind package provides a DNS server. Run the rpm -q bind command to see if the bind package is installed. If it is not installed, run the following command as the root user to install it: 
~]# yum install bind

6.1. BIND and SELinux

The default permissions on the /var/named/slaves/, /var/named/dynamic/ and /var/named/data/ directories allow zone files to be updated via zone transfers and dynamic DNS updates. Files in /var/named/ are labeled with the named_zone_t type, which is used for master zone files.
For a slave server, configure /etc/named.conf to place slave zones in /var/named/slaves/. The following is an example of a domain entry in /etc/named.conf for a slave DNS server that stores the zone file for testdomain.com in /var/named/slaves/: 
zone "testdomain.com" {
			type slave;
			masters { IP-address; };
			file "/var/named/slaves/db.testdomain.com";
		       };
If a zone file is labeled named_zone_t, the named_write_master_zones Boolean must be enabled to allow zone transfers and dynamic DNS to update the zone file. Also, the mode of the parent directory has to be changed to allow the named user or group read, write and execute access.
If zone files in /var/named/ are labeled with the named_cache_t type, a file system relabel or running restorecon -R /var/ will change their type to named_zone_t.

6.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
The following types are used with BIND. Different types allow you to configure flexible access:
named_zone_t
Used for master zone files. Other services cannot modify files of this type. named can only modify files of this type if the named_write_master_zones Boolean is enabled.
named_cache_t
By default, named can write to files labeled with this type, without additional Booleans being set. Files copied or created in the /var/named/slaves/,/var/named/dynamic/ and /var/named/data/ directories are automatically labeled with the named_cache_t type.
named_var_run_t
Files copied or created in the /var/run/bind/, /var/run/named/, and /var/run/unbound/ directories are automatically labeled with the named_var_run_t type.
named_conf_t
BIND-related configuration files, usually stored in the /etc/ directory, are automatically labeled with the named_conf_t type.
named_exec_t
BIND-related executable files, usually stored in the /usr/sbin/ directory, are automatically labeled with the named_exec_t type.
named_log_t
BIND-related log files, usually stored in the /var/log/ directory, are automatically labeled with the named_log_t type.
named_initrc_exec_t
Executable BIND-related files in the /etc/rc.d/init.d/ directory are automatically labeled with the named_initrc_exec_t type.

6.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
named_write_master_zones
When disabled, this Boolean prevents named from writing to zone files or directories labeled with the named_zone_t type. named does not usually need to write to zone files; but in the case that it needs to, or if a secondary server needs to write to zone files, enable this Boolean to allow this action.
named_bind_http_port
When enabled, this Boolean allows BIND to bind an Apache port.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

6.4. Configuration Examples

6.4.1. Dynamic DNS

BIND allows hosts to update their records in DNS and zone files dynamically. This is used when a host computer's IP address changes frequently and the DNS record requires real-time modification.
Use the /var/named/dynamic/ directory for zone files you want updated via dynamic DNS. Files created in or copied into /var/named/dynamic/ inherit Linux permissions that allow named to write to them. As such files are labeled with the named_cache_t type, SELinux allows named to write to them.
If a zone file in /var/named/dynamic/ is labeled with the named_zone_t type, dynamic DNS updates may not be successful for a certain period of time as the update needs to be written to a journal first before being merged. If the zone file is labeled with the named_zone_t type when the journal attempts to be merged, an error such as the following is logged: 
named[PID]: dumping master file: rename: /var/named/dynamic/zone-name: permission denied
Also, the following SELinux denial is logged: 
setroubleshoot: SELinux is preventing named (named_t) "unlink" to zone-name (named_zone_t)
To resolve this labeling issue, run the restorecon -R -v /var/named/dynamic command as the Linux root user.

Chapter 7. Concurrent Versioning System

The Concurrent Versioning System (CVS) is a free revision-control system. It is used to monitor and keep track of modifications to a central set of files which are usually accessed by several different users. It is commonly used by programmers to manage a source code repository and is widely used by open source programmers.
In Red Hat Enterprise Linux, the cvs package provides CVS. Run the rpm -q cvs command to see if the cvs package is installed. If it is not installed and you want to use CVS, run the following command as the root user to install it: 
~]# yum install cvs

7.1. CVS and SELinux

The cvs daemon runs as cvs_t. By default in Red Hat Enterprise Linux, CVS is only allowed to read and write certain directories. The label cvs_data_t defines which areas the cvs daemon has read and write access to. When using CVS with SELinux, assigning the correct label is essential for clients to have full access to the area reserved for CVS data.

7.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
The following types are used with CVS. Different types allow you to configure flexible access:
cvs_data_t
This type is used for data in a CVS repository. CVS can only gain full access to data if it has this type.
cvs_exec_t
This type is used for the /usr/bin/cvs binary.

7.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
allow_cvs_read_shadow
This Boolean allows the cvs daemon to access the /etc/shadow file for user authentication.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

7.4. Configuration Examples

7.4.1. Setting up CVS

This example describes a simple CVS setup and an SELinux configuration which allows remote access. Two hosts are used in this example; a CVS server with a host name of cvs-srv with an IP address of 192.168.1.1 and a client with a host name of cvs-client and an IP address of 192.168.1.100. Both hosts are on the same subnet (192.168.1.0/24). This is an example only and assumes that the cvs and xinetd packages are installed, that the SELinux targeted policy is used, and that SELinux is running in enforced mode.
This example will show that even with full DAC permissions, SELinux can still enforce policy rules based on file labels and only allow access to certain areas that have been specifically labeled for access by CVS.

Note

Steps 1-9 should be performed on the CVS server, cvs-srv.
  1. This example requires the cvs and xinetd packages. Run the rpm -q cvs command to see if the cvs package is installed. If it is not installed, run the following command as the root user to install cvs: 
    ~]# yum install cvs
    Run the rpm -q xinetd command to see if the xinetd package is installed. If it is not installed, run the following command as the root user to install xinetd: 
    ~]# yum install xinetd
  2. Create a group named CVS. This can be done via the groupadd CVS command as the root user, or by using the system-config-users tool.
  3. Create a user with a user name of cvsuser and make this user a member of the CVS group. This can be done using the system-config-users tool.
  4. Edit the /etc/services file and make sure that the CVS server has uncommented entries looking similar to the following: 
    cvspserver	2401/tcp			# CVS client/server operations
cvspserver	2401/udp			# CVS client/server operations
  5. Create the CVS repository in the root area of the file system. When using SELinux, it is best to have the repository in the root file system so that recursive labels can be given to it without affecting any other subdirectories. For example, as the root user, create a /cvs/ directory to house the repository: 
    [root@cvs-srv]# mkdir /cvs
  6. Give full permissions to the /cvs/ directory to all users: 
    [root@cvs-srv]# chmod -R 777 /cvs

    Warning

    This is an example only and these permissions should not be used in a production system.
  7. Edit the /etc/xinetd.d/cvs file and make sure that the CVS section is uncommented and configured to use the /cvs/ directory. The file should look similar to: 
    service cvspserver
{
	disable	= no
	port			= 2401
	socket_type		= stream
	protocol		= tcp
	wait			= no
	user			= root
	passenv			= PATH
	server			= /usr/bin/cvs
	env			= HOME=/cvs
	server_args		= -f --allow-root=/cvs pserver
#	bind			= 127.0.0.1
  8. Start the xinetd daemon by running the service xinetd start command as the root user.
  9. Add a rule which allows inbound connections using TCP on port 2401 by using the system-config-firewall tool.
  10. As the cvsuser user, run the following command: 
    [cvsuser@cvs-client]$ cvs -d /cvs init
  11. At this point, CVS has been configured but SELinux will still deny logins and file access. To demonstrate this, set the $CVSROOT variable on cvs-client and try to log in remotely. The following step should be performed on cvs-client: 
    [cvsuser@cvs-client]$ export CVSROOT=:pserver:cvsuser@192.168.1.1:/cvs
[cvsuser@cvs-client]$
[cvsuser@cvs-client]$ cvs login
Logging in to :pserver:cvsuser@192.168.1.1:2401/cvs
CVS password: ********
cvs [login aborted]: unrecognized auth response from 192.168.100.1: cvs pserver: cannot open /cvs/CVSROOT/config: Permission denied
    SELinux has blocked access. In order to get SELinux to allow this access, the following step should be performed on cvs-srv:
  12. Change the context of the /cvs/ directory as the root user in order to recursively label any existing and new data in the /cvs/ directory, giving it the cvs_data_t type: 
    [root@cvs-srv]# semanage fcontext -a -t cvs_data_t '/cvs(/.*)?'
[root@cvs-srv]# restorecon -R -v /cvs
  13. The client, cvs-client should now be able to log in and access all CVS resources in this repository: 
    [cvsuser@cvs-client]$ export CVSROOT=:pserver:cvsuser@192.168.1.1:/cvs
[cvsuser@cvs-client]$
[cvsuser@cvs-client]$ cvs login
Logging in to :pserver:cvsuser@192.168.1.1:2401/cvs
CVS password: ********
[cvsuser@cvs-client]$

Chapter 8. Squid Caching Proxy

Squid is a high-performance proxy caching server for web clients, supporting FTP, Gopher, and HTTP data objects. It reduces bandwidth and improves response times by caching and reusing frequently-requested web pages.[6]
In Red Hat Enterprise Linux, the squid package provides the Squid Caching Proxy. Run the rpm -q squid command to see if the squid package is installed. If it is not installed and you want to use squid, run the following command as the root user to install it: 
~]# yum install squid

8.1. Squid Caching Proxy and SELinux

When SELinux is enabled, squid runs confined by default. Confined processes run in their own domains, and are separated from other confined processes. If a confined process is compromised by an attacker, depending on SELinux policy configuration, an attacker's access to resources and the possible damage they can do is limited. The following example demonstrates the squid processes running in their own domain. This example assumes the squid package is installed:
  1. Run the getenforce command to confirm SELinux is running in enforcing mode: 
    ~]$ getenforce
Enforcing
    The getenforce command returns Enforcing when SELinux is running in enforcing mode.
  2. Run the service squid start command as the root user to start squid: 
    ~]# service squid start
Starting squid:                                            [  OK  ]
  3. Run the ps -eZ | grep squid command to view the squid processes: 
    ~]$ ps -eZ | grep squid
unconfined_u:system_r:squid_t:s0 2522 ?        00:00:00 squid
unconfined_u:system_r:squid_t:s0 2524 ?        00:00:00 squid
unconfined_u:system_r:squid_t:s0 2526 ?        00:00:00 ncsa_auth
unconfined_u:system_r:squid_t:s0 2527 ?        00:00:00 ncsa_auth
unconfined_u:system_r:squid_t:s0 2528 ?        00:00:00 ncsa_auth
unconfined_u:system_r:squid_t:s0 2529 ?        00:00:00 ncsa_auth
unconfined_u:system_r:squid_t:s0 2530 ?        00:00:00 ncsa_auth
unconfined_u:system_r:squid_t:s0 2531 ?        00:00:00 unlinkd
    The SELinux context associated with the squid processes is unconfined_u:system_r:squid_t:s0. The second last part of the context, squid_t, is the type. A type defines a domain for processes and a type for files. In this case, the squid processes are running in the squid_t domain.
SELinux policy defines how processes running in confined domains, such as squid_t, interact with files, other processes, and the system in general. Files must be labeled correctly to allow squid access to them.
When /etc/squid/squid.conf is configured so squid listens on a port other than the default TCP ports 3128, 3401 or 4827, the semanage port command must be used to add the required port number to the SELinux policy configuration. The following example demonstrates configuring squid to listen on a port that is not initially defined in SELinux policy configuration for squid, and, as a consequence, squid failing to start. This example also demonstrates how to then configure the SELinux system to allow squid to successfully listen on a non-standard port that is not already defined in the policy. This example assumes the squid package is installed. Run each command in the example as the root user:
  1. Run the service squid status command to confirm squid is not running: 
    ~]# service squid status
squid is stopped
    If the output differs, run the service squid stop command to stop the process: 
    ~]# service squid stop
Stopping squid:                                            [  OK  ]
  2. Run the semanage port -l | grep -w squid_port_t command to view the ports SELinux allows squid to listen on: 
    ~]# semanage port -l | grep -w -i squid_port_t
squid_port_t                   tcp      3401, 4827
squid_port_t                   udp      3401, 4827
  3. Edit /etc/squid/squid.conf as the root user. Configure the http_port option so it lists a port that is not configured in SELinux policy configuration for squid. In this example, squid is configured to listen on port 10000: 
    # Squid normally listens to port 3128
http_port 10000
  4. Run the setsebool command to make sure the squid_connect_any Boolean is set to off. This ensures squid is only permitted to operate on specific ports: 
    ~]# setsebool -P squid_connect_any 0
  5. Run the service squid start command to start squid: 
    ~]# service squid start
Starting squid: ....................                       [FAILED]
    An SELinux denial similar to the following is logged: 
    localhost setroubleshoot: SELinux is preventing the squid (squid_t) from binding to port 10000. For complete SELinux messages. run sealert -l 97136444-4497-4fff-a7a7-c4d8442db982
  6. For SELinux to allow squid to listen on port 10000, as used in this example, the following command is required: 
    ~]# semanage port -a -t squid_port_t -p tcp 10000
  7. Run service squid start again to start squid and have it listen on the new port: 
    ~]# service squid start
Starting squid:						   [  OK  ]
  8. Now that SELinux has been configured to allow squid to listen on a non-standard port (TCP 10000 in this example), squid starts successfully on this port.

8.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
The following types are used with squid. Different types allow you to configure flexible access:
httpd_squid_script_exec_t
This type is used for utilities such as cachemgr.cgi, which provides a variety of statistics about squid and its configuration.
squid_cache_t
Use this type for data that is cached by squid, as defined by the cache_dir directive in /etc/squid/squid.conf. By default, files created in or copied into /var/cache/squid/ and /var/spool/squid/ are labeled with the squid_cache_t type. Files for the squidGuard URL redirector plugin for squid created in or copied to /var/squidGuard/ are also labeled with the squid_cache_t type. Squid is only able to use files and directories that are labeled with this type for its cached data.
squid_conf_t
This type is used for the directories and files that squid uses for its configuration. Existing files, or those created in or copied to /etc/squid/ and /usr/share/squid/ are labeled with this type, including error messages and icons.
squid_exec_t
This type is used for the squid binary, /usr/sbin/squid.
squid_log_t
This type is used for logs. Existing files, or those created in or copied to /var/log/squid/ or /var/log/squidGuard/ must be labeled with this type.
squid_initrc_exec_t
This type is used for the initialization file required to start squid which is located at /etc/rc.d/init.d/squid.
squid_var_run_t
This type is used by files in /var/run/, especially the process id (PID) named /var/run/squid.pid which is created by squid when it runs.

8.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
squid_connect_any
When enabled, this Boolean permits squid to initiate a connection to a remote host on any port.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

8.4. Configuration Examples

8.4.1. Squid Connecting to Non-Standard Ports

The following example provides a real-world demonstration of how SELinux complements Squid by enforcing the above Boolean and by default only allowing access to certain ports. This example will then demonstrate how to change the Boolean and show that access is then allowed.
Note that this is an example only and demonstrates how SELinux can affect a simple configuration of Squid. Comprehensive documentation of Squid is beyond the scope of this document. Refer to the official Squid documentation for further details. This example assumes that the Squid host has two network interfaces, Internet access, and that any firewall has been configured to allow access on the internal interface using the default TCP port on which Squid listens (TCP 3128).
  1. As the root user, install the squid package. Run the rpm -q squid command to see if the squid package is installed. If it is not installed, run the yum install squid command as the root user to install it.
  2. Edit the main configuration file, /etc/squid/squid.conf and confirm that the cache_dir directive is uncommented and looks similar to the following: 
    cache_dir ufs /var/spool/squid 100 16 256
    This line specifies the default settings for the cache_dir directive to be used in this example; it consists of the Squid storage format (ufs), the directory on the system where the cache resides (/var/spool/squid), the amount of disk space in megabytes to be used for the cache (100), and finally the number of first-level and second-level cache directories to be created (16 and 256 respectively).
  3. In the same configuration file, make sure the http_access allow localnet directive is uncommented. This allows traffic from the localnet ACL which is automatically configured in a default installation of Squid on Red Hat Enterprise Linux. It will allow client machines on any existing RFC1918 network to have access through the proxy, which is sufficient for this simple example.
  4. In the same configuration file, make sure the visible_hostname directive is uncommented and is configured to the host name of the machine. The value should be the fully qualified domain name (FQDN) of the host: 
    visible_hostname squid.example.com
  5. As the root user, run the service squid start command to start squid. As this is the first time squid has started, this command will initialise the cache directories as specified above in the cache_dir directive and will then start the squid daemon. The output is as follows if squid starts successfully: 
    ~]# /sbin/service squid start
init_cache_dir /var/spool/squid... Starting squid: .       [  OK  ]
  6. Confirm that the squid process ID (PID) has started as a confined service, as seen here by the squid_var_run_t value: 
    ~]# ls -lZ /var/run/squid.pid 
-rw-r--r--. root squid unconfined_u:object_r:squid_var_run_t:s0 /var/run/squid.pid
  7. At this point, a client machine connected to the localnet ACL configured earlier is successfully able to use the internal interface of this host as its proxy. This can be configured in the settings for all common web browsers, or system-wide. Squid is now listening on the default port of the target machine (TCP 3128), but the target machine will only allow outgoing connections to other services on the Internet via common ports. This is a policy defined by SELinux itself. SELinux will deny access to non-standard ports, as shown in the next step:
  8. When a client makes a request using a non-standard port through the Squid proxy such as a website listening on TCP port 10000, a denial similar to the following is logged: 
    SELinux is preventing the squid daemon from connecting to network port 10000
  9. To allow this access, the squid_connect_any Boolean must be modified, as it is disabled by default. To enable the squid_connect_any Boolean, run the following command as the root user: 
    ~]# setsebool -P squid_connect_any on

    Note

    Do not use the -P option if you do not want setsebool changes to persist across reboots.
  10. The client will now be able to access non-standard ports on the Internet as Squid is now permitted to initiate connections to any port, on behalf of its clients.

[6] Refer to the Squid Caching Proxy project page for more information.

Chapter 9. MySQL

The MySQL database is a multi-user, multi-threaded SQL database server that consists of the MySQL server daemon (mysqld) and many client programs and libraries.[7]
In Red Hat Enterprise Linux, the mysql-server package provides MySQL. Run the rpm -q mysql-server command to see if the mysql-server package is installed. If it is not installed, run the following command as the root user to install it: 
~]# yum install mysql-server

9.1. MySQL and SELinux

When MySQL is enabled, it runs confined by default. Confined processes run in their own domains, and are separated from other confined processes. If a confined process is compromised by an attacker, depending on SELinux policy configuration, an attacker's access to resources and the possible damage they can do is limited. The following example demonstrates the MySQL processes running in their own domain. This example assumes the mysql package is installed:
  1. Run the getenforce command to confirm SELinux is running in enforcing mode: 
    ~]$ getenforce
Enforcing
    The getenforce command returns Enforcing when SELinux is running in enforcing mode.
  2. Run the service mysqld start command as the root user to start mysqld: 
    ~]# service mysqld start
Initializing MySQL database:  Installing MySQL system tables... [  OK  ]
Starting MySQL:                                            	[  OK  ]
  3. Run the ps -eZ | grep mysqld command to view the mysqld processes: 
    ~]$ ps -eZ | grep mysqld
unconfined_u:system_r:mysqld_safe_t:s0 6035 pts/1 00:00:00 mysqld_safe
unconfined_u:system_r:mysqld_t:s0 6123 pts/1   00:00:00 mysqld
    The SELinux context associated with the mysqld processes is unconfined_u:system_r:mysqld_t:s0. The second last part of the context, mysqld_t, is the type. A type defines a domain for processes and a type for files. In this case, the mysqld processes are running in the mysqld_t domain.

9.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
The following types are used with mysql. Different types allow you to configure flexible access:
mysqld_db_t
This type is used for the location of the MySQL database. In Red Hat Enterprise Linux, the default location for the database is /var/lib/mysql/, however this can be changed. If the location for the MySQL database is changed, the new location must be labeled with this type. Refer to the following example for instructions on how to change the default database location and how to label the new section appropriately.
mysqld_etc_t
This type is used for the MySQL main configuration file /etc/my.cnf and any other configuration files in the /etc/mysql/ directory.
mysqld_exec_t
This type is used for the mysqld binary located at /usr/libexec/mysqld, which is the default location for the MySQL binary on Red Hat Enterprise Linux. Other systems may locate this binary at /usr/sbin/mysqld which should also be labeled with this type.
mysqld_initrc_exec_t
This type is used for the initialization file for MySQL, located at /etc/rc.d/init.d/mysqld by default in Red Hat Enterprise Linux.
mysqld_log_t
Logs for MySQL need to be labeled with this type for proper operation. All log files in /var/log/ matching the mysql.* wildcard must be labeled with this type.
mysqld_var_run_t
This type is used by files in /var/run/mysqld/, specifically the process id (PID) named /var/run/mysqld/mysqld.pid which is created by the mysqld daemon when it runs. This type is also used for related socket files such as /var/lib/mysql/mysql.sock. Files such as these must be labeled correctly for proper operation as a confined service.

9.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
allow_user_mysql_connect
When enabled, this Boolean allows users to connect to MySQL.
exim_can_connect_db
When enabled, this Boolean allows the exim mailer to initiate connections to a database server.
ftpd_connect_db
When enabled, this Boolean allows ftp daemons to initiate connections to a database server.
httpd_can_network_connect_db
Enabling this Boolean is required for a web server to communicate with a database server.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

9.4. Configuration Examples

9.4.1. MySQL Changing Database Location

When using Red Hat Enterprise Linux 6, the default location for MySQL to store its database is /var/lib/mysql/. This is where SELinux expects it to be by default, and hence this area is already labeled appropriately for you, using the mysqld_db_t type.
The location where the database is stored can be changed depending on individual environment requirements or preferences, however it is important that SELinux is aware of this new location; that it is labeled accordingly. This example explains how to change the location of a MySQL database and then how to label the new location so that SELinux can still provide its protection mechanisms to the new area based on its contents.
Note that this is an example only and demonstrates how SELinux can affect MySQL. Comprehensive documentation of MySQL is beyond the scope of this document. Refer to the official MySQL documentation for further details. This example assumes that the mysql-server and setroubleshoot-server packages are installed, that the auditd service is running, and that there is a valid database in the default location of /var/lib/mysql/.
  1. Run the ls -lZ /var/lib/mysql command to view the SELinux context of the default database location for mysql: 
    ~]# ls -lZ /var/lib/mysql
drwx------. mysql mysql unconfined_u:object_r:mysqld_db_t:s0 mysql
    This shows mysqld_db_t which is the default context element for the location of database files. This context will have to be manually applied to the new database location that will be used in this example in order for it to function properly.
  2. Enter mysqlshow -u root -p and enter the mysqld root password to show the available databases: 
    ~]# mysqlshow -u root -p
Enter password: *******
+--------------------+
|     Databases      |
+--------------------+
| information_schema |
| mysql              |
| test               |
| wikidb             |
+--------------------+
  3. Shut down the mysqld daemon with the service mysqld stop command as the root user: 
    ~]# service mysqld stop
Stopping MySQL:                                            [  OK  ]
  4. Create a new directory for the new location of the database(s). In this example, /mysql/ is used: 
    ~]# mkdir -p /mysql
  5. Copy the database files from the old location to the new location: 
    ~]# cp -R /var/lib/mysql/* /mysql/
  6. Change the ownership of this location to allow access by the mysql user and group. This sets the traditional Unix permissions which SELinux will still observe. 
    ~]# chown -R mysql:mysql /mysql
  7. Run the ls -lZ /opt command to see the initial context of the new directory: 
    ~]# ls -lZ /opt
drwxr-xr-x. mysql mysql unconfined_u:object_r:usr_t:s0   mysql
    The context usr_t of this newly created directory is not currently suitable to SELinux as a location for MySQL database files. Once the context has been changed, MySQL will be able to function properly in this area.
  8. Open the main MySQL configuration file /etc/my.cnf with a text editor and modify the datadir option so that it refers to the new location. In this example the value that should be entered is /mysql. 
    [mysqld]
datadir=/mysql
    Save this file and exit.
  9. Run the service mysqld start command as the root user to start mysqld. The service should fail to start, and a denial will be logged to the /var/log/messages file. However, if the audit daemon is running alongside the setroubleshoot service, the denial will be logged to the /var/log/audit/audit.log file instead: 
    SELinux is preventing /usr/libexec/mysqld "write" access on /mysql. For complete SELinux messages. run sealert -l b3f01aff-7fa6-4ebe-ad46-abaef6f8ad71
    The reason for this denial is that /mysql/ is not labeled correctly for MySQL data files. SELinux is stopping MySQL from having access to the content labeled as usr_t. Perform the following steps to resolve this problem:
  10. Run the following semanage command to add a context mapping for /mysql. Note that semanage is not installed by default. If it is missing on your system, install the policycoreutils-python package. 
    ~]# semanage fcontext -a -t mysqld_db_t "/mysql(/.*)?"
  11. This mapping is written to the /etc/selinux/targeted/contexts/files/file_contexts.local file: 
    ~]# grep -i mysql /etc/selinux/targeted/contexts/files/file_contexts.local

/mysql(/.*)?    system_u:object_r:mysqld_db_t:s0
  12. Now use the restorecon command to apply this context mapping to the running system: 
    ~]# restorecon -R -v /mysql
  13. Now that the /mysql/ location has been labeled with the correct context for MySQL, the mysqld daemon starts: 
    ~]# service mysqld start
Starting MySQL:                                            [  OK  ]
  14. Confirm the context has changed for /mysql/: 
    ~]$ ls -lZ /opt
drwxr-xr-x. mysql mysql system_u:object_r:mysqld_db_t:s0 mysql
  15. The location has been changed and labeled, and the mysqld daemon has started successfully. At this point all running services should be tested to confirm normal operation.

[7] Refer to the MySQL project page for more information.

Chapter 10. PostgreSQL

PostgreSQL is an Object-Relational database management system (DBMS).[8]
In Red Hat Enterprise Linux 6, the postgresql-server package provides PostgreSQL. Run the rpm -q postgresql-server command to see if the postgresql-server package is installed. If it is not installed, run the following command as the root user to install it: 
~]# yum install postgresql-server

10.1. PostgreSQL and SELinux

When PostgreSQL is enabled, it runs confined by default. Confined processes run in their own domains, and are separated from other confined processes. If a confined process is compromised by an attacker, depending on SELinux policy configuration, an attacker's access to resources and the possible damage they can do is limited. The following example demonstrates the PostgreSQL processes running in their own domain. This example assumes the postgresql-server package is installed:
  1. Run the getenforce command to confirm SELinux is running in enforcing mode: 
    ~]$ getenforce
Enforcing
    The getenforce command returns Enforcing when SELinux is running in enforcing mode.
  2. Run the service postgresql start command as the root user to start postgresql: 
    ~]# service postgresql start
Starting postgresql service:                               [  OK  ]
  3. Run the ps -eZ | grep postgres command to view the postgresql processes: 
    ~]$ ps -eZ | grep postgres
unconfined_u:system_r:postgresql_t:s0 395 ?    00:00:00 postmaster
unconfined_u:system_r:postgresql_t:s0 397 ?    00:00:00 postmaster
unconfined_u:system_r:postgresql_t:s0 399 ?    00:00:00 postmaster
unconfined_u:system_r:postgresql_t:s0 400 ?    00:00:00 postmaster
unconfined_u:system_r:postgresql_t:s0 401 ?    00:00:00 postmaster
unconfined_u:system_r:postgresql_t:s0 402 ?    00:00:00 postmaster
    The SELinux context associated with the postgresql processes is unconfined_u:system_r:postgresql_t:s0. The second last part of the context, postgresql_t, is the type. A type defines a domain for processes and a type for files. In this case, the postgresql processes are running in the postgresql_t domain.

10.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
The following types are used with postgresql. Different types allow you to configure flexible access:
postgresql_db_t
This type is used for several locations. The locations labeled with this type are used for data files for PostgreSQL:
  • /usr/lib/pgsql/test/regres
  • /usr/share/jonas/pgsql
  • /var/lib/pgsql/data
  • /var/lib/postgres(ql)?
postgresql_etc_t
This type is used for configuration files in /etc/postgresql/.
postgresql_exec_t
This type is used for several locations. The locations labeled with this type are used for binaries for PostgreSQL:
  • /usr/bin/initdb(.sepgsql)?
  • /usr/bin/(se)?postgres
  • /usr/lib(64)?/postgresql/bin/.*
  • /usr/lib/phsql/test/regress/pg_regress
postgresql_initrc_exec_t
This type is used for the PostgreSQL initialization file located at /etc/rc.d/init.d/postgresql.
postgresql_log_t
This type is used for several locations. The locations labeled with this type are used for log files:
  • /var/lib/pgsql/logfile
  • /var/lib/pgsql/pgstartup.log
  • /var/lib/sepgsql/pgstartup.log
  • /var/log/postgresql
  • /var/log/postgres.log.*
  • /var/log/rhdb/rhdb
  • /var/log/sepostgresql.log.*
postgresql_var_run_t
This type is used for run-time files for PostgreSQL, such as the process id (PID) in /var/run/postgresql/.

10.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
allow_user_postgresql_connect
Having this Boolean enabled allows any user domain (as defined by PostgreSQL) to make connections to the database server.
postgresql_can_rsync
When enabled, this Boolean allows PostgreSQL to use the SSH protocol and the rsync utility.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

10.4. Configuration Examples

10.4.1. PostgreSQL Changing Database Location

When using Red Hat Enterprise Linux 6, the default location for PostgreSQL to store its database is /var/lib/pgsql/data. This is where SELinux expects it to be by default, and hence this area is already labeled appropriately for you, using the postgresql_db_t type.
The area where the database is located can be changed depending on individual environment requirements or preferences, however it is important that SELinux is aware of this new location; that it is labeled accordingly. This example explains how to change the location of a PostgreSQL database and then how to label the new location so that SELinux can still provide its protection mechanisms to the new area based on its contents.
Note that this is an example only and demonstrates how SELinux can affect PostgreSQL. Comprehensive documentation of PostgreSQL is beyond the scope of this document. Refer to the official PostgreSQL documentation for further details. This example assumes that the postgresql-server package is installed.
  1. Run the ls -lZ /var/lib/pgsql command to view the SELinux context of the default database location for postgresql: 
    ~]# ls -lZ /var/lib/pgsql
drwx------. postgres postgres system_u:object_r:postgresql_db_t:s0 data
    This shows postgresql_db_t which is the default context element for the location of database files. This context will have to be manually applied to the new database location that will be used in this example in order for it to function properly.
  2. Create a new directory for the new location of the database(s). In this example, /opt/postgresql/data/ is used. If you use a different location, replace the text in the following steps with your location: 
    ~]# mkdir -p /opt/postgresql/data
  3. Perform a directory listing of the new location. Note that the initial context of the new directory is usr_t. This context is not sufficient for SELinux to offer its protection mechanisms to PostgreSQL. Once the context has been changed, it will be able to function properly in the new area. 
    ~]# ls -lZ /opt/postgresql/
drwxr-xr-x. root root unconfined_u:object_r:usr_t:s0   data
  4. Change the ownership of the new location to allow access by the postgres user and group. This sets the traditional Unix permissions which SELinux will still observe. 
    ~]# chown -R postgres:postgres /opt/postgresql
  5. Open the PostgreSQL init file /etc/rc.d/init.d/postgresql with a text editor and modify the PGDATA and PGLOG variables to point to the new location: 
    ~]# vi /etc/rc.d/init.d/postgresql
PGDATA=/opt/postgresql/data
PGLOG=/opt/postgresql/data/pgstartup.log
    Save this file and exit the text editor.
  6. Initialize the database in the new location. 
    ~]$ su - postgres -c "initdb -D /opt/postgresql/data"
  7. Having changed the database location, starting the service will fail at this point: 
    ~]# service postgresql start
Starting postgresql service: 			[FAILED]
    SELinux has caused the service to not start. This is because the new location is not properly labelled. The following steps explain how to label the new location (/opt/postgresql/) and start the postgresql service properly:
  8. Run the semanage command to add a context mapping for /opt/postgresql/ and any other directories/files within it: 
    ~]# semanage fcontext -a -t postgresql_db_t "/opt/postgresql(/.*)?"
  9. This mapping is written to the /etc/selinux/targeted/contexts/files/file_contexts.local file: 
    ~]# grep -i postgresql /etc/selinux/targeted/contexts/files/file_contexts.local

/opt/postgresql(/.*)?    system_u:object_r:postgresql_db_t:s0
  10. Now use the restorecon command to apply this context mapping to the running system: 
    ~]# restorecon -R -v /opt/postgresql
  11. Now that the /opt/postgresql/ location has been labeled with the correct context for PostgreSQL, the postgresql service will start successfully: 
    ~]# service postgresql start
Starting postgreSQL service:                                            [  OK  ]
  12. Confirm the context is correct for /opt/postgresql/: 
    ~]$ ls -lZ /opt
drwxr-xr-x. root root system_u:object_r:postgresql_db_t:s0 postgresql
  13. Check with the ps command that the postgresql process displays the new location: 
    ~]# ps aux | grep -i postmaster

postgres 21564  0.3  0.3  42308  4032 ?        S    10:13   0:00 /usr/bin/postmaster -p 5432 -D /opt/postgresql/data/
  14. The location has been changed and labeled, and the postgresql daemon has started successfully. At this point all running services should be tested to confirm normal operation.

[8] Refer to the PostgreSQL project page for more information.

Chapter 11. rsync

The rsync utility performs fast file transfer and it is used for synchronizing data between systems. [9]
When using Red Hat Enterprise Linux, the rsync package provides rsync. Run the rpm -q rsync command to see if the rsync package is installed. If it is not installed, run the following command as the root user to install it: 
~]# yum install rsync

11.1. rsync and SELinux

SELinux requires files to have an extended attribute to define the file type. Policy governs the access daemons have to these files. If you want to share files using the rsync daemon, you must label the files and directories with the public_content_t type. Like most services, correct labeling is required for SELinux to perform its protection mechanisms over rsync.[10]

11.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
The following types are used with rsync. Different types all you to configure flexible access:
public_content_t
This is a generic type used for the location of files (and the actual files) to be shared via rsync. If a special directory is created to house files to be shared with rsync, the directory and its contents need to have this label applied to them.
rsync_exec_t
This type is used for the /usr/bin/rsync system binary.
rsync_log_t
This type is used for the rsync log file, located at /var/log/rsync.log by default. To change the location of the file rsync logs to, use the --log-file=FILE option to the rsync command at run-time.
rsync_var_run_t
This type is used for the rsyncd lock file, located at /var/run/rsyncd.lock. This lock file is used by the rsync server to manage connection limits.
rsync_data_t
This type is used for files and directories which you want to use as rsync domains and isolate them from the access scope of other services. Also, the public_content_t is a general SELinux context type, which can be used when a file or a directory interacts with multiple services (for example, FTP and NFS directory as an rsync domain).
rsync_etc_t
This type is used for rsync-related files in the /etc/ directory.

11.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
allow_rsync_anon_write
Having this Boolean enabled allows rsync in the rsync_t domain to manage files, links and directories that have a type of public_content_rw_t. Often these are public files used for public file transfer services. Files and directories must be labeled public_content_rw_t.
rsync_client
Having this Boolean enabled allows rsync to initiate connections to ports defined as rsync_port_t, as well as allowing rsync to manage files, links and directories that have a type of rsync_data_t. Note that the rsync daemon must be in the rsync_t domain in order for SELinux to enact its control over rsync. The configuration example in this chapter demonstrates rsync running in the rsync_t domain.
rsync_export_all_ro
Having this Boolean enabled allows rsync in the rsync_t domain to export NFS and CIFS volumes with read-only access to clients.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

11.4. Configuration Examples

11.4.1. Rsync as a daemon

When using Red Hat Enterprise Linux, rsync can be used as a daemon, so that multiple clients can directly communicate with it as a central server in order to house centralized files and keep them synchronized. The following example demonstrates running rsync as a daemon over a network socket in the correct domain, and how SELinux expects this daemon to be running on a pre-defined (in SELinux policy) TCP port. This example then shows how to modify SELinux policy to allow the rsync daemon to run normally on a non-standard port.
This example is performed on a single system to demonstrate SELinux policy and its control over local daemons and processes. Note that this is an example only and demonstrates how SELinux can affect rsync. Comprehensive documentation of rsync is beyond the scope of this document. See the official rsync documentation for further details. This example assumes that the rsync, setroubleshoot-server and audit packages are installed, that the SELinux targeted policy is used, and that SELinux is running in enforcing mode.

Procedure 11.1. Getting rsync to launch as rsync_t

  1. Run the getenforce command to confirm SELinux is running in enforcing mode: 
    ~]$ getenforce
Enforcing
    The getenforce command returns Enforcing when SELinux is running in enforcing mode.
  2. Run the which command to confirm that the rsync binary is in the system path: 
    ~]$ which rsync
/usr/bin/rsync
  3. When running rsync as a daemon, a configuration file should be used and saved as /etc/rsyncd.conf. Note that the following configuration file used in this example is very simple and is not indicative of all the possible options that are available, rather it is just enough to demonstrate the rsync daemon: 
    log file = /var/log/rsync.log
pid file = /var/run/rsyncd.pid
lock file = /var/run/rsync.lock
[files]
        path = /srv/files
        comment = file area
        read only = false
	timeout = 300
  4. Now that a simple configuration file exists for rsync to operate in daemon mode, this step demonstrates that simply running the rsync --daemon command is not sufficient for SELinux to offer its protection over rsync. See the following output: 
    ~]# rsync --daemon

~]# ps x | grep rsync
 8231 ?        Ss     0:00 rsync --daemon
 8233 pts/3    S+     0:00 grep rsync

~]# ps -eZ | grep rsync
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 8231 ? 00:00:00 rsync
    Note that in the output from the final ps command, the context shows the rsync daemon running in the unconfined_t domain. This indicates that rsync has not transitioned to the rsync_t domain as it was launched by the rsync --daemon command. At this point, SELinux cannot enforce its rules and policy over this daemon. See the following steps to see how to fix this problem.
    In the following steps, rsync transitions to the rsync_t domain because it launched it from a properly-labeled init script. Only then can SELinux and its protection mechanisms have an effect over rsync. This rsync process should be killed before proceeding to the next step.
  5. A custom init script for rsync is needed for this step. Save the following to /etc/rc.d/init.d/rsyncd. 
    #!/bin/bash

# Source function library.
. /etc/rc.d/init.d/functions

[ -f /usr/bin/rsync ] || exit 0

case "$1" in
start)
action "Starting rsyncd: " /usr/bin/rsync --daemon
;;
stop)
action "Stopping rsyncd: " killall rsync
;;
*)
echo "Usage: rsyncd {start|stop}"
exit 1
esac
exit 0
    The following steps show how to label this script as initrc_exec_t:
  6. Run the semanage command to add a context mapping for /etc/rc.d/init.d/rsyncd: 
    ~]# semanage fcontext -a -t initrc_exec_t "/etc/rc.d/init.d/rsyncd"
  7. This mapping is written to the /etc/selinux/targeted/contexts/files/file_contexts.local file: 
    ~]# grep rsync /etc/selinux/targeted/contexts/files/file_contexts.local

/etc/rc.d/init.d/rsyncd    system_u:object_r:initrc_exec_t:s0
  8. Now use the restorecon command to apply this context mapping to the running system: 
    ~]# restorecon -R -v /etc/rc.d/init.d/rsyncd
  9. Run the ls -lZ command to confirm the script has been labeled appropriately. Note that in the following output, the script has been labeled as initrc_exec_t: 
    ~]$ ls -lZ /etc/rc.d/init.d/rsyncd
-rwxr-xr-x. root root system_u:object_r:initrc_exec_t:s0 /etc/rc.d/init.d/rsyncd
  10. Turn on the rsync_server SELinux boolean: 
    ~]# setsebool rsync_server on
    Note that this setting is not permanent and as such, it will revert to its original state after a reboot. To make the setting permanent, use the -P option with the setsebool command.
  11. Launch rsyncd via the new script. Now that rsync has started from an init script that had been appropriately labeled, the process has started as rsync_t: 
    ~]# service rsyncd start
Starting rsyncd:                                           [  OK  ]

$ ps -eZ | grep rsync
unconfined_u:system_r:rsync_t:s0 9794 ?        00:00:00 rsync
    SELinux can now enforce its protection mechanisms over the rsync daemon as it is now runing in the rsync_t domain.
This example demonstrated how to get rsyncd running in the rsync_t domain. The next example shows how to get this daemon successfully running on a non-default port. TCP port 10000 is used in the next example.

Procedure 11.2. Running the rsync daemon on a non-default port

  1. Modify the /etc/rsyncd.conf file and add the port = 10000 line at the top of the file in the global configuration area (that is, before any file areas are defined). The new configuration file will look like: 
    log file = /var/log/rsyncd.log
pid file = /var/run/rsyncd.pid
lock file = /var/run/rsync.lock
port = 10000
[files]
        path = /srv/files
        comment = file area
        read only = false
	timeout = 300
  2. After launching rsync from the init script with this new setting, a denial similar to the following is logged by SELinux: 
    Jul 22 10:46:59 localhost setroubleshoot: SELinux is preventing the rsync (rsync_t) from binding to port 10000. For complete SELinux messages, run sealert -l c371ab34-639e-45ae-9e42-18855b5c2de8
  3. Run semanage to add TCP port 10000 to SELinux policy in rsync_port_t: 
    ~]# semanage port -a -t rsync_port_t -p tcp 10000
  4. Now that TCP port 10000 has been added to SELinux policy for rsync_port_t, rsyncd will start and operate normally on this port: 
    ~]# service rsyncd start
Starting rsyncd:                                           [  OK  ]

    ~]# netstat -lnp | grep 10000
tcp        0      0 0.0.0.0:10000   0.0.0.0:*      LISTEN      9910/rsync
SELinux has had its policy modified and is now permitting rsyncd to operate on TCP port 10000.

[9] Refer to the Rsync project page for more information.
[10] Refer to the rsync_selinux(8) manual page for more information about rsync and SELinux.

Chapter 12. Postfix

Postfix is an open-source Mail Transport Agent (MTA), which supports protocols like LDAP, SMTP AUTH (SASL), and TLS.[11]
In Red Hat Enterprise Linux, the postfix package provides postfix. Run the rpm -q postfix command to see if the postfix package is installed. If it is not installed, run the following command as the root user to install it: 
~]# yum install postfix

12.1. Postfix and SELinux

When Postfix is enabled, it runs confined by default. Confined processes run in their own domains, and are separated from other confined processes. If a confined process is compromised by an attacker, depending on SELinux policy configuration, an attacker's access to resources and the possible damage they can do is limited. The following example demonstrates the Postfix and related processes running in their own domain. This example assumes the postfix package is installed and that the Postfix service has been started:
  1. Run the getenforce command to confirm SELinux is running in enforcing mode: 
    ~]$ getenforce
Enforcing
    The getenforce command returns Enforcing when SELinux is running in enforcing mode.
  2. Run the service postfix start command as the root user to start postfix: 
    ~]# service postfix start
Starting postfix:                               [  OK  ]
  3. Run the ps -eZ | grep postfix command to view the postfix processes: 
    ~]$ ps -eZ | grep postfix
system_u:system_r:postfix_master_t:s0 1651 ?   00:00:00 master
system_u:system_r:postfix_pickup_t:s0 1662 ?   00:00:00 pickup
system_u:system_r:postfix_qmgr_t:s0 1663 ?     00:00:00 qmgr
    In the output above, the SELinux context associated with the Postfix master process is system_u:system_r:postfix_master_t:s0. The second last part of the context, postfix_master_t, is the type for this process. A type defines a domain for processes and a type for files. In this case, the master process is running in the postfix_master_t domain.

12.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
The following types are used with Postfix. Different types all you to configure flexible access:
postfix_etc_t
This type is used for configuration files for Postfix in the /etc/postfix/ directory.
postfix_data_t
This type is used for Postfix data files in the /var/lib/postfix/ directory.
postfix_var_run_t
This type is used for Postfix files stored in the /run/ directory.
postfix_initrc_exec_t
This type is used for transition of Postfix executable files to the postfix_initrc_t domain.
postfix_spool_t
This type is used for Postfix files stored in the /var/spool/ directory.

Note

To see the full list of files and their types for Postfix, run the following command: 
~]$ grep postfix /etc/selinux/targeted/contexts/files/file_contexts

12.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
allow_postfix_local_write_mail_spool
Having this Boolean enables Postfix to write to the local mail spool on the system. Postfix requires this Boolean to be enabled for normal operation when local spools are used.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

12.4. Configuration Examples

12.4.1. SpamAssassin and Postfix

SpamAssasin is an open-source mail filter that provides a way to filter unsolicited email (spam messages) from incoming email.[12]
When using Red Hat Enterprise Linux, the spamassassin package provides SpamAssassin. Run the rpm -q spamassassin command to see if the spamassassin package is installed. If it is not installed, run the following command as the root user to install it: 
~]# yum install spamassassin
SpamAssassin operates in tandom with a mailer such as Postfix to provide spam-filtering capabilities. In order for SpamAssassin to effectively intercept, analyze and filter mail, it must listen on a network interface. The default port for SpamAssassin is TCP/783, however this can be changed. The following example provides a real-world demonstration of how SELinux complements SpamAssassin by only allowing it access to a certain port by default. This example will then demonstrate how to change the port and have SpamAssassin operate on a non-default port.
Note that this is an example only and demonstrates how SELinux can affect a simple configuration of SpamAssassin. Comprehensive documentation of SpamAssassin is beyond the scope of this document. Refer to the official SpamAssassin documentation for further details. This example assumes the spamassassin is installed, that any firewall has been configured to allow access on the ports in use, that the SELinux targeted policy is used, and that SELinux is running in enforcing mode:

Procedure 12.1. Running SpamAssassin on a non-default port

  1. Run the semanage command to show the port that SELinux allows spamd to listen on by default: 
    ~]# semanage port -l | grep spamd
spamd_port_t		tcp	783
    This output shows that TCP/783 is defined in spamd_port_t as the port for SpamAssassin to operate on.
  2. Edit the /etc/sysconfig/spamassassin configuration file and modify it so that it will start SpamAssassin on the example port TCP/10000: 
    # Options to spamd
SPAMDOPTIONS="-d -p 10000 -c m5 -H"
    This line now specifies that SpamAssassin will operate on port 10000. The rest of this example will show how to modify SELinux policy to allow this socket to be opened.
  3. Start SpamAssassin and an error message similar to the following will appear: 
    ~]# service spamassassin start
Starting spamd: [2203] warn: server socket setup failed, retry 1: spamd: could not create INET socket on 127.0.0.1:10000: Permission denied
[2203] warn: server socket setup failed, retry 2: spamd: could not create INET socket on 127.0.0.1:10000: Permission denied
[2203] error: spamd: could not create INET socket on 127.0.0.1:10000: Permission denied
spamd: could not create INET socket on 127.0.0.1:10000: Permission denied
                                                           [FAILED]
    This output means that SELinux has blocked access to this port.
  4. A denial similar to the following will be logged by SELinux: 
    SELinux is preventing the spamd (spamd_t) from binding to port 10000.
  5. As the root user, run semanage to modify SELinux policy in order to allow SpamAssassin to operate on the example port (TCP/10000): 
    ~]# semanage port -a -t spamd_port_t -p tcp 10000
  6. Confirm that SpamAssassin will now start and is operating on TCP port 10000: 
    ~]# service spamassassin start
Starting spamd:					[ OK ]

~]# netstat -lnp | grep 10000
tcp	0	0 127.0.0.1:10000	0.0.0.0:*	LISTEN	2224/spamd.pid
  7. At this point, spamd is properly operating on TCP port 10000 as it has been allowed access to that port by SELinux policy.

[11] Refer to the Postfix project page for more information.
[12] Refer to the SpamAssassin project page for more information.

Chapter 13. DHCP

DHCPD is the daemon used in Red Hat Enterprise Linux to dynamically deliver and configure Layer 3 TCP/IP details for clients.
The dhcp package provides the DHCP server, dhcpd. Run the rpm -q dhcp command to see if the dhcp package is installed. If it is not installed, run the following command as the root user to install it: 
~]# yum install dhcp

13.1. DHCP and SELinux

When DHCPD is enabled, it runs confined by default. Confined processes run in their own domains, and are separated from other confined processes. If a confined process is compromised by an attacker, depending on SELinux policy configuration, an attacker's access to resources and the possible damage they can do is limited. The following example demonstrates the DHCPD and related processes running in their own domain. This example assumes the dhcp package is installed and that the DHCPD service has been started:
  1. Run the getenforce command to confirm SELinux is running in enforcing mode: 
    ~]$ getenforce
Enforcing
    The getenforce command returns Enforcing when SELinux is running in enforcing mode.
  2. Run the service dhcpd start command as the root user to start DHCPD: 
    ~]# service dhcpd start
Starting dhcpd:                               [  OK  ]
  3. Run the ps -eZ | grep dhcpd command to view the dhcpd processes: 
    ~]$ ps -eZ | grep dhcpd
unconfined_u:system_r:dhcpd_t:s0 5483 ?        00:00:00 dhcpd
    The SELinux context associated with the dhcpd process is unconfined_u:system_r:dhcpd_t:s0.

13.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
The following types are used with dhcpd:
dhcp_etc_t
This type is mainly used for files in /etc, including configuration files.
dhcpd_var_run_t
This type is used for the PID file for dhcpd, in /var/run.
dhcpd_exec_t
This type is used for transition of DHCP executable files to the dhcpd_t domain.
dhcpd_initrc_exec_t
This type is used for transition of DHCP executable files to the dhcpd_initrc_t domain.

Note

To see the full list of files and their types for dhcp, run the following command: 
~]$ grep dhcp /etc/selinux/targeted/contexts/files/file_contexts

Chapter 14. OpenShift by Red Hat

OpenShift by Red Hat is a Platform as a Service (PaaS) that enables developers to build and deploy web applications. OpenShift provides a wide selection of programming languages and frameworks including Java, Ruby, and PHP. It also provides integrated developer tools to support the application life cycle, including Eclipse integration, JBoss Developer Studio, and Jenkins. OpenShift uses an open source ecosystem to provide a platform for mobile applications, database services, and more. [13]

14.1. OpenShift and SELinux

SELinux provides better security control over applications that use OpenShift because all processes are labeled according to the SELinux policy. Therefore, SELinux protects OpenShift from possible malicious attacks within different gears running on the same node.
See the Dan Walsh's presentation for more information about SELinux and OpenShift.

14.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
The following types are used with OpenShift. Different types allow you to configure flexible access:

Process types

openshift_t
The OpenShift process is associated with the openshift_t SELinux type.

Types on executables

openshift_cgroup_read_exec_t
SELinux allows files with this type to transition an executable to the openshift_cgroup_read_t domain.
openshift_cron_exec_t
SELinux allows files with this type to transition an executable to the openshift_cron_t domain.
openshift_initrc_exec_t
SELinux allows files with this type to transition an executable to the openshift_initrc_t domain.

Writable types

openshift_cgroup_read_tmp_t
This type allows OpenShift control groups (cgroup) read and access temporary files in the /tmp/ directory.
openshift_cron_tmp_t
This type allows storing temporary files of the OpenShift cron jobs in /tmp/.
openshift_initrc_tmp_t
This type allows storing the OpenShift initrc temporary files in /tmp/.
openshift_log_t
Files with this type are treated as OpenShift log data, usually stored under the /var/log/ directory.
openshift_rw_file_t
OpenShift have permission to read and to write to files labeled with this type.
openshift_tmp_t
This type is used for storing the OpenShift temporary files in /tmp/.
openshift_tmpfs_t
This type allows storing the OpenShift data on a tmpfs file system.
openshift_var_lib_t
This type allows storing the OpenShift files in the /var/lib/ directory.
openshift_var_run_t
This type allows storing the OpenShift files in the /run/ or /var/run/ directory.

14.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
openshift_use_nfs
Having this Boolean enabled allows installing OpenShift on an NFS share.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

14.4. Configuration Examples

14.4.1. Changing the Default OpenShift Directory

By default, OpenShift stores its data in the /var/lib/openshift/ directory, which is labeled with the openshift_var_lib_t SELinux type. To allow OpenShift to store data in a different directory, label the new directory with the proper SELinux context.
The following procedure shows how to change the default OpenShift directory for storing data to /srv/openshift/:

Procedure 14.1. Changing the Default OpenShift Directory for Storing Data

  1. As root, create a new /openshift/ directory within the /srv/ directory. The new directory is labeled with the var_t type: 
    ~]# mkdir /srv/openshift
    ~]$ ls -Zd /srv/openshift
drwxr-xr-x. root root unconfined_u:object_r:var_t:s0   openshift/
  2. As root, use the semanage utility to map /srv/openshift/ to the proper SELinux context: 
    ~]# semanage fcontext -a -e /var/lib/openshift /srv/openshift
  3. Then, use the restorecon utility as root to apply the changes: 
    ~]# restorecon -R -v /srv/openshift
  4. The /srv/openshift/ directory is now labeled with the correct openshift_var_lib_t type: 
    ~]$ls -Zd /srv/openshift
drwxr-xr-x. root root unconfined_u:object_r:openshift_var_lib_t:s0   openshift/

Chapter 15. Red Hat Gluster Storage

Red Hat Gluster Storage provides flexible and affordable unstructured data storage for the enterprise. GlusterFS, a key building block of Gluster, is based on a stackable user-space design and aggregates various storage servers over a network and interconnects them into one large parallel network file system. The POSIX-compatible GlusterFS servers, which use the XFS file system format to store data on disks, can be accessed using industry standard access protocols including NFS and CIFS.
See the Red Hat Gluster Storage collection of guides for more information.
The glusterfs package provides Red Hat Gluster Storage. For detailed information about its installation process, see the Installation Guide for Red Hat Gluster Storage.

15.1. Red Hat Gluster Storage and SELinux

When enabled, SELinux serves as an additional security layer by providing flexible mandatory access control for the glusterd (GlusterFS Management Service) and glusterfsd (NFS server) processes as a part of Red Hat Gluster Storage. These processes have advanced process isolation unbounded with the glusterd_t SELinux type.

15.2. Types

The main permission control method used in SELinux targeted policy to provide advanced process isolation is Type Enforcement. All files and processes are labeled with a type: types define a SELinux domain for processes and a SELinux type for files. SELinux policy rules define how types access each other, whether it be a domain accessing a type, or a domain accessing another domain. Access is only allowed if a specific SELinux policy rule exists that allows it.
The following types are used with Red Hat Gluster Storage. Different types allow you to configure flexible access:

Process types

glusterd_t
The Gluster processes are associated with the glusterd_t SELinux type.

Types on executables

glusterd_initrc_exec_t
The SELinux-specific script type context for the Gluster init script files.
glusterd_exec_t
The SELinux-specific executable type context for the Gluster executable files.

Port Types

gluster_port_t
This type is defined for glusterd. By default, glusterd uses 204007-24027, and 38465-38469 TCP ports.

File Contexts

glusterd_brick_t
This type is used for files threated as glusterd brick data.
glusterd_conf_t
This type is associated with the glusterd configuration data, usually stored in the /etc/ directory.
glusterd_log_t
Files with this type are treated as glusterd log data, usually stored under the /var/log/ directory.
glusterd_tmp_t
This type is used for storing the glusterd temporary files in the /tmp/ directory.
glusterd_var_lib_t
This type allows storing the glusterd files in the /var/lib/ directory.
glusterd_var_run_t
This type allows storing the glusterd files in the /run/ or /var/run/ directory.

15.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you need to specify how you run your services. Use the following Booleans to set up SELinux:
gluster_export_all_ro
Having this Boolean enabled allows glusterfsd to share files and directory as read-only. This Boolean is disabled by default.
gluster_export_all_rw
Having this Boolean enabled allows glusterfsd to share files and directories with read and write access. This Boolean is enabled by default.
gluster_anon_write
Having this Boolean enabled allows glusterfsd to modify public files labeled with the public_content_rw_t SELinux type.

Note

Due to the continuous development of the SELinux policy, the list above might not contain all Booleans related to the service at all times. To list them, run the following command as root: 
~]# semanage boolean -l | grep service_name

15.4. Configuration Examples

15.4.1. Labeling Gluster Bricks

A Gluster brick is an export directory on a server in the trusted storage pool. In case that the brick is not labeled with the correct SELinux context, glusterd_brick_t, SELinux denies certain file access operations and generates various AVC messages.
The following procedure shows how to label Gluster bricks with the correct SELinux context. The procedure assumes that you previously created and formatted a logical volume, for example /dev/rhgs/gluster, to be used as the Gluster brick.
For detailed information about Gluster bricks, see the Red Hat Gluster Storage Volumes chapter in the Administration Guide for Red Hat Gluster Storage.

Procedure 15.1. How to Label a Gluster Brick

  1. Create a directory to mount the previously formatted logical volume. For example: 
    ~]# mkdir /mnt/brick1
  2. Mount the logical volume, in this case /dev/vg-group/gluster, to the /mnt/brick1/ directory created in the previous step. 
    ~]# mount /dev/vg-group/gluster /mnt/brick1/
    Note that the mount command mounts devices only temporarily. To mount the device permanently, add an entry similar as the following one to the /etc/fstab file: 
    /dev/vg-group/gluster    /mnt/brick1  xfs rw,inode64,noatime,nouuid      1 2
    For more information, see the fstab(5) manual page.
  3. Check the SELinux context of /mnt/brick1/: 
    ~]$ ls -lZd /mnt/brick1/
drwxr-xr-x. root root system_u:object_r:unlabeled_t:s0 /mnt/brick1/
    The directory is labeled with the unlabeled_t SELinux type.
  4. Change the SELinux type of /mnt/brick1/ to the glusterd_brick_t SELinux type: 
    ~]# semanage fcontext -a -t glusterd_brick_t "/mnt/brick1(/.*)?"
  5. Use the restorecon utility to apply the changes: 
    ~]# restorecon -Rv /mnt/brick1
  6. Finally, verify that the context has been successfully changed: 
    ~]$ ls -lZd /mnt/brick1
drwxr-xr-x. root root system_u:object_r:glusterd_brick_t:s0 /mnt/brick1/

Chapter 16. References

The following references are pointers to additional information that is relevant to SELinux but beyond the scope of this guide. Note that due to the rapid development of SELinux, some of this material may only apply to specific releases of Red Hat Enterprise Linux.

Books

SELinux by Example
Mayer, MacMillan, and Caplan
Prentice Hall, 2007
SELinux: NSA's Open Source Security Enhanced Linux
Bill McCarty
O'Reilly Media Inc., 2004

Tutorials and Help

Tutorials and talks from Russell Coker
http://www.coker.com.au/selinux/talks/ibmtu-2004/
Dan Walsh's Journal
http://danwalsh.livejournal.com/
Red Hat Knowledgebase
https://access.redhat.com/site/

General Information

NSA SELinux main website
http://www.nsa.gov/research/selinux/index.shtml
NSA SELinux FAQ
http://www.nsa.gov/research/selinux/faqs.shtml

Community

SELinux Project Wiki
http://selinuxproject.org/page/Main_Page
SELinux community page
http://selinux.sourceforge.net/
IRC
irc.freenode.net, #selinux

Appendix A. Revision History

Revision History
Revision 9-1Wed Mar 15 2017Mirek Jahoda
Version for 6.9 GA publication.
Revision 9-0Wed Dec 21 2016Mirek Jahoda
Version for 6.9 Beta publication.
Revision 8-0Wed May 3 2016Robert Krátký
Red Hat Enterprise Linux 6.8 GA release of the Managing Confined Services guide.
Revision 7-1Thu Jul 9 2015Barbora Ančincová
Red Hat Enterprise Linux 6.7 GA release of the Managing Confined Services guide.
Revision 6-0Fri Oct 10 2014Barbora Ančincová
Red Hat Enterprise Linux 6.4 GA release of the Managing Confined Services guide.
Revision 5-0Tue Nov 19 2013Tomáš Čapek
Red Hat Enterprise Linux 6.5 GA release of the Managing Confined Services guide.
Revision 4-0Fri Feb 22 2013Tomáš Čapek
Red Hat Enterprise Linux 6.4 GA release of the Managing Confined Services guide.
Revision 3-0Wed Jun 20 2012Martin Prpič
Red Hat Enterprise Linux 6.3 GA release of the Managing Confined Services guide.
Revision 2-0Tue Dec 6 2011Martin Prpič
Red Hat Enterprise Linux 6.2 GA release of the Managing Confined Services guide.
Revision 1-0Thu May 19 2011Martin Prpič
Red Hat Enterprise Linux 6.1 GA release of the Managing Confined Services guide.
Revision 0-0Tue Nov 9 2010Scott Radvan
6.0 GA release

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