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Security Guide

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Security Guide

Introduces basic concepts of system security, covering both local and network security aspects. Shows how to use the product inherent security software like AppArmor or the auditing system that reliably collects information about any security-relevant events.

Publication Date: December 19, 2018

About This Guide

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1 Security and Confidentiality

1.1 Overview
1.2 Passwords
1.3 System Integrity
1.4 File Access
1.5 Networking
1.6 Software Vulnerabilities
1.7 Malware
1.8 Important Security Tips
1.9 Reporting Security Issues

I Authentication

2 Authentication with PAM

2.1 What is PAM?
2.2 Structure of a PAM Configuration File
2.3 The PAM Configuration of sshd
2.4 Configuration of PAM Modules
2.5 Configuring PAM Using pam-config
2.6 Manually Configuring PAM
2.7 For More Information

3 Using NIS

3.1 Configuring NIS Servers
3.2 Configuring NIS Clients

4 Setting Up Authentication Servers and Clients Using YaST

4.1 Configuring an Authentication Server with YaST
4.2 Configuring an Authentication Client with YaST
4.3 SSSD

5 LDAP—A Directory Service

5.1 LDAP versus NIS
5.2 Structure of an LDAP Directory Tree
5.3 Configuring an LDAP Client with YaST
5.4 Configuring LDAP Users and Groups in YaST
5.5 Manually Configuring an LDAP Server
5.6 Manually Administering LDAP Data
5.7 For More Information

6 Network Authentication with Kerberos

6.1 Conceptual Overview
6.2 Kerberos Terminology
6.3 How Kerberos Works
6.4 User View of Kerberos
6.5 Installing and Administering Kerberos
6.6 Setting up Kerberos using LDAP and Kerberos Client
6.7 Kerberos and NFS
6.8 For More Information

7 Active Directory Support

7.1 Integrating Linux and Active Directory Environments
7.2 Background Information for Linux Active Directory Support
7.3 Configuring a Linux Client for Active Directory
7.4 Logging In to an Active Directory Domain
7.5 Changing Passwords

II Local Security

8 Configuring Security Settings with YaST

8.1 Security Overview
8.2 Predefined Security Configurations
8.3 Password Settings
8.4 Boot Settings
8.5 Login Settings
8.6 User Addition
8.7 Miscellaneous Settings

9 Authorization with PolKit

9.1 Conceptual Overview
9.2 Authorization Types
9.3 Querying Privileges
9.4 Modifying Configuration Files
9.5 Restoring the Default Privileges

10 Access Control Lists in Linux

10.1 Traditional File Permissions
10.2 Advantages of ACLs
10.3 Definitions
10.4 Handling ACLs
10.5 ACL Support in Applications
10.6 For More Information

11 Encrypting Partitions and Files

11.1 Setting Up an Encrypted File System with YaST
11.2 Encrypting Files with GPG

12 Certificate Store

12.1 Activating Certificate Store
12.2 Importing Certificates

13 Intrusion Detection with AIDE

13.1 Why Use AIDE?
13.2 Setting Up an AIDE Database
13.3 Local AIDE Checks
13.4 System Independent Checking
13.5 For More Information

III Network Security

14 X Window System and X Authentication

15 SSH: Secure Network Operations

15.1 ssh—Secure Shell
15.2 scp—Secure Copy
15.3 sftp—Secure File Transfer
15.4 The SSH Daemon (sshd)
15.5 SSH Authentication Mechanisms
15.6 Port Forwarding
15.7 For More Information

16 Masquerading and Firewalls

16.1 Packet Filtering with iptables
16.2 Masquerading Basics
16.3 Firewalling Basics
16.4 firewalld
16.5 For More Information

17 Configuring a VPN Server

17.1 Conceptual Overview
17.2 Setting Up a Simple Test Scenario
17.3 Setting Up Your VPN Server Using a Certificate Authority
17.4 Setting Up a VPN Server or Client Using YaST
17.5 For More Information

18 Managing X.509 Certification

18.1 The Principles of Digital Certification
18.2 YaST Modules for CA Management

IV Confining Privileges with AppArmor

19 Introducing AppArmor

19.1 AppArmor Components
19.2 Background Information on AppArmor Profiling

20 Getting Started

20.1 Installing AppArmor
20.2 Enabling and Disabling AppArmor
20.3 Choosing Applications to Profile
20.4 Building and Modifying Profiles
20.5 Updating Your Profiles

21 Immunizing Programs

21.1 Introducing the AppArmor Framework
21.2 Determining Programs to Immunize
21.3 Immunizing cron Jobs
21.4 Immunizing Network Applications

22 Profile Components and Syntax

22.1 Breaking an AppArmor Profile into Its Parts
22.2 Profile Types
22.3 Include Statements
22.4 Capability Entries (POSIX.1e)
22.5 Network Access Control
22.6 Profile Names, Flags, Paths, and Globbing
22.7 File Permission Access Modes
22.8 Mount Rules
22.9 Pivot Root Rules
22.10 PTrace Rules
22.11 Signal Rules
22.12 Execute Modes
22.13 Resource Limit Control
22.14 Auditing Rules

23 AppArmor Profile Repositories

24 Building and Managing Profiles with YaST

24.1 Manually Adding a Profile
24.2 Editing Profiles
24.3 Deleting a Profile
24.4 Managing AppArmor

25 Building Profiles from the Command Line

25.1 Checking the AppArmor Status
25.2 Building AppArmor Profiles
25.3 Adding or Creating an AppArmor Profile
25.4 Editing an AppArmor Profile
25.5 Unloading Unknown AppArmor Profiles
25.6 Deleting an AppArmor Profile
25.7 Two Methods of Profiling
25.8 Important File Names and Directories

26 Profiling Your Web Applications Using ChangeHat

26.1 Configuring Apache for mod_apparmor
26.2 Managing ChangeHat-Aware Applications

27 Confining Users with pam_apparmor

28 Managing Profiled Applications

28.1 Reacting to Security Event Rejections
28.2 Maintaining Your Security Profiles

29 Support

29.1 Updating AppArmor Online
29.2 Using the Man Pages
29.3 For More Information
29.4 Troubleshooting
29.5 Reporting Bugs for AppArmor

30 AppArmor Glossary

V SELinux

31 Configuring SELinux

31.1 Why Use SELinux?
31.2 Policy
31.3 Installing SELinux Packages and Modifying GRUB 2
31.4 SELinux Policy
31.5 Configuring SELinux
31.6 Managing SELinux
31.7 Troubleshooting

VI The Linux Audit Framework

32 Understanding Linux Audit

32.1 Introducing the Components of Linux Audit
32.2 Configuring the Audit Daemon
32.3 Controlling the Audit System Using auditctl
32.4 Passing Parameters to the Audit System
32.5 Understanding the Audit Logs and Generating Reports
32.6 Querying the Audit Daemon Logs with ausearch
32.7 Analyzing Processes with autrace
32.8 Visualizing Audit Data
32.9 Relaying Audit Event Notifications

33 Setting Up the Linux Audit Framework

33.1 Determining the Components to Audit
33.2 Configuring the Audit Daemon
33.3 Enabling Audit for System Calls
33.4 Setting Up Audit Rules
33.5 Configuring Audit Reports
33.6 Configuring Log Visualization

34 Introducing an Audit Rule Set

34.1 Adding Basic Audit Configuration Parameters
34.2 Adding Watches on Audit Log Files and Configuration Files
34.3 Monitoring File System Objects
34.4 Monitoring Security Configuration Files and Databases
34.5 Monitoring Miscellaneous System Calls
34.6 Filtering System Call Arguments
34.7 Managing Audit Event Records Using Keys

35 Useful Resources

A GNU Licenses

A.1 GNU Free Documentation License

List of Figures

3.1 NIS Server Setup
3.2 Master Server Setup
3.3 Changing the Directory and Synchronizing Files for a NIS Server
3.4 NIS Server Maps Setup
3.5 Setting Request Permissions for a NIS Server
3.6 Setting Domain and Address of a NIS Server
4.1 YaST Authentication Server Configuration
4.2 YaST LDAP Server—New Database
4.3 YaST Kerberos Authentication
4.4 YaST Editing Authentication Server Configuration
4.5 YaST Authentication Server Database Configuration
5.1 Structure of an LDAP Directory
5.2 LDAP and Kerberos Client Window
6.1 Kerberos Network Topology
6.2 LDAP and Kerberos Client Window
7.1 Schema of Winbind-based Active Directory Authentication
7.2 Main Window of User Logon Management
7.3 Enrolling into a Domain
7.4 Configuration Window of User Logon Management
7.5 Determining Windows Domain Membership
7.6 Providing Administrator Credentials
8.1 YaST Security Center and Hardening: Security Overview
10.1 Minimum ACL: ACL Entries Compared to Permission Bits
10.2 Extended ACL: ACL Entries Compared to Permission Bits
16.1 iptables: A Packet's Possible Paths
17.1 Routed VPN
17.2 Bridged VPN - Scenario 1
17.3 Bridged VPN - Scenario 2
17.4 Bridged VPN - Scenario 3
18.1 YaST CA Module—Basic Data for a Root CA
18.2 YaST CA Module—Using a CA
18.3 Certificates of a CA
18.4 YaST CA Module—Extended Settings
25.1 aa-notify Message in GNOME
26.1 Adminer Login Page
31.1 Selecting all SELinux Packages in YaST
32.1 Introducing the Components of Linux Audit
32.2 Flow Graph—Program versus System Call Relationship
32.3 Bar Chart—Common Event Types

List of Tables

5.1 Commonly Used Object Classes and Attributes
10.1 ACL Entry Types
10.2 Masking Access Permissions
13.1 Important AIDE Check Boxes
15.1
16.1 Important Sysconfig Variables for Static Port Configuration
18.1 X.509v3 Certificate
18.2 X.509 Certificate Revocation List (CRL)
18.3 Passwords during LDAP Export
29.1 Man Pages: Sections and Categories
32.1 Audit Status Flags

List of Examples

2.1 PAM Configuration for sshd (/etc/pam.d/sshd)
2.2 Default Configuration for the auth Section (common-auth)
2.3 Default Configuration for the account Section (common-account)
2.4 Default Configuration for the password Section (common-password)
2.5 Default Configuration for the session Section (common-session)
2.6 pam_env.conf
5.1 Excerpt from schema.core
5.2 An LDIF File
5.3 ldapadd with example.ldif
5.4 LDIF Data for Tux
5.5 Modified LDIF File tux.ldif
16.1 Callback Port Configuration for the nfs Kernel Module in /etc/modprobe.d/60-nfs.conf
16.2 Commands to Define a new firewalld RPC Service for NFS
17.1 VPN Server Configuration File
17.2 VPN Client Configuration File
20.1 Output of aa-unconfined
25.1 Learning Mode Exception: Controlling Access to Specific Resources
25.2 Learning Mode Exception: Defining Permissions for an Entry
31.1 Security Context Settings Using ls -Z
31.2 Verifying that SELinux is functional
31.3 Getting a List of Booleans and Verifying Policy Access
31.4 Getting File Context Information
31.5 The default context for directories in the root directory
31.6 Showing SELinux settings for processes with ps Zaux
31.7 Viewing Default File Contexts
31.8 Example Lines from /etc/audit/audit.log
31.9 Analyzing Audit Messages
31.10 Viewing Which Lines Deny Access
31.11 Creating a Policy Module Allowing an Action Previously Denied
32.1 Example output of auditctl -s
32.2 Example Audit Rules—Audit System Parameters
32.3 Example Audit Rules—File System Auditing
32.4 Example Audit Rules—System Call Auditing
32.5 Deleting Audit Rules and Events
32.6 Listing Rules with auditctl -l
32.7 A Simple Audit Event—Viewing the Audit Log
32.8 An Advanced Audit Event—Login via SSH
32.9 Example /etc/audisp/audispd.conf
32.10 Example /etc/audisp/plugins.d/syslog.conf

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