As things currently stand, all members of the marketing group have read/write access to all other group members' files. Restricting access to a file to only specific group members is the same two-step process that we've already covered.
Using ACLs to access files in the shared directory
by Donald A. Tevault
Mastering Linux Security and Hardening - Second Edition
- Title Page
- Copyright and Credits
- About Packt
- Contributors
- Preface
- Section 1: Setting up a Secure Linux System
- Running Linux in a Virtual Environment
- Looking at the threat landscape
- Why do security breaches happen?
- Keeping up with security news
- Differences between physical, virtual, and cloud setups
- Introducing VirtualBox and Cygwin
- Installing a virtual machine in VirtualBox
- Installing the EPEL repository on the CentOS 7 virtual machine
- Installing the EPEL repository on the CentOS 8 virtual machine
- Configuring a network for VirtualBox virtual machines
- Creating a virtual machine snapshot with VirtualBox
- Using Cygwin to connect to your virtual machines
- Using Windows 10 Pro Bash shell to interface with Linux virtual machines
- Keeping the Linux systems updated
- Summary
- Questions
- Further reading
- Securing User Accounts
- The dangers of logging in as the root user
- The advantages of using sudo
- Setting up sudo privileges for full administrative users
- Setting up sudo for users with only certain delegated privileges
- Advanced tips and tricks for using sudo
- The sudo timer
- View your sudo privileges
- Preventing users from having root shell access
- Preventing users from using shell escapes
- Preventing users from using other dangerous programs
- Limiting the user's actions with commands
- Letting users run as other users
- Preventing abuse via user's shell scripts
- Detecting and deleting default user accounts
- Locking down users' home directories the Red Hat or CentOS way
- Locking down users' home directories the Debian/Ubuntu way
- Enforcing strong password criteria
- Setting and enforcing password and account expiration
- Configuring default expiry data for useradd for Red Hat or CentOS only
- Setting expiry data on a per-account basis with useradd and usermod
- Setting expiry data on a per-account basis with chage
- Preventing brute-force password attacks
- Locking user accounts
- Locking the root user account
- Setting up security banners
- Detecting compromised passwords
- Understanding centralized user management
- Summary
- Questions
- Further reading
- Securing Your Server with a Firewall - Part 1
- Technical requirements
- An overview of firewalld
- An overview of iptables
- Uncomplicated firewall for Ubuntu systems
- Summary
- Questions
- Further reading
- Securing Your Server with a Firewall - Part 2
- Technical requirements
- nftables – a more universal type of firewall system
- firewalld for Red Hat systems
- Verifying the status of firewalld
- Working with firewalld zones
- Adding services to a firewalld zone
- Adding ports to a firewalld zone
- Blocking ICMP
- Using panic mode
- Logging dropped packets
- Using firewalld rich language rules
- Looking at iptables rules in RHEL/CentOS 7 firewalld
- Creating direct rules in RHEL/CentOS 7 firewalld
- Looking at nftables rules in RHEL/CentOS 8 firewalld
- Creating direct rules in RHEL/CentOS 8 firewalld
- Hands-on lab for firewalld commands
- Summary
- Questions
- Further reading
- Encryption Technologies
- GNU Privacy Guard (GPG)
- Encrypting partitions with Linux Unified Key Setup (LUKS)
- Encrypting directories with eCryptfs
- Home directory and disk encryption during Ubuntu installation
- Hands-on lab – encrypting a home directory for a new user account
- Creating a private directory within an existing home directory
- Hands-on lab – encrypting other directories with eCryptfs
- Encrypting the swap partition with eCryptfs
- Using VeraCrypt for cross-platform sharing of encrypted containers
- OpenSSL and the public key infrastructure
- Summary
- Questions
- Further reading
- SSH Hardening
- Ensuring that SSH protocol 1 is disabled
- Creating and managing keys for passwordless logins
- Disabling root user login
- Disabling username/password logins
- Configuring Secure Shell with strong encryption algorithms
- Setting system-wide encryption policies on RHEL 8/CentOS 8
- Configuring more detailed logging
- Configuring access control with whitelists and TCP Wrappers
- Configuring automatic logouts and security banners
- Configuring other miscellaneous security settings
- Setting up a chroot environment for SFTP users
- Sharing a directory with SSHFS
- Remotely connecting from Windows desktops
- Summary
- Questions
- Further reading
- Section 2: Mastering File and Directory Access Control (DAC)
- Mastering Discretionary Access Control
- Using chown to change ownership of files and directories
- Using chmod to set permissions on files and directories
- Using SUID and SGID on regular files
- The security implications of the SUID and SGID permissions
- Using extended file attributes to protect sensitive files
- Securing system configuration files
- Summary
- Questions
- Further reading
- Access Control Lists and Shared Directory Management
- Creating an ACL for either a user or a group
- Creating an inherited ACL for a directory
- Removing a specific permission by using an ACL mask
- Using the tar --acls option to prevent the loss of ACLs during a backup
- Creating a user group and adding members to it
- Creating a shared directory
- Setting the SGID bit and the sticky bit on the shared directory
- Using ACLs to access files in the shared directory
- Summary
- Questions
- Further reading
- Section 3: Advanced System Hardening Techniques
- Implementing Mandatory Access Control with SELinux and AppArmor
- How SELinux can benefit a systems administrator
- Setting security contexts for files and directories
- Troubleshooting with setroubleshoot
- Working with SELinux policies
- How AppArmor can benefit a systems administrator
- Looking at AppArmor profiles
- Working with AppArmor command-line utilities
- Troubleshooting AppArmor problems
- Exploiting a system with an evil Docker container
- Summary
- Questions
- Further reading
- Kernel Hardening and Process Isolation
- Understanding the /proc filesystem
- Setting kernel parameters with sysctl
- Configuring the sysctl.conf file
- Understanding process isolation
- Summary
- Questions
- Answers
- Further reading
- Scanning, Auditing, and Hardening
- Technical requirements
- Installing and updating ClamAV and maldet
- Scanning with ClamAV and maldet
- Scanning for rootkits with Rootkit Hunter
- Performing a quick malware analysis with strings and VirusTotal
- Understanding the auditd daemon
- Using ausearch and aureport
- Applying OpenSCAP policies with oscap
- Summary
- Questions
- Further reading
- Logging and Log Security
- Understanding the Linux system log files
- Understanding rsyslog
- Understanding journald
- Making things easier with Logwatch
- Setting up a remote log server
- Summary
- Questions
- Further reading
- Vulnerability Scanning and Intrusion Detection
- Security Tips and Tricks for the Busy Bee
- Technical requirements
- Auditing system services
- Password protecting the GRUB 2 bootloader
- Securely configuring BIOS/UEFI
- Using a security checklist for system setup
- Summary
- Questions
- Further reading
- Assessments
- Other Books You May Enjoy
Using ACLs to access files in the shared directory
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