SecDep/harden

#!/usr/bin/env bash
# Ensure bash path is found

# shellcheck source=/etc/os-release
# use shellcheck to declare which file to source

# Using set to make the script safer
set -e          # Exit on error
set -u          # Exit on undefined variable
set -x          # Print commands for debugging
set -a          # Export all variables
set -C          # Disable overwriting of files
set -o pipefail # Exit on pipe error
# set -euxaCo pipefail # All options

# Use the built-in trap command to catch error lines and signal numbers
trap 'printf "Error on line %d with signal %s" "$LINENO" "$?"' ERR # Exit on error
# Also use trap to catch interrupt signals and exit cleanly with a message to the user and a return code
trap 'printf "Interrupted on line %d with signal %s" "$LINENO" "$?"' INT SIGHUP SIGINT SIGTERM

# Get script name using parameter expansion to not spawn a new subprocess
SCRIPT_NAME="${0##*/}"

# We will be using printf instead of echo because it is more standardised.
# Also we will be using the test command's functionality as
# [[ because like this it constitutes a keyword and not a command.
# Functions will be defined as function "name" {body}" to make them
# more clear and () will not be used since using the keyword function renders them redundant

# We are taking for granted that the os-release file is in /etc as
# it has become a standard in most GNU/Linux distributions using systemd.
# We'll be using the -e flag just in case it is actually a symlink to another location.
# The get_distro function will use short if statements to check for the os-release file existence and readability.
# Then it will source it and output the distribution's name or exit in case of failure of either case.
function get_distro {
	if [[ -e /etc/os-release ]] && [[ -r /etc/os-release ]]; then # Check if file exists and is readable
		. /etc/os-release                                            # Source the file
		printf "%s" "$NAME"                                          # Output the distribution's name
	else                                                          # If the file does not exist or is not readable
		printf "%s" "File os-release not found or not readable"      # Output error message
		exit 1                                                       # Exit with error code 1
	fi
}

# The get_package_manager function will take the output of the get_distro function and determine
# which is the package manager used for the most popular server distros and exit if it is not found.
function get_package_manager {
	local distro                    # Declare distro as a local variable
	distro="$(get_distro)"          # Get the distribution name
	case "$distro" in               # Use case to check for the distribution name
		"Ubuntu" | "Debian GNU/Linux") # If the distribution is Ubuntu or Debian
			printf "%s" "apt"             # Output apt
			;;
		"CentOS Linux" | "Fedora" | "Red Hat Enterprise Linux Server") # If the distribution is CentOS, Fedora or RHEL
			printf "%s" "dnf"                                             # Output dnf
			;;

		"openSUSE Leap")      # If the distribution is OpenSUSE
			printf "%s" "zypper" # Output zypper
			;;
		*)
			# If the distribution is none of the above, output unsupported distribution
			# and exit with error code 1
			printf "%s" "Unsupported distribution"
			exit 1 # Exit with error code 1
			;;
	esac
}

# The install_packages function will take the output of the get_package_manager function and install any
# package passed as an argument to it. It will also check if the package manager is known and exit if it is not.
function install_packages {
	local package_manager                    # Declare package_manager as a local variable
	package_manager="$(get_package_manager)" # Get the package manager
	case "$package_manager" in               # Use case to check for the package manager
		"apt")                                  # If the package manager is apt
			sudo apt update                        # Update the package list
			sudo apt install -y "$@"               # Install the packages passed as arguments
			;;
		"dnf")                    # If the package manager is dnf
            sudo dnf upgrade -y      # Update the package list
			sudo dnf install -y "$@" # Install the packages passed as arguments
			;;
		"zypper")                    # If the package manager is zypper
            sudo zypper update -y       # Update the package list
			sudo zypper install -y "$@" # Install the packages passed as arguments
			;;
		*)
			# If the package manager is not one of the above, output unsupported package manager
			# and exit with error code 1
			printf "%s" "Unsupported package manager"
			exit 1 # Exit with error code 1
			;;
	esac
}

# The check_dependencies function will check if the dependencies defined in a local array are not installed
# and store the ones that are indeed absent in another local array.
# Then it will install the packages that are missing by invoking the install_packages function.
function check_dependencies {
	local dependencies=(curl git sudo vim ssh docker-ce docker.io docker docker-compose wget fail2ban) # Declare dependencies as a local array
	#> see what to do with name differences between distros if any <#
	local missing_dependencies=()              # Declare missing_dependencies as a local array
	for dependency in "${dependencies[@]}"; do # Loop through the dependencies array
		# If the dependency is not installed, add it to the missing_dependencies array
		! command -v "$dependency" &> /dev/null && missing_dependencies+=("$dependency")
	done
	# If the missing_dependencies array is not empty, install the packages
	[[ ${#missing_dependencies[@]} -ne 0 ]] && install_packages "${missing_dependencies[@]}"
}

# Global array of the service names to be restarted
services=()

# The hardenSSH function will use sed to modify the sshd_config file to have the following settings:
# - Allow ssh access to users in the sudo group only
# - Change the port to 22100 if it is available
# - Configure idle timeout to 5 minutes
# - Limit the number of authentication attempts to 3
# - Disable root login
# - Disable empty passwords
# - Disable ssh protocol 1
# - Disable password authentication and only allow public key authentication
# - Disable X11 forwarding for security reasons (X11 forwarding is not needed for ssh)
# - Disable agent forwarding to prevent ssh-agent hijacking
# Then it will store the sshd service name in the services array.
function hardenSSH {
	# Check if the sshd_config file exists and is readable
	# If it is, then modify it using sed and restart the sshd service
	# If it is not, then output an error message and exit with error code 1
	# The -i flag is used to modify the file in place
	# We split the sed command into multiple lines for readability purposes
	# and to avoid calling it multiple times
	if [[ -e /etc/ssh/sshd_config ]] && [[ -r /etc/ssh/sshd_config ]]; then
		sed -i \
			-e 's/^#AllowGroups.*/AllowGroups sudo/' \
			-e 's/^#Port.*/Port 22100/' \
			-e 's/^#ClientAliveInterval.*/ClientAliveInterval 300/' \
			-e 's/^#ClientAliveCountMax.*/ClientAliveCountMax 3/' \
			-e 's/^#PermitRootLogin.*/PermitRootLogin no/' \
			-e 's/^#PermitEmptyPasswords.*/PermitEmptyPasswords no/' \
			-e 's/^#Protocol.*/Protocol 2/' \
			-e 's/^#PasswordAuthentication.*/PasswordAuthentication no/' \
			-e 's/^#X11Forwarding.*/X11Forwarding no/' \
			-e 's/^#AllowAgentForwarding.*/AllowAgentForwarding no/' \
			/etc/ssh/sshd_config
		services+=("sshd") # Add sshd to the services array
	else
		printf "%s" "File sshd_config not found or not readable"
		exit 1
	fi
}

function getCorrectFirewall {
	local distro                    # Declare distro as a local variable
	distro="$(get_distro)"          # Get the distribution name
	case "$distro" in               # Use case to check for the distribution name
		"Ubuntu" | "Debian GNU/Linux") # If the distribution is Ubuntu or Debian
			apt install ufw -y # Install ufw
            printf "%s" "ufw" # Output ufw
			;;
		"CentOS Linux" | "Fedora" | "Red Hat Enterprise Linux Server") # If the distribution is CentOS, Fedora or RHEL
			dnf install firewalld -y # Install firewalld
            printf "%s" "firewalld" # Output firewalld
			;;

		"openSUSE Leap")      # If the distribution is OpenSUSE
			zypper install firewalld -y # Install firewalld
            printf "%s" "firewalld" # Output firewalld
			;;
		*)
			# If the distribution is none of the above, output unsupported distribution
			# and exit with error code 1
			printf "%s" "Unsupported distribution"
			exit 1 # Exit with error code 1
			;;
	esac

}

function getCorrectKernelSecurityModule {
	local distro                    # Declare distro as a local variable
	distro="$(get_distro)"          # Get the distribution name
	case "$distro" in               # Use case to check for the distribution name
		"Ubuntu") # If the distribution is Ubuntu
			apt install apparmor-profiles apparmor-utils apparmor-profiles-extra -y # Install apparmor
            printf "%s" "apparmor" # Output apparmor
			;;
        "Debian GNU/Linux") # If the distribution is Debian
            apt install apparmor apparmor-utils auditd python3-apparmor -y # Install apparmor
            printf "%s" "apparmor" # Output apparmor
            ;;
		"CentOS Linux" | "Fedora" | "Red Hat Enterprise Linux Server") # If the distribution is CentOS, Fedora or RHEL
			dnf install selinux container-selinux -y # Install selinux
            printf "%s" "selinux" # Output selinux
			;;

		"openSUSE Leap")      # If the distribution is OpenSUSE
			zypper install -t pattern apparmor -y # Install apparmor
            printf "%s" "apparmor" # Output apparmor
			;;
		*)
			# If the distribution is none of the above, output unsupported distribution
			# and exit with error code 1
			printf "%s" "Unsupported distribution"
			exit 1 # Exit with error code 1
			;;
    esac
}

function firewallInit {
    local firewall
    firewall="$(getCorrectFirewall)" # Get the correct firewall
    case "$firewall" in
        ufw)
            sudo ufw default allow outgoing # Allow outgoing connections
            sudo ufw default deny incoming  # Deny incoming connections
            sudo ufw allow 22100/tcp        # Allow ssh connections on port 22100
            sudo ufw enable                 # Enable the firewall
            sudo systemctl enable --now ufw       # Enable and start the firewall on boot
        ;;
        firewalld)
            sudo systemctl enable --now firewalld # Enable the firewall on boot and start it
            sudo firewall-cmd --permanent --add-port=22100/tcp # Allow ssh connections on port 22100
            sudo firewall-cmd --reload # Reload the firewall
        ;;
        *)
            printf "%s" "Unsupported firewall"
            exit 1
        ;;
    esac
}

function kernelSecurityModuleInit {
    local kernelSecurityModule
    kernelSecurityModule="$(getCorrectKernelSecurityModule)" # Get the correct kernel security module
    case "$kernelSecurityModule" in
        apparmor)
            sudo systemctl enable --now apparmor # Enable the kernel security module on boot and start it
            sudo aa-enforce /etc/apparmor.d/* # Enforce all apparmor profiles
        ;;
        selinux)
            sudo systemctl enable --now selinux # Enable the kernel security module on boot and start it
            printf "%s" "{\"selinux-enabled\":true}" | sudo tee /etc/docker/daemon.json # Enable selinux in docker
            sudo setenforce 1 # Enforce selinux
        ;;
        *)
            printf "%s" "Unsupported kernel security module"
            exit 1
        ;;
    esac
}

function dockerInit {
    # Add user to docker group to avoid using sudo when running docker commands
    sudo usermod -aG docker "$USER"
    # Get all arguments passed to the function and store them in the dockerImages array
    local dockerImages=("$@")
    # Check if the dockerImages array is empty and return 0 if it is
    [[ "${#dockerImages[@]}" -eq 0 ]] && return 0
    # Loop through the dockerImages array
    # The dockerImages array contains all the docker images to install and run
    for dockerImage in "${dockerImages[@]}"; do
        # No need to pull the docker image as the run command will do it automatically
        # Run the docker image in the background,
        # with the restar always option and the name of the docker image
        # The --security-opt=no-new-privileges option will prevent the docker image from gaining new privileges
        # The --cap-drop all option will drop all capabilities from the docker image
        # The --cap-add NET_ADMIN option will add the NET_ADMIN capability to the docker image
        docker run -d --restart always --name "$dockerImage" --security-opt=no-new-privileges --cap-drop all --cap-add NET_ADMIN
        "$dockerImage"
    done
}

# The apparmorConfig function will set up and configure apparmor with sane defaults.
function apparmorConfig {
    # Create a new apparmor profile for the docker daemon
    sudo aa-genprof docker
    # Enable the apparmor profile for the docker daemon
    sudo aa-enforce docker
    # Reload the apparmor profiles
    sudo systemctl reload apparmor
}

# The selinuxConfig function will set up and configure selinux with sane defaults.
function selinuxConfig {
    # Set the selinux boolean to allow docker to use the network
    sudo setsebool -P docker_connect_any 1
}

# This function will create a new apparmor profile for every docker image installed on the system.
function apparmorProfiles {
    # Get all the docker images installed on the system and store them in the dockerImages array
    local dockerImages=("$(docker images --format "{{.Repository}}")")
    # Loop through the dockerImages array
    for dockerImage in "${dockerImages[@]}"; do
        # Create a new apparmor profile for the docker image
        sudo aa-genprof "$dockerImage"
        # Enable the apparmor profile for the docker image
        sudo aa-enforce "$dockerImage"
    done
    # Reload the apparmor profiles
    sudo systemctl reload apparmor
}

function configureFail2ban {
FAIL2BAN_LOCAL=$(cat <<'EOF'
[Definition]
logtarget = /var/log/fail2ban/fail2ban.log
allowipv6 = auto
EOF
)
printf "%s" "$FAIL2BAN_LOCAL" | sudo tee /etc/fail2ban/fail2ban.local
FAIL2BAN_SSH_JAIL_LOCAL=$(cat <<'EOF'
[sshd]
enabled = true
filter = sshd
banaction = ufw
backend = systemd
maxretry = 3
# 3 failed attempts in 600 seconds = 10 minutes
findtime = 1d
bantime = 1d
ignoreip = 127.0.0.1/8
EOF
)
printf "%s" "$FAIL2BAN_SSH_JAIL_LOCAL" | sudo tee /etc/fail2ban/jail.local/sshd.local
FAIL2BAN_FILTER=$(cat <<'EOF'
[Definition]
failregex = ^.*DROP_.*SRC=<ADDR> DST=.*$
journalmatch = _TRANSPORT=kernel
EOF
)
printf "%s" "$FAIL2BAN_FILTER" | sudo tee /etc/fail2ban/filter.d/fwdrop.local
HARDEN_FAIL2BAN_SERVICE=$(cat <<'EOF'
[Service]
PrivateDevices=yes
PrivateTmp=yes
ProtectHome=read-only
ProtectSystem=strict
ReadWritePaths=-/var/run/fail2ban
ReadWritePaths=-/var/lib/fail2ban
ReadWritePaths=-/var/log/fail2ban
ReadWritePaths=-/var/spool/postfix/maildrop
ReadWritePaths=/run/xtables.lock
CapabilityBoundingSet=CAP_AUDIT_READ CAP_DAC_READ_SEARCH CAP_NET_ADMIN CAP_NET_RAW
EOF
)
printf "%s" "$HARDEN_FAIL2BAN_SERVICE" | sudo tee /etc/systemd/system/fail2ban.service.d/override.conf
sudo systemctl enable --now fail2ban
printf "%s" "LogLevel VERBOSE" | sudo tee -a /etc/ssh/sshd_config
sudo systemctl restart sshd
}

# The main function will call the check_dependencies function and exit if it fails.
# It will also output a message to the user to let them know that the script has finished.
function main {
	check_dependencies || exit 1  # Check dependencies and exit if it fails
    hardenSSH || exit 1          # Harden ssh and exit if it fails
    firewallInit || exit 1        # Initialize the firewall and exit if it fails
    kernelSecurityModuleInit || exit 1 # Initialize the kernel security module and exit if it fails
    configureFail2ban || exit 1        # Initialize fail2ban and exit if it fails
    dockerInit || exit 1          # Initialize docker and exit if it fails
    apparmorConfig      # Configure apparmor
    apparmorProfiles    # Create apparmor profiles for all docker images
    selinuxConfig       # Configure selinux
    # If number of arguments is greater than 0
    # Call the dockerInit function with the arguments passed to the script
    # Else exit with error code 1
    [[ $# -gt 0 ]] && dockerInit "$@" || exit 1
	printf "%s" "Script finished" # Output message to the user
}

# # The am_i_root function will check if the user is root and exit if they are not.
# function am_i_root {
# 	if [[ $EUID -ne 0 ]]; then        # Check if the user is root
# 		printf "%s" "Please run as root" # Output message to the user
# 		exit 1                           # Exit with error code 1
# 	fi
# }

# Call the main function
main "$@"

exit 0 # The right and proper way to exit a script