#!/usr/bin/env bash
set -e

EXITCODE=0

# bits of this were adapted from lxc-checkconfig
# see also https://github.com/lxc/lxc/blob/lxc-1.0.2/src/lxc/lxc-checkconfig.in

possibleConfigs=(
	'/proc/config.gz'
	"/boot/config-$(uname -r)"
	"/usr/src/linux-$(uname -r)/.config"
	'/usr/src/linux/.config'
)

if [ $# -gt 0 ]; then
	CONFIG="$1"
else
	: "${CONFIG:="${possibleConfigs[0]}"}"
fi

if ! command -v zgrep &> /dev/null; then
	zgrep() {
		zcat "$2" | grep "$1"
	}
fi

kernelVersion="$(uname -r)"
kernelMajor="${kernelVersion%%.*}"
kernelMinor="${kernelVersion#$kernelMajor.}"
kernelMinor="${kernelMinor%%.*}"

is_set() {
	zgrep "CONFIG_$1=[y|m]" "$CONFIG" > /dev/null
}
is_set_in_kernel() {
	zgrep "CONFIG_$1=y" "$CONFIG" > /dev/null
}
is_set_as_module() {
	zgrep "CONFIG_$1=m" "$CONFIG" > /dev/null
}

color() {
	local codes=()
	if [ "$1" = 'bold' ]; then
		codes=("${codes[@]}" '1')
		shift
	fi
	if [ "$#" -gt 0 ]; then
		local code=
		case "$1" in
			# see https://en.wikipedia.org/wiki/ANSI_escape_code#Colors
			black) code=30 ;;
			red) code=31 ;;
			green) code=32 ;;
			yellow) code=33 ;;
			blue) code=34 ;;
			magenta) code=35 ;;
			cyan) code=36 ;;
			white) code=37 ;;
		esac
		if [ "$code" ]; then
			codes=("${codes[@]}" "$code")
		fi
	fi
	local IFS=';'
	echo -en '\033['"${codes[*]}"'m'
}
wrap_color() {
	text="$1"
	shift
	color "$@"
	echo -n "$text"
	color reset
	echo
}

wrap_good() {
	echo "$(wrap_color "$1" white): $(wrap_color "$2" green)"
}
wrap_bad() {
	echo "$(wrap_color "$1" bold): $(wrap_color "$2" bold red)"
}
wrap_warning() {
	wrap_color >&2 "$*" red
}

check_flag() {
	if is_set_in_kernel "$1"; then
		wrap_good "CONFIG_$1" 'enabled'
	elif is_set_as_module "$1"; then
		wrap_good "CONFIG_$1" 'enabled (as module)'
	else
		wrap_bad "CONFIG_$1" 'missing'
		EXITCODE=1
	fi
}

check_flags() {
	for flag in "$@"; do
		echo -n "- "
		check_flag "$flag"
	done
}

check_command() {
	if command -v "$1" > /dev/null 2>&1; then
		wrap_good "$1 command" 'available'
	else
		wrap_bad "$1 command" 'missing'
		EXITCODE=1
	fi
}

check_device() {
	if [ -c "$1" ]; then
		wrap_good "$1" 'present'
	else
		wrap_bad "$1" 'missing'
		EXITCODE=1
	fi
}

check_distro_userns() {
	source /etc/os-release 2> /dev/null || /bin/true
	if [[ "${ID}" =~ ^(centos|rhel)$ && "${VERSION_ID}" =~ ^7 ]]; then
		# this is a CentOS7 or RHEL7 system
		grep -q "user_namespace.enable=1" /proc/cmdline || {
			# no user namespace support enabled
			wrap_bad "  (RHEL7/CentOS7" "User namespaces disabled; add 'user_namespace.enable=1' to boot command line)"
			EXITCODE=1
		}
	fi
}

if [ ! -e "$CONFIG" ]; then
	wrap_warning "warning: $CONFIG does not exist, searching other paths for kernel config ..."
	for tryConfig in "${possibleConfigs[@]}"; do
		if [ -e "$tryConfig" ]; then
			CONFIG="$tryConfig"
			break
		fi
	done
	if [ ! -e "$CONFIG" ]; then
		wrap_warning "error: cannot find kernel config"
		wrap_warning "  try running this script again, specifying the kernel config:"
		wrap_warning "    CONFIG=/path/to/kernel/.config $0 or $0 /path/to/kernel/.config"
		exit 1
	fi
fi

wrap_color "info: reading kernel config from $CONFIG ..." white
echo

echo 'Generally Necessary:'

echo -n '- '
if [ "$(stat -f -c %t /sys/fs/cgroup 2> /dev/null)" = '63677270' ]; then
	echo "$(wrap_good 'cgroup hierarchy' 'cgroupv2')"
else
	cgroupSubsystemDir="$(awk '/[, ](cpu|cpuacct|cpuset|devices|freezer|memory)[, ]/ && $3 == "cgroup" { print $2 }' /proc/mounts | head -n1)"
	cgroupDir="$(dirname "$cgroupSubsystemDir")"
	if [ -d "$cgroupDir/cpu" ] || [ -d "$cgroupDir/cpuacct" ] || [ -d "$cgroupDir/cpuset" ] || [ -d "$cgroupDir/devices" ] || [ -d "$cgroupDir/freezer" ] || [ -d "$cgroupDir/memory" ]; then
		echo "$(wrap_good 'cgroup hierarchy' 'properly mounted') [$cgroupDir]"
	else
		if [ "$cgroupSubsystemDir" ]; then
			echo "$(wrap_bad 'cgroup hierarchy' 'single mountpoint!') [$cgroupSubsystemDir]"
		else
			wrap_bad 'cgroup hierarchy' 'nonexistent??'
		fi
		EXITCODE=1
		echo "    $(wrap_color '(see https://github.com/tianon/cgroupfs-mount)' yellow)"
	fi
fi

if [ "$(cat /sys/module/apparmor/parameters/enabled 2> /dev/null)" = 'Y' ]; then
	echo -n '- '
	if command -v apparmor_parser &> /dev/null; then
		wrap_good 'apparmor' 'enabled and tools installed'
	else
		wrap_bad 'apparmor' 'enabled, but apparmor_parser missing'
		echo -n '    '
		if command -v apt-get &> /dev/null; then
			wrap_color '(use "apt-get install apparmor" to fix this)'
		elif command -v yum &> /dev/null; then
			wrap_color '(your best bet is "yum install apparmor-parser")'
		else
			wrap_color '(look for an "apparmor" package for your distribution)'
		fi
		EXITCODE=1
	fi
fi

flags=(
	NAMESPACES {NET,PID,IPC,UTS}_NS
	CGROUPS CGROUP_CPUACCT CGROUP_DEVICE CGROUP_FREEZER CGROUP_SCHED CPUSETS MEMCG
	KEYS
	VETH BRIDGE BRIDGE_NETFILTER
	IP_NF_FILTER IP_NF_TARGET_MASQUERADE
	NETFILTER_XT_MATCH_{ADDRTYPE,CONNTRACK,IPVS}
	NETFILTER_XT_MARK
	IP_NF_NAT NF_NAT

	# required for bind-mounting /dev/mqueue into containers
	POSIX_MQUEUE
)
check_flags "${flags[@]}"
if [ "$kernelMajor" -lt 4 ] || ([ "$kernelMajor" -eq 4 ] && [ "$kernelMinor" -lt 8 ]); then
	check_flags DEVPTS_MULTIPLE_INSTANCES
fi

if [ "$kernelMajor" -lt 5 ] || [ "$kernelMajor" -eq 5 -a "$kernelMinor" -le 1 ]; then
	check_flags NF_NAT_IPV4
fi

if [ "$kernelMajor" -lt 5 ] || [ "$kernelMajor" -eq 5 -a "$kernelMinor" -le 2 ]; then
	check_flags NF_NAT_NEEDED
fi

echo

echo 'Optional Features:'
{
	check_flags USER_NS
	check_distro_userns
}
{
	check_flags SECCOMP
}
{
	check_flags CGROUP_PIDS
}
{
	check_flags MEMCG_SWAP
	# Kernel v5.8+ removes MEMCG_SWAP_ENABLED.
	if [ "$kernelMajor" -lt 5 ] || [ "$kernelMajor" -eq 5 -a "$kernelMinor" -le 8 ]; then
		CODE=${EXITCODE}
		check_flags MEMCG_SWAP_ENABLED
		# FIXME this check is cgroupv1-specific
		if [ -e /sys/fs/cgroup/memory/memory.memsw.limit_in_bytes ]; then
			echo "    $(wrap_color '(cgroup swap accounting is currently enabled)' bold black)"
			EXITCODE=${CODE}
		elif is_set MEMCG_SWAP && ! is_set MEMCG_SWAP_ENABLED; then
			echo "    $(wrap_color '(cgroup swap accounting is currently not enabled, you can enable it by setting boot option "swapaccount=1")' bold black)"
		fi
	else
		# Kernel v5.8+ enables swap accounting by default.
		echo "    $(wrap_color '(cgroup swap accounting is currently enabled)' bold black)"
	fi
}
{
	if is_set LEGACY_VSYSCALL_NATIVE; then
		echo -n "- "
		wrap_bad "CONFIG_LEGACY_VSYSCALL_NATIVE" 'enabled'
		echo "    $(wrap_color '(dangerous, provides an ASLR-bypassing target with usable ROP gadgets.)' bold black)"
	elif is_set LEGACY_VSYSCALL_EMULATE; then
		echo -n "- "
		wrap_good "CONFIG_LEGACY_VSYSCALL_EMULATE" 'enabled'
	elif is_set LEGACY_VSYSCALL_NONE; then
		echo -n "- "
		wrap_bad "CONFIG_LEGACY_VSYSCALL_NONE" 'enabled'
		echo "    $(wrap_color '(containers using eglibc <= 2.13 will not work. Switch to' bold black)"
		echo "    $(wrap_color ' "CONFIG_VSYSCALL_[NATIVE|EMULATE]" or use "vsyscall=[native|emulate]"' bold black)"
		echo "    $(wrap_color ' on kernel command line. Note that this will disable ASLR for the,' bold black)"
		echo "    $(wrap_color ' VDSO which may assist in exploiting security vulnerabilities.)' bold black)"
	# else Older kernels (prior to 3dc33bd30f3e, released in v4.40-rc1) do
	#      not have these LEGACY_VSYSCALL options and are effectively
	#      LEGACY_VSYSCALL_EMULATE. Even older kernels are presumably
	#      effectively LEGACY_VSYSCALL_NATIVE.
	fi
}

if [ "$kernelMajor" -lt 4 ] || ([ "$kernelMajor" -eq 4 ] && [ "$kernelMinor" -le 5 ]); then
	check_flags MEMCG_KMEM
fi

if [ "$kernelMajor" -lt 3 ] || ([ "$kernelMajor" -eq 3 ] && [ "$kernelMinor" -le 18 ]); then
	check_flags RESOURCE_COUNTERS
fi

if [ "$kernelMajor" -lt 3 ] || ([ "$kernelMajor" -eq 3 ] && [ "$kernelMinor" -le 13 ]); then
	netprio=NETPRIO_CGROUP
else
	netprio=CGROUP_NET_PRIO
fi

if [ "$kernelMajor" -lt 5 ]; then
	check_flags IOSCHED_CFQ CFQ_GROUP_IOSCHED
fi

flags=(
	BLK_CGROUP BLK_DEV_THROTTLING
	CGROUP_PERF
	CGROUP_HUGETLB
	NET_CLS_CGROUP $netprio
	CFS_BANDWIDTH FAIR_GROUP_SCHED RT_GROUP_SCHED
	IP_NF_TARGET_REDIRECT
	IP_VS
	IP_VS_NFCT
	IP_VS_PROTO_TCP
	IP_VS_PROTO_UDP
	IP_VS_RR
)
check_flags "${flags[@]}"

if ! is_set EXT4_USE_FOR_EXT2; then
	check_flags EXT3_FS EXT3_FS_XATTR EXT3_FS_POSIX_ACL EXT3_FS_SECURITY
	if ! is_set EXT3_FS || ! is_set EXT3_FS_XATTR || ! is_set EXT3_FS_POSIX_ACL || ! is_set EXT3_FS_SECURITY; then
		echo "    $(wrap_color '(enable these ext3 configs if you are using ext3 as backing filesystem)' bold black)"
	fi
fi

check_flags EXT4_FS EXT4_FS_POSIX_ACL EXT4_FS_SECURITY
if ! is_set EXT4_FS || ! is_set EXT4_FS_POSIX_ACL || ! is_set EXT4_FS_SECURITY; then
	if is_set EXT4_USE_FOR_EXT2; then
		echo "    $(wrap_color 'enable these ext4 configs if you are using ext3 or ext4 as backing filesystem' bold black)"
	else
		echo "    $(wrap_color 'enable these ext4 configs if you are using ext4 as backing filesystem' bold black)"
	fi
fi

echo '- Network Drivers:'
echo "  - \"$(wrap_color 'overlay' blue)\":"
check_flags VXLAN BRIDGE_VLAN_FILTERING | sed 's/^/    /'
echo '      Optional (for encrypted networks):'
check_flags CRYPTO CRYPTO_AEAD CRYPTO_GCM CRYPTO_SEQIV CRYPTO_GHASH \
	XFRM XFRM_USER XFRM_ALGO INET_ESP | sed 's/^/      /'
if [ "$kernelMajor" -lt 5 ] || [ "$kernelMajor" -eq 5 -a "$kernelMinor" -le 3 ]; then
	check_flags INET_XFRM_MODE_TRANSPORT | sed 's/^/      /'
fi
echo "  - \"$(wrap_color 'ipvlan' blue)\":"
check_flags IPVLAN | sed 's/^/    /'
echo "  - \"$(wrap_color 'macvlan' blue)\":"
check_flags MACVLAN DUMMY | sed 's/^/    /'
echo "  - \"$(wrap_color 'ftp,tftp client in container' blue)\":"
check_flags NF_NAT_FTP NF_CONNTRACK_FTP NF_NAT_TFTP NF_CONNTRACK_TFTP | sed 's/^/    /'

# only fail if no storage drivers available
CODE=${EXITCODE}
EXITCODE=0
STORAGE=1

echo '- Storage Drivers:'
echo "  - \"$(wrap_color 'aufs' blue)\":"
check_flags AUFS_FS | sed 's/^/    /'
if ! is_set AUFS_FS && grep -q aufs /proc/filesystems; then
	echo "      $(wrap_color '(note that some kernels include AUFS patches but not the AUFS_FS flag)' bold black)"
fi
[ "$EXITCODE" = 0 ] && STORAGE=0
EXITCODE=0

echo "  - \"$(wrap_color 'btrfs' blue)\":"
check_flags BTRFS_FS | sed 's/^/    /'
check_flags BTRFS_FS_POSIX_ACL | sed 's/^/    /'
[ "$EXITCODE" = 0 ] && STORAGE=0
EXITCODE=0

echo "  - \"$(wrap_color 'devicemapper' blue)\":"
check_flags BLK_DEV_DM DM_THIN_PROVISIONING | sed 's/^/    /'
[ "$EXITCODE" = 0 ] && STORAGE=0
EXITCODE=0

echo "  - \"$(wrap_color 'overlay' blue)\":"
check_flags OVERLAY_FS | sed 's/^/    /'
[ "$EXITCODE" = 0 ] && STORAGE=0
EXITCODE=0

echo "  - \"$(wrap_color 'zfs' blue)\":"
echo -n "    - "
check_device /dev/zfs
echo -n "    - "
check_command zfs
echo -n "    - "
check_command zpool
[ "$EXITCODE" = 0 ] && STORAGE=0
EXITCODE=0

EXITCODE=$CODE
[ "$STORAGE" = 1 ] && EXITCODE=1

echo

check_limit_over() {
	if [ "$(cat "$1")" -le "$2" ]; then
		wrap_bad "- $1" "$(cat "$1")"
		wrap_color "    This should be set to at least $2, for example set: sysctl -w kernel/keys/root_maxkeys=1000000" bold black
		EXITCODE=1
	else
		wrap_good "- $1" "$(cat "$1")"
	fi
}

echo 'Limits:'
check_limit_over /proc/sys/kernel/keys/root_maxkeys 10000
echo

exit $EXITCODE