check-config.sh

#!/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}
    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