security-misc/usr/bin/remount-secure

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#!/bin/bash
## Copyright (C) 2019 - 2023 ENCRYPTED SUPPORT LP <adrelanos@whonix.org>
## See the file COPYING for copying conditions.
## noexec in /tmp and/or /home can break some malware but also legitimate
## applications.
## https://www.kicksecure.com/wiki/Dev/remount-secure
## https://forums.whonix.org/t/re-mount-home-and-other-with-noexec-and-nosuid-among-other-useful-mount-options-for-better-security/7707
#set -x
set -e
set -o pipefail
set -o nounset
init() {
if test -o xtrace ; then
output_command=true
else
output_command=echo
fi
$output_command "$0: INFO: START"
## dracut does not have id. Saving space in initial ramdisk.
if command -v id &>/dev/null ; then
if [ "$(id -u)" != "0" ]; then
$output_command "ERROR: must be run as root! sudo $0"
exit 1
fi
fi
mkdir --parents "/run/remount-secure"
exit_code=0
## dracut sets NEWROOT=/sysroot
[[ -v NEWROOT ]] || NEWROOT=""
if [ "$NEWROOT" = "" ]; then
$output_command "INFO: dracut detected: no"
else
$output_command "INFO: dracut detected: yes - NEWROOT: '$NEWROOT'"
fi
## Debugging.
#echo "ls -la /root/"
#ls -la / || true
#echo "ls -la /sysroot/"
#ls -la /sysroot/ || true
#echo "env"
#env || true
}
parse_options() {
## Thanks to:
## http://mywiki.wooledge.org/BashFAQ/035
while :
do
case ${1:-} in
0)
$output_command "WARNING: Not using remount-secure."
exit 0
shift
;;
1)
$output_command "INFO: level 1/3 (low)"
most_noexec_maybe=""
home_noexec_maybe=""
parsed=true
shift
;;
2)
$output_command "INFO: level 2/3 (medium)"
most_noexec_maybe=",noexec"
home_noexec_maybe=""
parsed=true
shift
;;
3)
$output_command "INFO: level 3/3 (high)"
most_noexec_maybe=",noexec"
home_noexec_maybe=",noexec"
parsed=true
shift
;;
--force)
$output_command "INFO: --force"
option_force=true
shift
;;
--)
shift
break
;;
-*)
echo "ERROR: unknown option: $1" >&2
exit 1
;;
*)
break
;;
esac
done
[[ -v option_force ]] || option_force=""
[[ -v parsed ]] || parsed=false
[[ -v home_noexec_maybe ]] || home_noexec_maybe=""
[[ -v most_noexec_maybe ]] || most_noexec_maybe=""
$output_command "INFO: using nosuid,nodev: yes"
if [ "$home_noexec_maybe" = "" ]; then
$output_command "INFO: using noexec for all: no"
else
$output_command "INFO: using noexec for all: yes"
return 0
fi
if [ "$most_noexec_maybe" = "" ]; then
$output_command "INFO: using noexec for most: no"
else
$output_command "INFO: using noexec for most (not all): yes"
return 0
fi
if [ "$parsed" = "true" ]; then
return 0
fi
$output_command "ERROR: syntax error. use either:
$0 0
$0 1
$0 2
$0 3"
exit 1
}
preparation() {
## Debugging.
#$output_command "INFO: 'findmnt --list' output at the START."
#$output_command "$(findmnt --list)"
#$output_command ""
true
}
remount_secure() {
$output_command ""
## ${FUNCNAME[1]} is the name of the calling function. I.e. the function
## which called this function.
status_file_name="${FUNCNAME[1]}"
## example status_file_name:
## _home
status_file_full_path="/run/remount-secure/${status_file_name}"
## example status_file_full_path:
## /run/remount-secure/_home
old_mount_options="$(findmnt --noheadings --output options -- "$mount_folder")" || true
## example old_mount_options:
## rw,nosuid,nodev,relatime,discard
$output_command "INFO: '$mount_folder' old_mount_options: '$old_mount_options'"
if echo "$old_mount_options" | grep --quiet "$intended_mount_options" ; then
$output_command "INFO: '$mount_folder' has already intended mount options. ($intended_mount_options)"
return 0
fi
## When this package is upgraded, the systemd unit will run again.
## If the user meanwhile manually relaxed mount options, this should not be undone.
if [ ! "$option_force" == "true" ]; then
if [ -e "$status_file_full_path" ]; then
$output_command "INFO: '$mount_folder' already remounted earlier. Not remounting again. Use --force if this is what you want."
return 0
fi
fi
if ! test -d "$mount_folder" ; then
$output_command "INFO: '$mount_folder' folder exists: no"
exit_code=102
return 0
fi
$output_command "INFO: '$mount_folder' folder exists: yes"
if findmnt --noheadings "$mount_folder" >/dev/null ; then
$output_command "INFO: '$mount_folder' already mounted, therefore using remount."
$output_command INFO: Executing: mount --options "remount,${intended_mount_options}" "$mount_folder"
mount --options "remount,${intended_mount_options}" "$mount_folder" || exit_code=100
else
$output_command "INFO: '$mount_folder' not yet mounted, therefore using mount bind."
$output_command INFO: Executing: mount --options "$intended_mount_options" --bind "$mount_folder" "$mount_folder"
mount --options "$intended_mount_options" --bind "$mount_folder" "$mount_folder" || exit_code=101
fi
new_mount_options="$(findmnt --noheadings --output options -- "$mount_folder")" || true
$output_command "INFO: '$mount_folder' new_mount_options: $new_mount_options"
touch "$status_file_full_path"
}
_boot() {
mount_folder="$NEWROOT/boot"
## https://lists.freedesktop.org/archives/systemd-devel/2015-February/028456.html
intended_mount_options="nosuid,nodev,noexec"
remount_secure
}
_boot_efi() {
## TODO: new, test
mount_folder="$NEWROOT/boot/efi"
intended_mount_options="nosuid,nodev,noexec"
remount_secure
}
_run() {
mount_folder="/run"
## https://lists.freedesktop.org/archives/systemd-devel/2015-February/028456.html
intended_mount_options="nosuid,nodev${most_noexec_maybe}"
remount_secure
}
_dev() {
mount_folder="/dev"
## /dev should be nosuid,noexec as per:
## https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1991975
intended_mount_options="nosuid,noexec"
remount_secure
}
_dev_shm() {
mount_folder="/dev/shm"
intended_mount_options="nosuid,nodev${most_noexec_maybe}"
remount_secure
}
_sys() {
## TODO: new, test
mount_folder="/sys"
intended_mount_options="nosuid,nodev,noexec"
remount_secure
}
_tmp() {
mount_folder="$NEWROOT/tmp"
intended_mount_options="nosuid,nodev${most_noexec_maybe}"
remount_secure
}
_var_tmp() {
mount_folder="$NEWROOT/var/tmp"
intended_mount_options="nosuid,nodev${most_noexec_maybe}"
remount_secure
}
_var_log() {
mount_folder="$NEWROOT/var/log"
intended_mount_options="nosuid,nodev,noexec"
remount_secure
}
_var() {
mount_folder="$NEWROOT/var"
## noexec: Not possible. Reason:
## Debian stores executable maintainer scripts in /var/lib/dpkg/info folder.
intended_mount_options="nosuid,nodev"
remount_secure
}
_usr() {
## TODO: new, test
mount_folder="$NEWROOT/usr"
intended_mount_options="nodev"
remount_secure
}
_home() {
mount_folder="$NEWROOT/home"
intended_mount_options="nosuid,nodev${home_noexec_maybe}"
remount_secure
}
_root() {
## TODO: new, test
mount_folder="$NEWROOT/root"
intended_mount_options="nosuid,nodev${home_noexec_maybe}"
remount_secure
}
_srv() {
## TODO: new, test
mount_folder="$NEWROOT/srv"
intended_mount_options="nosuid,nodev${most_noexec_maybe}"
remount_secure
}
_media() {
## TODO: new, test
mount_folder="$NEWROOT/media"
intended_mount_options="nosuid,nodev${most_noexec_maybe}"
remount_secure
}
_mnt() {
## TODO: new, test
mount_folder="$NEWROOT/mnt"
intended_mount_options="nosuid,nodev${most_noexec_maybe}"
remount_secure
}
_opt() {
## TODO: new, test
mount_folder="$NEWROOT/opt"
intended_mount_options="nosuid,nodev"
remount_secure
}
_etc() {
## TODO: new, test
## /etc cannot be noexec because various executables are there. To find, run:
## sudo find /etc -executable
mount_folder="$NEWROOT/etc"
intended_mount_options="nosuid,nodev"
remount_secure
}
end() {
## Debugging.
#$output_command "INFO: 'findmnt --list' output at the END."
#$output_command "$(findmnt --list)"
$output_command "INFO: exit_code: $exit_code"
$output_command "$0: INFO: END"
exit $exit_code
}
main() {
init
parse_options "$@"
preparation
_boot
_boot_efi
_run
_dev
_dev_shm
_tmp
_var_tmp
_var_log
_var
_usr
_home
_root
_srv
_media
_mnt
_opt
_etc
end
}
## TODO: see also hidepid /usr/lib/systemd/system/proc-hidepid.service
#mount --options defaults,nosuid,nodev,noexec,remount,subset=pid /proc
main "$@"