security-misc/usr/bin/remount-secure

#!/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://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

   if [ "$(id -u)" != "0" ]; then
      $output_command "ERROR: must be run as root! sudo $0"
      exit 1
   fi

   mkdir --parents "/run/remount-secure"
   exit_code=0
   mount_output="$(mount)"

   ## Debugging.
   $output_command "INFO: mount_output:"
   $output_command "$mount_output"
   $output_command ""
}

parse_options() {
   ## Thanks to:
   ## http://mywiki.wooledge.org/BashFAQ/035

   while :
   do
       case ${1:-} in
           --remountnoexec)
               $output_command "INFO: --remountnoexec"
               noexec_maybe=",noexec"
               shift
               ;;
           --force)
               $output_command "INFO: --force"
               option_force=true
               shift
               ;;
           --)
               shift
               break
               ;;
           -*)
               echo "unknown option: $1" >&2
               exit 1
               ;;
           *)
               break
               ;;
       esac
   done

   [[ -v noexec_maybe ]] || noexec_maybe=""
   [[ -v option_force ]] || option_force=""
}

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

   ## BUG: echo: write error: Broken pipe
   if echo "$mount_output" | grep --quiet "$mount_folder " ; then
      ## Already mounted. Using remount.
      $output_command INFO: Executing: mount -o "remount,${intended_mount_options}" "$mount_folder"
      mount -o "remount,${intended_mount_options}" "$mount_folder" || exit_code=100
   else
      ## Not yet mounted. Using mount bind.
      $output_command INFO: Executing: mount -o "$intended_mount_options" --bind "$mount_folder" "$mount_folder"
      mount -o "$intended_mount_options" --bind "$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"
}

_home() {
   mount_folder="/home"
   intended_mount_options="nosuid,nodev${noexec_maybe}"
   remount_secure "$@"
}

_run() {
   mount_folder="/run"
   ## https://lists.freedesktop.org/archives/systemd-devel/2015-February/028456.html
   intended_mount_options="nosuid,nodev${noexec_maybe}"
   remount_secure "$@"
}

_dev_shm() {
   mount_folder="/dev/shm"
   intended_mount_options="nosuid,nodev${noexec_maybe}"
   remount_secure "$@"
}

_tmp() {
   mount_folder="/tmp"
   intended_mount_options="nosuid,nodev${noexec_maybe}"
   remount_secure "$@"
}

## https://forums.whonix.org/t/re-mount-home-and-other-with-noexec-and-nosuid-among-other-useful-mount-options-for-better-security/7707/25
# _lib() {
#    mount_folder="/lib"
#    ## Not using noexec on /lib.
#    intended_mount_options="nosuid,nodev"
#    remount_secure "$@"
# }

end() {
   exit $exit_code
}

main() {
   init "$@"
   parse_options "$@"
   _home "$@"
   _run "$@"
   _dev_shm "$@"
   _tmp "$@"
   #_lib "$@"
   end "$@"
}

main "$@"