security-misc/usr/bin/permission-hardening

#!/bin/bash

## Copyright (C) 2012 - 2023 ENCRYPTED SUPPORT LP <adrelanos@whonix.org>
## See the file COPYING for copying conditions.

## https://forums.whonix.org/t/disable-suid-binaries/7706
## https://forums.whonix.org/t/re-mount-home-and-other-with-noexec-and-nosuid-among-other-useful-mount-options-for-better-security/7707

## To undo:
## sudo /usr/libexec/security-misc/permission-hardening-undo

#set -x
set -e
set -o pipefail

exit_code=0

mkdir --parents /var/lib/permission-hardening/private
mkdir --parents /var/lib/permission-hardening/existing_mode
mkdir --parents /var/lib/permission-hardening/new_mode
dpkg_admindir_parameter_existing_mode="--admindir /var/lib/permission-hardening/existing_mode"
dpkg_admindir_parameter_new_mode="--admindir /var/lib/permission-hardening/new_mode"

echo_wrapper_ignore() {
   echo "run: $@"
   "$@" 2>/dev/null || true
}

echo_wrapper_silent_ignore() {
   #echo "run: $@"
   "$@" 2>/dev/null || true
}

echo_wrapper_audit() {
   echo "run: $@"
   return_code=0
   "$@" || \
      { \
      return_code="$?" ; \
      exit_code=203 ; \
      echo "ERROR: above command failed with exit code '$return_code'! calling function name: '${FUNCNAME[1]}'" >&2 ; \
      };
}

echo_wrapper_silent_audit() {
   #echo "run (debugging): $@"
   return_code=0
   "$@" || \
      { \
      return_code="$?" ; \
      exit_code=204 ; \
      echo "ERROR: above command '$@' failed with exit code '$return_code'! calling function name: '${FUNCNAME[1]}'" >&2 ; \
      };
}

sanity_tests() {
   echo_wrapper_silent_audit which \
      capsh getcap setcap stat find dpkg-statoverride getent xargs grep 1>/dev/null
}

add_nosuid_statoverride_entry() {
   local fso_to_process
   fso_to_process="$fso"
   local should_be_counter
   should_be_counter="$(find "$fso_to_process" -perm /u=s,g=s | wc -l)" || true
   local counter_actual
   counter_actual=0

   local line
   while read -r line; do
      true "line: $line"
      counter_actual="$(( counter_actual + 1 ))"

      local arr file_name existing_mode existing_owner existing_group
      arr=($line)
      file_name="${arr[0]}"
      existing_mode="${arr[1]}"
      existing_owner="${arr[2]}"
      existing_group="${arr[3]}"

      if [ "$arr" = "" ]; then
         echo "ERROR: arr is empty. line: '$line'" >&2
         continue
      fi
      if [ "$file_name" = "" ]; then
         echo "ERROR: file_name is empty. line: '$line'" >&2
         continue
      fi
      if [ "$existing_mode" = "" ]; then
         echo "ERROR: existing_mode is empty. line: '$line'" >&2
         continue
      fi
      if [ "$existing_owner" = "" ]; then
         echo "ERROR: existing_owner is empty. line: '$line'" >&2
         continue
      fi
      if [ "$existing_group" = "" ]; then
         echo "ERROR: existing_group is empty. line: '$line'" >&2
         continue
      fi

      ## -h file      True if file is a symbolic Link.
      ## -u file      True if file has its set-user-id bit set.
      ## -g file      True if file has its set-group-id bit set.

      if test -h "$file_name" ; then
         ## https://forums.whonix.org/t/disable-suid-binaries/7706/14
         true "skip symlink: $file_name"
         continue
      fi

      if test -d "$file_name" ; then
         true "skip directory: $file_name"
         continue
      fi

      local setuid setuid_output setsgid setsgid_output
      setuid=""
      setuid_output=""
      if test -u "$file_name" ; then
         setuid=true
         setuid_output="set-user-id"
      fi
         setsgid=""
         setsgid_output=""
      if test -g "$file_name" ; then
         setsgid=true
         setsgid_output="set-group-id"
      fi

      local setuid_or_setsgid
      setuid_or_setsgid=""
      if [ "$setuid" = "true" ] || [ "$setsgid" = "true" ]; then
         setuid_or_setsgid=true
      fi
      if [ "$setuid_or_setsgid" = "" ]; then
         continue
      fi

      ## Remove suid / gid and execute permission for 'group' and 'others'.
      ## Similar to: chmod og-ugx /path/to/filename
      ## Removing execution permission is useful to make binaries such as 'su' fail closed rather
      ## than fail open if suid was removed from these.
      ## Do not remove read access since no security benefit and easier to manually undo for users.
      ## Are there suid or sgid binaries which are still useful if suid / sgid has been removed from these?
      new_mode="744"

      local is_exact_whitelisted
      is_exact_whitelisted=""
      for white_list_entry in $exact_white_list ; do
         if [ "$file_name" = "$white_list_entry" ]; then
            is_exact_whitelisted="true"
            ## Stop looping through the whitelist.
            break
         fi
      done

      local is_match_whitelisted
      is_match_whitelisted=""
      for matchwhite_list_entry in $match_white_list ; do
         if echo "$file_name" | grep --quiet --fixed-strings "$matchwhite_list_entry" ; then
            is_match_whitelisted="true"
            ## Stop looping through the match_white_list.
            break
         fi
      done

      local is_disable_whitelisted
      is_disable_whitelisted=""
      for disablematch_list_entry in $disable_white_list ; do
         if echo "$file_name" | grep --quiet --fixed-strings "$disablematch_list_entry" ; then
            is_disable_whitelisted="true"
            ## Stop looping through the disablewhitelist.
            break
         fi
      done

      if [ "$whitelists_disable_all" = "true" ]; then
         true "INFO: whitelists_disable_all=true - $setuid_output $setsgid_output found - file_name: '$file_name' | existing_mode: '$existing_mode'"
      elif [ "$is_disable_whitelisted" = "true" ]; then
         true "INFO: white list disabled - $setuid_output $setsgid_output found - file_name: '$file_name' | existing_mode: '$existing_mode'"
      else
         if [ "$is_exact_whitelisted" = "true" ]; then
            true "INFO: SKIP whitelisted - $setuid_output $setsgid_output found - file_name: '$file_name' | existing_mode: '$existing_mode'"
            continue
         fi
         if [ "$is_match_whitelisted" = "true" ]; then
            true "INFO: SKIP matchwhitelisted - $setuid_output $setsgid_output found - file_name: '$file_name' | existing_mode: '$existing_mode' | matchwhite_list_entry: '$matchwhite_list_entry'"
            continue
         fi
      fi

      echo "INFO: $setuid_output $setsgid_output found - file_name: '$file_name' | existing_mode: '$existing_mode' | new_mode: '$new_mode'"

      if dpkg-statoverride $dpkg_admindir_parameter_existing_mode --list "$file_name" >/dev/null ; then
         true "OK Existing mode already saved previously. No need to save again."
      else
         ## Save existing_mode in separate database.
         ## Not using --update as not intending to enforce existing_mode.
         echo_wrapper_silent_audit dpkg-statoverride $dpkg_admindir_parameter_existing_mode --add "$existing_owner" "$existing_group" "$existing_mode" "$file_name"
      fi

      ## No need to check "dpkg-statoverride --list" for existing entries.
      ## If existing_mode was correct already, we would not have reached this point.
      ## Since existing_mode is incorrect, remove from dpkg-statoverride and re-add.

      ## Remove from real database.
      echo_wrapper_silent_ignore dpkg-statoverride --remove "$file_name"

      ## Remove from separate database.
      echo_wrapper_silent_ignore dpkg-statoverride $dpkg_admindir_parameter_new_mode --remove "$file_name"

      ## Add to real database and use --update to make changes on disk.
      echo_wrapper_audit dpkg-statoverride --add --update "$existing_owner" "$existing_group" "$new_mode" "$file_name"

      ## Not using --update as this is only for recording.
      echo_wrapper_silent_audit dpkg-statoverride $dpkg_admindir_parameter_new_mode --add "$existing_owner" "$existing_group" "$new_mode" "$file_name"

      ## /lib will hit ARG_MAX if using bash 'shopt -s globstar' and '/lib/**'.
      ## Using 'find' with '-perm /u=s,g=s' is faster and avoids ARG_MAX.
      ## https://forums.whonix.org/t/disable-suid-binaries/7706/17
   done < <( find "$fso_to_process" -perm /u=s,g=s -print0 | xargs -I{} -0 stat -c "%n %a %U %G" {} )

   ## Sanity test.
   if [ ! "$should_be_counter" = "$counter_actual" ]; then
      echo "INFO: fso_to_process: '$fso_to_process' | counter_actual   : '$counter_actual'"
      echo "INFO: fso_to_process: '$fso_to_process' | should_be_counter: '$should_be_counter'"
      exit_code=202
      echo "ERROR: counter does not check out." >&2
   fi
}

set_file_perms() {
   true "INFO: START parsing config_file: '$config_file'"
   local line
   while read -r line || [[ -n "${line}" ]]; do
      if [ "$line" = "" ]; then
         continue
      fi

      if [[ "$line" =~ ^# ]]; then
         continue
      fi

      if [[ "$line" =~ [0-9a-zA-Z/] ]]; then
         true "OK line contains only white listed characters."
      else
         exit_code=200
         echo "ERROR: cannot parse line with invalid character. line: '$line'" >&2
         ## Safer to exit with error in this case.
         ## https://forums.whonix.org/t/disable-suid-binaries/7706/59
         exit "$exit_code"
      fi

      if [ "$line" = 'whitelists_disable_all=true' ]; then
         whitelists_disable_all=true
         echo "INFO: whitelists_disable_all=true - all whitelists disabled."
         continue
      fi

      #global fso
      local mode_from_config owner_from_config group_from_config capability_from_config
      if ! read -r fso mode_from_config owner_from_config group_from_config capability_from_config <<< "$line" ; then
         exit_code=201
         echo "ERROR: cannot parse. line: '$line'" >&2
         ## Debugging.
         du -hs /tmp || true
         echo "test -w /tmp: '$(test -w /tmp)'" >&2 || true
         ## Safer to exit with error in this case.
         ## https://forums.whonix.org/t/disable-suid-binaries/7706/59
         exit "$exit_code"
      fi

      ## Debugging.
      #echo "line: '$line'"
      #echo "fso: '$fso'"
      #echo "mode_from_config: '$mode_from_config'"
      #echo "owner_from_config: '$owner_from_config'"

      local fso_without_trailing_slash
      fso_without_trailing_slash="${fso%/}"

      if [ "$mode_from_config" = "disablewhitelist" ]; then
         ## TODO: test/add white spaces inside file name support
         disable_white_list+="$fso "
         continue
      fi

      if [ "$mode_from_config" = "exactwhitelist" ]; then
         ## TODO: test/add white spaces inside file name support
         exact_white_list+="$fso "
         continue
      fi

      if [ "$mode_from_config" = "matchwhitelist" ]; then
         ## TODO: test/add white spaces inside file name support
         match_white_list+="$fso "
         continue
      fi

      if [ ! -e "$fso" ]; then
         true "INFO: fso: '$fso' - does not exist. This is likely normal."
         continue
      fi

      ## Use dpkg-statoverride so permissions are not reset during upgrades.

      if [ "$mode_from_config" = "nosuid" ]; then
         ## If mode_from_config is "nosuid" the config does not set owner and
         ## group. Therefore do not enforce owner/group check.

         add_nosuid_statoverride_entry
      else
         local string_length_of_mode_from_config
         string_length_of_mode_from_config="${#mode_from_config}"
         if [ "$string_length_of_mode_from_config" -gt "4" ]; then
            echo "ERROR: Mode '$mode_from_config' is invalid!" >&2
            continue
         fi
         if [ "$string_length_of_mode_from_config" -lt "3" ]; then
            echo "ERROR: Mode '$mode_from_config' is invalid!" >&2
            continue
         fi

         if ! grep --quiet --fixed-strings "${owner_from_config}:" /var/lib/permission-hardening/private/passwd ; then
            echo "ERROR: owner_from_config '$owner_from_config' does not exist!" >&2
            continue
         fi

         if ! grep --quiet --fixed-strings "${group_from_config}:" /var/lib/permission-hardening/private/group ; then
            echo "ERROR: group_from_config '$group_from_config' does not exist!" >&2
            continue
         fi

         local mode_for_grep
         mode_for_grep="$mode_from_config"
         first_character_of_mode_from_config="${mode_from_config::1}"
         if [ "$first_character_of_mode_from_config" = "0" ]; then
            ## Remove leading '0'.
            mode_for_grep="${mode_from_config:1}"
         fi

         local stat_output
         stat_output=""
         if ! stat_output="$(stat -c "%n %a %U %G" "$fso_without_trailing_slash")" ; then
            echo "ERROR: failed to run 'stat' for fso_without_trailing_slash: '$fso_without_trailing_slash'!" >&2
            continue
         fi

         local arr file_name existing_mode existing_owner existing_group
         arr=($stat_output)
         file_name="${arr[0]}"
         existing_mode="${arr[1]}"
         existing_owner="${arr[2]}"
         existing_group="${arr[3]}"

         if [ "$arr" = "" ]; then
            echo "ERROR: arr is empty. stat_output: '$stat_output' | line: '$line'" >&2
            continue
         fi
         if [ "$file_name" = "" ]; then
            echo "ERROR: file_name is empty. stat_output: '$stat_output' | line: '$line'" >&2
            continue
         fi
         if [ "$existing_mode" = "" ]; then
            echo "ERROR: existing_mode is empty. stat_output: '$stat_output' | line: '$line'" >&2
            continue
         fi
         if [ "$existing_owner" = "" ]; then
            echo "ERROR: existing_owner is empty. stat_output: '$stat_output' | line: '$line'" >&2
            continue
         fi
         if [ "$existing_group" = "" ]; then
            echo "ERROR: $existing_group is empty. stat_output: '$stat_output' | line: '$line'" >&2
            continue
         fi

         ## Check there is an entry for the fso.
         ##
         ## example: dpkg-statoverride --list | grep /home
         ## output:
         ## root root 755 /home
         ##
         ## dpkg-statoverride does not show leading '0'.
         local dpkg_statoverride_list_output=""
         local dpkg_statoverride_list_exit_code=0
         dpkg_statoverride_list_output="$(dpkg-statoverride --list "$fso_without_trailing_slash")" || { dpkg_statoverride_list_exit_code=$? ; true; };

         if [ "$dpkg_statoverride_list_exit_code" = "0" ]; then
            true "There is an fso entry. Check if owner/group/mode match."
            local grep_line
            grep_line="$owner_from_config $group_from_config $mode_for_grep $fso_without_trailing_slash"
            if echo "$dpkg_statoverride_list_output" | grep --quiet --fixed-strings "$grep_line" ; then
               true "OK The owner/group/mode matches. No further action required."
            else
               true "The owner/group/mode do not match, therefore remove and re-add the entry to update it."
               ## fso_without_trailing_slash instead of fso to prevent
               ## "dpkg-statoverride: warning: stripping trailing /"

               if dpkg-statoverride $dpkg_admindir_parameter_existing_mode --list "$fso_without_trailing_slash" >/dev/null ; then
                  true "OK Existing mode already saved previously. No need to save again."
               else
                  ## Save existing_mode in separate database.
                  ## Not using --update as not intending to enforce existing_mode.
                  echo_wrapper_silent_audit dpkg-statoverride $dpkg_admindir_parameter_existing_mode --add "$existing_owner" "$existing_group" "$existing_mode" "$fso_without_trailing_slash"
               fi

               echo_wrapper_silent_ignore dpkg-statoverride $dpkg_admindir_parameter_new_mode --remove "$fso_without_trailing_slash"

               ## Remove from and add to real database.
               echo_wrapper_silent_ignore dpkg-statoverride --remove "$fso_without_trailing_slash"
               echo_wrapper_audit dpkg-statoverride --add --update "$owner_from_config" "$group_from_config" "$mode_from_config" "$fso_without_trailing_slash"

               ## Save in separate database.
               ## Not using --update as this is only for saving.
               echo_wrapper_silent_audit dpkg-statoverride $dpkg_admindir_parameter_new_mode --add "$owner_from_config" "$group_from_config" "$mode_from_config" "$fso_without_trailing_slash"
            fi
         else
            true "There is no fso entry. Therefore add one."

            if dpkg-statoverride $dpkg_admindir_parameter_existing_mode --list "$fso_without_trailing_slash" >/dev/null ; then
               true "OK Existing mode already saved previously. No need to save again."
            else
               ## Save existing_mode in separate database.
               ## Not using --update as not intending to enforce existing_mode.
               echo_wrapper_silent_audit dpkg-statoverride $dpkg_admindir_parameter_existing_mode --add "$existing_owner" "$existing_group" "$existing_mode" "$fso_without_trailing_slash"
            fi

            ## Add to real database.
            echo_wrapper_audit dpkg-statoverride --add --update "$owner_from_config" "$group_from_config" "$mode_from_config" "$fso_without_trailing_slash"

            ## Save in separate database.
            ## Not using --update as this is only for saving.
            echo_wrapper_silent_audit dpkg-statoverride $dpkg_admindir_parameter_new_mode --add "$owner_from_config" "$group_from_config" "$mode_from_config" "$fso_without_trailing_slash"
         fi
      fi
      if [ "$capability_from_config" = "" ]; then
	      continue
      fi

      if [ "$capability_from_config" = "none" ]; then
         ## https://forums.whonix.org/t/disable-suid-binaries/7706/45
         # sudo setcap -r /bin/ping 2>/dev/null
         # Failed to set capabilities on file '/bin/ping' (No data available)
         # The value of the capability argument is not permitted for a file. Or the file is not a regular (non-symlink) file
         ## Therefore use echo_wrapper_ignore.
         echo_wrapper_ignore setcap -r "$fso"
         getcap_output="$(getcap "$fso")"
         if [ ! "$getcap_output" = "" ]; then
            exit_code=205
            echo "ERROR: removing capabilities for fso '$fso' failed!" >&2
            continue
         fi
      else
         if ! capsh --print | grep --fixed-strings "Bounding set" | grep --quiet "$capability_from_config" ; then
            echo "ERROR: capability_from_config '$capability_from_config' does not exist!" >&2
            continue
         fi

         ## feature request: dpkg-statoverride: support for capabilities
         ## https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=502580
         echo_wrapper_audit setcap "${capability_from_config}+ep" "$fso"
      fi
   done < "$config_file"
   true "INFO: END parsing config_file: '$config_file'"
}

parse_config_folder() {
  touch /var/lib/permission-hardening/private/passwd
  chmod og-rwx /var/lib/permission-hardening/private/passwd
  touch /var/lib/permission-hardening/private/group
  chmod og-rwx /var/lib/permission-hardening/private/group

  local passwd_file_contents_temp
  # Query contents of password and group databases only once and buffer them
  #
  # If we don't buffer we sometimes get incorrect results when checking for entries using
  # 'if getent passwd | grep --quiet '^root:'; ...' since 'grep' exits after the first match in
  # this case causing 'getent' to receive SIGPIPE, which then fails the pipeline since
  # 'set -o pipefail' is set for this script.
  passwd_file_contents_temp=$(getent passwd)
  echo "$passwd_file_contents_temp" | tee /var/lib/permission-hardening/private/passwd >/dev/null
  group_file_contents_temp=$(getent group)
  echo "$group_file_contents_temp" | tee /var/lib/permission-hardening/private/group >/dev/null

  passwd_file_contents=$(cat /var/lib/permission-hardening/private/passwd)
  group_file_contents=$(cat /var/lib/permission-hardening/private/group)

  shopt -s nullglob
  for config_file in /etc/permission-hardening.d/*.conf /usr/local/etc/permission-hardening.d/*.conf; do
    set_file_perms
  done
}

sanity_tests
parse_config_folder

echo "\
INFO: To compare the current and previous permission modes:
1. Install 'meld' (or similar) for an easier comparison of file changes:
   sudo apt install --no-install-recommends meld

2. Use 'meld' to view the differences:
   meld /var/lib/permission-hardening/existing_mode/statoverride /var/lib/permission-hardening/new_mode/statoverride"

if [ ! "$exit_code" = "0" ]; then
   echo "ERROR: Will exit with non-zero exit code: '$exit_code'" >&2
fi

exit "$exit_code"