enable_asan_mode

#!/bin/bash -e

if [ $# -ne 1 ]; then
    echo "Usage:" 1>&2
    echo "  sudo $0 enable       ... enables ASanification of system libraries on your system" 1>&2
    echo "  sudo $0 disable      ... reverts the changes and restores the system back to normal" 1>&2
    echo "  $0 status            ... prints current mode" 1>&2
    exit 1
fi

LIBSYSTEM_B="/usr/lib/libSystem.B.dylib"
LIBSYSTEM_B_BACKUP="${LIBSYSTEM_B}-asan-mode-backup"
LIBSYSTEM_B_ASAN="/usr/lib/libSystem.B_asan.dylib"

# If this file is present on the system and we are using a development build
# then the usual memory resource limits won't be applied.
# rdar://problem/43520116
DISABLE_MEM_LIMIT_COOKIE_FILE="/usr/local/share/launchd-disable-memory-limits"
DISABLE_MEM_LIMIT_COOKIE_CONTENTS="kEnableAsanDisableMemLimit"

function is_mac_os() {
  if [ $(sw_vers -productName | grep -c '^Mac OS') -ne 0 ]; then
      # Mac OS.
      return 0
  else
      # Something else.
      return 1
  fi
}

function show_have_asan_mode_on_msg() {
    echo "Looks like your system already has ASan mode enabled, or you have a custom ${LIBSYSTEM_B} file. Not activating." 1>&2
}

if ! is_mac_os; then
    # Check assumption that ${LIBSYSTEM_B} is in the dyld shared cache.
    if [ "$(dyld_shared_cache_util -list | grep -c "^${LIBSYSTEM_B}$")" -eq 0 ]; then
        echo "Error: Non macOS platform detected but ${LIBSYSTEM_B} is not in your dyld shared cache." 1>&2
        exit 1
    fi
fi

case "$1" in
  enable)
      if [[ $(id -u) != 0 ]]; then echo "Must be run as root." 1>&2; exit 1; fi

      if is_mac_os; then
          if [ -f ${LIBSYSTEM_B_BACKUP} ]; then
              if [ "`md5 -q ${LIBSYSTEM_B_BACKUP}`" != "`md5 -q ${LIBSYSTEM_B}`" ]; then
                  show_have_asan_mode_on_msg
                  exit 1
              fi
          fi
          ditto ${LIBSYSTEM_B} ${LIBSYSTEM_B_BACKUP}
      else
          # libSystem.B.dylib does not exist on non-macos platforms because it
          # lives in the dyld cache so we don't have a back up file. Instead
          # the presence of `libSystem.B.dylib` indicates that we are using ASan mode.
          if [ -f ${LIBSYSTEM_B} ]; then
              show_have_asan_mode_on_msg
              exit 1
          fi
          # Disable memory limits because ASan adds memory overhead.
          echo "${DISABLE_MEM_LIMIT_COOKIE_CONTENTS}" > "${DISABLE_MEM_LIMIT_COOKIE_FILE}"
      fi

      ditto ${LIBSYSTEM_B_ASAN} ${LIBSYSTEM_B}
      echo "ASan mode activated. You probably want to reboot now." 1>&2
      exit 0
  ;;
  disable)
      if [[ $(id -u) != 0 ]]; then echo "Must be run as root." 1>&2; exit 1; fi
      if is_mac_os; then
          ditto ${LIBSYSTEM_B_BACKUP} ${LIBSYSTEM_B}
      else
          if [ ! -f "${LIBSYSTEM_B}" ]; then
              echo "ASan mode cannot be disabled if it is not already enabled" 2>&1
              exit 1
          fi
          if [ "`md5 -q ${LIBSYSTEM_B_ASAN}`" != "`md5 -q ${LIBSYSTEM_B}`" ]; then
              echo "You appear to have a custom ${LIBSYSTEM_B} file. Not deactivating." 1>&2
              exit 1
          fi
          # Safe to do because we've checked this is the ASan version and the normal versions
          # lives in the dyld shared cache.
          rm -f ${LIBSYSTEM_B}
          if [ ! -f "${DISABLE_MEM_LIMIT_COOKIE_FILE}" ] ; then
              echo "Warning: Can't find \"${DISABLE_MEM_LIMIT_COOKIE_FILE}\" so skipping delete" 2>&1
          else
              # Check the contents of the cookie file and only delete if it matches.
              # If it doesn't match we don't delete because we assume the user wants
              # to keep the cookie file around.
              if [ "$(grep -c "^${DISABLE_MEM_LIMIT_COOKIE_CONTENTS}$" "${DISABLE_MEM_LIMIT_COOKIE_FILE}")" -eq 1 ]; then
                  rm -f "${DISABLE_MEM_LIMIT_COOKIE_FILE}"
              else
                  echo "Warning: Not removing \"${DISABLE_MEM_LIMIT_COOKIE_FILE}\" because it has been modified" 2>&1
              fi
          fi
      fi
      echo "ASan mode deactivated. You probably want to reboot now." 1>&2
      exit 0
  ;;
  status)
      if is_mac_os; then
          if [ ! -f ${LIBSYSTEM_B_BACKUP} ]; then
              echo "ASan mode is disabled." 1>&2
              exit 0
          fi

          if [ "`md5 -q ${LIBSYSTEM_B_BACKUP}`" == "`md5 -q ${LIBSYSTEM_B}`" ]; then
              echo "ASan mode is disabled." 1>&2
              exit 0
          fi
      else
          if [ ! -f ${LIBSYSTEM_B} ]; then
              echo "ASan mode is disabled." 1>&2
              exit 0
          fi
      fi

      if [ "`md5 -q ${LIBSYSTEM_B_ASAN}`" == "`md5 -q ${LIBSYSTEM_B}`" ]; then
          echo "ASan mode is enabled." 1>&2
          exit 0
      fi

      echo "Cannot tell whether ASan mode is enabled or not. You seem to have a custom ${LIBSYSTEM_B} file." 1>&2
      exit 1
  ;;
  *)
      echo "Invalid argument. Run '$0' for usage instructions." 1>&2
      exit 1
  ;;
esac