scripts/image_signing/common_minimal.sh

#!/bin/sh
#
# Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
#
# Note: This file must be written in dash compatible way as scripts that use 
# this may run in the Chrome OS client enviornment.  

# Determine script directory
SCRIPT_DIR=$(dirname $0)
PROG=$(basename $0)
GPT=cgpt

# The tag when the rootfs is changed.
TAG_NEEDS_TO_BE_SIGNED="/root/.need_to_be_signed"

# List of Temporary files and mount points.
TEMP_FILE_LIST=$(mktemp)
TEMP_DIR_LIST=$(mktemp)

# Finds and loads the 'shflags' library, or return as failed.
load_shflags() {
  # Load shflags
  if [ -f /usr/lib/shflags ]; then
    . /usr/lib/shflags
  elif [ -f "${SCRIPT_DIR}/shflags" ]; then
    . "${SCRIPT_DIR}/shflags"
  elif [ -f "${SCRIPT_DIR}/lib/shflags/shflags" ]; then
    . "${SCRIPT_DIR}/lib/shflags/shflags"
  else
    echo "ERROR: Cannot find the required shflags library."
    return 1
  fi

  # Add debug option for debug output below
  DEFINE_boolean debug $FLAGS_FALSE "Provide debug messages" "d"
}

# Functions for debug output
# ----------------------------------------------------------------------------

# Reports error message and exit(1)
# Args: error message
err_die() {
  echo "ERROR: $*" 1>&2
  exit 1
}

# Returns true if we're running in debug mode.
#
# Note that if you don't set up shflags by calling load_shflags(), you
# must set $FLAGS_debug and $FLAGS_TRUE yourself.  The default
# behavior is that debug will be off if you define neither $FLAGS_TRUE
# nor $FLAGS_debug.
is_debug_mode() {
  [ "${FLAGS_debug:-not$FLAGS_TRUE}" = "$FLAGS_TRUE" ]
}

# Prints messages (in parameters) in debug mode
# Args: debug message
debug_msg() {
  if is_debug_mode; then
    echo "DEBUG: $*" 1>&2
  fi
}

# Functions for temporary files and directories
# ----------------------------------------------------------------------------

# Create a new temporary file and return its name.
# File is automatically cleaned when cleanup_temps_and_mounts() is called.
make_temp_file() {
  local tempfile=$(mktemp)
  echo "$tempfile" >> $TEMP_FILE_LIST
  echo $tempfile
}

# Create a new temporary directory and return its name.
# Directory is automatically deleted and any filesystem mounted on it unmounted
# when cleanup_temps_and_mounts() is called.
make_temp_dir() {
  local tempdir=$(mktemp -d)
  echo "$tempdir" >> $TEMP_DIR_LIST
  echo $tempdir
}

cleanup_temps_and_mounts() {
  for i in $(cat $TEMP_FILE_LIST); do
    rm -f $i
  done
  set +e  # umount may fail for unmounted directories
  for i in $(cat $TEMP_DIR_LIST); do
    if [ -n "$i" ]; then
      if has_needs_to_be_resigned_tag "$i"; then
        echo "Warning: image may be modified. Please resign image."
      fi
      sudo umount -d $i 2>/dev/null
      rm -rf $i
    fi
  done
  set -e
  rm -rf $TEMP_DIR_LIST $TEMP_FILE_LIST
}

trap "cleanup_temps_and_mounts" EXIT

# Functions for partition management
# ----------------------------------------------------------------------------

# Read GPT table to find the starting location of a specific partition.
# Args: DEVICE PARTNUM
# Returns: offset (in sectors) of partition PARTNUM
partoffset() {
  sudo $GPT show -b -i $2 $1
}

# Read GPT table to find the size of a specific partition.
# Args: DEVICE PARTNUM
# Returns: size (in sectors) of partition PARTNUM
partsize() {
  sudo $GPT show -s -i $2 $1
}

# Tags a file system as "needs to be resigned".
# Args: MOUNTDIRECTORY
tag_as_needs_to_be_resigned() {
  local mount_dir="$1"
  sudo touch "$mount_dir/$TAG_NEEDS_TO_BE_SIGNED"
}

# Determines if the target file system has the tag for resign
# Args: MOUNTDIRECTORY
# Returns: true if the tag is there otherwise false
has_needs_to_be_resigned_tag() {
  local mount_dir="$1"
  [ -f "$mount_dir/$TAG_NEEDS_TO_BE_SIGNED" ]
}

# Determines if the target file system is a Chrome OS root fs
# Args: MOUNTDIRECTORY
# Returns: true if MOUNTDIRECTORY looks like root fs, otherwise false
is_rootfs_partition() {
  local mount_dir="$1"
  [ -f "$mount_dir/$(dirname "$TAG_NEEDS_TO_BE_SIGNED")" ]
}

# Mount a partition read-only from an image into a local directory
# Args: IMAGE PARTNUM MOUNTDIRECTORY
mount_image_partition_ro() {
  local image=$1
  local partnum=$2
  local mount_dir=$3
  local offset=$(partoffset "$image" "$partnum")
  sudo mount -o loop,ro,offset=$((offset * 512)) "$image" "$mount_dir"
}

# Mount a partition from an image into a local directory
# Args: IMAGE PARTNUM MOUNTDIRECTORY
mount_image_partition() {
  local image=$1
  local partnum=$2
  local mount_dir=$3
  local offset=$(partoffset "$image" "$partnum")
  # Forcibly call enable_rw_mount.  It should fail on unsupported filesystems
  # and be idempotent on ext*.
  enable_rw_mount "$image" $((offset * 512)) 2> /dev/null
  sudo mount -o loop,offset=$((offset * 512)) "$image" "$mount_dir"
  if is_rootfs_partition "$mount_dir"; then
    tag_as_needs_to_be_resigned "$mount_dir"
  fi
}

# Extract a partition to a file
# Args: IMAGE PARTNUM OUTPUTFILE
extract_image_partition() {
  local image=$1
  local partnum=$2
  local output_file=$3
  local offset=$(partoffset "$image" "$partnum")
  local size=$(partsize "$image" "$partnum")
  dd if=$image of=$output_file bs=512 skip=$offset count=$size conv=notrunc >/dev/null 2>&1
}

# Replace a partition in an image from file
# Args: IMAGE PARTNUM INPUTFILE
replace_image_partition() {
  local image=$1
  local partnum=$2
  local input_file=$3
  local offset=$(partoffset "$image" "$partnum")
  local size=$(partsize "$image" "$partnum")
  dd if=$input_file of=$image bs=512 seek=$offset count=$size conv=notrunc
}

# For details, see crosutils.git/common.sh
enable_rw_mount() {
  local rootfs="$1"
  local offset="${2-0}"

  # Make sure we're checking an ext2 image
  if ! is_ext2 "$rootfs" $offset; then
    echo "enable_rw_mount called on non-ext2 filesystem: $rootfs $offset" 1>&2
    return 1
  fi

  local ro_compat_offset=$((0x464 + 3))  # Set 'highest' byte
  # Dash can't do echo -ne, but it can do printf "\NNN"
  # We could use /dev/zero here, but this matches what would be
  # needed for disable_rw_mount (printf '\377').
  printf '\000' |
    sudo dd of="$rootfs" seek=$((offset + ro_compat_offset)) \
            conv=notrunc count=1 bs=1
}

# For details, see crosutils.git/common.sh
is_ext2() {
  local rootfs="$1"
  local offset="${2-0}"

  # Make sure we're checking an ext2 image
  local sb_magic_offset=$((0x438))
  local sb_value=$(sudo dd if="$rootfs" skip=$((offset + sb_magic_offset)) \
                   count=2 bs=1 2>/dev/null)
  local expected_sb_value=$(printf '\123\357')
  if [ "$sb_value" = "$expected_sb_value" ]; then
    return 0
  fi
  return 1
}

disable_rw_mount() {
  local rootfs="$1"
  local offset="${2-0}"

  # Make sure we're checking an ext2 image
  if ! is_ext2 "$rootfs" $offset; then
    echo "disable_rw_mount called on non-ext2 filesystem: $rootfs $offset" 1>&2
    return 1
  fi

  local ro_compat_offset=$((0x464 + 3))  # Set 'highest' byte
  # Dash can't do echo -ne, but it can do printf "\NNN"
  # We could use /dev/zero here, but this matches what would be
  # needed for disable_rw_mount (printf '\377').
  printf '\377' |
    sudo dd of="$rootfs" seek=$((offset + ro_compat_offset)) \
            conv=notrunc count=1 bs=1
}

rw_mount_disabled() {
  local rootfs="$1"
  local offset="${2-0}"

  # Make sure we're checking an ext2 image
  if ! is_ext2 "$rootfs" $offset; then
    return 2
  fi

  local ro_compat_offset=$((0x464 + 3))  # Set 'highest' byte
  local ro_value=$(sudo dd if="$rootfs" skip=$((offset + ro_compat_offset)) \
                   count=1 bs=1 2>/dev/null)
  local expected_ro_value=$(printf '\377')
  if [ "$ro_value" = "$expected_ro_value" ]; then
    return 0
  fi
  return 1
}

# Misc functions
# ----------------------------------------------------------------------------

# Returns true if all files in parameters exist.
# Args: List of files
ensure_files_exist() {
  local filename return_value=0
  for filename in "$@"; do
    if [ ! -f "$filename" -a ! -b "$filename" ]; then
      echo "ERROR: Cannot find required file: $filename"
      return_value=1
    fi
  done

  return $return_value
}

# Check if the 'chronos' user already has a password
# Args: rootfs
no_chronos_password() {
  local rootfs=$1
  sudo grep -q '^chronos:\*:' "$rootfs/etc/shadow"
}

trap "cleanup_temps_and_mounts" EXIT