scripts/update_payload/payload.py

#
# Copyright (C) 2013 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

"""Tools for reading, verifying and applying Chrome OS update payloads."""

from __future__ import absolute_import
from __future__ import print_function

import hashlib
import io
import mmap
import struct
import zipfile

import update_metadata_pb2

from update_payload import checker
from update_payload import common
from update_payload.error import PayloadError


#
# Helper functions.
#
def _ReadInt(file_obj, size, is_unsigned, hasher=None):
  """Reads a binary-encoded integer from a file.

  It will do the correct conversion based on the reported size and whether or
  not a signed number is expected. Assumes a network (big-endian) byte
  ordering.

  Args:
    file_obj: a file object
    size: the integer size in bytes (2, 4 or 8)
    is_unsigned: whether it is signed or not
    hasher: an optional hasher to pass the value through

  Returns:
    An "unpacked" (Python) integer value.

  Raises:
    PayloadError if an read error occurred.
  """
  return struct.unpack(common.IntPackingFmtStr(size, is_unsigned),
                       common.Read(file_obj, size, hasher=hasher))[0]


#
# Update payload.
#
class Payload(object):
  """Chrome OS update payload processor."""

  class _PayloadHeader(object):
    """Update payload header struct."""

    # Header constants; sizes are in bytes.
    _MAGIC = b'CrAU'
    _VERSION_SIZE = 8
    _MANIFEST_LEN_SIZE = 8
    _METADATA_SIGNATURE_LEN_SIZE = 4

    def __init__(self):
      self.version = None
      self.manifest_len = None
      self.metadata_signature_len = None
      self.size = None

    def ReadFromPayload(self, payload_file, hasher=None):
      """Reads the payload header from a file.

      Reads the payload header from the |payload_file| and updates the |hasher|
      if one is passed. The parsed header is stored in the _PayloadHeader
      instance attributes.

      Args:
        payload_file: a file object
        hasher: an optional hasher to pass the value through

      Returns:
        None.

      Raises:
        PayloadError if a read error occurred or the header is invalid.
      """
      # Verify magic
      magic = common.Read(payload_file, len(self._MAGIC), hasher=hasher)
      if magic != self._MAGIC:
        raise PayloadError('invalid payload magic: %s' % magic)

      self.version = _ReadInt(payload_file, self._VERSION_SIZE, True,
                              hasher=hasher)
      self.manifest_len = _ReadInt(payload_file, self._MANIFEST_LEN_SIZE, True,
                                   hasher=hasher)
      self.size = (len(self._MAGIC) + self._VERSION_SIZE +
                   self._MANIFEST_LEN_SIZE)
      self.metadata_signature_len = 0

      if self.version == common.BRILLO_MAJOR_PAYLOAD_VERSION:
        self.size += self._METADATA_SIGNATURE_LEN_SIZE
        self.metadata_signature_len = _ReadInt(
            payload_file, self._METADATA_SIGNATURE_LEN_SIZE, True,
            hasher=hasher)

  def __init__(self, payload_file, payload_file_offset=0):
    """Initialize the payload object.

    Args:
      payload_file: update payload file object open for reading
      payload_file_offset: the offset of the actual payload
    """
    if zipfile.is_zipfile(payload_file):
      with zipfile.ZipFile(payload_file) as zfp:
        self.payload_file = zfp.open("payload.bin", "r")
    elif isinstance(payload_file, str):
      payload_fp = open(payload_file, "rb")
      payload_bytes = mmap.mmap(
          payload_fp.fileno(), 0, access=mmap.ACCESS_READ)
      self.payload_file = io.BytesIO(payload_bytes)
    else:
      self.payload_file = payload_file
    self.payload_file_offset = payload_file_offset
    self.manifest_hasher = None
    self.is_init = False
    self.header = None
    self.manifest = None
    self.data_offset = None
    self.metadata_signature = None
    self.payload_signature = None
    self.metadata_size = None

  @property
  def is_incremental(self):
    return any([part.HasField("old_partition_info") for part in self.manifest.partitions])

  @property
  def is_partial(self):
    return self.manifest.partial_update

  def _ReadHeader(self):
    """Reads and returns the payload header.

    Returns:
      A payload header object.

    Raises:
      PayloadError if a read error occurred.
    """
    header = self._PayloadHeader()
    header.ReadFromPayload(self.payload_file, self.manifest_hasher)
    return header

  def _ReadManifest(self):
    """Reads and returns the payload manifest.

    Returns:
      A string containing the payload manifest in binary form.

    Raises:
      PayloadError if a read error occurred.
    """
    if not self.header:
      raise PayloadError('payload header not present')

    return common.Read(self.payload_file, self.header.manifest_len,
                       hasher=self.manifest_hasher)

  def _ReadMetadataSignature(self):
    """Reads and returns the metadata signatures.

    Returns:
      A string containing the metadata signatures protobuf in binary form or
      an empty string if no metadata signature found in the payload.

    Raises:
      PayloadError if a read error occurred.
    """
    if not self.header:
      raise PayloadError('payload header not present')

    return common.Read(
        self.payload_file, self.header.metadata_signature_len,
        offset=self.payload_file_offset + self.header.size +
        self.header.manifest_len)

  def ReadDataBlob(self, offset, length):
    """Reads and returns a single data blob from the update payload.

    Args:
      offset: offset to the beginning of the blob from the end of the manifest
      length: the blob's length

    Returns:
      A string containing the raw blob data.

    Raises:
      PayloadError if a read error occurred.
    """
    return common.Read(self.payload_file, length,
                       offset=self.payload_file_offset + self.data_offset +
                       offset)

  def Init(self):
    """Initializes the payload object.

    This is a prerequisite for any other public API call.

    Raises:
      PayloadError if object already initialized or fails to initialize
      correctly.
    """
    if self.is_init:
      raise PayloadError('payload object already initialized')

    self.manifest_hasher = hashlib.sha256()

    # Read the file header.
    self.payload_file.seek(self.payload_file_offset)
    self.header = self._ReadHeader()

    # Read the manifest.
    manifest_raw = self._ReadManifest()
    self.manifest = update_metadata_pb2.DeltaArchiveManifest()
    self.manifest.ParseFromString(manifest_raw)

    # Read the metadata signature (if any).
    metadata_signature_raw = self._ReadMetadataSignature()
    if metadata_signature_raw:
      self.metadata_signature = update_metadata_pb2.Signatures()
      self.metadata_signature.ParseFromString(metadata_signature_raw)

    self.metadata_size = self.header.size + self.header.manifest_len
    self.data_offset = self.metadata_size + self.header.metadata_signature_len

    if self.manifest.signatures_offset and self.manifest.signatures_size:
      payload_signature_blob = self.ReadDataBlob(
          self.manifest.signatures_offset, self.manifest.signatures_size)
      payload_signature = update_metadata_pb2.Signatures()
      payload_signature.ParseFromString(payload_signature_blob)
      self.payload_signature = payload_signature

    self.is_init = True

  def _AssertInit(self):
    """Raises an exception if the object was not initialized."""
    if not self.is_init:
      raise PayloadError('payload object not initialized')

  def ResetFile(self):
    """Resets the offset of the payload file to right past the manifest."""
    self.payload_file.seek(self.payload_file_offset + self.data_offset)

  def IsDelta(self):
    """Returns True iff the payload appears to be a delta."""
    self._AssertInit()
    return (any(partition.HasField('old_partition_info')
                for partition in self.manifest.partitions))

  def IsFull(self):
    """Returns True iff the payload appears to be a full."""
    return not self.IsDelta()

  def Check(self, pubkey_file_name=None, metadata_sig_file=None,
            metadata_size=0, report_out_file=None, assert_type=None,
            block_size=0, part_sizes=None, allow_unhashed=False,
            disabled_tests=()):
    """Checks the payload integrity.

    Args:
      pubkey_file_name: public key used for signature verification
      metadata_sig_file: metadata signature, if verification is desired
      metadata_size: metadata size, if verification is desired
      report_out_file: file object to dump the report to
      assert_type: assert that payload is either 'full' or 'delta'
      block_size: expected filesystem / payload block size
      part_sizes: map of partition label to (physical) size in bytes
      allow_unhashed: allow unhashed operation blobs
      disabled_tests: list of tests to disable

    Raises:
      PayloadError if payload verification failed.
    """
    self._AssertInit()

    # Create a short-lived payload checker object and run it.
    helper = checker.PayloadChecker(
        self, assert_type=assert_type, block_size=block_size,
        allow_unhashed=allow_unhashed, disabled_tests=disabled_tests)
    helper.Run(pubkey_file_name=pubkey_file_name,
               metadata_sig_file=metadata_sig_file,
               metadata_size=metadata_size,
               part_sizes=part_sizes,
               report_out_file=report_out_file)