host/lib/update_payload/payload.py

# Copyright (c) 2013 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.

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

import hashlib
import struct

import applier
import block_tracer
import checker
import common
from error import PayloadError
import update_metadata_pb2


#
# 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."""

    def __init__(self, version, manifest_len):
      self.version = version
      self.manifest_len = manifest_len

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

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

    Args:
      payload_file: update payload file object open for reading

    """
    self.payload_file = payload_file
    self.manifest_hasher = None
    self.is_init = False
    self.header = None
    self.manifest = None
    self.data_offset = 0

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

    Returns:
      A payload header object.
    Raises:
      PayloadError if a read error occurred.

    """
    # Verify magic
    magic = common.Read(self.payload_file, len(self._MAGIC),
                        hasher=self.manifest_hasher)
    if magic != self._MAGIC:
      raise PayloadError('invalid payload magic: %s' % magic)

    return self._PayloadHeader(
        _ReadInt(self.payload_file, self._VERSION_SIZE, True,
                 hasher=self.manifest_hasher),
        _ReadInt(self.payload_file, self._MANIFEST_LEN_SIZE, True,
                 hasher=self.manifest_hasher))

  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 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.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')

    # Initialize hash context.
    # pylint: disable=E1101
    self.manifest_hasher = hashlib.sha256()

    # Read the file header.
    self.header = self._ReadHeader()

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

    # Store data offset.
    self.data_offset = (len(self._MAGIC) + self._VERSION_SIZE +
                        self._MANIFEST_LEN_SIZE + self.header.manifest_len)

    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.data_offset)

  def IsDelta(self):
    """Returns True iff the payload appears to be a delta."""
    self._AssertInit()
    return (self.manifest.HasField('old_kernel_info') or
            self.manifest.HasField('old_rootfs_info'))

  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,
            report_out_file=None, assert_type=None, block_size=0,
            allow_unhashed=False):
    """Checks the payload integrity.

    Args:
      pubkey_file_name: public key used for signature verification
      metadata_sig_file: metadata signature, 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
      allow_unhashed: allow unhashed operation blobs
    Raises:
      PayloadError if payload verification failed.

    """
    self._AssertInit()

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

  def Apply(self, dst_kernel_part, dst_rootfs_part, src_kernel_part=None,
            src_rootfs_part=None):
    """Applies the update payload.

    Args:
      dst_kernel_part: name of dest kernel partition file
      dst_rootfs_part: name of dest rootfs partition file
      src_kernel_part: name of source kernel partition file (optional)
      src_rootfs_part: name of source rootfs partition file (optional)
    Raises:
      PayloadError if payload application failed.

    """
    self._AssertInit()

    # Create a short-lived payload applier object and run it.
    helper = applier.PayloadApplier(self)
    helper.Run(dst_kernel_part, dst_rootfs_part,
               src_kernel_part=src_kernel_part,
               src_rootfs_part=src_rootfs_part)

  def TraceBlock(self, block, skip, trace_out_file, is_kernel):
    """Traces the origin(s) of a given dest partition block.

    The tracing tries to find origins transitively, when possible (it currently
    only works for move operations, where the mapping of src/dst is
    one-to-one). It will dump a list of operations and source blocks
    responsible for the data in the given dest block.

    Args:
      block: the block number whose origin to trace
      skip: the number of first origin mappings to skip
      trace_out_file: file object to dump the trace to
      is_kernel: trace through kernel (True) or rootfs (False) operations

    """
    self._AssertInit()

    # Create a short-lived payload block tracer object and run it.
    helper = block_tracer.PayloadBlockTracer(self)
    helper.Run(block, skip, trace_out_file, is_kernel)