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# Generator of fuzzed qcow2 images
#
# Copyright (C) 2014 Maria Kustova <maria.k@catit.be>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#
import random
import struct
import fuzz
from math import ceil
from os import urandom
MAX_IMAGE_SIZE = 10 * (1 << 20)
# Standard sizes
UINT32_S = 4
UINT64_S = 8
class Field(object):
"""Atomic image element (field).
The class represents an image field as quadruple of a data format
of value necessary for its packing to binary form, an offset from
the beginning of the image, a value and a name.
The field can be iterated as a list [format, offset, value].
"""
__slots__ = ('fmt', 'offset', 'value', 'name')
def __init__(self, fmt, offset, val, name):
self.fmt = fmt
self.offset = offset
self.value = val
self.name = name
def __iter__(self):
return iter([self.fmt, self.offset, self.value])
def __repr__(self):
return "Field(fmt='%s', offset=%d, value=%s, name=%s)" % \
(self.fmt, self.offset, str(self.value), self.name)
class FieldsList(object):
"""List of fields.
The class allows access to a field in the list by its name and joins
several list in one via in-place addition.
"""
def __init__(self, meta_data=None):
if meta_data is None:
self.data = []
else:
self.data = [Field(f[0], f[1], f[2], f[3])
for f in meta_data]
def __getitem__(self, name):
return [x for x in self.data if x.name == name]
def __iter__(self):
return iter(self.data)
def __iadd__(self, other):
self.data += other.data
return self
def __len__(self):
return len(self.data)
class Image(object):
""" Qcow2 image object.
This class allows to create qcow2 images with random valid structures and
values, fuzz them via external qcow2.fuzz module and write the result to
a file.
"""
@staticmethod
def _size_params():
"""Generate a random image size aligned to a random correct
cluster size.
"""
cluster_bits = random.randrange(9, 21)
cluster_size = 1 << cluster_bits
img_size = random.randrange(0, MAX_IMAGE_SIZE + 1, cluster_size)
return (cluster_bits, img_size)
@staticmethod
def _get_available_clusters(used, number):
"""Return a set of indices of not allocated clusters.
'used' contains indices of currently allocated clusters.
All clusters that cannot be allocated between 'used' clusters will have
indices appended to the end of 'used'.
"""
append_id = max(used) + 1
free = set(range(1, append_id)) - used
if len(free) >= number:
return set(random.sample(free, number))
else:
return free | set(range(append_id, append_id + number - len(free)))
@staticmethod
def _get_adjacent_clusters(used, size):
"""Return an index of the first cluster in the sequence of free ones.
'used' contains indices of currently allocated clusters. 'size' is the
length of the sequence of free clusters.
If the sequence of 'size' is not available between 'used' clusters, its
first index will be append to the end of 'used'.
"""
def get_cluster_id(lst, length):
"""Return the first index of the sequence of the specified length
or None if the sequence cannot be inserted in the list.
"""
if len(lst) != 0:
pairs = []
pair = (lst[0], 1)
for i in range(1, len(lst)):
if lst[i] == lst[i-1] + 1:
pair = (lst[i], pair[1] + 1)
else:
pairs.append(pair)
pair = (lst[i], 1)
pairs.append(pair)
random.shuffle(pairs)
for x, s in pairs:
if s >= length:
return x - length + 1
return None
append_id = max(used) + 1
free = list(set(range(1, append_id)) - used)
idx = get_cluster_id(free, size)
if idx is None:
return append_id
else:
return idx
@staticmethod
def _alloc_data(img_size, cluster_size):
"""Return a set of random indices of clusters allocated for guest data.
"""
num_of_cls = img_size/cluster_size
return set(random.sample(range(1, num_of_cls + 1),
random.randint(0, num_of_cls)))
def create_header(self, cluster_bits, backing_file_name=None):
"""Generate a random valid header."""
meta_header = [
['>4s', 0, "QFI\xfb", 'magic'],
['>I', 4, random.randint(2, 3), 'version'],
['>Q', 8, 0, 'backing_file_offset'],
['>I', 16, 0, 'backing_file_size'],
['>I', 20, cluster_bits, 'cluster_bits'],
['>Q', 24, self.image_size, 'size'],
['>I', 32, 0, 'crypt_method'],
['>I', 36, 0, 'l1_size'],
['>Q', 40, 0, 'l1_table_offset'],
['>Q', 48, 0, 'refcount_table_offset'],
['>I', 56, 0, 'refcount_table_clusters'],
['>I', 60, 0, 'nb_snapshots'],
['>Q', 64, 0, 'snapshots_offset'],
['>Q', 72, 0, 'incompatible_features'],
['>Q', 80, 0, 'compatible_features'],
['>Q', 88, 0, 'autoclear_features'],
# Only refcount_order = 4 is supported by current (07.2014)
# implementation of QEMU
['>I', 96, 4, 'refcount_order'],
['>I', 100, 0, 'header_length']
]
self.header = FieldsList(meta_header)
if self.header['version'][0].value == 2:
self.header['header_length'][0].value = 72
else:
self.header['incompatible_features'][0].value = \
random.getrandbits(2)
self.header['compatible_features'][0].value = random.getrandbits(1)
self.header['header_length'][0].value = 104
max_header_len = struct.calcsize(
self.header['header_length'][0].fmt) + \
self.header['header_length'][0].offset
end_of_extension_area_len = 2 * UINT32_S
free_space = self.cluster_size - max_header_len - \
end_of_extension_area_len
# If the backing file name specified and there is enough space for it
# in the first cluster, then it's placed in the very end of the first
# cluster.
if (backing_file_name is not None) and \
(free_space >= len(backing_file_name)):
self.header['backing_file_size'][0].value = len(backing_file_name)
self.header['backing_file_offset'][0].value = \
self.cluster_size - len(backing_file_name)
def set_backing_file_name(self, backing_file_name=None):
"""Add the name of the backing file at the offset specified
in the header.
"""
if (backing_file_name is not None) and \
(not self.header['backing_file_offset'][0].value == 0):
data_len = len(backing_file_name)
data_fmt = '>' + str(data_len) + 's'
self.backing_file_name = FieldsList([
[data_fmt, self.header['backing_file_offset'][0].value,
backing_file_name, 'bf_name']
])
else:
self.backing_file_name = FieldsList()
def set_backing_file_format(self, backing_file_fmt=None):
"""Generate the header extension for the backing file
format.
"""
self.backing_file_format = FieldsList()
offset = struct.calcsize(self.header['header_length'][0].fmt) + \
self.header['header_length'][0].offset
if backing_file_fmt is not None:
# Calculation of the free space available in the first cluster
end_of_extension_area_len = 2 * UINT32_S
high_border = (self.header['backing_file_offset'][0].value or
(self.cluster_size - 1)) - \
end_of_extension_area_len
free_space = high_border - offset
ext_size = 2 * UINT32_S + ((len(backing_file_fmt) + 7) & ~7)
if free_space >= ext_size:
ext_data_len = len(backing_file_fmt)
ext_data_fmt = '>' + str(ext_data_len) + 's'
ext_padding_len = 7 - (ext_data_len - 1) % 8
self.backing_file_format = FieldsList([
['>I', offset, 0xE2792ACA, 'ext_magic'],
['>I', offset + UINT32_S, ext_data_len, 'ext_length'],
[ext_data_fmt, offset + UINT32_S * 2, backing_file_fmt,
'bf_format']
])
offset = self.backing_file_format['bf_format'][0].offset + \
struct.calcsize(self.backing_file_format[
'bf_format'][0].fmt) + ext_padding_len
return offset
def create_feature_name_table(self, offset):
"""Generate a random header extension for names of features used in
the image.
"""
def gen_feat_ids():
"""Return random feature type and feature bit."""
return (random.randint(0, 2), random.randint(0, 63))
end_of_extension_area_len = 2 * UINT32_S
high_border = (self.header['backing_file_offset'][0].value or
(self.cluster_size - 1)) - \
end_of_extension_area_len
free_space = high_border - offset
# Sum of sizes of 'magic' and 'length' header extension fields
ext_header_len = 2 * UINT32_S
fnt_entry_size = 6 * UINT64_S
num_fnt_entries = min(10, (free_space - ext_header_len) /
fnt_entry_size)
if not num_fnt_entries == 0:
feature_tables = []
feature_ids = []
inner_offset = offset + ext_header_len
feat_name = 'some cool feature'
while len(feature_tables) < num_fnt_entries * 3:
feat_type, feat_bit = gen_feat_ids()
# Remove duplicates
while (feat_type, feat_bit) in feature_ids:
feat_type, feat_bit = gen_feat_ids()
feature_ids.append((feat_type, feat_bit))
feat_fmt = '>' + str(len(feat_name)) + 's'
feature_tables += [['B', inner_offset,
feat_type, 'feature_type'],
['B', inner_offset + 1, feat_bit,
'feature_bit_number'],
[feat_fmt, inner_offset + 2,
feat_name, 'feature_name']
]
inner_offset += fnt_entry_size
# No padding for the extension is necessary, because
# the extension length is multiple of 8
self.feature_name_table = FieldsList([
['>I', offset, 0x6803f857, 'ext_magic'],
# One feature table contains 3 fields and takes 48 bytes
['>I', offset + UINT32_S, len(feature_tables) / 3 * 48,
'ext_length']
] + feature_tables)
offset = inner_offset
else:
self.feature_name_table = FieldsList()
return offset
def set_end_of_extension_area(self, offset):
"""Generate a mandatory header extension marking end of header
extensions.
"""
self.end_of_extension_area = FieldsList([
['>I', offset, 0, 'ext_magic'],
['>I', offset + UINT32_S, 0, 'ext_length']
])
def create_l_structures(self):
"""Generate random valid L1 and L2 tables."""
def create_l2_entry(host, guest, l2_cluster):
"""Generate one L2 entry."""
offset = l2_cluster * self.cluster_size
l2_size = self.cluster_size / UINT64_S
entry_offset = offset + UINT64_S * (guest % l2_size)
cluster_descriptor = host * self.cluster_size
if not self.header['version'][0].value == 2:
cluster_descriptor += random.randint(0, 1)
# While snapshots are not supported, bit #63 = 1
# Compressed clusters are not supported => bit #62 = 0
entry_val = (1 << 63) + cluster_descriptor
return ['>Q', entry_offset, entry_val, 'l2_entry']
def create_l1_entry(l2_cluster, l1_offset, guest):
"""Generate one L1 entry."""
l2_size = self.cluster_size / UINT64_S
entry_offset = l1_offset + UINT64_S * (guest / l2_size)
# While snapshots are not supported bit #63 = 1
entry_val = (1 << 63) + l2_cluster * self.cluster_size
return ['>Q', entry_offset, entry_val, 'l1_entry']
if len(self.data_clusters) == 0:
# All metadata for an empty guest image needs 4 clusters:
# header, rfc table, rfc block, L1 table.
# Header takes cluster #0, other clusters ##1-3 can be used
l1_offset = random.randint(1, 3) * self.cluster_size
l1 = [['>Q', l1_offset, 0, 'l1_entry']]
l2 = []
else:
meta_data = set([0])
guest_clusters = random.sample(range(self.image_size /
self.cluster_size),
len(self.data_clusters))
# Number of entries in a L1/L2 table
l_size = self.cluster_size / UINT64_S
# Number of clusters necessary for L1 table
l1_size = int(ceil((max(guest_clusters) + 1) / float(l_size**2)))
l1_start = self._get_adjacent_clusters(self.data_clusters |
meta_data, l1_size)
meta_data |= set(range(l1_start, l1_start + l1_size))
l1_offset = l1_start * self.cluster_size
# Indices of L2 tables
l2_ids = []
# Host clusters allocated for L2 tables
l2_clusters = []
# L1 entries
l1 = []
# L2 entries
l2 = []
for host, guest in zip(self.data_clusters, guest_clusters):
l2_id = guest / l_size
if l2_id not in l2_ids:
l2_ids.append(l2_id)
l2_clusters.append(self._get_adjacent_clusters(
self.data_clusters | meta_data | set(l2_clusters),
1))
l1.append(create_l1_entry(l2_clusters[-1], l1_offset,
guest))
l2.append(create_l2_entry(host, guest,
l2_clusters[l2_ids.index(l2_id)]))
self.l2_tables = FieldsList(l2)
self.l1_table = FieldsList(l1)
self.header['l1_size'][0].value = int(ceil(UINT64_S * self.image_size /
float(self.cluster_size**2)))
self.header['l1_table_offset'][0].value = l1_offset
def __init__(self, backing_file_name=None, backing_file_fmt=None):
"""Create a random valid qcow2 image with the correct inner structure
and allowable values.
"""
cluster_bits, self.image_size = self._size_params()
self.cluster_size = 1 << cluster_bits
self.create_header(cluster_bits, backing_file_name)
self.set_backing_file_name(backing_file_name)
offset = self.set_backing_file_format(backing_file_fmt)
offset = self.create_feature_name_table(offset)
self.set_end_of_extension_area(offset)
self.data_clusters = self._alloc_data(self.image_size,
self.cluster_size)
self.create_l_structures()
# Container for entire image
self.data = FieldsList()
# Percentage of fields will be fuzzed
self.bias = random.uniform(0.2, 0.5)
def __iter__(self):
return iter([self.header,
self.backing_file_format,
self.feature_name_table,
self.end_of_extension_area,
self.backing_file_name,
self.l1_table,
self.l2_tables])
def _join(self):
"""Join all image structure elements as header, tables, etc in one
list of fields.
"""
if len(self.data) == 0:
for v in self:
self.data += v
def fuzz(self, fields_to_fuzz=None):
"""Fuzz an image by corrupting values of a random subset of its fields.
Without parameters the method fuzzes an entire image.
If 'fields_to_fuzz' is specified then only fields in this list will be
fuzzed. 'fields_to_fuzz' can contain both individual fields and more
general image elements as a header or tables.
In the first case the field will be fuzzed always.
In the second a random subset of fields will be selected and fuzzed.
"""
def coin():
"""Return boolean value proportional to a portion of fields to be
fuzzed.
"""
return random.random() < self.bias
if fields_to_fuzz is None:
self._join()
for field in self.data:
if coin():
field.value = getattr(fuzz, field.name)(field.value)
else:
for item in fields_to_fuzz:
if len(item) == 1:
for field in getattr(self, item[0]):
if coin():
field.value = getattr(fuzz,
field.name)(field.value)
else:
for field in getattr(self, item[0])[item[1]]:
try:
field.value = getattr(fuzz, field.name)(
field.value)
except AttributeError:
# Some fields can be skipped depending on
# their prerequisites
pass
def write(self, filename):
"""Write an entire image to the file."""
image_file = open(filename, 'w')
self._join()
for field in self.data:
image_file.seek(field.offset)
image_file.write(struct.pack(field.fmt, field.value))
for cluster in sorted(self.data_clusters):
image_file.seek(cluster * self.cluster_size)
image_file.write(urandom(self.cluster_size))
# Align the real image size to the cluster size
image_file.seek(0, 2)
size = image_file.tell()
rounded = (size + self.cluster_size - 1) & ~(self.cluster_size - 1)
if rounded > size:
image_file.seek(rounded - 1)
image_file.write("\0")
image_file.close()
def create_image(test_img_path, backing_file_name=None, backing_file_fmt=None,
fields_to_fuzz=None):
"""Create a fuzzed image and write it to the specified file."""
image = Image(backing_file_name, backing_file_fmt)
image.fuzz(fields_to_fuzz)
image.write(test_img_path)
return image.image_size
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