# Generator of fuzzed qcow2 images # # Copyright (C) 2014 Maria Kustova # # 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 . # from __future__ import absolute_import import random import struct from . import fuzz from math import ceil from os import urandom from itertools import chain 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, name]. """ __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, self.name]) def __repr__(self): return "Field(fmt=%r, offset=%r, value=%r, name=%r)" % \ (self.fmt, self.offset, self.value, self.name) class FieldsList(object): """List of fields. The class allows access to a field in the list by its name. """ def __init__(self, meta_data=None): if meta_data is None: self.data = [] else: self.data = [Field(*f) 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 __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. """ def __init__(self, backing_file_name=None): """Create a random valid qcow2 image with the correct header and stored backing file name. """ cluster_bits, self.image_size = self._size_params() self.cluster_size = 1 << cluster_bits self.header = FieldsList() self.backing_file_name = FieldsList() self.backing_file_format = FieldsList() self.feature_name_table = FieldsList() self.end_of_extension_area = FieldsList() self.l2_tables = FieldsList() self.l1_table = FieldsList() self.refcount_table = FieldsList() self.refcount_blocks = FieldsList() self.ext_offset = 0 self.create_header(cluster_bits, backing_file_name) self.set_backing_file_name(backing_file_name) self.data_clusters = self._alloc_data(self.image_size, self.cluster_size) # Percentage of fields will be fuzzed self.bias = random.uniform(0.2, 0.5) def __iter__(self): return chain(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, self.refcount_table, self.refcount_blocks) def create_header(self, cluster_bits, backing_file_name=None): """Generate a random valid header.""" meta_header = [ ['>4s', 0, b"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 # Extensions start at the header last field offset and the field size self.ext_offset = 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 - self.ext_offset - \ 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'] ]) def set_backing_file_format(self, backing_file_fmt=None): """Generate the header extension for the backing file format.""" 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 - self.ext_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', self.ext_offset, 0xE2792ACA, 'ext_magic'], ['>I', self.ext_offset + UINT32_S, ext_data_len, 'ext_length'], [ext_data_fmt, self.ext_offset + UINT32_S * 2, backing_file_fmt, 'bf_format'] ]) self.ext_offset = \ struct.calcsize( self.backing_file_format['bf_format'][0].fmt) + \ ext_padding_len + \ self.backing_file_format['bf_format'][0].offset def create_feature_name_table(self): """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 - self.ext_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 = self.ext_offset + ext_header_len feat_name = b'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', self.ext_offset, 0x6803f857, 'ext_magic'], # One feature table contains 3 fields and takes 48 bytes ['>I', self.ext_offset + UINT32_S, len(feature_tables) // 3 * 48, 'ext_length'] ] + feature_tables) self.ext_offset = inner_offset def set_end_of_extension_area(self): """Generate a mandatory header extension marking end of header extensions. """ self.end_of_extension_area = FieldsList([ ['>I', self.ext_offset, 0, 'ext_magic'], ['>I', self.ext_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 = self._get_metadata() 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 create_refcount_structures(self): """Generate random refcount blocks and refcount table.""" def allocate_rfc_blocks(data, size): """Return indices of clusters allocated for refcount blocks.""" cluster_ids = set() diff = block_ids = set([x // size for x in data]) while len(diff) != 0: # Allocate all yet not allocated clusters new = self._get_available_clusters(data | cluster_ids, len(diff)) # Indices of new refcount blocks necessary to cover clusters # in 'new' diff = set([x // size for x in new]) - block_ids cluster_ids |= new block_ids |= diff return cluster_ids, block_ids def allocate_rfc_table(data, init_blocks, block_size): """Return indices of clusters allocated for the refcount table and updated indices of clusters allocated for blocks and indices of blocks. """ blocks = set(init_blocks) clusters = set() # Number of entries in one cluster of the refcount table size = self.cluster_size // UINT64_S # Number of clusters necessary for the refcount table based on # the current number of refcount blocks table_size = int(ceil((max(blocks) + 1) / float(size))) # Index of the first cluster of the refcount table table_start = self._get_adjacent_clusters(data, table_size + 1) # Clusters allocated for the current length of the refcount table table_clusters = set(range(table_start, table_start + table_size)) # Clusters allocated for the refcount table including # last optional one for potential l1 growth table_clusters_allocated = set(range(table_start, table_start + table_size + 1)) # New refcount blocks necessary for clusters occupied by the # refcount table diff = set([c // block_size for c in table_clusters]) - blocks blocks |= diff while len(diff) != 0: # Allocate clusters for new refcount blocks new = self._get_available_clusters((data | clusters) | table_clusters_allocated, len(diff)) # Indices of new refcount blocks necessary to cover # clusters in 'new' diff = set([x // block_size for x in new]) - blocks clusters |= new blocks |= diff # Check if the refcount table needs one more cluster if int(ceil((max(blocks) + 1) / float(size))) > table_size: new_block_id = (table_start + table_size) // block_size # Check if the additional table cluster needs # one more refcount block if new_block_id not in blocks: diff.add(new_block_id) table_clusters.add(table_start + table_size) table_size += 1 return table_clusters, blocks, clusters def create_table_entry(table_offset, block_cluster, block_size, cluster): """Generate a refcount table entry.""" offset = table_offset + UINT64_S * (cluster // block_size) return ['>Q', offset, block_cluster * self.cluster_size, 'refcount_table_entry'] def create_block_entry(block_cluster, block_size, cluster): """Generate a list of entries for the current block.""" entry_size = self.cluster_size // block_size offset = block_cluster * self.cluster_size entry_offset = offset + entry_size * (cluster % block_size) # While snapshots are not supported all refcounts are set to 1 return ['>H', entry_offset, 1, 'refcount_block_entry'] # Size of a block entry in bits refcount_bits = 1 << self.header['refcount_order'][0].value # Number of refcount entries per refcount block # Convert self.cluster_size from bytes to bits to have the same # base for the numerator and denominator block_size = self.cluster_size * 8 // refcount_bits meta_data = self._get_metadata() 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 block_clusters = set([random.choice(list(set(range(1, 4)) - meta_data))]) block_ids = set([0]) table_clusters = set([random.choice(list(set(range(1, 4)) - meta_data - block_clusters))]) else: block_clusters, block_ids = \ allocate_rfc_blocks(self.data_clusters | meta_data, block_size) table_clusters, block_ids, new_clusters = \ allocate_rfc_table(self.data_clusters | meta_data | block_clusters, block_ids, block_size) block_clusters |= new_clusters meta_data |= block_clusters | table_clusters table_offset = min(table_clusters) * self.cluster_size block_id = None # Clusters allocated for refcount blocks block_clusters = list(block_clusters) # Indices of refcount blocks block_ids = list(block_ids) # Refcount table entries rfc_table = [] # Refcount entries rfc_blocks = [] for cluster in sorted(self.data_clusters | meta_data): if cluster // block_size != block_id: block_id = cluster // block_size block_cluster = block_clusters[block_ids.index(block_id)] rfc_table.append(create_table_entry(table_offset, block_cluster, block_size, cluster)) rfc_blocks.append(create_block_entry(block_cluster, block_size, cluster)) self.refcount_table = FieldsList(rfc_table) self.refcount_blocks = FieldsList(rfc_blocks) self.header['refcount_table_offset'][0].value = table_offset self.header['refcount_table_clusters'][0].value = len(table_clusters) 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: for field in self: 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: # If fields with the requested name were not generated # getattr(self, item[0])[item[1]] returns an empty list for field in getattr(self, item[0])[item[1]]: field.value = getattr(fuzz, field.name)(field.value) def write(self, filename): """Write an entire image to the file.""" image_file = open(filename, 'wb') for field in self: 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(b'\x00') image_file.close() @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 _get_metadata(self): """Return indices of clusters allocated for image metadata.""" ids = set() for x in self: ids.add(x.offset // self.cluster_size) return ids 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) image.set_backing_file_format(backing_file_fmt) image.create_feature_name_table() image.set_end_of_extension_area() image.create_l_structures() image.create_refcount_structures() image.fuzz(fields_to_fuzz) image.write(test_img_path) return image.image_size