From: Zooko O'Whielacronx Date: Fri, 30 Mar 2007 01:12:35 +0000 (-0700) Subject: change HashTree to use new hashutil convenience methods, thus fixing a security flaw X-Git-Url: https://git.rkrishnan.org/listings/about.html?a=commitdiff_plain;h=c70b4773d36dfad57a8829ed541d0f3045e7df8f;p=tahoe-lafs%2Ftahoe-lafs.git change HashTree to use new hashutil convenience methods, thus fixing a security flaw --- diff --git a/src/allmydata/chunk.py b/src/allmydata/chunk.py index 3ee903e5..5454b65f 100644 --- a/src/allmydata/chunk.py +++ b/src/allmydata/chunk.py @@ -51,11 +51,9 @@ import sha import os #import os.path -from allmydata.util import bencode +from allmydata.util.hashutil import tagged_hash, tagged_pair_hash -__all__ = ['CompleteChunkFile', 'PartialChunkFile'] - -__version__ = '1.0.0' +__version__ = '1.0.0-allmydata' BLOCK_SIZE = 65536 MAX_CHUNK_SIZE = BLOCK_SIZE + 4096 @@ -171,557 +169,20 @@ class HashTree(CompleteBinaryTreeMixin, list): then this is used as the bottom row of the hash tree. The augmenting is done so that if the augmented element is at - index C{i}, then its value is C{hash(bencode.bencode((i, '')))}. + index C{i}, then its value is C{hash(tagged_hash('Merkle tree empty leaf', '%d'%i))}. """ # Augment the list. start = len(L) end = roundup_pow2(len(L)) L = L + [None] * (end - start) for i in range(start, end): - L[i] = hash(bencode.bencode((i, ''))) + L[i] = tagged_hash('Merkle tree empty leaf', "%d"%i) # Form each row of the tree. rows = [L] while len(rows[-1]) != 1: last = rows[-1] - rows += [[hash(last[2*i] + last[2*i+1]) for i in xrange(len(last)//2)]] + rows += [[tagged_pair_hash('Merkle tree internal node', last[2*i], last[2*i+1]) for i in xrange(len(last)//2)]] # Flatten the list of rows into a single list. rows.reverse() self[:] = sum(rows, []) - -class BlockFile: - """ - Reads and writes blocks of data to a binary file. - - It is assumed that the binary file does not change in size. - - @ivar file_name: Full path to file. - @ivar file_size: Size of file in bytes. - @ivar block_size: Size of each block. - """ - def __init__(self, file_name, mode, block_size, file_size=None): - """ - Initialize block reader or writer on given file name. - - If mode is 'r', the file must already exist and it is opened for - reading only. If mode is 'w', the file will be created with size - C{file_size} if it does not exist, and it is opened for reading - and writing. - - Note that C{file_size} is ignored if the file already exists. - """ - self.mode = mode - self.file_name = os.path.abspath(file_name) - assert self.mode in ['r', 'w'] - - if mode == 'r': - f = open(self.file_name, 'rb') - f.close() - - # Create file if it doesn't exist. - created = False - if mode == 'w' and not os.path.exists(self.file_name): - created = True - buf = ' ' * 1024 - f = open(self.file_name, 'wb') - for i in xrange(file_size // len(buf)): - f.write(buf) - f.write(' ' * (file_size % len(buf))) - f.close() - - self.file_size = os.stat(self.file_name).st_size - if created: - assert self.file_size == file_size - self.block_size = block_size - self.__block_count = self.file_size // self.block_size - if self.file_size % self.block_size == 0: - self.last_block_size = self.block_size - else: - self.last_block_size = self.file_size % self.block_size - self.__block_count += 1 - - def __getitem__(self, i): - """ - Get block i. - """ - if i < 0 or i >= len(self): - raise IndexError('block index out of range: ' + repr(i)) - f = open(self.file_name, 'rb') - try: - f.seek(i * self.block_size) - ans = f.read(self.block_size) - finally: - f.close() - return ans - - def __setitem__(self, i, s): - """ - Set block i. - """ - if self.mode != 'w': - raise ValueError('file opened for reading only') - if i < 0 or i >= len(self): - raise IndexError('block index out of range: ' + repr(i)) - if i < len(self) - 1: - if len(s) != self.block_size: - raise ValueError('length of value must equal block_size') - else: - if len(s) != self.last_block_size: - raise ValueError('length of value must equal last_block_size') - f = open(self.file_name, 'rb+') - try: - f.seek(i * self.block_size) - f.write(s) - finally: - f.close() - - def __len__(self): - """ - Get number of blocks. - """ - return int(self.__block_count) - - -class MetaFile(CompleteBinaryTreeMixin): - """ - A L{HashTree} stored on disk, with a timestamp. - - The list of hashes can be accessed using subscripting and - C{__len__}, in the same manner as for L{HashTree}. - - Note that the constructor takes the entire list associated with - the L{HashTree}, not just the bottom row of the tree. - - @ivar meta_name: Full path to metafile. - """ - def __init__(self, meta_name, mode, L=None): - """ - Open an existing meta-file for reading or writing. - - If C{mode} is 'r', the meta-file must already exist and it is - opened for reading only, and the list C{L} is ignored. If C{mode} - is 'w', the file will be created if it does not exist (from the - list of hashes given in C{L}), and it is opened for reading and - writing. - """ - self.meta_name = os.path.abspath(meta_name) - self.mode = mode - assert self.mode in ['r', 'w'] - - # A timestamp is stored at index 0. The MetaFile instance - # offsets all indices passed to __getitem__, __setitem__ by - # this offset, and pretends it has length equal to - # self.sublength. - self.offset = 1 - - if self.mode == 'w': - suggested_length = len(hash('')) * (len(L)+self.offset) - else: - suggested_length = None - - created = False - if self.mode == 'w' and not os.path.exists(self.meta_name): - created = True - - self.block_file = BlockFile(self.meta_name, self.mode, - len(hash('')), - suggested_length) - self.sublength = len(self.block_file) - self.offset - - if created: - for i in xrange(len(L)): - self.block_file[i + self.offset] = L[i] - - def __getitem__(self, i): - if i < 0 or i >= self.sublength: - raise IndexError('bad meta-file block index') - return self.block_file[i + self.offset] - - def __setitem__(self, i, value): - if i < 0 or i >= self.sublength: - raise IndexError('bad meta-file block index') - self.block_file[i + self.offset] = value - - def __len__(self): - return self.sublength - - def set_timestamp(self, file_name): - """ - Set meta file's timestamp equal to the timestamp for C{file_name}. - """ - st = os.stat(file_name) - timestamp = bencode.bencode((st.st_size, st.st_mtime)) - self.block_file[0] = sha.new(timestamp).digest() - - def check_timestamp(self, file_name): - """ - True if meta file's timestamp equals timestamp for C{file_name}. - """ - st = os.stat(file_name) - timestamp = bencode.bencode((st.st_size, st.st_mtime)) - return self.block_file[0] == sha.new(timestamp).digest() - - -class CompleteChunkFile(BlockFile): - """ - Reads chunks from a fully-downloaded file. - - A chunk C{i} is created from block C{i}. Block C{i} is unencoded - data read from the file by the L{BlockFile}. Chunk C{i} is - an encoded string created from block C{i}. - - Chunks can be read using list subscripting. The total number of - chunks (equals the total number of blocks) is given by L{__len__}. - - @ivar file_name: Full path to file. - @ivar file_size: Size of file in bytes. - @ivar file_hash: Hash of file. - @ivar meta_name: Full path to metafile, or C{None}. - @ivar tree: L{HashTree} or L{MetaFile} instance for the file. - One can extract a hash from any node in the hash - tree. - """ - - def __init__(self, file_name, meta_name=None, callback=None): - """ - Initialize reader on the given file name. - - The entire file will be read and the hash will be computed from - the file. This may take a long time, so C{callback()} is called - frequently during this process. This allows you to reduce CPU - usage if you wish. - - The C{meta_name} argument is optional. If it is specified, then the - hashes for C{file_name} will be stored under the file - C{meta_name}. If a C{CompleteChunkFile} is created on the same - file and metafile in the future, then the hashes will not need to - be recomputed and the constructor will return instantly. The - metafile contains a file and date stamp, so that if the file stored - in C{file_name} is modified, then the hashes will be recomputed. - """ - BlockFile.__init__(self, file_name, 'r', block_size=65536) - - # Whether we need to compute the hash tree - compute_tree = False - - self.meta_name = meta_name - if self.meta_name != None: - self.meta_name = os.path.abspath(self.meta_name) - self.meta = None - if self.meta_name == None: - compute_tree = True - else: - try: - meta = MetaFile(self.meta_name, 'r') - assert meta.check_timestamp(self.file_name) - except (IOError, AssertionError): - compute_tree = True - - # Compute the hash tree if needed. - if compute_tree: - chunk_hashes = [None] * len(self) - for i in xrange(len(self)): - triple = (self.file_size, i, BlockFile.__getitem__(self, i)) - chunk_hashes[i] = hash(bencode.bencode(triple)) - if callback: - callback() - self.tree = HashTree(chunk_hashes) - del chunk_hashes - - # If a meta-file was given, make self.tree be a MetaFile instance. - if self.meta_name != None: - if compute_tree: - # Did we compute the hash tree? Then store it to disk. - self.tree = MetaFile(self.meta_name, 'w', self.tree) - # Update its timestamp to be consistent with the file we - # just hashed. - self.tree.set_timestamp(self.file_name) - else: - # Read existing file from disk. - self.tree = MetaFile(self.meta_name, 'r') - - self.file_hash = self.tree[0] - - def __getitem__(self, i): - """ - Get chunk C{i}. - - Raises C{ValueError} if the file's contents changed since the - CompleteFileChunkReader was instantiated. - """ - return encode_chunk(BlockFile.__getitem__(self, i), i, - self.file_size, self.tree) - - -def encode_chunk(block, index, file_size, tree): - """ - Encode a chunk. - - Given a block at index C{index} in a file with size C{file_size}, - and a L{HashTree} or L{MetaFile} instance C{tree}, computes and - returns a chunk string for the given block. - - The C{tree} argument needs to have correct hashes only at certain - indices. Check out the code for details. In any case, if a hash - is wrong an exception will be raised. - """ - block_count = (len(tree) + 1) // 2 - if index < 0 or index >= block_count: - raise IndexError('block index out of range: ' + repr(index)) - - suffix = bencode.bencode((file_size, index, block)) - current = len(tree) - block_count + index - prefix = [] - while current > 0: - sibling = tree.sibling(current) - prefix += [tree[current], tree[sibling]] - current = tree.parent(current) - prefix = ''.join(prefix) - - # Encode the chunk - chunk = bencode.bencode((prefix, suffix)) - - # Check to make sure it decodes properly. - decode_chunk(chunk, file_size, tree) - return chunk - - -def decode_chunk(chunk, file_size, tree): - """ - Decode a chunk. - - Given file with size C{file_size} and a L{HashTree} or L{MetaFile} - instance C{tree}, return C{(index, block, tree_items)}. Here - C{index} is the block index where string C{block} should be placed - in the file. Also C{tree_items} is a dict mapping indices within - the L{HashTree} or L{MetaFile} tree object associated with the - given file to the corresponding hashes at those indices. These - have been verified against the file's hash, so it is known that - they are correct. - - Raises C{ValueError} if chunk verification fails. - """ - file_hash = tree[0] - block_count = (len(tree) + 1) // 2 - try: - # Decode the chunk - try: - (prefix, suffix) = bencode.bdecode(chunk) - except: - raise AssertionError() - - assert isinstance(prefix, str) - assert isinstance(suffix, str) - - # Verify the suffix against the hashes in the prefix. - hash_len = len(hash('')) - L = [prefix[hash_len*i:hash_len*(i+1)] for i in range(len(prefix)//hash_len)] - L += [file_hash] - assert L[0] == hash(suffix) - branches = [] - for i in range(0, len(L)-1, 2): - if hash(L[i] + L[i+1]) == L[i+2]: - branches += [0] - elif hash(L[i+1] + L[i]) == L[i+2]: - branches += [1] - else: - raise AssertionError() - - # Decode the suffix - try: - (claim_file_size, claim_index, block) = bencode.bdecode(suffix) - except: - raise AssertionError() - - assert isinstance(claim_file_size, int) or isinstance(claim_file_size, long) - assert isinstance(claim_index, int) or isinstance(claim_index, long) - assert isinstance(block, str) - - assert file_size == claim_file_size - - # Compute the index of the block, and check it. - found_index = sum([branches[i]*2**i for i in range(len(branches))]) - assert found_index == claim_index - - # Now fill in the tree_items dict. - tree_items = {} - current = (len(tree) - block_count) + found_index - i = 0 - while current > 0 and i + 1 < len(L): - tree_items[current] = L[i] - # Next item is our sibling. - tree_items[tree.sibling(current)] = L[i+1] - i += 2 - current = tree.parent(current) - - return (found_index, block, tree_items) - except AssertionError: - raise ValueError('corrupt chunk') - - -class PartialChunkFile(BlockFile): - """ - Reads and writes chunks to a partially downloaded file. - - @ivar file_name: Full path to file. - @ivar file_size: Size of file in bytes. - @ivar file_hash: Hash of file. - @ivar meta_name: Full path to metafile. - @ivar tree: L{MetaFile} instance for the file. - The hashes in this hash tree are valid only for - nodes that we have been sent hashes for. - """ - def __init__(self, file_name, meta_name, file_hash=None, file_size=None): - """ - Initialize reader/writer for the given file name and metafile name. - - If neither C{file_name} nor C{meta_file} exist, then both are - created. The C{file_hash} and C{file_size} arguments are used to - initialize the two files. - - If both C{file_name} and C{meta_file} exist, then the hash and - file size arguments are ignored, and those values are instead read - from the files. - - If one file exists and the other does not, an C{IOError} is raised. - """ - self.meta_name = os.path.abspath(meta_name) - meta_exists = os.path.exists(self.meta_name) - file_exists = os.path.exists(os.path.abspath(file_name)) - - BlockFile.__init__(self, os.path.abspath(file_name), 'w', - BLOCK_SIZE, file_size) - - if file_exists and not meta_exists: - raise IOError('metafile ' + repr(self.meta_name) + - ' missing for file ' + repr(self.file_name)) - if meta_exists and not file_exists: - raise IOError('file ' + repr(self.file_name) + - ' missing for metafile ' + repr(self.meta_name)) - tree_count = 2 * roundup_pow2(len(self)) - 1 - self.tree = MetaFile(self.meta_name, 'w', [hash('')] * tree_count) - - if not meta_exists and not file_exists: - self.tree[0] = file_hash - - self.file_hash = self.tree[0] - - def __getitem__(self, i): - """ - Get chunk C{i}. - - Raises C{ValueError} if chunk has not yet been downloaded or is - corrupted. - """ - return encode_chunk(BlockFile.__getitem__(self, i), i, - self.file_size, self.tree) - - def __setitem__(self, i, chunk): - """ - Set chunk C{i}. - - Raises C{ValueError} if the chunk is invalid. - """ - (index, block, tree_items) = decode_chunk(chunk, - self.file_size, self.tree) - if index != i: - raise ValueError('incorrect index for chunk') - BlockFile.__setitem__(self, index, block) - for (tree_index, tree_value) in tree_items.items(): - self.tree[tree_index] = tree_value - - -def test(filename1='temp-out', metaname1='temp-out.meta', - filename2='temp-out2', metaname2='temp-out2.meta'): - """ - Unit tests. - """ - print 'Testing:' - - import random - ntests = 100 - max_file_size = 200000 - - # Test CompleteChunkFile. - - if os.path.exists(metaname1): - os.remove(metaname1) - - for i in range(ntests): - fsize = random.randrange(max_file_size) - # Make some random string of size 'fsize' to go in the file. - s = ''.join([sha.new(str(j)).digest() for j in range(fsize//20+1)]) - assert len(s) >= fsize - s = s[:fsize] - f = open(filename1, 'wb') - f.write(s) - f.close() - C = CompleteChunkFile(filename1) - for j in range(len(C)): - C[j] - C = CompleteChunkFile(filename1, metaname1) - for j in range(len(C)): - C[j] - C = CompleteChunkFile(filename1, metaname1) - for j in range(len(C)): - C[j] - os.remove(metaname1) - - os.remove(filename1) - - print ' CompleteChunkFile: OK' - - # Test PartialChunkFile - - for i in range(ntests): - fsize = random.randrange(max_file_size) - # Make some random string of size 'fsize' to go in the file. - s = ''.join([sha.new(str(j)).digest() for j in range(fsize//20+1)]) - assert len(s) >= fsize - s = s[:fsize] - f = open(filename1, 'wb') - f.write(s) - f.close() - C1 = CompleteChunkFile(filename1) - if os.path.exists(filename2): - os.remove(filename2) - - if os.path.exists(metaname2): - os.remove(metaname2) - C2 = PartialChunkFile(filename2, metaname2, C1.file_hash, C1.file_size) - assert len(C1) == len(C2) - assert C2.tree[0] == C1.tree[0] - for j in range(len(C2)): - try: - C2[j] - ok = False - except ValueError: - ok = True - if not ok: - raise AssertionError() - for j in range(len(C2)//2): - k = random.randrange(len(C2)) - if len(C1) > 1: - assert C1[k] != C1[(k+1)%len(C1)] - try: - C2[k] = C1[(k+1)%len(C1)] - ok = False - except ValueError: - ok = True - if not ok: - raise AssertionError() - C2[k] = C1[k] - assert C2[k] == C1[k] - for j in range(len(C2)): - C2[j] = C1[j] - assert C2[j] == C1[j] - - os.remove(filename1) - os.remove(filename2) - os.remove(metaname2) - - print ' PartialChunkFile: OK' - - -if __name__ == '__main__': - test()