bpo-38334: Fix seeking backward on an encrypted zipfile.ZipExtFile. (GH-16937)
Test by Daniel Hillier.
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@ -1934,6 +1934,44 @@ class DecryptionTests(unittest.TestCase):
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self.assertRaises(TypeError, self.zip.open, "test.txt", pwd="python")
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self.assertRaises(TypeError, self.zip.extract, "test.txt", pwd="python")
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def test_seek_tell(self):
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self.zip.setpassword(b"python")
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txt = self.plain
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test_word = b'encryption'
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bloc = txt.find(test_word)
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bloc_len = len(test_word)
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with self.zip.open("test.txt", "r") as fp:
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fp.seek(bloc, os.SEEK_SET)
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self.assertEqual(fp.tell(), bloc)
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fp.seek(-bloc, os.SEEK_CUR)
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self.assertEqual(fp.tell(), 0)
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fp.seek(bloc, os.SEEK_CUR)
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self.assertEqual(fp.tell(), bloc)
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self.assertEqual(fp.read(bloc_len), txt[bloc:bloc+bloc_len])
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# Make sure that the second read after seeking back beyond
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# _readbuffer returns the same content (ie. rewind to the start of
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# the file to read forward to the required position).
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old_read_size = fp.MIN_READ_SIZE
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fp.MIN_READ_SIZE = 1
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fp._readbuffer = b''
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fp._offset = 0
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fp.seek(0, os.SEEK_SET)
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self.assertEqual(fp.tell(), 0)
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fp.seek(bloc, os.SEEK_CUR)
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self.assertEqual(fp.read(bloc_len), txt[bloc:bloc+bloc_len])
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fp.MIN_READ_SIZE = old_read_size
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fp.seek(0, os.SEEK_END)
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self.assertEqual(fp.tell(), len(txt))
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fp.seek(0, os.SEEK_SET)
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self.assertEqual(fp.tell(), 0)
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# Read the file completely to definitely call any eof integrity
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# checks (crc) and make sure they still pass.
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fp.read()
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class AbstractTestsWithRandomBinaryFiles:
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@classmethod
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def setUpClass(cls):
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@ -792,10 +792,10 @@ class ZipExtFile(io.BufferedIOBase):
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# Chunk size to read during seek
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MAX_SEEK_READ = 1 << 24
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def __init__(self, fileobj, mode, zipinfo, decrypter=None,
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def __init__(self, fileobj, mode, zipinfo, pwd=None,
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close_fileobj=False):
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self._fileobj = fileobj
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self._decrypter = decrypter
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self._pwd = pwd
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self._close_fileobj = close_fileobj
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self._compress_type = zipinfo.compress_type
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@ -810,11 +810,6 @@ class ZipExtFile(io.BufferedIOBase):
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self.newlines = None
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# Adjust read size for encrypted files since the first 12 bytes
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# are for the encryption/password information.
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if self._decrypter is not None:
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self._compress_left -= 12
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self.mode = mode
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self.name = zipinfo.filename
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@ -835,6 +830,30 @@ class ZipExtFile(io.BufferedIOBase):
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except AttributeError:
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pass
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self._decrypter = None
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if pwd:
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if zipinfo.flag_bits & 0x8:
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# compare against the file type from extended local headers
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check_byte = (zipinfo._raw_time >> 8) & 0xff
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else:
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# compare against the CRC otherwise
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check_byte = (zipinfo.CRC >> 24) & 0xff
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h = self._init_decrypter()
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if h != check_byte:
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raise RuntimeError("Bad password for file %r" % zipinfo.orig_filename)
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def _init_decrypter(self):
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self._decrypter = _ZipDecrypter(self._pwd)
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# The first 12 bytes in the cypher stream is an encryption header
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# used to strengthen the algorithm. The first 11 bytes are
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# completely random, while the 12th contains the MSB of the CRC,
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# or the MSB of the file time depending on the header type
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# and is used to check the correctness of the password.
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header = self._fileobj.read(12)
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self._compress_left -= 12
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return self._decrypter(header)[11]
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def __repr__(self):
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result = ['<%s.%s' % (self.__class__.__module__,
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self.__class__.__qualname__)]
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@ -1061,6 +1080,8 @@ class ZipExtFile(io.BufferedIOBase):
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self._decompressor = _get_decompressor(self._compress_type)
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self._eof = False
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read_offset = new_pos
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if self._decrypter is not None:
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self._init_decrypter()
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while read_offset > 0:
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read_len = min(self.MAX_SEEK_READ, read_offset)
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@ -1524,32 +1545,16 @@ class ZipFile:
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# check for encrypted flag & handle password
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is_encrypted = zinfo.flag_bits & 0x1
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zd = None
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if is_encrypted:
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if not pwd:
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pwd = self.pwd
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if not pwd:
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raise RuntimeError("File %r is encrypted, password "
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"required for extraction" % name)
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else:
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pwd = None
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zd = _ZipDecrypter(pwd)
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# The first 12 bytes in the cypher stream is an encryption header
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# used to strengthen the algorithm. The first 11 bytes are
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# completely random, while the 12th contains the MSB of the CRC,
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# or the MSB of the file time depending on the header type
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# and is used to check the correctness of the password.
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header = zef_file.read(12)
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h = zd(header[0:12])
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if zinfo.flag_bits & 0x8:
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# compare against the file type from extended local headers
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check_byte = (zinfo._raw_time >> 8) & 0xff
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else:
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# compare against the CRC otherwise
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check_byte = (zinfo.CRC >> 24) & 0xff
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if h[11] != check_byte:
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raise RuntimeError("Bad password for file %r" % name)
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return ZipExtFile(zef_file, mode, zinfo, zd, True)
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return ZipExtFile(zef_file, mode, zinfo, pwd, True)
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except:
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zef_file.close()
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raise
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@ -0,0 +1 @@
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Fixed seeking backward on an encrypted :class:`zipfile.ZipExtFile`.
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