[Python-checkins] cpython (merge 3.2 -> 3.3): Issue #1159051: GzipFile now raises EOFError when reading a corrupted file

Tue Jan 22 16:17:04 CET 2013

http://hg.python.org/cpython/rev/87171e88847b
changeset: 81657:87171e88847b
branch: 3.3
parent: 81654:2e2351733a6f
parent: 81656:174332b89a0d
user: Serhiy Storchaka <storchaka at gmail.com>
date: Tue Jan 22 17:07:49 2013 +0200
summary:
 Issue #1159051: GzipFile now raises EOFError when reading a corrupted file
with truncated header or footer.
Added tests for reading truncated gzip, bzip2, and lzma files.
files:
 Lib/gzip.py | 81 ++++++++++++++----------------
 Lib/test/test_bz2.py | 14 +++++
 Lib/test/test_gzip.py | 14 +++++
 Lib/test/test_lzma.py | 14 +++++
 Misc/NEWS | 3 +
 5 files changed, 82 insertions(+), 44 deletions(-)

diff --git a/Lib/gzip.py b/Lib/gzip.py
--- a/Lib/gzip.py
+++ b/Lib/gzip.py
@@ -65,9 +65,6 @@
 # or unsigned.
 output.write(struct.pack("<L", value))
 
-def read32(input):
- return struct.unpack("<I", input.read(4))[0]
-
 class _PaddedFile:
 """Minimal read-only file object that prepends a string to the contents
 of an actual file. Shouldn't be used outside of gzip.py, as it lacks
@@ -281,27 +278,31 @@
 self.crc = zlib.crc32(b"") & 0xffffffff
 self.size = 0
 
+ def _read_exact(self, n):
+ data = self.fileobj.read(n)
+ while len(data) < n:
+ b = self.fileobj.read(n - len(data))
+ if not b:
+ raise EOFError("Compressed file ended before the "
+ "end-of-stream marker was reached")
+ data += b
+ return data
+
 def _read_gzip_header(self):
 magic = self.fileobj.read(2)
 if magic == b'':
- raise EOFError("Reached EOF")
+ return False
 
 if magic != b'037円213円':
 raise IOError('Not a gzipped file')
- method = ord( self.fileobj.read(1) )
+
+ method, flag, self.mtime = struct.unpack("<BBIxx", self._read_exact(8))
 if method != 8:
 raise IOError('Unknown compression method')
- flag = ord( self.fileobj.read(1) )
- self.mtime = read32(self.fileobj)
- # extraflag = self.fileobj.read(1)
- # os = self.fileobj.read(1)
- self.fileobj.read(2)
 
 if flag & FEXTRA:
 # Read & discard the extra field, if present
- xlen = ord(self.fileobj.read(1))
- xlen = xlen + 256*ord(self.fileobj.read(1))
- self.fileobj.read(xlen)
+ self._read_exact(struct.unpack("<H", self._read_exact(2)))
 if flag & FNAME:
 # Read and discard a null-terminated string containing the filename
 while True:
@@ -315,12 +316,13 @@
 if not s or s==b'000円':
 break
 if flag & FHCRC:
- self.fileobj.read(2) # Read & discard the 16-bit header CRC
+ self._read_exact(2) # Read & discard the 16-bit header CRC
 
 unused = self.fileobj.unused()
 if unused:
 uncompress = self.decompress.decompress(unused)
 self._add_read_data(uncompress)
+ return True
 
 def write(self,data):
 self._check_closed()
@@ -354,20 +356,16 @@
 
 readsize = 1024
 if size < 0: # get the whole thing
- try:
- while True:
- self._read(readsize)
- readsize = min(self.max_read_chunk, readsize * 2)
- except EOFError:
- size = self.extrasize
+ while self._read(readsize):
+ readsize = min(self.max_read_chunk, readsize * 2)
+ size = self.extrasize
 else: # just get some more of it
- try:
- while size > self.extrasize:
- self._read(readsize)
- readsize = min(self.max_read_chunk, readsize * 2)
- except EOFError:
- if size > self.extrasize:
- size = self.extrasize
+ while size > self.extrasize:
+ if not self._read(readsize):
+ if size > self.extrasize:
+ size = self.extrasize
+ break
+ readsize = min(self.max_read_chunk, readsize * 2)
 
 offset = self.offset - self.extrastart
 chunk = self.extrabuf[offset: offset + size]
@@ -385,12 +383,9 @@
 if self.extrasize <= 0 and self.fileobj is None:
 return b''
 
- try:
- # For certain input data, a single call to _read() may not return
- # any data. In this case, retry until we get some data or reach EOF.
- while self.extrasize <= 0:
- self._read()
- except EOFError:
+ # For certain input data, a single call to _read() may not return
+ # any data. In this case, retry until we get some data or reach EOF.
+ while self.extrasize <= 0 and self._read():
 pass
 if size < 0 or size > self.extrasize:
 size = self.extrasize
@@ -413,12 +408,9 @@
 if self.extrasize == 0:
 if self.fileobj is None:
 return b''
- try:
- # Ensure that we don't return b"" if we haven't reached EOF.
- while self.extrasize == 0:
- # 1024 is the same buffering heuristic used in read()
- self._read(max(n, 1024))
- except EOFError:
+ # Ensure that we don't return b"" if we haven't reached EOF.
+ # 1024 is the same buffering heuristic used in read()
+ while self.extrasize == 0 and self._read(max(n, 1024)):
 pass
 offset = self.offset - self.extrastart
 remaining = self.extrasize
@@ -431,13 +423,14 @@
 
 def _read(self, size=1024):
 if self.fileobj is None:
- raise EOFError("Reached EOF")
+ return False
 
 if self._new_member:
 # If the _new_member flag is set, we have to
 # jump to the next member, if there is one.
 self._init_read()
- self._read_gzip_header()
+ if not self._read_gzip_header():
+ return False
 self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
 self._new_member = False
 
@@ -454,7 +447,7 @@
 self.fileobj.prepend(self.decompress.unused_data, True)
 self._read_eof()
 self._add_read_data( uncompress )
- raise EOFError('Reached EOF')
+ return False
 
 uncompress = self.decompress.decompress(buf)
 self._add_read_data( uncompress )
@@ -470,6 +463,7 @@
 # a new member on the next call
 self._read_eof()
 self._new_member = True
+ return True
 
 def _add_read_data(self, data):
 self.crc = zlib.crc32(data, self.crc) & 0xffffffff
@@ -484,8 +478,7 @@
 # We check the that the computed CRC and size of the
 # uncompressed data matches the stored values. Note that the size
 # stored is the true file size mod 2**32.
- crc32 = read32(self.fileobj)
- isize = read32(self.fileobj) # may exceed 2GB
+ crc32, isize = struct.unpack("<II", self._read_exact(8))
 if crc32 != self.crc:
 raise IOError("CRC check failed %s != %s" % (hex(crc32),
 hex(self.crc)))
diff --git a/Lib/test/test_bz2.py b/Lib/test/test_bz2.py
--- a/Lib/test/test_bz2.py
+++ b/Lib/test/test_bz2.py
@@ -577,6 +577,20 @@
 bz2f.seek(-150, 1)
 self.assertEqual(bz2f.read(), self.TEXT[500-150:])
 
+ def test_read_truncated(self):
+ # Drop the eos_magic field (6 bytes) and CRC (4 bytes).
+ truncated = self.DATA[:-10]
+ with BZ2File(BytesIO(truncated)) as f:
+ self.assertRaises(EOFError, f.read)
+ with BZ2File(BytesIO(truncated)) as f:
+ self.assertEqual(f.read(len(self.TEXT)), self.TEXT)
+ self.assertRaises(EOFError, f.read, 1)
+ # Incomplete 4-byte file header, and block header of at least 146 bits.
+ for i in range(22):
+ with BZ2File(BytesIO(truncated[:i])) as f:
+ self.assertRaises(EOFError, f.read, 1)
+
+
 class BZ2CompressorTest(BaseTest):
 def testCompress(self):
 bz2c = BZ2Compressor()
diff --git a/Lib/test/test_gzip.py b/Lib/test/test_gzip.py
--- a/Lib/test/test_gzip.py
+++ b/Lib/test/test_gzip.py
@@ -389,6 +389,20 @@
 datac = gzip.compress(data)
 self.assertEqual(gzip.decompress(datac), data)
 
+ def test_read_truncated(self):
+ data = data1*50
+ # Drop the CRC (4 bytes) and file size (4 bytes).
+ truncated = gzip.compress(data)[:-8]
+ with gzip.GzipFile(fileobj=io.BytesIO(truncated)) as f:
+ self.assertRaises(EOFError, f.read)
+ with gzip.GzipFile(fileobj=io.BytesIO(truncated)) as f:
+ self.assertEqual(f.read(len(data)), data)
+ self.assertRaises(EOFError, f.read, 1)
+ # Incomplete 10-byte header.
+ for i in range(2, 10):
+ with gzip.GzipFile(fileobj=io.BytesIO(truncated[:i])) as f:
+ self.assertRaises(EOFError, f.read, 1)
+
 
 class TestOpen(BaseTest):
 def test_binary_modes(self):
diff --git a/Lib/test/test_lzma.py b/Lib/test/test_lzma.py
--- a/Lib/test/test_lzma.py
+++ b/Lib/test/test_lzma.py
@@ -669,6 +669,20 @@
 with LZMAFile(BytesIO(COMPRESSED_XZ[:128])) as f:
 self.assertRaises(EOFError, f.read)
 
+ def test_read_truncated(self):
+ # Drop stream footer: CRC (4 bytes), index size (4 bytes),
+ # flags (2 bytes) and magic number (2 bytes).
+ truncated = COMPRESSED_XZ[:-12]
+ with LZMAFile(BytesIO(truncated)) as f:
+ self.assertRaises(EOFError, f.read)
+ with LZMAFile(BytesIO(truncated)) as f:
+ self.assertEqual(f.read(len(INPUT)), INPUT)
+ self.assertRaises(EOFError, f.read, 1)
+ # Incomplete 12-byte header.
+ for i in range(12):
+ with LZMAFile(BytesIO(truncated[:i])) as f:
+ self.assertRaises(EOFError, f.read, 1)
+
 def test_read_bad_args(self):
 f = LZMAFile(BytesIO(COMPRESSED_XZ))
 f.close()
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -150,6 +150,9 @@
 Library
 -------
 
+- Issue #1159051: GzipFile now raises EOFError when reading a corrupted file
+ with truncated header or footer.
+
 - Issue #16993: shutil.which() now preserves the case of the path and extension
 on Windows.
 
-- 
Repository URL: http://hg.python.org/cpython
