EOFError in tarfile.open

[jvoisin]

BPO	39067
Nosy	@ronaldoussoren
Files	crash-f4032ed3c7c2ae59a8f4424e0e73ce8b11ad3ef90155b008968f5b1b08499bc4

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-12-16.14:21:45.223>
labels = ['3.7', 'type-bug', 'library', 'docs']
title = 'EOFError in tarfile.open'
updated_at = <Date 2019-12-17.09:45:27.593>
user = 'https://bugs.python.org/jvoisin'

bugs.python.org fields:

activity = <Date 2019-12-17.09:45:27.593>
actor = 'jvoisin'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation', 'Library (Lib)']
creation = <Date 2019-12-16.14:21:45.223>
creator = 'jvoisin'
dependencies = []
files = ['48784']
hgrepos = []
issue_num = 39067
keywords = []
message_count = 5.0
messages = ['358490', '358492', '358493', '358494', '358540']
nosy_count = 3.0
nosy_names = ['ronaldoussoren', 'docs@python', 'jvoisin']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue39067'
versions = ['Python 3.7']

[jvoisin]

The attached file produces the following stacktrace when opened via tarfile.open, on Python 3.7.5rc1:

$ cat tarrepro.py 
import tarfile
import sys

with tarfile.open(sys.argv[1], errorlevel=2) as t:
  for member in t.getmembers():
    pass
$

$ python3 tarrepro.py crash-f4032ed3c7c2ae59a8f4424e0e73ce8b11ad3ef90155b008968f5b1b08499bc4
Traceback (most recent call last):
  File "tarrepro.py", line 4, in <module>
    with tarfile.open(sys.argv[1], errorlevel=2) as t:
  File "/usr/lib/python3.7/tarfile.py", line 1574, in open
    return func(name, "r", fileobj, **kwargs)
  File "/usr/lib/python3.7/tarfile.py", line 1646, in gzopen
    t = cls.taropen(name, mode, fileobj, **kwargs)
  File "/usr/lib/python3.7/tarfile.py", line 1622, in taropen
    return cls(name, mode, fileobj, **kwargs)
  File "/usr/lib/python3.7/tarfile.py", line 1485, in __init__
    self.firstmember = self.next()
  File "/usr/lib/python3.7/tarfile.py", line 2290, in next
    tarinfo = self.tarinfo.fromtarfile(self)
  File "/usr/lib/python3.7/tarfile.py", line 1094, in fromtarfile
    buf = tarfile.fileobj.read(BLOCKSIZE)
  File "/usr/lib/python3.7/gzip.py", line 276, in read
    return self._buffer.read(size)
  File "/usr/lib/python3.7/_compression.py", line 68, in readinto
    data = self.read(len(byte_view))
  File "/usr/lib/python3.7/gzip.py", line 463, in read
    if not self._read_gzip_header():
  File "/usr/lib/python3.7/gzip.py", line 421, in _read_gzip_header
    self._read_exact(extra_len)
  File "/usr/lib/python3.7/gzip.py", line 400, in _read_exact
    raise EOFError("Compressed file ended before the "
EOFError: Compressed file ended before the end-of-stream marker was reached

[ronaldoussoren]

Looks like expected behaviour, the attached file is an incomplete compressed file that does not seem to contain data (according to gzcat)

gzcat: crash-f4032ed3c7c2ae59a8f4424e0e73ce8b11ad3ef90155b008968f5b1b08499bc4: unexpected end of file
gzcat: crash-f4032ed3c7c2ae59a8f4424e0e73ce8b11ad3ef90155b008968f5b1b08499bc4: uncompress failed

[jvoisin]

Unfortunately, the documentation ( https://docs.python.org/3/library/tarfile.html) doesn't mention that EOFError is an exception that could be raised when using tarfile.open :/

[ronaldoussoren]

The stdlib documentation does in general not contain exhaustive documentation on exceptions that might be raised.

[jvoisin]

Does it means that the right™ way to process untrusted tar files is
to wrap every call to functions from tarfile.py in a `try: … except Exception:` block?