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Code Issues Releases Activity

gh-121285: Remove backtracking when parsing tarfile headers (GH-121286)

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* Remove backtracking when parsing tarfile headers
* Rewrite PAX header parsing to be stricter
* Optimize parsing of GNU extended sparse headers v0.0

Co-authored-by: Kirill Podoprigora <kirill.bast9@mail.ru>
Co-authored-by: Gregory P. Smith <greg@krypto.org>
This commit is contained in:
Seth Michael Larson 2024-08-31 17:17:05 -05:00 committed by GitHub
parent 0cba289870
commit 34ddb64d08
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GPG Key ID: B5690EEEBB952194
3 changed files with 112 additions and 35 deletions
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103
Lib/tarfile.py
View File

@ -845,6 +845,9 @@ _NAMED_FILTERS = {
# Sentinel for replace() defaults, meaning "don't change the attribute"
_KEEP = object()
# Header length is digits followed by a space.
_header_length_prefix_re = re.compile(br"([0-9]{1,20}) ")
class TarInfo(object):
"""Informational class which holds the details about an
archive member given by a tar header block.
@ -1432,37 +1435,59 @@ class TarInfo(object):
else:
pax_headers = tarfile.pax_headers.copy()
# Check if the pax header contains a hdrcharset field. This tells us
# the encoding of the path, linkpath, uname and gname fields. Normally,
# these fields are UTF-8 encoded but since POSIX.1-2008 tar
# implementations are allowed to store them as raw binary strings if
# the translation to UTF-8 fails.
match = re.search(br"\d+ hdrcharset=([^\n]+)\n", buf)
if match is not None:
pax_headers["hdrcharset"] = match.group(1).decode("utf-8")
# For the time being, we don't care about anything other than "BINARY".
# The only other value that is currently allowed by the standard is
# "ISO-IR 10646 2000 UTF-8" in other words UTF-8.
hdrcharset = pax_headers.get("hdrcharset")
if hdrcharset == "BINARY":
encoding = tarfile.encoding
else:
encoding = "utf-8"
# Parse pax header information. A record looks like that:
# "%d %s=%s\n" % (length, keyword, value). length is the size
# of the complete record including the length field itself and
# the newline. keyword and value are both UTF-8 encoded strings.
regex = re.compile(br"(\d+) ([^=]+)=")
# the newline.
pos = 0
while match := regex.match(buf, pos):
length, keyword = match.groups()
length = int(length)
if length == 0:
encoding = None
raw_headers = []
while len(buf) > pos and buf[pos] != 0x00:
if not (match := _header_length_prefix_re.match(buf, pos)):
raise InvalidHeaderError("invalid header")
try:
length = int(match.group(1))
except ValueError:
raise InvalidHeaderError("invalid header")
# Headers must be at least 5 bytes, shortest being '5 x=\n'.
# Value is allowed to be empty.
if length < 5:
raise InvalidHeaderError("invalid header")
if pos + length > len(buf):
raise InvalidHeaderError("invalid header")
value = buf[match.end(2) + 1:match.start(1) + length - 1]
header_value_end_offset = match.start(1) + length - 1 # Last byte of the header
keyword_and_value = buf[match.end(1) + 1:header_value_end_offset]
raw_keyword, equals, raw_value = keyword_and_value.partition(b"=")
# Check the framing of the header. The last character must be '\n' (0x0A)
if not raw_keyword or equals != b"=" or buf[header_value_end_offset] != 0x0A:
raise InvalidHeaderError("invalid header")
raw_headers.append((length, raw_keyword, raw_value))
# Check if the pax header contains a hdrcharset field. This tells us
# the encoding of the path, linkpath, uname and gname fields. Normally,
# these fields are UTF-8 encoded but since POSIX.1-2008 tar
# implementations are allowed to store them as raw binary strings if
# the translation to UTF-8 fails. For the time being, we don't care about
# anything other than "BINARY". The only other value that is currently
# allowed by the standard is "ISO-IR 10646 2000 UTF-8" in other words UTF-8.
# Note that we only follow the initial 'hdrcharset' setting to preserve
# the initial behavior of the 'tarfile' module.
if raw_keyword == b"hdrcharset" and encoding is None:
if raw_value == b"BINARY":
encoding = tarfile.encoding
else: # This branch ensures only the first 'hdrcharset' header is used.
encoding = "utf-8"
pos += length
# If no explicit hdrcharset is set, we use UTF-8 as a default.
if encoding is None:
encoding = "utf-8"
# After parsing the raw headers we can decode them to text.
for length, raw_keyword, raw_value in raw_headers:
# Normally, we could just use "utf-8" as the encoding and "strict"
# as the error handler, but we better not take the risk. For
# example, GNU tar <= 1.23 is known to store filenames it cannot
@ -1470,17 +1495,16 @@ class TarInfo(object):
# hdrcharset=BINARY header).
# We first try the strict standard encoding, and if that fails we
# fall back on the user's encoding and error handler.
keyword = self._decode_pax_field(keyword, "utf-8", "utf-8",
keyword = self._decode_pax_field(raw_keyword, "utf-8", "utf-8",
tarfile.errors)
if keyword in PAX_NAME_FIELDS:
value = self._decode_pax_field(value, encoding, tarfile.encoding,
value = self._decode_pax_field(raw_value, encoding, tarfile.encoding,
tarfile.errors)
else:
value = self._decode_pax_field(value, "utf-8", "utf-8",
value = self._decode_pax_field(raw_value, "utf-8", "utf-8",
tarfile.errors)
pax_headers[keyword] = value
pos += length
# Fetch the next header.
try:
@ -1495,7 +1519,7 @@ class TarInfo(object):
elif "GNU.sparse.size" in pax_headers:
# GNU extended sparse format version 0.0.
self._proc_gnusparse_00(next, pax_headers, buf)
self._proc_gnusparse_00(next, raw_headers)
elif pax_headers.get("GNU.sparse.major") == "1" and pax_headers.get("GNU.sparse.minor") == "0":
# GNU extended sparse format version 1.0.
@ -1517,15 +1541,24 @@ class TarInfo(object):
return next
def _proc_gnusparse_00(self, next, pax_headers, buf):
def _proc_gnusparse_00(self, next, raw_headers):
"""Process a GNU tar extended sparse header, version 0.0.
"""
offsets = []
for match in re.finditer(br"\d+ GNU.sparse.offset=(\d+)\n", buf):
offsets.append(int(match.group(1)))
numbytes = []
for match in re.finditer(br"\d+ GNU.sparse.numbytes=(\d+)\n", buf):
numbytes.append(int(match.group(1)))
for _, keyword, value in raw_headers:
if keyword == b"GNU.sparse.offset":
try:
offsets.append(int(value.decode()))
except ValueError:
raise InvalidHeaderError("invalid header")
elif keyword == b"GNU.sparse.numbytes":
try:
numbytes.append(int(value.decode()))
except ValueError:
raise InvalidHeaderError("invalid header")
next.sparse = list(zip(offsets, numbytes))
def _proc_gnusparse_01(self, next, pax_headers):

42
Lib/test/test_tarfile.py
View File

@ -1261,6 +1261,48 @@ class PaxReadTest(LongnameTest, ReadTest, unittest.TestCase):
finally:
tar.close()
def test_pax_header_bad_formats(self):
# The fields from the pax header have priority over the
# TarInfo.
pax_header_replacements = (
b" foo=bar\n",
b"0 \n",
b"1 \n",
b"2 \n",
b"3 =\n",
b"4 =a\n",
b"1000000 foo=bar\n",
b"0 foo=bar\n",
b"-12 foo=bar\n",
b"000000000000000000000000036 foo=bar\n",
)
pax_headers = {"foo": "bar"}
for replacement in pax_header_replacements:
with self.subTest(header=replacement):
tar = tarfile.open(tmpname, "w", format=tarfile.PAX_FORMAT,
encoding="iso8859-1")
try:
t = tarfile.TarInfo()
t.name = "pax" # non-ASCII
t.uid = 1
t.pax_headers = pax_headers
tar.addfile(t)
finally:
tar.close()
with open(tmpname, "rb") as f:
data = f.read()
self.assertIn(b"11 foo=bar\n", data)
data = data.replace(b"11 foo=bar\n", replacement)
with open(tmpname, "wb") as f:
f.truncate()
f.write(data)
with self.assertRaisesRegex(tarfile.ReadError, r"method tar: ReadError\('invalid header'\)"):
tarfile.open(tmpname, encoding="iso8859-1")
class WriteTestBase(TarTest):
# Put all write tests in here that are supposed to be tested

2
Misc/NEWS.d/next/Security/2024-07-02-13-39-20.gh-issue-121285.hrl-yI.rst Normal file
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@ -0,0 +1,2 @@
Remove backtracking from tarfile header parsing for ``hdrcharset``, PAX, and
GNU sparse headers.