https://github.com/python/cpython/commit/4eaf4891c12589e3c7bdad5f5b076e4c839... commit: 4eaf4891c12589e3c7bdad5f5b076e4c8392dd06 branch: 3.12 author: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> committer: gpshead <greg@krypto.org> date: 2024-08-31T22:35:24Z summary: [3.12] gh-121285: Remove backtracking when parsing tarfile headers (GH-121286) (GH-123543) gh-121285: Remove backtracking when parsing tarfile headers (GH-121286) * Remove backtracking when parsing tarfile headers * Rewrite PAX header parsing to be stricter * Optimize parsing of GNU extended sparse headers v0.0 (cherry picked from commit 34ddb64d088dd7ccc321f6103d23153256caa5d4) Co-authored-by: Seth Michael Larson <seth@python.org> Co-authored-by: Kirill Podoprigora <kirill.bast9@mail.ru> Co-authored-by: Gregory P. Smith <greg@krypto.org> files: A Misc/NEWS.d/next/Security/2024-07-02-13-39-20.gh-issue-121285.hrl-yI.rst M Lib/tarfile.py M Lib/test/test_tarfile.py diff --git a/Lib/tarfile.py b/Lib/tarfile.py index e1487e3864d44b..0a0f31eca06c04 100755 --- a/Lib/tarfile.py +++ b/Lib/tarfile.py @@ -843,6 +843,9 @@ def data_filter(member, dest_path): # 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. @@ -1412,37 +1415,59 @@ def _proc_pax(self, tarfile): 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") + + 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") - value = buf[match.end(2) + 1:match.start(1) + length - 1] + 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 @@ -1450,17 +1475,16 @@ def _proc_pax(self, tarfile): # 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: @@ -1475,7 +1499,7 @@ def _proc_pax(self, tarfile): 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. @@ -1497,15 +1521,24 @@ def _proc_pax(self, tarfile): 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): diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py index 3fbd25e742b181..e28d0311826e2b 100644 --- a/Lib/test/test_tarfile.py +++ b/Lib/test/test_tarfile.py @@ -1237,6 +1237,48 @@ def test_pax_number_fields(self): 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 diff --git a/Misc/NEWS.d/next/Security/2024-07-02-13-39-20.gh-issue-121285.hrl-yI.rst b/Misc/NEWS.d/next/Security/2024-07-02-13-39-20.gh-issue-121285.hrl-yI.rst new file mode 100644 index 00000000000000..81f918bfe2b255 --- /dev/null +++ b/Misc/NEWS.d/next/Security/2024-07-02-13-39-20.gh-issue-121285.hrl-yI.rst @@ -0,0 +1,2 @@ +Remove backtracking from tarfile header parsing for ``hdrcharset``, PAX, and +GNU sparse headers.