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@ -0,0 +1,245 @@
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From 4eaf4891c12589e3c7bdad5f5b076e4c8392dd06 Mon Sep 17 00:00:00 2001
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From: "Miss Islington (bot)"
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<31488909+miss-islington@users.noreply.github.com>
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Date: Sun, 1 Sep 2024 00:35:24 +0200
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Subject: [PATCH] [3.12] gh-121285: Remove backtracking when parsing tarfile
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headers (GH-121286) (GH-123543)
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gh-121285: Remove backtracking when parsing tarfile headers (GH-121286)
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* Remove backtracking when parsing tarfile headers
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* Rewrite PAX header parsing to be stricter
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* Optimize parsing of GNU extended sparse headers v0.0
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(cherry picked from commit 34ddb64d088dd7ccc321f6103d23153256caa5d4)
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Co-authored-by: Seth Michael Larson <seth@python.org>
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Co-authored-by: Kirill Podoprigora <kirill.bast9@mail.ru>
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Co-authored-by: Gregory P. Smith <greg@krypto.org>
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---
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Lib/tarfile.py | 103 ++++++++++++------
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Lib/test/test_tarfile.py | 42 +++++++
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...-07-02-13-39-20.gh-issue-121285.hrl-yI.rst | 2 +
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3 files changed, 112 insertions(+), 35 deletions(-)
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create mode 100644 Misc/NEWS.d/next/Security/2024-07-02-13-39-20.gh-issue-121285.hrl-yI.rst
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diff --git a/Lib/tarfile.py b/Lib/tarfile.py
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index e1487e3864d44b..0a0f31eca06c04 100755
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--- a/Lib/tarfile.py
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+++ b/Lib/tarfile.py
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@@ -843,6 +843,9 @@ def data_filter(member, dest_path):
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# Sentinel for replace() defaults, meaning "don't change the attribute"
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_KEEP = object()
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+# Header length is digits followed by a space.
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+_header_length_prefix_re = re.compile(br"([0-9]{1,20}) ")
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+
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class TarInfo(object):
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"""Informational class which holds the details about an
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archive member given by a tar header block.
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@@ -1412,37 +1415,59 @@ def _proc_pax(self, tarfile):
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else:
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pax_headers = tarfile.pax_headers.copy()
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- # Check if the pax header contains a hdrcharset field. This tells us
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- # the encoding of the path, linkpath, uname and gname fields. Normally,
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- # these fields are UTF-8 encoded but since POSIX.1-2008 tar
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- # implementations are allowed to store them as raw binary strings if
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- # the translation to UTF-8 fails.
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- match = re.search(br"\d+ hdrcharset=([^\n]+)\n", buf)
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- if match is not None:
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- pax_headers["hdrcharset"] = match.group(1).decode("utf-8")
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-
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- # For the time being, we don't care about anything other than "BINARY".
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- # The only other value that is currently allowed by the standard is
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- # "ISO-IR 10646 2000 UTF-8" in other words UTF-8.
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- hdrcharset = pax_headers.get("hdrcharset")
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- if hdrcharset == "BINARY":
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- encoding = tarfile.encoding
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- else:
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- encoding = "utf-8"
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-
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# Parse pax header information. A record looks like that:
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# "%d %s=%s\n" % (length, keyword, value). length is the size
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# of the complete record including the length field itself and
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- # the newline. keyword and value are both UTF-8 encoded strings.
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- regex = re.compile(br"(\d+) ([^=]+)=")
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+ # the newline.
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pos = 0
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- while match := regex.match(buf, pos):
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- length, keyword = match.groups()
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- length = int(length)
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- if length == 0:
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+ encoding = None
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+ raw_headers = []
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+ while len(buf) > pos and buf[pos] != 0x00:
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+ if not (match := _header_length_prefix_re.match(buf, pos)):
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+ raise InvalidHeaderError("invalid header")
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+ try:
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+ length = int(match.group(1))
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+ except ValueError:
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+ raise InvalidHeaderError("invalid header")
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+ # Headers must be at least 5 bytes, shortest being '5 x=\n'.
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+ # Value is allowed to be empty.
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+ if length < 5:
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+ raise InvalidHeaderError("invalid header")
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+ if pos + length > len(buf):
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+ raise InvalidHeaderError("invalid header")
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+
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+ header_value_end_offset = match.start(1) + length - 1 # Last byte of the header
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+ keyword_and_value = buf[match.end(1) + 1:header_value_end_offset]
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+ raw_keyword, equals, raw_value = keyword_and_value.partition(b"=")
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+
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+ # Check the framing of the header. The last character must be '\n' (0x0A)
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+ if not raw_keyword or equals != b"=" or buf[header_value_end_offset] != 0x0A:
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raise InvalidHeaderError("invalid header")
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- value = buf[match.end(2) + 1:match.start(1) + length - 1]
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+ raw_headers.append((length, raw_keyword, raw_value))
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+
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+ # Check if the pax header contains a hdrcharset field. This tells us
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+ # the encoding of the path, linkpath, uname and gname fields. Normally,
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+ # these fields are UTF-8 encoded but since POSIX.1-2008 tar
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+ # implementations are allowed to store them as raw binary strings if
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+ # the translation to UTF-8 fails. For the time being, we don't care about
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+ # anything other than "BINARY". The only other value that is currently
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+ # allowed by the standard is "ISO-IR 10646 2000 UTF-8" in other words UTF-8.
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+ # Note that we only follow the initial 'hdrcharset' setting to preserve
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+ # the initial behavior of the 'tarfile' module.
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+ if raw_keyword == b"hdrcharset" and encoding is None:
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+ if raw_value == b"BINARY":
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+ encoding = tarfile.encoding
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+ else: # This branch ensures only the first 'hdrcharset' header is used.
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+ encoding = "utf-8"
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+ pos += length
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+
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+ # If no explicit hdrcharset is set, we use UTF-8 as a default.
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+ if encoding is None:
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+ encoding = "utf-8"
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+
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+ # After parsing the raw headers we can decode them to text.
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+ for length, raw_keyword, raw_value in raw_headers:
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# Normally, we could just use "utf-8" as the encoding and "strict"
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# as the error handler, but we better not take the risk. For
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# example, GNU tar <= 1.23 is known to store filenames it cannot
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@@ -1450,17 +1475,16 @@ def _proc_pax(self, tarfile):
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# hdrcharset=BINARY header).
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# We first try the strict standard encoding, and if that fails we
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# fall back on the user's encoding and error handler.
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- keyword = self._decode_pax_field(keyword, "utf-8", "utf-8",
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+ keyword = self._decode_pax_field(raw_keyword, "utf-8", "utf-8",
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tarfile.errors)
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if keyword in PAX_NAME_FIELDS:
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- value = self._decode_pax_field(value, encoding, tarfile.encoding,
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+ value = self._decode_pax_field(raw_value, encoding, tarfile.encoding,
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tarfile.errors)
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else:
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- value = self._decode_pax_field(value, "utf-8", "utf-8",
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+ value = self._decode_pax_field(raw_value, "utf-8", "utf-8",
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tarfile.errors)
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pax_headers[keyword] = value
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- pos += length
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# Fetch the next header.
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try:
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@@ -1475,7 +1499,7 @@ def _proc_pax(self, tarfile):
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elif "GNU.sparse.size" in pax_headers:
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# GNU extended sparse format version 0.0.
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- self._proc_gnusparse_00(next, pax_headers, buf)
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+ self._proc_gnusparse_00(next, raw_headers)
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elif pax_headers.get("GNU.sparse.major") == "1" and pax_headers.get("GNU.sparse.minor") == "0":
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# GNU extended sparse format version 1.0.
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@@ -1497,15 +1521,24 @@ def _proc_pax(self, tarfile):
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return next
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- def _proc_gnusparse_00(self, next, pax_headers, buf):
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+ def _proc_gnusparse_00(self, next, raw_headers):
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"""Process a GNU tar extended sparse header, version 0.0.
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"""
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offsets = []
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- for match in re.finditer(br"\d+ GNU.sparse.offset=(\d+)\n", buf):
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- offsets.append(int(match.group(1)))
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numbytes = []
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- for match in re.finditer(br"\d+ GNU.sparse.numbytes=(\d+)\n", buf):
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- numbytes.append(int(match.group(1)))
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+ for _, keyword, value in raw_headers:
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+ if keyword == b"GNU.sparse.offset":
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+ try:
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+ offsets.append(int(value.decode()))
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+ except ValueError:
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+ raise InvalidHeaderError("invalid header")
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+
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+ elif keyword == b"GNU.sparse.numbytes":
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+ try:
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+ numbytes.append(int(value.decode()))
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+ except ValueError:
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+ raise InvalidHeaderError("invalid header")
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+
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next.sparse = list(zip(offsets, numbytes))
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def _proc_gnusparse_01(self, next, pax_headers):
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diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
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index 3fbd25e742b181..e28d0311826e2b 100644
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--- a/Lib/test/test_tarfile.py
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+++ b/Lib/test/test_tarfile.py
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@@ -1237,6 +1237,48 @@ def test_pax_number_fields(self):
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finally:
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tar.close()
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+ def test_pax_header_bad_formats(self):
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+ # The fields from the pax header have priority over the
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+ # TarInfo.
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+ pax_header_replacements = (
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+ b" foo=bar\n",
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+ b"0 \n",
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+ b"1 \n",
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+ b"2 \n",
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+ b"3 =\n",
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+ b"4 =a\n",
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+ b"1000000 foo=bar\n",
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+ b"0 foo=bar\n",
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+ b"-12 foo=bar\n",
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+ b"000000000000000000000000036 foo=bar\n",
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+ )
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+ pax_headers = {"foo": "bar"}
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+
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+ for replacement in pax_header_replacements:
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+ with self.subTest(header=replacement):
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+ tar = tarfile.open(tmpname, "w", format=tarfile.PAX_FORMAT,
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+ encoding="iso8859-1")
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+ try:
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+ t = tarfile.TarInfo()
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+ t.name = "pax" # non-ASCII
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+ t.uid = 1
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+ t.pax_headers = pax_headers
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+ tar.addfile(t)
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+ finally:
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+ tar.close()
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+
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+ with open(tmpname, "rb") as f:
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+ data = f.read()
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+ self.assertIn(b"11 foo=bar\n", data)
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+ data = data.replace(b"11 foo=bar\n", replacement)
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+
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+ with open(tmpname, "wb") as f:
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+ f.truncate()
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+ f.write(data)
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+
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+ with self.assertRaisesRegex(tarfile.ReadError, r"method tar: ReadError\('invalid header'\)"):
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+ tarfile.open(tmpname, encoding="iso8859-1")
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+
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class WriteTestBase(TarTest):
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# Put all write tests in here that are supposed to be tested
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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
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new file mode 100644
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index 00000000000000..81f918bfe2b255
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--- /dev/null
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+++ b/Misc/NEWS.d/next/Security/2024-07-02-13-39-20.gh-issue-121285.hrl-yI.rst
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@@ -0,0 +1,2 @@
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+Remove backtracking from tarfile header parsing for ``hdrcharset``, PAX, and
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+GNU sparse headers.
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