gh-102950: Implement PEP 706 – Filter for tarfile.extractall (#102953)

Doc/library/shutil.rst

@@ -662,7 +662,7 @@ provided.  They rely on the :mod:`zipfile` and :mod:`tarfile` modules.
    Remove the archive format *name* from the list of supported formats.
 
 
-.. function:: unpack_archive(filename[, extract_dir[, format]])
+.. function:: unpack_archive(filename[, extract_dir[, format[, filter]]])
 
    Unpack an archive. *filename* is the full path of the archive.
 
@@ -676,6 +676,14 @@ provided.  They rely on the :mod:`zipfile` and :mod:`tarfile` modules.
    registered for that extension.  In case none is found,
    a :exc:`ValueError` is raised.
 
+   The keyword-only *filter* argument is passed to the underlying unpacking
+   function. For zip files, *filter* is not accepted.
+   For tar files, it is recommended to set it to ``'data'``,
+   unless using features specific to tar and UNIX-like filesystems.
+   (See :ref:`tarfile-extraction-filter` for details.)
+   The ``'data'`` filter will become the default for tar files
+   in Python 3.14.
+
    .. audit-event:: shutil.unpack_archive filename,extract_dir,format shutil.unpack_archive
 
    .. warning::
@@ -688,6 +696,9 @@ provided.  They rely on the :mod:`zipfile` and :mod:`tarfile` modules.
    .. versionchanged:: 3.7
       Accepts a :term:`path-like object` for *filename* and *extract_dir*.
 
+   .. versionchanged:: 3.12
+      Added the *filter* argument.
+
 .. function:: register_unpack_format(name, extensions, function[, extra_args[, description]])
 
    Registers an unpack format. *name* is the name of the format and
@@ -695,11 +706,14 @@ provided.  They rely on the :mod:`zipfile` and :mod:`tarfile` modules.
    ``.zip`` for Zip files.
 
    *function* is the callable that will be used to unpack archives. The
-   callable will receive the path of the archive, followed by the directory
+   callable will receive:
-   the archive must be extracted to.
 
-   When provided, *extra_args* is a sequence of ``(name, value)`` tuples that
+   - the path of the archive, as a positional argument;
-   will be passed as keywords arguments to the callable.
+   - the directory the archive must be extracted to, as a positional argument;
+   - possibly a *filter* keyword argument, if it was given to
+     :func:`unpack_archive`;
+   - additional keyword arguments, specified by *extra_args* as a sequence
+     of ``(name, value)`` tuples.
 
    *description* can be provided to describe the format, and will be returned
    by the :func:`get_unpack_formats` function.

Doc/library/tarfile.rst

@@ -36,6 +36,13 @@ Some facts and figures:
 .. versionchanged:: 3.3
    Added support for :mod:`lzma` compression.
 
+.. versionchanged:: 3.12
+   Archives are extracted using a :ref:`filter <tarfile-extraction-filter>`,
+   which makes it possible to either limit surprising/dangerous features,
+   or to acknowledge that they are expected and the archive is fully trusted.
+   By default, archives are fully trusted, but this default is deprecated
+   and slated to change in Python 3.14.
+
 
 .. function:: open(name=None, mode='r', fileobj=None, bufsize=10240, **kwargs)
 
@@ -209,6 +216,38 @@ The :mod:`tarfile` module defines the following exceptions:
    Is raised by :meth:`TarInfo.frombuf` if the buffer it gets is invalid.
 
 
+.. exception:: FilterError
+
+   Base class for members :ref:`refused <tarfile-extraction-refuse>` by
+   filters.
+
+   .. attribute:: tarinfo
+
+      Information about the member that the filter refused to extract,
+      as :ref:`TarInfo <tarinfo-objects>`.
+
+.. exception:: AbsolutePathError
+
+   Raised to refuse extracting a member with an absolute path.
+
+.. exception:: OutsideDestinationError
+
+   Raised to refuse extracting a member outside the destination directory.
+
+.. exception:: SpecialFileError
+
+   Raised to refuse extracting a special file (e.g. a device or pipe).
+
+.. exception:: AbsoluteLinkError
+
+   Raised to refuse extracting a symbolic link with an absolute path.
+
+.. exception:: LinkOutsideDestinationError
+
+   Raised to refuse extracting a symbolic link pointing outside the destination
+   directory.
+
+
 The following constants are available at the module level:
 
 .. data:: ENCODING
@@ -319,11 +358,8 @@ be finalized; only the internally used file object will be closed. See the
    *debug* can be set from ``0`` (no debug messages) up to ``3`` (all debug
    messages). The messages are written to ``sys.stderr``.
 
-   If *errorlevel* is ``0``, all errors are ignored when using :meth:`TarFile.extract`.
+   *errorlevel* controls how extraction errors are handled,
-   Nevertheless, they appear as error messages in the debug output, when debugging
+   see :attr:`the corresponding attribute <~TarFile.errorlevel>`.
-   is enabled.  If ``1``, all *fatal* errors are raised as :exc:`OSError`
-   exceptions. If ``2``, all *non-fatal* errors are raised as :exc:`TarError`
-   exceptions as well.
 
    The *encoding* and *errors* arguments define the character encoding to be
    used for reading or writing the archive and how conversion errors are going
@@ -390,7 +426,7 @@ be finalized; only the internally used file object will be closed. See the
    available.
 
 
-.. method:: TarFile.extractall(path=".", members=None, *, numeric_owner=False)
+.. method:: TarFile.extractall(path=".", members=None, *, numeric_owner=False, filter=None)
 
    Extract all members from the archive to the current working directory or
    directory *path*. If optional *members* is given, it must be a subset of the
@@ -404,6 +440,12 @@ be finalized; only the internally used file object will be closed. See the
    are used to set the owner/group for the extracted files. Otherwise, the named
    values from the tarfile are used.
 
+   The *filter* argument specifies how ``members`` are modified or rejected
+   before extraction.
+   See :ref:`tarfile-extraction-filter` for details.
+   It is recommended to set this explicitly depending on which *tar* features
+   you need to support.
+
    .. warning::
 
       Never extract archives from untrusted sources without prior inspection.
@@ -411,14 +453,20 @@ be finalized; only the internally used file object will be closed. See the
       that have absolute filenames starting with ``"/"`` or filenames with two
       dots ``".."``.
 
+      Set ``filter='data'`` to prevent the most dangerous security issues,
+      and read the :ref:`tarfile-extraction-filter` section for details.
+
    .. versionchanged:: 3.5
       Added the *numeric_owner* parameter.
 
    .. versionchanged:: 3.6
       The *path* parameter accepts a :term:`path-like object`.
 
+   .. versionchanged:: 3.12
+      Added the *filter* parameter.
 
-.. method:: TarFile.extract(member, path="", set_attrs=True, *, numeric_owner=False)
+
+.. method:: TarFile.extract(member, path="", set_attrs=True, *, numeric_owner=False, filter=None)
 
    Extract a member from the archive to the current working directory, using its
    full name. Its file information is extracted as accurately as possible. *member*
@@ -426,9 +474,8 @@ be finalized; only the internally used file object will be closed. See the
    directory using *path*. *path* may be a :term:`path-like object`.
    File attributes (owner, mtime, mode) are set unless *set_attrs* is false.
 
-   If *numeric_owner* is :const:`True`, the uid and gid numbers from the tarfile
+   The *numeric_owner* and *filter* arguments are the same as
-   are used to set the owner/group for the extracted files. Otherwise, the named
+   for :meth:`extractall`.
-   values from the tarfile are used.
 
    .. note::
 
@@ -439,6 +486,9 @@ be finalized; only the internally used file object will be closed. See the
 
       See the warning for :meth:`extractall`.
 
+      Set ``filter='data'`` to prevent the most dangerous security issues,
+      and read the :ref:`tarfile-extraction-filter` section for details.
+
    .. versionchanged:: 3.2
       Added the *set_attrs* parameter.
 
@@ -448,6 +498,9 @@ be finalized; only the internally used file object will be closed. See the
    .. versionchanged:: 3.6
       The *path* parameter accepts a :term:`path-like object`.
 
+   .. versionchanged:: 3.12
+      Added the *filter* parameter.
+
 
 .. method:: TarFile.extractfile(member)
 
@@ -460,6 +513,55 @@ be finalized; only the internally used file object will be closed. See the
    .. versionchanged:: 3.3
       Return an :class:`io.BufferedReader` object.
 
+.. attribute:: TarFile.errorlevel
+   :type: int
+
+   If *errorlevel* is ``0``, errors are ignored when using :meth:`TarFile.extract`
+   and :meth:`TarFile.extractall`.
+   Nevertheless, they appear as error messages in the debug output when
+   *debug* is greater than 0.
+   If ``1`` (the default), all *fatal* errors are raised as :exc:`OSError` or
+   :exc:`FilterError` exceptions. If ``2``, all *non-fatal* errors are raised
+   as :exc:`TarError` exceptions as well.
+
+   Some exceptions, e.g. ones caused by wrong argument types or data
+   corruption, are always raised.
+
+   Custom :ref:`extraction filters <tarfile-extraction-filter>`
+   should raise :exc:`FilterError` for *fatal* errors
+   and :exc:`ExtractError` for *non-fatal* ones.
+
+   Note that when an exception is raised, the archive may be partially
+   extracted. It is the user’s responsibility to clean up.
+
+.. attribute:: TarFile.extraction_filter
+
+   .. versionadded:: 3.12
+
+   The :ref:`extraction filter <tarfile-extraction-filter>` used
+   as a default for the *filter* argument of :meth:`~TarFile.extract`
+   and :meth:`~TarFile.extractall`.
+
+   The attribute may be ``None`` or a callable.
+   String names are not allowed for this attribute, unlike the *filter*
+   argument to :meth:`~TarFile.extract`.
+
+   If ``extraction_filter`` is ``None`` (the default),
+   calling an extraction method without a *filter* argument will raise a
+   ``DeprecationWarning``,
+   and fall back to the :func:`fully_trusted <fully_trusted_filter>` filter,
+   whose dangerous behavior matches previous versions of Python.
+
+   In Python 3.14+, leaving ``extraction_filter=None`` will cause
+   extraction methods to use the :func:`data <data_filter>` filter by default.
+
+   The attribute may be set on instances or overridden in subclasses.
+   It also is possible to set it on the ``TarFile`` class itself to set a
+   global default, although, since it affects all uses of *tarfile*,
+   it is best practice to only do so in top-level applications or
+   :mod:`site configuration <site>`.
+   To set a global default this way, a filter function needs to be wrapped in
+   :func:`staticmethod()` to prevent injection of a ``self`` argument.
 
 .. method:: TarFile.add(name, arcname=None, recursive=True, *, filter=None)
 
@@ -535,8 +637,23 @@ permissions, owner etc.), it provides some useful methods to determine its type.
 It does *not* contain the file's data itself.
 
 :class:`TarInfo` objects are returned by :class:`TarFile`'s methods
-:meth:`getmember`, :meth:`getmembers` and :meth:`gettarinfo`.
+:meth:`~TarFile.getmember`, :meth:`~TarFile.getmembers` and
+:meth:`~TarFile.gettarinfo`.
 
+Modifying the objects returned by :meth:`~!TarFile.getmember` or
+:meth:`~!TarFile.getmembers` will affect all subsequent
+operations on the archive.
+For cases where this is unwanted, you can use :mod:`copy.copy() <copy>` or
+call the :meth:`~TarInfo.replace` method to create a modified copy in one step.
+
+Several attributes can be set to ``None`` to indicate that a piece of metadata
+is unused or unknown.
+Different :class:`TarInfo` methods handle ``None`` differently:
+
+- The :meth:`~TarFile.extract` or :meth:`~TarFile.extractall` methods will
+  ignore the corresponding metadata, leaving it set to a default.
+- :meth:`~TarFile.addfile` will fail.
+- :meth:`~TarFile.list` will print a placeholder string.
 
 .. class:: TarInfo(name="")
 
@@ -569,24 +686,39 @@ A ``TarInfo`` object has the following public data attributes:
 
 
 .. attribute:: TarInfo.name
+   :type: str
 
    Name of the archive member.
 
 
 .. attribute:: TarInfo.size
+   :type: int
 
    Size in bytes.
 
 
 .. attribute:: TarInfo.mtime
+   :type: int | float
 
-   Time of last modification.
+   Time of last modification in seconds since the :ref:`epoch <epoch>`,
+   as in :attr:`os.stat_result.st_mtime`.
 
+   .. versionchanged:: 3.12
+
+      Can be set to ``None`` for :meth:`~TarFile.extract` and
+      :meth:`~TarFile.extractall`, causing extraction to skip applying this
+      attribute.
 
 .. attribute:: TarInfo.mode
+   :type: int
 
-   Permission bits.
+   Permission bits, as for :func:`os.chmod`.
 
+   .. versionchanged:: 3.12
+
+      Can be set to ``None`` for :meth:`~TarFile.extract` and
+      :meth:`~TarFile.extractall`, causing extraction to skip applying this
+      attribute.
 
 .. attribute:: TarInfo.type
 
@@ -598,35 +730,76 @@ A ``TarInfo`` object has the following public data attributes:
 
 
 .. attribute:: TarInfo.linkname
+   :type: str
 
    Name of the target file name, which is only present in :class:`TarInfo` objects
    of type :const:`LNKTYPE` and :const:`SYMTYPE`.
 
 
 .. attribute:: TarInfo.uid
+   :type: int
 
    User ID of the user who originally stored this member.
 
+   .. versionchanged:: 3.12
+
+      Can be set to ``None`` for :meth:`~TarFile.extract` and
+      :meth:`~TarFile.extractall`, causing extraction to skip applying this
+      attribute.
 
 .. attribute:: TarInfo.gid
+   :type: int
 
    Group ID of the user who originally stored this member.
 
+   .. versionchanged:: 3.12
+
+      Can be set to ``None`` for :meth:`~TarFile.extract` and
+      :meth:`~TarFile.extractall`, causing extraction to skip applying this
+      attribute.
 
 .. attribute:: TarInfo.uname
+   :type: str
 
    User name.
 
+   .. versionchanged:: 3.12
+
+      Can be set to ``None`` for :meth:`~TarFile.extract` and
+      :meth:`~TarFile.extractall`, causing extraction to skip applying this
+      attribute.
 
 .. attribute:: TarInfo.gname
+   :type: str
 
    Group name.
 
+   .. versionchanged:: 3.12
+
+      Can be set to ``None`` for :meth:`~TarFile.extract` and
+      :meth:`~TarFile.extractall`, causing extraction to skip applying this
+      attribute.
 
 .. attribute:: TarInfo.pax_headers
+   :type: dict
 
    A dictionary containing key-value pairs of an associated pax extended header.
 
+.. method:: TarInfo.replace(name=..., mtime=..., mode=..., linkname=...,
+                            uid=..., gid=..., uname=..., gname=...,
+                            deep=True)
+
+   .. versionadded:: 3.12
+
+   Return a *new* copy of the :class:`!TarInfo` object with the given attributes
+   changed. For example, to return a ``TarInfo`` with the group name set to
+   ``'staff'``, use::
+
+       new_tarinfo = old_tarinfo.replace(gname='staff')
+
+   By default, a deep copy is made.
+   If *deep* is false, the copy is shallow, i.e. ``pax_headers``
+   and any custom attributes are shared with the original ``TarInfo`` object.
 
 A :class:`TarInfo` object also provides some convenient query methods:
 
@@ -676,9 +849,258 @@ A :class:`TarInfo` object also provides some convenient query methods:
    Return :const:`True` if it is one of character device, block device or FIFO.
 
 
+.. _tarfile-extraction-filter:
+
+Extraction filters
+------------------
+
+.. versionadded:: 3.12
+
+The *tar* format is designed to capture all details of a UNIX-like filesystem,
+which makes it very powerful.
+Unfortunately, the features make it easy to create tar files that have
+unintended -- and possibly malicious -- effects when extracted.
+For example, extracting a tar file can overwrite arbitrary files in various
+ways (e.g.  by using absolute paths, ``..`` path components, or symlinks that
+affect later members).
+
+In most cases, the full functionality is not needed.
+Therefore, *tarfile* supports extraction filters: a mechanism to limit
+functionality, and thus mitigate some of the security issues.
+
+.. seealso::
+
+   :pep:`706`
+      Contains further motivation and rationale behind the design.
+
+The *filter* argument to :meth:`TarFile.extract` or :meth:`~TarFile.extractall`
+can be:
+
+* the string ``'fully_trusted'``: Honor all metadata as specified in the
+  archive.
+  Should be used if the user trusts the archive completely, or implements
+  their own complex verification.
+
+* the string ``'tar'``: Honor most *tar*-specific features (i.e. features of
+  UNIX-like filesystems), but block features that are very likely to be
+  surprising or malicious. See :func:`tar_filter` for details.
+
+* the string ``'data'``: Ignore or block most features specific to UNIX-like
+  filesystems. Intended for extracting cross-platform data archives.
+  See :func:`data_filter` for details.
+
+* ``None`` (default): Use :attr:`TarFile.extraction_filter`.
+
+  If that is also ``None`` (the default), raise a ``DeprecationWarning``,
+  and fall back to the ``'fully_trusted'`` filter, whose dangerous behavior
+  matches previous versions of Python.
+
+  In Python 3.14, the ``'data'`` filter will become the default instead.
+  It's possible to switch earlier; see :attr:`TarFile.extraction_filter`.
+
+* A callable which will be called for each extracted member with a
+  :ref:`TarInfo <tarinfo-objects>` describing the member and the destination
+  path to where the archive is extracted (i.e. the same path is used for all
+  members)::
+
+      filter(/, member: TarInfo, path: str) -> TarInfo | None
+
+  The callable is called just before each member is extracted, so it can
+  take the current state of the disk into account.
+  It can:
+
+  - return a :class:`TarInfo` object which will be used instead of the metadata
+    in the archive, or
+  - return ``None``, in which case the member will be skipped, or
+  - raise an exception to abort the operation or skip the member,
+    depending on :attr:`~TarFile.errorlevel`.
+    Note that when extraction is aborted, :meth:`~TarFile.extractall` may leave
+    the archive partially extracted. It does not attempt to clean up.
+
+Default named filters
+~~~~~~~~~~~~~~~~~~~~~
+
+The pre-defined, named filters are available as functions, so they can be
+reused in custom filters:
+
+.. function:: fully_trusted_filter(/, member, path)
+
+   Return *member* unchanged.
+
+   This implements the ``'fully_trusted'`` filter.
+
+.. function:: tar_filter(/, member, path)
+
+  Implements the ``'tar'`` filter.
+
+  - Strip leading slashes (``/`` and :attr:`os.sep`) from filenames.
+  - :ref:`Refuse <tarfile-extraction-refuse>` to extract files with absolute
+    paths (in case the name is absolute
+    even after stripping slashes, e.g. ``C:/foo`` on Windows).
+    This raises :class:`~tarfile.AbsolutePathError`.
+  - :ref:`Refuse <tarfile-extraction-refuse>` to extract files whose absolute
+    path (after following symlinks) would end up outside the destination.
+    This raises :class:`~tarfile.OutsideDestinationError`.
+  - Clear high mode bits (setuid, setgid, sticky) and group/other write bits
+    (:attr:`~stat.S_IWGRP`|:attr:`~stat.S_IWOTH`).
+
+  Return the modified ``TarInfo`` member.
+
+.. function:: data_filter(/, member, path)
+
+  Implements the ``'data'`` filter.
+  In addition to what ``tar_filter`` does:
+
+  - :ref:`Refuse <tarfile-extraction-refuse>` to extract links (hard or soft)
+    that link to absolute paths, or ones that link outside the destination.
+
+    This raises :class:`~tarfile.AbsoluteLinkError` or
+    :class:`~tarfile.LinkOutsideDestinationError`.
+
+    Note that such files are refused even on platforms that do not support
+    symbolic links.
+
+  - :ref:`Refuse <tarfile-extraction-refuse>` to extract device files
+    (including pipes).
+    This raises :class:`~tarfile.SpecialFileError`.
+
+  - For regular files, including hard links:
+
+    - Set the owner read and write permissions
+      (:attr:`~stat.S_IRUSR`|:attr:`~stat.S_IWUSR`).
+    - Remove the group & other executable permission
+      (:attr:`~stat.S_IXGRP`|:attr:`~stat.S_IXOTH`)
+      if the owner doesn’t have it (:attr:`~stat.S_IXUSR`).
+
+  - For other files (directories), set ``mode`` to ``None``, so
+    that extraction methods skip applying permission bits.
+  - Set user and group info (``uid``, ``gid``, ``uname``, ``gname``)
+    to ``None``, so that extraction methods skip setting it.
+
+  Return the modified ``TarInfo`` member.
+
+
+.. _tarfile-extraction-refuse:
+
+Filter errors
+~~~~~~~~~~~~~
+
+When a filter refuses to extract a file, it will raise an appropriate exception,
+a subclass of :class:`~tarfile.FilterError`.
+This will abort the extraction if :attr:`TarFile.errorlevel` is 1 or more.
+With ``errorlevel=0`` the error will be logged and the member will be skipped,
+but extraction will continue.
+
+
+Hints for further verification
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Even with ``filter='data'``, *tarfile* is not suited for extracting untrusted
+files without prior inspection.
+Among other issues, the pre-defined filters do not prevent denial-of-service
+attacks. Users should do additional checks.
+
+Here is an incomplete list of things to consider:
+
+* Extract to a :func:`new temporary directory <tempfile.mkdtemp>`
+  to prevent e.g. exploiting pre-existing links, and to make it easier to
+  clean up after a failed extraction.
+* When working with untrusted data, use external (e.g. OS-level) limits on
+  disk, memory and CPU usage.
+* Check filenames against an allow-list of characters
+  (to filter out control characters, confusables, foreign path separators,
+  etc.).
+* Check that filenames have expected extensions (discouraging files that
+  execute when you “click on them”, or extension-less files like Windows special device names).
+* Limit the number of extracted files, total size of extracted data,
+  filename length (including symlink length), and size of individual files.
+* Check for files that would be shadowed on case-insensitive filesystems.
+
+Also note that:
+
+* Tar files may contain multiple versions of the same file.
+  Later ones are expected to overwrite any earlier ones.
+  This feature is crucial to allow updating tape archives, but can be abused
+  maliciously.
+* *tarfile* does not protect against issues with “live” data,
+  e.g. an attacker tinkering with the destination (or source) directory while
+  extraction (or archiving) is in progress.
+
+
+Supporting older Python versions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Extraction filters were added to Python 3.12, but may be backported to older
+versions as security updates.
+To check whether the feature is available, use e.g.
+``hasattr(tarfile, 'data_filter')`` rather than checking the Python version.
+
+The following examples show how to support Python versions with and without
+the feature.
+Note that setting ``extraction_filter`` will affect any subsequent operations.
+
+* Fully trusted archive::
+
+    my_tarfile.extraction_filter = (lambda member, path: member)
+    my_tarfile.extractall()
+
+* Use the ``'data'`` filter if available, but revert to Python 3.11 behavior
+  (``'fully_trusted'``) if this feature is not available::
+
+    my_tarfile.extraction_filter = getattr(tarfile, 'data_filter',
+                                           (lambda member, path: member))
+    my_tarfile.extractall()
+
+* Use the ``'data'`` filter; *fail* if it is not available::
+
+    my_tarfile.extractall(filter=tarfile.data_filter)
+
+  or::
+
+    my_tarfile.extraction_filter = tarfile.data_filter
+    my_tarfile.extractall()
+
+* Use the ``'data'`` filter; *warn* if it is not available::
+
+   if hasattr(tarfile, 'data_filter'):
+       my_tarfile.extractall(filter='data')
+   else:
+       # remove this when no longer needed
+       warn_the_user('Extracting may be unsafe; consider updating Python')
+       my_tarfile.extractall()
+
+
+Stateful extraction filter example
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+While *tarfile*'s extraction methods take a simple *filter* callable,
+custom filters may be more complex objects with an internal state.
+It may be useful to write these as context managers, to be used like this::
+
+    with StatefulFilter() as filter_func:
+        tar.extractall(path, filter=filter_func)
+
+Such a filter can be written as, for example::
+
+    class StatefulFilter:
+        def __init__(self):
+            self.file_count = 0
+
+        def __enter__(self):
+            return self
+
+        def __call__(self, member, path):
+            self.file_count += 1
+            return member
+
+        def __exit__(self, *exc_info):
+            print(f'{self.file_count} files extracted')
+
+
 .. _tarfile-commandline:
 .. program:: tarfile
 
+
 Command-Line Interface
 ----------------------
 
@@ -748,6 +1170,13 @@ Command-line options
 
    Verbose output.
 
+.. cmdoption:: --filter <filtername>
+
+   Specifies the *filter* for ``--extract``.
+   See :ref:`tarfile-extraction-filter` for details.
+   Only string names are accepted (that is, ``fully_trusted``, ``tar``,
+   and ``data``).
+
 .. _tar-examples:
 
 Examples
@@ -757,7 +1186,7 @@ How to extract an entire tar archive to the current working directory::
 
    import tarfile
    tar = tarfile.open("sample.tar.gz")
-   tar.extractall()
+   tar.extractall(filter='data')
    tar.close()
 
 How to extract a subset of a tar archive with :meth:`TarFile.extractall` using

Doc/whatsnew/3.12.rst

@@ -137,6 +137,13 @@ New Features
   (Design by Pablo Galindo. Contributed by Pablo Galindo and Christian Heimes
   with contributions from Gregory P. Smith [Google] and Mark Shannon
   in :gh:`96123`.)
+* The extraction methods in :mod:`tarfile`, and :func:`shutil.unpack_archive`,
+  have a new a *filter* argument that allows limiting tar features than may be
+  surprising or dangerous, such as creating files outside the destination
+  directory.
+  See :ref:`tarfile-extraction-filter` for details.
+  In Python 3.14, the default will switch to ``'data'``.
+  (Contributed by Petr Viktorin in :pep:`706`.)
 
 
 Other Language Changes
@@ -630,6 +637,10 @@ Deprecated
 * The *onerror* argument of :func:`shutil.rmtree` is deprecated as will be removed
   in Python 3.14. Use *onexc* instead. (Contributed by Irit Katriel in :gh:`102828`.)
 
+* Extracting tar archives without specifying *filter* is deprecated until
+  Python 3.14, when ``'data'`` filter will become the default.
+  See :ref:`tarfile-extraction-filter` for details.
+
 
 Pending Removal in Python 3.13
 ------------------------------
@@ -992,6 +1003,10 @@ Changes in the Python API
   exception instance, rather than to a ``(typ, exc, tb)`` tuple.
   (Contributed by Irit Katriel in :gh:`103176`.)
 
+* When extracting tar files using :mod:`tarfile` or
+  :func:`shutil.unpack_archive`, pass the *filter* argument to limit features
+  that may be surprising or dangerous.
+  See :ref:`tarfile-extraction-filter` for details.
 
 Build Changes
 =============

Lib/shutil.py

@@ -1245,7 +1245,7 @@ def _unpack_zipfile(filename, extract_dir):
     finally:
         zip.close()
 
-def _unpack_tarfile(filename, extract_dir):
+def _unpack_tarfile(filename, extract_dir, *, filter=None):
     """Unpack tar/tar.gz/tar.bz2/tar.xz `filename` to `extract_dir`
     """
     import tarfile  # late import for breaking circular dependency
@@ -1255,7 +1255,7 @@ def _unpack_tarfile(filename, extract_dir):
         raise ReadError(
             "%s is not a compressed or uncompressed tar file" % filename)
     try:
-        tarobj.extractall(extract_dir)
+        tarobj.extractall(extract_dir, filter=filter)
     finally:
         tarobj.close()
 
@@ -1288,7 +1288,7 @@ def _find_unpack_format(filename):
                 return name
     return None
 
-def unpack_archive(filename, extract_dir=None, format=None):
+def unpack_archive(filename, extract_dir=None, format=None, *, filter=None):
     """Unpack an archive.
 
     `filename` is the name of the archive.
@@ -1302,6 +1302,9 @@ def unpack_archive(filename, extract_dir=None, format=None):
     was registered for that extension.
 
     In case none is found, a ValueError is raised.
+
+    If `filter` is given, it is passed to the underlying
+    extraction function.
     """
     sys.audit("shutil.unpack_archive", filename, extract_dir, format)
 
@@ -1311,6 +1314,10 @@ def unpack_archive(filename, extract_dir=None, format=None):
     extract_dir = os.fspath(extract_dir)
     filename = os.fspath(filename)
 
+    if filter is None:
+        filter_kwargs = {}
+    else:
+        filter_kwargs = {'filter': filter}
     if format is not None:
         try:
             format_info = _UNPACK_FORMATS[format]
@@ -1318,7 +1325,7 @@ def unpack_archive(filename, extract_dir=None, format=None):
             raise ValueError("Unknown unpack format '{0}'".format(format)) from None
 
         func = format_info[1]
-        func(filename, extract_dir, **dict(format_info[2]))
+        func(filename, extract_dir, **dict(format_info[2]), **filter_kwargs)
     else:
         # we need to look at the registered unpackers supported extensions
         format = _find_unpack_format(filename)
@@ -1326,7 +1333,7 @@ def unpack_archive(filename, extract_dir=None, format=None):
             raise ReadError("Unknown archive format '{0}'".format(filename))
 
         func = _UNPACK_FORMATS[format][1]
-        kwargs = dict(_UNPACK_FORMATS[format][2])
+        kwargs = dict(_UNPACK_FORMATS[format][2]) | filter_kwargs
         func(filename, extract_dir, **kwargs)
 
 

Lib/tarfile.py

@@ -46,6 +46,7 @@ import time
 import struct
 import copy
 import re
+import warnings
 
 try:
     import pwd
@@ -65,7 +66,11 @@ symlink_exception = (AttributeError, NotImplementedError, OSError)
 __all__ = ["TarFile", "TarInfo", "is_tarfile", "TarError", "ReadError",
            "CompressionError", "StreamError", "ExtractError", "HeaderError",
            "ENCODING", "USTAR_FORMAT", "GNU_FORMAT", "PAX_FORMAT",
-           "DEFAULT_FORMAT", "open"]
+           "DEFAULT_FORMAT", "open","fully_trusted_filter", "data_filter",
+           "tar_filter", "FilterError", "AbsoluteLinkError",
+           "OutsideDestinationError", "SpecialFileError", "AbsolutePathError",
+           "LinkOutsideDestinationError"]
+
 
 #---------------------------------------------------------
 # tar constants
@@ -154,6 +159,8 @@ else:
 def stn(s, length, encoding, errors):
     """Convert a string to a null-terminated bytes object.
     """
+    if s is None:
+        raise ValueError("metadata cannot contain None")
     s = s.encode(encoding, errors)
     return s[:length] + (length - len(s)) * NUL
 
@@ -707,9 +714,127 @@ class ExFileObject(io.BufferedReader):
         super().__init__(fileobj)
 #class ExFileObject
 
+
+#-----------------------------
+# extraction filters (PEP 706)
+#-----------------------------
+
+class FilterError(TarError):
+    pass
+
+class AbsolutePathError(FilterError):
+    def __init__(self, tarinfo):
+        self.tarinfo = tarinfo
+        super().__init__(f'member {tarinfo.name!r} has an absolute path')
+
+class OutsideDestinationError(FilterError):
+    def __init__(self, tarinfo, path):
+        self.tarinfo = tarinfo
+        self._path = path
+        super().__init__(f'{tarinfo.name!r} would be extracted to {path!r}, '
+                         + 'which is outside the destination')
+
+class SpecialFileError(FilterError):
+    def __init__(self, tarinfo):
+        self.tarinfo = tarinfo
+        super().__init__(f'{tarinfo.name!r} is a special file')
+
+class AbsoluteLinkError(FilterError):
+    def __init__(self, tarinfo):
+        self.tarinfo = tarinfo
+        super().__init__(f'{tarinfo.name!r} is a symlink to an absolute path')
+
+class LinkOutsideDestinationError(FilterError):
+    def __init__(self, tarinfo, path):
+        self.tarinfo = tarinfo
+        self._path = path
+        super().__init__(f'{tarinfo.name!r} would link to {path!r}, '
+                         + 'which is outside the destination')
+
+def _get_filtered_attrs(member, dest_path, for_data=True):
+    new_attrs = {}
+    name = member.name
+    dest_path = os.path.realpath(dest_path)
+    # Strip leading / (tar's directory separator) from filenames.
+    # Include os.sep (target OS directory separator) as well.
+    if name.startswith(('/', os.sep)):
+        name = new_attrs['name'] = member.path.lstrip('/' + os.sep)
+    if os.path.isabs(name):
+        # Path is absolute even after stripping.
+        # For example, 'C:/foo' on Windows.
+        raise AbsolutePathError(member)
+    # Ensure we stay in the destination
+    target_path = os.path.realpath(os.path.join(dest_path, name))
+    if os.path.commonpath([target_path, dest_path]) != dest_path:
+        raise OutsideDestinationError(member, target_path)
+    # Limit permissions (no high bits, and go-w)
+    mode = member.mode
+    if mode is not None:
+        # Strip high bits & group/other write bits
+        mode = mode & 0o755
+        if for_data:
+            # For data, handle permissions & file types
+            if member.isreg() or member.islnk():
+                if not mode & 0o100:
+                    # Clear executable bits if not executable by user
+                    mode &= ~0o111
+                # Ensure owner can read & write
+                mode |= 0o600
+            elif member.isdir() or member.issym():
+                # Ignore mode for directories & symlinks
+                mode = None
+            else:
+                # Reject special files
+                raise SpecialFileError(member)
+        if mode != member.mode:
+            new_attrs['mode'] = mode
+    if for_data:
+        # Ignore ownership for 'data'
+        if member.uid is not None:
+            new_attrs['uid'] = None
+        if member.gid is not None:
+            new_attrs['gid'] = None
+        if member.uname is not None:
+            new_attrs['uname'] = None
+        if member.gname is not None:
+            new_attrs['gname'] = None
+        # Check link destination for 'data'
+        if member.islnk() or member.issym():
+            if os.path.isabs(member.linkname):
+                raise AbsoluteLinkError(member)
+            target_path = os.path.realpath(os.path.join(dest_path, member.linkname))
+            if os.path.commonpath([target_path, dest_path]) != dest_path:
+                raise LinkOutsideDestinationError(member, target_path)
+    return new_attrs
+
+def fully_trusted_filter(member, dest_path):
+    return member
+
+def tar_filter(member, dest_path):
+    new_attrs = _get_filtered_attrs(member, dest_path, False)
+    if new_attrs:
+        return member.replace(**new_attrs, deep=False)
+    return member
+
+def data_filter(member, dest_path):
+    new_attrs = _get_filtered_attrs(member, dest_path, True)
+    if new_attrs:
+        return member.replace(**new_attrs, deep=False)
+    return member
+
+_NAMED_FILTERS = {
+    "fully_trusted": fully_trusted_filter,
+    "tar": tar_filter,
+    "data": data_filter,
+}
+
 #------------------
 # Exported Classes
 #------------------
+
+# Sentinel for replace() defaults, meaning "don't change the attribute"
+_KEEP = object()
+
 class TarInfo(object):
     """Informational class which holds the details about an
        archive member given by a tar header block.
@@ -790,12 +915,44 @@ class TarInfo(object):
     def __repr__(self):
         return "<%s %r at %#x>" % (self.__class__.__name__,self.name,id(self))
 
+    def replace(self, *,
+                name=_KEEP, mtime=_KEEP, mode=_KEEP, linkname=_KEEP,
+                uid=_KEEP, gid=_KEEP, uname=_KEEP, gname=_KEEP,
+                deep=True, _KEEP=_KEEP):
+        """Return a deep copy of self with the given attributes replaced.
+        """
+        if deep:
+            result = copy.deepcopy(self)
+        else:
+            result = copy.copy(self)
+        if name is not _KEEP:
+            result.name = name
+        if mtime is not _KEEP:
+            result.mtime = mtime
+        if mode is not _KEEP:
+            result.mode = mode
+        if linkname is not _KEEP:
+            result.linkname = linkname
+        if uid is not _KEEP:
+            result.uid = uid
+        if gid is not _KEEP:
+            result.gid = gid
+        if uname is not _KEEP:
+            result.uname = uname
+        if gname is not _KEEP:
+            result.gname = gname
+        return result
+
     def get_info(self):
         """Return the TarInfo's attributes as a dictionary.
         """
+        if self.mode is None:
+            mode = None
+        else:
+            mode = self.mode & 0o7777
         info = {
             "name":     self.name,
-            "mode":     self.mode & 0o7777,
+            "mode":     mode,
             "uid":      self.uid,
             "gid":      self.gid,
             "size":     self.size,
@@ -818,6 +975,9 @@ class TarInfo(object):
         """Return a tar header as a string of 512 byte blocks.
         """
         info = self.get_info()
+        for name, value in info.items():
+            if value is None:
+                raise ValueError("%s may not be None" % name)
 
         if format == USTAR_FORMAT:
             return self.create_ustar_header(info, encoding, errors)
@@ -948,6 +1108,12 @@ class TarInfo(object):
             devmajor = stn("", 8, encoding, errors)
             devminor = stn("", 8, encoding, errors)
 
+        # None values in metadata should cause ValueError.
+        # itn()/stn() do this for all fields except type.
+        filetype = info.get("type", REGTYPE)
+        if filetype is None:
+            raise ValueError("TarInfo.type must not be None")
+
         parts = [
             stn(info.get("name", ""), 100, encoding, errors),
             itn(info.get("mode", 0) & 0o7777, 8, format),
@@ -956,7 +1122,7 @@ class TarInfo(object):
             itn(info.get("size", 0), 12, format),
             itn(info.get("mtime", 0), 12, format),
             b"        ", # checksum field
-            info.get("type", REGTYPE),
+            filetype,
             stn(info.get("linkname", ""), 100, encoding, errors),
             info.get("magic", POSIX_MAGIC),
             stn(info.get("uname", ""), 32, encoding, errors),
@@ -1462,6 +1628,8 @@ class TarFile(object):
 
     fileobject = ExFileObject   # The file-object for extractfile().
 
+    extraction_filter = None    # The default filter for extraction.
+
     def __init__(self, name=None, mode="r", fileobj=None, format=None,
             tarinfo=None, dereference=None, ignore_zeros=None, encoding=None,
             errors="surrogateescape", pax_headers=None, debug=None,
@@ -1936,7 +2104,10 @@ class TarFile(object):
             members = self
         for tarinfo in members:
             if verbose:
-                _safe_print(stat.filemode(tarinfo.mode))
+                if tarinfo.mode is None:
+                    _safe_print("??????????")
+                else:
+                    _safe_print(stat.filemode(tarinfo.mode))
                 _safe_print("%s/%s" % (tarinfo.uname or tarinfo.uid,
                                        tarinfo.gname or tarinfo.gid))
                 if tarinfo.ischr() or tarinfo.isblk():
@@ -1944,8 +2115,11 @@ class TarFile(object):
                             ("%d,%d" % (tarinfo.devmajor, tarinfo.devminor)))
                 else:
                     _safe_print("%10d" % tarinfo.size)
-                _safe_print("%d-%02d-%02d %02d:%02d:%02d" \
+                if tarinfo.mtime is None:
-                            % time.localtime(tarinfo.mtime)[:6])
+                    _safe_print("????-??-?? ??:??:??")
+                else:
+                    _safe_print("%d-%02d-%02d %02d:%02d:%02d" \
+                                % time.localtime(tarinfo.mtime)[:6])
 
             _safe_print(tarinfo.name + ("/" if tarinfo.isdir() else ""))
 
@@ -2032,32 +2206,63 @@ class TarFile(object):
 
         self.members.append(tarinfo)
 
-    def extractall(self, path=".", members=None, *, numeric_owner=False):
+    def _get_filter_function(self, filter):
+        if filter is None:
+            filter = self.extraction_filter
+            if filter is None:
+                warnings.warn(
+                    'Python 3.14 will, by default, filter extracted tar '
+                    + 'archives and reject files or modify their metadata. '
+                    + 'Use the filter argument to control this behavior.',
+                    DeprecationWarning)
+                return fully_trusted_filter
+            if isinstance(filter, str):
+                raise TypeError(
+                    'String names are not supported for '
+                    + 'TarFile.extraction_filter. Use a function such as '
+                    + 'tarfile.data_filter directly.')
+            return filter
+        if callable(filter):
+            return filter
+        try:
+            return _NAMED_FILTERS[filter]
+        except KeyError:
+            raise ValueError(f"filter {filter!r} not found") from None
+
+    def extractall(self, path=".", members=None, *, numeric_owner=False,
+                   filter=None):
         """Extract all members from the archive to the current working
            directory and set owner, modification time and permissions on
            directories afterwards. `path' specifies a different directory
            to extract to. `members' is optional and must be a subset of the
            list returned by getmembers(). If `numeric_owner` is True, only
            the numbers for user/group names are used and not the names.
+
+           The `filter` function will be called on each member just
+           before extraction.
+           It can return a changed TarInfo or None to skip the member.
+           String names of common filters are accepted.
         """
         directories = []
 
+        filter_function = self._get_filter_function(filter)
         if members is None:
             members = self
 
-        for tarinfo in members:
+        for member in members:
+            tarinfo = self._get_extract_tarinfo(member, filter_function, path)
+            if tarinfo is None:
+                continue
             if tarinfo.isdir():
-                # Extract directories with a safe mode.
+                # For directories, delay setting attributes until later,
+                # since permissions can interfere with extraction and
+                # extracting contents can reset mtime.
                 directories.append(tarinfo)
-                tarinfo = copy.copy(tarinfo)
+            self._extract_one(tarinfo, path, set_attrs=not tarinfo.isdir(),
-                tarinfo.mode = 0o700
+                              numeric_owner=numeric_owner)
-            # Do not set_attrs directories, as we will do that further down
-            self.extract(tarinfo, path, set_attrs=not tarinfo.isdir(),
-                         numeric_owner=numeric_owner)
 
         # Reverse sort directories.
-        directories.sort(key=lambda a: a.name)
+        directories.sort(key=lambda a: a.name, reverse=True)
-        directories.reverse()
 
         # Set correct owner, mtime and filemode on directories.
         for tarinfo in directories:
@@ -2067,12 +2272,10 @@ class TarFile(object):
                 self.utime(tarinfo, dirpath)
                 self.chmod(tarinfo, dirpath)
             except ExtractError as e:
-                if self.errorlevel > 1:
+                self._handle_nonfatal_error(e)
-                    raise
-                else:
-                    self._dbg(1, "tarfile: %s" % e)
 
-    def extract(self, member, path="", set_attrs=True, *, numeric_owner=False):
+    def extract(self, member, path="", set_attrs=True, *, numeric_owner=False,
+                filter=None):
         """Extract a member from the archive to the current working directory,
            using its full name. Its file information is extracted as accurately
            as possible. `member' may be a filename or a TarInfo object. You can
@@ -2080,35 +2283,70 @@ class TarFile(object):
            mtime, mode) are set unless `set_attrs' is False. If `numeric_owner`
            is True, only the numbers for user/group names are used and not
            the names.
-        """
-        self._check("r")
 
+           The `filter` function will be called before extraction.
+           It can return a changed TarInfo or None to skip the member.
+           String names of common filters are accepted.
+        """
+        filter_function = self._get_filter_function(filter)
+        tarinfo = self._get_extract_tarinfo(member, filter_function, path)
+        if tarinfo is not None:
+            self._extract_one(tarinfo, path, set_attrs, numeric_owner)
+
+    def _get_extract_tarinfo(self, member, filter_function, path):
+        """Get filtered TarInfo (or None) from member, which might be a str"""
         if isinstance(member, str):
             tarinfo = self.getmember(member)
         else:
             tarinfo = member
 
+        unfiltered = tarinfo
+        try:
+            tarinfo = filter_function(tarinfo, path)
+        except (OSError, FilterError) as e:
+            self._handle_fatal_error(e)
+        except ExtractError as e:
+            self._handle_nonfatal_error(e)
+        if tarinfo is None:
+            self._dbg(2, "tarfile: Excluded %r" % unfiltered.name)
+            return None
         # Prepare the link target for makelink().
         if tarinfo.islnk():
+            tarinfo = copy.copy(tarinfo)
             tarinfo._link_target = os.path.join(path, tarinfo.linkname)
+        return tarinfo
+
+    def _extract_one(self, tarinfo, path, set_attrs, numeric_owner):
+        """Extract from filtered tarinfo to disk"""
+        self._check("r")
 
         try:
             self._extract_member(tarinfo, os.path.join(path, tarinfo.name),
                                  set_attrs=set_attrs,
                                  numeric_owner=numeric_owner)
         except OSError as e:
-            if self.errorlevel > 0:
+            self._handle_fatal_error(e)
-                raise
-            else:
-                if e.filename is None:
-                    self._dbg(1, "tarfile: %s" % e.strerror)
-                else:
-                    self._dbg(1, "tarfile: %s %r" % (e.strerror, e.filename))
         except ExtractError as e:
-            if self.errorlevel > 1:
+            self._handle_nonfatal_error(e)
-                raise
+
+    def _handle_nonfatal_error(self, e):
+        """Handle non-fatal error (ExtractError) according to errorlevel"""
+        if self.errorlevel > 1:
+            raise
+        else:
+            self._dbg(1, "tarfile: %s" % e)
+
+    def _handle_fatal_error(self, e):
+        """Handle "fatal" error according to self.errorlevel"""
+        if self.errorlevel > 0:
+            raise
+        elif isinstance(e, OSError):
+            if e.filename is None:
+                self._dbg(1, "tarfile: %s" % e.strerror)
             else:
-                self._dbg(1, "tarfile: %s" % e)
+                self._dbg(1, "tarfile: %s %r" % (e.strerror, e.filename))
+        else:
+            self._dbg(1, "tarfile: %s %s" % (type(e).__name__, e))
 
     def extractfile(self, member):
         """Extract a member from the archive as a file object. `member' may be
@@ -2195,9 +2433,13 @@ class TarFile(object):
         """Make a directory called targetpath.
         """
         try:
-            # Use a safe mode for the directory, the real mode is set
+            if tarinfo.mode is None:
-            # later in _extract_member().
+                # Use the system's default mode
-            os.mkdir(targetpath, 0o700)
+                os.mkdir(targetpath)
+            else:
+                # Use a safe mode for the directory, the real mode is set
+                # later in _extract_member().
+                os.mkdir(targetpath, 0o700)
         except FileExistsError:
             pass
 
@@ -2240,6 +2482,9 @@ class TarFile(object):
             raise ExtractError("special devices not supported by system")
 
         mode = tarinfo.mode
+        if mode is None:
+            # Use mknod's default
+            mode = 0o600
         if tarinfo.isblk():
             mode |= stat.S_IFBLK
         else:
@@ -2261,7 +2506,6 @@ class TarFile(object):
                     os.unlink(targetpath)
                 os.symlink(tarinfo.linkname, targetpath)
             else:
-                # See extract().
                 if os.path.exists(tarinfo._link_target):
                     os.link(tarinfo._link_target, targetpath)
                 else:
@@ -2286,15 +2530,19 @@ class TarFile(object):
             u = tarinfo.uid
             if not numeric_owner:
                 try:
-                    if grp:
+                    if grp and tarinfo.gname:
                         g = grp.getgrnam(tarinfo.gname)[2]
                 except KeyError:
                     pass
                 try:
-                    if pwd:
+                    if pwd and tarinfo.uname:
                         u = pwd.getpwnam(tarinfo.uname)[2]
                 except KeyError:
                     pass
+            if g is None:
+                g = -1
+            if u is None:
+                u = -1
             try:
                 if tarinfo.issym() and hasattr(os, "lchown"):
                     os.lchown(targetpath, u, g)
@@ -2306,6 +2554,8 @@ class TarFile(object):
     def chmod(self, tarinfo, targetpath):
         """Set file permissions of targetpath according to tarinfo.
         """
+        if tarinfo.mode is None:
+            return
         try:
             os.chmod(targetpath, tarinfo.mode)
         except OSError as e:
@@ -2314,10 +2564,13 @@ class TarFile(object):
     def utime(self, tarinfo, targetpath):
         """Set modification time of targetpath according to tarinfo.
         """
+        mtime = tarinfo.mtime
+        if mtime is None:
+            return
         if not hasattr(os, 'utime'):
             return
         try:
-            os.utime(targetpath, (tarinfo.mtime, tarinfo.mtime))
+            os.utime(targetpath, (mtime, mtime))
         except OSError as e:
             raise ExtractError("could not change modification time") from e
 
@@ -2395,13 +2648,26 @@ class TarFile(object):
         members = self.getmembers()
 
         # Limit the member search list up to tarinfo.
+        skipping = False
         if tarinfo is not None:
-            members = members[:members.index(tarinfo)]
+            try:
+                index = members.index(tarinfo)
+            except ValueError:
+                # The given starting point might be a (modified) copy.
+                # We'll later skip members until we find an equivalent.
+                skipping = True
+            else:
+                # Happy fast path
+                members = members[:index]
 
         if normalize:
             name = os.path.normpath(name)
 
         for member in reversed(members):
+            if skipping:
+                if tarinfo.offset == member.offset:
+                    skipping = False
+                continue
             if normalize:
                 member_name = os.path.normpath(member.name)
             else:
@@ -2410,6 +2676,10 @@ class TarFile(object):
             if name == member_name:
                 return member
 
+        if skipping:
+            # Starting point was not found
+            raise ValueError(tarinfo)
+
     def _load(self):
         """Read through the entire archive file and look for readable
            members.
@@ -2500,6 +2770,7 @@ class TarFile(object):
 #--------------------
 # exported functions
 #--------------------
+
 def is_tarfile(name):
     """Return True if name points to a tar archive that we
        are able to handle, else return False.
@@ -2528,6 +2799,10 @@ def main():
     parser = argparse.ArgumentParser(description=description)
     parser.add_argument('-v', '--verbose', action='store_true', default=False,
                         help='Verbose output')
+    parser.add_argument('--filter', metavar='<filtername>',
+                        choices=_NAMED_FILTERS,
+                        help='Filter for extraction')
+
     group = parser.add_mutually_exclusive_group(required=True)
     group.add_argument('-l', '--list', metavar='<tarfile>',
                        help='Show listing of a tarfile')
@@ -2539,8 +2814,12 @@ def main():
                        help='Create tarfile from sources')
     group.add_argument('-t', '--test', metavar='<tarfile>',
                        help='Test if a tarfile is valid')
+
     args = parser.parse_args()
 
+    if args.filter and args.extract is None:
+        parser.exit(1, '--filter is only valid for extraction\n')
+
     if args.test is not None:
         src = args.test
         if is_tarfile(src):
@@ -2571,7 +2850,7 @@ def main():
 
         if is_tarfile(src):
             with TarFile.open(src, 'r:*') as tf:
-                tf.extractall(path=curdir)
+                tf.extractall(path=curdir, filter=args.filter)
             if args.verbose:
                 if curdir == '.':
                     msg = '{!r} file is extracted.'.format(src)

Lib/test/test_shutil.py

@@ -33,6 +33,7 @@ except ImportError:
 from test import support
 from test.support import os_helper
 from test.support.os_helper import TESTFN, FakePath
+from test.support import warnings_helper
 
 TESTFN2 = TESTFN + "2"
 TESTFN_SRC = TESTFN + "_SRC"
@@ -1841,12 +1842,14 @@ class TestArchives(BaseTest, unittest.TestCase):
 
     ### shutil.unpack_archive
 
-    def check_unpack_archive(self, format):
+    def check_unpack_archive(self, format, **kwargs):
-        self.check_unpack_archive_with_converter(format, lambda path: path)
+        self.check_unpack_archive_with_converter(
-        self.check_unpack_archive_with_converter(format, pathlib.Path)
+            format, lambda path: path, **kwargs)
-        self.check_unpack_archive_with_converter(format, FakePath)
+        self.check_unpack_archive_with_converter(
+            format, pathlib.Path, **kwargs)
+        self.check_unpack_archive_with_converter(format, FakePath, **kwargs)
 
-    def check_unpack_archive_with_converter(self, format, converter):
+    def check_unpack_archive_with_converter(self, format, converter, **kwargs):
         root_dir, base_dir = self._create_files()
         expected = rlistdir(root_dir)
         expected.remove('outer')
@@ -1856,36 +1859,48 @@ class TestArchives(BaseTest, unittest.TestCase):
 
         # let's try to unpack it now
         tmpdir2 = self.mkdtemp()
-        unpack_archive(converter(filename), converter(tmpdir2))
+        unpack_archive(converter(filename), converter(tmpdir2), **kwargs)
         self.assertEqual(rlistdir(tmpdir2), expected)
 
         # and again, this time with the format specified
         tmpdir3 = self.mkdtemp()
-        unpack_archive(converter(filename), converter(tmpdir3), format=format)
+        unpack_archive(converter(filename), converter(tmpdir3), format=format,
+                       **kwargs)
         self.assertEqual(rlistdir(tmpdir3), expected)
 
-        self.assertRaises(shutil.ReadError, unpack_archive, converter(TESTFN))
+        with self.assertRaises(shutil.ReadError):
-        self.assertRaises(ValueError, unpack_archive, converter(TESTFN), format='xxx')
+            unpack_archive(converter(TESTFN), **kwargs)
+        with self.assertRaises(ValueError):
+            unpack_archive(converter(TESTFN), format='xxx', **kwargs)
+
+    def check_unpack_tarball(self, format):
+        self.check_unpack_archive(format, filter='fully_trusted')
+        self.check_unpack_archive(format, filter='data')
+        with warnings_helper.check_warnings(
+                ('Python 3.14', DeprecationWarning)):
+            self.check_unpack_archive(format)
 
     def test_unpack_archive_tar(self):
-        self.check_unpack_archive('tar')
+        self.check_unpack_tarball('tar')
 
     @support.requires_zlib()
     def test_unpack_archive_gztar(self):
-        self.check_unpack_archive('gztar')
+        self.check_unpack_tarball('gztar')
 
     @support.requires_bz2()
     def test_unpack_archive_bztar(self):
-        self.check_unpack_archive('bztar')
+        self.check_unpack_tarball('bztar')
 
     @support.requires_lzma()
     @unittest.skipIf(AIX and not _maxdataOK(), "AIX MAXDATA must be 0x20000000 or larger")
     def test_unpack_archive_xztar(self):
-        self.check_unpack_archive('xztar')
+        self.check_unpack_tarball('xztar')
 
     @support.requires_zlib()
     def test_unpack_archive_zip(self):
         self.check_unpack_archive('zip')
+        with self.assertRaises(TypeError):
+            self.check_unpack_archive('zip', filter='data')
 
     def test_unpack_registry(self):
 

Misc/NEWS.d/next/Library/2023-03-23-15-24-38.gh-issue-102953.YR4KaK.rst

@@ -0,0 +1,4 @@
+The extraction methods in :mod:`tarfile`, and :func:`shutil.unpack_archive`,
+have a new a *filter* argument that allows limiting tar features than may be
+surprising or dangerous, such as creating files outside the destination
+directory. See :ref:`tarfile-extraction-filter` for details.