From ef282220bd6e759c125c82351355d27627a0c08f Mon Sep 17 00:00:00 2001

From: Victor Stinner <vstinner@python.org>

Date: Thu, 15 Sep 2022 17:35:24 +0200

Subject: [PATCH] 00387: CVE-2020-10735: Prevent DoS by very large int()

gh-95778: CVE-2020-10735: Prevent DoS by very large int() (GH-96504)

Converting between `int` and `str` in bases other than 2

(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now

raises a `ValueError` if the number of digits in string form is above a

limit to avoid potential denial of service attacks due to the algorithmic

complexity. This is a mitigation for CVE-2020-10735

(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command

line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length

Limitation` documentation.  The default limit is 4300

digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback

from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6 in RHEL:

* Use "Python 3.6.8-48" version in the documentation, whereas this

  version will never be released

* Only add _Py_global_config_int_max_str_digits global variable:

  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.

* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is

  set to the default limit. Adapt test_int_max_str_digits() for that.

* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and

  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only

  if the Py_BUILD_CORE macro is defined.

* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca9452033ef95bc7d7fc404b8161068226002)

gh-95778: Mention sys.set_int_max_str_digits() in error message (#96874)

When ValueError is raised if an integer is larger than the limit,

mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc915e82e5ea6e3b473205417d63494808d)

gh-96848: Fix -X int_max_str_digits option parsing (#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with

no value (invalid) when the PYTHONINTMAXSTRDIGITS environment

variable is set to a valid limit.

(cherry picked from commit 41351662bcd21672d8ccfa62fe44d72027e6bcf8)

---

 Doc/library/functions.rst         |   8 ++

 Doc/library/json.rst              |  11 ++

 Doc/library/stdtypes.rst          | 159 ++++++++++++++++++++++++

 Doc/library/sys.rst               |  53 ++++++--

 Doc/library/test.rst              |  10 ++

 Doc/using/cmdline.rst             |  14 +++

 Doc/whatsnew/3.6.rst              |  15 +++

 Include/longobject.h              |  38 ++++++

 Include/pydebug.h                 |   2 +

 Lib/test/support/__init__.py      |  10 ++

 Lib/test/test_ast.py              |   8 ++

 Lib/test/test_cmd_line.py         |  35 ++++++

 Lib/test/test_compile.py          |  13 ++

 Lib/test/test_decimal.py          |  18 +++

 Lib/test/test_int.py              | 196 ++++++++++++++++++++++++++++++

 Lib/test/test_json/test_decode.py |   8 ++

 Lib/test/test_sys.py              |  11 +-

 Lib/test/test_xmlrpc.py           |  10 ++

 Modules/main.c                    |   7 ++

 Objects/longobject.c              | 168 ++++++++++++++++++++++++-

 Python/ast.c                      |  26 +++-

 Python/pylifecycle.c              |   2 +

 Python/sysmodule.c                |  46 ++++++-

 23 files changed, 853 insertions(+), 15 deletions(-)

diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst

index bc528dd..b0806b2 100644

--- a/Doc/library/functions.rst

+++ b/Doc/library/functions.rst

@@ -748,6 +748,14 @@ are always available.  They are listed here in alphabetical order.

    .. versionchanged:: 3.6

       Grouping digits with underscores as in code literals is allowed.

+   .. versionchanged:: 3.6.8-48

+      :class:`int` string inputs and string representations can be limited to

+      help avoid denial of service attacks. A :exc:`ValueError` is raised when

+      the limit is exceeded while converting a string *x* to an :class:`int` or

+      when converting an :class:`int` into a string would exceed the limit.

+      See the :ref:`integer string conversion length limitation

+      <int_max_str_digits>` documentation.

+

 .. function:: isinstance(object, classinfo)

diff --git a/Doc/library/json.rst b/Doc/library/json.rst

index 98ca86e..330e53f 100644

--- a/Doc/library/json.rst

+++ b/Doc/library/json.rst

@@ -18,6 +18,11 @@ is a lightweight data interchange format inspired by

 `JavaScript <https://en.wikipedia.org/wiki/JavaScript>`_ object literal syntax

 (although it is not a strict subset of JavaScript [#rfc-errata]_ ).

+.. warning::

+   Be cautious when parsing JSON data from untrusted sources. A malicious

+   JSON string may cause the decoder to consume considerable CPU and memory

+   resources. Limiting the size of data to be parsed is recommended.

+

 :mod:`json` exposes an API familiar to users of the standard library

 :mod:`marshal` and :mod:`pickle` modules.

@@ -245,6 +250,12 @@ Basic Usage

    be used to use another datatype or parser for JSON integers

    (e.g. :class:`float`).

+   .. versionchanged:: 3.6.8-48

+      The default *parse_int* of :func:`int` now limits the maximum length of

+      the integer string via the interpreter's :ref:`integer string

+      conversion length limitation <int_max_str_digits>` to help avoid denial

+      of service attacks.

+

    *parse_constant*, if specified, will be called with one of the following

    strings: ``'-Infinity'``, ``'Infinity'``, ``'NaN'``.

    This can be used to raise an exception if invalid JSON numbers

diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst

index 00e1f4c..1dc3253 100644

--- a/Doc/library/stdtypes.rst

+++ b/Doc/library/stdtypes.rst

@@ -4671,6 +4671,165 @@ types, where they are relevant.  Some of these are not reported by the

       [<class 'bool'>]

+.. _int_max_str_digits:

+

+Integer string conversion length limitation

+===========================================

+

+CPython has a global limit for converting between :class:`int` and :class:`str`

+to mitigate denial of service attacks. This limit *only* applies to decimal or

+other non-power-of-two number bases. Hexadecimal, octal, and binary conversions

+are unlimited. The limit can be configured.

+

+The :class:`int` type in CPython is an abitrary length number stored in binary

+form (commonly known as a "bignum"). There exists no algorithm that can convert

+a string to a binary integer or a binary integer to a string in linear time,

+*unless* the base is a power of 2. Even the best known algorithms for base 10

+have sub-quadratic complexity. Converting a large value such as ``int('1' *

+500_000)`` can take over a second on a fast CPU.

+

+Limiting conversion size offers a practical way to avoid `CVE-2020-10735

+<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735>`_.

+

+The limit is applied to the number of digit characters in the input or output

+string when a non-linear conversion algorithm would be involved.  Underscores

+and the sign are not counted towards the limit.

+

+When an operation would exceed the limit, a :exc:`ValueError` is raised:

+

+.. doctest::

+

+   >>> import sys

+   >>> sys.set_int_max_str_digits(4300)  # Illustrative, this is the default.

+   >>> _ = int('2' * 5432)

+   Traceback (most recent call last):

+   ...

+   ValueError: Exceeds the limit (4300) for integer string conversion: value has 5432 digits; use sys.set_int_max_str_digits() to increase the limit.

+   >>> i = int('2' * 4300)

+   >>> len(str(i))

+   4300

+   >>> i_squared = i*i

+   >>> len(str(i_squared))

+   Traceback (most recent call last):

+   ...

+   ValueError: Exceeds the limit (4300) for integer string conversion: value has 8599 digits; use sys.set_int_max_str_digits() to increase the limit.

+   >>> len(hex(i_squared))

+   7144

+   >>> assert int(hex(i_squared), base=16) == i*i  # Hexadecimal is unlimited.

+

+The default limit is 4300 digits as provided in

+:data:`sys.int_info.default_max_str_digits <sys.int_info>`.

+The lowest limit that can be configured is 640 digits as provided in

+:data:`sys.int_info.str_digits_check_threshold <sys.int_info>`.

+

+Verification:

+

+.. doctest::

+

+   >>> import sys

+   >>> assert sys.int_info.default_max_str_digits == 4300, sys.int_info

+   >>> assert sys.int_info.str_digits_check_threshold == 640, sys.int_info

+   >>> msg = int('578966293710682886880994035146873798396722250538762761564'

+   ...           '9252925514383915483333812743580549779436104706260696366600'

+   ...           '571186405732').to_bytes(53, 'big')

+   ...

+

+.. versionadded:: 3.6.8-48

+

+Affected APIs

+-------------

+

+The limitation only applies to potentially slow conversions between :class:`int`

+and :class:`str` or :class:`bytes`:

+

+* ``int(string)`` with default base 10.

+* ``int(string, base)`` for all bases that are not a power of 2.

+* ``str(integer)``.

+* ``repr(integer)``

+* any other string conversion to base 10, for example ``f"{integer}"``,

+  ``"{}".format(integer)``, or ``b"%d" % integer``.

+

+The limitations do not apply to functions with a linear algorithm:

+

+* ``int(string, base)`` with base 2, 4, 8, 16, or 32.

+* :func:`int.from_bytes` and :func:`int.to_bytes`.

+* :func:`hex`, :func:`oct`, :func:`bin`.

+* :ref:`formatspec` for hex, octal, and binary numbers.

+* :class:`str` to :class:`float`.

+* :class:`str` to :class:`decimal.Decimal`.

+

+Configuring the limit

+---------------------

+

+Before Python starts up you can use an environment variable or an interpreter

+command line flag to configure the limit:

+

+* :envvar:`PYTHONINTMAXSTRDIGITS`, e.g.

+  ``PYTHONINTMAXSTRDIGITS=640 python3`` to set the limit to 640 or

+  ``PYTHONINTMAXSTRDIGITS=0 python3`` to disable the limitation.

+* :option:`-X int_max_str_digits <-X>`, e.g.

+  ``python3 -X int_max_str_digits=640``

+* :data:`sys.flags.int_max_str_digits` contains the value of

+  :envvar:`PYTHONINTMAXSTRDIGITS` or :option:`-X int_max_str_digits <-X>`.

+  If both the env var and the ``-X`` option are set, the ``-X`` option takes

+  precedence. A value of *-1* indicates that both were unset, thus a value of

+  :data:`sys.int_info.default_max_str_digits` was used during initilization.

+

+From code, you can inspect the current limit and set a new one using these

+:mod:`sys` APIs:

+

+* :func:`sys.get_int_max_str_digits` and :func:`sys.set_int_max_str_digits` are

+  a getter and setter for the interpreter-wide limit. Subinterpreters have

+  their own limit.

+

+Information about the default and minimum can be found in :attr:`sys.int_info`:

+

+* :data:`sys.int_info.default_max_str_digits <sys.int_info>` is the compiled-in

+  default limit.

+* :data:`sys.int_info.str_digits_check_threshold <sys.int_info>` is the lowest

+  accepted value for the limit (other than 0 which disables it).

+

+.. versionadded:: 3.6.8-48

+

+.. caution::

+

+   Setting a low limit *can* lead to problems. While rare, code exists that

+   contains integer constants in decimal in their source that exceed the

+   minimum threshold. A consequence of setting the limit is that Python source

+   code containing decimal integer literals longer than the limit will

+   encounter an error during parsing, usually at startup time or import time or

+   even at installation time - anytime an up to date ``.pyc`` does not already

+   exist for the code. A workaround for source that contains such large

+   constants is to convert them to ``0x`` hexadecimal form as it has no limit.

+

+   Test your application thoroughly if you use a low limit. Ensure your tests

+   run with the limit set early via the environment or flag so that it applies

+   during startup and even during any installation step that may invoke Python

+   to precompile ``.py`` sources to ``.pyc`` files.

+

+Recommended configuration

+-------------------------

+

+The default :data:`sys.int_info.default_max_str_digits` is expected to be

+reasonable for most applications. If your application requires a different

+limit, set it from your main entry point using Python version agnostic code as

+these APIs were added in security patch releases in versions before 3.11.

+

+Example::

+

+   >>> import sys

+   >>> if hasattr(sys, "set_int_max_str_digits"):

+   ...     upper_bound = 68000

+   ...     lower_bound = 4004

+   ...     current_limit = sys.get_int_max_str_digits()

+   ...     if current_limit == 0 or current_limit > upper_bound:

+   ...         sys.set_int_max_str_digits(upper_bound)

+   ...     elif current_limit < lower_bound:

+   ...         sys.set_int_max_str_digits(lower_bound)

+

+If you need to disable it entirely, set it to ``0``.

+

+

 .. rubric:: Footnotes

 .. [1] Additional information on these special methods may be found in the Python

diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst

index 9198466..6144f8f 100644

--- a/Doc/library/sys.rst

+++ b/Doc/library/sys.rst

@@ -296,6 +296,7 @@ always available.

    :const:`bytes_warning`        :option:`-b`

    :const:`quiet`                :option:`-q`

    :const:`hash_randomization`   :option:`-R`

+   :const:`int_max_str_digits`   :option:`-X int_max_str_digits <-X>` (:ref:`integer string conversion length limitation <int_max_str_digits>`)

    ============================= =============================

    .. versionchanged:: 3.2

@@ -310,6 +311,9 @@ always available.

    .. versionchanged:: 3.4

       Added ``isolated`` attribute for :option:`-I` ``isolated`` flag.

+   .. versionchanged:: 3.6.8-48

+      Added the ``int_max_str_digits`` attribute.

+

 .. data:: float_info

    A :term:`struct sequence` holding information about the float type. It

@@ -468,6 +472,15 @@ always available.

    .. versionadded:: 3.6

+

+.. function:: get_int_max_str_digits()

+

+   Returns the current value for the :ref:`integer string conversion length

+   limitation <int_max_str_digits>`. See also :func:`set_int_max_str_digits`.

+

+   .. versionadded:: 3.6.8-48

+

+

 .. function:: getrefcount(object)

    Return the reference count of the *object*.  The count returned is generally one

@@ -730,19 +743,31 @@ always available.

    .. tabularcolumns:: |l|L|

-   +-------------------------+----------------------------------------------+

-   | Attribute               | Explanation                                  |

-   +=========================+==============================================+

-   | :const:`bits_per_digit` | number of bits held in each digit.  Python   |

-   |                         | integers are stored internally in base       |

-   |                         | ``2**int_info.bits_per_digit``               |

-   +-------------------------+----------------------------------------------+

-   | :const:`sizeof_digit`   | size in bytes of the C type used to          |

-   |                         | represent a digit                            |

-   +-------------------------+----------------------------------------------+

+   +----------------------------------------+-----------------------------------------------+

+   | Attribute                              | Explanation                                   |

+   +========================================+===============================================+

+   | :const:`bits_per_digit`                | number of bits held in each digit.  Python    |

+   |                                        | integers are stored internally in base        |

+   |                                        | ``2**int_info.bits_per_digit``                |

+   +----------------------------------------+-----------------------------------------------+

+   | :const:`sizeof_digit`                  | size in bytes of the C type used to           |

+   |                                        | represent a digit                             |

+   +----------------------------------------+-----------------------------------------------+

+   | :const:`default_max_str_digits`        | default value for                             |

+   |                                        | :func:`sys.get_int_max_str_digits` when it    |

+   |                                        | is not otherwise explicitly configured.       |

+   +----------------------------------------+-----------------------------------------------+

+   | :const:`str_digits_check_threshold`    | minimum non-zero value for                    |

+   |                                        | :func:`sys.set_int_max_str_digits`,           |

+   |                                        | :envvar:`PYTHONINTMAXSTRDIGITS`, or           |

+   |                                        | :option:`-X int_max_str_digits <-X>`.         |

+   +----------------------------------------+-----------------------------------------------+

    .. versionadded:: 3.1

+   .. versionchanged:: 3.6.8-48

+      Added ``default_max_str_digits`` and ``str_digits_check_threshold``.

+

 .. data:: __interactivehook__

@@ -1001,6 +1026,14 @@ always available.

    Availability: Unix.

+.. function:: set_int_max_str_digits(n)

+

+   Set the :ref:`integer string conversion length limitation

+   <int_max_str_digits>` used by this interpreter. See also

+   :func:`get_int_max_str_digits`.

+

+   .. versionadded:: 3.6.8-48

+

 .. function:: setprofile(profilefunc)

    .. index::

diff --git a/Doc/library/test.rst b/Doc/library/test.rst

index 04d6cd8..5153162 100644

--- a/Doc/library/test.rst

+++ b/Doc/library/test.rst

@@ -625,6 +625,16 @@ The :mod:`test.support` module defines the following functions:

    .. versionadded:: 3.6

+.. function:: adjust_int_max_str_digits(max_digits)

+

+   This function returns a context manager that will change the global

+   :func:`sys.set_int_max_str_digits` setting for the duration of the

+   context to allow execution of test code that needs a different limit

+   on the number of digits when converting between an integer and string.

+

+   .. versionadded:: 3.6.8-48

+

+

 The :mod:`test.support` module defines the following classes:

 .. class:: TransientResource(exc, **kwargs)

diff --git a/Doc/using/cmdline.rst b/Doc/using/cmdline.rst

index 65aa3ad..f5f76c4 100644

--- a/Doc/using/cmdline.rst

+++ b/Doc/using/cmdline.rst

@@ -422,6 +422,9 @@ Miscellaneous options

    * ``-X showalloccount`` to output the total count of allocated objects for

      each type when the program finishes. This only works when Python was built with

      ``COUNT_ALLOCS`` defined.

+   * ``-X int_max_str_digits`` configures the :ref:`integer string conversion

+     length limitation <int_max_str_digits>`.  See also

+     :envvar:`PYTHONINTMAXSTRDIGITS`.

    It also allows passing arbitrary values and retrieving them through the

    :data:`sys._xoptions` dictionary.

@@ -438,6 +441,9 @@ Miscellaneous options

    .. versionadded:: 3.6

       The ``-X showalloccount`` option.

+   .. versionadded:: 3.6.8-48

+      The ``-X int_max_str_digits`` option.

+

 Options you shouldn't use

 ~~~~~~~~~~~~~~~~~~~~~~~~~

@@ -571,6 +577,14 @@ conflict.

    .. versionadded:: 3.2.3

+.. envvar:: PYTHONINTMAXSTRDIGITS

+

+   If this variable is set to an integer, it is used to configure the

+   interpreter's global :ref:`integer string conversion length limitation

+   <int_max_str_digits>`.

+

+   .. versionadded:: 3.6.8-48

+

 .. envvar:: PYTHONIOENCODING

    If this is set before running the interpreter, it overrides the encoding used

diff --git a/Doc/whatsnew/3.6.rst b/Doc/whatsnew/3.6.rst

index 0095844..d669c5c 100644

--- a/Doc/whatsnew/3.6.rst

+++ b/Doc/whatsnew/3.6.rst

@@ -2438,3 +2438,18 @@ In 3.6.7 the :mod:`tokenize` module now implicitly emits a ``NEWLINE`` token

 when provided with input that does not have a trailing new line.  This behavior

 now matches what the C tokenizer does internally.

 (Contributed by Ammar Askar in :issue:`33899`.)

+

+

+Notable security feature in 3.6.8-48

+=====================================

+

+Converting between :class:`int` and :class:`str` in bases other than 2

+(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal)

+now raises a :exc:`ValueError` if the number of digits in string form is

+above a limit to avoid potential denial of service attacks due to the

+algorithmic complexity. This is a mitigation for `CVE-2020-10735

+<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735>`_.

+This limit can be configured or disabled by environment variable, command

+line flag, or :mod:`sys` APIs. See the :ref:`integer string conversion

+length limitation <int_max_str_digits>` documentation.  The default limit

+is 4300 digits in string form.

diff --git a/Include/longobject.h b/Include/longobject.h

index efd409c..d8a080a 100644

--- a/Include/longobject.h

+++ b/Include/longobject.h

@@ -209,6 +209,44 @@ PyAPI_FUNC(long) PyOS_strtol(const char *, char **, int);

 PyAPI_FUNC(PyObject *) _PyLong_GCD(PyObject *, PyObject *);

 #endif /* !Py_LIMITED_API */

+#ifdef Py_BUILD_CORE

+/*

+ * Default int base conversion size limitation: Denial of Service prevention.

+ *

+ * Chosen such that this isn't wildly slow on modern hardware and so that

+ * everyone's existing deployed numpy test suite passes before

+ * https://github.com/numpy/numpy/issues/22098 is widely available.

+ *

+ * $ python -m timeit -s 's = "1"*4300' 'int(s)'

+ * 2000 loops, best of 5: 125 usec per loop

+ * $ python -m timeit -s 's = "1"*4300; v = int(s)' 'str(v)'

+ * 1000 loops, best of 5: 311 usec per loop

+ * (zen2 cloud VM)

+ *

+ * 4300 decimal digits fits a ~14284 bit number.

+ */

+#define _PY_LONG_DEFAULT_MAX_STR_DIGITS 4300

+/*

+ * Threshold for max digits check.  For performance reasons int() and

+ * int.__str__() don't checks values that are smaller than this

+ * threshold.  Acts as a guaranteed minimum size limit for bignums that

+ * applications can expect from CPython.

+ *

+ * % python -m timeit -s 's = "1"*640; v = int(s)' 'str(int(s))'

+ * 20000 loops, best of 5: 12 usec per loop

+ *

+ * "640 digits should be enough for anyone." - gps

+ * fits a ~2126 bit decimal number.

+ */

+#define _PY_LONG_MAX_STR_DIGITS_THRESHOLD 640

+

+#if ((_PY_LONG_DEFAULT_MAX_STR_DIGITS != 0) && \

+   (_PY_LONG_DEFAULT_MAX_STR_DIGITS < _PY_LONG_MAX_STR_DIGITS_THRESHOLD))

+# error "_PY_LONG_DEFAULT_MAX_STR_DIGITS smaller than threshold."

+#endif

+

+#endif /* Py_BUILD_CORE */

+

 #ifdef __cplusplus

 }

 #endif

diff --git a/Include/pydebug.h b/Include/pydebug.h

index 6e23a89..657c552 100644

--- a/Include/pydebug.h

+++ b/Include/pydebug.h

@@ -28,6 +28,8 @@ PyAPI_DATA(int) Py_IsolatedFlag;

 PyAPI_DATA(int) Py_LegacyWindowsStdioFlag;

 #endif

+PyAPI_DATA(int) _Py_global_config_int_max_str_digits;

+

 /* this is a wrapper around getenv() that pays attention to

    Py_IgnoreEnvironmentFlag.  It should be used for getting variables like

    PYTHONPATH and PYTHONHOME from the environment */

diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py

index e33096e..99920ac 100644

--- a/Lib/test/support/__init__.py

+++ b/Lib/test/support/__init__.py

@@ -2912,3 +2912,13 @@ class FakePath:

             raise self.path

         else:

             return self.path

+

+@contextlib.contextmanager

+def adjust_int_max_str_digits(max_digits):

+    """Temporarily change the integer string conversion length limit."""

+    current = sys.get_int_max_str_digits()

+    try:

+        sys.set_int_max_str_digits(max_digits)

+        yield

+    finally:

+        sys.set_int_max_str_digits(current)

diff --git a/Lib/test/test_ast.py b/Lib/test/test_ast.py

index e68d0de..7f2d793 100644

--- a/Lib/test/test_ast.py

+++ b/Lib/test/test_ast.py

@@ -571,6 +571,14 @@ class ASTHelpers_Test(unittest.TestCase):

         exec(code, ns)

         self.assertIn('sleep', ns)

+    def test_literal_eval_str_int_limit(self):

+        with support.adjust_int_max_str_digits(4000):

+            ast.literal_eval('3'*4000)  # no error

+            with self.assertRaises(SyntaxError) as err_ctx:

+                ast.literal_eval('3'*4001)

+            self.assertIn('Exceeds the limit ', str(err_ctx.exception))

+            self.assertIn(' Consider hexadecimal ', str(err_ctx.exception))

+

 class ASTValidatorTests(unittest.TestCase):

diff --git a/Lib/test/test_cmd_line.py b/Lib/test/test_cmd_line.py

index 5922ed9..fe456ee 100644

--- a/Lib/test/test_cmd_line.py

+++ b/Lib/test/test_cmd_line.py

@@ -502,6 +502,41 @@ class CmdLineTest(unittest.TestCase):

         self.assertEqual(proc.returncode, 0, proc)

         self.assertEqual(proc.stdout.strip(), b'0')

+    def test_int_max_str_digits(self):

+        code = "import sys; print(sys.flags.int_max_str_digits, sys.get_int_max_str_digits())"

+

+        assert_python_failure('-X', 'int_max_str_digits', '-c', code)

+        assert_python_failure('-X', 'int_max_str_digits=foo', '-c', code)

+        assert_python_failure('-X', 'int_max_str_digits=100', '-c', code)

+        assert_python_failure('-X', 'int_max_str_digits', '-c', code,

+                              PYTHONINTMAXSTRDIGITS='4000')

+

+        assert_python_failure('-c', code, PYTHONINTMAXSTRDIGITS='foo')

+        assert_python_failure('-c', code, PYTHONINTMAXSTRDIGITS='100')

+

+        def res2int(res):

+            out = res.out.strip().decode("utf-8")

+            return tuple(int(i) for i in out.split())

+

+        res = assert_python_ok('-c', code)

+        self.assertEqual(res2int(res), (sys.get_int_max_str_digits(), sys.get_int_max_str_digits()))

+        res = assert_python_ok('-X', 'int_max_str_digits=0', '-c', code)

+        self.assertEqual(res2int(res), (0, 0))

+        res = assert_python_ok('-X', 'int_max_str_digits=4000', '-c', code)

+        self.assertEqual(res2int(res), (4000, 4000))

+        res = assert_python_ok('-X', 'int_max_str_digits=100000', '-c', code)

+        self.assertEqual(res2int(res), (100000, 100000))

+

+        res = assert_python_ok('-c', code, PYTHONINTMAXSTRDIGITS='0')

+        self.assertEqual(res2int(res), (0, 0))

+        res = assert_python_ok('-c', code, PYTHONINTMAXSTRDIGITS='4000')

+        self.assertEqual(res2int(res), (4000, 4000))

+        res = assert_python_ok(

+            '-X', 'int_max_str_digits=6000', '-c', code,

+            PYTHONINTMAXSTRDIGITS='4000'

+        )

+        self.assertEqual(res2int(res), (6000, 6000))

+

 def test_main():

     test.support.run_unittest(CmdLineTest)

diff --git a/Lib/test/test_compile.py b/Lib/test/test_compile.py

index 13cc882..00e6468 100644

--- a/Lib/test/test_compile.py

+++ b/Lib/test/test_compile.py

@@ -189,6 +189,19 @@ if 1:

         self.assertEqual(eval("0o777"), 511)

         self.assertEqual(eval("-0o0000010"), -8)

+    def test_int_literals_too_long(self):

+        n = 3000

+        source = f"a = 1\nb = 2\nc = {'3'*n}\nd = 4"

+        with support.adjust_int_max_str_digits(n):

+            compile(source, "<long_int_pass>", "exec")  # no errors.

+        with support.adjust_int_max_str_digits(n-1):

+            with self.assertRaises(SyntaxError) as err_ctx:

+                compile(source, "<long_int_fail>", "exec")

+            exc = err_ctx.exception

+            self.assertEqual(exc.lineno, 3)

+            self.assertIn('Exceeds the limit ', str(exc))

+            self.assertIn(' Consider hexadecimal ', str(exc))

+

     def test_unary_minus(self):

         # Verify treatment of unary minus on negative numbers SF bug #660455

         if sys.maxsize == 2147483647:

diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py

index 8808a67..4459b82 100644

--- a/Lib/test/test_decimal.py

+++ b/Lib/test/test_decimal.py

@@ -2442,6 +2442,15 @@ class CUsabilityTest(UsabilityTest):

 class PyUsabilityTest(UsabilityTest):

     decimal = P

+    def setUp(self):

+        super().setUp()

+        self._previous_int_limit = sys.get_int_max_str_digits()

+        sys.set_int_max_str_digits(7000)

+

+    def tearDown(self):

+        sys.set_int_max_str_digits(self._previous_int_limit)

+        super().tearDown()

+

 class PythonAPItests(unittest.TestCase):

     def test_abc(self):

@@ -4499,6 +4508,15 @@ class CCoverage(Coverage):

 class PyCoverage(Coverage):

     decimal = P

+    def setUp(self):

+        super().setUp()

+        self._previous_int_limit = sys.get_int_max_str_digits()

+        sys.set_int_max_str_digits(7000)

+

+    def tearDown(self):

+        sys.set_int_max_str_digits(self._previous_int_limit)

+        super().tearDown()

+

 class PyFunctionality(unittest.TestCase):

     """Extra functionality in decimal.py"""

diff --git a/Lib/test/test_int.py b/Lib/test/test_int.py

index a36076e..6cd9a5e 100644

--- a/Lib/test/test_int.py

+++ b/Lib/test/test_int.py

@@ -1,4 +1,5 @@

 import sys

+import time

 import unittest

 from test import support

@@ -514,5 +515,200 @@ class IntTestCases(unittest.TestCase):

         self.assertEqual(int('1_2_3_4_5_6_7', 32), 1144132807)

+class IntStrDigitLimitsTests(unittest.TestCase):

+

+    int_class = int  # Override this in subclasses to reuse the suite.

+

+    def setUp(self):

+        super().setUp()

+        self._previous_limit = sys.get_int_max_str_digits()

+        sys.set_int_max_str_digits(2048)

+

+    def tearDown(self):

+        sys.set_int_max_str_digits(self._previous_limit)

+        super().tearDown()

+

+    def test_disabled_limit(self):

+        self.assertGreater(sys.get_int_max_str_digits(), 0)

+        self.assertLess(sys.get_int_max_str_digits(), 20_000)

+        with support.adjust_int_max_str_digits(0):

+            self.assertEqual(sys.get_int_max_str_digits(), 0)

+            i = self.int_class('1' * 20_000)

+            str(i)

+        self.assertGreater(sys.get_int_max_str_digits(), 0)

+

+    def test_max_str_digits_edge_cases(self):

+        """Ignore the +/- sign and space padding."""

+        int_class = self.int_class

+        maxdigits = sys.get_int_max_str_digits()

+

+        int_class('1' * maxdigits)