diff options
| -rw-r--r-- | Lib/test/test_int.py | 82 | ||||
| -rw-r--r-- | Misc/NEWS.d/next/Security/2022-08-07-16-53-38.gh-issue-95778.ch010gps.rst | 2 | ||||
| -rw-r--r-- | Objects/longobject.c | 26 |
3 files changed, 105 insertions, 5 deletions
diff --git a/Lib/test/test_int.py b/Lib/test/test_int.py index 54a96ad6645..cbbddf50637 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 @@ -626,6 +627,87 @@ class IntStrDigitLimitsTests(unittest.TestCase): with self.assertRaises(ValueError): str(i) + def test_denial_of_service_prevented_int_to_str(self): + """Regression test: ensure we fail before performing O(N**2) work.""" + maxdigits = sys.get_int_max_str_digits() + assert maxdigits < 50_000, maxdigits # A test prerequisite. + get_time = time.process_time + if get_time() <= 0: # some platforms like WASM lack process_time() + get_time = time.monotonic + + huge_int = int(f'0x{"c"*65_000}', base=16) # 78268 decimal digits. + digits = 78_268 + with support.adjust_int_max_str_digits(digits): + start = get_time() + huge_decimal = str(huge_int) + seconds_to_convert = get_time() - start + self.assertEqual(len(huge_decimal), digits) + # Ensuring that we chose a slow enough conversion to measure. + # It takes 0.1 seconds on a Zen based cloud VM in an opt build. + if seconds_to_convert < 0.005: + raise unittest.SkipTest('"slow" conversion took only ' + f'{seconds_to_convert} seconds.') + + # We test with the limit almost at the size needed to check performance. + # The performant limit check is slightly fuzzy, give it a some room. + with support.adjust_int_max_str_digits(int(.995 * digits)): + with self.assertRaises(ValueError) as err: + start = get_time() + str(huge_int) + seconds_to_fail_huge = get_time() - start + self.assertIn('conversion', str(err.exception)) + self.assertLess(seconds_to_fail_huge, seconds_to_convert/8) + + # Now we test that a conversion that would take 30x as long also fails + # in a similarly fast fashion. + extra_huge_int = int(f'0x{"c"*500_000}', base=16) # 602060 digits. + with self.assertRaises(ValueError) as err: + start = get_time() + # If not limited, 8 seconds said Zen based cloud VM. + str(extra_huge_int) + seconds_to_fail_extra_huge = get_time() - start + self.assertIn('conversion', str(err.exception)) + self.assertLess(seconds_to_fail_extra_huge, seconds_to_convert/8) + + def test_denial_of_service_prevented_str_to_int(self): + """Regression test: ensure we fail before performing O(N**2) work.""" + maxdigits = sys.get_int_max_str_digits() + assert maxdigits < 100_000, maxdigits # A test prerequisite. + get_time = time.process_time + if get_time() <= 0: # some platforms like WASM lack process_time() + get_time = time.monotonic + + digits = 133700 + huge = '8'*digits + with support.adjust_int_max_str_digits(digits): + start = get_time() + int(huge) + seconds_to_convert = get_time() - start + # Ensuring that we chose a slow enough conversion to measure. + # It takes 0.1 seconds on a Zen based cloud VM in an opt build. + if seconds_to_convert < 0.005: + raise unittest.SkipTest('"slow" conversion took only ' + f'{seconds_to_convert} seconds.') + + with support.adjust_int_max_str_digits(digits - 1): + with self.assertRaises(ValueError) as err: + start = get_time() + int(huge) + seconds_to_fail_huge = get_time() - start + self.assertIn('conversion', str(err.exception)) + self.assertLess(seconds_to_fail_huge, seconds_to_convert/8) + + # Now we test that a conversion that would take 30x as long also fails + # in a similarly fast fashion. + extra_huge = '7'*1_200_000 + with self.assertRaises(ValueError) as err: + start = get_time() + # If not limited, 8 seconds in the Zen based cloud VM. + int(extra_huge) + seconds_to_fail_extra_huge = get_time() - start + self.assertIn('conversion', str(err.exception)) + self.assertLess(seconds_to_fail_extra_huge, seconds_to_convert/8) + def test_power_of_two_bases_unlimited(self): """The limit does not apply to power of 2 bases.""" maxdigits = sys.get_int_max_str_digits() diff --git a/Misc/NEWS.d/next/Security/2022-08-07-16-53-38.gh-issue-95778.ch010gps.rst b/Misc/NEWS.d/next/Security/2022-08-07-16-53-38.gh-issue-95778.ch010gps.rst index ea3b85d632e..8eb8a34884d 100644 --- a/Misc/NEWS.d/next/Security/2022-08-07-16-53-38.gh-issue-95778.ch010gps.rst +++ b/Misc/NEWS.d/next/Security/2022-08-07-16-53-38.gh-issue-95778.ch010gps.rst @@ -11,4 +11,4 @@ limitation <int_max_str_digits>` 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, and Ned Deily. +from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson. diff --git a/Objects/longobject.c b/Objects/longobject.c index a53eabee4cc..ec18ec32b8a 100644 --- a/Objects/longobject.c +++ b/Objects/longobject.c @@ -38,7 +38,8 @@ PyObject *_PyLong_One = NULL; #define IS_SMALL_INT(ival) (-NSMALLNEGINTS <= (ival) && (ival) < NSMALLPOSINTS) #define IS_SMALL_UINT(ival) ((ival) < NSMALLPOSINTS) -#define _MAX_STR_DIGITS_ERROR_FMT "Exceeds the limit (%d) for integer string conversion: value has %zd digits" +#define _MAX_STR_DIGITS_ERROR_FMT_TO_INT "Exceeds the limit (%d) for integer string conversion: value has %zd digits" +#define _MAX_STR_DIGITS_ERROR_FMT_TO_STR "Exceeds the limit (%d) for integer string conversion" static PyObject * get_small_int(sdigit ival) @@ -1722,6 +1723,23 @@ long_to_decimal_string_internal(PyObject *aa, size_a = Py_ABS(Py_SIZE(a)); negative = Py_SIZE(a) < 0; + /* quick and dirty pre-check for overflowing the decimal digit limit, + based on the inequality 10/3 >= log2(10) + + explanation in https://github.com/python/cpython/pull/96537 + */ + if (size_a >= 10 * _PY_LONG_MAX_STR_DIGITS_THRESHOLD + / (3 * PyLong_SHIFT) + 2) { + PyInterpreterState *interp = _PyInterpreterState_GET(); + int max_str_digits = interp->int_max_str_digits; + if ((max_str_digits > 0) && + (max_str_digits / (3 * PyLong_SHIFT) <= (size_a - 11) / 10)) { + PyErr_Format(PyExc_ValueError, _MAX_STR_DIGITS_ERROR_FMT_TO_STR, + max_str_digits); + return -1; + } + } + /* quick and dirty upper bound for the number of digits required to express a in base _PyLong_DECIMAL_BASE: @@ -1787,8 +1805,8 @@ long_to_decimal_string_internal(PyObject *aa, Py_ssize_t strlen_nosign = strlen - negative; if ((max_str_digits > 0) && (strlen_nosign > max_str_digits)) { Py_DECREF(scratch); - PyErr_Format(PyExc_ValueError, _MAX_STR_DIGITS_ERROR_FMT, - max_str_digits, strlen_nosign); + PyErr_Format(PyExc_ValueError, _MAX_STR_DIGITS_ERROR_FMT_TO_STR, + max_str_digits); return -1; } } @@ -2462,7 +2480,7 @@ digit beyond the first. PyInterpreterState *interp = _PyInterpreterState_GET(); int max_str_digits = interp->int_max_str_digits; if ((max_str_digits > 0) && (digits > max_str_digits)) { - PyErr_Format(PyExc_ValueError, _MAX_STR_DIGITS_ERROR_FMT, + PyErr_Format(PyExc_ValueError, _MAX_STR_DIGITS_ERROR_FMT_TO_INT, max_str_digits, digits); return NULL; } |