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gh-95778: Add pre-check for int-to-str conversion by mdickinson · Pull Request #96537 · python/cpython · GitHub
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gh-95778: Add pre-check for int-to-str conversion #96537

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Merged
gpshead merged 14 commits into from
Sep 4, 2022
Merged

gh-95778: Add pre-check for int-to-str conversion #96537

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2fbc9ce
Add pre-check for int-to-str conversion
mdickinson Sep 3, 2022
d16db91
Avoid potential undefined behaviour from overflow
mdickinson Sep 3, 2022
66a07ac
Reworked, even cruder bound, that avoids potential issues with intege…
mdickinson Sep 3, 2022
6eadbda
Rename the error message constants.
gpshead Sep 4, 2022
195686c
Add a DoS prevention success timed regression test.
gpshead Sep 4, 2022
87bd23d
Improve the test to check close to the limit.
gpshead Sep 4, 2022
de9ed4d
Use fewer digits in the test to speed it up on slow hosts.
gpshead Sep 4, 2022
dbd8da9
Misc: Fix a typo in the header comment.
gpshead Sep 4, 2022
c49a737
Change timers if process_time() returns 0. #wasm
gpshead Sep 4, 2022
35c5ea7
Merge branch 'main' into fix/int-to-str-dos
gpshead Sep 4, 2022
730915d
Update comment to suggest reading the PR for detail
gpshead Sep 4, 2022
56f08c2
Minor comment typo fix (restart CI).
gpshead Sep 4, 2022
4dae3e0
cleanup the test.
gpshead Sep 4, 2022
adb1784
Add Mark's name to the NEWS entry.
gpshead Sep 4, 2022
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19 changes: 17 additions & 2 deletions Objects/longobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,7 @@ medium_value(PyLongObject *x)
#define IS_SMALL_UINT(ival) ((ival) < _PY_NSMALLPOSINTS)

#define _MAX_STR_DIGITS_ERROR_FMT "Exceeds the limit (%d) for integer string conversion: value has %zd digits"
#define _MAX_STR_DIGITS_ERROR_FMT2 "Exceeds the limit (%d) for integer string conversion"
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static inline void
_Py_DECREF_INT(PyLongObject *op)
Expand Down Expand Up @@ -1758,6 +1759,20 @@ 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 digit limit,
based on the inequality 10/3 >= log2(10) */
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) && (size_a >= 10 * max_str_digits
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/ (3 * PyLong_SHIFT) + 2)) {
PyErr_Format(PyExc_ValueError, _MAX_STR_DIGITS_ERROR_FMT2,
max_str_digits);
return -1;
}
}

/* quick and dirty upper bound for the number of digits
required to express a in base _PyLong_DECIMAL_BASE:

Expand Down Expand Up @@ -1823,8 +1838,8 @@ 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_FMT2,
max_str_digits);
return -1;
}
}
Expand Down