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gh-143050: Correct PyLong_FromString() to use _PyLong_Negate() (#145901)

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The long_from_string_base() might return a small integer, when the
_pylong.py is used to do conversion.  Hence, we must be careful here to
not smash it "small int" bit by using the _PyLong_FlipSign().

Co-authored-by: Victor Stinner <vstinner@python.org>
This commit is contained in:
Sergey B Kirpichev 2026-03-31 16:17:49 +03:00 • committed by GitHub
parent 829e4d0b14
commit db5936c5b8
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GPG key ID: B5690EEEBB952194
4 changed files with 34 additions and 18 deletions
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18
Include/internal/pycore_long.h
View file

@ -232,6 +232,20 @@ _PyLong_IsPositive(const PyLongObject *op)
return (op->long_value.lv_tag & SIGN_MASK) == 0;
}
/* Return true if the argument is a small int */
static inline bool
_PyLong_IsSmallInt(const PyLongObject *op)
{
assert(PyLong_Check(op));
bool is_small_int = (op->long_value.lv_tag & IMMORTALITY_BIT_MASK) != 0;
assert(PyLong_CheckExact(op) || (!is_small_int));
assert(_Py_IsImmortal(op) || (!is_small_int));
assert((_PyLong_IsCompact(op)
&& _PY_IS_SMALL_INT(_PyLong_CompactValue(op)))
|| (!is_small_int));
return is_small_int;
}
static inline Py_ssize_t
_PyLong_DigitCount(const PyLongObject *op)
{
@ -293,7 +307,9 @@ _PyLong_SetDigitCount(PyLongObject *op, Py_ssize_t size)
#define NON_SIZE_MASK ~(uintptr_t)((1 << NON_SIZE_BITS) - 1)
static inline void
_PyLong_FlipSign(PyLongObject *op) {
_PyLong_FlipSign(PyLongObject *op)
{
assert(!_PyLong_IsSmallInt(op));
unsigned int flipped_sign = 2 - (op->long_value.lv_tag & SIGN_MASK);
op->long_value.lv_tag &= NON_SIZE_MASK;
op->long_value.lv_tag |= flipped_sign;

10
Lib/test/test_capi/test_long.py
View file

@ -803,6 +803,16 @@ def to_digits(num):
self.assertEqual(pylongwriter_create(negative, digits), num,
(negative, digits))
def test_bug_143050(self):
with support.adjust_int_max_str_digits(0):
# Bug coming from using _pylong.int_from_string(), that
# currently requires > 6000 decimal digits.
int('-' + '0' * 7000, 10)
_testcapi.test_immortal_small_ints()
# Test also nonzero small int
int('-' + '0' * 7000 + '123', 10)
_testcapi.test_immortal_small_ints()
if __name__ == "__main__":
unittest.main()

4
Modules/_testcapi/immortal.c
View file

@ -31,13 +31,13 @@ test_immortal_small_ints(PyObject *self, PyObject *Py_UNUSED(ignored))
for (int i = -5; i <= 1024; i++) {
PyObject *obj = PyLong_FromLong(i);
assert(verify_immortality(obj));
int has_int_immortal_bit = ((PyLongObject *)obj)->long_value.lv_tag & IMMORTALITY_BIT_MASK;
int has_int_immortal_bit = _PyLong_IsSmallInt((PyLongObject *)obj);
assert(has_int_immortal_bit);
}
for (int i = 1025; i <= 1030; i++) {
PyObject *obj = PyLong_FromLong(i);
assert(obj);
int has_int_immortal_bit = ((PyLongObject *)obj)->long_value.lv_tag & IMMORTALITY_BIT_MASK;
int has_int_immortal_bit = _PyLong_IsSmallInt((PyLongObject *)obj);
assert(!has_int_immortal_bit);
Py_DECREF(obj);
}

20
Objects/longobject.c
View file

@ -3119,11 +3119,11 @@ PyLong_FromString(const char *str, char **pend, int base)
}
/* Set sign and normalize */
if (sign < 0) {
_PyLong_FlipSign(z);
}
long_normalize(z);
z = maybe_small_long(z);
if (sign < 0) {
_PyLong_Negate(&z);
}
if (pend != NULL) {
*pend = (char *)str;
@ -3623,21 +3623,11 @@ long_richcompare(PyObject *self, PyObject *other, int op)
Py_RETURN_RICHCOMPARE(result, 0, op);
}
static inline int
/// Return 1 if the object is one of the immortal small ints
_long_is_small_int(PyObject *op)
{
PyLongObject *long_object = (PyLongObject *)op;
int is_small_int = (long_object->long_value.lv_tag & IMMORTALITY_BIT_MASK) != 0;
assert((!is_small_int) || PyLong_CheckExact(op));
return is_small_int;
}
void
_PyLong_ExactDealloc(PyObject *self)
{
assert(PyLong_CheckExact(self));
if (_long_is_small_int(self)) {
if (_PyLong_IsSmallInt((PyLongObject *)self)) {
// See PEP 683, section Accidental De-Immortalizing for details
_Py_SetImmortal(self);
return;
@ -3652,7 +3642,7 @@ _PyLong_ExactDealloc(PyObject *self)
static void
long_dealloc(PyObject *self)
{
if (_long_is_small_int(self)) {
if (_PyLong_IsSmallInt((PyLongObject *)self)) {
/* This should never get called, but we also don't want to SEGV if
* we accidentally decref small Ints out of existence. Instead,
* since small Ints are immortal, re-set the reference count.