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gh-91421: Use constant value check during runtime (GH-91422) (GH-91492)

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The left-hand side expression of the if-check can be converted to a
constant by the compiler, but the addition on the right-hand side is
performed during runtime.

Move the addition from the right-hand side to the left-hand side by
turning it into a subtraction there. Since the values are known to
be large enough to not turn negative, this is a safe operation.

Prevents a very unlikely integer overflow on 32 bit systems.

Fixes GH-91421.
(cherry picked from commit 0859368335)

Co-authored-by: Tobias Stoeckmann <stoeckmann@users.noreply.github.com>
This commit is contained in:
Miss Islington (bot) 2022-04-13 18:38:37 -07:00 • committed by GitHub
parent 89697f7374
commit 72114c06fd
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2 changed files with 2 additions and 1 deletions
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1
Misc/NEWS.d/next/Core and Builtins/2022-04-10-22-57-27.gh-issue-91421.dHhv6U.rst Normal file
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@ -0,0 +1 @@
Fix a potential integer overflow in _Py_DecodeUTF8Ex.

2
Objects/unicodeobject.c
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@ -5373,7 +5373,7 @@ _Py_DecodeUTF8Ex(const char *s, Py_ssize_t size, wchar_t **wstr, size_t *wlen,
/* Note: size will always be longer than the resulting Unicode
character count */
if (PY_SSIZE_T_MAX / (Py_ssize_t)sizeof(wchar_t) < (size + 1)) {
if (PY_SSIZE_T_MAX / (Py_ssize_t)sizeof(wchar_t) - 1 < size) {
return -1;
}