Possible null pointer dereference of freevars in _PyCompile_LookupArg

[federicovalenso]

Bug report

Bug description:

freevars is checked for null, but later possible dereference happens. Maybe replacing Py_DECREF by Py_XDECREF should do the trick.

CPython versions tested on:

3.11

Operating systems tested on:

No response

Linked PRs

• gh-126238: Fix possible null pointer dereference of freevars in _PyCompile_LookupArg #126239
• [3.12] Fix possible null pointer dereference of freevars in _PyCompile_LookupArg (gh-126238) #126474
• [3.13] Fix possible null pointer dereference of freevars in _PyCompile_LookupArg (gh-126238) #126475

[federicovalenso]

FYI @sobolevn

[ZeroIntensity]

Yeah, that looks incorrect. Simply changing it to Py_XDECREF should work. PR welcome :)