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gh-140067: Fix memory leak in sub-interpreter creation (#140111) (#140261)

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Fix memory leak in sub-interpreter creation caused by overwriting of the previously used `_malloced` field. Now the pointer is stored in the first word of the memory block to avoid it being overwritten accidentally. 

Co-authored-by: Kumar Aditya <kumaraditya@python.org>
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Kumar Aditya 2025-10-18 16:36:58 +05:30 • committed by GitHub
parent c8729c9909
commit 58c44c2bf2
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4 changed files with 11 additions and 12 deletions
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15
Python/pystate.c
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@ -457,16 +457,19 @@ _PyInterpreterState_Enable(_PyRuntimeState *runtime)
static PyInterpreterState *
alloc_interpreter(void)
{
// Aligned allocation for PyInterpreterState.
// the first word of the memory block is used to store
// the original pointer to be used later to free the memory.
size_t alignment = _Alignof(PyInterpreterState);
size_t allocsize = sizeof(PyInterpreterState) + alignment - 1;
size_t allocsize = sizeof(PyInterpreterState) + sizeof(void *) + alignment - 1;
void *mem = PyMem_RawCalloc(1, allocsize);
if (mem == NULL) {
return NULL;
}
PyInterpreterState *interp = _Py_ALIGN_UP(mem, alignment);
assert(_Py_IS_ALIGNED(interp, alignment));
interp->_malloced = mem;
return interp;
void *ptr = _Py_ALIGN_UP((char *)mem + sizeof(void *), alignment);
((void **)ptr)[-1] = mem;
assert(_Py_IS_ALIGNED(ptr, alignment));
return ptr;
}
static void
@ -481,7 +484,7 @@ free_interpreter(PyInterpreterState *interp)
interp->obmalloc = NULL;
}
assert(_Py_IS_ALIGNED(interp, _Alignof(PyInterpreterState)));
PyMem_RawFree(interp->_malloced);
PyMem_RawFree(((void **)interp)[-1]);
}
}