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

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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>
This commit is contained in:
Shamil 2025-10-14 17:42:17 +03:00 • committed by GitHub
parent 07e617ecc2
commit 59547a251f
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3 changed files with 10 additions and 12 deletions
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6
Include/internal/pycore_interp_structs.h
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@ -769,12 +769,6 @@ struct _is {
* and should be placed at the beginning. */
struct _ceval_state ceval;
/* This structure is carefully allocated so that it's correctly aligned
* to avoid undefined behaviors during LOAD and STORE. The '_malloced'
* field stores the allocated pointer address that will later be freed.
*/
void *_malloced;
PyInterpreterState *next;
int64_t id;

1
Misc/NEWS.d/next/Core_and_Builtins/2025-10-14-17-07-37.gh-issue-140067.ID2gOm.rst Normal file
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@ -0,0 +1 @@
Fix memory leak in sub-interpreter creation.

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]);
}
}