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gh-111784: Add PyCapsule_ImportCapsule and fix segfault in _elementtree.c #112053

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gh-111784: Add PyCapsule_ImportCapsule and fix segfault in _elementtree.c #112053

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5 changes: 5 additions & 0 deletions Include/pycapsule.h
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,11 @@ PyAPI_FUNC(void *) PyCapsule_Import(
const char *name, /* UTF-8 encoded string */
int no_block);

PyAPI_FUNC(PyObject *) PyCapsule_ImportCapsule(
const char *name,
int no_block
);

#ifdef __cplusplus
}
#endif
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8 changes: 7 additions & 1 deletion Modules/_elementtree.c
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Expand Up @@ -98,6 +98,7 @@ typedef struct {
PyTypeObject *TreeBuilder_Type;
PyTypeObject *XMLParser_Type;

PyObject *expat_capsule;
struct PyExpat_CAPI *expat_capi;
} elementtreestate;

Expand Down Expand Up @@ -137,6 +138,7 @@ elementtree_clear(PyObject *m)
Py_CLEAR(st->parseerror_obj);
Py_CLEAR(st->deepcopy_obj);
Py_CLEAR(st->elementpath_obj);
Py_CLEAR(st->expat_capsule);
Py_CLEAR(st->comment_factory);
Py_CLEAR(st->pi_factory);

Expand Down Expand Up @@ -167,6 +169,7 @@ elementtree_traverse(PyObject *m, visitproc visit, void *arg)
Py_VISIT(st->parseerror_obj);
Py_VISIT(st->deepcopy_obj);
Py_VISIT(st->elementpath_obj);
Py_VISIT(st->expat_capsule);
Py_VISIT(st->comment_factory);
Py_VISIT(st->pi_factory);

Expand Down Expand Up @@ -4343,7 +4346,10 @@ module_exec(PyObject *m)
goto error;

/* link against pyexpat */
st->expat_capi = PyCapsule_Import(PyExpat_CAPSULE_NAME, 0);
if (!(st->expat_capsule = PyCapsule_ImportCapsule(PyExpat_CAPSULE_NAME, 0)))
goto error;
if (!(st->expat_capi = PyCapsule_GetPointer(st->expat_capsule, PyExpat_CAPSULE_NAME)))
goto error;
if (st->expat_capi) {
/* check that it's usable */
if (strcmp(st->expat_capi->magic, PyExpat_CAPI_MAGIC) != 0 ||
Expand Down
51 changes: 51 additions & 0 deletions Objects/capsule.c
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Expand Up @@ -224,6 +224,57 @@ _PyCapsule_SetTraverse(PyObject *op, traverseproc traverse_func, inquiry clear_f
}


PyObject *
PyCapsule_ImportCapsule(const char *name, int no_block)
{
PyObject *object = NULL;
char *trace;
size_t name_length = (strlen(name) + 1) * sizeof(char);
char *name_dup = (char *)PyMem_Malloc(name_length);

if (!name_dup) {
return PyErr_NoMemory();
}

memcpy(name_dup, name, name_length);

trace = name_dup;
while (trace) {
char *dot = strchr(trace, '.');
if (dot) {
*dot++ = '\0';
}

if (object == NULL) {
object = PyImport_ImportModule(trace);
if (!object) {
PyErr_Format(PyExc_ImportError, "PyCapsule_Import could not import module \"%s\"", trace);
}
} else {
PyObject *object2 = PyObject_GetAttrString(object, trace);
Py_SETREF(object, object2);
}
if (!object) {
goto EXIT;
}

trace = dot;
}

/* compare attribute name to module.name by hand */
if (!PyCapsule_IsValid(object, name)) {
PyErr_Format(PyExc_AttributeError,
"PyCapsule_Import \"%s\" is not valid",
name);
}
EXIT:
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We don't need here Py_XDECREF(object) as in the PyCapsule_Import, because we do it later manually. So, we can control a process of capsule's deallocation

if (name_dup) {
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name_dup is always non-NULL here, as we return MemoryError at line 236 if PyMem_Malloc fails.

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@Eclips4 Eclips4 Nov 14, 2023 •
edited
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It's not a final version 😅
Currently we just talking about idea, sadly, but this solution is incorrect :(
FYI, it's just copied from PyCapsule_Import

PyMem_Free(name_dup);
}
return object;
}


void *
PyCapsule_Import(const char *name, int no_block)
{
Expand Down