gh-99537: Use Py_SETREF() function in C code (#99656)

vstinner · web-flow · commit 7e3f09cad9b7 · 2022-11-22T14:22:22.000+01:00
Fix potential race condition in code patterns:

* Replace "Py_DECREF(var); var = new;" with "Py_SETREF(var, new);"
* Replace "Py_XDECREF(var); var = new;" with "Py_XSETREF(var, new);"
* Replace "Py_CLEAR(var); var = new;" with "Py_XSETREF(var, new);"

Other changes:

* Replace "old = var; var = new; Py_DECREF(var)"
  with "Py_SETREF(var, new);"
* Replace "old = var; var = new; Py_XDECREF(var)"
  with "Py_XSETREF(var, new);"
* And remove the "old" variable.
diff --git a/Doc/includes/custom2.c b/Doc/includes/custom2.c
@@ -42,22 +42,18 @@ static int
 Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
 {
     static char *kwlist[] = {"first", "last", "number", NULL};
-    PyObject *first = NULL, *last = NULL, *tmp;
+    PyObject *first = NULL, *last = NULL;
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist,
                                      &first, &last,
                                      &self->number))
         return -1;
 
     if (first) {
-        tmp = self->first;
-        self->first = Py_NewRef(first);
-        Py_XDECREF(tmp);
+        Py_XSETREF(self->first, Py_NewRef(first));
     }
     if (last) {
-        tmp = self->last;
-        self->last = Py_NewRef(last);
-        Py_XDECREF(tmp);
+        Py_XSETREF(self->last, Py_NewRef(last));
     }
     return 0;
 }
diff --git a/Doc/includes/custom3.c b/Doc/includes/custom3.c
@@ -42,22 +42,18 @@ static int
 Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
 {
     static char *kwlist[] = {"first", "last", "number", NULL};
-    PyObject *first = NULL, *last = NULL, *tmp;
+    PyObject *first = NULL, *last = NULL;
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "|UUi", kwlist,
                                      &first, &last,
                                      &self->number))
         return -1;
 
     if (first) {
-        tmp = self->first;
-        self->first = Py_NewRef(first);
-        Py_DECREF(tmp);
+        Py_SETREF(self->first, Py_NewRef(first));
     }
     if (last) {
-        tmp = self->last;
-        self->last = Py_NewRef(last);
-        Py_DECREF(tmp);
+        Py_SETREF(self->last, Py_NewRef(last));
     }
     return 0;
 }
@@ -77,7 +73,6 @@ Custom_getfirst(CustomObject *self, void *closure)
 static int
 Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
 {
-    PyObject *tmp;
     if (value == NULL) {
         PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
         return -1;
@@ -87,9 +82,7 @@ Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
                         "The first attribute value must be a string");
         return -1;
     }
-    tmp = self->first;
-    self->first = Py_NewRef(value);
-    Py_DECREF(tmp);
+    Py_SETREF(self->first, Py_NewRef(value));
     return 0;
 }
 
@@ -102,7 +95,6 @@ Custom_getlast(CustomObject *self, void *closure)
 static int
 Custom_setlast(CustomObject *self, PyObject *value, void *closure)
 {
-    PyObject *tmp;
     if (value == NULL) {
         PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute");
         return -1;
@@ -112,9 +104,7 @@ Custom_setlast(CustomObject *self, PyObject *value, void *closure)
                         "The last attribute value must be a string");
         return -1;
     }
-    tmp = self->last;
-    self->last = Py_NewRef(value);
-    Py_DECREF(tmp);
+    Py_SETREF(self->last, Py_NewRef(value));
     return 0;
 }
 
diff --git a/Doc/includes/custom4.c b/Doc/includes/custom4.c
@@ -58,22 +58,18 @@ static int
 Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
 {
     static char *kwlist[] = {"first", "last", "number", NULL};
-    PyObject *first = NULL, *last = NULL, *tmp;
+    PyObject *first = NULL, *last = NULL;
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "|UUi", kwlist,
                                      &first, &last,
                                      &self->number))
         return -1;
 
     if (first) {
-        tmp = self->first;
-        self->first = Py_NewRef(first);
-        Py_DECREF(tmp);
+        Py_SETREF(self->first, Py_NewRef(first));
     }
     if (last) {
-        tmp = self->last;
-        self->last = Py_NewRef(last);
-        Py_DECREF(tmp);
+        Py_SETREF(self->last, Py_NewRef(last));
     }
     return 0;
 }
@@ -102,9 +98,7 @@ Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
                         "The first attribute value must be a string");
         return -1;
     }
-    Py_INCREF(value);
-    Py_CLEAR(self->first);
-    self->first = value;
+    Py_XSETREF(self->first, Py_NewRef(value));
     return 0;
 }
 
@@ -126,9 +120,7 @@ Custom_setlast(CustomObject *self, PyObject *value, void *closure)
                         "The last attribute value must be a string");
         return -1;
     }
-    Py_INCREF(value);
-    Py_CLEAR(self->last);
-    self->last = value;
+    Py_XSETREF(self->last, Py_NewRef(value));
     return 0;
 }
 
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
@@ -1256,7 +1256,6 @@ deque_remove(dequeobject *deque, PyObject *value)
 static int
 deque_ass_item(dequeobject *deque, Py_ssize_t i, PyObject *v)
 {
-    PyObject *old_value;
     block *b;
     Py_ssize_t n, len=Py_SIZE(deque), halflen=(len+1)>>1, index=i;
 
@@ -1282,9 +1281,7 @@ deque_ass_item(dequeobject *deque, Py_ssize_t i, PyObject *v)
         while (--n >= 0)
             b = b->leftlink;
     }
-    old_value = b->data[i];
-    b->data[i] = Py_NewRef(v);
-    Py_DECREF(old_value);
+    Py_SETREF(b->data[i], Py_NewRef(v));
     return 0;
 }
 
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
@@ -6247,13 +6247,10 @@ datetime_astimezone(PyDateTime_DateTime *self, PyObject *args, PyObject *kw)
     }
     else {
         /* Result is already aware - just replace tzinfo. */
-        temp = result->tzinfo;
-        result->tzinfo = Py_NewRef(PyDateTime_TimeZone_UTC);
-        Py_DECREF(temp);
+        Py_SETREF(result->tzinfo, Py_NewRef(PyDateTime_TimeZone_UTC));
     }
 
     /* Attach new tzinfo and let fromutc() do the rest. */
-    temp = result->tzinfo;
     if (tzinfo == Py_None) {
         tzinfo = local_timezone(result);
         if (tzinfo == NULL) {
@@ -6263,8 +6260,7 @@ datetime_astimezone(PyDateTime_DateTime *self, PyObject *args, PyObject *kw)
     }
     else
       Py_INCREF(tzinfo);
-    result->tzinfo = tzinfo;
-    Py_DECREF(temp);
+    Py_SETREF(result->tzinfo, tzinfo);
 
     temp = (PyObject *)result;
     result = (PyDateTime_DateTime *)
diff --git a/Modules/_elementtree.c b/Modules/_elementtree.c
@@ -537,8 +537,7 @@ element_get_text(ElementObject* self)
             if (!tmp)
                 return NULL;
             self->text = tmp;
-            Py_DECREF(res);
-            res = tmp;
+            Py_SETREF(res, tmp);
         }
     }
 
@@ -559,8 +558,7 @@ element_get_tail(ElementObject* self)
             if (!tmp)
                 return NULL;
             self->tail = tmp;
-            Py_DECREF(res);
-            res = tmp;
+            Py_SETREF(res, tmp);
         }
     }
 
diff --git a/Modules/_functoolsmodule.c b/Modules/_functoolsmodule.c
@@ -1243,8 +1243,7 @@ lru_cache_clear_list(lru_list_elem *link)
 {
     while (link != NULL) {
         lru_list_elem *next = link->next;
-        Py_DECREF(link);
-        link = next;
+        Py_SETREF(link, next);
     }
 }
 
diff --git a/Modules/_io/stringio.c b/Modules/_io/stringio.c
@@ -193,8 +193,7 @@ write_str(stringio *self, PyObject *obj)
     if (self->writenl) {
         PyObject *translated = PyUnicode_Replace(
             decoded, &_Py_STR(newline), self->writenl, -1);
-        Py_DECREF(decoded);
-        decoded = translated;
+        Py_SETREF(decoded, translated);
     }
     if (decoded == NULL)
         return -1;
diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
@@ -320,8 +320,7 @@ _PyIncrementalNewlineDecoder_decode(PyObject *myself,
         out = PyUnicode_DATA(modified);
         PyUnicode_WRITE(kind, out, 0, '\r');
         memcpy(out + kind, PyUnicode_DATA(output), kind * output_len);
-        Py_DECREF(output);
-        output = modified; /* output remains ready */
+        Py_SETREF(output, modified); /* output remains ready */
         self->pendingcr = 0;
         output_len++;
     }
@@ -336,8 +335,7 @@ _PyIncrementalNewlineDecoder_decode(PyObject *myself,
             PyObject *modified = PyUnicode_Substring(output, 0, output_len -1);
             if (modified == NULL)
                 goto error;
-            Py_DECREF(output);
-            output = modified;
+            Py_SETREF(output, modified);
             self->pendingcr = 1;
         }
     }
@@ -865,8 +863,7 @@ _textiowrapper_set_decoder(textio *self, PyObject *codec_info,
             self->decoder, self->readtranslate ? Py_True : Py_False, NULL);
         if (incrementalDecoder == NULL)
             return -1;
-        Py_CLEAR(self->decoder);
-        self->decoder = incrementalDecoder;
+        Py_XSETREF(self->decoder, incrementalDecoder);
     }
 
     return 0;
diff --git a/Modules/_json.c b/Modules/_json.c
@@ -709,9 +709,7 @@ _parse_object_unicode(PyScannerObject *s, PyObject *pystr, Py_ssize_t idx, Py_ss
             if (memokey == NULL) {
                 goto bail;
             }
-            Py_INCREF(memokey);
-            Py_DECREF(key);
-            key = memokey;
+            Py_SETREF(key, Py_NewRef(memokey));
             idx = next_idx;
 
             /* skip whitespace between key and : delimiter, read :, skip whitespace */
diff --git a/Modules/_pickle.c b/Modules/_pickle.c
@@ -1829,8 +1829,7 @@ get_deep_attribute(PyObject *obj, PyObject *names, PyObject **pparent)
     n = PyList_GET_SIZE(names);
     for (i = 0; i < n; i++) {
         PyObject *name = PyList_GET_ITEM(names, i);
-        Py_XDECREF(parent);
-        parent = obj;
+        Py_XSETREF(parent, obj);
         (void)_PyObject_LookupAttr(parent, name, &obj);
         if (obj == NULL) {
             Py_DECREF(parent);
@@ -3717,9 +3716,7 @@ save_global(PicklerObject *self, PyObject *obj, PyObject *name)
     else {
   gen_global:
         if (parent == module) {
-            Py_INCREF(lastname);
-            Py_DECREF(global_name);
-            global_name = lastname;
+            Py_SETREF(global_name, Py_NewRef(lastname));
         }
         if (self->proto >= 4) {
             const char stack_global_op = STACK_GLOBAL;
diff --git a/Modules/_sqlite/cursor.c b/Modules/_sqlite/cursor.c
@@ -1123,8 +1123,7 @@ pysqlite_cursor_iternext(pysqlite_Cursor *self)
         PyObject *factory = self->row_factory;
         PyObject *args[] = { (PyObject *)self, row, };
         PyObject *new_row = PyObject_Vectorcall(factory, args, 2, NULL);
-        Py_DECREF(row);
-        row = new_row;
+        Py_SETREF(row, new_row);
     }
     return row;
 }
diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
@@ -523,8 +523,7 @@ set_eval_frame_record(PyObject *self, PyObject *list)
         PyErr_SetString(PyExc_TypeError, "argument must be a list");
         return NULL;
     }
-    Py_CLEAR(record_list);
-    record_list = Py_NewRef(list);
+    Py_XSETREF(record_list, Py_NewRef(list));
     _PyInterpreterState_SetEvalFrameFunc(PyInterpreterState_Get(), record_eval);
     Py_RETURN_NONE;
 }
diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
@@ -1105,8 +1105,7 @@ fromBignumObj(TkappObject *tkapp, Tcl_Obj *value)
     PyMem_Free(bytes);
     if (res != NULL && bigValue.sign == MP_NEG) {
         PyObject *res2 = PyNumber_Negative(res);
-        Py_DECREF(res);
-        res = res2;
+        Py_SETREF(res, res2);
     }
     mp_clear(&bigValue);
     return res;
diff --git a/Modules/_zoneinfo.c b/Modules/_zoneinfo.c
@@ -1074,8 +1074,7 @@ load_data(PyZoneInfo_ZoneInfo *self, PyObject *file_obj)
         // that the dstoff is set correctly in that case.
         if (PyObject_IsTrue(tti->dstoff)) {
             _ttinfo *tti_after = &(self->tzrule_after.std);
-            Py_DECREF(tti_after->dstoff);
-            tti_after->dstoff = Py_NewRef(tti->dstoff);
+            Py_SETREF(tti_after->dstoff, Py_NewRef(tti->dstoff));
         }
     }
 
diff --git a/Modules/audioop.c b/Modules/audioop.c
@@ -1471,8 +1471,7 @@ audioop_ratecv_impl(PyObject *module, Py_buffer *fragment, int width,
                 len = (Py_ssize_t)(ncp - PyBytes_AsString(str));
                 rv = PyBytes_FromStringAndSize
                     (PyBytes_AsString(str), len);
-                Py_DECREF(str);
-                str = rv;
+                Py_SETREF(str, rv);
                 if (str == NULL)
                     goto exit;
                 rv = Py_BuildValue("(O(iO))", str, d, samps);
diff --git a/Modules/cjkcodecs/multibytecodec.c b/Modules/cjkcodecs/multibytecodec.c
@@ -980,8 +980,7 @@ _multibytecodec_MultibyteIncrementalEncoder_setstate_impl(MultibyteIncrementalEn
         goto errorexit;
     }
 
-    Py_CLEAR(self->pending);
-    self->pending = pending;
+    Py_XSETREF(self->pending, pending);
     memcpy(self->state.c, statebytes+1+statebytes[0],
            sizeof(self->state.c));
 
@@ -1438,8 +1437,7 @@ mbstreamreader_iread(MultibyteStreamReaderObject *self,
             memcpy(ctrdata + self->pendingsize,
                     PyBytes_AS_STRING(cres),
                     PyBytes_GET_SIZE(cres));
-            Py_DECREF(cres);
-            cres = ctr;
+            Py_SETREF(cres, ctr);
             self->pendingsize = 0;
         }
 
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
@@ -834,8 +834,7 @@ teedataobject_safe_decref(PyObject *obj)
            Py_REFCNT(obj) == 1) {
         PyObject *nextlink = ((teedataobject *)obj)->nextlink;
         ((teedataobject *)obj)->nextlink = NULL;
-        Py_DECREF(obj);
-        obj = nextlink;
+        Py_SETREF(obj, nextlink);
     }
     Py_XDECREF(obj);
 }
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
@@ -2069,17 +2069,15 @@ factorial_odd_part(unsigned long n)
         Py_DECREF(partial);
         if (tmp == NULL)
             goto error;
-        Py_DECREF(inner);
-        inner = tmp;
+        Py_SETREF(inner, tmp);
         /* Now inner is the product of all odd integers j in the range (0,
            n/2**i], giving the inner product in the formula above. */
 
         /* outer *= inner; */
         tmp = PyNumber_Multiply(outer, inner);
         if (tmp == NULL)
             goto error;
-        Py_DECREF(outer);
-        outer = tmp;
+        Py_SETREF(outer, tmp);
     }
     Py_DECREF(inner);
     return outer;
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
@@ -1202,8 +1202,7 @@ path_converter(PyObject *o, void *p)
         }
 
         /* still owns a reference to the original object */
-        Py_DECREF(o);
-        o = res;
+        Py_SETREF(o, res);
     }
 
     if (is_unicode) {

Original file line number	Diff line number	Diff line change
`@@ -42,22 +42,18 @@ static int`
`42`	`42`	`Custom_init(CustomObject self, PyObject args, PyObject *kwds)`
`43`	`43`	`{`
`44`	`44`	`static char *kwlist[] = {"first", "last", "number", NULL};`
`45`		`- PyObject first = NULL, last = NULL, *tmp;`
	`45`	`+ PyObject first = NULL, last = NULL;`
`46`	`46`
`47`	`47`	`if (!PyArg_ParseTupleAndKeywords(args, kwds, "\|OOi", kwlist,`
`48`	`48`	`&first, &last,`
`49`	`49`	`&self->number))`
`50`	`50`	`return -1;`
`51`	`51`
`52`	`52`	`if (first) {`
`53`		`- tmp = self->first;`
`54`		`- self->first = Py_NewRef(first);`
`55`		`- Py_XDECREF(tmp);`
	`53`	`+ Py_XSETREF(self->first, Py_NewRef(first));`
`56`	`54`	`}`
`57`	`55`	`if (last) {`
`58`		`- tmp = self->last;`
`59`		`- self->last = Py_NewRef(last);`
`60`		`- Py_XDECREF(tmp);`
	`56`	`+ Py_XSETREF(self->last, Py_NewRef(last));`
`61`	`57`	`}`
`62`	`58`	`return 0;`
`63`	`59`	`}`
Original file line number	Diff line number	Diff line change
`@@ -58,22 +58,18 @@ static int`
`58`	`58`	`Custom_init(CustomObject self, PyObject args, PyObject *kwds)`
`59`	`59`	`{`
`60`	`60`	`static char *kwlist[] = {"first", "last", "number", NULL};`
`61`		`- PyObject first = NULL, last = NULL, *tmp;`
	`61`	`+ PyObject first = NULL, last = NULL;`
`62`	`62`
`63`	`63`	`if (!PyArg_ParseTupleAndKeywords(args, kwds, "\|UUi", kwlist,`
`64`	`64`	`&first, &last,`
`65`	`65`	`&self->number))`
`66`	`66`	`return -1;`
`67`	`67`
`68`	`68`	`if (first) {`
`69`		`- tmp = self->first;`
`70`		`- self->first = Py_NewRef(first);`
`71`		`- Py_DECREF(tmp);`
	`69`	`+ Py_SETREF(self->first, Py_NewRef(first));`
`72`	`70`	`}`
`73`	`71`	`if (last) {`
`74`		`- tmp = self->last;`
`75`		`- self->last = Py_NewRef(last);`
`76`		`- Py_DECREF(tmp);`
	`72`	`+ Py_SETREF(self->last, Py_NewRef(last));`
`77`	`73`	`}`
`78`	`74`	`return 0;`
`79`	`75`	`}`
`@@ -102,9 +98,7 @@ Custom_setfirst(CustomObject self, PyObject value, void *closure)`
`102`	`98`	`"The first attribute value must be a string");`
`103`	`99`	`return -1;`
`104`	`100`	`}`
`105`		`- Py_INCREF(value);`
`106`		`- Py_CLEAR(self->first);`
`107`		`- self->first = value;`
	`101`	`+ Py_XSETREF(self->first, Py_NewRef(value));`
`108`	`102`	`return 0;`
`109`	`103`	`}`
`110`	`104`
`@@ -126,9 +120,7 @@ Custom_setlast(CustomObject self, PyObject value, void *closure)`
`126`	`120`	`"The last attribute value must be a string");`
`127`	`121`	`return -1;`
`128`	`122`	`}`
`129`		`- Py_INCREF(value);`
`130`		`- Py_CLEAR(self->last);`
`131`		`- self->last = value;`
	`123`	`+ Py_XSETREF(self->last, Py_NewRef(value));`
`132`	`124`	`return 0;`
`133`	`125`	`}`
`134`	`126`
Original file line number	Diff line number	Diff line change
`@@ -1256,7 +1256,6 @@ deque_remove(dequeobject deque, PyObject value)`
`1256`	`1256`	`static int`
`1257`	`1257`	`deque_ass_item(dequeobject deque, Py_ssize_t i, PyObject v)`
`1258`	`1258`	`{`
`1259`		`- PyObject *old_value;`
`1260`	`1259`	`block *b;`
`1261`	`1260`	`Py_ssize_t n, len=Py_SIZE(deque), halflen=(len+1)>>1, index=i;`
`1262`	`1261`
`@@ -1282,9 +1281,7 @@ deque_ass_item(dequeobject deque, Py_ssize_t i, PyObject v)`
`1282`	`1281`	`while (--n >= 0)`
`1283`	`1282`	`b = b->leftlink;`
`1284`	`1283`	`}`
`1285`		`- old_value = b->data[i];`
`1286`		`- b->data[i] = Py_NewRef(v);`
`1287`		`- Py_DECREF(old_value);`
	`1284`	`+ Py_SETREF(b->data[i], Py_NewRef(v));`
`1288`	`1285`	`return 0;`
`1289`	`1286`	`}`
`1290`	`1287`
Original file line number	Diff line number	Diff line change
`@@ -537,8 +537,7 @@ element_get_text(ElementObject* self)`
`537`	`537`	`if (!tmp)`
`538`	`538`	`return NULL;`
`539`	`539`	`self->text = tmp;`
`540`		`- Py_DECREF(res);`
`541`		`- res = tmp;`
	`540`	`+ Py_SETREF(res, tmp);`
`542`	`541`	`}`
`543`	`542`	`}`
`544`	`543`
`@@ -559,8 +558,7 @@ element_get_tail(ElementObject* self)`
`559`	`558`	`if (!tmp)`
`560`	`559`	`return NULL;`
`561`	`560`	`self->tail = tmp;`
`562`		`- Py_DECREF(res);`
`563`		`- res = tmp;`
	`561`	`+ Py_SETREF(res, tmp);`
`564`	`562`	`}`
`565`	`563`	`}`
`566`	`564`
Original file line number	Diff line number	Diff line change
`@@ -1243,8 +1243,7 @@ lru_cache_clear_list(lru_list_elem *link)`
`1243`	`1243`	`{`
`1244`	`1244`	`while (link != NULL) {`
`1245`	`1245`	`lru_list_elem *next = link->next;`
`1246`		`- Py_DECREF(link);`
`1247`		`- link = next;`
	`1246`	`+ Py_SETREF(link, next);`
`1248`	`1247`	`}`
`1249`	`1248`	`}`
`1250`	`1249`