gh-128212: Fix race in _PyUnicode_CheckConsistency (GH-128367)

colesbury · web-flow · commit 8eebe4e6d02b · 2025-01-02T14:02:54.000-05:00
There was a data race on the utf8 field between `PyUnicode_SET_UTF8` and
`_PyUnicode_CheckConsistency`. Use the `_PyUnicode_UTF8()` accessor,
which uses an atomic load internally, to avoid the data race.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
@@ -688,7 +688,7 @@ _PyUnicode_CheckConsistency(PyObject *op, int check_content)
                                  || kind == PyUnicode_2BYTE_KIND
                                  || kind == PyUnicode_4BYTE_KIND);
             CHECK(ascii->state.ascii == 0);
-            CHECK(compact->utf8 != data);
+            CHECK(_PyUnicode_UTF8(op) != data);
         }
         else {
             PyUnicodeObject *unicode = _PyUnicodeObject_CAST(op);

Original file line number	Diff line number	Diff line change
`@@ -688,7 +688,7 @@ _PyUnicode_CheckConsistency(PyObject *op, int check_content)`
`688`	`688`	`\|\| kind == PyUnicode_2BYTE_KIND`
`689`	`689`	`\|\| kind == PyUnicode_4BYTE_KIND);`
`690`	`690`	`CHECK(ascii->state.ascii == 0);`
`691`		`- CHECK(compact->utf8 != data);`
	`691`	`+ CHECK(_PyUnicode_UTF8(op) != data);`
`692`	`692`	`}`
`693`	`693`	`else {`
`694`	`694`	`PyUnicodeObject *unicode = _PyUnicodeObject_CAST(op);`