bpo-38020: Fixes crash in os.readlink() on Windows (GH-15663)

zooba · web-flow · commit 993ac9241883 · 2019-09-03T12:50:51.000-07:00
diff --git a/Misc/NEWS.d/next/Windows/2019-09-03-11-47-37.bpo-38020.xFZ2j0.rst b/Misc/NEWS.d/next/Windows/2019-09-03-11-47-37.bpo-38020.xFZ2j0.rst
@@ -0,0 +1,2 @@
+Fixes potential crash when calling :func:`os.readlink` (or indirectly
+through :func:`~os.path.realpath`) on a file that is not a supported link.
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
@@ -7818,7 +7818,7 @@ os_readlink_impl(PyObject *module, path_t *path, int dir_fd)
     HANDLE reparse_point_handle;
     char target_buffer[_Py_MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
     _Py_REPARSE_DATA_BUFFER *rdb = (_Py_REPARSE_DATA_BUFFER *)target_buffer;
-    PyObject *result;
+    PyObject *result = NULL;
 
     /* First get a handle to the reparse point */
     Py_BEGIN_ALLOW_THREADS
@@ -7872,7 +7872,7 @@ os_readlink_impl(PyObject *module, path_t *path, int dir_fd)
             name[1] = L'\\';
         }
         result = PyUnicode_FromWideChar(name, nameLen);
-        if (path->narrow) {
+        if (result && path->narrow) {
             Py_SETREF(result, PyUnicode_EncodeFSDefault(result));
         }
     }

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Fixes potential crash when calling :func:`os.readlink` (or indirectly
	`2`	+through :func:`~os.path.realpath`) on a file that is not a supported link.
Original file line number	Diff line number	Diff line change
`@@ -7818,7 +7818,7 @@ os_readlink_impl(PyObject module, path_t path, int dir_fd)`
`7818`	`7818`	`HANDLE reparse_point_handle;`
`7819`	`7819`	`char target_buffer[_Py_MAXIMUM_REPARSE_DATA_BUFFER_SIZE];`
`7820`	`7820`	`_Py_REPARSE_DATA_BUFFER rdb = (_Py_REPARSE_DATA_BUFFER )target_buffer;`
`7821`		`- PyObject *result;`
	`7821`	`+ PyObject *result = NULL;`
`7822`	`7822`
`7823`	`7823`	`/* First get a handle to the reparse point */`
`7824`	`7824`	`Py_BEGIN_ALLOW_THREADS`
`@@ -7872,7 +7872,7 @@ os_readlink_impl(PyObject module, path_t path, int dir_fd)`
`7872`	`7872`	`name[1] = L'\\';`
`7873`	`7873`	`}`
`7874`	`7874`	`result = PyUnicode_FromWideChar(name, nameLen);`
`7875`		`- if (path->narrow) {`
	`7875`	`+ if (result && path->narrow) {`
`7876`	`7876`	`Py_SETREF(result, PyUnicode_EncodeFSDefault(result));`
`7877`	`7877`	`}`
`7878`	`7878`	`}`