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

(cherry picked from commit 993ac92418839427d4068d6ae8e618b06b5d9294)

Co-authored-by: Steve Dower <steve.dower@python.org>

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
new file mode 100644 (file)
index 0000000..e6ddaba
--- /dev/null
+++ 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
index c178facc4beee2c04e5c61086f2ceaa5ab9a1a32..b9e8c0d94c20e1fcf44c9b6f2067dba6bf01f52e 100644 (file)
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -7821,7 +7821,7 @@ 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
@@ -7875,7 +7875,7 @@ 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));
         }
     }