[3.12] gh-105436: The environment block should end with two null wchar_t values (GH-105495) (#105700)

gh-105436: The environment block should end with two null wchar_t values (GH-105495)
(cherry picked from commit 4f7d3b602d47d61137e82145f601dccfe6f6cd3c)

Co-authored-by: Dora203 <66343334+sku2000@users.noreply.github.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/Modules/_winapi.c b/Modules/_winapi.c
index bbc9fac..d6d2f4a 100644
--- a/Modules/_winapi.c
+++ b/Modules/_winapi.c
@@ -796,6 +796,17 @@ getenvironment(PyObject* environment)
     }
 
     envsize = PyList_GET_SIZE(keys);
+
+    if (envsize == 0) {
+        // A environment block must be terminated by two null characters --
+        // one for the last string and one for the block.
+        buffer = PyMem_Calloc(2, sizeof(wchar_t));
+        if (!buffer) {
+            PyErr_NoMemory();
+        }
+        goto cleanup;
+    }
+
     if (PyList_GET_SIZE(values) != envsize) {
         PyErr_SetString(PyExc_RuntimeError,
             "environment changed size during iteration");
@@ -869,7 +880,8 @@ getenvironment(PyObject* environment)
     *p++ = L'\0';
     assert(p == end);
 
- error:
+cleanup:
+error:
     Py_XDECREF(keys);
     Py_XDECREF(values);
     return buffer;