pythongh-148850: Fix memory sanitizer false positive in os.getrandom (pythonGH-148851)

Co-authored-by: Petr Viktorin <encukou@gmail.com>

Author: petervanvugt

Include/pyport.h

@@ -553,6 +553,7 @@ extern "C" {
 #    if !defined(_Py_MEMORY_SANITIZER)
 #      define _Py_MEMORY_SANITIZER
 #      define _Py_NO_SANITIZE_MEMORY __attribute__((no_sanitize_memory))
+#      define _Py_MSAN_UNPOISON(PTR, SIZE)  (__msan_unpoison(PTR, SIZE))
 #    endif
 #  endif
 #  if __has_feature(address_sanitizer)
@@ -591,6 +592,9 @@ extern "C" {
 #ifndef _Py_NO_SANITIZE_MEMORY
 #  define _Py_NO_SANITIZE_MEMORY
 #endif
+#ifndef _Py_MSAN_UNPOISON
+#  define _Py_MSAN_UNPOISON(PTR, SIZE)
+#endif
 
 /* AIX has __bool__ redefined in it's system header file. */
 #if defined(_AIX) && defined(__bool__)

Misc/NEWS.d/next/Core_and_Builtins/2026-04-21-19-29-29.gh-issue-148850.MSH0J_.rst

@@ -0,0 +1 @@
+Fix the memory sanitizer false positive in :func:`os.getrandom`.

Modules/posixmodule.c

@@ -17195,6 +17195,8 @@ os_getrandom_impl(PyObject *module, Py_ssize_t size, int flags)
         goto error;
     }
 
+    _Py_MSAN_UNPOISON(data, size);
+
     return PyBytesWriter_FinishWithSize(writer, n);
 
 error: