bpo-35161: Fix stack-use-after-scope in grp.getgr{nam,gid} and pwd.getpw{nam,uid}. (GH-10319)

Reported by ASAN.

Modules/grpmodule.c

@@ -124,11 +124,12 @@ grp_getgrgid_impl(PyObject *module, PyObject *id)
         Py_DECREF(py_int_id);
     }
 #ifdef HAVE_GETGRGID_R
-    Py_BEGIN_ALLOW_THREADS
     int status;
     Py_ssize_t bufsize;
+    /* Note: 'grp' will be used via pointer 'p' on getgrgid_r success. */
     struct group grp;
 
+    Py_BEGIN_ALLOW_THREADS
     bufsize = sysconf(_SC_GETGR_R_SIZE_MAX);
     if (bufsize == -1) {
         bufsize = DEFAULT_BUFFER_SIZE;
@@ -204,11 +205,12 @@ grp_getgrnam_impl(PyObject *module, PyObject *name)
     if (PyBytes_AsStringAndSize(bytes, &name_chars, NULL) == -1)
         goto out;
 #ifdef HAVE_GETGRNAM_R
-    Py_BEGIN_ALLOW_THREADS
     int status;
     Py_ssize_t bufsize;
+    /* Note: 'grp' will be used via pointer 'p' on getgrnam_r success. */
     struct group grp;
 
+    Py_BEGIN_ALLOW_THREADS
     bufsize = sysconf(_SC_GETGR_R_SIZE_MAX);
     if (bufsize == -1) {
         bufsize = DEFAULT_BUFFER_SIZE;

Modules/pwdmodule.c

@@ -131,11 +131,12 @@ pwd_getpwuid(PyObject *module, PyObject *uidobj)
         return NULL;
     }
 #ifdef HAVE_GETPWUID_R
-    Py_BEGIN_ALLOW_THREADS
     int status;
     Py_ssize_t bufsize;
+    /* Note: 'pwd' will be used via pointer 'p' on getpwuid_r success. */
     struct passwd pwd;
 
+    Py_BEGIN_ALLOW_THREADS
     bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
     if (bufsize == -1) {
         bufsize = DEFAULT_BUFFER_SIZE;
@@ -212,11 +213,12 @@ pwd_getpwnam_impl(PyObject *module, PyObject *name)
     if (PyBytes_AsStringAndSize(bytes, &name_chars, NULL) == -1)
         goto out;
 #ifdef HAVE_GETPWNAM_R
-    Py_BEGIN_ALLOW_THREADS
     int status;
     Py_ssize_t bufsize;
+    /* Note: 'pwd' will be used via pointer 'p' on getpwnam_r success. */
     struct passwd pwd;
 
+    Py_BEGIN_ALLOW_THREADS
     bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
     if (bufsize == -1) {
         bufsize = DEFAULT_BUFFER_SIZE;