gh-116447: Fix possible UB in arraymodule and getargs (#116459)

Author: sobolevn

Modules/arraymodule.c

@@ -247,7 +247,7 @@ BB_setitem(arrayobject *ap, Py_ssize_t i, PyObject *v)
     if (!PyArg_Parse(v, "b;array item must be integer", &x))
         return -1;
     if (i >= 0)
-        ((char *)ap->ob_item)[i] = x;
+        ((unsigned char *)ap->ob_item)[i] = x;
     return 0;
 }
 

Python/getargs.c

@@ -612,7 +612,7 @@ convertsimple(PyObject *arg, const char **p_format, va_list *p_va, int flags,
     switch (c) {
 
     case 'b': { /* unsigned byte -- very short int */
-        char *p = va_arg(*p_va, char *);
+        unsigned char *p = va_arg(*p_va, unsigned char *);
         long ival = PyLong_AsLong(arg);
         if (ival == -1 && PyErr_Occurred())
             RETURN_ERR_OCCURRED;
@@ -633,7 +633,7 @@ convertsimple(PyObject *arg, const char **p_format, va_list *p_va, int flags,
 
     case 'B': {/* byte sized bitfield - both signed and unsigned
                   values allowed */
-        char *p = va_arg(*p_va, char *);
+        unsigned char *p = va_arg(*p_va, unsigned char *);
         unsigned long ival = PyLong_AsUnsignedLongMask(arg);
         if (ival == (unsigned long)-1 && PyErr_Occurred())
             RETURN_ERR_OCCURRED;