py/objstringio.c: Fix segfault in stringio_write.

Fixes issue #10402:
	printing to io.StringIO subclass leads to seg fault.
	stringio_write function does not check o_in is type_stringio.
	This checks for proper type and raises TypeError if it isn't.

Signed-off-by: Carlos Gil Gonzalez <carlosgilglez@gmail.com>

py/objstringio.c

@@ -77,6 +77,13 @@ STATIC void stringio_copy_on_write(mp_obj_stringio_t *o) {
 
 STATIC mp_uint_t stringio_write(mp_obj_t o_in, const void *buf, mp_uint_t size, int *errcode) {
     (void)errcode;
+
+    if (!mp_obj_is_type(o_in, &mp_type_stringio)) {
+
+        if (!mp_obj_is_type(o_in, &mp_type_bytesio)) {
+            mp_raise_TypeError(MP_ERROR_TEXT("expecting a StringIO or BytesIO object"));
+        }
+    }
     mp_obj_stringio_t *o = MP_OBJ_TO_PTR(o_in);
     check_stringio_is_open(o);
 

tests/io/stringio_type_check.py

@@ -0,0 +1,31 @@
+import sys
+
+sys.path[0] = ".frozen"  # avoid local dir io import
+
+import io
+
+
+class TestStream(io.StringIO):
+    def __init_(self, alloc_size):
+        super().__init__(alloc_size)
+
+
+class ByteStream(io.BytesIO):
+    def __init_(self, alloc_size):
+        super().__init__(alloc_size)
+
+
+test_stringio = TestStream(100)
+
+test_bytesio = ByteStream(100)
+
+try:
+    print("hello", file=test_stringio)
+except Exception as e:
+    print(e)
+
+
+try:
+    print("hello", file=test_bytesio)
+except Exception as e:
+    print(e)

tests/io/stringio_type_check.py.exp

@@ -0,0 +1,2 @@
+expecting a StringIO or BytesIO object
+expecting a StringIO or BytesIO object