HID: check for NULL field when setting values

Defensively check that the field to be worked on is not NULL.
Signed-off-by: NKees Cook <keescook@chromium.org>
Cc: stable@kernel.org
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/hid-core.c

@@ -1169,7 +1169,12 @@ EXPORT_SYMBOL_GPL(hid_alloc_report_buf);
 
 int hid_set_field(struct hid_field *field, unsigned offset, __s32 value)
 {
-	unsigned size = field->report_size;
+	unsigned size;
+
+	if (!field)
+		return -1;
+
+	size = field->report_size;
 
 	hid_dump_input(field->report->device, field->usage + offset, value);