thinkpad_acpi: fix possible NULL pointer dereference if kstrdup failed

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/misc/thinkpad_acpi.c

@@ -5826,7 +5826,7 @@ static void __init get_thinkpad_model_data(struct thinkpad_id_data *tp)
 
 	tp->model_str = kstrdup(dmi_get_system_info(DMI_PRODUCT_VERSION),
 					GFP_KERNEL);
-	if (strnicmp(tp->model_str, "ThinkPad", 8) != 0) {
+	if (tp->model_str && strnicmp(tp->model_str, "ThinkPad", 8) != 0) {
 		kfree(tp->model_str);
 		tp->model_str = NULL;
 	}