virt: vbox: fix memory leak in hgcm_call_preprocess_linaddr

In hgcm_call_preprocess_linaddr memory is allocated for bounce_buf but
is not released if copy_form_user fails. In order to prevent memory leak
in case of failure, the assignment to bounce_buf_ret is moved before the
error check. This way the allocated bounce_buf will be released by the
caller.

Fixes: 579db9d ("virt: Add vboxguest VMMDEV communication code")
Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20190930204223.3660-1-navid.emamdoost@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/virt/vboxguest/vboxguest_utils.c

@@ -220,6 +220,8 @@ static int hgcm_call_preprocess_linaddr(
 	if (!bounce_buf)
 		return -ENOMEM;
 
+	*bounce_buf_ret = bounce_buf;
+
 	if (copy_in) {
 		ret = copy_from_user(bounce_buf, (void __user *)buf, len);
 		if (ret)
@@ -228,7 +230,6 @@ static int hgcm_call_preprocess_linaddr(
 		memset(bounce_buf, 0, len);
 	}
 
-	*bounce_buf_ret = bounce_buf;
 	hgcm_call_add_pagelist_size(bounce_buf, len, extra);
 	return 0;
 }