Convert vhost to struct_size

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

drivers/vhost/vhost.c

@@ -1286,7 +1286,8 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 		return -EOPNOTSUPP;
 	if (mem.nregions > max_mem_regions)
 		return -E2BIG;
-	newmem = kvzalloc(size + mem.nregions * sizeof(*m->regions), GFP_KERNEL);
+	newmem = kvzalloc(struct_size(newmem, regions, mem.nregions),
+			GFP_KERNEL);
 	if (!newmem)
 		return -ENOMEM;