vhost_vdpa: switch to vmemdup_user()

Replace opencoded alloc and copy with vmemdup_user()
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Link: https://lore.kernel.org/r/1605057288-60400-1-git-send-email-tiantao6@hisilicon.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

drivers/vhost/vdpa.c

@@ -245,14 +245,10 @@ static long vhost_vdpa_set_config(struct vhost_vdpa *v,
 		return -EFAULT;
 	if (vhost_vdpa_config_validate(v, &config))
 		return -EINVAL;
-	buf = kvzalloc(config.len, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
 
-	if (copy_from_user(buf, c->buf, config.len)) {
-		kvfree(buf);
-		return -EFAULT;
-	}
+	buf = vmemdup_user(c->buf, config.len);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
 
 	ops->set_config(vdpa, config.off, buf, config.len);