From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cong Wang <xiyou.wangcong@gmail.com>
Subject: Re: [Patch net] mlx5: check for malformed packets
Date: Sun, 2 Dec 2018 21:11:13 -0800
Message-ID: <CAM_iQpUH+18SgwPZUd7PiAiGauEfgiFb0nozKsNnawQcrzZrmQ@mail.gmail.com>
References: <20181201203837.3306-1-xiyou.wangcong@gmail.com> <955711f0-eb24-4512-c9a3-429bdad8bcad@mellanox.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Cc: Linux Kernel Network Developers <netdev@vger.kernel.org>,
        Saeed Mahameed <saeedm@mellanox.com>
To: Tariq Toukan <tariqt@mellanox.com>
Return-path: <netdev-owner@vger.kernel.org>
Received: from mail-pl1-f196.google.com ([209.85.214.196]:39367 "EHLO
        mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1725811AbeLCFL3 (ORCPT
        <rfc822;netdev@vger.kernel.org>); Mon, 3 Dec 2018 00:11:29 -0500
Received: by mail-pl1-f196.google.com with SMTP id 101so5827274pld.6
        for <netdev@vger.kernel.org>; Sun, 02 Dec 2018 21:11:25 -0800 (PST)
In-Reply-To: <955711f0-eb24-4512-c9a3-429bdad8bcad@mellanox.com>
Sender: netdev-owner@vger.kernel.org
List-ID: <netdev.vger.kernel.org>

On Sun, Dec 2, 2018 at 12:56 AM Tariq Toukan <tariqt@mellanox.com> wrote:
>
>
>
> On 01/12/2018 10:38 PM, Cong Wang wrote:
> > +     if (*proto == htons(ETH_P_IP)) {
> > +             if (unlikely(*network_depth > skb->len - sizeof(struct iphdr)))
> > +                     return false;
> > +             return true;
>
> Or just do the following?
>         return *network_depth <= skb->len - sizeof(struct iphdr));
>
> We'll lose the compiler hint though, so I'm not sure which is better.


It is very important to keep this unlikely(), as it is on a hot path.


>
> > +     } else if (*proto == htons(ETH_P_IPV6)) {
>
> No need for an else here, the first if block always returns.


Yeah, but not sure if this makes a difference on the generated
asm code. I will give it a try anyway.

Thanks.