netdev - Re: [Patch net] mlx5: check for malformed packets

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Date:   Sun, 2 Dec 2018 21:11:13 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Tariq Toukan <tariqt@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [Patch net] mlx5: check for malformed packets

On Sun, Dec 2, 2018 at 12:56 AM Tariq Toukan <tariqt@...lanox.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.