linux-kernel - Re: [PATCH v3,bpf-next] bpf: Don't redirect packets with invalid pkt

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Date:   Fri, 15 Jul 2022 11:17:59 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Zhengchao Shao <shaozhengchao@...wei.com>,
        bpf <bpf@...r.kernel.org>, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, martin.lau@...ux.dev,
        song@...nel.org, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Menglong Dong <imagedong@...cent.com>,
        Petr Machata <petrm@...dia.com>, Arnd Bergmann <arnd@...db.de>,
        David Ahern <dsahern@...nel.org>,
        Talal Ahmad <talalahmad@...gle.com>,
        Kees Cook <keescook@...omium.org>, Hao Luo <haoluo@...gle.com>,
        jolsa@...nel.org, weiyongjun1@...wei.com,
        YueHaibing <yuehaibing@...wei.com>
Subject: Re: [PATCH v3,bpf-next] bpf: Don't redirect packets with invalid pkt_len

On Fri, Jul 15, 2022 at 6:30 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Fri, 15 Jul 2022 11:22:33 +0800 Zhengchao Shao wrote:
> > +#ifdef CONFIG_DEBUG_NET
> > +     if (unlikely(!skb->len)) {
> > +             pr_err("%s\n", __func__);
> > +             skb_dump(KERN_ERR, skb, false);
> > +             WARN_ON_ONCE(1);
> > +     }
>
> Is there a reason to open code WARN_ONCE() like that?
>
> #ifdef CONFIG_DEBUG_NET
>         if (WARN_ONCE(!skb->len, "%s\n", __func__))
>                 skb_dump(KERN_ERR, skb, false);
>
> or
>
>         if (IS_ENABLED(CONFIG_DEBUG_NET) &&
>             WARN_ONCE(!skb->len, "%s\n", __func__))
>                 skb_dump(KERN_ERR, skb, false);


Also the skb_dump() needs to be done once.

DO_ONCE_LITE(skb_dump, KERN_ERR, skb, false);