netdev - Re: [PATCH v2] ethernet: call __skb_pull() in eth_type

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Date:	Tue, 4 May 2010 10:05:22 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v2] ethernet: call __skb_pull() in eth_type_trans()

On Mon, May 3, 2010 at 10:44 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> Hmm, I feel very uncompfortable with this patch.
>
> I am pretty sure some callers dont check minimum ethernet frame length.
>
> At least a WARN_ON_ONCE() is needed, just in case...
> In fact our stack has different requirements.
>
> Check net/ipv4/ip_gre.c for example.
>
>                if (tunnel->dev->type == ARPHRD_ETHER) {
>                        if (!pskb_may_pull(skb, ETH_HLEN)) {
>                                stats->rx_length_errors++;
>                                stats->rx_errors++;
>                                goto drop;
>                        }
>
>                        iph = ip_hdr(skb);
>                        skb->protocol = eth_type_trans(skb, tunnel->dev);
>                        skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN);
>                }
>

So the minimal packet length eth_type_trans() requires should be
ETH_HLEN, not ETH_ZLEN.

-- 
Regards，
Changli Gao(xiaosuo@...il.com)