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

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Message-Id: <20100503.005945.123415755.davem@davemloft.net>
Date:	Mon, 03 May 2010 00:59:45 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	xiaosuo@...il.com
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH] ethernet: call __skb_pull() in eth_type_trans()

From: Changli Gao <xiaosuo@...il.com>
Date: Mon,  3 May 2010 06:50:17 +0800

> call __skb_pull() in eth_type_trans().
> 
> Since the callers of eth_type_trans() always feed it long enough packets,
> we can use __skb_pull() to save some cycles.
> 
> Signed-off-by: Changli Gao <xiaosuo@...il.com>

Although they should, assuming that some runts won't show up here and
never check for that condition at all is dangerous.

At least we should have a WARN_ON() check for skb->len < ETH_ZLEN here
or similar.

So many other things get layered into ethernet, which means adding
this length assumption without any checks is bound to lead to
unpleasant surprises for somebody.
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