Re: skb->h not initialized

From: Pablo Neira Ayuso
Date: Thu Dec 28 2006 - 13:13:58 EST

Jan Engelhardt wrote:
> while writing a netfilter match module I found that, when run,
> skb-> is not set to the TCP header (it is assured that the packet
> _is_ TCP), as this printk shows me:
> skb: nh.iph=cb5bc4dc mac.raw=cb5bc4ce head=cb5bc400
> data=cb5bc4dc tail=cb5bc510 end=cb5bc580
> Is it intended that skb-> is not set to skb->data + length of ip
> header (skb->data+protoff as far as netfilter matches are concerned)?

The netfilter hooks are placed in the network layer, therefore skb->
is not set in the input path since the packet did not reach the
transport layer yet (prerouting/input), but it is set in the output path
because it already passed by the transport layer (output/postrouting).

BTW, I'm unsure that this can be of interest in the linux-kernel list,
please there's no need to cc everyone. Use netfilter or linux-net
instead next time.

The dawn of the fourth age of Linux firewalling is coming; a time of
great struggle and heroic deeds -- J.Kadlecsik got inspired by J.Morris
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