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Subject: Re: [RFC PATCH] af_packet: don't to defrag shared skb
From: Johannes Berg <johannes@sipsolutions.net>
To: David Miller <davem@davemloft.net>
Cc: eric@regit.org, netdev@vger.kernel.org,
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	Eric Dumazet <eric.dumazet@gmail.com>
Date: Fri, 07 Dec 2012 23:23:37 +0100
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Oh I should say ... IP is like black magic to me ;-)

> -	if (!pskb_may_pull(skb, sizeof(struct iphdr)))
> +	if (!skb_copy_bits(skb, 0, &iph, sizeof(iph)))
>  		return skb;
>  
> -	iph = ip_hdr(skb);
> -	if (iph->ihl < 5 || iph->version != 4)
> +	if (iph.ihl < 5 || iph.version != 4)
>  		return skb;
> -	if (!pskb_may_pull(skb, iph->ihl*4))
> -		return skb;
> -	iph = ip_hdr(skb);
> -	len = ntohs(iph->tot_len);
> -	if (skb->len < len || len < (iph->ihl * 4))
> +
> +	len = ntohs(iph.tot_len);
> +	if (skb->len < len || len < (iph.ihl * 4))
>  		return skb;
>  
> -	if (ip_is_fragment(ip_hdr(skb))) {
> +	if (ip_is_fragment(&iph)) {
>  		skb = skb_share_check(skb, GFP_ATOMIC);
>  		if (skb) {
> +			if (!pskb_may_pull(skb, iph.ihl*4))
> +				return skb;

I moved this here but I have no idea what it does. Asking if we can pull
this here seems a bit pointless, and in the previous place it seemed
similarly pointless since we only use the static part of the IP header
and don't look at any options... So to me it seems this pskb_may_pull()
could just be removed, and that most likely means I'm messing with code
I don't understand :-)

johannes