From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net] ip: generate unique IP identificator if local
 fragmentation is allowed
Date: Wed, 18 Sep 2013 12:20:18 -0400 (EDT)
Message-ID: <20130918.122018.1088822749792394509.davem@davemloft.net>
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From: Ansis Atteka <aatteka@nicira.com>
Date: Tue, 17 Sep 2013 15:25:00 -0700

> @@ -1317,6 +1317,7 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
>  		ttl = ip_select_ttl(inet, &rt->dst);
>  
>  	iph = (struct iphdr *)skb->data;
> +
>  	iph->version = 4;
>  	iph->ihl = 5;
>  	iph->tos = inet->tos;
> @@ -1324,7 +1325,7 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
>  	iph->ttl = ttl;
>  	iph->protocol = sk->sk_protocol;
>  	ip_copy_addrs(iph, fl4);
> -	ip_select_ident(iph, &rt->dst, sk);
> +	ip_select_ident(skb, &rt->dst, sk);
>  
>  	if (opt) {
>  		iph->ihl += opt->optlen>>2;

This transformation is not equivalent.

ip_select_ident() is going to use ip_hdr() which obtains the header
pointer via skb_network_header().

But here, the code is using skb->data for this, which is different.