Re: Question about ip_rcv() function

[David S. Miller]

On Wed, 23 Jun 2004 14:45:47 -0400 (EDT)
rahul b jain cs student <rbj2@xxxxxxxxxxxx> wrote:

> can anyone explain what is the difference between the following two pieces
> of code.
> 
> 1. if (!pskb_may_pull(skb, sizeof(struct iphdr)))
>                 goto inhdr_error;
> 
>    iph = skb->nh.iph;
> 
> 2. if (!pskb_may_pull(skb, iph->ihl*4))
>                 goto inhdr_error;
> 
>    iph = skb->nh.iph;

We can't dereference any of the iphdr fields (such as iph->ihl) until
we know that at least "sizeof(struct iphdr)" bytes are there first.
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