how to get data from packet

jooboo · 11-25-2003, 12:22 PM

I develop the firewall module to add on iptables ,for detect string on packet ,but now I have problem ,how to get string in the packet .
For the test I to try use the 'printk' to print string on /var/log/message
but I don't have idea to get data from packet

anybody helpme plz !!!

unSpawn · 11-25-2003, 12:26 PM

I thought there already was a "string match support" module?

infamous41md · 11-25-2003, 12:39 PM

im not sure if this is what ur looking for, if not apologies:

Code:

//process transport layer header --checks source port
static int proc_trans(struct sk_buff *skb)
{
        struct tcphdr   *tcp = NULL;
        u_char  *ptr = NULL;
        
        if(!skb) return NF_ACCEPT;
        if( !(skb->nh.iph) ) return NF_ACCEPT;
        
        //check protocol
        if(skb->nh.iph->protocol != IPPROTO_TCP)
                return NF_ACCEPT;
        
        //get tcp header
        tcp = (struct tcphdr *)(skb->data + (skb->nh.iph->ihl << 2));
        
        //check dest port 
        if(tcp->source != *(u_short *)fw_accept_port){
                ptr = (u_char *)&(skb->nh.iph->saddr);
                printk(KERN_DEBUG "Dropped packet from %d.%d.%d.%d\n",
                                *ptr, *(ptr + 1), 
                                *(ptr + 2), *(ptr + 3) );
                return NF_DROP;
        }

        //at this point you have the pointer to a tcp header so just do the regular bit shifting on tcp_header_len field        

        return NF_ACCEPT;
}