CODEWITHSUNDEEP
cipnetfilter
이호영
이호영

Reputation: 11

I don't know why ip_hdr(skb) return NULL

static unsigned int main_hook(unsigned int hooknum , struct sk_buff *skb , const struct net_device *in , const struct net_device *out, int (*okfn)(struct sk_buff*))
{    
        int i=0;
        struct iphdr *iph = ip_hdr(skb);
        unsigned long saddr = 0 , daddr = 0;
        unsigned long snet = 0; //dnet =0;
        int dst_cnt=0 , src_cnt=0;

        //printk("netfilter called\n");

        //down(&sema);
        Netfilter_Execute++;

        saddr = iph->saddr;
        daddr = iph->daddr;

when I execute this module program, the linux shut down and reboot. When I test the program, iph is null so saddr = iph->saddr and daddr = iph->daddr was wrong.

I don't know why iph = ip_hdr(skb) returns NULL.

Upvotes: 0

Views: 560

Answers (2)

Reuven Plevinsky
Reuven Plevinsky

Reputation: 201

try: instead of struct iphdr *iph = ip_hdr(skb);, type struct iphdr *iph = (struct iphdr *)skb_network_header(skb);

Upvotes: 1

ahmed_kamal1432
ahmed_kamal1432

Reputation: 49

The problem may be depend on which hook you use, you have to mind where your hook place related to the kernel routing module.

Let me show you these 2 examples

  1. If you use

    NF_IP_LOCAL_OUT

    The packet that you receive in your hook doesn't go throw the Routing module in the kernel so it will not have a header

  2. If you use

    NF_IP_LOCAL_IN

    The packet will go throw the Routing module but the Routing module will remove the header of the packet and route it to an internal process

Upvotes: 1

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