Problem in printing TCP header ports values

[Guest ha-as]

Hello,

 

In my application writen in C for linux system. I have a post hook filter which tries to print out the outgoing packets source and destination ports for TCP connections only. When I print the value of the ports I get strange values, here's the code for the post_hook:

 

Code:

static struct nf_hook_ops nfho_post; // Struct holding set of hook function options

 

unsigned int nf_hook_post(unsigned int hooknum,

struct sk_buff *skb,

const struct net_device *in,

const struct net_device *out,

int (*okfn) (struct sk_buff *))

{

struct iphdr *iph;

struct tcphdr *th;

 

if (skb == NULL)

{

printk(KERN_INFO "%s: Socket buffer NULL.\n", __FUNCTION__);

return NF_ACCEPT;

}

 

if(skb_is_nonlinear(skb))

skb_linearize(skb);

 

iph = ip_hdr(skb);

if(iph == NULL)

{

printk("%s: IP header NULL.\n", __FUNCTION__);

return NF_ACCEPT;

}

 

/* Handles only TCP connection: if transport protocol isn't TCP, we don't care about it. */

if(iph->protocol != IPPROTO_TCP)

return NF_ACCEPT;

 

th = tcp_hdr(skb);

if(th == NULL)

{

printk("%s: TCP header NULL.\n", __FUNCTION__);

return NF_ACCEPT;

}

 

printk("1 Source port=%u, Destination port=%u.\n", ntohl((unsigned short int) th->source)

,ntohl((unsigned short int) th->dest));

 

printk("2 Source port=%u, Destination port=%u.\n", htonl((unsigned short int) th->source)

,htonl((unsigned short int) th->dest));

 

printk("3 Source port=%u, Destination port=%u.\n", (unsigned short int) th->source

,(unsigned short int) th->dest);

 

return NF_ACCEPT;

}

I tried to print the values using different methods but until now I did not succed. So please can anyone tell me what is the problem and how to solve it?

 

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