Re: a problem with netfilter

["U.Mutlu" <for-gmane@mutluit.com>]

Bozeanu Andrei wrote, On 10/17/2012 02:34 PM:
> Hey all,
>
> I am writing a linux firewall kernel module (something a bit specific)
> using Netfilter, in C. I extract the
> TCP header and the IP header using the functions tcp_hdr() and ip_hdr()
> on the skb. I extract the source and
> destination IPs without any problem, yet, when I try to see the source
> port and the destination port i get wrong
> values.
>
> sport = ntohs(tcp_hdr(skb)->source);
> dport= ntohs(tcp_hdr(skb)->dest);

Just guessing: maybe ntohs has already been applied to source and dest, so try it w/o ntohs()...

> I use printk to send the info to the syslog and
> printk(KERN_INFO "got data on port %hu from source port %hu\n", dport,
> sport);
>
> the result i get is
> "got data on port 17680 from port 84"
> "got data on port 17680 from port 84"
> "got data on port 17680 from port 100"
>
> while netstat shows me that the right values for these ports are dport =
> 56188 and sport = 22.
>
> I must be doing something wrong or missing something of the bigger
> picture, I would apreciate any insight
> on why this behavior is generated.
>
> Thank you all,
> A.