Thanks Jeff for the reply. Yes; after changing the double pointer to a
Normal Pointer., I can see that ., "if" block was skipped.

-Thnx,
VKS

On Tue, Nov 22, 2011 at 12:50 AM, Jeff Haran [off-list ref] wrote:

** **

** **

*From:* kernelnewbies-bounces at kernelnewbies.org [mailto:
kernelnewbies-bounces at kernelnewbies.org] *On Behalf Of *Kesava Srinivas
*Sent:* Monday, November 21, 2011 11:03 AM
*To:* kernelnewbies at kernelnewbies.org
*Subject:* sock_buff is NULL !****

** **

HI Team,

Trying to make this code work; but some how it is entering the if
condition mentioned below.sock_buff is still a NULL Pointer.I can see that
Function was registered with the Ipv4 Hooks. Any ideas/scenarios where the
sock_buff remains as NULL Pointer??? Testing this code by trying to do ssh
with this machine.

Any Help is really appreciated !!

#########
static struct nf_hook_ops netfilter_ops;
struct sk_buff *sock_buff;

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*)) {
 sock_buff = *skb;
        if(!sock_buff){
           printk(KERN_ERR "Entered unexpected loop \n");
               return NF_ACCEPT;
         }/* Check for sk_buff NULL */
}
int init_module()
{
        netfilter_ops.hook              =       (nf_hookfn *) main_hook;
        netfilter_ops.hooknum           =       NF_INET_PRE_ROUTING;
        netfilter_ops.pf                =       PF_INET;
        netfilter_ops.priority          =       NF_IP_PRI_FIRST;
        nf_register_hook(&netfilter_ops);


}
######################


-Thnx,
VKS****

** **

Which kernel version are you using? The function prototype of a netfilter
hook does vary from kernel version to kernel version, but in the kernels
I?ve seen the skb parameter is a typed sk_buff *skb, not sk_buff **skb. In
other words, you get passed a pointer to the sk_buff, not the address of a
pointer to an sk_buff.****

** **

Jeff Haran****

** **

-- 
-VKS
Masters,Computer Science&Engineering.
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