I used the following code with the output, I don't understand why this doesn't work. struct iphdr *iph = ip_hdr(skb); char *tmp = NULL; int optlen = iph->ihl*4 - sizeof(struct iphdr); if (optlen > 0) { printk("ihl=%d\n", iph->ihl); printk("optlen=%d\n", optlen); tmp = kzalloc(sizeof(struct iphdr), GFP_ATOMIC); memcpy(tmp, iph, sizeof(struct iphdr)); memcpy(iph + optlen, tmp, sizeof(struct iphdr)); kfree(tmp); skb_pull(skb, optlen); skb_reset_network_header(skb); iph = ip_hdr(skb); printk("new ihl=%d\n", iph->ihl); iph->ihl -= optlen>>2; printk("newest ihl=%d\n", iph->ihl); } The output is: [ 401.754279] ihl=8 [ 401.754288] optlen=12 [ 401.754293] new ihl=15 [ 401.754296] newest ihl=12 On Tue, Jan 28, 2014 at 8:54 PM, Guibin(Bill) Tian <gbtian@gmail.com> wrote:

Hi, In the kernel, I added some customized options to the ip_options struct, and I send the ip packet with these option fields set.

After I receive the packet, I extract these options and try to remove them from the ip packet because I don't want these options be delivered to upper layer.

In the method ip_rcv_finish of the file ip_input.c, I added following code:

/*********My code to process the options****/ process_my_options(skb); /*********My code to remove the options ****/ //skb_pull(skb, sizeof(struct iphdr) + 12); //skb_push(skb, sizeof(struct iphdr)); //skb_reset_network_header(skb); //iph->ihl -= 3;

/*********Normal process of the ip packet.****/ if (iph->ihl > 5 && ip_rcv_options(skb)) goto drop;

The question is at how to remove the options. I tried some code but none of them works correctly. Can anybody give me some suggestion? Thanks.