Re: How to remove ip options from existing skbuff?

["Guibin(Bill) Tian" <gbtian@xxxxxxxxx>]

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@xxxxxxxxx> 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.

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