<div dir="ltr">I used the following code with the output, I don't understand why this doesn't work.<div><br></div><div> struct iphdr *iph = ip_hdr(skb);<br></div><div><div> char *tmp = NULL;</div>
<div> int optlen = iph->ihl*4 - sizeof(struct iphdr);</div><div><span class="" style="white-space:pre"> </span>if (optlen > 0)</div><div><span class="" style="white-space:pre"> </span>{</div><div><span class="" style="white-space:pre"> </span>printk("ihl=%d\n", iph->ihl);</div>
<div><span class="" style="white-space:pre"> </span>printk("optlen=%d\n", optlen);</div><div><span class="" style="white-space:pre"> </span>tmp = kzalloc(sizeof(struct iphdr), GFP_ATOMIC);</div><div><span class="" style="white-space:pre"> </span>memcpy(tmp, iph, sizeof(struct iphdr));</div>
<div><span class="" style="white-space:pre"> </span>memcpy(iph + optlen, tmp, sizeof(struct iphdr));</div><div><span class="" style="white-space:pre"> </span>kfree(tmp);</div><div><div><span class="" style="white-space:pre"> skb_pull(skb, optlen);</span></div>
<div><span class="" style="white-space:pre"> </span>skb_reset_network_header(skb);</div><div><br></div><div><span class="" style="white-space:pre"> </span>iph = ip_hdr(skb);</div><div><span class="" style="white-space:pre"> </span>printk("new ihl=%d\n", iph->ihl);</div>
<div><span class="" style="white-space:pre"> </span>iph->ihl -= optlen>>2;</div><div><span class="" style="white-space:pre"> </span>printk("newest ihl=%d\n", iph->ihl);</div></div>
<div><span class="" style="white-space:pre"> </span>}<br></div><div><br></div><div>The output is:<br></div><div><br></div><div><div>[ 401.754279] ihl=8</div><div>[ 401.754288] optlen=12</div><div>[ 401.754293] new ihl=15</div>
<div>[ 401.754296] newest ihl=12</div></div><div><br></div><div><br></div></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Tue, Jan 28, 2014 at 8:54 PM, Guibin(Bill) Tian <span dir="ltr"><<a href="mailto:gbtian@gmail.com" target="_blank">gbtian@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hi, <div>In the kernel, I added some customized options to the ip_options struct, and I send the ip packet with these option fields set. </div>
<div><br></div><div>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. </div>
<div><br></div><div>In the method ip_rcv_finish of the file ip_input.c, I added following code: </div><div><br></div><div><div><span style="white-space:pre-wrap">/*********My code to process the options****/</span></div>
<div><span style="white-space:pre-wrap"> process_my_options(skb);</span></div><div><span style="white-space:pre-wrap">/*********My code to remove the options ****/<br></span></div><div><span style="white-space:pre-wrap"> </span>//skb_pull(skb, sizeof(struct iphdr) + 12);<br>
</div><div><span style="white-space:pre-wrap"> </span>//skb_push(skb, sizeof(struct iphdr));</div><div><span style="white-space:pre-wrap"> </span>//skb_reset_network_header(skb);</div><div><span style="white-space:pre-wrap"> //</span>iph->ihl -= 3;</div>
<div><br></div><div><span style="white-space:pre-wrap">/*********Normal process of the ip packet.****/</span><br></div><div><span style="white-space:pre-wrap"> </span>if (iph->ihl > 5 && ip_rcv_options(skb))</div>
<div><span style="white-space:pre-wrap"> </span>goto drop;</div></div><div><br></div><div><br></div><div>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.</div>
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