iptables reject and redirect to url

自己寫的，較舊版本的iptable沒有redirect url功能。

//Reference:
//http://gpl.back2roots.org/source/puma5/netgear/CG3300D_V1.00.15_src/apps/fw_modules/ipt_REJECT.c
//http://bbs.chinaunix.net/thread-1960367-1-1.html
//http://blog.chinaunix.net/uid-27087754-id-3279302.html
//http://blog.csdn.net/yadon_z/article/details/7983402
//http://code.google.com/p/wl500g/source/browse/branches/rt-n/kernel-2.6/606-netfilter-webstr.patch?r=2456
#define MAX_HTTP_REDIRECT_CONTENT 512
static void send_http_redirect(struct sk_buff *oldskb, int hook, const char *data){   char http_content[MAX_HTTP_REDIRECT_CONTENT], *pHttp_content;   sprintf(http_content, "HTTP/1.1 307 FoundrnServer: ZyXEL: Content Filter/1.03nLocation:%srn", data);
   strcat(http_content, "Date: Thu, 17 Feb 2000 12:46:46 GMTrnContent-Type: text/htmlrnAccept-Ranges: bytesrnContent-Length: 256rn");
   strcat(http_content, "Cache-control: no-cachernPragma: no-cachernExpires: 0rnConnection: closernrn");   struct sk_buff *nskb;
	const struct iphdr *oiph;
	struct iphdr *niph;
	struct tcphdr *oth;
	struct tcphdr _otcph, *tcph;
	unsigned int addr_type;
   unsigned int otcplen;   /* IP header checks: fragment. */
	if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
		return;   oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
				 sizeof(_otcph), &_otcph);
   otcplen = oldskb->len - ip_hdr(oldskb)->ihl*4;
	if (oth == NULL)
		return;   /* No RST for RST. */
	if (oth->rst)
		return;   /* Check checksum */
	if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
		return;
	oiph = ip_hdr(oldskb);     unsigned char *http_data = (void *)oth + oth->doff*4;
   unsigned int datalen = (oldskb)->len - (oiph->ihl*4) - (oth->doff*4);   /*debug message*/
   /*
   char show_data[20];
   memset(show_data, 0, sizeof(show_data));
   memcpy(show_data, http_data, sizeof(show_data) - 1);
   printk(KERN_EMERG "__[Kernel]datalen=%d http data=%sn", datalen,show_data);   if (datalen < 10){
      return;
   }
   */   if(memcmp(http_data, "GET", sizeof("GET") - 1) != 0 &&
      memcmp(http_data, "POST", sizeof("POST") - 1) != 0){
      return;
   }   nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
			 LL_MAX_HEADER + strlen(http_content), GFP_ATOMIC);
	if (!nskb)
		return;   skb_reserve(nskb, LL_MAX_HEADER);   skb_reset_network_header(nskb);
	niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
	niph->version	= 4;
	niph->ihl	= sizeof(struct iphdr) / 4;
	niph->tos	= 0;
	niph->id	= 0;
	niph->frag_off	= htons(IP_DF);
	niph->protocol	= IPPROTO_TCP;
	niph->check	= 0;
	niph->saddr	= oiph->daddr;
	niph->daddr	= oiph->saddr;   tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
	memset(tcph, 0, sizeof(*tcph));
	tcph->source	= oth->dest;
	tcph->dest	= oth->source;
	tcph->doff	= sizeof(struct tcphdr) / 4;     pHttp_content = (char *)skb_put(nskb, strlen(http_content));
   strcpy(pHttp_content, http_content);   tcph->seq = oth->ack_seq;
	tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin
				      + otcplen - (oth->doff<<2));   tcph->fin = 1;
   tcph->psh = 1;
   tcph->ack = 1;   tcph->rst	= 0;   nskb->csum = csum_partial((char *)tcph + tcph->doff*4,
			strlen(http_content), 0);   tcph->check	= tcp_v4_check(sizeof(struct tcphdr) + strlen(http_content),
				       niph->saddr, niph->daddr,
				       csum_partial(tcph,
						    sizeof(struct tcphdr), nskb->csum));   addr_type = RTN_UNSPEC;
	if (hook != NF_INET_FORWARD
#ifdef CONFIG_BRIDGE_NETFILTER
	    || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED)
#endif
	   )
		addr_type = RTN_LOCAL;   /* ip_route_me_harder expects skb->dst to be set */
	dst_hold(oldskb->dst);
	nskb->dst = oldskb->dst;   if (ip_route_me_harder(nskb, addr_type))
		goto free_nskb;   niph->ttl	= dst_metric(nskb->dst, RTAX_HOPLIMIT);
	nskb->ip_summed = CHECKSUM_NONE;   /* "Never happens" */
	if (nskb->len > dst_mtu(nskb->dst))
		goto free_nskb;   nf_ct_attach(nskb, oldskb);   ip_local_out(nskb);   return;   free_nskb:
	kfree_skb(nskb);   }