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TCP包增一个ICMP头

发送加头,接收解头。checksum失效,需要额外处理

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#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/sctp.h>
#include <linux/icmp.h>
#include <linux/slab.h>

#include <net/ip.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <net/icmp.h>                   /* for icmp_send */
#include <net/route.h>
#include <net/ip6_checksum.h>
#include <net/netns/generic.h>      /* net_generic() */

#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>

#ifdef CONFIG_IP_VS_IPV6
#include <net/ipv6.h>
#include <linux/netfilter_ipv6.h>
#include <net/ip6_route.h>
#endif

#include <net/ip_vs.h>
#include <linux/dns_resolver.h>



#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/version.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/icmp.h>
#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <linux/kallsyms.h>
#include <linux/inetdevice.h>
#include <linux/netdevice.h>
#include <net/ip.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <net/icmp.h>
#include <net/arp.h>
#include <net/route.h>
#include <net/neighbour.h>
#include <net/netevent.h>
#if (LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 32))
#include <net/net_namespace.h>
#endif
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>

#include <linux/inet.h>
#include <linux/skbuff.h>
#include <linux/kthread.h>

int icmp_port = 80;
module_param(icmp_port, int, 0644);

struct addhdr {
	u32 saddr, daddr;
	u16 sport, dport;
	u16 len;
	u16 magic;
};

static unsigned int local_out(void *priv, struct sk_buff *skb, const struct nf_hook_state *state)
{
	struct iphdr *iph = ip_hdr(skb);
	struct tcphdr *th;
	struct icmphdr *icmp;
	struct addhdr *add;
	int delta;

	iph = ip_hdr(skb);
	th = tcp_hdr(skb);
	if (iph->protocol != IPPROTO_TCP)
		return NF_ACCEPT;

	if (ntohs(th->source) != icmp_port && ntohs(th->dest) != icmp_port)
		return NF_ACCEPT;

	if (skb->len + sizeof(struct icmphdr) + sizeof(struct addhdr) > 1500)
		return NF_ACCEPT;

	delta = sizeof(struct icmphdr) + sizeof(struct addhdr) + sizeof(struct ethhdr) - skb_headroom(skb);
	if (delta > 0 && pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC))
		return NF_ACCEPT;

	iph = ip_hdr(skb);
	th = tcp_hdr(skb);

	if (skb->ip_summed != CHECKSUM_COMPLETE) {
		th->check = 0;
		skb->csum = 0;
		th->check = tcp_v4_check(skb->len - ip_hdrlen(skb), iph->saddr, iph->daddr, skb_checksum(skb, ip_hdrlen(skb), skb->len - ip_hdrlen(skb), 0));
		skb->ip_summed = CHECKSUM_COMPLETE;
	}

	skb_push(skb, sizeof(struct icmphdr) + sizeof(struct addhdr));
	memcpy(skb->data, skb->data + sizeof(struct icmphdr) + sizeof(struct addhdr), ip_hdrlen(skb));
	skb_reset_network_header(skb);
	iph = ip_hdr(skb);
	iph->protocol = IPPROTO_ICMP;
	iph->tot_len = htons(skb->len);

	icmp = (struct icmphdr *)(skb->data + ip_hdrlen(skb));
	icmp->type = ICMP_ECHO;
	icmp->code = 0;
	icmp->un.echo.id = 1;
	icmp->un.echo.sequence = 1;

	add = (struct addhdr *)(skb->data + ip_hdrlen(skb) + sizeof(struct icmphdr));
	add->saddr = iph->saddr;
	add->daddr = iph->daddr;
	add->sport = th->source;
	add->dport = th->dest;
	add->len = skb->len;
	add->magic = skb->len;

	skb_set_transport_header(skb, ip_hdrlen(skb));

	icmp->checksum = 0;
	icmp->checksum = csum_fold(csum_partial(skb->data + ip_hdrlen(skb), skb->len - ip_hdrlen(skb), 0));

	ip_send_check(iph);
	skb->ip_summed = CHECKSUM_NONE;

	return NF_ACCEPT;
}

static unsigned int pre_route(void *priv, struct sk_buff *skb, const struct nf_hook_state *state)
{
	struct iphdr *iph;
	struct tcphdr *th;
	struct icmphdr *icmp;
	struct addhdr *add;

	if (!pskb_may_pull(skb, sizeof(struct iphdr) + sizeof(struct tcphdr) + sizeof(struct icmphdr) + sizeof(struct addhdr)))
		return NF_ACCEPT;

	iph = ip_hdr(skb);
	if (iph->protocol != IPPROTO_ICMP)
		return NF_ACCEPT;

	icmp = (struct icmphdr*)(skb->data + ip_hdrlen(skb));
	if (icmp->type != ICMP_ECHO || icmp->code != 0)
		return NF_ACCEPT;

	add = (struct addhdr*)(skb->data + ip_hdrlen(skb) + sizeof(struct icmphdr));
	th = (struct tcphdr*)(skb->data + ip_hdrlen(skb) + sizeof(struct icmphdr) + sizeof(struct addhdr));
	if (ntohs(th->source) != icmp_port && ntohs(th->dest) != icmp_port)
		return NF_ACCEPT;

	//if (add->saddr != iph->saddr || add->daddr != iph->daddr || 
	if (add->sport != th->source || add->dport != th->dest || add->len != skb->len || add->magic != skb->len)
		return NF_ACCEPT;

	skb_pull(skb, sizeof(struct icmphdr) + sizeof(struct addhdr));
	// sizeof(struct icmphdr) + sizeof(struct addhdr) > ip_hdrlen(skb)
	memcpy(skb->data, skb->data - sizeof(struct icmphdr) - sizeof(struct addhdr), ip_hdrlen(skb));
	memcpy(skb->data - sizeof(struct ethhdr), skb->data - sizeof(struct icmphdr) - sizeof(struct addhdr) - sizeof(struct ethhdr), sizeof(struct ethhdr));
	skb_reset_network_header(skb);
	iph = ip_hdr(skb);
	iph->protocol = IPPROTO_TCP;
	iph->tot_len = htons(skb->len);

	ip_send_check(iph);
	skb->ip_summed = CHECKSUM_UNNECESSARY;
	skb_set_transport_header(skb, ip_hdrlen(skb));
	th = tcp_hdr(skb);
	skb_set_mac_header(skb, -(int)sizeof(struct ethhdr));

	return NF_ACCEPT;
}

static const struct nf_hook_ops ip_vs_ops[] = {
	{
		.hook     = local_out,
		.pf       = NFPROTO_IPV4,
		.hooknum  = NF_INET_LOCAL_OUT,
		.priority = 0,
	},
	{
		.hook     = pre_route,
		.pf       = NFPROTO_IPV4,
		.hooknum  = NF_INET_PRE_ROUTING,
		.priority = 0,
	},
};

static int net_init(void)
{
	if (nf_register_net_hooks(&init_net, ip_vs_ops, ARRAY_SIZE(ip_vs_ops)))
		return -1;

	return 0;
}

static void net_cleanup(void)
{
	nf_unregister_net_hooks(&init_net, ip_vs_ops, ARRAY_SIZE(ip_vs_ops));
}

module_init(net_init);
module_exit(net_cleanup);
MODULE_LICENSE("GPL");