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#include <linux/types.h>
#include <linux/init.h>
#include <linux/netfilter.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <linux/if.h>
 
#include <linux/netfilter_ipv4/ip_nat.h>
#include <linux/netfilter_ipv4/ip_nat_rule.h>
#include <linux/netfilter_ipv4/ip_nat_protocol.h>
 
static int
icmp_in_range(const struct ip_conntrack_tuple *tuple,
	      enum ip_nat_manip_type maniptype,
	      const union ip_conntrack_manip_proto *min,
	      const union ip_conntrack_manip_proto *max)
{
	return (tuple->src.u.icmp.id >= min->icmp.id
		&& tuple->src.u.icmp.id <= max->icmp.id);
}
 
static int
icmp_unique_tuple(struct ip_conntrack_tuple *tuple,
		  const struct ip_nat_range *range,
		  enum ip_nat_manip_type maniptype,
		  const struct ip_conntrack *conntrack)
{
	static u_int16_t id = 0;
	unsigned int range_size
		= (unsigned int)range->max.icmp.id - range->min.icmp.id + 1;
	unsigned int i;
 
	/* If no range specified... */
	if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED))
		range_size = 0xFFFF;
 
	for (i = 0; i < range_size; i++, id++) {
		tuple->src.u.icmp.id = range->min.icmp.id + (id % range_size);
		if (!ip_nat_used_tuple(tuple, conntrack))
			return 1;
	}
	return 0;
}
 
static void
icmp_manip_pkt(struct iphdr *iph, size_t len,
	       const struct ip_conntrack_manip *manip,
	       enum ip_nat_manip_type maniptype)
{
	struct icmphdr *hdr = (struct icmphdr *)((u_int32_t *)iph + iph->ihl);
 
	hdr->checksum = ip_nat_cheat_check(hdr->un.echo.id ^ 0xFFFF,
					   manip->u.icmp.id,
					   hdr->checksum);
	hdr->un.echo.id = manip->u.icmp.id;
}
 
static unsigned int
icmp_print(char *buffer,
	   const struct ip_conntrack_tuple *match,
	   const struct ip_conntrack_tuple *mask)
{
	unsigned int len = 0;
 
	if (mask->src.u.icmp.id)
		len += sprintf(buffer + len, "id=%u ",
			       ntohs(match->src.u.icmp.id));
 
	if (mask->dst.u.icmp.type)
		len += sprintf(buffer + len, "type=%u ",
			       ntohs(match->dst.u.icmp.type));
 
	if (mask->dst.u.icmp.code)
		len += sprintf(buffer + len, "code=%u ",
			       ntohs(match->dst.u.icmp.code));
 
	return len;
}
 
static unsigned int
icmp_print_range(char *buffer, const struct ip_nat_range *range)
{
	if (range->min.icmp.id != 0 || range->max.icmp.id != 0xFFFF)
		return sprintf(buffer, "id %u-%u ",
			       ntohs(range->min.icmp.id),
			       ntohs(range->max.icmp.id));
	else return 0;
}
 
struct ip_nat_protocol ip_nat_protocol_icmp
= { { NULL, NULL }, "ICMP", IPPROTO_ICMP,
    icmp_manip_pkt,
    icmp_in_range,
    icmp_unique_tuple,
    icmp_print,
    icmp_print_range
};