nf_nat_proto_icmp.c

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/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2006 Netfilter Core Team <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/types.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/ip.h>
#include <linux/icmp.h>

#include <linux/netfilter.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_core.h>
#include <net/netfilter/nf_nat_l4proto.h>

static bool
icmp_in_range(const struct nf_conntrack_tuple *tuple,
          enum nf_nat_manip_type maniptype,
          const union nf_conntrack_man_proto *min,
          const union nf_conntrack_man_proto *max)
{
    return ntohs(tuple->src.u.icmp.id) >= ntohs(min->icmp.id) &&
           ntohs(tuple->src.u.icmp.id) <= ntohs(max->icmp.id);
}

static void
icmp_unique_tuple(const struct nf_nat_l3proto *l3proto,
          struct nf_conntrack_tuple *tuple,
          const struct nf_nat_range *range,
          enum nf_nat_manip_type maniptype,
          const struct nf_conn *ct)
{
    static u_int16_t id;
    unsigned int range_size;
    unsigned int i;

    range_size = ntohs(range->max_proto.icmp.id) -
             ntohs(range->min_proto.icmp.id) + 1;
    /* If no range specified... */
    if (!(range->flags & NF_NAT_RANGE_PROTO_SPECIFIED))
        range_size = 0xFFFF;

    for (i = 0; ; ++id) {
        tuple->src.u.icmp.id = htons(ntohs(range->min_proto.icmp.id) +
                         (id % range_size));
        if (++i == range_size || !nf_nat_used_tuple(tuple, ct))
            return;
    }
    return;
}

static bool
icmp_manip_pkt(struct sk_buff *skb,
           const struct nf_nat_l3proto *l3proto,
           unsigned int iphdroff, unsigned int hdroff,
           const struct nf_conntrack_tuple *tuple,
           enum nf_nat_manip_type maniptype)
{
    struct icmphdr *hdr;

    if (!skb_make_writable(skb, hdroff + sizeof(*hdr)))
        return false;

    hdr = (struct icmphdr *)(skb->data + hdroff);
    inet_proto_csum_replace2(&hdr->checksum, skb,
                 hdr->un.echo.id, tuple->src.u.icmp.id, 0);
    hdr->un.echo.id = tuple->src.u.icmp.id;
    return true;
}

const struct nf_nat_l4proto nf_nat_l4proto_icmp = {
    .l4proto        = IPPROTO_ICMP,
    .manip_pkt      = icmp_manip_pkt,
    .in_range       = icmp_in_range,
    .unique_tuple       = icmp_unique_tuple,
#if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
    .nlattr_to_range    = nf_nat_l4proto_nlattr_to_range,
#endif
};