root/net/ipv4/netfilter/nf_nat_proto_gre.c

DEFINITIONS

1. gre_unique_tuple
2. gre_manip_pkt
3. nf_nat_proto_gre_init
4. nf_nat_proto_gre_fini
5. nf_nat_need_gre

/*
 * nf_nat_proto_gre.c
 *
 * NAT protocol helper module for GRE.
 *
 * GRE is a generic encapsulation protocol, which is generally not very
 * suited for NAT, as it has no protocol-specific part as port numbers.
 *
 * It has an optional key field, which may help us distinguishing two
 * connections between the same two hosts.
 *
 * GRE is defined in RFC 1701 and RFC 1702, as well as RFC 2784
 *
 * PPTP is built on top of a modified version of GRE, and has a mandatory
 * field called "CallID", which serves us for the same purpose as the key
 * field in plain GRE.
 *
 * Documentation about PPTP can be found in RFC 2637
 *
 * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
 *
 * Development of this code funded by Astaro AG (http://www.astaro.com/)
 *
 */

#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>

#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_rule.h>
#include <net/netfilter/nf_nat_protocol.h>
#include <linux/netfilter/nf_conntrack_proto_gre.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
MODULE_DESCRIPTION("Netfilter NAT protocol helper module for GRE");

/* generate unique tuple ... */
static bool
gre_unique_tuple(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 key;
        __be16 *keyptr;
        unsigned int min, i, range_size;

        /* If there is no master conntrack we are not PPTP,
           do not change tuples */
        if (!ct->master)
                return false;

        if (maniptype == IP_NAT_MANIP_SRC)
                keyptr = &tuple->src.u.gre.key;
        else
                keyptr = &tuple->dst.u.gre.key;

        if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
                pr_debug("%p: NATing GRE PPTP\n", ct);
                min = 1;
                range_size = 0xffff;
        } else {
                min = ntohs(range->min.gre.key);
                range_size = ntohs(range->max.gre.key) - min + 1;
        }

        pr_debug("min = %u, range_size = %u\n", min, range_size);

        for (i = 0; i < range_size; i++, key++) {
                *keyptr = htons(min + key % range_size);
                if (!nf_nat_used_tuple(tuple, ct))
                        return true;
        }

        pr_debug("%p: no NAT mapping\n", ct);
        return false;
}

/* manipulate a GRE packet according to maniptype */
static bool
gre_manip_pkt(struct sk_buff *skb, unsigned int iphdroff,
              const struct nf_conntrack_tuple *tuple,
              enum nf_nat_manip_type maniptype)
{
        const struct gre_hdr *greh;
        struct gre_hdr_pptp *pgreh;
        const struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
        unsigned int hdroff = iphdroff + iph->ihl * 4;

        /* pgreh includes two optional 32bit fields which are not required
         * to be there.  That's where the magic '8' comes from */
        if (!skb_make_writable(skb, hdroff + sizeof(*pgreh) - 8))
                return false;

        greh = (void *)skb->data + hdroff;
        pgreh = (struct gre_hdr_pptp *)greh;

        /* we only have destination manip of a packet, since 'source key'
         * is not present in the packet itself */
        if (maniptype != IP_NAT_MANIP_DST)
                return true;
        switch (greh->version) {
        case GRE_VERSION_1701:
                /* We do not currently NAT any GREv0 packets.
                 * Try to behave like "nf_nat_proto_unknown" */
                break;
        case GRE_VERSION_PPTP:
                pr_debug("call_id -> 0x%04x\n", ntohs(tuple->dst.u.gre.key));
                pgreh->call_id = tuple->dst.u.gre.key;
                break;
        default:
                pr_debug("can't nat unknown GRE version\n");
                return false;
        }
        return true;
}

static const struct nf_nat_protocol gre = {
        .protonum               = IPPROTO_GRE,
        .me                     = THIS_MODULE,
        .manip_pkt              = gre_manip_pkt,
        .in_range               = nf_nat_proto_in_range,
        .unique_tuple           = gre_unique_tuple,
#if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
        .range_to_nlattr        = nf_nat_proto_range_to_nlattr,
        .nlattr_to_range        = nf_nat_proto_nlattr_to_range,
#endif
};

static int __init nf_nat_proto_gre_init(void)
{
        return nf_nat_protocol_register(&gre);
}

static void __exit nf_nat_proto_gre_fini(void)
{
        nf_nat_protocol_unregister(&gre);
}

module_init(nf_nat_proto_gre_init);
module_exit(nf_nat_proto_gre_fini);

void nf_nat_need_gre(void)
{
        return;
}
EXPORT_SYMBOL_GPL(nf_nat_need_gre);